Membrane Tumor Necrosis Factor (TNF) Drives Progression to Fibrosis after Kidney Injury via TNFR1 Activation

Background: Global TNF blockade reduces AKI-to-CKD transition, but the underlying mechanisms are unclear. TNF signaling is complex as it involves soluble and membrane-bound forms of TNF (sTNF and mTNF respectively) and of its two receptors, TNFR1 and TNFR2. As a result, TNF controls multiple signaling pathways with overlapping, separate, or even opposite functions. We hypothesized that targeting individual components of TNF signaling would increase our understanding of kidney disease progression and point to more specific targets for therapies. Methods: We used mouse models of kidney injury and progression to fibrosis, wild-type mice, knockout mice, or mice with TNF or TNFR1 mutations that prevent cleavage and release of their soluble forms, and single-cell/nuclei RNAseq data analysis. Results: Using pharmacological and genetic approaches, we show that mTNF, rather than sTNF, drives progression to fibrosis after kidney injury. In addition, mice that cannot cleave TNFR1, therefore cannot terminate its signaling, show increased fibrosis after injury. The latter phenotype is also mTNF-dependent. Serum creatinine and BUN levels on day 1 post-injury were not different between groups, suggesting that the observed outcomes are not the result of initial injury susceptibility differences. Kidney accumulation of macrophages, a key TNF-expressing cell type, accompanies mTNF-TNFR1-driven progression to fibrosis. Single-cell/nuclei RNAseq analysis showed that, during the transition to fibrosis, TNFR1 gene signature is enriched in endothelial and tubular cell subpopulations, suggesting that these cells potentially receive the profibrotic mTNF-TNFR1 signals. Conclusion: Our results identify that the mTNF-TNFR1 signaling axis drives AKI-to-CKD transition and represents a potential target for therapeutic interventions. Funding: NIDDK Support, Private Foundation Support