Tissue Engineering

Tissue EngineeringLecture 10, 3/10/15Paper ReviewMechanical Regulation of Mesenchymal Stem Cell RegulationWhat is the motivation of this study?This article came out in 2014, and it attempts to give a global overview of how different mechanical forces impact stem cell behavior.This will help new students, and new faculty, in this area get a grasp of where the field is now before they start their experiments.They give an overview of all the different types of mechanical forces that impact stem cell behavior.They also give some mechanistic information on what internal components of the cells are responsible for translating mechanical cues into biochemical signals.2Figure 1: Akarawin Hongdusit

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Figure 1: Akarawin Hongdusit, Extra Slide 1

Figure 1: Akarawin Hongdusit, Extra Slide 2Biomaterials overviewFibronectin-coated PDMS

UVO, 30minOHOHOHCollagen-coated poly(acrylamide)

3D Poly(ethylene glycol)

3D alginate

Table 1 (through Huebsch):Jonathan Hummel

Table 1 (Pek through Steward): Michael Mulroy

Possible mechanotransducing elements

Substrate StiffnessCompressionCompressionTensionTensionFluid FlowShapeShapePressureTable 2 (fluid flow and hydrostatic pressure):Hiu Yeung

10Table 2 (fluid flow and hydrostatic pressure):Hiu Yeung

11Table 2 (Compression): Brittany Shepler

Brittany Shepler, cont.

Table 2. Tension (Singyuk Hou)Application of tensile strain to cultured MSCs

Effect of tension

OsteogensisBMP-2Calcium depositionOsteogenic mRNAIL-6 and IL-8ERKCollagen 1OsteopontinOsteocalcinALP activityP38,PI3Cbfa-1, Ets-1ChondrogensissGAG synthesis rateStretch-activated calcium channel

Materials formation from differentiated MSCs:Calcium phosphate (Hydroxyapatite): Major inorganic component of bone

Collagen 1: Main organic component of bone,served as nucleation site for mineral components.

Osteocalcin: Protein hormone secreted by osteoblast, marker associated with mineralization

Osteopontin: Protein binding to cell surface receptors, other matrix proteins and calcium deposits, involved in osteopontin-cell adhesion, signaling and hydroxyapatite crystal formation

BMP-2 (Bone morphogenic protein-2): Protein belonging to TGF-alpha family, a hormone secreted by osteoblast to stimulate formationof bone

Osteogenesis

http://www.quora.com/What-are-bone-cells-made-out-of-And-how-do-they-fill-up-with-calcium

Enzyme activities in differentiated MSCs (All up-regulated)

ALP (Alkaline Phosphatase): Key enzymethat provides high concentrations of phosphate at the site of mineral deposition; Maker for osteoblast.

ERK(Extracellular signal-regulated kinase): Kinase belonging to MAPK (mitogen-activated protein kinase) family,involved in MAPK signaling pathway p38 and PI3: Kinases belonging to MAPK family

Transcription factors expression differentiated MSCs:Cbfa-1 (RunX) and Ets-1: Play important roles in regulating the expression of a wide variety of genes responsible for the osteoblast phenotypeincluding osteocalcin, osteopontin,type I collagen and ALP

Int J Biol Sci2012; 8(2):272-288.

Secretion of molecules from other cells:

IL6: Cytokine secreted byT cellsandmacrophagesto stimulate immune response

IL8: Chemokineproduced bymacrophages, epithelial cells, airway smooth muscle cells,endothelial cells and so forth

They :---Bind to RANKL---Inhibit bone resorption (decomposition of bone minerals and collagen into blood)http://www.pathophys.org/osteoporosis/ChondrogensissGAG (sulphated glycosaminoglycan) : Chondrocytes secret chondroitin ( sGAG) to produce and maintain the cartilaginous matrix, rate of sGAG synthesis is markerfor chondrogenic differentiation of MSCs

Stretch-activated calcium ion channel: Regulating intracellular calcium level. sGAG synthesisRate is dependent on the ion channel.

http://medcell.med.yale.edu/histology/connective_tissue_lab/hyaline_cartilage.phpFigure 2: Christine Davis

Conclusions, PerspectivesMechanical forces on stem cells includes static stiffness and active loading.

Various cell-surface receptors are mechano-sensitive, transduced to stem cell behavior through the cytoskeleton.

We still dont fully understand what the mechanical environment is like in vivo.

Most studies are isolating 1 force at a time, likely not the case in vivo.

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