Shifts in dietary carbohydrate-lipid exposure regulate expression of the non-alcoholic fatty liver disease-associated gene PNPLA3/adiponutrin in mouse liver and HepG2 human liver cells

Abstract

Objective Patatin-like phospholipase domain containing 3 (PNPLA3, adiponutrin) has been identified as a modifier of lipid metabolism. To better understand the physiological role of PNPLA3/adiponutrin, we have investigated its regulation in intact mice and human hepatocytes under various nutritional/metabolic conditions. Material/Methods PNPLA3 gene expression was determined by real-time PCR in liver of C57BL/6 mice after dietary treatments and in HepG2 cells exposed to various nutritional/metabolic stimuli. Intracellular lipid content was determined in HepG2 cells after siRNA-mediated knockdown of PNPLA3. Results In vivo, mice fed a high-carbohydrate (HC) liquid diet had elevated hepatic lipid content, and PNPLA3 mRNA and protein expression, compared to chow-fed mice. Elevated expression was completely abrogated by addition of unsaturated lipid emulsion to the HC diet. By contrast, in mice with high-fat diet-induced steatosis, Pnpla3 expression did not differ compared to low-fat fed mice. In HepG2 cells, Pnpla3 expression was reversibly suppressed by glucose depletion and increased by glucose refeeding, but unchanged by addition of insulin and glucagon. Several unsaturated fatty acids each significantly decreased Pnpla3 mRNA, similar to lipid emulsion in vivo. However, Pnpla3 knockdown in HepG2 cells did not alter total lipid content in high glucose- or oleic acid-treated cells. Conclusions Our results provide evidence that PNPLA3 expression is an early signal/signature of carbohydrate-induced lipogenesis, but its expression is not associated with steatosis per se. Under lipogenic conditions due to high-carbohydrate feeding, certain unsaturated fatty acids can effectively suppress both lipogenesis and PNPLA3 expression, both in vivo and in a hepatocyte cell line.

Non‐alcoholic fatty liver disease phosphoproteomics: A functional piece of the precision puzzle

“…This differential activation of signaling networks in NASH and SS versus NOR specimens suggests a central role for these carbohydrate metabolism phosphosites in mediating the disease processes driving the development of NASH. These are consistent with recent findings examining the role of polymorphisms in patatin‐like phospholipase domain containing3 (PNPLA3), strongly associated with NAFLD in humans, which showed that excess carbohydrate relative to fat potently regulates PNPLA3 . More work is needed to fully understand how aberrant carbohydrate metabolism drives NAFLD progression.…”

PNPLA3 Expression Is Related to Liver Steatosis in Morbidly Obese Women with Non-Alcoholic Fatty Liver Disease

“…Because PNPLA3 has previously been reported to influence lipid metabolism in animal models and in in vitro studies [ 40 , 41 ], we evaluated the interplay of PNPLA3 liver expression with the expression of the main lipid metabolism-related genes. In the current first human study in this sense, PNPLA3 expression positively correlated with LXRα , PPARα , and SREBP2 liver expression.…”

The Chinese medicine Chai Hu Li Zhong Tang protects against non-alcoholic fatty liver disease by activating AMPKα

“…HepG2 cells (ATCC, Manassas, VA, U.S.A.) were cultured in 79% Dulbecco’s modified Eagle’s medium (DMEM, 10569044, Gibco, Waltham, MA, U.S.A.) that contained 20% FBS (10099-141, Gibco) and 1% penicillin-streptomycin (100 U/ml, 15140-122, Gibco) [ 24 ]. Other groups of HepG2 cells were cultured in medium that contained a 1% long chain fat emulsion (0338-0519-48, Intralipid® 20%, Baxter, Deerfield, IL, U.S.A.) for 48 h; those cells were used to construct the NAFLD cell model [ 25 ]. Next, the cells were treated with either CHLZT-containing serum (defined as Compound-S) or AICAR-containing serum (defined as AICAR-S) at final concentrations of 20%.…”