Molecular Mechanisms of Liver Fibrosis

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Hepatic stellate cell (HSC) activation encompasses aphenotype that includes enhanced migration, proliferation, and matrix deposition. Migration is critical for coordinately situating HSC for matrix deposition and development of cirrhosis. Our Long-Term Objectives are to understand the molecular underpinnings of HSC biology that lead to cirrhosis with the goal of identifying therapeutic targets. Recently,we identified a critical role of synectin in the process of HSC migration and fibrosis. Synectin is a cytosolic protein that mediates signal transduction, vesicle trafficking, and ultimately gene expression. Synectin is chosen for this proposal as a significant protein warranting detailed investigation because, as we demonstrate, it is upregulated in human cirrhosis and is required for murine fibrogenesis. Mechanistically, we implicate synectin inHSC migration through both short term receptor signaling as well as longer term epigenetic regulation of gene expression networks. Our preliminary data show that depletion of HSC synectin reduces migration signaling downstream of the receptor tyrosine kinase, platelet derived growth factor receptor alpha (PDGFRα); attenuates transcription of a set of HSC activation genes including one that encodes the multifunctional signaling protein, IGFBP3 (insulin growth factor binding protein-3); and abrogates murine fibrosis in vivo. These important observations have led us to propose the central hypothesis that synectin increases HSC migration and fibrosis by promoting PDGFRα signaling and by regulating a network of genes that include IGFBP3. This hypothesis leads to the following Specific Aims: 1) Synectin promotes HSC migration by regulating PDGFRα targeting and signal activation. Aim 1a will determine how synectin recruits and binds specific vesicle trafficking proteins that maintain PDGFRα protein levels, target the protein to endosomes and activate migration signaling. Aim 1b will uncover how disruption of synectin function leads to autophagic degradation of PDGFRα and attenuated HSC migration. 2) Synectin epigenetically controls IGFBP3 gene expression to promote HSC migration. Aim 2a will identify how synectin regulates a specific histone methyl transferase, EZH2 and how this governs IGFBP3 gene expressionthrough histone methylation. Aim 2b will determine how IGFBP3 production stimulates HSC migration. 3) Synectin regulates fibrosis in vivo. Aim 3a will use a novel fibrosis regression model in mice with HSC selective modifications to synectin and PDGFRα to further ascertain the proposed role of these proteins in vivo. Aim 3b will use a synectin neutralizing peptide that selectively targets HSC in coordination with magnetic resonance elastography (MRE) imaging, and mice with genetic deletion of IGFBP3 to elucidate how synectin promotes fibrosis in vivo. In total, this proposal will utilize conceptually and technically innovative approaches and concepts to test a novel hypothesis pertaining to synectin as a “master regulator” of HSC signals that lead to migration and fibrosis. RELEVANCE (See instructions): Liver injury from alcohol and other etiologies can culminate in cirrhosis with significant associated morbidity and mortality.