Regulation of Lipolysis By Perilipin : influence of Obesity and Exercise Training

Abstract

Obesity is the result of excess energy storage due to an imbalance between energy storage and energy utilization. Excess energy is stored as triacylglycerol (TAG) in adipose tissue in various regions throughout the body. In order to reduce excess fat stores, one must increase the utilization of fat stores for energy. Lipolysis is the process where TAG are hydrolyzed to provide free fatty acids as an energy substrate to other organs during times of energy demand. Blunted catecholamine stimulated lipolysis has been well documented in obese adults. The purpose of this study was to evaluate the effects of obesity and exercise training on lipolysis and lipolytic protein expression in abdominal subcutaneous adipose tissue (SCAT) in men. Lean endurance trained (n=10), lean sedentary (n=10), and obese sedentary (n=8) men were recruited for this study. Abdominal SCAT was obtained using needle aspiration. Western blots were used to determine the protein content of adipose triglyceride lipase (ATGL), comparative gene identification 58 (CGI-58), hormone sensitive lipase (HSL), and perilipin. Microdialysis was used to evaluate abdominal SCAT lipolysis in vivo. Two probes were inserted into abdominal SCAT. One probe served as a control (perfused with a Ringer solution) while the second probe was perfused with isoproterenol, followed by a mixture of isoproterenol and phentolamine. Ethanol was added to the perfusates to measure local blood flow. The obese men in this study were tested before and after 8 weeks of aerobic exercise training. Unstimulated, resting lipolysis was higher in exercise trained compared to obese men. [Beta]-adrenergic stimulation increased lipolysis above baseline in exercise trained and sedentary but not obese men. Blood flow was not different in exercise trained, sedentary, and obese during any treatment. Perilipin protein content was lower in the sedentary compared to exercise trained men but not different than obese men. There were no differences in ATGL, HSL, or CGI-58 protein content in any of the groups. In response to 8 weeks of exercise training in the obese group, unstimulated, resting lipolysis did not change. [Beta]-adrenergic stimulated lipolysis did not stimulate lipolysis before exercise training but increased above baseline after exercise training. Lipolysis during an acute exercise bout was not different before training but was higher than baseline after exercise training. Adipose tissue blood flow was lower than baseline during an acute exercise bout after exercise training. There were no other differences in blood flow during any treatment. ATGL increased in response to an acute exercise bout before exercise training. Resting levels increased in response to 8 weeks of exercise training. Perilipin increased in response to acute exercise before exercise training. Perilipin tended to be higher at rest after 8 weeks of exercise training. Based on our results, exercise training increases perilipin protein content in lean men which appears to be a key component for a reduced [beta]-adrenergic responsiveness in SED compared to lean. It also appears that acute exercise increases ATGL and perilipin in obese men. Eight weeks of exercise training increased ATGL and tended to increase perilipin in obese men. ATGL and perilipin are likely the key components to increasing [beta]-adrenergic lipolysis in obese men after exercise training.