Extracellular matrix microarchitecture modulates cellular behavior and extracellular vesicle phenotypes in biomimetic tendon models.

Tendon disease is a highly prevalent musculoskeletal disorder characterized by extracellular matrix (ECM) disorganization and fibroblast activation, contributing to fibrotic tissue healing and impaired function. While extracellular vesicles (EVs) have emerged as key mediators of intercellular communication and drivers of fibrosis in various tissues, their role in tendon pathology remains poorly understood. In this study, we developed a physiologically relevant 3D in vitro model that recapitulates biophysical features of healthy and fibrotic tendon microenvironments to investigate EV-mediated contributions to tendon remodeling. Primary tendon-derived cells on diseased scaffolds had increased proliferation, higher collagen III and fibronectin protein expression, and inferior cellular alignment. Proteomic profiling of EVs revealed temporally regulated, microenvironment-dependent cargo reflective of disease progression in vitro. Diseased EVs were enriched in cytoskeletal, ECM-remodeling, and inflammatory proteins, including vimentin (VIM), Annexin A2 (ANXA2), MMP2, and INHBA, suggesting an EV-mediated role in promoting matrix remodeling, fibroblast activation, and chronic inflammation. Notably, the temporal analysis demonstrated the late-stage emergence of stress-responsive and myofibroblast-associated proteins such as ENO1 and DES, underscoring the model's ability to capture the progressive nature of tendon pathology. In contrast, EVs from the healthy mimetic model demonstrated cargo associated with metabolic homeostasis and lipid transport, including APOA2 and CKM. Collectively, these findings highlight the utility of our tendon model as a dynamic platform for studying tendon pathology and establishing EVs as both sensitive indicators of microenvironmental state and potential mediators of fibrotic progression. This work provides a foundation for future studies exploring the diagnostic and therapeutic potential of EVs in tendinopathy.