Calcium oxalate-induced renal epithelial cell injury is mediated by receptor-interacting serine/threonine kinase 2 (RIPK2).

Abstract

Ectopic deposition of calcium oxalate in the parenchyma (nephrocalcinosis) or as stones in the collecting system (nephrolithiasis) causes inflammation and oxidative stress in renal tissue. Receptor interacting serine/threonine kinase 2 (RIPK2) is a well-known mediator of oxidative stress and inflammation. However, its role in nephrocalcinosis or nephrolithiasis remains unexplored. Normal rat kidney-52E (NRK-52E) and primary renal cells were treated with calcium oxalate-monohydrate (COM) to induce nephrocalcinosis like pathological changes. siRNAs and commercially available inhibitor was used to block RIPK2's activity. Oxidative stress, inflammation, apoptosis, crystal adhesion, and changes in cell morphology were measured as endpoint markers. Exposure to COM but not to adenine, H2O2, and high-glucose significantly upregulated RIPK2 levels and induced oxidative stress, intracellular-calcium overload, and mitochondrial dysfunction. This was accompanied by nuclear factor-kappa B (NF-κB) pathway activation, increased levels of pro-inflammatory cytokines, decreased levels of anti-inflammatory cytokines, and enhanced apoptosis and epithelial-mesenchymal transition (EMT). RIPK2 silencing or pharmacological inhibition effectively mitigated these pathological changes and restored levels of antioxidant enzymes. Mechanistically, RIPK2 inhibition disrupted the NF-κB/TGF-β1 signaling and reduced CaOx crystal adhesion. Preliminary data from our previously conducted in vivo CaOx mouse model study confirmed the CaOx-induced RIPK2 upregulation. Our data strongly supports the involvement of RIPK2 in CaOx-induced renal cell damage.