Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, Oregon, USA.
Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, Oregon, USA.
J Biol Chem. 2021 Jan-Jun;296:100442. doi: 10.1016/j.jbc.2021.100442. Epub 2021 Feb 19.
The adipocyte hormone leptin regulates glucose homeostasis both centrally and peripherally. A key peripheral target is the pancreatic β-cell, which secretes insulin upon glucose stimulation. Leptin is known to suppress glucose-stimulated insulin secretion by promoting trafficking of K channels to the β-cell surface, which increases K conductance and causes β-cell hyperpolarization. We have previously shown that leptin-induced K channel trafficking requires protein kinase A (PKA)-dependent actin remodeling. However, whether PKA is a downstream effector of leptin signaling or PKA plays a permissive role is unknown. Using FRET-based reporters of PKA activity, we show that leptin increases PKA activity at the cell membrane and that this effect is dependent on N-methyl-D-aspartate receptors, CaMKKβ, and AMPK, which are known to be involved in the leptin signaling pathway. Genetic knockdown and rescue experiments reveal that the increased PKA activity upon leptin stimulation requires the membrane-targeted PKA-anchoring protein AKAP79/150, indicating that PKA activated by leptin is anchored to AKAP79/150. Interestingly, disrupting protein phosphatase 2B (PP2B) anchoring to AKAP79/150, known to elevate basal PKA signaling, leads to increased surface K channels even in the absence of leptin stimulation. Our findings uncover a novel role of AKAP79/150 in coordinating leptin and PKA signaling to regulate K channel trafficking in β-cells, hence insulin secretion. The study further advances our knowledge of the downstream signaling events that may be targeted to restore insulin secretion regulation in β-cells defective in leptin signaling, such as those from obese individuals with type 2 diabetes.
脂肪细胞激素瘦素通过中枢和外周途径调节葡萄糖稳态。一个关键的外周靶标是胰岛β细胞，它在葡萄糖刺激下分泌胰岛素。瘦素被认为通过促进 K 通道向β细胞表面转运来抑制葡萄糖刺激的胰岛素分泌，这会增加 K 电导并导致β细胞超极化。我们之前已经表明，瘦素诱导的 K 通道转运需要蛋白激酶 A（PKA）依赖性肌动蛋白重塑。然而，PKA 是瘦素信号通路的下游效应物还是发挥许可作用尚不清楚。我们使用基于 FRET 的 PKA 活性报告器表明，瘦素增加了细胞膜上的 PKA 活性，并且这种作用依赖于 N-甲基-D-天冬氨酸受体、CaMKKβ 和 AMPK，这些都是已知参与瘦素信号通路的物质。基因敲低和挽救实验表明，瘦素刺激后 PKA 活性的增加需要膜靶向的 PKA 锚定蛋白 AKAP79/150，这表明瘦素激活的 PKA 被锚定到 AKAP79/150。有趣的是，破坏 AKAP79/150 上的蛋白磷酸酶 2B（PP2B）锚定，已知会增加基础 PKA 信号，即使在没有瘦素刺激的情况下，也会导致表面 K 通道增加。我们的发现揭示了 AKAP79/150 在协调瘦素和 PKA 信号以调节β细胞中 K 通道转运从而调节胰岛素分泌方面的新作用。该研究进一步加深了我们对下游信号事件的了解，这些事件可能成为靶向目标，以恢复在瘦素信号缺陷的β细胞（例如 2 型糖尿病肥胖个体的β细胞）中调节胰岛素分泌的功能。
