Objective: To investigate the role of mucosal-associated invariant T (MAIT) cells in the regulatory mechanism of adipose browning.
Methods: A mouse model with functional deficiency of MAIT cells was established for comparison with the wild-type mice for levels of brown adipose tissue markers in response to cold stimulation using Western blotting and RT-PCR. Flow cytometry was used to analyze the changes in the number, activation level and cytokine secretion ability of MAIT cells in mouse adipose tissue after cold stimulation. In a co-culture system of MAIT cells and adipocytes, the effect of interleukin-4 (IL-4) blocking antibodies on the expressions of brown adipose tissue markers in the adipocytes was evaluated using Western blotting and RT-PCR. In a mouse model of MAIT cell deficiency, the changes in adipose browning-related indicators in response to cold stimulation were analyzed using metabolic cages, immunohistochemistry, Western blotting and the Seahorse method.
Results: In both the mouse models of functional deficiency of MAIT cells and wild-type mice, cold stimulation significantly increased the expression levels of brown adipose tissue markers UCP-1 and PGC1-α and upregulated CD69 and IL-4 expressions in the adipose tissue without significantly affecting the number of MAIT cells in the adipose tissue. In the coculture experiment, the adipocytes showed obviously increased browning level after co-culture with MAIT cells (P < 0.05), but blocking IL-4 signaling strongly downregulated the browning level (P < 0.05). The MAIT cell-deficient mice showed obviously lower levels of energy expenditure, adipose browning and metabolism of the adipocytes compared with the wild-type mice in response to cold stimulation (P < 0.05).
Conclusion: MAIT cells participate in adipose browning in mice, and cold stimulation promotes MAIT cell secretion of IL-4 to positively regulate adipose browning.
目的: 探究黏膜相关恒定T(MAIT)细胞与脂肪棕色化之间的关系以及调节脂肪棕色化的分子机制。
方法: 构建MAIT细胞功能缺陷小鼠模型，对比野生型小鼠及MAIT细胞缺陷小鼠，通过Western blot和RT-PCR检测冷刺激前后小鼠脂肪棕色化标志物的水平差异，并通过流式细胞术检测了小鼠脂肪组织内MAIT细胞在冷刺激前后数量、活化水平以及细胞因子分泌能力的差异。采用MAIT细胞与脂肪细胞共培养的方式，通过Western blot和RT-PCR检测是否存在MAIT细胞以及是否加入白介素4 (IL-4)封闭抗体的条件下脂肪细胞棕色化标志物的表达差异。利用MAIT细胞缺陷的小鼠模型，通过代谢笼、免疫组化、Western blot和Seahorse方法检测MAIT细胞缺陷小鼠在冷刺激条件下的脂肪棕色化相关指标。
结果: Western blot和RT-PCR结果显示小鼠冷刺激后脂肪组织棕色化标志物UCP-1、PGC1-α的表达水平均上调，在此情景下小鼠脂肪组织内MAIT细胞数量差异无统计学意义(P>0.05)，CD69的表达水平上调(P < 0.05)，效应细胞因子IL-4的表达水平上调(P < 0.05)。体外共培养实验显示，脂肪细胞与MAIT细胞共培养后的棕色化水平上调(P < 0.05)，若阻断IL-4信号则棕色化水平下调(P < 0.05)。对MAIT细胞缺陷的小鼠进行冷刺激后，其能量消耗水平低于野生型小鼠(P < 0.05)，脂肪棕色化水平低于野生型小鼠(P < 0.05)，且脂肪细胞代谢水平低于野生型小鼠。
结论: 本研究首次通过MAIT细胞功能缺陷小鼠模型验证MAIT细胞参与脂肪棕色化，动物实验及体外实验进一步显示冷刺激通过促进MAIT细胞分泌IL-4调控脂肪细胞棕色化。
Keywords: brown adipose tissue; mucosal-associated invariant T cells; obesity.