Adipose triglyceride lipase regulates basal lipolysis and lipid droplet size in adipocytes

In adipocytes, lipid droplet {(LD)} size reflects a balance of triglyceride synthesis (lipogenesis) and hydrolysis (lipolysis). Perilipin A {(Peri} A) is the most abundant phosphoprotein on the surface of adipocyte {LDs} and has a crucial role in lipid storage and lipolysis. Adipose triglyceride lipase {(ATGL)} and hormone-sensitive lipase {(HSL)} are the major rate-determining enzymes for lipolysis in adipocytes. Each of these proteins {(Peri} A, {ATGL,} and {HSL)} has been demonstrated to regulate lipid storage and release in the adipocyte. However, in the absence of protein kinase A {(PKA)} stimulation (basal state), the lipases {(ATGL} and {HSL)} are located mainly in the cytoplasm, and their contribution to basal rates of lipolysis and influence on {LD} size are poorly understood. In this study, we utilize an adenoviral system to knockdown or overexpress {ATGL} and {HSL} in an engineered model system of adipocytes in the presence or absence of Peri A. We are able to demonstrate in our experimental model system that in the basal state, {LD} size, triglyceride storage, and fatty acid release are mainly influenced by the expression of {ATGL.} These results demonstrate for the first time the relative contributions of {ATGL,} {HSL,} and Peri A on determination of {LD} size in the absence of {PKA} stimulation.