The Huntington's disease gene product, huntingtin, is indispensable for neural tube formation, but its role is obscure. We studied neurulation in htt-null embryonic stem cells and htt-morpholino zebrafish embryos and found a previously unknown, evolutionarily recent function for this ancient protein. We found that htt was essential for homotypic interactions between neuroepithelial cells; it permitted neurulation and rosette formation by regulating metalloprotease ADAM10 activity and Ncadherin cleavage. This function was embedded in the N terminus of htt and was phenocopied by treatment of htt knockdown zebrafish with an ADAM10 inhibitor. Notably, in htt-null cells, reversion of the rosetteless phenotype occurred only with expression of evolutionarily recent htt heterologues from deuterostome organisms. Conversely, all of the heterologues that we tested, including htt from Drosophila melanogaster and Dictyostelium discoideum, exhibited anti-apoptotic activity. Thus, anti-apoptosis may have been one of htt’s ancestral function(s), but, in deuterostomes, htt evolved to acquire a unique regulatory activity for controlling neural adhesion via ADAM10-Ncadherin, with implications for brain evolution and development.

T he pathogenesis of postangioplasty restenosis involves migration and proliferation of vascular smooth muscle cells (VSMCs), which constitute a major component of postangioplasty neointimal lesions.1-4 VSMC migration and proliferation are regulated by growth factors, adhesion molecules, proteases, and intracellular proteins. Among them, the cadherin-β-catenin complex and its cognate intracellular pathway have been increasingly appreciated as important regulators of these processes. 5-8Matrix metalloproteinase-8 (MMP8) was once thought to be produced exclusively by polymorphonuclear leukocytes, but more recent studies have shown that various other cell types including stem/progenitor cells express this protease.9 Compared with some other members of the MMP family, MMP8 has been less investigated for its proteolytic substrates and biological roles. Herman et al 10 were the first to reveal that VSMCs, endothelial cells, and macrophages in atherosclerotic plaques express MMP8. Subsequently other investigators showed a correlation between increased MMP8 expression and rapid atherosclerotic lesion progression.11,12 A causal role of MMP8 in atherosclerosis development was demonstrated by our recent study, which showed that in apolipoprotein E (apoE)-deficient mice fed a Western diet for 12 weeks, MMP8 knockout resulted in a significant reduction of atherosclerotic lesions with decreased macrophage and VSMC contents. 13 The study also revealed a role of MMP8 in vascular recruitment of leukocytes, 13 providing a mechanistic explanation for the effect of MMP8 knockout on macrophage content in atherosclerotic lesions.In the present study, we sought to investigate whether MMP8 also plays a role in neointima formation after vessel © 2013 American Heart Association, Inc. Objective-We investigated the role of matrix metalloproteinase-8 (MMP8) in neointima formation and in vascular smooth muscle cell (VSMC) migration and proliferation. Approach and Results-After carotid artery wire injuring, MMP8-/-/apoE -/-mice had fewer proliferating cells in neointimal lesions and smaller lesion sizes. Ex vivo assays comparing VSMCs isolated from MMP8 knockout and wild-type mice showed that MMP8 knockout decreased proliferation and migration. Proteomics analysis revealed that a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) had lower concentrations in MMP8 knockout VSMC culture media than in MMP8 wild-type VSMC culture media. Western blot, flow cytometric, and immunocytochemical analyses showed that MMP8 knockout VSMCs contained more pro-ADAM10 but less mature ADAM10, more N-cadherin, and β-catenin in the plasma membrane but less β-catenin in the nucleus and less cyclin D1. Treatment of MMP8 wildtype VSMCs with an ADAM10 inhibitor, GI254023X, or siRNA knockdown of ADAM10 in MMP8 wild-type VSMCs inhibited proliferation and migration, increased N-cadherin and β-catenin in the plasma membrane, reduced β-catenin in the nucleus, and decreased cyclin D1 expression. Incubation of MMP8 knockout VSMCs with a recombinant ADAM...

CD23, the low affinity receptor for IgE, exists in membrane and soluble forms. Soluble CD23 fragments are released from membrane CD23 by the endogenous metalloprotease, ADAM10. When purified tonsil B cells are incubated with IL-4 and anti-CD40 to induce class switching to IgE in vitro, membrane CD23 is up-regulated and soluble CD23 accumulates in the medium prior to IgE synthesis. We have uncoupled the effects of membrane CD23 cleavage and accumulation of soluble CD23 on IgE synthesis in this system. We show that siRNA inhibition of CD23 synthesis or inhibition of membrane CD23 cleavage by an ADAM10 inhibitor, GI254023X, suppress IL-4 and anti-CD40-stimulated IgE synthesis. Addition of a recombinant trimeric soluble CD23, ‘triCD23’, enhances IgE synthesis in this system. This occurs even when endogenous membrane CD23 is protected from cleavage by GI254023X, indicating that IgE synthesis is positively controlled by soluble CD23. We show that triCD23 binds to cells co-expressing membrane IgE and membrane CD21 and caps these proteins on the B cell membrane. Up-regulation of IgE by soluble CD23 occurs after class switch recombination and its effects are isotype-specific. These results suggest that membrane IgE and membrane CD21 co-operate in the soluble CD23-mediated positive regulation of IgE synthesis on cells committed to IgE synthesis. Feedback regulation may occur when the concentration of secreted IgE becomes great enough to allow binding to membrane CD23, thus preventing further release of soluble CD23. We interpret these results with the aid of a model for the up-regulation of IgE by soluble CD23.