Dual functions for WNT5A during cartilage development and in disease.

Area of Science:

• Developmental Biology
• Skeletal Biology
• Molecular Signaling

Background:

• Wnt5a's role in jaw development is suggested by genetic data but its specific function in facial skeletogenesis remains unclear.
• Previous studies indicate Wnt5a's involvement in skeletal development, but the precise mechanisms in craniofacial cartilage formation are not fully understood.

Purpose of the Study:

• To investigate the specific role of Wnt5a in facial skeletogenesis, focusing on its effects on chondrogenesis and cartilage matrix.
• To elucidate the signaling pathways (canonical vs. non-canonical) through which Wnt5a influences cartilage development and matrix maintenance.

Main Methods:

• Expression analysis of WNT5A in developing chicken skull and Meckel's cartilage.
• In vivo manipulation using retroviral vectors to overexpress WNT5A in mandibular prominence.
• In vitro studies using micromass cultures of mandibular mesenchyme treated with Wnt5a-conditioned media (CM).
• Analysis of cartilage differentiation, matrix components (Collagen II, aggrecan), and matrix-degrading enzymes (MMPs, ADAMTS5).
• Investigation of Wnt signaling pathways (canonical and JNK/PCP) using luciferase assays and pathway-specific inhibitors (DKK1, TCS JNK 6o).

Main Results:

• Wnt5a overexpression in vivo led to reduced or missing mandibular bones and Meckel's cartilage.
• In vitro, Wnt5a-CM initially allowed cartilage differentiation but resulted in significant matrix loss, decreased Collagen II and aggrecan, and upregulation of MMPs and ADAMTS5.
• Wnt5a-CM inhibited canonical Wnt signaling and activated JNK/PCP signaling.
• Inhibition of MMPs and Aggrecanase (Marimastat) rescued cartilage matrix, while JNK pathway antagonism partially rescued the Wnt5a-induced phenotype, implicating non-canonical pathways in matrix degradation.

Conclusions:

• WNT5A has a dual role: it represses canonical Wnt signaling to promote normal chondrogenesis and, in excess, stimulates mature cartilage matrix degradation through non-canonical pathways.
• These findings reveal novel functions of WNT5A in skeletal development and offer insights into potential therapeutic targets for cartilage-related diseases.