Abnormal metabolism of nonesterified fatty acids (NEFAs) and their derivatives has been reported to be the main cause of intracellular lipotoxic injury. Normally, NEFAs are stored in lipid droplets (LDs) in the form of triglyceride (TG), which could reduce the lipotoxicity of cytosolic NEFAs. Previous studies have implicated that Perilipin 5 (Plin5), an LD-binding protein, regulates the storage and hydrolysis of TG in LD. However, its roles and underlying mechanisms in the liver remain unknown. Here we found that Plin5 expression was increased in steatotic livers. Using Plin5 knockout mice, we found that Plin5 deficiency resulted in reduced hepatic lipid content and smaller-sized LDs, which was due to the elevated lipolysis rate and fatty acid utilization. Plin5-deficient hepatocytes showed increased mitochondria proliferation, which could be explained by the increased expression and activity of PPARα stimulated by the increased NEFA levels. Meanwhile, Plin5-deficient livers also exhibited enhanced mitochondrial oxidative capacity. We also found that Plin5 deficiency induces lipotoxic injury in hepatocytes, attributed to lipid peroxidation. Mechanistically, we found that Plin5 blocks adipose triglyceride lipase (ATGL)-mediated lipolysis by competitively binding to comparative gene identification-58 (CGI-58) and disrupting the interaction between CGI-58 and ATGL.
Conclusion: Plin5 is an important protective factor against hepatic lipotoxicity induced by NEFAs generated from lipolysis. This provides an important new insight into the regulation of hepatic lipid storage and relation between lipid storage and lipotoxicity.
© 2014 by the American Association for the Study of Liver Diseases.