Abstract 11592: Lipid Droplet Associated Hydrolase (LDAH) Enhances Triacylglycerol Accumulation by Antagonizing Adipose Triglyceride Lipase (ATGL)

Abstract

Lipid droplets (LDs) are lipid storage depots as well as metabolically dynamic organelles. LD-associated hydrolase (LDAH) is a newly identified protein that is highly expressed in liver and adipose tissues, where triacylglycerol (TAG) is the main form of lipid stored in LDs. However, to date the role of LDAH in TAG metabolism has not been reported. In this study we show that upon oleic acid loading LDAH translocalizes from the endoplasmic reticulum (ER) to the LD surface, and increases the size of LDs by promoting fusion in a tubulin-dependent fashion. LDAH overexpression in HEK 293 cells increased the net TAG content, while LDAH knockdown decreased TAG levels. Mutations in two predicted acyltransferase motifs aiming to assess if changes in TAG content is due to LDAH’s direct enzymatic activity did not affect TAG levels. However, an LDAH splicing variant missing 90 amino acid at C-terminus also localized to LDs, but failed to increase both LD fusion and TAG levels. Consistent with the increase in LD size and area, LDAH increased the level of Perilipin3, a major LD associated protein in HEK293 cells, but decreased the level of adipose triglyceride lipase (ATGL) that regulates rate-limiting step of TAG hydrolysis. ATGL ubiquitination, which ultimately leads to protein degradation, was higher in LDAH-overexpressing cells, and treatment with MG132 to block the activity of the 26S proteasome complex attenuated the reduction in ATGL. Coexpression of ATGL with LDAH reduced LDAH-mediated increase in LD size, total area of LDs, and TAG content. Alternatively, LDAH delayed TAG hydrolysis by ATGL upon treatment with β-adrenergic agonists. In conclusion, the data support a role of LDAH in facilitating LD growth and TAG accumulation, and uncover a mutually antagonistic interaction between LDAH and the catabolic enzyme ATGL.