Rab30 regulates lipid homeostasis in the hepatocyte during fasting

In order to facilitate inter-tissue communication and exchange of proteins, lipoproteins, and metabolites with the circulation, hepatocytes have an intricate and efficient intracellular trafficking system regulated by small Rab GTPases. Rab30, a putative Golgi-localized Rab GTPase, is induced in the mouse liver by fasting and its expression is further amplified in liver-specific carnitine palmitoyltransferase 2 knockout mice (Cpt2L-/-) that lack the ability to oxidize fatty acids in a Pparα-dependent manner. Live-cell super-resolution imaging and biochemical in vivo proximity labeling demonstrated that Rab30-marked vesicles are highly dynamic and interact with proteins throughout the secretory pathway. Rab30 whole-body, liver-specific, and Rab30;Cpt2 liver-specific double knockout (DKO) mice are viable and display intact Golgi ultrastructure. However, the loss of Rab30 in Rab30;Cpt2 DKO mice suppresses serum dyslipidemia observed in Cpt2L-/- single knockout mice. Corresponding with decreased serum triglyceride and cholesterol levels, Rab30;Cpt2 DKO mice exhibit decreased circulating but not hepatic ApoA4 protein, indicative of a trafficking defect. Together, these data suggest a role for Rab30 in the selective sorting of lipoproteins to influence hepatocyte and circulating triglyceride levels particularly during times of excessive lipid burden.