Table_1_High-Fat Diet and Feeding Regime Impairs Number, Phenotype, and Cytotoxicity of Natural Killer Cells in C57BL/6 Mice.pdf

Overweight and obesity are major public health challenges worldwide. Obesity is associated with a higher risk for the development of several cancer types, but specific mechanisms underlying the link of obesity and cancer are still unclear. Natural killer (NK) cells are circulating lymphoid cells promoting the elimination of virus-infected and tumor cells. Previous investigations demonstrated conflicting results concerning the influence of obesity on functional NK cell parameters in small animal models. The aim of the present study was to clarify potential obesity-associated alterations of murine NK cells in vivo, implementing different feeding regimes. Therefore, C57BL/6 mice were fed a normal-fat diet (NFD) or high-fat diet (HFD) under restrictive and ad libitum feeding regimes. Results showed diet and feeding-regime dependent differences in body weight, visceral fat mass and plasma cytokine concentrations. Flow cytometry analyses demonstrated significant changes in total cell counts as well as frequencies of immune cell populations in peripheral blood comparing mice fed NFD or HFD in an ad libitum or restrictive manner. Mice fed the HFD showed significantly decreased frequencies of total NK cells and the mature CD11b+CD27+ NK cell subset compared to mice fed the NFD. Feeding HFD resulted in significant changes in the expression of the maturation markers KLRG1 and CD127 in NK cells. Furthermore, real-time PCR analyses of NK-cell related functional parameters in adipose tissue revealed significant diet and feeding-regime dependent differences. Most notable, real-time cytotoxicity assays demonstrated an impaired cytolytic activity of splenic NK cells toward murine colon cancer cells in HFD-fed mice compared to NFD-fed mice. In conclusion, our data demonstrate that feeding a high-fat diet influences the frequency, phenotype and function of NK cells in C57BL/6 mice. Interestingly, restricted feeding of HFD compared to ad libitum feeding resulted in a partial prevention of the obesity-associated alterations on immune cells and especially on NK cells, nicely fitting with the current concept of an advantage for interval fasting for improved health.

超重与肥胖是全球范围内的重大公共卫生挑战。肥胖与多种癌症的发病风险升高密切相关，但肥胖与癌症之间关联的具体潜在机制仍未阐明。自然杀伤（NK）细胞是一类循环淋巴样细胞，可介导清除病毒感染细胞与肿瘤细胞。既往针对小型动物模型的相关研究中，关于肥胖对NK细胞功能参数的影响，所得结果存在分歧。本研究旨在明确高脂饮食喂养环境下，小鼠NK细胞体内发生的潜在肥胖相关改变，采用了不同的喂养方案。为此，将C57BL/6小鼠分为四组，分别以正常脂肪饮食（NFD）或高脂饮食（HFD），配合限制性喂养与自由进食两种喂养方式进行饲养。结果显示，小鼠的体重、内脏脂肪量及血浆细胞因子浓度均存在依赖于饮食类型与喂养方案的差异。流式细胞术（Flow cytometry）分析结果表明，与正常脂肪饮食喂养的小鼠相比，无论是自由进食还是限制性喂养的高脂饮食小鼠，其外周血总细胞数及各类免疫细胞群的占比均出现显著变化。高脂饮食喂养的小鼠，其外周血总NK细胞及成熟CD11b+CD27+ NK细胞亚群的占比显著低于正常脂肪饮食喂养组。高脂饮食还可导致NK细胞表面成熟标志物KLRG1与CD127的表达发生显著改变。此外，对脂肪组织中NK细胞相关功能参数的实时聚合酶链反应（real-time PCR）分析显示，其表达水平同样存在依赖于饮食类型与喂养方案的显著差异。最为值得关注的是，实时细胞毒性试验结果表明，与正常脂肪饮食喂养组相比，高脂饮食喂养小鼠的脾脏NK细胞对小鼠结肠癌细胞的溶解活性出现明显受损。综上，本研究数据证实，高脂饮食喂养可影响C57BL/6小鼠NK细胞的占比、表型与功能。有趣的是，与自由进食高脂饮食相比，限制性高脂饮食喂养可部分阻止肥胖相关的免疫细胞（尤其是NK细胞）改变，这与当前"间歇性禁食（interval fasting）有益于改善健康"的主流观点高度契合。