ADAMTS metalloproteases generate active versican fragments that regulate interdigital web regression

Area of Science:

• Developmental Biology
• Molecular Genetics
• Extracellular Matrix Biology

Background:

• Syndactyly, or webbed digits, is a congenital condition often linked to abnormal apoptosis during embryonic development.
• Secreted metalloproteases, particularly ADAMTS (A Disintegrin And Metalloproteinase with Thrombospondin Motifs) enzymes, play crucial roles in extracellular matrix remodeling.
• Versican, a major proteoglycan in the extracellular matrix, is a known substrate for ADAMTS proteases, but its specific role in digit development is unclear.

Purpose of the Study:

• To investigate the role of specific ADAMTS metalloproteases (Adamts5, Adamts20, Adamts9) in mouse digit development.
• To elucidate the mechanism by which ADAMTS proteases regulate apoptosis and extracellular matrix processing in interdigital tissues.
• To determine the contribution of versican cleavage by ADAMTS proteases to the regression of interdigital webs.

Main Methods:

• Generation and analysis of compound mutant mice with combinatorial deletions of Adamts5, Adamts20 (bt), and Adamts9 alleles.
• Histological examination of interdigital tissues to assess apoptosis and cell morphology.
• Biochemical analysis of versican cleavage and assessment of extracellular matrix composition.
• Functional assays involving the application of versican fragments to mutant tissues.

Main Results:

• Combinatorial mutations in Adamts5, Adamts20 (bt), and Adamts9 resulted in fully penetrant soft-tissue syndactyly in mice.
• Interdigital webs in mutant mice showed reduced apoptosis and decreased versican cleavage, while the BMP-FGF signaling axis remained unaffected.
• Haploinsufficiency of Vcan (versican) or Fbln1 (fibulin-1, a versican processing cofactor) exacerbated syndactyly in bt mice, highlighting the importance of cleaved versican.
• Direct application of an ADAMTS-processed versican fragment induced apoptosis in the interdigital webs of mutant mice.

Conclusions:

• ADAMTS proteases cooperatively maintain versican proteolysis above a critical threshold, creating a permissive environment for interdigital apoptosis.
• Cleavage of versican by ADAMTS proteases is essential for the regression of interdigital webs during digit development.
• The study demonstrates that proteolytic action on the extracellular matrix generates bioactive fragments, such as versican fragments, which actively regulate developmental processes like apoptosis.