Seipin Regulates Caveolin-1 Trafficking and Organelle Crosstalk

Caveolin-1 (CAV1), the main structural component of caveolae, is essential in various biological processes, including mechanotransduction, lipid metabolism, and endocytosis. Deregulation of CAV1 dynamics is linked to various pathologies, including cellular senescence, cancer, insulin resistance, and lipodystrophy. However, mechanisms regulating CAV1 trafficking and function remain poorly understood. Here, we show that seipin, a crucial lipid droplet (LD) biogenesis factor, modulates CAV1 trafficking. Deletion of seipin resulted in the accumulation of saturated lipids, leading to ceramide and sphingomyelin overproduction, which disrupted the membrane order of the trans-Golgi network (TGN). In seipin deficiency, CAV1 location to the plasma membrane (PM) was impaired, reducing caveolae. Instead, CAV1 accumulated in TGN and late endosome compartments, which fused with LDs and delivered the protein. In wild-type (WT) cells, this process was minimal but significantly enhanced by treatment with palmitate, ceramide, or Stearoyl-CoA desaturase-1 (SCD1) inhibition. Conversely, in seipin-deficient cells, inhibiting Fatty Acid Synthase (FASN) or overexpressing SCD1 restored CAV1 localization to the PM and reduced its accumulation in LDs. Our findings reveal that seipin controls the funneling of palmitate toward glycerolipids synthesis and storage in LDs versus conversion to ceramides in the ER. This balance is crucial to cellular protein trafficking by controlling the TGN membrane order. Therefore, our study identifies seipin as a critical regulator of cellular lipid metabolism, protein trafficking, and organelle homeostasis. These findings shed light on the processes regulating CAV1 trafficking and show that convergent pathophysiological mechanisms associated with defects in CAV1 and seipin contribute to metabolic disorders, including insulin resistance and lipodystrophies.