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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 after AKI (2 and 6 wk) 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 with 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, whereas pathways associated with differentiated proximal tubules such as organic acid transport were significantly downregulated. TNIK gene knockdown drove reduced cell viability and increased apoptosis, including differentially expressed poly(ADP-ribose) polymerase (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 after injury. Modulating TNIK activity may represent a prorepair therapeutic strategy after AKI. [ABSTRACT FROM AUTHOR]

Epithelial cells that line lung airways produce and secrete proteins with important roles in barrier function and host defense. Secretion of airway goblet cells is controlled by autophagy proteins during inflammatory conditions, resulting in accumulation of mucin proteins. We hypothesized that autophagy proteins would also be important in the function of club cells, dominant secretory airway epithelial cells that are dysregulated in chronic lung disease. We found that in the absence of an inflammatory stimulus, mice with club cells deficient for the autophagy protein Atg5 had a markedly diminished expression of secreted host defense proteins secretoglobulin family 1A, member 1 (Scgb1a1) and surfactant proteins A1 and D (Sftpa1 and Sftpd), as well as abnormal club cell morphology. Adult mice with targeted loss of Atg5 also showed diminished levels of host defense proteins in regenerating cells following ablation with naphthalene. A mouse strain with global deficiency of Atg16-like 1 (Atg16l1), an Atg5 binding partner, had a similar loss of host defense proteins and abnormal club cell morphology. Cigarette smoke exposure reduced levels of Scgb1a1 in wild-type mice as expected. Smoke exposure was not required to trigger club cell abnormalities in mice bearing the human ATG16 variant Atg16l1 T300A/T300A , which had low Scgb1a1 levels independent of this environmental stress. Evaluation of lung tissues from former smokers with severe chronic obstructive pulmonary disease showed evidence of reduced autophagy and SCGB1A1 expression in club cells. Thus, autophagy proteins are required for the function of club cells, independent of the cellular stress of cigarette smoke, with roles that appear to be distinct from those of other secretory cell types.

Proper colonic injury response requires myeloid-derived cells and Toll-like receptor/Myd88 signaling. However, the precise role of Myd88 signaling specifically in myeloid-derived cells that occurs during tissue damage is unclear. Therefore, we created a mouse line with Myd88 expression restricted to myeloid lineages (Myd88(-/-); LysM(Cre/+); ROSA26(Myd88/+); herein Mlcr). In these mice, Myd88 was appropriately expressed and mediated responses to bacterial ligand exposure in targeted cells. Importantly, the severe colonic epithelial phenotype observed in dextran sodium sulfate-injured Myd88(-/-) mice was rescued by the genetic modification of Mlcr mice. During injury, myeloid cell activation and enrichment of Ptsg2-expressing stromal cells occurred within the mesenchyme that surrounded the crypt bases of Mlcr and Myd88(+/-) mice but not Myd88(-/-) mice. Interestingly, these cellular changes to the crypt base mesenchyme also occurred, but to a lesser extent in uninjured Mlcr mice. These results show that Myd88 expression in myeloid cells was sufficient to rescue intestinal injury responses, and surprisingly, these cells appear to require an additional Myd88-dependent signal from a non-myeloid cell type during homeostasis.