Targeting pyruvate carboxylase reduces gluconeogenesis and adiposity and improves insulin resistance.

We measured the mRNA and protein expression of the key gluconeogenic enzymes in human liver biopsy specimens and found that only hepatic pyruvate carboxylase protein levels related strongly with glycemia. We assessed the role of pyruvate carboxylase in regulating glucose and lipid metabolism in rats through a loss-of-function approach using a specific antisense oligonucleotide (ASO) to decrease expression predominantly in liver and adipose tissue. Pyruvate carboxylase ASO reduced plasma glucose concentrations and the rate of endogenous glucose production in vivo. Interestingly, pyruvate carboxylase ASO also reduced adiposity, plasma lipid concentrations, and hepatic steatosis in high fat-fed rats and improved hepatic insulin sensitivity. Pyruvate carboxylase ASO had similar effects in Zucker Diabetic Fatty rats. Pyruvate carboxylase ASO did not alter de novo fatty acid synthesis, lipolysis, or hepatocyte fatty acid oxidation. In contrast, the lipid phenotype was attributed to a decrease in hepatic and adipose glycerol synthesis, which is important for fatty acid esterification when dietary fat is in excess. Tissue-specific inhibition of pyruvate carboxylase is a potential therapeutic approach for nonalcoholic fatty liver disease, hepatic insulin resistance, and type 2 diabetes.

Role of patatin-like phospholipase domain-containing 3 on lipid-induced hepatic steatosis and insulin resistance in rats.

UNLABELLED: Genome-wide array studies have associated the patatin-like phospholipase domain-containing 3 (PNPLA3) gene polymorphisms with hepatic steatosis. However, it is unclear whether PNPLA3 functions as a lipase or a lipogenic enzyme and whether PNPLA3 is involved in the pathogenesis of hepatic insulin resistance. To address these questions we treated high-fat-fed rats with specific antisense oligonucleotides to decrease hepatic and adipose pnpla3 expression. Reducing pnpla3 expression prevented hepatic steatosis, which could be attributed to decreased fatty acid esterification measured by the incorporation of [U-(13) C]-palmitate into hepatic triglyceride. While the precursors for phosphatidic acid (PA) (long-chain fatty acyl-CoAs and lysophosphatidic acid [LPA]) were not decreased, we did observe an ∼20% reduction in the hepatic PA content, ∼35% reduction in the PA/LPA ratio, and ∼60%-70% reduction in transacylation activity at the level of acyl-CoA:1-acylglycerol-sn-3-phosphate acyltransferase. These changes were associated with an ∼50% reduction in hepatic diacylglycerol (DAG) content, an ∼80% reduction in hepatic protein kinase Cε activation, and increased hepatic insulin sensitivity, as reflected by a 2-fold greater suppression of endogenous glucose production during the hyperinsulinemic-euglycemic clamp. Finally, in humans, hepatic PNPLA3 messenger RNA (mRNA) expression was strongly correlated with hepatic triglyceride and DAG content, supporting a potential lipogenic role of PNPLA3 in humans. CONCLUSION: PNPLA3 may function primarily in a lipogenic capacity and inhibition of PNPLA3 may be a novel therapeutic approach for treatment of nonalcoholic fatty liver disease-associated hepatic insulin resistance.