Complementary interplay between matrix metalloproteinase-9, vascular endothelial growth factor and osteoclast...

Area of Science:

• Skeletal Biology
• Developmental Biology
• Molecular Medicine

Background:

• Long bone development relies on endochondral ossification, a process balancing hypertrophic cartilage formation and ossification.
• Dysregulation can lead to skeletal disorders like dysplasias and heterotopic ossification.
• Key regulators include matrix metalloproteinase-9 (MMP-9), vascular endothelial growth factor (VEGF), and osteoclasts, but their interplay is unclear.

Purpose of the Study:

• To investigate the functional relationship among MMP-9, VEGF, and osteoclasts in endochondral ossification.
• To elucidate how these factors coordinate for proper growth plate development.

Main Methods:

• Analysis of gene-deficient mouse models (MMP-9-/-, VEGF inhibition, osteoclast deficiency).
• Assessment of growth plate ossification, hypertrophic cartilage accumulation, vascularization, and extracellular matrix organization.
• Evaluation of VEGF expression and bioavailability in MMP-9 deficient models.

Main Results:

• MMP-9, VEGF, and osteoclast deficiency each impair growth plate ossification and lead to hypertrophic cartilage accumulation.
• MMP-9 deficiency increases VEGF expression, but VEGF bioavailability remains limited, suggesting partial regulation by MMP-9.
• VEGF inhibition impairs osteoclast recruitment, while MMP-9 deficiency causes osteoclast accumulation; osteoclast deficiency impairs ossification despite normal MMP-9.

Conclusions:

• MMP-9, VEGF, and osteoclasts possess complementary, non-overlapping functions crucial for endochondral bone formation.
• MMP-9 influences VEGF bioavailability and hypertrophic cartilage remodeling.
• Osteoclasts have functions beyond those compensated for by MMP-9 or VEGF in ossification.
• This study provides a molecular framework for understanding defects in endochondral bone formation disorders.