高鹽飲食對腎臟免疫的影響

Abstract

鹽對地球多數生物來說是不可或缺的，適當濃度的鹽能維持細胞與器官正常的生理功能。但最近越來越多研究顯示高鹽飲食有可能是高血壓、慢性發炎以及自體免疫疾病發展的重要因子，而現代人鹽攝取量也逐年增加，因此，研究高鹽飲食與免疫疾病之間的關係是十分重要的。 過去的研究指出未分化的CD4+ T細胞會受到外加10-40 mM的鹽往輔助型T細胞17(T helper 17 cells;Th17 cells)分化，而高鹽所誘導的分化在體外及體內的實驗都證實受到血清糖皮質激酶1(serum glucocorticoid kinase 1;SGK1)及介白素-23受體(IL-23R)的表現所調控，高鹽也會影響巨噬細胞的功能及極化。然而一般生理狀況下，在身體內具有如此高的鹽濃度只可能在腎臟發現，因此我們想知道腎臟是否為發生Th17 cells活化的重要場所，以及如果Th17 cells的活化真的發生在腎臟，半乳糖凝集素3(galectin-3;Gal3)是否會抑制Th17 cells的活化。 我們給予8~12週大的C57BL/6公鼠餵食高鹽飼料(8% NaCl )當作實驗組，控制組則給予一般飼料(0.4% NaCl )，兩組皆可自由飲水，藉此來觀察餵食高鹽飼料組別與控制組是否有差異性。 實驗結果顯示餵食高鹽飼料的組別尿液裡的鈉離子、氯離子濃度明顯高於控制組，但血壓及血漿內鈉離子、氯離子濃度並無明顯差別。腎臟萃取的RNA在檢測Th17 cells相關基因表現上兩組並沒有差別，但galetin-3的表現則在高鹽組升高。因此，我們從腎臟分離出CD45+細胞看高鹽是否會影響Th17 cells的活化，結果顯示餵食高鹽組別相對於控制組在和Th17 cells活化相關基因表現量有明顯上升的趨勢，代表餵食高鹽飼料後Th17 cells的活化可能會發生在腎臟。但進一步從腎臟分離出的CD11b+巨噬細胞及CD4+ Th cells並沒有Th17 cells活化的情形。另外，培養的巨噬細胞在高鹽環境下似乎也有促進Th17 cells活化的情形，但galectin-3的表現反而下降。巨噬細胞實驗與我們發現餵食高鹽飼料後整個腎臟與CD45+細胞的galectin-3表現量會上升剛好相反，這之間的關係及作用機制仍需更多的實驗來完成。 總結來說，餵食高鹽飼料可能會導致在腎臟有Th17 cells活化的情形，細胞實驗也能互相驗證，但我們目前還未找出Th17 cells活化的情形發生在腎臟哪些細胞上，以及腎臟中的變化是否會影響身體其他部分的免疫反應仍需更多實驗來釐清。

Like the majority of other lives on earth, humans cannot survive without salt. An ideal concentration of salt, or sodium chloride (NaCl), is required for proper functioning of cells and organ systems. A high intake of dietary salt has been implicated in the development of hypertension, chronic inflammation, and autoimmune diseases. And modern people increase salt intake year by year. Therefore, it is important to study the relationship between high-salt diet and immune diseases. Recent evidence has shown that Th17 cells can be preferentially induced by treating CD4+ T cells in cell culture medium with an additional 10-40 mM NaCl. High-salt treatment enhances the differentiation of Th17 cells by upregulation of serum glucocorticoid kinase 1 (SGK1) and IL-23 receptor (IL-23R) both in vitro and in vivo. High-salt treatment also affects the function and polarization of macrophages. However, a high level of sodium or hyperosmolality can only be found in the kidneys in normal physiology. We would like to know whether the hypertonic renal medulla is the exact niche for Th17 cells activation. If the hypertonic renal medulla is the exact niche for Th17 cells activation, we would like to know whether galectin-3 inhibit the activation of Th17 cells in renal medulla. We fed 8% NaCl diets to 8~12-week-old C57BL/6 male mice as a high salt diet (HSD) group, and control mice were fed with 0.4% NaCl diets. Both groups had free access to tap water. Experimental results show that urine Na+, Cl- concentrations were higher in HSD group, but blood pressure and plasma Na+, Cl- concentration did not have the significant changes. RNA extracted from kidney did not differ in the detection of Th17 cells-associated gene expression, except for increased galectin-3 expression in HSD group. We then isolated CD45+ cell from control and HSD kidneys to analyze gene expression associated with Th17 cells, and the data showed higher expression levels of Il23/Il23r/Il17 in HSD group than control group. Then we isolated CD11b+ macrophages and CD4+ Th cells from control and HSD kidneys to repeat the same analyses, but there’s no difference between groups. In addition, cultured macrophages seemed to promote Th17 cells activation in high salt environment. Although we found that galectin-3 expression increased in the kidneys and CD45+ cells after high-salt diet, the galectin-3 expression in high salt-treated macrophages in vitro was in contrast. The role of galectin-3 in regulating high salt-induced Th17 activation still needs more experiments to verify. In conclusion, mice fed high-salt diets may result in the activation of Th17 cells in the kidney, and cell culture experiments can be used to verify each other. But we have not yet identified which cells in the kidney are responsible for activation of Th17 cells and whether the activation of Th17 cells in kidney will affect the other body parts after high salt intake. We need more experiments to clarify.