1Heidelberg University, Medical Faculty Heidelberg, Institute of Experimental Cardiology, 69120 Heidelberg, Germany; Heidelberg University Hospital, Department of Internal Medicine VIII, 69120 Heidelberg, Germany; German Center for Cardiovascular Research (DZHK), Partner Site Heidelberg/Mannheim, 69120 Heidelberg, Germany; Molecular Medicine Partnership Unit, Heidelberg University, 69120 Heidelberg, Deutschland
Adipose triglyceride lipase (ATGL), along with its coactivator ABHD5, is a lipid droplet-associated protein that catalyzes the hydrolysis of triglycerides. Mutations in the ATGL and ABHD5 genes are the underlying cause of Neutral Lipid Storage Disease (NLSD), which leads to the accumulation of lipid droplets. We discovered that ABHD5 not only serves as a coactivator of ATGL but also proteolytically cleaves a N-terminal fragment of the class IIa histone deacetylase 4 (HDAC4). This fragment, referred to as HDAC4-NT, exerts a cardioprotective effect. Through gene therapy using this fragment, we successfully rescued cardiac dysfunction in an ABHD5- deficient mouse. Here we show that ATGL is also required for sufficient proteolysis of HDAC4 in cultured cells and cardiac tissue of ATGL-deficient mice. Based on the fact that ABHD5 functions as a serine protease, we hypothesize that ATGL serves as a cofactor of ABHD5’s proteolytic activity. To conduct further structure-function relationship studies we have established an ABHD5/HDAC4 cleavage assay. This assay is based on recombinant proteins which we purified from insect cells. The assay will also enable us to conduct small molecule screenings to identify ABHD5 activators. Our results show that ATGL also influences proteolysis of HDAC4. To identify the critical domains supporting putative coactivator function, we conducted side directed mutagenesis (ATGL-p.Ser47Ala, ATGL-p.Arg221Pro, and ATGL-847delC). To demonstrate in vivo relevance, we established a mouse model for adeno-associated virus 9 (AAV9)-mediated expression of ATGL in cardiac tissue. Whereas ATGL-WT rescued cardiac function of ATGL-deficient mice, a lipase dead mutant (ATGL-S47A) failed to rescue heart function. These data establish ATGL as an essential factor for ABHD5-induced proteolysis of HDAC4 as a cardioprotective mechanism.