Reactive Oxygen Species & Signal Trans Duct Ion 2

8/3/2019 Reactive Oxygen Species & Signal Trans Duct Ion 2

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P R E S E N T E D B Y S H A N O O S U R O O W A N

Reactive oxygen species &

signal transduction


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A radical is an atom/ group of atoms having one/moreunpaired electrons.

There are many types of radicals, but the most prominent

in biological systems are derived from oxygen collectivelyknown as Reactive Oxygen Species (ROS),

Oxygen in its ground state has 2 unpairedelectrons........Remember? O8: 1s2 2s2 2p4

So it is easy for Oxygen to accept electrons to form freeradicals (Reactive Oxygen Species in this case!)


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ROS formation in cells

These are formed as normal aerobic processes that

occur in the body; some as necessary intermediatesof enzymatic reactions.

Most are produced in the ETC when oxygen is

reduced to water in the mitochondria.O2 reduction H2O

During this conversion various reactive oxygen

species are formed!

O2 .O2 H2O2 .OH- H2O

(oxygen) (superoxide) (hydrogen peroxide) (hydroxyl ion) (water)


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Overproduction of ROS

Neutrophils are specialized in ROS formation whichdestroy pathogens as part of host defence.

When cells are exposed to abnormal environmentssuch as hypoxia and hyperoxia.

From ionizing radiation in biological systems.Ionizing radiation will ionize molecular oxygen bypushing an electron in its outer orbit.

If oxygen species are overproduced it will bedifficult for the cell to detoxify them and repair thedamages they make! Result: Oxidative stress!

So Oxidative stress is an imbalance btw reactiveoxygen species and antioxidants!


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Harmful activities of ROS

Damage to a number of macromolecules such aslipids, proteins and DNA caused by ROS implicatethem in many disease processes, ranging from

arthritis, atherosclerosis, pulmonary fibrosis,cancer, neurodegenerative diseases, and aging

Toxic effects such as damage to cell membranesinitiated by lipid peroxidation.

A common target for peroxidation is unsaturatedfatty acids present in membrane phospholipids


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Lipid peroxidation....

Consequences of lipid peroxidation: increased membrane rigidity decreased activity of membrane-bound enzymes (e.g. sodium pumps) altered activity of membrane receptors.

altered permiability
http://www.vivo.colostate.edu/hbooks/molecules/sodium_pump.htmlhttp://www.vivo.colostate.edu/hbooks/molecules/sodium_pump.html


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Antioxidants of the body

1. Intracellular antioxidants:

vitamin E

ascorbate(vitamin C)

glutathione (glutamate-cysteine-glycine) [GSH]

2. Enzymatic antioxidants:

Superoxide dismutases(SODs)

Catalase

Gluthione peroxidase


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Intracellular antioxidants

Vitamin E; a lipid soluble antioxidant that trapsperoxy radicals while doing so it itself becomes aradical

Vitamin C regenerates back vitamin E from itsradical form


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Enzymatic antioxidants

Superoxide dismutases (SODs) Mostly found in the mitochondria

They depend on cofactors such as manganese, copper or zincfor their antioxidant activity.

They convert 2 superoxide ions into oxygen and hydrogenperoxide

Catalase hydrolyses hydrogen peroxide into water andoxygen! Site of location; peroxisomes

Glutathione peroxidase also hydrolyze hydrogenperoxide and can convert organic peroxides to alcohol


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SIGNALTRANSDUCTION


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Extracellular Signal(growth factor/cytokines/neurotransmitter/hormone)

Binds to specific Receptor

Interaction of receptor-ligand complex

Generates a wide variety of intracellular signals:

1. Changes in ion concentration

2. Activation of trimeric GTP binding regulatory proteins

3. Activation of receptor kinases

Downstream signaling by secondary messengers

(cAMP, Ca2+, phospholipid metabolites)

Activation of transcription factors for transcription of

specific genes for diverse cellular functions


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Oxidants and signal transduction

Oxidants modulate cell signaling events bymodifying cell surface receptors, phosphatases andprotein phosphorylation, etc.

These phenomena are important in transactivationof transcription factors

activation/inactivation of gene transcription thatmay regulate steps in the development of disease.


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ROS and Signal Transduction

ROS are important mediators in signal transduction

Receptor + hormone(upstream signaling)

Receptor-ligand complex

Intracellular ROS production

(downstream signaling)

activates

Other pathways

promote regions of intermediate response genes governing cellproliferation, differentiation, etc. ROS are involved in both upregulation and

downregulation pathways!


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ROS and Signal Transduction

ROS are not only injurious by-products of cellularmetabolism but also essential participants in cellsignaling and regulation

The cellular functions/toxic properties of ROS is

dependent on their concentration. For e.g. when produced in low concentrations by

nitric oxide synthase(NOS) NO functions as asignaling molecule mediating vasodilation

While when produced in high concentrations inmacrophages, it is a toxic oxidant for microbicidalkilling


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Cellular sources and regulation of ROS

Cellular production of ROS occurs from bothenzymatic and nonenzymatic sources

any electron-transferring protein or enzymatic

system can result in the formation of ROS as by-products

ROS are mostly produced in the mitochondria,H2O2 can diffuse out in the cytoplasm while O2.-

remains trapped in. O2

-generating microsomal NADH oxidoreductasemay function as a potential pulmonary artery O2sensor in pulmonary artery smooth muscle cells


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Nuclear membranes contain cytochrome oxidases and ETC.Electron leaks from these enzymatic systems gives rise toROS that can damage cellular DNA

Peroxisomes are an important source of total cellular H2O2

production. They contain a number of H2O2-generatingenzymes including glycolate oxidase, d-amino acid oxidase.

Peroxisomal catalase utilizes H2O2 produced by theseoxidases to oxidize a variety of other substrates inperoxidative reactions e.g. detoxification of alcohol in theliver

Intracellular soluble enzymes such as xanthine oxidase,aldehyde oxidase, can generate ROS during catalytic cycling


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Autooxidation of small molecules such as dopamine,epinephrine can be an important source of intracellularROS production.

Prooxidant effects of dopamine autooxidation is

implicated in the pathogenesis of neurodegenerativediseases such as Parkinson's disease

Plasma membrane-associated oxidases have beenimplicated as the sources of most growth factor- and/orcytokine-stimulated oxidant production

The phagocytic NADPH oxidase, which serves aspecialized function in host defense against invadingmicroorganisms


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functional components of the phagocytic NADPH arepresent in nonphagocytic cells.

P22phox is a component of NADPH oxidase and plays akey role in its activation

Expression of p22phoxhas been demonstrated in theadventitial smooth muscle cells of coronary arteries andthe aorta

Increased aortic adventitial O2 production contributes

to hypertension by blocking the vasodilatory effects ofNO

ROS production in coronary arteries is related tohypertension


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ROS in cell signaling


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ROS signaling by receptors

The following receptors are involved in ROSsignaling :-

Cytokine receptors

Receptor tyrosine kinases (RTKs)

Receptor serine/threonine kinases

G-protein coupled receptor

These receptors will generate intracellular signals for ROSproduction

i li b ki


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ROS signaling by cytokine receptors

1.TNF-

Mediate ROS formation inmitochondria

Activates the TF nuclear factor(NF)-kB

nuclear factor (NF)-kBdependent transcription

Makes cancer cells resistant toapoptosis

Activates apoptosis signal-regulating kinase-1 (ASK 1)

How?

Oxidant dependentdimerization of ASK 1

ASK1 has been found to beinvolved in cancer, diabetes,cardiovascular andneurodegenerative diseases


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TNF- is an autocrine cytokine involved in ROS signaling bycytokine receptors (upstream transduction)

The ROS produced have various implications in downstreamsignaling such as:- the expression of cell adhesion molecules from genes production of chemokines In pathophysiological conditions such as induction of cardiac myocyte

hypertrophy

2.IFN-

(activator of the phagocytic NADPH oxidase)

Stimulates cyclooygenase-dependent peroxideproduction in human hepatocyte

Resistance to bacteria


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ROS signaling by RTKs

A number of growth factors that bind to RTKsgenerate intracellular ROS essential for mitogenicsignaling :- Mitogens will be produced

Produced mitogens activate MAPK ( Mitogen activatedprotein kinase)

that trigger mitosis

These growth factors that act on receptor tyrosine

kinases (RTKs) include :- PDGF (plasma dependent growth factor)

EGF (epidermal growth factor)

FGF (fibroblast growth factor)

G


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PDGF

Increases intracellularconcentrations ofhydrogen peroxides

Induce tyrosine

phosphorylation

MAPK activation

DNA synthesis &chemotaxis

Regulates gene expressionby .O2 dependent

pathways

.O2 produced

involved in theupregulation of inducibleNOS & NO dependentrelease of PGE2 infibroblasts

induces fever


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Receptor serine/threonine kinases

These are receptors of the transforming growthfactor (TGF-) superfamily

TGF-

Stimulates extracellular production of ROS

Regulates a number of physiological actions

Apoptosis, collagen synthesis, growth inhibitoryeffects


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G protein-coupled receptors

The ligands for these receptors include:- ANG II (Angiotensin II)

Serotonin (5-hydroxytryptamine)

Bradykinin

Thrombin


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Angiotensin II

activates both NADH- and NADPH-dependent O2production in vascular smooth muscle cells

A variety of physiological actions of ANG II aremediated by ROS

its vasopressor activity, smooth muscle cell

hypertrophy, activation of cell survival PK Akt/PKB,induction of insulin-like growth factor-1 receptor


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Mechanisms of ROS actionROS act via two mechanisms:-

1) alterations in intracellular redox state

2) oxidative modifications of proteins


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Alterations in intracellular

redox states The cytosol is maintained under strong reducing

conditions

This is accomplished by the redox-bufferingcapacity of intracellular thiols, primarilyglutathione (GSH)and thioredoxin (TRX).

They reduce both H2O2 and lipid peroxides,reactions that are catalyzed by peroxidases

e.g. GSH peroxidase catalyzes the reaction H2O2 +2GSH 2H2O + GSSG

GSH and TRX are antioxidants that play importantroles in cell signaling


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Alterations in intracellular

redox states

During oxidative stress , the concentration of theoxidized form of GSH increases

[H2O2 + 2GSH 2H2O + GSSG]

Decreased cell proliferation in vascular endothelial

cellsincreased proliferation of fibroblasts

induces the binding of some TFs to DNA.


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Conclusion

ROS are mediators of cell signaling

They cause a series of changes during cell signaling


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References

http://www.jleukbio.org/content/65/3/337.full.pdf

http://www.sciencedirect.com/science/article/pii/S0014579300016690

http://jcb.rupress.org/content/194/1/7 http://www.heribert-hirt.info/pdf/prr85_ros.pdf

http://ajplung.physiology.org/content/279/6/L1005.full
http://www.jleukbio.org/content/65/3/337.full.pdfhttp://www.sciencedirect.com/science/article/pii/S0014579300016690http://www.sciencedirect.com/science/article/pii/S0014579300016690http://jcb.rupress.org/content/194/1/7http://www.heribert-hirt.info/pdf/prr85_ros.pdfhttp://ajplung.physiology.org/content/279/6/L1005.fullhttp://ajplung.physiology.org/content/279/6/L1005.fullhttp://ajplung.physiology.org/content/279/6/L1005.fullhttp://ajplung.physiology.org/content/279/6/L1005.fullhttp://www.heribert-hirt.info/pdf/prr85_ros.pdfhttp://www.heribert-hirt.info/pdf/prr85_ros.pdfhttp://www.heribert-hirt.info/pdf/prr85_ros.pdfhttp://jcb.rupress.org/content/194/1/7http://www.sciencedirect.com/science/article/pii/S0014579300016690http://www.sciencedirect.com/science/article/pii/S0014579300016690http://www.jleukbio.org/content/65/3/337.full.pdf

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Reactive Oxygen Species & Signal Trans Duct Ion 2