Abstract
Objective: Sphingosine 1-phosphate (S1P) is implicated in brown adipose tissue (BAT) formation and energy consumption; however, the mechanistic role of sphingolipids, including S1P, in BAT remains unclear. Here, we sought to elucidate the physiological significance of sphingolipids in BAT.
Methods: Global sphingosine kinase 1 (SphK1)-deficient mice and their wild-type littermates were housed at both room temperature and cold environment to capture the physiological phenotypes. Subsequently, qRT-PCR, immunostaining, immunoblotting, and determinations of S1P and triglyceride were performed in isolated BAT and cultured brown adipocytes.
Results: In BAT, SphK1 was localized largely in the lysosomes of brown adipocytes, and SphK1 and its product S1P levels were upregulated in cold-activated BAT. Genetic deletion of Sphk1 resulted in a reduced number of brown adipocyte lysosomes, which was accompanied by impairment of lysosomal functions, including proteolytic activity and motility. Interestingly, Sphk1–/– mice exhibited mild hypothermia and greater triglyceride content with larger lipid droplets dominating in the brown adipocytes. Triglyceride accumulation in brown adipocytes induced by the lysosome inhibitor chloroquine was blunted in Sphk1–/– mice compared to wild-type mice, suggesting a reduced lysosome-mediated lipolysis in Sphk1–/– mice.
Conclusion: Our results indicate a novel role of SphK1 in lysosomal integrity, which is required for lipolysis and thermogenesis in BAT.
