Hepatic Phospholipid Remodeling Modulates Insulin Sensitivity and Systemic Metabolism

The liver plays a central role in regulating glucose and lipid metabolism. Aberrant insulin action in the liver is a major driver of selective insulin resistance, in which insulin fails to suppress glucose production but continues to activate lipogenesis in the liver, resulting in hyperglycemia and hypertriglyceridemia. The underlying mechanisms of selective insulin resistance are not fully understood. Here It is shown that hepatic membrane phospholipid composition controlled by lysophosphatidylcholine acyltransferase 3 (LPCAT3) regulates insulin signaling and systemic glucose and lipid metabolism. Hyperinsulinemia induced by high-fat diet (HFD) feeding augments hepatic Lpcat3 expression and membrane unsaturation. Loss of Lpcat3 in the liver improves insulin resistance and blunts lipogenesis in both HFD-fed and genetic ob/ob mouse models. Mechanistically, Lpcat3 deficiency directly facilitates insulin receptor endocytosis, signal transduction, and hepatic glucose production suppression and indirectly enhances fibroblast growth factor 21 (FGF21) secretion, energy expenditure, and glucose uptake in adipose tissue. These findings identify hepatic LPCAT3 and membrane phospholipid composition as a novel regulator of insulin sensitivity and provide insights into the pathogenesis of selective insulin resistance.

Exercise ameliorates insulin resistance and improves SIRT6-mediated insulin signaling transduction in liver of obese rats

Physical exercise is essential for the amelioration of insulin resistance (IR). The mechanisms in charge of improved IR, regulated by exercise, are insufficiently studied. Previous research revealed that Sirtuin 6 (SIRT6) - mediated insulin signaling acts a crucial element in hepatic IR. The objective of our research was to determine the effects of exercise on SIRT6-mediated insulin signaling in liver of IR rats. Forty male Sprague Dawley rats were randomly assigned to four groups (n = 10 rats each): control rats fed with standard chow (Lean group); sedentary rats fed with a high-fat diet (HFD-SED); rats fed with HFD and submitted to 8 week chronic swimming exercise training (HFD-CE); and rats fed HFD and submitted to one acute swimming exercise training (HFD-AE). HFD feeding lead to increased body weight, accumulation of hepatic triglyceride and serum free fatty acids, and enhanced gluconeogenesis. Besides, HFD feeding decreased body insulin sensitivity. Hepatic USP10 and SIRT6 protein levels decreased under obese status. Both chronic and acute exercise intervention alleviated physiological and metabolic status, increased hepatic USP10 and SIRT6 levels, improved insulin signaling transduction, and inhibited gluconeogenesis. These results showed that exercise intervention regulated SIRT6-mediated insulin signaling, which contributes to our understanding of the molecular mechanisms behind IR, in that a regular exercise can mitigate the effects of IR.