Overexpression of Sirt6 promotes M2�macrophage transformation, alleviating renal injury in diabetic nephropathy

Abstract

In this study, we aimed to investigate the associations between Sirt6, macrophages and diabetic nephropathy (DN). Immunohistochemical, western blot and RT-qPCR analyses were performed to detect the expression levels of Sirt6, the markers of podocytes and monocytes and related inflammatory factors in the tissues of rats with streptozocin-induced DN. A series of cell experiments in isolated culture or the co-culture of macrophages and podocytes were conducted to examine the effects of the overexpression of Sirt6 on macrophage transformation, podocyte apoptosis and associated genes, and analyses were performed using RT-qPCR, flow cytometry and western blot analysis, where appropriate. In the rat model of DN, injured podocytes were represented by the decreased protein expression levels of Nephrin and Sirt6, and by an increased Desmin expression. Additionally, the M1 phenotype transformation of macrophages was evidenced by the increased expression levels of CD86, tumor necrosis factor (TNF)-α and inducible nitric oxide synthase (iNOS), and by the decreased expression levels of CD206, Sirt6, interleukin (IL)-4 and IL-10. In vitro assays of macrophages and podocytes demonstrated that glucose promoted macrophage M1 transformation and podocyte apoptosis in a dose-dependent manner and attenuated Sirt6 expression. Macrophages transformed into the M2 phenotype following the overexpression of Sirt6 by the successful transfection of macrophages with a Sirt6 overexpression plasmid. Sirt6 was also overexpressed in podocytes. In a Transwell co-culture system, the overexpression of Sirt6 in macrophages (but not the overexpression of Sirt6 in podocytes) protected the podocytes from high-glucose-induced injury. However, the apoptosis of the podocytes overexpressing Sirt6 (induced by transfection with a Sirt6 overexpression plasmid) still increased when these podocytes were co-cultured with macrophages in high-glucose medium. These protective effects were evidenced by the inhibition of apoptosis, the upregulation of the expression levels of Bcl-2 and CD206, as well as by the decreased expression levels of Bax and CD86. On the whole, the findings of this study suggest that Sirt6 protects podocytes against injury in a mimicked diabetic kidney microenvironment by activating M2 macrophages, indicating that Sirt6 can act as an immune response regulatory factor in DN-associated renal inflammatory injury.

Protective Effects of SIRT6 Overexpression against DSS-Induced Colitis in Mice

“…Colonic tissue is severely damaged by DSS treatment, and multiple types of cells participate in the histological and physiological changes, such as epithelial cells, macrophages, and neutrophils [ 33 ]. Interestingly, SIRT6 plays an important role in regulating these types of cells in the process of protecting the individual from damage or stress [ 34 , 35 ]. SIRT6 is globally overexpressed in TG mice used in this study, so we conjecture that SIRT6 functions in various cells to prevent against DSS-induced colitis in mice.…”

Protective Effects of Two Safflower Derived Compounds, Kaempferol and Hydroxysafflor Yellow A, on Hyperglycaemic Stress-Induced Podocyte Apoptosis via Modulating of Macrophage M1/M2 Polarization

“…A previous study has revealed that both increased M1 and decreased M2 play a crucial role in podocyte injury in vivo [ 37 ]. A series of cell experiments in isolated culture or the coculture of macrophages and podocytes was conducted to examine their interaction [ 20 , 38 , 39 ]. Our results showed that (HG) MS, the isolated culture of HG-treated macrophage, induced podocyte apoptosis.…”

Macrophage Phenotype and Fibrosis in Diabetic Nephropathy

“…Zhang et al suggested that the inhibition of M1 macrophage activation and the promotion of M2 macrophage transformation prevented podocyte injury [71]. Similarly, activation of M2 by Sirt6 protected podocytes against injury in a mimicked diabetic kidney microenvironment [72].…”