Mechanical Regulation of Mesenchymal Stem Cell Regulation Tissue Engineering Lecture 10, 3/10/15 Paper Review Mechanical Regulation of Mesenchymal Stem Cell Regulation

What 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.

Figure 1: Akarawin Hongdusit

Figure 1: Akarawin Hongdusit, Extra Slide 1

Figure 1: Akarawin Hongdusit, Extra Slide 2

Biomaterials overview Fibronectin-coated PDMS Collagen-coated poly(acrylamide) OH OH OH UVO, 30min 3D Poly(ethylene glycol) 3D alginate

Table 1 (through Huebsch): Jonathan Hummel

Table 1 (Pek through Steward): Michael Mulroy

Possible mechanotransducing elements Compression Tension Fluid Flow Pressure Shape Substrate Stiffness

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

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

Table 2 (Compression): Brittany Shepler

Brittany Shepler, cont.

Table 2. Tension (Singyuk Hou) Application of tensile strain to cultured MSCs Effect of tension Osteogensis BMP-2 Calcium deposition Osteogenic mRNA IL-6 and IL-8 ERK Collagen 1 Osteopontin Osteocalcin ALP activity P38,PI3 Cbfa-1, Ets-1 Chondrogensis sGAG synthesis rate Stretch-activated calcium channel

Osteogenesis 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 formation of bone 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 enzyme that 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 phenotype including osteocalcin, osteopontin, type I collagen and ALP Int J Biol Sci 2012; 8(2):272-288.

Secretion of molecules from other cells: IL6: Cytokine secreted by T cells and macrophages  to stimulate immune response IL8: Chemokine produced by macrophages, 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/

Chondrogensis sGAG (sulphated glycosaminoglycan) : Chondrocytes secret chondroitin ( sGAG) to produce and maintain the cartilaginous matrix, rate of sGAG synthesis is marker for chondrogenic differentiation of MSCs Stretch-activated calcium ion channel: Regulating intracellular calcium level. sGAG synthesis Rate is dependent on the ion channel. http://medcell.med.yale.edu/histology/connective_tissue_lab/hyaline_cartilage.php

Figure 2: Christine Davis

Conclusions, Perspectives Mechanical 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 don’t 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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