| Summary: | 博士 === 國立臺灣大學 === 動物科學技術學研究所 === 105 === With the high prevalence of obesity, non-alcoholic fatty liver disease (NAFLD) becomes one of the most common liver diseases in the world. Although, the NAFLD is a non-viral and reversible disease, it tends to progress from simple steatosis to nonalcoholic steatohepatitis (NASH), then to irreversible fibrosis and cirrhosis, eventually even to hepatocellular carcinoma (HCC). Up to date, there is no reliable biomarkers used to identify NAFLD, and further discern NAFLD, NASH, and liver fibrosis progression. Invasive and costly liver biopsy remains a standard procedure to diagnose and stage NAFLD. Since the liver account for most pf lipogenesis in both human and chicken, chicken is suggested as a suitable model for studying human NAFLD. However, there is no appropriate NAFLD biomarker fin the chickens. Therefore, the aim of this study is to identify the potential non-invasive plasma biomarkers is the chicken NAFLD model.
In the study, laying hens progressed into NAFLD spontaneously with age. By using transcriptomic and proteomic analysis, four plasma proteins were identified as potential biomarkers including, acetoacetyl-CoA synthetase (AACS), dipeptidyl-peptidase 4 (DPP4), glutamine synthetase (GLUL) and glutathione S-transferase (GST). The potential of these proteins as biomarkers for NAFLD were confirmed further by feeding chickens with a diet containing hepato-protective nutrients, betaine or DHA, the diet and by supplementing the nutrients into the medium of chicken primary hepatocytes. Results showed that both betaine and DHA supplementations suppressed the development of fatty liver, and both transcript and protein levels of the selected biomarkers showed positive correlation with the degrees of hepatic lipid accumulation. Thus, these results verify the potential of these proteins as NAFLD biomarkers. To examine whether these biomarkers as suitable for diagnosing liver fibrosis, chickens were induced for liver fibrosis by carbon tetrachloride (CCl4) to induce liver fibrosis. Betaine supplementation in drinking water was used to exam its amelioration on CCl4-induced liver fibrosis. Results suggested of hepatic mRNA and plasma DPP4 and GST level were elevated in liver fibrosis group, and betaine supplementation inhibited the development of liver fibrosis with lower plasma DPP4 and GST concentrations. Accordingly, these four biomarkers were concluded as effective biomarker to diagnose NAFLD in chickens.
Among the organs liver has a high regenerative capacity. A surgical removal of a portion of the liver is one of treatment strategies for patients with liver cirrhosis or HCC. The study also aimed to investigate the role of ADP-ribosylation factor 6 (Arf6) and phosphatidylinositol 4-phosphate 5-kinase A (PIP5K1A) in liver regeneration. Previous studies have showed that knockout of Arf6 gene cause embryonic lethality due to defect liver development in mice, and Arf6 is required for hepatocyte growth factor (HGF)-dependent formation of hepatic cord formation, which indicates the essential role of Arf6 to mediate HGF signaling. HGF is known as a critical and major growth factor to induce liver regeneration. Using Arf6 knockdown approach, we showed that Arf6 mediates HGF-stimulated hepatocyte proliferation and AKT phosphorylation by recruiting of PIP2-producng enzyme, PIP5K1A to HGF receptor (c-Met) in HepG2 cells. To validate the observation in in vivo models, Pip5k1a knockout mice with 2/3 partial hepatectomy were used to investigate the role of PIP5K1A in liver regeneration. A significant inhibition of liver regeneration and hepatocyte proliferation in Pip5k1a knockout mice were observed. These results suggest the essential role of Arf6-PIP5K1A-AKT to mediate HGF signaling in hepatocyte proliferation to liver regeneration process.
In conclusion, transcriptomic and proteomic studies, AACS, DPP4, GST and GLUL were concluded as potential biomarkers for NAFLD and DPP4 and GST for liver fibrosis in the chicken models. Both betaine and DHA supplementation in chicken diet effectively ameliorated NAFLD and liver fibrosis induced by CCl4. In a separate study, Arf6-PIP5K1A-AKT cascade was conclude to mediate HGF signaling transduction in liver regeneration. These findings may shed new light to reveal the molecular mechanism of liver regeneration, and provide a potential diagnostic markers and therapeutic strategies for treating liver diseases.
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