Adiponectin receptor 1 enhances fatty acid metabolism and cell viability in HepG2 cells through PI3K/AKT pathway
Date Issued
2011
Date
2011
Author(s)
Chou, I-Pin
Abstract
Hepatic lipid overloading mainly in the form of triglyceride accumulation, which can result in the inflammatory response, cause hepatocyte damage, fibrosis, and eventually progress to cirrhosis, is associated with nonalcoholic fatty liver disease. The most abundant saturated fatty acid in plasma is palmitate, which is also common in a wide range of plant and animal sources. However, it is found lipotoxic in a variety of cell types, including hepatocytes.
Exposure of human hepatocytes HepG2 to 0.2 mM or 0.4 mM palmitate for 24 hours resulted in raising lipid accumulation and decreasing ATP production and cell viability, suggesting the lipotoxicity of palmitate. Expression of genes related to fatty acid metabolism and cell apoptosis was affected by palmitate treatment. Expression of rate-limiting regulator in fatty acid oxidation carnitine palmitoyltransferase I (CPT1) was elevated in transcription level, and other genes, such as acyl-coA oxidase (ACO), cytochrome c oxidase, peroxisome-proliferator-activated receptor-co-activator 1-alpha(PGC1-alpha), peroxisome-proliferator- activated receptor-alpha(PPAR-alpha) and acetyl-CoA carboxylase (ACC) were increased slightly, while fatty acid synthase (FAS) was increased significantly. On the other hand, the mRNA expression of caspase 3 was increased significantly. In brief, palmitate contributed to cell dysfunction, and led to cell death ultimately.
Adiponectin and its receptors play important roles in regulating lipid metabolism. In the second experiment, we over-expressed adiponectin receptor 1 in HepG2 cells by lentivirus system to define its role in the development of fatty liver syndrome. First of all, mRNA level of adiponectin receptor 1 in adiponectin receptor 1 transfected-HepG2 (AdipoR1) cells was 1.5-fold higher than the mock vector transfected-HepG2 cells (mock). Meanwhile, the protein expression of FLAG, which was constructed at the adiponectin receptor 1 vector, was 5-fold higher than the mock. When AdipoR1 cells were cultured with palmitate, fatty acid transport protein 2 (FATP2), ACO, CPT1, cytochrome c oxidase, and PPAR-alpha were significantly increased, but FAS, ACC, and PGC1-alpha were significantly decreased compared to mock group. In addition, ATP production was increased whereas the lipid accumulation was reduced in AdipoR1 transfected-HepG2 cells. These results suggest that adiponectin receptor 1 improves fatty acid metabolism, by increasing fatty acid up take and oxidation. We then investigated the cell death of palmitate-treated AdipoR1 cells. At 20 hours, cell viability of AdipoR1 cells was significantly higher than that of mock group, furthermore, annexin V positive cells of which was much lower. Additionally, the gene expression of caspase 3 was decreased significantly in AdipoR1 cells. Namely, adiponectin receptor 1 ameliorates palmitate-induced apoptosis in HepG2 cells.
Meanwhile the phosphorylation of AKT was increased in AdipoR1 cells, and when PI3 kinase inhibitor was applied, the protective effect of adiponectin receptor 1 was absent, with which ATP production was decreased again and so did the cell viability by palmitate. Taken together, adiponectin receptor 1 enhances fatty acid metabolism and cell viability when treated with palmitate partially by activating AKT signaling. Therefore adiponectin receptor 1 serves a potential therapeutic target in nonalcoholic fatty liver disease.
Subjects
adiponectin receptor
HepG2
apoptosis
cytotoxicity
SDGs
Type
thesis
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