Department of Cellular and Molecular Function Analysis, Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Japan.
Department of Physiology, Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Japan.
J Lipid Res. 2023 Nov;64(11):100450. doi: 10.1016/j.jlr.2023.100450. Epub 2023 Sep 24.
Sphingosine 1-phosphate (S1P) has been implicated in brown adipose tissue (BAT) formation and energy consumption; however, the mechanistic role of sphingolipids, including S1P, in BAT remains unclear. Here, we showed that, in mice, BAT activation by cold exposure upregulated mRNA and protein expression of the S1P-synthesizing enzyme sphingosine kinase 1 (SphK1) and S1P production in BAT. Treatment of wild-type brown adipocytes with exogenous S1P or S1P receptor subtype-selective agonists stimulated triglyceride (TG) breakdown only marginally, compared with noradrenaline. However, genetic deletion of Sphk1 resulted in hypothermia and diminished body weight loss upon cold exposure, suggesting that SphK1 is involved in thermogenesis through mechanisms different from receptor-mediated, extracellular action of S1P. In BAT of wild-type mice, SphK1 was localized largely in the lysosomes of brown adipocytes. In the brown adipocytes of Sphk1 mice, the number of lysosomes was reduced and lysosomal function, including proteolytic activity, acid esterase activity, and motility, was impaired. Concordantly, nuclear translocation of transcription factor EB, a master transcriptional regulator of lysosome biogenesis, was reduced, leading to decreased mRNA expression of the lysosome-related genes in Sphk1 BAT. Moreover, BAT of Sphk1 mice showed greater TG accumulation with dominant larger lipid droplets in brown adipocytes. Inhibition of lysosomes with chloroquine resulted in a less extent of triglyceride accumulation in Sphk1 brown adipocytes compared with wild-type brown adipocytes, suggesting a reduced lysosome-mediated TG breakdown in Sphk1 mice. Our results indicate a novel role of SphK1 in lysosomal integrity, which is required for TG breakdown and thermogenesis in BAT.
鞘氨醇 1-磷酸（S1P）被认为与棕色脂肪组织（BAT）的形成和能量消耗有关；然而，鞘脂类物质（包括 S1P）在 BAT 中的作用机制仍不清楚。在这里，我们表明，在小鼠中，冷暴露激活 BAT 会上调 S1P 合成酶鞘氨醇激酶 1（SphK1）的 mRNA 和蛋白表达以及 BAT 中的 S1P 产生。与去甲肾上腺素相比，外源性 S1P 或 S1P 受体亚型选择性激动剂处理野生型棕色脂肪细胞仅轻微刺激甘油三酯（TG）分解。然而，SphK1 的基因缺失导致冷暴露时体温过低和体重减轻减少，表明 SphK1 通过不同于受体介导的、细胞外 S1P 作用的机制参与产热。在野生型小鼠的 BAT 中，SphK1 主要定位于棕色脂肪细胞的溶酶体中。在 Sphk1 小鼠的棕色脂肪细胞中，溶酶体的数量减少，溶酶体功能，包括蛋白水解活性、酸性酯酶活性和运动性受损。相应地，转录因子 EB 的核易位减少，溶酶体生物发生的主要转录调节因子，导致 Sphk1 BAT 中溶酶体相关基因的 mRNA 表达减少。此外，Sphk1 小鼠的 BAT 显示出更大的 TG 积累，棕色脂肪细胞中具有更大的脂质滴。用氯喹抑制溶酶体导致 Sphk1 棕色脂肪细胞中 TG 积累的程度低于野生型棕色脂肪细胞，表明 Sphk1 小鼠中溶酶体介导的 TG 分解减少。我们的结果表明 SphK1 在溶酶体完整性中具有新的作用，这对于 BAT 中的 TG 分解和产热是必需的。
