MSX2 stimulates chondrocyte maturation by controlling Ihh expression.

Area of Science:

• Skeletal biology
• Developmental biology
• Molecular genetics

Background:

• The homeobox gene Msx2 is known to regulate skeletal development, affecting both enchondral and membranous ossification.
• The precise molecular mechanisms by which Msx2 influences chondrogenesis remain largely undefined.

Purpose of the Study:

• To investigate the role of Msx2 in chondrocyte differentiation and maturation.
• To elucidate the molecular pathways through which Msx2 exerts its effects on chondrogenesis.

Main Methods:

• Primary mouse chondrocytes and embryonic metatarsal explants were used.
• Experiments involved BMP2 treatment, Msx2 overexpression (wild-type and constitutively active), Msx2 knockdown, and treatment with cyclopamine (hedgehog pathway inhibitor).
• Gene expression analysis (Msx2, alkaline phosphatase, collagen type X, Ihh) and assessment of chondrocyte maturation and calcification were performed.

Main Results:

• BMP2 treatment upregulated Msx2 expression and promoted chondrocyte differentiation and calcification.
• Overexpression of Msx2 (particularly constitutively active Msx2) enhanced BMP2-induced calcification and upregulated alkaline phosphatase and collagen type X.
• Msx2 overexpression stimulated chondrocyte maturation to prehypertrophic and hypertrophic stages, while Msx2 knockdown inhibited maturation.
• Msx2's action was dependent on BMP2/Smad signaling and involved the upregulation of Indian hedgehog (Ihh) expression, as blocking Ihh signaling inhibited Msx2-induced chondrogenesis.

Conclusions:

• Msx2 plays a crucial role in promoting chondrocyte maturation during skeletal development.
• Msx2 exerts its chondrogenic effects at least partially through the upregulation of Indian hedgehog (Ihh) expression.
• The function of Msx2 in chondrogenesis is integrated with the BMP2/Smad signaling pathway.