Extracellular Matrix Hydrogels Promote Expression of Muscle-Tendon Junction Proteins

Abstract

Muscle and tendon injuries are prevalent and range from minor sprains and strains to traumatic, debilitating injuries. However, the interactions between these tissues during injury and recovery remain unclear. Three-dimensional tissue models that incorporate both tissues and a physiologically relevant junction between muscle and tendon may aide in understanding how the two tissues interact. Here, we use tissue specific extracellular matrix (ECM) derived from muscle and tendon to determine how cells of each tissue interact with the microenvironment of the opposite tissue resulting in junction specific features. ECM materials were derived from the achilles tendon and gastrocnemius muscle, decellularized, and processed to form tissue specific pre-hydrogel digests. C2C12 myoblasts and tendon fibroblasts were cultured in tissue-specific ECM conditioned media or encapsulated in tissue-specific ECM hydrogels to determine cell-matrix interactions and the effects on a muscle-tendon junction marker, paxillin. ECM conditioned media had only a minor effect on upregulation of paxillin in cells cultured in monolayer. However, cells cultured within ECM hydrogels had 50-70% higher paxillin expression than cells cultured in type I collagen hydrogels. Contraction of the ECM hydrogels varied by the type of ECM used. Subsequent experiments with varying density of type I collagen (and thus contraction) showed no correlation between paxillin expression and the amount of gel contraction, suggesting that a constituent of the ECM was the driver of paxillin expression in the ECM hydrogels. Using tissue specific ECM allowed for the de-construction of the cell-matrix interactions similar to muscle-tendon junctions to study the expression of MTJ specific proteins.Impact StatementThe muscle-tendon junction is an important feature of muscle-tendon units; however, despite cross-talk between the two tissue types, it is overlooked in current research. Deconstructing the cell-matrix interactions will allow the opportunity to study significant junction specific features and markers that should be included in tissue models of the muscle-tendon unit, while gaining a deeper understanding of the natural junction. This research aims to inform future methods to engineer a more relevant multi-tissue platform to study the muscle-tendon unit.

Extracellular matrix deposition precedes muscle-tendon integration during murine forelimb morphogenesis

“…Together with our results demonstrating that COL22A1 interface between muscle and tendon reversibly elongates under tensile loading, these data indicate that COL22A1 connects the ECM between muscle and tendon. While multiple cell types have been hypothesized to synthesize COL22A1 at the MTJ, including muscle (Kim et al, 2020;Koch et al, 2004;Subramanian and Schilling, 2015), tendon/connective tissue (Scott et al, 2019;Yaseen et al, 2021), or both (Gaffney et al, 2021;Petrany et al, 2020), our data revealed that COL22A1 integration requires the presence of muscle in the limb.…”