iPLA2beta deficiency protects mice from diet-induced obesity and steatosis by replenishing the loss of hepatic phospholipids containing unsaturated fatty acids

It is known that a decrease of hepatic phospholipid (PL) contents is associated with steatosis in non-alcoholic fatty liver disease patients and in rodents. We have previously reported that calcium-independent phospholipase A2 Group VIA (iPLA2beta) deficiency alleviates steatosis in morbidly obese ob/ob KO mice, by replenishing the loss of PL thus supporting the reported role of iPLA2beta in PL remodeling. Here we tested whether iPLA2beta deficiency could protect against diet-induced steatosis and whether hepatic PL composition could be modified. Feeding of WT mice with HFD (35% fat w/w) for 6 months increased body- and liver weights as well as ALT, AST, LDH, ALP, serum lipids (cholesterol and non-esterified fatty acids), and hepatic steatosis scores. All of these parameters were attenuated in whole-body iPLA2beta KO mice fed with HFD. We analyzed PL profiling by LC/MS-MS. Like ob/ob livers where all PL subclasses are decreased, HFD feeding in WT mice did significantly decrease nearly all PL subclasses except for phosphatidylethanolamine (PE). These decreases in phosphatidylcholine (PC), phosphatidylserine (PS) and phosphatidylinositol (PI) could be mainly observed in species containing mono- or polyunsaturated fatty acids (PC 34:1, PC 34:3, PC 34:2, PC 36:3, PC 36:2, PC 36:5, PC 38:5; PS 36:1, PS 36:4; PI 34:2, PI 36:3, PI 36:4, PI 28:4, PI 38:5, PI 40:4), while PE containing saturated C 16:0 and C 18:0 fatty acids PE 34:0 was the only species that increased. This resulted in an increase of the ratio between saturated and unsaturated fatty acids in total PL, PC, and PE. The decrease of total PL, unsaturated PL, and the ratio could be reversed by iPLA2beta deficiency. Consistent with our results in ob/ob livers, iPLA2beta in HFD livers was also specific for the hydrolysis of PC and PE that contained either C 16:0 or C 18:0 fatty acids on sn-1 position. However despite of steatosis protection, three out of six HFD-fed KO mice exhibited ear dermatitis suggesting systemic inflammation likely due to iPLA2beta role in immune cells. Taken together, altered hepatic membrane homeostasis with a loss of especially unsaturated PL occurred during HFD feeding. iPLA2beta deficiency rescued this loss by replenishing unsaturated fatty-acid containing PL hence restoring the membrane balance leading to steatosis protection. This study should be confirmed by using hepatocyte-specific iPLA2beta KO mice prior to establishing a strategy to inactivate hepatocyte iPLA2beta for treatment of NAFLD.