Department of Medicine, Division of Metabolism, Endocrinology and Nutrition, University of Washington Medicine Diabetes Institute, University of Washington, Seattle, WA 98109, USA.
Department of Physiology and Biophysics, University of Washington, Seattle, WA 98109, USA.
Int J Mol Sci. 2022 Jun 7;23(12):6380. doi: 10.3390/ijms23126380.
Both hypothalamic microglial inflammation and melanocortin pathway dysfunction contribute to diet-induced obesity (DIO) pathogenesis. Previous studies involving models of altered microglial signaling demonstrate altered DIO susceptibility with corresponding POMC neuron cytological changes, suggesting a link between microglia and the melanocortin system. We addressed this hypothesis using the specific microglial silencing molecule, CX3CL1 (fractalkine), to determine whether reducing hypothalamic microglial activation can restore POMC/melanocortin signaling to protect against DIO. We performed metabolic analyses in high fat diet (HFD)-fed mice with targeted viral overexpression of CX3CL1 in the hypothalamus. Electrophysiologic recording in hypothalamic slices from POMC-MAPT-GFP mice was used to determine the effects of HFD feeding and microglial silencing via minocycline or CX3CL1 on GFP-labeled POMC neurons. Finally, mice with hypothalamic overexpression of CX3CL1 received central treatment with the melanocortin receptor antagonist SHU9119 to determine whether melanocortin signaling is required for the metabolic benefits of CX3CL1. Hypothalamic overexpression of CX3CL1 increased leptin sensitivity and POMC gene expression, while reducing weight gain in animals fed an HFD. In electrophysiological recordings from hypothalamic slice preparations, HFD feeding was associated with reduced POMC neuron excitability and increased amplitude of inhibitory postsynaptic currents. Microglial silencing using minocycline or CX3CL1 treatment reversed these HFD-induced changes in POMC neuron electrophysiologic properties. Correspondingly, blockade of melanocortin receptor signaling in vivo prevented both the acute and chronic reduction in food intake and body weight mediated by CX3CL1. Our results show that suppressing microglial activation during HFD feeding reduces DIO susceptibility via a mechanism involving increased POMC neuron excitability and melanocortin signaling.
下丘脑小胶质细胞炎症和黑色素皮质素途径功能障碍均有助于饮食诱导的肥胖（DIO）发病机制。涉及小胶质细胞信号改变模型的先前研究表明，DIO 易感性发生改变，相应的 POMC 神经元细胞学变化表明小胶质细胞与黑色素皮质素系统之间存在联系。我们使用特定的小胶质细胞沉默分子 CX3CL1（ fractalkine）来解决这一假设，以确定减少下丘脑小胶质细胞激活是否可以恢复 POMC/黑色素皮质素信号以预防 DIO。我们在高脂肪饮食（HFD）喂养的小鼠中进行了代谢分析，这些小鼠的下丘脑靶向病毒过表达了 CX3CL1。使用 POMC-MAPT-GFP 小鼠下丘脑切片中的电生理记录来确定 HFD 喂养和通过米诺环素或 CX3CL1 对 GFP 标记的 POMC 神经元的小胶质细胞沉默的影响。最后，接受下丘脑过表达 CX3CL1 的小鼠接受了中枢性黑色素皮质素受体拮抗剂 SHU9119 的治疗，以确定黑色素皮质素信号是否是 CX3CL1 代谢益处所必需的。下丘脑过表达 CX3CL1 可增加瘦素敏感性和 POMC 基因表达，同时减少 HFD 喂养动物的体重增加。在来自下丘脑切片制剂的电生理记录中，HFD 喂养与 POMC 神经元兴奋性降低和抑制性突触后电流幅度增加有关。使用米诺环素或 CX3CL1 治疗进行小胶质细胞沉默可逆转 POMC 神经元电生理特性的这些 HFD 诱导变化。相应地，体内阻断黑色素皮质素受体信号转导可防止 CX3CL1 介导的急性和慢性食物摄入量和体重下降。我们的研究结果表明，在 HFD 喂养期间抑制小胶质细胞激活可通过增加 POMC 神经元兴奋性和黑色素皮质素信号转导来降低 DIO 易感性。
