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ADAMTS metalloproteases generate active versican fragments that regulate interdigital web regression.

ABSTRACT: We show that combinatorial mouse alleles for the secreted metalloproteases Adamts5, Adamts20 (bt), and Adamts9 result in fully penetrant soft-tissue syndactyly. Interdigital webs in Adamts5(-/-);bt/bt mice had reduced apoptosis and decreased cleavage of the proteoglycan versican; however, the BMP-FGF axis, which regulates interdigital apoptosis was unaffected. BMP4 induced apoptosis, but without concomitant versican proteolysis. Haploinsufficiency of either Vcan or Fbln1, a cofactor for versican processing by ADAMTS5, led to highly penetrant syndactyly in bt mice, suggesting that cleaved versican was essential for web regression. The local application of an aminoterminal versican fragment corresponding to ADAMTS-processed versican, induced cell death in Adamts5(-/-);bt/bt webs. Thus, ADAMTS proteases cooperatively maintain versican proteolysis above a required threshold to create a permissive environment for apoptosis. The data highlight the developmental significance of proteolytic action on the ECM, not only as a clearance mechanism, but also as a means to generate bioactive versican fragments.

SUBMITTER: McCulloch DR

PROVIDER: S-EPMC2780442 | biostudies-literature | 2009 Nov

REPOSITORIES: biostudies-literature

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ADAMTS metalloproteases generate active versican fragments that regulate interdigital web regression.

McCulloch Daniel R DR Nelson Courtney M CM Dixon Laura J LJ Silver Debra L DL Wylie James D JD Lindner Volkhard V Sasaki Takako T Cooley Marion A MA Argraves W Scott WS Apte Suneel S SS

Developmental cell 20091101 5

We show that combinatorial mouse alleles for the secreted metalloproteases Adamts5, Adamts20 (bt), and Adamts9 result in fully penetrant soft-tissue syndactyly. Interdigital webs in Adamts5(-/-);bt/bt mice had reduced apoptosis and decreased cleavage of the proteoglycan versican; however, the BMP-FGF axis, which regulates interdigital apoptosis was unaffected. BMP4 induced apoptosis, but without concomitant versican proteolysis. Haploinsufficiency of either Vcan or Fbln1, a cofactor for versican ...[more]

PMID: 19922873

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Project description:We identify a role for two evolutionarily related, secreted metalloproteases of the ADAMTS family (A disintegrin-like and metalloprotease domain with thrombospondin type-1 motif), ADAMTS20 and ADAMTS9, in palatogenesis. Adamts20 mutations cause the mouse white spotting mutant belted (bt), whereas Adamts9 is essential for survival beyond 7.5 days of gestation (E7.5). Functional overlap of Adamts9 with Adamts20 was established in bt/bt:Adamts9+/- mice, which have increased white spotting relative to bt mice, as previously reported, and a fully penetrant cleft palate. Palatal closure was delayed, although eventually completed, in both bt/+;Adamts9+/- and bt/bt mice, demonstrating a cooperative role of these related genes. Adamts9 and Adamts20 are both expressed in palatal mesenchyme, with Adamts9 expressed exclusively in microvascular endothelial cells. Palatal shelves from bt/bt:Adamts9+/- mice fused in culture, suggesting an intact TGF signaling pathway in palatal epithelium, and indicating a temporally specific delay in palatal shelf elevation and growth toward the midline. Palatal shelf mesenchymal cells showed a statistically significant decrease of cell proliferation at E13.5 and E14.5, as well as decreased processing of versican, an ADAMTS substrate, at these stages. Vcan haploinsufficiency led to a greater penetrance of cleft palate in bt mice, and impaired proliferation was also seen in palatal mesenchymal cells of these mice, suggesting a role for ADAMTS-mediated versican proteolysis in palatal closure. In a parallel with recent work identifying a role for a bioactive ADAMTS-generated versican fragment in regulating apoptosis during interdigital web regression, we propose that versican proteolysis may influence palatal mesenchymal cell proliferation. Palatal shelves were dissected from four E13.75 Adamts9+/-:bt/bt embyos (correspond to the 4 samples: Palate_Adamts9+/-:bt/bt_Rep1, Palate_Adamts9+/-:bt/bt_Rep2, Palate_Adamts9+/-:bt/bt_Rep3 and Palate_Adamts9+/-:bt/bt_Rep4) and age-matched 3 wild-type C57Bl/6 embryos (correspond to the 3 samples: Palate_WT_Rep1, Palate_WT_Rep2, and Palate_WT_Rep3) that were used as the controls

Project description:The primordium of the limb contains a number of progenitors far superior to those necessary to form the skeletal components of this appendage. During the course of development, precursors that do not follow the skeletogenic program are removed by cell senescence and apoptosis. The formation of the digits provides the most representative example of embryonic remodeling via cell degeneration. In the hand/foot regions of the embryonic vertebrate limb (autopod), the interdigital tissue and the zones of interphalangeal joint formation undergo massive degeneration that accounts for jointed and free digit morphology. Developmental senescence and caspase-dependent apoptosis are considered responsible for these remodeling processes. Our study uncovers a new upstream level of regulation of remodeling by the epigenetic regulators Uhrf1 and Uhrf2 genes. These genes are spatially and temporally expressed in the pre-apoptotic regions. UHRF1 and UHRF2 showed a nuclear localization associated with foci of methylated cytosine. Interestingly, nuclear labeling increased in cells progressing through the stages of degeneration prior to TUNEL positivity. Functional analysis in cultured limb skeletal progenitors via the overexpression of either UHRF1 or UHRF2 inhibited chondrogenesis and induced cell senescence and apoptosis accompanied with changes in global and regional DNA methylation. Uhrfs modulated canonical cell differentiation factors, such as Sox9 and Scleraxis, promoted apoptosis via up-regulation of Bak1, and induced cell senescence, by arresting progenitors at the S phase and upregulating the expression of p21. Expression of Uhrf genes in vivo was positively modulated by FGF signaling. In the micromass culture assay Uhrf1 was down-regulated as the progenitors lost stemness and differentiated into cartilage. Together, our findings emphasize the importance of tuning the balance between cell differentiation and cell stemness as a central step in the initiation of the so-called "embryonic programmed cell death" and suggest that the structural organization of the chromatin, via epigenetic modifications, may be a precocious and critical factor in these regulatory events.

Project description:Two inherent challenges in the mechanistic interpretation of protease-deficient phenotypes are defining the specific substrate cleavages whose reduction generates the phenotypes and determining whether the phenotypes result from loss of substrate function, substrate accumulation, or loss of a function(s) embodied in the substrate fragments. Hence, recapitulation of a protease-deficient phenotype by a cleavage-resistant substrate would stringently validate the importance of a proteolytic event and clarify the underlying mechanisms. Versican is a large proteoglycan required for development of the circulatory system and proper limb development, and is cleaved by ADAMTS proteases at the Glu441-Ala442 peptide bond located in its alternatively spliced GAGβ domain. Specific ADAMTS protease mutants have impaired interdigit web regression leading to soft tissue syndactyly that is associated with reduced versican proteolysis. Versikine, the N-terminal proteolytic fragment generated by this cleavage, restores interdigit apoptosis in ADAMTS mutant webs. Here, we report a new mouse transgene, Vcan AA, with validated mutations in the GAGβ domain that specifically abolish this proteolytic event. Vcan AA/AA mice have partially penetrant hindlimb soft tissue syndactyly. However, Adamts20 inactivation in Vcan AA/AA mice leads to fully penetrant, more severe syndactyly affecting all limbs, suggesting that ADAMTS20 cleavage of versican at other sites or of other substrates is an additional requirement for web regression. Indeed, immunostaining with a neoepitope antibody against a cleavage site in the versican GAGα domain demonstrated reduced staining in the absence of ADAMTS20. Significantly, mice with deletion of Vcan exon 8, encoding the GAGβ domain, consistently developed soft tissue syndactyly, whereas mice unable to include exon 7, encoding the GAGα domain in Vcan transcripts, consistently had fully separated digits. These findings suggest that versican is cleaved within each GAG-bearing domain during web regression, and affirms that proteolysis in the GAGβ domain, via generation of versikine, has an essential role in interdigital web regression.

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ADAMTS metalloproteases generate active versican fragments that regulate interdigital web regression.

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ADAMTS metalloproteases generate active versican fragments that regulate interdigital web regression.

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