Regenerative MRL/MpJ Tendon Cells Exhibit Sex Differences in Morphology, Proliferation, Mechanosensitivity, and Cell-Matrix Remodeling

Clinical and animal studies have reported the influence of sex on the incidence and progression of tendinopathy, which results in disparate structural and biomechanical outcomes. However, there remains a paucity in our understanding of the sex-specific biological mechanisms underlying effective tendon healing. To overcome this hurdle, our group has investigated the impact of sex on tendon regeneration using the super-healer Murphy Roths Large (MRL/MpJ) mouse strain. Despite a shared scarless healing capacity, we have shown that MRL/MpJ patellar tendons exhibit sexually dimorphic regulation of gene expression for pathways involved in fibrosis, cell migration, and extracellular matrix (ECM) remodeling following an acute midsubstance injury. Moreover, we previously found decreased matrix metalloproteinase-2 (MMP-2) activity in female MRL/MpJ tendons after injury. Thus, we hypothesized that MRL/MpJ scarless tendon healing is mediated by sex-specific and temporally distinct orchestration of cell-ECM interactions. Accordingly, the present study comparatively evaluated MRL/MpJ tendon cells under two-dimensional (glass) and three-dimensional (nanofiber scaffolds) culture platforms to examine cell behavior under biochemical and biophysical cues associated with tendon homeostasis and healing. Female MRL/MpJ cells showed reduced 2D migration and spreading area accompanied with enhanced mechanosensing, 2D ECM alignment, and fibronectin-dependent cell proliferation. Interestingly, female MRL/MpJ cells cultured on 3D isotropic scaffolds showed diminished ECM deposition and alignment. Regardless of culture condition and sex, MRL/MpJ cells outperformed B6 cells and elicited a universal regenerative cellular phenotype. These results illustrate the utility of these in vitro systems for elucidating regenerative tendon cell biology, which will facilitate the long-term development of more equitable therapeutics.