Perilipin

Perilipin, also known as lipid droplet-associated protein or PLIN, is a protein that, in humans, is encoded by the PLIN gene. The perilipins are a family of proteins that associate with the surface of lipid droplets. Phosphorylation of perilipin is essential for the mobilization of fats in adipose tissue.

Function
Perilipin is a protein that coats lipid droplets in adipocytes, the fat-storing cells in adipose tissue. Perilipin acts as a protective coating from the body’s natural lipases, such as hormone-sensitive lipase, which break triglycerides into glycerol and free fatty acids for use in metabolism, a process called lipolysis. In humans, perilipin is expressed in three different isoforms, A, B, and C, and perilipin A is the most abundant protein associated with the adipocyte lipid droplets.

Perilipin is hyperphosphorylated by PKA following β-adrenergic receptor activation. Phosphorylated perilipin changes conformation, exposing the stored lipids to hormone-sensitive lipase-mediated lipolysis. Although PKA also phosphorylates hormone-sensitive lipase, which can increase its activity, the more than 50-fold increase in fat mobilization (triggered by epinephrine) is primarily due to perilipin phosphorylation.

Clinical significance
Perilipin is an important regulator of lipid storage. Perilipin expression is elevated in obese animals and humans. Perilipin-null mice eat more food than wild-type mice, but gain 1/3 less fat than wild-type mice on the same diet; perilipin-null mice are thinner, with more lean muscle mass. Perilipin-null mice also exhibit enhanced leptin production and a greater tendency to develop insulin resistance than wild-type mice.

Polymorphisms in the human perilipin (PLIN) gene have been associated with variance in body-weight regulation and may be a genetic influence on obesity risk in humans. In particular, variants 13041A>G and 14995A>T have been associated with increased risk of obesity in women and 11482G>A has been associated with decreased perilipin expression and increased lipolysis in women.

Perilipin family of proteins
Perilipin is part of a gene family with five currently-known members. In vertebrates, closely related genes include adipophilin (also known as adipose differentiation-related protein), TIP47, and LSDP5 (also called MLDP and OXPAT). Insects express related proteins, LSD1 and LSD2, in fat bodies.