Myofibers Cultured in Viscoelastic Hydrogels Reveal the Effects of Integrin-Binding and Mechanosensing on Muscle Satellite Cells

Abstract

Quiescent skeletal muscle satellite cells (SCs) located on myofibers activate in response to muscle injury to regenerate muscle; however, identifying the role of specific matrix signals on SC behavior in vivo is difficult. Therefore, we developed a viscoelastic hydrogel with tunable properties to encapsulate myofibers while maintaining stem cell niche polarity and SC-myofiber interactions to investigate how matrix signals, including viscoelasticity and integrin-binding ligand RGD, influence SC behavior during muscle regeneration. Viscoelastic hydrogels support long-term myofiber culture, minimizing myofiber hypercontraction and SC hyperproliferation compared to Matrigel. Pax7 is continuously expressed in SCs on myofibers embedded in hydrogels with higher stress relaxation but SCs differentiate when embedded in elastic hydrogels. Increasing RGD concentrations promotes SC activation and YAP/TAZ nuclear translocation as revealed by photo-expansion microscopy. Deleting YAP/TAZ eliminates RGD-mediated activation of SCs, and thus, YAP/TAZ nuclear translocation regulates RGD ligand-induced SC activation and subsequent proliferation.

Keywords: muscle satellite cell, myofiber, viscoelastic hydrogel, mechanosensing, expansion microscopy