Hepatic stellate cells (HSC) are the key effector cells of liver fibrosis. In the injured liver, quiescent HSC undergo a phenotypic change characterized by increased proliferation capacity, motility, contractility, and the ability to secret excess amounts of extracellular matrix (ECM) proteins into the extracellular space. Most current experimental approaches are aimed towards inhibiting or impeding accumulation of fibrogenic cells or deposition of ECM proteins, yet this has not resulted in development of any useful treatments for patients. We believe that there is a knowledge deficit in the basic cellular and subcellular functions of HSC. Specifically, the general molecular mechanisms causing matrix and pro-fibrogenic material release from HSC are unknown. SNARE (Soluble-NSF-attachment) proteins are the proposed machinery that direct intracellular trafficking and exocytosis of vesicular cargo. The prototypic SNARE machinery required for docking and fusion consist of synaptobrevin or vesicle associated membrane (VAMP), syntaxin-1, and synaptosomal-associated protein 25 (SNAP-25). We found that HSC lack the t-SNARE protein, SNAP-25, but express a homologous protein, SNAP-23. In this study we aim to investigate the role of SNAP-23 in liver fibrosis in vitro and in vivo.
Myofibroblast phenotype is critical to the function of activated HSC. Although our initial goal was to study the role of SNAP-23 on exocytosis of matrix-containing vesicles, we found that downregulation of SNAP-23 dramatically influenced HSC myofibroblast phenotype. Specifically, we showed in vitro that HSC lacking SNAP-23 reduced actin polymerization, disorganized filamentous actin structure, and loss of motility. We then examined whether SNAP-23 heterozygote mice were protected from liver fibrosis/cirrhosis in vivo. We found that these mice had delayed onset of liver fibrosis but ultimately developed cirrhosis at later time points.
Taken together, these studies suggest that SNAP-23 is important in the regulation of actin organization in HSC, which has important functional consequences. However, we have yet to demonstrate conclusively that SNAP-23 has a strong influence on development of advanced fibrosis and cirrhosis in the injured liver.
|Commitee:||Baldini, Giulia, Raney, Kevin, Schuller, Maria, Storrie, Brian|
|School:||University of Arkansas for Medical Sciences|
|Department:||Interdisciplinary Biomedical Sciences|
|School Location:||United States -- Arkansas|
|Source:||DAI-B 78/12(E), Dissertation Abstracts International|
|Subjects:||Biology, Cellular biology|
|Keywords:||Cytoskeletal organization, Hepatic stellate cells, Liver fibrosis, SNAP-23, SNARE proteins|
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