PLIN5 phosphorylation orchestrates mitochondria lipid-droplet coupling to control hepatic lipid flux and steatosis

Steatotic liver disease is common, yet the mechanisms by which hepatocytes cope with surges in dietary fatty acids remain unclear. Here we use single-cell tissue imaging (scPhenomics) and spatial proteomics to map lipid handling across dietary states. Fasting remodeled mitochondria and lipid droplets (LDs), increasing mitochondria-LD contacts, whereas contacts were infrequent in Western diet (WD)-fed male mice. Fasting also elevated perilipin-5 (PLIN5), a mediator of mitochondria-LD tethering. PLIN5 overexpression modulated contact formation in a phosphorylation-dependent manner: the S155A variant enhanced organelle contacts and LD expansion, whereas the S155E variant reduced contacts and yielded fewer, smaller LDs. Overexpression of the S155A variant in WD reduced lipotoxicity. These data reveal an adaptive organelle-interaction program that channels lipids during nutrient stress and is attenuated by an obesogenic diet. Our work establishes scPhenomics for spatially resolved cell-state analysis and identifies PLIN5 phosphorylation as a lever to tune hepatocyte lipid flux, suggesting therapeutic potential for targeting mitochondria-LD coupling.