Activation of the Nlrp3 inflammasome via mitochondrial ROS in glomerular cells aggravates experimental diabetic nephropathy

Introduction: Sterile inflammation and activation of the NLRP3-Inflammosome have been implicated in diabetes. Mitochondrial ROS are a known trigger of the inflammasome. Whether inflammosome activation is causally involved in the pathogenesis of diabetic nephropathy and whether resident or bone marrow derived inflammatory cells are involved remains unkown.

Methods: Murine models of type-2 and type-1 diabetes and diabetic patients (n = 67) with microalbuminuria were analyzed. dNP was quantified based on albuminuria and histological changes. Expression levels of cl-caspase-1, IL1b and IL18 was determined by immunoblot and ELISA. A group of mice was injected with the IL-1 receptor antagonist, anakinra, and the mitochondria-specific antioxidant MitoTEMPO. In addition bone marrow transplantation experiments were conducted. In vitro a constitutive NLRP3 mutant (R260W) was transduced into endothelial cells (ECs)/podocytes.

Results: In renal cortex extracts of diabetic mice an increase of NLRP3 expression and maturation of IL-1b were observed. Serum-Il1b positively correlated with albuminuria in diabetic patients. NLRP3-/-, caspase1-/- mice, anakinra treated mice as well as MitoTEMPO treated mice were protected against dNP. Confocal immunofluorescence labeling revealed that inflammasome activation is enhanced in glomerular cells in mice and humans with DN. The severity of dNP was unchanged in bone marrow chimeras (NLRP3-/- >db/db), whereas NLRP3-/- mice transplanted with wt-bone marrow remained protected against dNP. In vitro we observed inhibition of the glucose-stimulated inflammasome in podocytes and ECs which was abolished in cells transduced with R260W.

Conclusion: Taken together, these results strongly support that ROS-depended activation of the NLRP3-inflammasome in residual glomerular cells contributes to dNP.