Increased Lipolysis in Adipose Tissues is Associated with Elevation of Systemic Free Fatty Acids and Insulin Resistance in Perilipin Null Mice

Elevated plasma levels of free fatty acids (FFAs) are thought to restrict glucose utilization and induce insulin resistance. Plasma FFA concentrations are primarily governed by lipolysis in adipocytes. Perilipin surrounds the lipid droplet in adipocytes and has a dual role in lipolysis regulation. Perilipin null mice studied by two independent laboratories exhibited similar phenotypes of reduced adipose mass and resistance to diet-induced obesity, but have inconsistent metabolic parameters such as plasma levels of FFA, glucose, and insulin. This discrepancy may be due to differences in genetic background, generation, and nutritional status of the animals examined. In this study, we examined the major metabolic parameters in 129/SvEv perilipin null mice fasted for 4 h and observed increased plasma concentrations of FFA, glycerol, glucose, and insulin. An increase in the score for the homeostasis model assessment of insulin resistance index confirmed the insulin resistance in perilipin null mice, which may be attributed to the plasma FFA elevation. Basal lipolysis was increased in adipose tissues or primary adipocytes isolated from perilipin null mice with increased mass and activity of hormone-sensitive lipase and adipose triglyceride lipase. The increased lipolytic action may accelerate FFA efflux from the adipose tissues to the bloodstream, thereby accounting for systemic FFA elevation and, hence, insulin resistance in perilipin null mice.