**4. Formation of hepatic LDs**

LDs are specialized and dynamic cytosolic organelles, which mainly consist of a phospholipid monolayer with a core of neutral hydrophobic lipids (mostly TG and cholesterol ester, CE) [45]. As lipid storage reservoirs, LDs regulate the in- and out-flux of lipids, controlled by protein targeting process to prevent their accumulation and conversion to a toxic species. The most frequent proteins found in LDs are PLINs, especially PLIN2 and PLIN3 [21], which are involved in the formation of the LDs, during which enzymes including diacylglycerol O-acyltransferase 1, 2 (DGAT1, 2) and glycerol-3-phosphate acyltransferase 4 (GPAT4) localize around the droplet surface and further synthesize TG to store in the LDs. Researches hypothesized that LDs are formed when neutral lipids accumulate on the membranes of the ER, during which a lens is initially formed and then transforms into a budding LDs, and eventually buds off into the cytoplasm [46, 47].

The initial size of the LDs, fusion of cytoplasmic LDs, and *in situ* TG synthesis contributed to LDs growth. LDs form in the ER, where neutral lipids accumulate within the leaflet of the membrane bilayer. Once formed, small nascent LDs could be
