Hypoxia Inducible Lipid Droplet Associated protein inhibits Adipose Triglyceride Lipase.

Elaborate control mechanisms of intracellular triacylglycerol (TAG) breakdown are critically involved in the maintenance of energy homeostasis. Hypoxia inducible lipid droplet associated protein (HILPDA)/Hypoxia inducible gene-2 (Hig-2) has been shown to affect intracellular TAG levels, yet, the underlying molecular mechanisms are unclear. Here, we show that HILPDA inhibits adipose triglyceride lipase (ATGL), the enzyme catalyzing the first step of intracellular TAG hydrolysis. HILPDA shares structural similarity with G0/G1 switch gene 2 (G0S2), an established inhibitor of ATGL. HILPDA inhibits ATGL activity in a dose-dependent manner with an IC50 value of 2 M. ATGL inhibition depends on the direct physical interaction of both proteins and involves the N- terminal, hydrophobic region of HILPDA and the N-terminal, patatin-domain containing segment of ATGL. Finally, confocal microscopy combined with Foerster resonance energy transfer-fluorescence lifetime imaging microscopy (FRET-FLIM) analysis indicated that HILPDA and ATGL colocalize and physically interact intracellularly. These findings provide a rational biochemical explanation for the tissue-specific increased TAG accumulation in HILPDA overexpressing transgenic mouse models