Targeting hepatocyte-specific SLC2A8 blocks hepatic steatosis and dissociates TCA cycle flux inhibition from glutamine anaplerosis

Abstract

Background: Excess TCA cycle and glutamine anaplerosis are hallmarks of metabolic dysfunction-associated steatotic liver disease and steatohepatitis. Blocking glutamine metabolism attenuates metabolic dysfunction-associated steatohepatitis. However, inhibiting TCA cycle flux by blocking plasma membrane carbohydrate transport is limited by the ubiquitous tissue distribution, function, and homology among the SLC2A family of facilitative carbohydrate transporters, and the potential for carbohydrate blockade to invoke or exacerbate glutamine anaplerosis. Here, we quantify alterations in hepatocyte carbon flux, define the broader metabolic consequences of hepatocyte-specific GLUT8/SLC2A8 inhibition, and delineate the antisteatotic efficacy of a novel small-molecule GLUT8-selective inhibitor. Methods: We generated mice with floxed SLC2A8 alleles and expressed hepatocyte-specific Cre by breeding these mice with albumin-Cre transgenic mice, or by administering AAV8 encoding hepatocyte-specific iCre. We performed stable-isotope glucose, fructose, and glutamine metabolic labeling in isolated GLUT8WT and GLUT8LKO hepatocytes and performed metabolic phenotyping in lean and diet-induced obese GLUT8WT and GLUT8LKO mice. Finally, we performed high-throughput screening to identify a GLUT8-selective inhibitor, which we characterized using in vitro models of triglyceride accumulation. Results: Hepatocyte-specific SLC2A8 deletion reduced diet-induced hepatic and peripheral fat accumulation and increased thermogenesis during ZT12-24 (eg, the dark phase). It also disrupted TCA cycle flux without inducing compensatory glutamine utilization. High-throughput screening identified a small-molecule, GLUT8-selective inhibitor, P20, which blocked hepatocyte TG accumulation and inflammation in in vitro steatotic and inflammatory models. Conclusions: Deleting the hepatocyte carbohydrate transporter GLUT8 suppresses TCA cycle flux without inducing compensatory glutamine anaplerosis. The net effect of this is liver protection against multiple forms of dietary insult. Given that selective pharmacological GLUT8 inhibition is feasible, GLUT8 may be a viable target to abate metabolic dysfunction-associated steatohepatitis and other complications of obesity.