miR-3099-5p alters cellular lipid levels and induces mitochondrial dysfunction by targeting FACL4 in mouse hepatic...

Aberrant endoplasmic reticulum (ER) and mitochondria function mediated by deregulated levels of tethering proteins at the mitochondria-associated ER membranes (MAM) sites is a hallmark of several diseases, yet very little is known of the regulatory mechanisms of these tethering proteins. Here, using mouse hepatic cells, we present data to show that miR-3099-5p binds to the 3'UTR of one such MAM protein, FACL4 and regulates its levels within the cell. Hepatic levels of miR-3099-5p are up-regulated during diabetes with a concomitant down-regulation of FACL4 levels. Overexpressing miR-3099-5p levels in mouse Hepa1-6 cells effectively down-regulates FACL4 levels, the effect being prevented by the miR-3099-5p inhibitor. miR-3099-5p-FACL4 interaction leads to accumulation of arachidonic acid and its reduced incorporation into phospholipids. Further, while this interaction did not impact mitochondrial ROS or calcium levels, it altered mitochondrial membrane potential and mitochondrial permeability transition pore opening together with increased apoptosis. FACL4 inhibition alone exerted effects similar to miR-3099-5p overexpression including accumulation of arachidonic acid, altering mitochondrial membrane potential and mitochondrial permeability transition pore opening and induction of apoptosis. Interestingly, arachidonic acid overloading in Hepa1-6 cells was sufficient to induce apoptosis and impair mitochondrial membrane potential; such arachidonic acid supplementation also significantly reversed the effects of miR-3099-5p inhibition on apoptosis and mitochondrial membrane potential. These findings suggest that FACL4 mediates the deleterious effects of miR-3099-5p in mouse hepatic cells and interrogating such miRNA mediated changes in hepatic FACL4 levels might be explored to address aberrant hepatic metabolism during diabetes.