RORβ Deficiency Inhibits Endochondral Ossification in Mice by Mediating the HIF-1α/VEGFA Signaling Pathway

Area of Science:

• Endocrinology
• Developmental Biology
• Orthopedics

Background:

• Retinoic acid receptor-related orphan receptor beta (RORβ) is a transcription factor involved in bone metabolism.
• RORβ's role in early skeletal development and endochondral ossification is not well understood.
• Osteoporosis is a significant health concern, particularly in aging populations.

Purpose of the Study:

• To investigate the role of RORβ in endochondral ossification and early skeletal development.
• To characterize the skeletal phenotypes of RORβ-deficient mice.
• To elucidate the molecular mechanisms underlying RORβ's function in bone formation.

Main Methods:

• Generation of a Rorβ gene knockout (KO) mouse model using CRISPR/Cas9.
• Phenotypic analysis of Rorβ KO mice at 4 weeks of age, including bone mineral density, bone length, and microarchitecture.
• Histological examination of growth plates and analysis of chondrocyte differentiation.
• Assessment of osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs).
• Molecular analysis of key signaling pathways, including HIF-1α and VEGFA.

Main Results:

• Rorβ KO mice displayed dwarfism, reduced femur length, and decreased bone mass and quality.
• Trabecular bone was fragile with fewer osteoblasts and impaired BMSC osteogenic differentiation.
• Endochondral ossification was disrupted, characterized by a thinner growth plate and disorganized hypertrophic zone.
• Expression of proliferation and hypertrophic differentiation markers (Ki67, Collagen X) was significantly reduced.
• RORβ deficiency led to downregulation of HIF-1α and VEGFA in growth plate and BMSCs.

Conclusions:

• RORβ is essential for normal endochondral ossification and skeletal development.
• Loss of RORβ results in skeletal defects through impaired HIF-1α/VEGFA signaling.
• RORβ deficiency contributes to early-onset osteoporosis and may be implicated in skeletal dysplasias.