HIF1α gates tendon response to overload and drives tendinopathy independently of vascular recruitment

Tendons are sparsely vascularized connective tissues that link muscles to bones, withstanding some of the highest mechanical stresses in the body. Mechanical overloading and tissue hypervascularity are implicated in tendinopathy, a common musculoskeletal disorder, yet their mechanistic roles remain unclear. Here, we identify hypoxia-inducible factor 1α (HIF1α) as not only a marker but also a driver of tendinopathy. Histological and multiomics evaluation of human tendinopathic samples revealed extensive extracellular matrix remodeling, including pathological collagen cross-linking coinciding with active hypoxic signaling. Hypothesizing a causal contribution of hypoxia signaling, we generated mice with tenocyte-targeted deletions of the von Hippel-Lindau (Vhl) gene, which controls hypoxia signaling by regulating HIFα degradation. Vhl inactivation was sufficient to induce pathological hallmarks of tendinopathy, such as collagen matrix disorganization, cross-linking, altered mechanics, and neurovascular ingrowth. This phenotype was HIF1α dependent given that codeleting HIF1α rescued tendon morphology and mechanics. Moreover, deleting vascular endothelial growth factor A (Vegfa) alongside VHL effectively suppressed neovascularization but failed to rescue extracellular matrix abnormalities or restore mechanical function, emphasizing a direct role of HIF1α in driving tendon disease independently of angiogenesis. Mechanistically, we found that HIF1α activation was strain dependent in primary cultured human tendon cells and induced by mechanical overload in murine tendon explants. Furthermore, genetically removing Hif1α from tenocytes prevented aberrant tendon remodeling in response to chronic overload. These findings position HIF1α signaling as a central driver of tendinopathy that acts through a maladaptive tissue response to chronic overload, providing mechanistic insights that could be leveraged for therapeutic approaches.