Regional and Sexual Dimorphism in Murine Skeletal Responses to Osteocytic HIF Pathway Modulation.

Abstract

Hypoxia-inducible factors (HIFs) are transcription factors stabilized under hypoxia and degraded under normoxia by the E3 ubiquitin ligase Von Hippel-Lindau (Vhl). In osteocytes, the central orchestrators of bone homeostasis, Vhl and HIFs promote an osteoanabolic transcriptional program. In this study, we assessed unique impacts of osteocytic Vhl deletion versus individual HIF-α paralog stabilization on bone structure, mineralization, and mechanics as a function of sex and skeletal region. Microcomputed tomography revealed that osteocytic Vhl deletion robustly increased trabecular bone mass in both sexes and at both axial and appendicular regions, while HIF-2α accumulation increased femoral metaphyseal bone mass in both sexes while enhancing vertebral bone mass only in males. Vhl deletion paradoxically reduced mineral heterogeneity in male vertebrae, despite raising peak and mean calcium content in both sexes. In contrast, HIF-2α stabilization impaired cortical mineralization and mechanics, especially in females. While cortical mineralization was disrupted in both genotypes, Vhl deletion improved whole bone mechanical properties, suggesting that enhanced geometry and mass offset compromised tissue quality. HIF-1α stabilization exerted negligible impacts on any outcome.