168-OR: Perilipin 2 Regulates Fatty Acid Trafficking to Mitochondria through Microlipophagy in Beta Cells

Perilipin 2 (PLIN2) is the major structural protein of triglycerides (TG) storing lipid droplets (LD) and increased in lipid loaded and type 2 diabetic pancreatic beta cells. PLIN2 is protective for beta cells since its knockdown increases fatty acid (FA) flux to mitochondria and impairs mitochondrial function. Here, we addressed a pathway by which PLIN2 deficiency compromises mitochondrial integrity in beta cells. When the incorporation of Bodipy C12 (C12, a fluorescent long chain FA analog) into organelles was followed in INS1 cells over 8 h, C12 incorporation into LD was seen in both control and shPLIN2 cells during the first hour indicating that PLIN2 downregulation does not affect the initial triglycerides (TG) synthesis and its incorporation into LD. C12 started to accumulate into mitochondria after 4 to 8 h only in shPLIN2 cells indicating that FA transfer to mitochondria occurs after LD formation under PLIN2 deficiency. Treatment with a lysosomal lipase inhibitor Lali2 increased TG level and prevented C12 transfer into mitochondria in shPLIN2 cells, indicating that lysosomal degradation of LD precedes FA transfer to mitochondria. Microlipophagy appears to mediate LD degradation in shPLIN2 cells since a macroautophagy blocker 3MA did not prevent FA flux to mitochondria. Importantly, Lali2 rescued mitochondrial fragmentation (p<0.05 vs DMSO control) and glucose-stimulated insulin secretion (p<0.05) in shPLIN2 INS1 cells. Mitochondrial fragmentation and its rescue by Lali2 were also seen in shPLIN2 treated human beta cells (p<0.05). As for a mechanism mediating FA transfer to mitochondria, the direct contact between lysosome and mitochondria was increased (p<0.01) before FA flux to mitochondria occurs in shPLIN2 cells. Collectively, PLIN2 deficiency in beta cells impairs mitochondrial integrity through lysosomal TG degradation followed by FA delivery to mitochondria. These data highlight the importance of regulation of microlipophagy by PLIN2 for beta cell function.