Project Summary/Abstract Severe muscle injuries resulting from trauma, strain, or contusion are very common yet still present a significant clinical challenge since there is no therapy currently available to restore full function to the damaged tissue. Instead, severe muscle injuries often heal via fibrosis, leading to contracture, pain, and disability. Since skeletal muscle is known to respond strongly to mechanical stimuli, recent studies have shown that the use of mechanical cues alone can effectively stimulate tissue regeneration. Investigation has provided evidence that the immune system, which plays a critical role in tissue repair, may be modulated by mechanical stimulation of the injured tissue. In this proposal, I will focus on investigating the role of mechanical signaling in immune cell-muscle interactions, specifically between macrophages and muscle progenitor cells (MPCs) since macrophages have been shown to play an important role in guiding MPC behavior during repair. I hypothesize that the regenerative effects of macrophages on injured skeletal muscle through their interactions with MPCs will be enhanced under specific conditions of applied cyclic tensile loading leading to improved recovery. I will develop an in vitro model of injured skeletal muscle containing myofibers and MPCs and introduce polarized macrophages into this system. I will design and fabricate a cyclic tensile loading device and use this system to explore the effects of cyclic tensile loading parameters, such as strain and frequency, on macrophage modulation of myofiber regeneration and functional repair of the injured skeletal muscle constructs. I will further evaluate potential mechanisms behind the observed results to understand how mechanical cues may be impacting the interaction between macrophages and MPCs. I hope that the proposed work can offer new insight into how mechanical stimulation can be used clinically as a method of promoting skeletal muscle repair. The knowledge that arises from these studies may enable the optimization of physical therapies to provide better outcomes in the clinical setting and may offer new therapeutic avenues for healing severe muscle injuries.