Tnik depletion induces inflammation and apoptosis ininjured renal proximal tubule epithelial cells.

In the aftermath of acute kidney injury (AKI), surviving proximal tubule epithelia repopulate injured tubules to promote repair. However, a portion of cells fail to repair (termed Failed Repair Proximal Tubule Cells, FR-PTCs) and exert ongoing proinflammatory and profibrotic effects. To better understand the molecular drivers of the FR-PTC state, we reanalyzed a mouse ischemia-reperfusion injury single nucleus RNA-sequencing (snRNA-seq) atlas to identify Traf2 and Nck Interacting Kinase, Tnik, to be exclusively expressed in FR-PTCs, but not in healthy or acutely injured proximal tubules post AKI (2 and 6 weeks) in mice. We confirmed expression of Tnik protein in injured mouse and human tissues by immunofluorescence. Then, to determine the functional role of Tnik in FR-PTCs, we depleted Tnik using siRNA in two human renal proximal tubule epithelial cell lines (primary and immortalized hRPTECs) and analyzed each by bulk RNA-sequencing. Pathway analysis revealed significant upregulation of inflammatory signaling pathways, while pathways associated with differentiated proximal tubule such as organic acid transport were significantly downregulated. TNIK knockdown drove reduced cell viability and increased apoptosis, including differentially expressed PARP family members, cleaved PARP-1 fragments and increased Annexin V binding to phosphatidylserine. Together, these results indicate that Tnik upregulation in FR-PTCs acts in a compensatory fashion to suppress inflammation and promote proximal tubule epithelial cell survival following injury. Modulating Tnik activity may represent a pro-repair therapeutic strategy after AKI.