GPAT Gene Silencing in Muscle Reduces Diacylglycerols Content and Improves Insulin Action in Diet-Induced Insulin Resistance.

Iwona Kojta,Monika Imierska,Emilia Sokołowska,Kamila Roszczyc-Owsiejczuk,Agnieszka Błachnio-Zabielska,Piotr Zabielski

doi:10.3390/ijms21197369

Abstract

Skeletal muscle is an important tissue responsible for glucose and lipid metabolism. High-fat diet (HFD) consumption is associated with the accumulation of bioactive lipids: long chain acyl-CoA, diacylglycerols (DAG) and ceramides. This leads to impaired insulin signaling in skeletal muscle. There is little data on the involvement of DAG in the development of these disorders. Therefore, to clarify this enigma, the gene encoding glycerol-3-phosphate acyltransferase enzyme (GPAT, responsible for DAG synthesis) was silenced through shRNA interference in the gastrocnemius muscle of animals with diet-induced insulin resistance. This work shows that HFD induces insulin resistance, which is accompanied by an increase in the concentration of plasma fatty acids and the level of bioactive lipids in muscle. The increase in these lipids inhibits the insulin pathway and reduces muscle glucose uptake. GPAT silencing through electroporation with shRNA plasmid leads to a reduction in DAG and triacylglycerol (TAG) content, an increase in the activity of the insulin pathway and glucose uptake without a significant effect on ceramide content. This work clearly shows that DAG accumulation has a significant effect on the induction of muscle insulin resistance and that inhibition of DAG synthesis through GPAT modulation may be a potential target in the treatment of insulin resistance.

Highlights

High-fat diet (HFD) consumption and obesity are associated with intracellular lipid accumulation, which leads to various pathological conditions, e.g., insulin resistance and type 2 diabetes (T2D)
long chain acyl-CoA (LCA-CoA) indirectly affects the function of the insulin pathway because it can be used as a substrate for the de novo synthesis of other bioactive lipids, such as diacylglycerols and ceramides
Our work is the first in which we comprehensively studied the role of GPAT-derived DAG in the induction of insulin pathway dysfunction and reduction of glucose uptake in skeletal muscle

Summary

Introduction

High-fat diet (HFD) consumption and obesity are associated with intracellular lipid accumulation, which leads to various pathological conditions, e.g., insulin resistance and type 2 diabetes (T2D). There are three groups of biologically active lipids that are potentially involved in the induction of muscle insulin resistance: LCA-CoA, ceramides and DAG. Ceramide has been shown to inhibit the insulin pathway at the level of protein kinase B (Akt/PKB) by activating phosphatase A2 (PPA2), which maintains Akt/PKB in an unphosphorylated state [20]. Another group of biologically active lipids that inhibit the activity of the insulin pathway are DAGs. Cellular DAG can be generated as a result of phospholipid breakdown, or it can be synthesized de novo via the esterification of LCA-CoA to glycerol 3-phosphate [21]. We studied the effect of in vivo shRNA-mediated GPAT gene silencing on bioactive lipid accumulation and the insulin signaling pathway in the gastrocnemius muscle of mice with diet-induced insulin resistance

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