Renal fibrosis is a common mechanism leading to kidney failure in chronic kidney diseases (CKDs), including obstructive nephropathy (ON). Dysregulated inflammation is central to the development of renal fibrosis, but how local immune cells within the tissue microenvironment integrate and coordinate to drive this condition remains largely unknown. Herein, we documented that neutrophils were abundantly recruited and expelled neutrophil extracellular traps (NETs) in human and mouse fibrotic kidneys. Importantly, circulating levels of NETs components displayed a significant correlation with worsened kidney function in ON patients. In the unilateral ureteral obstruction (UUO) mouse model, blocking NETs by protein-arginine deiminase type 4 (PAD4) deletion or DNase treatment significantly impaired NETs formation and inhibited renal fibrosis and inflammation, whereas NETs adoptive transfer exacerbated the fibrotic process. Moreover, NET-mediated renal fibrosis was associated with enhanced infiltration of cytotoxic CD8+ T cells, which produced granzyme B (GZMB) to drive tubular cell epithelial-mesenchymal transition (EMT) and fibroblast activation. Accordingly, pharmacological inhibition of GZMB resulted in blunted kidney inflammation and fibrosis. Furthermore, NETs profoundly potentiated the production of T-cell chemokines CXCL9/10/11 in macrophages, but not in tubular cells or fibroblasts, thus driving T-cell infiltration and fueling inflammatory cascades in the kidneys. Mechanistically, the NET-macrophage interaction was partially mediated by the TLR2/4 signaling. Thus, our work reveals a previously unexplored role of the collaboration between NETs and macrophages in supporting CD8+ T cell infiltration, which orchestrates kidney inflammation and fibrosis.

Obstructive nephropathy is one of the leading causes of kidney injury and renal fibrosis in pediatric patients. Although considerable advances have been made in understanding the pathophysiology of obstructive nephropathy, most of them were based on animal experiments and a comprehensive understanding of obstructive nephropathy in pediatric patients at the molecular level remains limited. Here, we performed a comparative proteomics analysis of obstructed kidneys from pediatric patients with ureteropelvic junction obstruction and healthy kidney tissues. Intriguingly, the proteomics revealed extensive metabolic reprogramming in kidneys from individuals with ureteropelvic junction obstruction. Moreover, we uncovered the dysregulation of NAD⁺ metabolism and NAD⁺-related metabolic pathways, including mitochondrial dysfunction, the Krebs cycle, and tryptophan metabolism, which led to decreased NAD⁺ levels in obstructed kidneys. Importantly, the major NADase CD38 was strongly induced in human and experimental obstructive nephropathy. Genetic deletion or pharmacological inhibition of CD38 as well as NAD⁺ supplementation significantly recovered NAD⁺ levels in obstructed kidneys and reduced obstruction-induced renal fibrosis, partially through the mechanisms of blunting the recruitment of immune cells and NF-κB signaling. Thus, our work not only provides an enriched resource for future investigations of obstructive nephropathy but also establishes CD38-mediated NAD⁺ decline as a potential therapeutic target for obstruction-induced renal fibrosis.