Perilipin (PLIN) proteins and the regulation of intramuscular lipolysis

Although it has been known for many years that intramuscular triglycerides (IMTGs) are an important fuel for during exercise, the processes that regulate intramuscular lipolysis are still largely unknown. In terms of health and disease, insulin-resistant obese and sedentary individuals have very high muscle lipid, while endurance trained athletes have as much or more IMTG content, and yet are very insulin sensitive. This underscores the need for understanding what is different between these two populations, and studying the regulation of IMTG lipolysis and synthesis.

In adipose tissue, where lipolysis has been better studied, a lipid droplet protein known as perilipin (or PLIN1) plays a pivotal role in regulating lipolysis and fatty acid release in response to adrenergic stimulation. However, PLIN1 is not found in skeletal muscle and therefore research has focused on other PLIN family members during muscle contraction-induced lipolysis. More specifically, research has focused on the interaction of PLINs 2, 3 and 5 with the regulatory lipase (adipose triglyceride lipase (ATGL)) and its co-activator, comparative gene identification (CGI)-58. Recently, some PLINs have been found in the muscle mitochondrial fraction and this can be altered with muscle contraction that induces lipolysis and/or endurance training, although the reasons(s) for this are still unclear.