Renal macrophages induce hypertension and kidney fibrosis in Angiotensin II salt mice model

The immune system is involved in hypertension development with different immune cells reported to have either pro or anti-hypertensive effects. In hypertension, immune cells have been thought to infiltrate blood pressure-regulating organs, resulting in either elevation or reduction of blood pressure. There is controversy over whether macrophages play a detrimental or beneficial role in the development of hypertension, and the few existing studies have yielded conflicting results. This study aimed to determine the effects of angiotensin II (Ang II) salt-induced hypertension on renal immune cells and to determine whether renal macrophages are involved in the induction of hypertension. Hypertension was induced by administration of Ang II and saline for two weeks. The effects of hypertension on kidney immune cells were assessed using flow cytometry. Macrophage infiltration in the kidney was assessed by immunohistochemistry and kidney fibrosis was assessed using trichrome stain and kidney real time-qPCR. Liposome encapsulated clodronate was used to deplete macrophages in C57BL/6J mice and investigate the direct role of macrophages in hypertension induction. Ang II saline mice group developed hypertension, had increased renal macrophages, and had increased expression of Acta2 and Col1a1 and kidney fibrotic areas. Macrophage depletion blunted hypertension development and reduced the expression of Acta2 and Col1a1 in the kidney and kidney fibrotic areas in Ang II saline group. The results of this study demonstrate that macrophages infiltrate the kidneys and increase kidney fibrosis in Ang II salt-induced hypertension, and depletion of macrophages suppresses the development of hypertension and decreases kidney fibrosis. This indicates that macrophages play a direct role in hypertension development. Hence macrophages have a potential to be considered as therapeutic target in hypertension management.