Tethered Jagged-1 Synergizes with Culture Substrate Stiffness to Modulate Notch-Induced Myogenic Progenitor Differentiation.

INTRODUCTION: Notch signaling is amongst the key intrinsic mechanisms regulating satellite cell fate, promoting the transition of activated satellite cells to highly proliferative myogenic progenitor cells and preventing their premature differentiation. Although much is known about the biochemical milieu that drives myogenic progression, less is known about the spatial cues providing spatiotemporal control of skeletal muscle repair in the context of Notch signaling. METHODS: Using a murine injury model, we quantified in vivo biophysical changes that occur within the skeletal muscle during regeneration. Employing tunable poly(ethylene glycol)-based hydrogel substrates, we modeled the measured changes in bulk stiffness in the context of Notch ligand signaling, which are present in the regenerative milieu at the time of injury. RESULTS: Following injury, there is a transient increase in the bulk stiffness of the tibialis anterior muscle that may be explained in part by changes in extracellular matrix deposition. When presented to primary myoblasts, Jagged-1, Jagged-2, and Dll1 in a tethered format elicited greater degrees of Notch activity compared to their soluble form. Only tethered Jagged-1 effects were tuned by substrate stiffness, with the greatest Notch activation observed on stiff hydrogels matching the stiffness of regenerating muscle. When exposed to tethered Jagged-1 on stiff hydrogels, fewer primary myoblasts expressed myogenin, and pharmacological inhibitor studies suggest this effect is Notch and RhoA dependent. CONCLUSION: Our study proposes that tethered Jagged-1 presented in the context of transient tissue stiffening serves to tune Notch activity in myogenic progenitors during skeletal muscle repair and delay differentiation.