Hypoxia-inducible factor 1a and Hypoxia in Tendon Fibroblasts

Tendons are soft, connective tissues that are essential for joint stability and mobility. Tendons are susceptible to injury, such as rupture and tendinopathy, and limited therapeutic strategies are available to restore native structure and function. The inability to restore adult tendon function is largely due to the limited capacity for tendon fibroblasts (TFs) to regenerate or remodel their surrounding extracellular matrix (ECM). Our preliminary findings show that the embryonic Achilles tendon in mice is hypoxic, suggesting low oxygen availability drives ECM deposition by TFs in the developing tendon. Postnatally, tendon structure and function rely on expression of hypoxia inducible factor-1α (HIF-1α) by TFs. Yet, overexpression of HIF-1α has been observed in biopsies of patients with tendinopathy, introducing a gap in our understanding of the role of HIF-1α and hypoxia in tendon development and disease. The overarching objective of our research is to identify how oxygen and HIF-1α contribute to tendon extracellular matrix deposition. We isolated TFs from wild-type and HIF-1α knockout transgenic murine tail tendon, then used controlled tissue culture conditions to adjust oxygen availability while measuring the temporal response of TFs. We used RNA-sequencing approaches to identify transcriptional changes in tendon cells due to oxygen and/or HIF-1α availability. Our RNA-sequencing analyses revealed hypoxia and HIF-1α contribute to tendon fibroblast gene expression of genes affiliated with cell adhesion, proliferation, angiogenesis, actin cytoskeleton, collagen fibril organization, and tendon-ECM composition and alignment.