Tim-3 aggravates podocyte injury in diabetic nephropathy by promoting macrophage activation via the NF-κB/TNF-α pathway

Huimin Yang, Tingting Xie, Dengren Li, Xianhong Du, Tixiao Wang, Chunyang Li, Xiaojia Song, Leiqi Xu, Fan Yi, Xiaohong Liang, Lifen Gao, Xiangdong Yang, Chunhong Ma

Diabetic nephropathy (DN) is the most common microvascular complication of diabetes mellitus. Macrophages are the most abundant immune cells in the diabetic kidney. T cell immunoglobulin domain and mucin domain-3 (Tim-3) has diverse regulatory roles in macrophages. Yang et al. demonstrate that the immune checkpoint molecule Tim-3 accelerates podocyte injury, which aggravates the progression of DN by triggering the NF-κB/TNF-α signaling pathway in macrophages.

Tim-3 aggravates podocyte injury in diabetic nephropathy by promoting macrophage activation via the NF-κB/TNF-α pathway

Objective: Macrophage-mediated inflammation plays a significant role in the development and progression of diabetic nephropathy (DN). However, the underlying mechanisms remain unclear. Studies suggest that T cell immunoglobulin domain and mucin domain-3 (Tim-3) has complicated roles in regulating macrophage activation, but its roles in the progression of DN are still completely unknown.

Methods: We downregulated Tim-3 expression in kidney (intrarenal injection of Tim-3 shRNA expressing lentivirus or global Tim-3 knockout mice) and induced DN by streptozotocin (STZ). We analyzed the degree of renal injury, especially the podocyte injury induced by activated macrophages in vitro and in vivo. Then, we transferred different bone marrow derived macrophages (BMs) into STZ-induced Tim-3 knockdown mice to examine the effects of Tim-3 on macrophages in DN.

Results: First, we found that Tim-3 expression on renal macrophages was increased in patients with DN and in two diabetic mouse models, i.e. STZ-induced diabetic mice and db/db mice, and positively correlated with renal dysfunction of DN patients. Tim-3 deficiency ameliorated renal damage in STZ-induced diabetes with concurrent increase in protein levels of Nephrin and WT-1. Similar effects were observed in mice with Tim-3 knockdown diabetic mice. Second, adoptive transfer of Tim-3-expressing macrophages, but not Tim-3 knockout macrophages, accelerated diabetic renal injury in DN mice, suggesting a key role for Tim-3 on macrophages in the development of DN. Furthermore, we found NF-κB activation and TNF-α excretion were upregulated by Tim-3 in diabetic kidneys, and podocyte injury was associated with the Tim-3-mediated activation of the NF-κB/TNF-α signaling pathway in DN macrophages both in vivo and in vitro.

Conclusions: These results suggest that Tim-3 functions as a key regulator in renal inflammatory processes and serves as a potential therapeutic target for renal injury in DN.