keratan-sulfate and Fatty-Liver

Lumican, an extracellular matrix proteoglycan was previously shown to be upregulated with increasing severity of nonalcoholic steatohepatitis (NASH). Although lumican is involved in collagen fibrillogenesis in extra-hepatic tissues, little is known about the role of lumican in hepatic disease. We therefore determined lumican expression in etiologies other than clinical NASH. Our results indicated that lumican is upregulated in clinical samples of hepatitis C virus infection, in experimental rodent models of chronic and acute liver injury and could additionally be induced in vitro in response to the pro-fibrotic cytokine transforming growth factor β1 (TGFβ1) and to lipotoxic palmitic acid. Together, these results suggested a role for lumican in hepatic fibrosis. To investigate the functional role of lumican in hepatic fibrosis, lumican null (Null) and wild-type (WT) littermates were administered carbon tetrachloride intra-peritoneally. Serum and liver tissue were analyzed for indices of liver injury, fibrosis, matrix turnover, and proliferation. Hepatic fibrosis was greatly reduced in null animals (P<0.05). Paradoxically, gene expression of fibrosis-related genes such as TGFβ1 and collagen 1 was numerically higher in null animals though statistically insignificant from WT animals. On the other hand, α smooth muscle actin expression (α-SMA), a marker for activated fibroblasts, the main contributors of collagen production was significantly higher (P<0.05) in null animals as compared with WT littermates. Among the matrix metalloproteases (MMP), MMP13 was significantly increased (P<0.05) in null animals. Ultra-structural imaging indicated differences in the organization and spatial distribution of hepatic collagen fibrils of null and WT mice. Cell proliferation was significantly increased (P<0.05) in null animals. We conclude that lumican is a prerequisite for hepatic fibrosis. The protective effect of lumican deficiency in hepatic fibrosis appears to be downstream of collagen production and mediated through the combined effects of impaired collagen fibrillogenesis, increased matrix turnover, and an enhanced proliferative response.

Topics: Animals; Carbon Tetrachloride; Cell Line; Cell Proliferation; Chondroitin Sulfate Proteoglycans; Collagen; Diet; Fatty Liver; Hepatocytes; Histocytochemistry; Humans; Keratan Sulfate; Liver; Liver Cirrhosis, Experimental; Lumican; Mice; Mice, Inbred C57BL; Statistics, Nonparametric; Transforming Growth Factor beta1

The basis of hepatocellular injury and progressive fibrosis in a subset of patients with nonalcoholic fatty liver disease (NAFLD) is poorly understood. We sought to identify hepatic proteins that are differentially abundant across the histologic spectrum of NAFLD. Hepatic protein abundance was measured in liver samples from four groups (n = 10 each) of obese (body mass index >30 kg/m(2)) patients: (1) obese normal group (normal liver histology), (2) simple steatosis (SS), (3) nonalcoholic steatohepatitis (NASH)-mild (steatohepatitis with fibrosis stage 0-1), and (4) NASH-progressive (steatohepatitis with fibrosis stage 2-4). Hepatic peptides were analyzed on an API Qstar XL quadrupole time-of-flight mass spectrometer using Analyst QS software. Linear trends tests were performed and used to screen for differential abundance. Nine known proteins were expressed with differential abundance between study groups. For seven proteins differential abundance is likely to have been on the basis increased hepatic lipid content and/or inflammation. Lumican, a 40-kDa keratin sulfate proteoglycan that regulates collagen fibril assembly and activates transforming growth factor-beta and smooth muscle actin, was expressed similarly in obese normal and SS but was overexpressed in a progressive manner in NASH-mild versus SS (124%, P < 0.001), NASH-progressive versus NASH-mild (156%, P < 0.001) and NASH-progressive versus obese normal (178%, P < 0.001). Fatty acid binding protein-1 (FABP-1), which is protective against the detergent effects of excess free fatty acids, facilitates intracellular free fatty acid transport and is an important ligand for peroxisome proliferator-activated receptor-mediated transcription, was overexpressed in SS when compared to the obese normal group (128%, P < 0.001), but was paradoxically underexpressed in NASH-mild versus SS (73%, P < 0.001), NASH-progressive versus NASH-mild (81%, P < 0.001), and NASH-progressive versus obese normal (59%, P < 0.001).. Histologically progressive NAFLD is associated with overexpression of lumican, an important mediator of fibrosis in nonhepatic tissues, whereas FABP-1 is paradoxically underexpressed in NASH, suggesting a new potential mechanism of lipotoxicity in NAFLD. Further studies are needed to determine the biologic basis of lumican and/or FABP-1 dysregulation in NAFLD.

Topics: Adult; Chondroitin Sulfate Proteoglycans; Fatty Acid-Binding Proteins; Fatty Liver; Female; Humans; Immunohistochemistry; Keratan Sulfate; Liver; Lumican; Male; Middle Aged; Obesity; Polymerase Chain Reaction; Proteomics; RNA, Messenger; Tandem Mass Spectrometry