Effects of a CCR2 antagonist on macrophages and Toll-like receptor 9 expression in a mouse model of diabetic nephropathy

The pathogenesis of diabetic nephropathy (DN) is related to macrophage (M phi) recruitment to the kidneys, tumor necrosis factor-alpha (TNF-alpha) production, and oxidative stress. Toll-like receptor 9 (TLR9) activation is reportedly involved in systemic inflammation, and it exacerbates this condition in metabolic syndrome. Therefore, we hypothesized that TLR9 plays a role in the pathogenesis of DN. Two subsets of kidney M phi s in DN model (db/db) mice were analyzed using flow cytometry to evaluate their distribution and TLR9 expression and function. Mice were administered the CCR2 antagonist INCB3344 for 8 wk; changes in M phi distribution and function and its therapeutic effects on DN pathology were examined. Bone marrow-derived CD11b(high) (BM-M phi) and tissue-resident CD11b(low) M phi s (Res-M phi) were identified in the mouse kidneys. As DN progressed, the BM-M phi number, TLR9 expression, and TNF-alpha production increased significantly. In Res-M phi s, reactive oxygen species (ROS) production and phagocytic activity were enhanced. INCB3344 decreased albuminuria, serum creatinine level, BM-M phi abundance, TLR9 expression, and TNF-alpha production by BM-M phi s and ROS production by Res-M phi s. Both increased activation of BM-M phi via TLR9 and TNF-alpha production and increased ROS production by Res-M phi s were involved in DN progression. Thus, inactivating M phi s and their TLR9 expression by INCB3344 is a potential therapeutic strategy for DN. NEW & NOTEWORTHY We classified kidney macrophages (M phi s) into bone marrow-derived M phi s (BM-M phi s) expressing high CD11b and tissue-specific resident Mop (Res-M phi s) expressing low CD11b. In diabetic nephropathy (DN) model mice, Toll-like receptor 9 (TLR9) expression and TNF-alpha production via TLR9 activation in BM-M phi s and ROS production in Res-M phi s were enhanced. Furthermore, CCR2 antagonist suppressed the kidney infiltration of BM-M phi s and their function and the ROS production by Res-M phi s, with concomitant TLR9 suppression. Our study presents a new therapeutic strategy for DN.