C O N T E M P O R A R Y R E V I E W

Exosomes in Toxicology Relevance to Chemical

Exposure and Pathogenesis of Environmentally Linked

DiseasesDilshan S Harischandra12 Shivani Ghaisas2 Dharmin Rokad andAnumantha G Kanthasamy3

Parkinson Disorders Research Program Department of Biomedical Sciences Iowa Center for AdvancedNeurotoxicology Iowa State University Ames Iowa 50011

1Present address The Perelman School of Medicine University of Pennsylvania Philadelphia PA 19104

2These authors contributed equally to this study3To whom correspondence should be addressed at Department of Biomedical Sciences Parkinson Disorders Research Laboratory Iowa State University2062 Veterinary Medicine Building Ames IA 50011 Fax (515) 294-2315 E-mail akanthasiastateedu

ABSTRACT

Chronic exposure to environmental toxins has been known to initiate or aggravate various neurological disorderscarcinomas and other adverse health effects Uptake by naıve cells of pathogenic factors such as danger-associatedmolecules mRNAs miRNAs or aggregated proteins leads to disruption in cellular homeostasis further resulting ininflammation and disease propagation Although early research tended to focus solely on exosomal removal of unwantedcellular contents more recent reports indicate that these nano-vesicles play an active role in intercellular signaling Notonly is the exosomal cargo cell type-specific but it also differs between healthy and dying cells Moreover followingexosome uptake by naıve cells the contents from these vesicles can alter the fate of recipient cells Since exosomes cantraverse long distances they can influence distantly located cells and tissues This review briefly explores the role played byenvironmental toxins in stimulating exosome release in the context of progressive neurodegenerative diseases such asAlzheimerrsquos Parkinsonrsquos and Huntingtonrsquos as well as certain cancers such as lung liver ovarian and tracheal carcinomas

Key words exosome cell-to-cell transmission neurodegeneration environmental toxins cancer protein aggregation

Intracellular communication is an essential biological phenom-enon for the regulation of normal tissue function which inturn is important for the development and adaptation of multi-cellular organisms Cells also communicate with one anotherfollowing genetic or environmental stimuli and can help passinformation in the form of signaling molecules and transcrip-tion modulators Until recently researchers have had only alimited understanding of these signaling pathways which areoften thought to be mediated through hormones cytokinesgrowth factors and neurotransmitters and their specific recog-nition by cell-surface receptors However in the last 2 decades

a novel mechanism for intercellular communication hasemerged that involves the transfer of extracellular vesicles(EVs) These vesicles play a key role in cell-to-cell communica-tion exerting their effects locally as well as across multiple or-gan systems EVs are often classified based on theirapproximate size origin and cargo As determined by their bio-genesis the 3 major subclasses of EVs are apoptotic bodiesmicrovesicles and exosomes (Figure 1) Apoptotic bodies thelargest EVs in this group (50ndash5000 nm) are released whenplasma membrane blebbing occurs during programmed celldeath In contrast microvesicles and exosomes are much

VC The Author 2017 Published by Oxford University Press on behalf of the Society of ToxicologyAll rights reserved For Permissions please e-mail journalspermissionsoupcom

3

TOXICOLOGICAL SCIENCES 158(1) 2017 3ndash13

doi 101093toxscikfx074Advance Access Publication Date May 15 2017Contemporary Review

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smaller in size and are generated by budding from the plasmamembrane or are derived from the endo-lysosomal pathway re-spectively Furthermore exosome biogenesis (Figure 2) differsfrom that of other EVs as the former is facilitated by the fusionof a multivesicular body (MVB) with the plasma membraneVarious published reviews (Colombo et al 2013 2014 Theryet al 2002) have provided in-depth information on exosomebiogenesis and hence will not be covered in this review

Interest in exosome research has increased in the past fewyears mainly due to mounting evidence that implicates theirdynamic role in immune activation oncogenesis as well as celldeath In this review we summarize recent progress in thestudy of exosomes as biomarkers how exposure to environ-mental toxins alters the exosomal cargo and its relevance tovarious human disorders

EXOSOME-MEDIATED INTERCELLULARCOMMUNICATION

Exosome involvement in cell-to-cell communication was firstestablished by Dr Graca Raposo who in 1996 demonstrated thatB lymphoblastoid cells released exosomes containing MHC class

II molecules inducing antigen-specific MHC class II restricted Tcell responses (Raposo et al 1996) This novel form of antigenpresentation provided insight into the exosomersquos role in im-mune cell activation and cell-to-cell transmission of biologicallyactive components The study was the first to implicate exo-somes in antigen presentation in vivo Since then exosomeswere primarily studied in immune cells in the context of anti-gen presentation and were soon found to play an importantrole in the pathogenesis and progression of various diseases in-cluding carcinomas cardiovascular neurodegenerative and in-fectious diseases (Azmi et al 2013 Graner et al 2013 Hoshinoet al 2015 Rajendran et al 2006)

Today exosomes have been identified in all biological fluidsincluding blood urine saliva and cerebrospinal fluid (CSF) andtheir number and cargo are known to vary depending upon celltype and health status (eg tumorigenic vs normal)Nonetheless various in vitro and in vivo studies have demon-strated that exosomes contain a variety of biomolecules (egmiRNAs small RNAs DNA as well as signaling peptides andlipids) some of which have been implicated in creating a favor-able microenvironment for neoplasia Neoplastic cells can se-crete factors such as vascular endothelial growth factor andtransforming growth factor b (TGF-b) that form blood vessels

Microvesicles

Exosomes Apoptotic blebs MVB

B

A

Figure 1 A Schematic representation of EVs Exosomes are formed from MVBs MVBs fuse with the plasma membrane releasing their contents (exosomes) into the ex-

tracellular space Microvesicles are formed by budding of the plasma membrane and most are larger than exosomes As a cell dies its plasma membrane shows bleb-

bing ultimately breaking down into large vesicles of varied diameter called apoptotic bodies B Electron Micrograph of exosomes isolated from an MN9D neuronal cell

line

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and produce mitogen thus supporting the growth of newlytransformed tumor cells (Challagundla et al 2014 Massague2008) Importantly the miRNA cargo can also modulate thegene expression of various biomolecules For example breastcancer cells secreting miR-200 are able to transform normalcells into neoplastic cells (Le et al 2014) Similarly miR-105 de-creased the expression of tight junction protein-1 thuscompromising the vascular-endothelial barrier and metastasiz-ing neoplastic cells (Zhou et al 2014) Metastasis is guided bythe expression of specific integrins The exosomal integrins a6b4

and a6b1 are associated with lung metastasis while avb5 is linkedwith liver metastasis (Hoshino et al 2015) Integrins are acti-vated by tetraspanins such as Tspan8 CD9 CD81 and CD63which are abundant in exosomes In the case of prostate cancercells insulin-like growth factor-1 c-Src and focal adhesion ki-nase are packaged in exosomes along with integrins and aid theproliferation and migration of the cells (DeRita et al 2017)Exosomes can also contain FasL and PD-L1 both of which pro-mote the apoptosis of immune cells or aberrant surveillancethus allowing tumors to grow undetected (Peng et al 2011) Theimmunomodulatory effects of exosomes are best described inthe context of parasitic infections For example when exosomesisolated from Leishmania donovani are added to leukocytes in-flammatory cytokine production is suppressed which repro-grams the leukocytes to a Th2 profile (Silverman et al 2010) Infact mice challenged with these exosomes prior to infectionshowed higher parasite titers compared with mice that had not

been pre-exposed to the exosomes In addition to disease-specificexosome cargo exosomes contain certain membrane and cyto-solic proteins commonly used as exosome-specific markersThese exosomal proteins belong to various functional groupssuch as tetraspanins (CD9 CD63 and CD81) flotillins integrinsheat shock proteins (HSC70 and HSC90) membrane transporters(GTPases) and lipid-bound proteins (Figure 3)

ROLE OF EXOSOMES IN DISEASEPATHOGENESIS

Role of Environmental Toxicants in Exosome-mediatedCarcinogenesisCancer biology fuels most discoveries in exosome signalingSimply put ldquocancerrdquo is a disease of abnormal and unregulatedcell growth with the potential to spread to other parts of thebody Cancer is one of the leading causes of global mortalitywith an estimated 16 million newly diagnosed cases in 2016One of the major questions in cancer biology is ldquohow do cancer-ous cells grow metastasize and evade immune detectionrdquoCancerous cells release many signaling molecules that dampenthe immune response to the unregulated cell growth as well asldquorecruitrdquo naıve neighboring cells This intercellular communica-tion can occur via the release of exosomes that can carry a vari-ety of biomolecules capable of binding to and activating orsilencing downstream signaling pathways

Figure 2 Schematic representation of exosome biogenesis and cellular pathways of protein clearance Cytosolic proteins or proteins internalized by the cell via endo-

cytosis are packaged into early endosomes characterized by presence of Rab5 Substitution of Rab5 with Rab7 begins the transition of early to late endosomes (LEs)

Depending upon the cellular signal (including Rab proteins) the fate of the LEs could be one of the following (i) to transport the protein cargo to the Golgi network (ii)

get recycled via the retromer pathway (iii) fuse with lysosomes effectively degrading the protein cargo or (iv) mature into MVBs that ultimately lead to the expulsion

of exosomes

HARISCHANDRA ET AL | 5

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Exposure to tobacco smoke and air pollutants such as asbes-tos arsenic (As) radon and soot increases the risk of lung orbronchiolar carcinogenesis Xu et al (2015) induced humanbronchial epithelial (HBE) cells to release miR-21 which in turnstimulated normal HBE cells to proliferate simply by exposingthe cells to 1 mM arsenite Furthermore these exosomes alsoincreased the expression of phosphatase and tensin homologcementing the fact that exogenous miRNAs when taken up bynaıve cells via endocytosis of circulating exosomes can func-tion as endogenous miRNAs Nicotine-derived nitrosoamineketone (NNK or 4-(methylnitrosamino)-1-(3-pyridyl)-1-buta-none) is a potent carcinogen present in tobacco smokeChronically exposing male rats to NNK down-regulated thetumor suppressor miR-206 (Wu et al 2013) which is an effectalso seen in metastatic lung cancer Although not conclusivelydemonstrated Wu et al speculated that following exposure toNNK exosomes derived from the tumor cells release biomole-cules and other miRNAs that potentially down-regulate tumorsuppressive factors including miR-206 and miR-133b Otherreports have shown that exosomes derived from highly meta-static lung cancer cells induced carcinogenesis in HBE cells byincreasing vimentin expression and thus inducing the epithelialto mesenchymal transition (EMT) (Rahman et al 2016) thatserves as the basis for cancer propagation

Exposure to ionizing radiation principally seen in radiother-apy can lead to genomic instability in distinct cell populations

Radiation of the tracheal mucosa can trigger invasive trachealcarcinomas activating TGF-b integrins and CXCL12 (Barcellos-Hoff et al 1994 Mishra et al 2008) This increase in growth fac-tors and adhesion proteins leads to cellular remodeling and amicroenvironment conducive to tumor metastasis Similarlyexosomes derived from highly cancerous melanomas poten-tially re-program bone marrow progenitors by signaling throughtyrosine kinase MET (Peinado et al 2012) These re-programmed cells now develop neoplastic behavior thus prop-agating the cancer In short exposure to environmental toxinsor carcinogens triggers genotoxic or mutagenic changes in sus-ceptible cells which in turn release exosomes containingmiRNAs integrins cytokines or chemokines that modulate themicroenvironment and potentiate tumorigenesis Besides creat-ing a favorable environment for cell metastasis exosomes alsoplay an important role in fostering chemo- and radiotherapy-resistant tumors Exosomes produced by the irradiated headand neck cancer cell lines BHY and FaDu promoted the survivalof irradiated recipient cells and increased the proliferation ofnonirradiated recipient cells (Mutschelknaus et al 2016)

The role of exosomes as important mediators of tumorigene-sis can be further validated in other chemical-induced carcino-genesis For example media from arsenite-transformed humanhepatic epithelial cells L-02 when added to normal L-02 orTHLE-3 (liver cell lines) cells induces the proinflammatory cyto-kines IL-6 and IL-8 and constitutively activates the STAT3

Tetraspanins (CD63 CD81 CD9)

MHC Class I

MHC Class II

Transferrin Receptor

Targetingadhesion molecules

RNA

-synuclein monomer

-synuclein aggregates

Rab 57

HSP 7090

Intergrins

ICAMs

Flotillin

Cholesterol

Transmembrane Proteins

Oligomeric proteins

Annexins Cytoskeletal proteins

Metabolic enzymes

Small RNAs

Signaling molecules

Flotill

Figure 3 Typical structure and content of exosomes Depending on their cellular origin exosomes can contain a diverse cargo Thus exosomes isolated from immune

cells enterocytes and even melanocytes have the antigen-presenting receptors MHC Class III and scaffolding proteins such as tetraspanins Since exosomes are a part

of vesicular trafficking various proteins involved in this pathway such as Rab proteins Annexins and cytoskeletal proteins constitute the exosomal payload In addi-

tion the cargo can also contain metabolic components such as enzymes lipids small carbohydrates as well as small RNAs and miRNAs

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pathway resulting in tumor progression (Chen et al 2017) Theauthors found that this proinflammatory activation was medi-ated by exosomes Media from arsenite-exposed L-02 cellswhen depleted of exosomes did not provoke inflammation innormal L-02 or THLE-3 cells Moreover among the various otherbiomolecules ferried by these nano-sized vesicles miR-155 wasalso transferred to the normal liver cells where it specificallytargeted and down-regulated the tumor suppressor gene QKIactivating NF-jB and promoting IL-6 and IL-8 production thussupporting oncogenesis

The persistent use of platinum-containing drugs such as cis-diamminedichloroplatinum(II) (cisplatin) cis-diammine(11-cyclobutanedicarboxylato)platinum(II) (carboplatin) and pacli-taxel to treat ovarian cancer results in recurrences in 80 ofcases due to acquired drug resistance Resistant cancer cellshave greater drug efflux potential increased DNA damagerepair and antioxidant properties thus making them immuneto chemotherapeutics (Stewart 2007) To understand how theseplatinum-resistant cancer cells influence cancer progressionCrow et al (2017) showed that a platinum-resistant epithelialovarian cell line released exosomes containing miR-21 which ispostulated to promote EMT an important step in cancer pro-gression Notably these platinum-resistant cells had somaticmutations in SMAD4mdasha transcription factor that is involved inintracellular communication and EMT (Pohl et al 2010) Theauthors hypothesized that exosomal miR-21 could increase thechances of or even induce somatic mutations in the SMAD4gene in the presence of platinum-containing drugs thusincreasing cell survival and promoting cancer progression Earlylife exposure to endocrine-disrupting compounds such as dieth-ylstilbestrol and genistein especially during reproductive tractdevelopment could lead to the development of uterine fibroids(tumors arising from the myometrium and tumor stem cells) inlater life Yang et al (2016) hypothesized that tumor stem cellsrelease exosomes encapsulating important effectors of WntHedgehog and b-catenin which are signaling factors vital formaintaining cell proliferation

Advancements in nanotechnology are increasingly beingapplied in consumer product manufacturing drug deliveryprosthetics efficient fuel batteries etc (Brenza et al 2016 Yanget al 2017 Zhang et al 2012) However studies assessing theenvironmental impact of nanomaterials their possible bioaccu-mulation and associated toxicities are not keeping pace Forinstance lead sulfide quantum dots (PbS-QD) have been pro-posed for biomedical imaging By transferring energy thesenanoparticles can fluoresce in the far-red range and hence arevaluable bio-imagers However the same energy transfer canalso generate reactive oxygen species leading to oxidative stressand cell death Human embryonic kidney cells responded toPbS-QD exposure by releasing altered exosomal cargo contain-ing markers of DNA damage as well as factors promotinginflammation including p53 as well as IL-8 and CXCL5 whichare potent activators of neutrophil chemotaxis and thusinflammation at the site of QD accumulation (Kim et al 2015)

The link between chronic inflammation and cancer has beenfairly well established (Chai et al 2015) and the potentialproinflammatory role of exosomes is also emerging Forinstance Leveuroanen et al (2013) showed that the exosomal cargoisolated from bronchoalveolar lavage from healthy controls andpatients suffering from intermittent asthma a chronic inflam-matory condition of the lungs was strikingly different in com-position The exosomal miRNAs isolated from intermittentasthma patients transcriptionally regulate the production offactors such as IL-13 IL-10 IL-6 and IL-8 that are known

mediators of airway obstruction and immune cell infiltrationThus asthmatic lung epithelial cells are primed for immunecell infiltration and inflammation following exposure to partic-ulate matter IL-13 plays a critical role in the initiation and pro-gression of asthma attacks IL-13 and IL-12 in turn aretranscriptionally regulated in part by miR-21 (Lu et al 2009)Down-regulation of this miRNA can result in an exaggeratedproduction of these interleukins when the lung epitheliaencounter even small amounts of particulate pollutantsInterestingly it has been observed that miR-21 expression posi-tively correlates with increased resistance of nonsmall cell lungcancer against epidermal growth factor receptor (EGFR) tyrosinekinase inhibitor treatment (Li et al 2014) Cigarette smoke is awell-known carcinogen Continued exposure to cigarette smokecan induce broncho-alveolar macrophages to shed exosomesand other microvesicles that in turn induce the epithelia to pro-duce proinflammatory cytokines (Cordazzo et al 2014)Exposure to cigarette smoke is also positively correlated to theoverexpression of miRNAs that affect EGFR function thus driv-ing proliferation of epithelial cells and initiating lung carcino-mas (Goldkorn and Filosto 2010)

Thus different components of the exosomal cargo have spe-cific functions that aid in deregulating immune surveillanceand promoting the tumor growth niche leading to malignantand resistant tumors

Exosomes in Neurological DisordersExosomes play an important role in brain development andphysiology of the central nervous system which requires pre-cise orchestration of cellular events through the coordinatedinformation exchange between distally located cellsNevertheless exosomes are often identified as the ldquoTrojanhorse of neurodegenerationrdquo (Ghidoni et al 2008) because theircargo could contain potentially pathogenic proteinsImportantly a variety of genetic and environmental factors canstimulate the release of exosomes and their composition Giventhat environmental toxicants such as metals and pesticides aswell as traumatic brain injury (TBI) play a particularly signifi-cant role in the onset of neurodegenerative diseases (Berry et al2010 Gardner et al 2015 Harischandra et al 2015a Rokad et al2016) here we focus on recent literature on the role of environ-mental factors in exosome biogenesis and disease progression

Neurodegenerative disorders including Alzheimerrsquos disease(AD) Parkinsonrsquos disease (PD) Huntingtonrsquos disease (HD) amyo-trophic lateral sclerosis (ALS) and prion diseases share com-mon cellular pathological features such as aggregation ofdisease-specific proteins (Ross and Poirier 2004) These diseasesare also described as protein misfolding diseases where inevery instance the native form of b-amyloid (Ab) tau a-synu-clein (aSyn) Huntingtin or prion protein (PrP) acquires anabnormal b-sheet structure that is absent under normal condi-tions Recent experimental evidence indicates that these pro-teins also share prion-like behavior as abnormally foldedproteins interact with each other to form cross-b species thatassemble into a ldquonucleusrdquomdashan ordered aggregate possessingthe ability of selfpropagation (Nelson et al 2005) Howeverunlike classical prion diseases these ldquoprionoidrdquo (Aguzzi andLakkaraju 2016) proteins have yet to be documented as trans-missible between individuals A wealth of evidence supportsthe theory that the exosomal pathway may be exploited for thecell-to-cell transmission of prionoids Furthermore pathogenicforms of Ab aSyn and PrPSc have been identified in exosomeshighlighting the prospect of a potential intercellular spread of

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these misfolded proteins (Danzer et al 2012 Emmanouilidouet al 2010 Guo et al 2016 Rajendran et al 2006)

The idea that exosomes are involved in the intercellular dis-semination of aggregated aSyn gained considerable attentionwhen pathogenic aSyn species were discovered in CSF exo-somes from patients with PD and dementia with Lewy bodiesboth of which are complex and multifaceted disorders whoseetiology is not fully understood Evidence for gene-environmentinteractions triggering neurodegenerative disorders is providedby the juvenile-onset Parkinsonism-related gene ATP13A2PARK9 (Gitler et al 2009 Santoro et al 2011) AlthoughATP13A2rsquos exact function is unknown it belongs to a largegroup of lysosomal transport proteins in the 5-P type ATPasefamily involved in transporting multiple cations (eg manganese[Mn] zinc cadmium selenium) from the cytosol to the lysoso-mal lumen (Kong et al 2014 Schmidt et al 2009) Importantlyoverexpression of ATP13A2PARK9 increases aSyn secretionthrough exosomes in H4 cells and mouse primary cortical cells(Tsunemi et al 2014) Furthermore Rentschler et al (2012)showed that ATP13A2PARK9 polymorphisms influence theneurotoxic effects of Mn in humans However given the possi-bility that neurons can pick up exosomes carrying toxic proteincargo capable of triggering their degeneration whether exoso-mal release of aSyn is a cellular protective adaptation or solelypathological has yet to be defined

Given the multifactorial etiology of PD and other neurodege-nerative diseases considerable effort has been devoted tostudying chronic exposure to neurotoxic metals such as copper(Cu) lead mercury Mn cadmium and As and their potentialfor promoting protein aggregation (Goldman 2014) Forinstance transition metals such as Mn are known to increaseaSyn expression (Cai et al 2010 Peres et al 2016) and the exoso-mal release of aSyn (Harischandra et al 2015b) Since Mn expo-sure triggers transient or sustained increases of intracellularcalcium levels (Xu et al 2009) which has been linked to therapid secretion of exosomes in neuronal cells (Emmanouilidouet al 2010) this may provide mechanistic insight into how envi-ronmental neurotoxicants regulate exosome biogenesis andexosomal aSyn release Importantly aSyn-containing exosomeshave been shown to provide a catalytic environment for thenucleation of aSyn aggregation (Grey et al 2015) thus providingfurther evidence for a role of exosomes in regulating cell-to-celltransmission of aSyn in PD pathogenesis

Several pesticides are neurotoxic Exposure to such neuro-toxins is associated with an increased risk of developing neuro-degenerative diseases (Kamel and Hoppin 2004 Kanthasamyet al 2005 Rokad et al 2016) Rotenone is one such pesticideused in horticulture and water management (fish control) thatincreases aSyn expression and its accumulation in the brainwhere it contributes to nigral degeneration (Betarbet et al 2000)Pan-Montojo et al (2010) showed that intragastric administra-tion of rotenone resulted in the formation of pathological aSynin the enteric nervous system the dorsal motor nucleus of thevagus nerve and the substantia nigra of wild-type mice In alater work Pan-Montojo et al (2012) reported that rotenone pro-motes the exosomal release of aSyn from enteric neurons andthat the aSyn-containing exosomes are taken up by presynapticsympathetic neurites and retrogradely transported to the somaproviding direct evidence for a role of environmental toxins inaSyn exosomal release Their findings give credence to the cur-rent understanding of PD progression which proposes thataSyn pathology is present in the periphery before it reaches thebrain where it triggers the motor symptoms of PD (Braak et al2006 Shannon et al 2012) Indeed much interest is now

focused on the microbiome-gut-brain axis and environmentalfactors in the pathogenesis of neurodegenerative diseases(Ghaisas et al 2016)

These environmental triggers can also manipulate cellularprotein quality control (PQC) mechanisms leading to proteostaticstress in cells (Cook et al 2012) and PQC impairment can promotethe transcellular flux of these proteins through exosomes (Howittand Hill 2016) In fact when autophagic (Danzer et al 2012) andlysosomal (Alvarez-Erviti et al 2011) mechanisms fail to clear thetoxic aSyn oligomers cells release these oligomers via exosomesto protect the cell from misfolded aSyn-induced cellular stressImportantly several pesticides including rotenone are known tocause oxidative modification of DJ-1 (PD-associated proteinencoded by PARK7 gene) accumulation of aSyn and proteasomalimpairment (Betarbet et al 2006) while paraquat has been shownto induce autophagic flux leading to aberrant aSyn accumulationin the brain (Dagda et al 2013)

AD is another major neurodegenerative disorder associatedwith environmental exposure to metals solvents and pesti-cides (Yegambaram et al 2015) Furthermore Ab peptide accu-mulation in exosomes has been known since the early 2000s inboth transgenic animals and AD patient brains suggesting arole for exosomes in AD pathogenesis (Rajendran et al 2006Takahashi et al 2002) However the role of environmental tox-ins in exosome biogenesis and AD pathogeneses is still unclearRecent reports of increased AD pathology in young people livingin areas with high air pollution (Calderon-Garciduenas et al2012) and in tobacco smokers (Chen 2012) together with find-ings of elevated brain levels of Ab40 and Ab42 in mice exposedto inhaled particulate matter (Kim et al 2012) provide strongevidence for the inhalation of airborne particulates as an envi-ronmental risk for common forms of AD Although no publishedreports have explored air pollutants in the context of exosomesand AD Moon et al (2014) showed cigarette smoke extractinduced the formation of lung epithelial cell-derived exosomesenriched with CCN1 They also showed CCN1 enhances IL-18(Moon et al 2014) an AD-associated proinflammatory cytokinethat increases Ab production in neuronal cells (Sutinen et al2012) Furthermore industrial air pollutants such as magneticiron oxide nanoparticles can significantly increase exosomebiogenesis and can induce systemic T-cell activation (Zhu et al2012) Since it appears that exposure to environmental neuro-toxicants greatly alters exosome biogenesis and Abtau aggre-gates in the exosomes more in-depth research is urgentlyneeded

Prion diseases are a class of fatal neurodegenerative dis-eases characterized by prion replication widespread proteinaggregation and spongiform degeneration of major brainregions controlling motor function (Harischandra et al 2014)The existence of sporadic forms of prion diseases such as scra-pie implies an environmental source for the infectious agentIndeed several transition metals are known to bind PrP andmetal-ion occupancy of PrP plays a pivotal role in the pathogen-esis of prion diseases (Choi et al 2006) Studies done by our lab-oratory and others show that binding to Mn (Choi et al 2010)Cu (Yen et al 2016) and Cd (Kanthasamy et al 2012) facilitatesthe structural conversion of PrP protein leading to its aggrega-tion and toxicity Importantly PrP is one of the most commonlyidentified cargo proteins in exosomes (Fevrier et al 2004) whichcan aid in the horizontal transmission of pathological prion pro-tein (PrPSc) (Liu et al 2016) A recent study shows that stimulat-ing the release of exosomes increases intercellular transfer ofprions (Guo et al 2016) highlighting an integral role for exo-somes in facilitating the unique transmissible nature of prions

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Furthermore exosomes are known to shuttle many miRNAsbetween donor and recipient cells and regulate prion expres-sion The small RNA miR-146a increases during metal-inducedneurotoxicity and oxidative stress conditions and has beenidentified in rare human prion diseases including sporadicCreutzfeldt-Jakob disease and Gerstmann-Streuroaussler-Scheinkersyndrome (Lukiw et al 2011)

ALS is another fatal progressive neurodegenerative diseaseaffecting predominantly motor neurons in the spinal cord andmotor cortex Previous studies have shown that environmentaltoxicants can alter superoxide dismutase and TAR-DNA-bindingprotein (TDP)-43 expression both of which are associated witha subset of ALS cases In addition TDP-43 has been linked tosporadic and familial frontotemporal lobar degeneration (FTLD)resulting in a proteinopathy phenotype in the frontal and ante-rior temporal lobes of the brain Interestingly paraquat expo-sure induces caspase-dependent accumulation of TDP-43fragments (Meyerowitz et al 2011) which causes inclusion for-mation and cellular toxicity (Zhang et al 2009) Given the pre-vious reports on TDP-43 enrichment in exosomes isolated fromTDP-43-expressing neuroblastoma cells exosomes extractedfrom the CSF of patients with ALS andor FTLD provide evidenceof their possible role in propagating TDP-43 between cells(Nonaka et al 2013 Thompson et al 2016) Furthermore thetransmission of misfolded wild-type CuZn SOD between cellsseems to be mediated through exosomal release and uptake ofprotein aggregates (Grad et al 2014) providing further evidenceof exosome-mediated prion-like intercellular transmission ofmisfolded proteins

TBI is another example of how environmental factors andlifestyle can influence the development of neurodegenerativediseases later in life Head injury is a signature injury in boxingfootball and military combat (Bahrami et al 2016 Mac Donaldet al 2011) Researchers have made a strong case linking TBIand neurological ailments such as AD PD and general demen-tia One such study conducted with 7130 participants identified117 cases of PD and 865 individuals with a history of TBI (Craneet al 2016) and another study found that middle-to-older agedpatients diagnosed with trauma have a 44 increased risk ofbeing diagnosed with PD (Gardner et al 2015) Furthermore anincrease in circulating exosomes in the blood of TBI patients

following injury has been reported (Graner et al 2013 Taylorand Gercel-Taylor 2014) Similarly increased exosomes andaltered cargo have been identified in cultured cortical neuronsin a stretch injury model of mild TBI (Ko et al 2016)Collectively such findings suggest that exosomes represent apotential biomarker and diagnostic tool for TBI A study per-formed by Zhang et al 2015) demonstrated that exosomes iso-lated from mesenchymal stem cells significantly increased thenumber of endothelial cells at the site of lesion thus restoringthe blood-brain barrier in a rodent model of TBI Although thespecific exosomal content that improved endothelial cell func-tion and immature neuron proliferation was not identified it isposited that the mesenchymal stem cells released growth fac-tors via EVs that in turn stimulated neurogenesis and improvedmemory in the rats following TBI

Gulf War Illness (GWI) is a chronic multi-symptom neurolog-ical disorder comprising cognitive dysfunction tremors andpsychological disturbance in approximately 25 of veteranswho were deployed to the Persian Gulf War 1990ndash1991 (Pariharet al 2013) Although the precise cause of GWI is unknowncombined exposure to the nerve gas drug pyridostigmine bro-mide and the pesticides DEET and permethrin has been pro-posed as one of the foremost causes (Parihar et al 2013) Therole of pesticide exposure in epigenetic alterations and geneexpression changes is well established (Jin et al 2014 Songet al 2011) and GWI toxicants were recently shown to induceepigenetic changes in a rat model of GWI (Pierce et al 2016)Here exosome RNA-seq analysis of circulating rat exosomesidentified GWI-induced changes in 2 rat exosomal piRNAs (an82-fold upregulation of rno-piR-007899 and a 72-fold downre-gulation of rno-piR-019162) demonstrating a role for environ-mental chemical exposure in exosomal small RNA cargochanges (Pierce et al 2016) This particularly interesting effectcould be exploited for reliable quantitative biomarkers in diag-nosing these neurological diseases

FUTURE DIRECTIONS

In summary there is a small but significant pool of researchthat elucidates the role of toxins and exosomes in carcinogene-sis or neurodegeneration (Table 1) With the capability of

Table 1 Environmental Toxicant-induced Exosomal Release and Associated Disease Pathogenesis

Environmental Toxicants Disease Pathogenesis Exosome Cargo References

Arsenite Lung carcinogenesis livercarcinogenesis

miR-21 miR-155 Xu et al (2015) Chen et al (2017)

Ionizing radiation Tracheal carcinoma miRNAs integrins and chemokines Mutschelknaus et al (2016)Diethylstilbestrol

genesteinUterine fibroids ovarian cancer Effectors of Wnt Hedgehog

and b-cateninYang et al (2016)

Cigarette smoke Lung carcinoma AD miR-21 IL-13 mediators ofWntb-catenin pathway CNN1

Wang et al (2015) Moon et al(2014)

Mn PD Synucleopathies otherneurodegenerative disease

aSyn Harischandra et al (2015b)

Monensin Prion disease PrP Guo Bellingham and Hill (2016)Rotenone PD Synucleopathies other

neurodegenerative diseaseaSyn Pan-Montojo et al (2012)

Paraquat Amyotrophic lateral sclerosis TDP-43 CuZn SOD Grad et al (2014)TBI Neuroinflammation Interleukins Amyloid-b40 Amyloid-b42

Spectrin breakdown productsGraner et al (2013) Taylor and

Gercel-Taylor (2014)Pyridostigmine bromide

PermethrinGWI rno-piR-007899 rno-piR-019162 Pierce et al (2016)

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transferring various biomolecules including miRNAs lipidsand signaling peptides over long distances exosomes havebecome an attractive research focus for understanding diseaseprogression for biomarker discovery and even as possible cell-based therapeutic delivery platforms Three reasons why exo-somes show tremendous potential in the field of nanomedi-cines are (1) exosomes can cross the blood-brain barrier todeliver therapeutic drugs or antioxidants (2) exosome mem-branes are rich in sphingomyelin cholesterol and glycerophos-pholipids with long saturated fatty acyl chains andphosphatidylserine which increases their stability and poten-tially favors their uptake thus making them effective drugdelivery vehicles and (3) exosomes derived from the same spe-cies typically should have only minimal immunogenicity thusreducing the potential risk of an immune response Howeverthe challenge here is to develop target-specific exosomes Alsodespite the abundant literature citing the potential diagnosticor therapeutic importance of these nanovesicles it is prematureto correlate changes in exosomal cargo with a disease stategiven the paucity of human studies validating results seen inpreclinical experiments Thus it is imperative to understandthe functional differences between cell type-specific anddisease-related exosomal contents As summarized in thisreview of recent reports chronic exposure to environmentaltoxins can stimulate exosome biogenesis and subsequent dis-ease pathogenesis In many cases the exosomes isolated fromtargeted patient populations contain altered cargo Howeverthe links between toxin exposure altered exosomal content anddisease progression are not clearly understood Hence futurestudies need to focus on understanding how environmentaltoxins tweak the biochemical pathways involved in selectingcellular material as exosome cargo and on how released cargoreprograms the cellular microenvironment leading to diseaseprogression

ACKNOWLEDGMENTS

We also like to thank Dr Huajun Jin and Gary Zenitsky forassistance in preparing this review

FUNDING

This work was supported by the National Institutes of HealthR01 grants (ES19267 ES10586 ES026892 and NS074443) to AGKThe W Eugene and Linda Lloyd Endowed Chair to AGK is alsoacknowledged

REFERENCESAguzzi A and Lakkaraju A K (2016) Cell biology of prions and

prionoids A status report Trends Cell Biol 26 40ndash51Alvarez-Erviti L Seow Y Schapira A H Gardiner C Sargent

I L Wood M J and Cooper J M (2011) Lysosomal dysfunc-tion increases exosome-mediated alpha-synuclein releaseand transmission Neurobiol Dis 42 360ndash367

Azmi A S Bao B and Sarkar F H (2013) Exosomes in cancerdevelopment metastasis and drug resistance A compre-hensive review Cancer Metastasis Rev 32 623ndash642

Bahrami N Sharma D Rosenthal S Davenport E M UrbanJ E Wagner B Jung Y Vaughan C G Gioia G A Stitzel JD et al (2016) Subconcussive head impact exposure andwhite matter tract changes over a single season of youthfootball Radiology 281 919ndash926

Barcellos-Hoff M H Derynck R Tsang M L and WeatherbeeJ A (1994) Transforming growth factor-beta activation in ir-radiated murine mammary gland J Clin Invest 93 892ndash899

Berry C La Vecchia C and Nicotera P (2010) Paraquat andParkinsonrsquos disease Cell Death Differ 17 1115ndash1125

Betarbet R Canet-Aviles R M Sherer T B MastroberardinoP G McLendon C Kim J H Lund S Na H M Taylor GBence N F et al (2006) Intersecting pathways to neurode-generation in Parkinsonrsquos disease Effects of the pesticide ro-tenone on DJ-1 alpha-synuclein and the ubiquitin-proteasome system Neurobiol Dis 22 404ndash420

Betarbet R Sherer T B MacKenzie G Garcia-Osuna MPanov A V and Greenamyre J T (2000) Chronic systemicpesticide exposure reproduces features of Parkinsonrsquos dis-ease Nat Neurosci 3 1301ndash1306

Braak H de Vos R A Bohl J and Del Tredici K (2006) Gastricalpha-synuclein immunoreactive inclusions in Meissnerrsquosand Auerbachrsquos plexuses in cases staged for Parkinsonrsquosdisease-related brain pathology Neurosci Lett 396 67ndash72

Brenza T M Ghaisas S Ramirez J E Harischandra DAnantharam V Kalyanaraman B Kanthasamy A G andNarasimhan B (2016) Neuronal protection against oxidativeinsult by polyanhydride nanoparticle-based mitochondria-targeted antioxidant therapy Nanomedicine 13 809ndash820

Cai T Yao T Zheng G Chen Y Du K Cao Y Shen XChen J and Luo W (2010) Manganese induces the overex-pression of alpha-synuclein in PC12 cells via ERK activationBrain Res 1359 201ndash207

Calderon-Garciduenas L Kavanaugh M Block M DrsquoAngiulliA Delgado-Chavez R Torres-Jardon R Gonzalez-MacielA Reynoso-Robles R Osnaya N Villarreal-Calderon Ret al (2012) Neuroinflammation hyperphosphorylated taudiffuse amyloid plaques and down-regulation of the cellularprion protein in air pollution exposed children and youngadults J Alzheimers Dis 28 93ndash107

Chai E Z P Siveen K S Shanmugam M K Arfuso F andSethi G (2015) Analysis of the intricate relationship be-tween chronic inflammation and cancer Biochem J 4681ndash15

Challagundla K B Fanini F Vannini I Wise P Murtadha MMalinconico L Cimmino A and Fabbri M (2014)microRNAs in the tumor microenvironment Solving the rid-dle for a better diagnostics Expert Rev Mol Diagn 14565ndash574

Chen C Luo F Liu X Lu L Xu H Yang Q Xue J Shi L LiJ Zhang A et al (2017) NF-kB-regulated exosomal miR-155promotes the inflammation associated with arsenite carci-nogenesis Cancer Lett 388 21ndash33

Chen R (2012) Association of environmental tobacco smokewith dementia and Alzheimerrsquos disease among never smok-ers Alzheimers Dement 8 590ndash595

Choi C J Anantharam V Martin D P Nicholson E M RichtJ A Kanthasamy A and Kanthasamy A G (2010)Manganese upregulates cellular prion protein and contrib-utes to altered stabilization and proteolysis Relevance torole of metals in pathogenesis of prion disease Toxicol Sci115 535ndash546

Choi C J Kanthasamy A Anantharam V and KanthasamyA G (2006) Interaction of metals with prion protein Possiblerole of divalent cations in the pathogenesis of prion diseasesNeurotoxicology 27 777ndash787

Colombo M Moita C van Niel G Kowal J Vigneron JBenaroch P Manel N Moita L F Thery C and Raposo G(2013) Analysis of ESCRT functions in exosome biogenesis

10 | TOXICOLOGICAL SCIENCES 2017 Vol 158 No 1

Dow

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ay 2020

composition and secretion highlights the heterogeneity ofextracellular vesicles J Cell Sci 126 5553ndash5565

Colombo M Raposo G and Thery C (2014) Biogenesis secre-tion and intercellular interactions of exosomes and otherextracellular vesicles Annu Rev Cell Dev Biol 30 255ndash289

Cook C Stetler C and Petrucelli L (2012) Disruption of proteinquality control in Parkinsonrsquos disease Cold Spring HarbPerspect Med 2 a009423

Cordazzo C Petrini S Neri T Lombardi S Carmazzi YPedrinelli R Paggiaro P and Celi A (2014) Rapid sheddingof proinflammatory microparticles by human mononuclearcells exposed to cigarette smoke is dependent on Ca2thornmobi-lization Inflamm Res 63 539ndash547

Crane P K Gibbons L E Dams-OrsquoConnor K Trittschuh ELeverenz J B Keene C D Sonnen J Montine T JBennett D A Leurgans S et al (2016) Association of trau-matic brain injury with late-life neurodegenerative condi-tions and neuropathologic findings JAMA Neurol 73 1062

Crow J Atay S Banskota S Artale B Schmitt S andGodwin A K (2017) Exosomes as mediators of platinum re-sistance in ovarian cancer Oncotarget 8 11917ndash11936

Dagda R K Das Banerjee T and Janda E (2013) HowParkinsonian toxins dysregulate the autophagy machineryInt J Mol Sci 14 22163ndash22189

Danzer K M Kranich L R Ruf W P Cagsal-Getkin OWinslow A R Zhu L Vanderburg C R and McLean P J(2012) Exosomal cell-to-cell transmission of alpha synucleinoligomers Mol Neurodegener 7 42

DeRita R M Zerlanko B Singh A Lu H Iozzo R V BenovicJ L and Languino L R (2017) c-Src Insulin-like growth fac-tor I receptor G-protein-coupled receptor kinases and focaladhesion kinase are enriched into prostate cancer cell exo-somes J Cell Biochem 118 66ndash73

Emmanouilidou E Melachroinou K Roumeliotis T Garbis SD Ntzouni M Margaritis L H Stefanis L and Vekrellis K(2010) Cell-produced alpha-synuclein is secreted in acalcium-dependent manner by exosomes and impacts neu-ronal survival J Neurosci 30 6838ndash6851

Fevrier B Vilette D Archer F Loew D Faigle W Vidal MLaude H and Raposo G (2004) Cells release prions in asso-ciation with exosomes Proc Natl Acad Sci USA 1019683ndash9688

Gardner R C Burke J F Nettiksimmons J Goldman STanner C M and Yaffe K (2015) Traumatic brain injury inlater life increases risk for Parkinson disease Ann Neurol 77987ndash995

Ghaisas S Maher J and Kanthasamy A (2016) Gut micro-biome in health and disease Linking the microbiome-gut-brain axis and environmental factors in the pathogenesis ofsystemic and neurodegenerative diseases Pharmacol Ther158 52ndash62

Ghidoni R Benussi L and Binetti G (2008) Exosomes TheTrojan horses of neurodegeneration Med Hypotheses 701226ndash1227

Gitler A D Chesi A Geddie M L Strathearn K EHamamichi S Hill K J Caldwell K A Caldwell G ACooper A A Rochet J C et al (2009) Alpha-synuclein ispart of a diverse and highly conserved interaction networkthat includes PARK9 and manganese toxicity Nat Genet 41308ndash315

Goldkorn T and Filosto S (2010) Lung Injury and Cancer Am JRespir Cell Mol Biol 43 259ndash268

Goldman S M (2014) Environmental toxins and Parkinsonrsquosdisease Annu Rev Pharmacol Toxicol 54 141ndash164

Grad L I Yerbury J J Turner B J Guest W C PokrishevskyE OrsquoNeill M A Yanai A Silverman J M Zeineddine RCorcoran L et al (2014) Intercellular propagated misfoldingof wild-type CuZn superoxide dismutase occurs viaexosome-dependent and -independent mechanisms ProcNatl Acad Sci USA 111 3620ndash3625

Graner M W Epple L M Dusto N L Lencioni A M Nega MHerring M Winston B Madsen H Bemis L T andAnchordoquy T J (2013) Circulating exosomes as new bio-markers for brain disease and injury pp 87230Rndash87230R-12Available at httpdxdoiorg101117122027435 AccessedApril 28 2017

Grey M Dunning C J Gaspar R Grey C Brundin P Sparr Eand Linse S (2015) Acceleration of alpha-synuclein aggrega-tion by exosomes J Biol Chem 290 2969ndash2982

Guo B B Bellingham S A and Hill A F (2016) Stimulating therelease of exosomes increases the intercellular transfer ofprions J Biol Chem 291 5128ndash5137

Harischandra D S Jin H Anantharam V Kanthasamy Aand Kanthasamy A G (2015a) alpha-Synuclein protectsagainst manganese neurotoxic insult during the early stagesof exposure in a dopaminergic cell model of Parkinsonrsquos dis-ease Toxicol Sci 143 454ndash468

Harischandra D S Kondru N Martin D P Kanthasamy AJin H Anantharam V and Kanthasamy A G (2014) Role ofproteolytic activation of protein kinase Cdelta in the patho-genesis of prion disease Prion 8 143ndash153

Harischandra D S Lawana V Rhokad D Jin H AnantharamV Kanthasamy A and Kanthasamy A (2015b) Lysosomaldysfunction caused by the environmental neurotoxicantmanganese increases exosome-mediated cell-to-cell trans-fer of a-synuclein by a prion-like mechanism NeurotoxicolTeratol 49 109

Hoshino A Costa-Silva B Shen T-L Rodrigues GHashimoto A Tesic Mark M Molina H Kohsaka S DiGiannatale A Ceder S et al (2015) Tumour exosomeintegrins determine organotropic metastasis Nature 527329ndash335

Howitt J and Hill A F (2016) Exosomes in the pathology ofneurodegenerative diseases J Biol Chem 291 26589ndash26597

Jin H Kanthasamy A Harischandra D S Kondru N GhoshA Panicker N Anantharam V Rana A and KanthasamyA G (2014) Histone hyperacetylation up-regulates proteinkinase Cdelta in dopaminergic neurons to induce cell deathRelevance to epigenetic mechanisms of neurodegenerationin Parkinson disease J Biol Chem 289 34743ndash34767

Kamel F and Hoppin J A (2004) Association of pesticide expo-sure with neurologic dysfunction and disease Environ HealthPerspect 112 950ndash958

Kanthasamy A G Choi C Jin H Harischandra D SAnantharam V and Kanthasamy A (2012) Effect of diva-lent metals on the neuronal proteasomal system prion pro-tein ubiquitination and aggregation Toxicol Lett 214288ndash295

Kanthasamy A G Kitazawa M Kanthasamy A andAnantharam V (2005) Dieldrin-induced neurotoxicityRelevance to Parkinsonrsquos disease pathogenesisNeurotoxicology 26 701ndash719

Kim J H Kim H R Lee B R Choi E S In S I and Kim E(2015) Carcinogenic activity of PbS quantum dots screenedusing exosomal biomarkers secreted from HEK293 cells Int JNanomed 10 5513ndash5527

Kim S H Knight E M Saunders E L Cuevas A K PopovechM Chen L C and Gandy S (2012) Rapid doubling of

HARISCHANDRA ET AL | 11

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Alzheimerrsquos amyloid-beta40 and 42 levels in brains of miceexposed to a nickel nanoparticle model of air pollutionF1000Res 1 70

Ko J Hemphill M A Gabrieli D Wu L Yelleswarapu VLawrence G Pennycooke W Singh A Meaney D F andIssadore D (2016) Smartphone-enabled optofluidic exo-some diagnostic for concussion recovery Sci Rep 6 31215

Kong S M Chan B K Park J S Hill K J Aitken J B Cottle LFarghaian H Cole A R Lay P A Sue C M et al (2014)Parkinsonrsquos disease-linked human PARK9ATP13A2 main-tains zinc homeostasis and promotes alpha-Synuclein exter-nalization via exosomes Hum Mol Genet 23 2816ndash2833

Le M T Hamar P Guo C Basar E Perdigao-Henriques RBalaj L and Lieberman J (2014) miR-200-containing extra-cellular vesicles promote breast cancer cell metastasisJ Clin Invest 124 5109ndash5128

Leveuroanen B Bhakta N R Torregrosa Paredes P Barbeau RHiltbrunner S Pollack J L Skold C M Svartengren MGrunewald J Gabrielsson S et al (2013) Altered microRNAprofiles in bronchoalveolar lavage fluid exosomes in asth-matic patients J Allergy Clin Immunol 131 894ndash903

Li B Ren S Li X Wang Y Garfield D Zhou S Chen X SuC Chen M Kuang P et al (2014) MiR-21 overexpression isassociated with acquired resistance of EGFR-TKI in non-small cell lung cancer Lung Cancer 83 146ndash153

Liu S Hossinger A Hofmann J P Denner P and Vorberg IM (2016) Horizontal transmission of cytosolic Sup35 prionsby extracellular vesicles MBio 7(4) e00915ndashe00916

Lu T X Munitz A and Rothenberg M E (2009) MicroRNA-21is up-regulated in allergic airway inflammation and regu-lates IL-12p35 expression J Immunol 182 4994ndash5002

Lukiw W J Dua P Pogue A I Eicken C and Hill J M (2011)Upregulation of micro RNA-146a (miRNA-146a) a marker forinflammatory neurodegeneration in sporadic Creutzfeldt-Jakob disease (sCJD) and Gerstmann-Straussler-Scheinker(GSS) syndrome J Toxicol Environ Health A 74 1460ndash1468

Mac Donald C L Johnson A M Cooper D Nelson E CWerner N J Shimony J S Snyder A Z Raichle M EWitherow J R Fang R et al (2011) Detection of blast-related traumatic brain injury in US military personnel NEngl J Med 364 2091ndash2100

Massague J (2008) TGFbeta in cancer Cell 134 215ndash230Meyerowitz J Parker S J Vella L J Ng D Price K A Liddell

J R Caragounis A Li Q X Masters C L Nonaka T et al(2011) C-Jun N-terminal kinase controls TDP-43 accumula-tion in stress granules induced by oxidative stress MolNeurodegener 6 57

Mishra P J Mishra P J Humeniuk R Medina D J AlexeG Mesirov J P Ganesan S Glod J W and Banerjee D(2008) Carcinoma-associated fibroblast-like differentiationof human mesenchymal stem cells Cancer Res 684331ndash4339

Moon H G Kim S H Gao J Quan T Qin Z Osorio J CRosas I O Wu M Tesfaigzi Y and Jin Y (2014) CCN1 se-cretion and cleavage regulate the lung epithelial cell func-tions after cigarette smoke Am J Physiol Lung Cell MolPhysiol 307 L326ndashL337

Mutschelknaus L Peters C Winkler K Yentrapalli R HeiderT Atkinson M J and Moertl S (2016) Exosomes Derivedfrom Squamous Head and Neck Cancer Promote CellSurvival after Ionizing Radiation PLoS One 11(3) e0152213

Nelson R Sawaya M R Balbirnie M Madsen A O Riekel CGrothe R and Eisenberg D (2005) Structure of the cross-beta spine of amyloid-like fibrils Nature 435 773ndash778

Nonaka T Masuda-Suzukake M Arai T Hasegawa YAkatsu H Obi T Yoshida M Murayama S Mann D MAkiyama H et al (2013) Prion-like properties of pathologicalTDP-43 aggregates from diseased brains Cell Rep 4 124ndash134

Pan-Montojo F Anichtchik O Dening Y Knels L Pursche SJung R Jackson S Gille G Spillantini M G ReichmannH et al (2010) Progression of Parkinsonrsquos disease pathologyis reproduced by intragastric administration of rotenone inmice PLoS One 5 e8762

Pan-Montojo F Schwarz M Winkler C Arnhold MOrsquoSullivan G A Pal A Said J Marsico G Verbavatz J MRodrigo-Angulo M et al (2012) Environmental toxins triggerPD-like progression via increased alpha-synuclein releasefrom enteric neurons in mice Sci Rep 2 898

Parihar V K Hattiangady B Shuai B and Shetty A K (2013)Mood and memory deficits in a model of Gulf War illness arelinked with reduced neurogenesis partial neuron loss and mildinflammation in the hippocampus Neuropsychopharmacology38 2348ndash2362

Peinado H Aleckovic M Lavotshkin S Matei I Costa-SilvaB Moreno-Bueno G Hergueta-Redondo M Williams CGarcia-Santos G Ghajar C et al (2012) Melanoma exo-somes educate bone marrow progenitor cells toward a pro-metastatic phenotype through MET Nat Med 18 883ndash891

Peng P Yan Y and Keng S (2011) Exosomes in the ascites ofovarian cancer patients Origin and effects on anti-tumor im-munity Oncol Rep 25 749ndash762

Peres T V Parmalee N L Martinez-Finley E J and AschnerM (2016) Untangling the manganese-alpha-synuclein webFront Neurosci 10 364

Pierce L M Kurata W E Matsumoto K W Clark M E andFarmer D M (2016) Long-term epigenetic alterations in a ratmodel of Gulf War Illness Neurotoxicology 55 20ndash32

Pohl M Radacz Y Pawlik N Schoeneck A Baldus S EMunding J Schmiegel W Schwarte-Waldhoff I andReinacher-Schick A (2010) SMAD4 mediates mesenchymal-epithelial reversion in SW480 colon carcinoma cellsAnticancer Res 30 2603-13

Rahman M A Barger J F Lovat F Gao M Otterson G A andNana-Sinkam P (2016) Lung cancer exosomes as drivers ofepithelial mesenchymal transition Oncotarget 754852ndash54866

Rajendran L Honsho M Zahn T R Keller P Geiger K DVerkade P and Simons K (2006) Alzheimerrsquos disease beta-amyloid peptides are released in association with exosomesProc Natl Acad Sci USA 103 11172ndash11177

Raposo G Nijman H W Stoorvogel W Liejendekker RHarding C V Melief C J and Geuze H J (1996) B lympho-cytes secrete antigen-presenting vesicles J Exp Med 1831161ndash1172

Rentschler G Covolo L Haddad A A Lucchini R G Zoni Sand Broberg K (2012) ATP13A2 (PARK9) polymorphisms in-fluence the neurotoxic effects of manganese Neurotoxicology33 697ndash702

Rokad D Ghaisas S Harischandra D S Jin H AnantharamV Kanthasamy A and Kanthasamy A G (2016) Role ofneurotoxicants and traumatic brain injury in alpha-synuclein protein misfolding and aggregation Brain Res Bulldoi 101016jbrainresbull201612003 In Press

Ross C A and Poirier M A (2004) Protein aggregation and neu-rodegenerative disease Nat Med 10(Suppl) S10ndashS17

Santoro L Breedveld G J Manganelli F Iodice R Pisciotta CNolano M Punzo F Quarantelli M Pappata S Di FonzoA et al (2011) Novel ATP13A2 (PARK9) homozygous

12 | TOXICOLOGICAL SCIENCES 2017 Vol 158 No 1

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mutation in a family with marked phenotype variabilityNeurogenetics 12 33ndash39

Schmidt K Wolfe D M Stiller B and Pearce D A (2009)Cd2thorn Mn2thorn Ni2thorn and Se2thorn toxicity to Saccharomyces cere-visiae lacking YPK9p the orthologue of human ATP13A2Biochem Biophys Res Commun 383 198ndash202

Shannon K M Keshavarzian A Dodiya H B Jakate S andKordower J H (2012) Is alpha-synuclein in the colon a bio-marker for premotor Parkinsonrsquos disease Evidence from 3cases Mov Disord 27 716ndash719

Silverman J M Clos J Horakova E Wang A Y Wiesgigl MKelly I Lynn M A McMaster W R Foster L J Levings MK et al (2010) Leishmania exosomes modulate innate andadaptive immune responses through effects on monocytesand dendritic cells J Immunol 185 5011ndash5022

Song C Kanthasamy A Jin H Anantharam V andKanthasamy A G (2011) Paraquat induces epigeneticchanges by promoting histone acetylation in cell culturemodels of dopaminergic degeneration Neurotoxicology 32586ndash595

Stewart D J (2007) Mechanisms of resistance to cisplatin andcarboplatin Crit Rev Oncol Hematol 63 12ndash31

Sutinen E M Pirttila T Anderson G Salminen A and OjalaJ O (2012) Pro-inflammatory interleukin-18 increasesAlzheimerrsquos disease-associated amyloid-beta production inhuman neuron-like cells J Neuroinflammation 9 199

Takahashi R H Milner T A Li F Nam E E Edgar M AYamaguchi H Beal M F Xu H Greengard P and GourasG K (2002) Intraneuronal Alzheimer abeta42 accumulatesin multivesicular bodies and is associated with synaptic pa-thology Am J Pathol 161 1869ndash1879

Taylor D D and Gercel-Taylor C (2014) Exosome platformfor diagnosis and monitoring of traumatic brain injuryPhilos Trans R Soc Lond B Biol Sci 369(1652) 101098rstb20130503

Thery C Zitvogel L and Amigorena S (2002) ExosomesComposition biogenesis and function Nat Rev Immunol 2569ndash579

Thompson A G Gray E Heman-Ackah S M Mager I TalbotK Andaloussi S E Wood M J and Turner M R (2016)Extracellular vesicles in neurodegenerative disease - patho-genesis to biomarkers Nat Rev Neurol 12 346ndash357

Tsunemi T Hamada K and Krainc D (2014) ATP13A2PARK9regulates secretion of exosomes and alpha-synucleinJ Neurosci 34 15281ndash15287

Wu J Yang T Li X Yang Q Liu R Huang J Li Y Yang Cand Jiang Y (2013) Alteration of serum miR-206 and miR-133b is associated with lung carcinogenesis induced by 4-

(methylnitrosamino)-1-(3-pyridyl)-1-butanone Toxicol ApplPharmacol 267 238ndash246

Xu B Xu Z F and Deng Y (2009) Effect of manganese expo-sure on intracellular Ca2thorn homeostasis and expression ofNMDA receptor subunits in primary cultured neuronsNeurotoxicology 30 941ndash949

Xu Y Luo F Liu Y Shi L Lu X Xu W and Liu Q (2015)Exosomal miR-21 derived from arsenite-transformed humanbronchial epithelial cells promotes cell proliferation associ-ated with arsenite carcinogenesis Arch Toxicol 891071ndash1082

Yang J Hu J Weng M Tan R Tian L Yang J Amine JZheng J Chen H and Pan F (2017) Fe-Cluster pushingelectrons to N-doped graphitic layers with Fe3C(Fe) hybridnanostructure to enhance O2 reduction catalysis of Zn-airbatteries ACS Appl Mater Interfaces 9 4587ndash4596

Yang Q Diamond M P and Al-Hendy A (2016) Early life ad-verse environmental exposures increase the risk of uterinefibroid development Role of epigenetic regulation FrontPharmacol 7 40

Yegambaram M Manivannan B Beach T G and Halden R U(2015) Role of environmental contaminants in the etiologyof Alzheimerrsquos disease A review Curr Alzheimer Res 12116ndash146

Yen C F Harischandra D S Kanthasamy A and SivasankarS (2016) Copper-induced structural conversion templatesprion protein oligomerization and neurotoxicity Sci Adv 2e1600014

Zhang H Shih J Zhu J and Kotov N A (2012) Layered nano-composites from gold nanoparticles for neural prosthetic de-vices Nano Lett 12 3391ndash3398

Zhang Y Chopp M Meng Y Katakowski M Xin HMahmood A and Xiong Y (2015) Effect of exosomes de-rived from multipluripotent mesenchymal stromal cells onfunctional recovery and neurovascular plasticity in rats aftertraumatic brain injury J Neurosurg 122 856ndash867

Zhang Y J Xu Y F Cook C Gendron T F Roettges P LinkC D Lin W L Tong J Castanedes-Casey M Ash P et al(2009) Aberrant cleavage of TDP-43 enhances aggregationand cellular toxicity Proc Natl Acad Sci USA 106 7607ndash7612

Zhou W Fong M Y Min Y Somlo G Liu L Palomares M RYu Y Chow A OrsquoConnor S T Chin A R et al (2014)Cancer-secreted miR-105 destroys vascular endothelial bar-riers to promote metastasis Cancer Cell 25 501ndash515

Zhu M Li Y Shi J Feng W Nie G and Zhao Y (2012)Exosomes as extrapulmonary signaling conveyors fornanoparticle-induced systemic immune activation Small 8404ndash412

HARISCHANDRA ET AL | 13

Dow

nloaded from httpsacadem

icoupcomtoxsciarticle-abstract158133827743 by guest on 26 M

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mutation in a family with marked phenotype variabilityNeurogenetics 12 33ndash39

Schmidt K Wolfe D M Stiller B and Pearce D A (2009)Cd2thorn Mn2thorn Ni2thorn and Se2thorn toxicity to Saccharomyces cere-visiae lacking YPK9p the orthologue of human ATP13A2Biochem Biophys Res Commun 383 198ndash202

Shannon K M Keshavarzian A Dodiya H B Jakate S andKordower J H (2012) Is alpha-synuclein in the colon a bio-marker for premotor Parkinsonrsquos disease Evidence from 3cases Mov Disord 27 716ndash719

Silverman J M Clos J Horakova E Wang A Y Wiesgigl MKelly I Lynn M A McMaster W R Foster L J Levings MK et al (2010) Leishmania exosomes modulate innate andadaptive immune responses through effects on monocytesand dendritic cells J Immunol 185 5011ndash5022

Song C Kanthasamy A Jin H Anantharam V andKanthasamy A G (2011) Paraquat induces epigeneticchanges by promoting histone acetylation in cell culturemodels of dopaminergic degeneration Neurotoxicology 32586ndash595

Stewart D J (2007) Mechanisms of resistance to cisplatin andcarboplatin Crit Rev Oncol Hematol 63 12ndash31

Sutinen E M Pirttila T Anderson G Salminen A and OjalaJ O (2012) Pro-inflammatory interleukin-18 increasesAlzheimerrsquos disease-associated amyloid-beta production inhuman neuron-like cells J Neuroinflammation 9 199

Takahashi R H Milner T A Li F Nam E E Edgar M AYamaguchi H Beal M F Xu H Greengard P and GourasG K (2002) Intraneuronal Alzheimer abeta42 accumulatesin multivesicular bodies and is associated with synaptic pa-thology Am J Pathol 161 1869ndash1879

Taylor D D and Gercel-Taylor C (2014) Exosome platformfor diagnosis and monitoring of traumatic brain injuryPhilos Trans R Soc Lond B Biol Sci 369(1652) 101098rstb20130503

Thery C Zitvogel L and Amigorena S (2002) ExosomesComposition biogenesis and function Nat Rev Immunol 2569ndash579

Thompson A G Gray E Heman-Ackah S M Mager I TalbotK Andaloussi S E Wood M J and Turner M R (2016)Extracellular vesicles in neurodegenerative disease - patho-genesis to biomarkers Nat Rev Neurol 12 346ndash357

Tsunemi T Hamada K and Krainc D (2014) ATP13A2PARK9regulates secretion of exosomes and alpha-synucleinJ Neurosci 34 15281ndash15287

Wu J Yang T Li X Yang Q Liu R Huang J Li Y Yang Cand Jiang Y (2013) Alteration of serum miR-206 and miR-133b is associated with lung carcinogenesis induced by 4-

(methylnitrosamino)-1-(3-pyridyl)-1-butanone Toxicol ApplPharmacol 267 238ndash246

Xu B Xu Z F and Deng Y (2009) Effect of manganese expo-sure on intracellular Ca2thorn homeostasis and expression ofNMDA receptor subunits in primary cultured neuronsNeurotoxicology 30 941ndash949

Xu Y Luo F Liu Y Shi L Lu X Xu W and Liu Q (2015)Exosomal miR-21 derived from arsenite-transformed humanbronchial epithelial cells promotes cell proliferation associ-ated with arsenite carcinogenesis Arch Toxicol 891071ndash1082

Yang J Hu J Weng M Tan R Tian L Yang J Amine JZheng J Chen H and Pan F (2017) Fe-Cluster pushingelectrons to N-doped graphitic layers with Fe3C(Fe) hybridnanostructure to enhance O2 reduction catalysis of Zn-airbatteries ACS Appl Mater Interfaces 9 4587ndash4596

Yang Q Diamond M P and Al-Hendy A (2016) Early life ad-verse environmental exposures increase the risk of uterinefibroid development Role of epigenetic regulation FrontPharmacol 7 40

Yegambaram M Manivannan B Beach T G and Halden R U(2015) Role of environmental contaminants in the etiologyof Alzheimerrsquos disease A review Curr Alzheimer Res 12116ndash146

Yen C F Harischandra D S Kanthasamy A and SivasankarS (2016) Copper-induced structural conversion templatesprion protein oligomerization and neurotoxicity Sci Adv 2e1600014

Zhang H Shih J Zhu J and Kotov N A (2012) Layered nano-composites from gold nanoparticles for neural prosthetic de-vices Nano Lett 12 3391ndash3398

Zhang Y Chopp M Meng Y Katakowski M Xin HMahmood A and Xiong Y (2015) Effect of exosomes de-rived from multipluripotent mesenchymal stromal cells onfunctional recovery and neurovascular plasticity in rats aftertraumatic brain injury J Neurosurg 122 856ndash867

Zhang Y J Xu Y F Cook C Gendron T F Roettges P LinkC D Lin W L Tong J Castanedes-Casey M Ash P et al(2009) Aberrant cleavage of TDP-43 enhances aggregationand cellular toxicity Proc Natl Acad Sci USA 106 7607ndash7612

Zhou W Fong M Y Min Y Somlo G Liu L Palomares M RYu Y Chow A OrsquoConnor S T Chin A R et al (2014)Cancer-secreted miR-105 destroys vascular endothelial bar-riers to promote metastasis Cancer Cell 25 501ndash515

Zhu M Li Y Shi J Feng W Nie G and Zhao Y (2012)Exosomes as extrapulmonary signaling conveyors fornanoparticle-induced systemic immune activation Small 8404ndash412

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