Mitochondria-ER-lipid droplet crosstalk regulates metabolic adaptation to shear stress via VMP1.

Kidney tubular epithelial cells adapt to physiological urinary flow through rapid metabolic remodeling,1,2 but the mechanisms coordinating this response remain poorly understood. Shear stress promotes lipid catabolism and mitochondrial activity in these cells,3,4 but how changes in mitochondrial dynamics contribute to this metabolic adaptation remains poorly understood.5,6,7,8,9 Here, we show that physiological shear stress rapidly remodels mitochondrial morphology in kidney epithelial cells in vitro and in the zebrafish pronephros, characterized by the emergence of a distinct pool of donut-shaped mitochondria. This remodeling is accompanied by a transient stabilization of mitochondria-endoplasmic reticulum (ER) contact sites (MERCs), occurring independently of any increase in overall ER volume. Using split-TurboID proximity labeling and mass spectrometry, we detected subtle changes in the molecular environment of MERCs during shear stress, including increased proximity of proteins implicated in lipid transfer and membrane contact-site biology. We further show that shear stress promotes the formation of ER-lipid droplet (LD)-mitochondria contact sites and facilitates the local transfer of fatty acids from LDs to mitochondria. This lipid transfer requires vacuolar membrane protein 1 (VMP1), a component of membrane contact sites, whose depletion perturbs LDs and compromises metabolic adaptation to shear stress. Together, our findings identify ER-LD-mitochondria contact sites as dynamic platforms that coordinate lipid transfer and mitochondrial remodeling during the early adaptation of kidney epithelial cells to physiological shear stress, highlighting membrane contact sites as important components of the cellular response to mechanical forces.