Membrane Bound O-Acyltransferase 7 (MBOAT7)-Driven Lysophosphatidylinositol (LPI) Acylation in Adipocytes Contributes to Systemic Glucose Homeostasis

Abstract

Non-alcoholic fatty liver disease (NAFLD) is becoming increasingly common and is a leading cause of end stage liver diseases such as cirrhosis and hepatocellular carcinoma. The rise in NAFLD closely parallels the global epidemic of obesity and type 2 diabetes mellitus (T2DM), and there is a clear interrelationship between abnormal lipid metabolism, insulin resistance, and NAFLD progression. Several genetic loci have been identified as contributors to NAFLD progression, all of which are consistently linked to abnormal lipid metabolic processes in the liver. The common loss-of-function variant rs641738 (C>T) near the gene encoding Membrane-Bound O-Acyltransferase 7 (MBOAT7) is associated with increased susceptibility to NAFLD as well as the entire spectrum of NAFLD progression. The MBOAT7 gene encodes a lipid metabolic enzyme that is capable of esterifying polyunsaturated fatty acyl-CoAs to LPI substrates to generate phosphatidylinositol (PI) lipids. We previously showed that antisense oligonucleotide (ASO)-mediated knockdown of Mboat7 in mice promoted high fat diet-induced hepatic steatosis, hyperinsulinemia, and systemic insulin resistance (Helsley et al., 2019). Thereafter, other groups showed that hepatocyte-specific genetic deletion of Mboat7 promoted striking fatty liver and NAFLD progression but does not alter insulin sensitivity, suggesting the potential for cell autonomous roles. Here, we show that MBOAT7 function in adipocytes contributes to diet-induced metabolic disturbances including hyperinsulinemia and systemic insulin resistance. The expression of Mboat7 in white adipose tissue closely correlates with diet-induced obesity across a panel of ~100 inbred strains of mice fed a high fat/high sucrose diet. Moreover, adipocyte-specific genetic deletion of Mboat7 is sufficient to promote hyperinsulinemia, systemic insulin resistance, and mild fatty liver. Unlike in the liver, where Mboat7 plays a relatively minor role in maintaining arachidonic acid (AA)-containing PI pools, Mboat7 is the major source of AA-containing PI pools in adipose tissue. Our data demonstrate that MBOAT7 is a critical regulator of adipose tissue PI homeostasis, and adipocyte MBOAT7-driven PI biosynthesis is closely linked to hyperinsulinemia and insulin resistance in mice.