**3.2 Triacylglycerol synthesis**

TG, synthesized by glycerol-3-phosphate acyltransferase (GPAT) or monoacylglycerol pathway *via* esterify fatty acyl-CoAs, is the major form of fat accumulated in the liver with NAFLD. The accumulation of TG in the liver, proved to be related to insulin resistance, is due to the abnormal balance between the hepatic DNL, TG synthesis, hepatic lipolysis, and lipid secretion. Although TG synthesis primarily occurs at the endoplasmic reticulum (ER), it can also occur at lipid droplets (LDs), mitochondria, and the nuclear envelope [42]. Several studies indicate that mitochondrial GPAT1 occupies 30–50% of the total GPAT activity in the liver, participating in hepatic steatosis [42]. The overexpression of GPAT1 in the rat liver was reported causing hepatic steatosis and insulin resistance in the absence of obesity or high-fat feeding [43]. In contrast, GPAT1 knockout mice showed remarkably lower hepatic TG concentrations and were prevented from hepatic steatosis and hepatic insulin resistance induced by HFD [44]. Inhibiting the activation of GPAT-1 might mitigate the progression of NAFLD.
