Background Inflammation is a key driver of the transition of acute-kidney-injury to progressive fibrosis and chronic-kidney-disease (AKI-to-CKD transition). Blocking a-disintegrin-and-metalloprotease-17 (ADAM17)-dependent ectodomain shedding, in particular of epidermal-growth-factor-receptor (EGFR) ligands and of the type 1 inflammatory cytokine tumor-necrosis-factor (TNF), reduces pro-inflammatory and pro-fibrotic responses after ischemic AKI or unilateral ureteral obstruction (UUO), a classical fibrosis model. Metalloprotease or EGFR inhibition show significant undesirable side effects in humans. In retrospective studies anti-TNF biologics reduce the incidence and progression of CKD in humans. Whether TNF has a role in AKI-to-CKD transition and how TNF inhibition compares to EGFR inhibition is largely unknown. Methods Bilateral ischemic kidney injury, scRNAseq, proteomics. Results Here we show that TNF or EGFR inhibition reduce AKI-to-CKD transition and fibrosis equally by about 25%, while combination has no additional effect. EGFR inhibition reduced kidney TNF expression by about 50% largely by reducing accumulation of TNF expressing immune cells in the kidney early after AKI, while TNF inhibition did not affect EGFR activation or immune cell accumulation. Using scRNAseq data we show that TNF is predominantly expressed by immune cells in AKI but not in proximal-tubule-cells (PTC), and PTC-TNF knockout did not affect AKI-to-CKD transition in UUO. Thus, the anti-inflammatory and anti-fibrotic effects of the anti-TNF biologic etanercept in AKI-to-CKD transition rely on blocking TNF that is released from immune cells recruited or accumulating in response to PTC-EGFR signals. Conclusion Short-term anti-TNF biologics during or after AKI could be helpful in the prevention of AKI-to-CKD transition.
Background: Elevated levels of circulating Tumor-Necrosis-Factor-Receptors 1 and 2 (cTNFR1/2) predict CKD progression. Whether acute kidney injury drives cTNFR1/2 elevations and whether they predict disease outcomes after AKI remains unknown. Methods: We used AKI patient serum and urine samples, mouse models of kidney injury (ischemic, obstructive, toxic) and progression to fibrosis, nephrectomy, and related single cell RNA-sequencing datasets. Results: We show that TNFR1/2 serum and urine levels are highly elevated in all mouse models of kidney injury tested, beginning within one-hour post-injury, and correlate with its severity. Consistent with this, serum and urine TNFR1/2 levels are increased in AKI patients and correlate with severity of kidney failure. Interestingly, the extracellular vesicle (EV)-bound forms of cTNFR1/2 correlate with renal function better than their soluble forms. TNF neutralization does not affect early cTNFR1/2 elevations, suggesting that cTNFR1/2 levels do not reflect injury-induced TNF activity. Kidney tissue expression of TNFR1/2 after AKI is only mildly increased and bilateral nephrectomies lead to strong cTNFR1/2 elevations, suggesting release of these receptors by extrarenal sources. cTNFR1/2 remain elevated for weeks after severe kidney injury and at these later timepoints cTNFR1/2 correlate to remaining kidney injury. During AKI-to-CKD transition, kidney expression of TNFR1/2 and cTNFR2 levels, correlate with development of fibrosis. Conclusions: Our data demonstrate that AKI drives acute increases in cTNFR1/2 serum levels which negatively correlate with kidney function, in particular their EV-bound forms. Sustained TNFR1/2 elevations after kidney injury during AKI-to-CKD transition correlate with persistent tissue injury and progression to kidney fibrosis.
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