(720d) Targeting Phospholipid Metabolism to Prevent Hepatocyte Lipotoxicity

Lipotoxicity is defined as the cellular injury resulting from exposure to elevated levels of lipids. At the cellular level, lipotoxicity is associated with endoplasmic reticulum (ER) stress, oxidative stress, high levels of reactive oxygen species (ROS), increased mitochondrial metabolism, and apoptosis. On a clinically relevant scale, lipotoxicity can manifest as non-alcoholic fatty liver disease (NAFLD) or non-alcoholic steatohepatitis (NASH), which are associated with a range of other metabolic syndromes such as obesity and insulin resistance. Even though NAFLD is estimated to affect 30% of the US population, the molecular mechanisms that underlie disease progression are not fully understood. In vitro studies have found that saturated fatty acids (SFAs) initiate apoptosis due to lipotoxicity while monounsaturated fatty acids (MUFAs) do not. In addition, when cells are treated with both an SFA and a MUFA, they are “rescued” and do not experience apoptosis due to lipotoxicity. We hypothesize that blocking phospholipids from incorporating excess palmitate (PA), an abundant SFA in plasma, can rescue hepatocytes from lipotoxicity. Our current studies have focused on blocking PA incorporation at two points in phospholipid metabolism: the phospholipid remodeling stage (i.e., Lands’ cycle) and the de novo phosphotidylcholine (PC) biosynthesis stage (i.e., Kennedy pathway). To inhibit flux through these reactions, we used the pharmacological inhibitor PACOCF₃ to block de novo PC synthesis as well as siRNA knockdown of two steps in the Lands’ cycle. By inhibiting these reactions, we have observed partial rescue of hepatocytes from lipotoxic effects when treated with PA. In addition, we observed the formation of myelin figures in hepatocytes that were treated with PA, but not in hepatocytes treated with a MUFA; myelin figures are thought to be indicative of dysregulated phospholipid metabolism. This presentation will focus on the role of phospholipid metabolism in lipotoxicity as well as how phospholipid metabolism can be altered to alleviate lipotoxic effects.