ATGL-mediated lipolysis is essential for myocellular mitochondrial function and augments PPARδ-induced improvements in mitochondrial respiration

Defects in ATGL-mediated myocellular LD lipolysis results in mitochondrial dysfunction of unknown origin, which can be rescued by PPAR agonists. Here we examine whether ATGL-mediated lipolysis is required to maintain mitochondrial network connectivity and function. Moreover, we explored if the functional implications of ATGL deficiency for mitochondrial network dynamics and function can be alleviated by promoting PPAR and/or PPAR{delta} transcriptional activity. To this end, we cultured human primary myotubes from patients with neutral lipid storage disease with myopathy (NLSDM), a rare metabolic disorder caused by a mutation in the PNPLA2 gene. These myotubes possess dysfunctional ATGL and compromised LD lipolysis. In addition, mitochondria-LD contacts, mitochondrial network dynamics, and TMRM intensity were abrogated. Using a humanized ATGL inhibitor in myotubes cultured form healthy donors, revealed similar results. Upon stimulating PPAR{delta} transcriptional activity, mitochondrial respiration improved by more than 50% in human primary myotubes from healthy lean individuals. This increase in respiration was dampened in myotubes with dysfunctional ATGL. Stimulation of PPAR{delta} transcriptional activity had no effect on mitochondria-LD contacts, mitochondrial network dynamics, and TMRM intensity. Our results demonstrate that dysfunctional ATGL results in compromised mitochondrial-LD contacts and mitochondrial dynamics, and that functional ATGL is required to improve mitochondrial respiratory capacity upon stimulation of PPAR{delta} transcriptional activity.