Phototunable Hydrogel Materials to Study Epigenetic Remodeling in Mesenchymal Stem Cells

Bone marrow derived human mesenchymal stem cells (hMSCs) are a promising cell source for many regenerative therapies; however, ex vivo expansion of hMSCs on stiff materials, such as tissue culture plastic or glass-based microbeads suspended in bioreactors is necessary to achieve therapeutic cell numbers. During this expansion the regenerative capacity of hMSCs decreases through a loss of multipotency which can influence therapeutic outcomes. For that reason, the goal of this thesis is to better understand changes in cellular processes that occur as a result of mechanotransduction. We use phototunable poly(ethylene glycol) (PEG) hydrogel platforms that allow for spatial and temporal control over the stiffness to study the role of epigenetic remodeling during mechanotransduction. First, we use a photodegradable hydrogel platform based on the cleavage of nitrobenzyl groups to spatially control the presentation of stiff and soft mechanical cues. We find that epigenetic remodeling and differentiation in hMSCs is dependent on both the ratio and organization of the mechanical cues presented. In addition, we use this platform to study the influence of the organization of mechanics found during heart valve fibrosis on valvular interstitial cells (VICs) and find that VICs respond in a more fibrotic manner to disorganized/disease-like hydrogels. Using a more rapid photodegradable hydrogel culture system based on crosslinkers with allyl sulfide groups that can undergo amplified photodegradation, precise temporal control of mechanical dosing is achieved. We find that with mechanical dosing, epigenetic remodeling in hMSCs becomes persistent, suggesting its role in mechanical memory. Finally, we investigate the mechanism behind mechanically induced epigenetic remodeling in hMSCs. Hydrogels with pendent dibenzylcyclooctyne groups that can be crosslinked during a secondary photoinitiated polymerization reaction are used to control the presentation of stiff mechanical cues in situ. We find that nuclear tension is a key mediator in epigenetic remodeling by upregulating epigenetic modifiers and that disruption of nuclear mechanosensing might play a role in bone degeneration. Collectively, these findings demonstrate that phototunable hydrogels can be used to modulate the presentation of mechanical cues to shed light on the mechanotransduction cascade in vitro.

Full pdf - https://www.colorado.edu/mse/node/525/attachment