Single-Cell Profiling of AKI in a Murine Model Reveals Novel Transcriptional Signatures, Profibrotic Phenotype, and Epithelial-to-Stromal Crosstalk
Authors: Rudman-Melnick Valeria , Adam Mike , Potter Andrew , Chokshi Saagar M. , Ma Qing , Drake Keri A. , Schuh Meredith P. , Kofron J. Matthew , Devarajan Prasad , Potter S. Steven 
Published: October 2020

Significance StatementBecause current management of the rapid renal-function decline in AKI is merely supportive, deeper understanding of the AKI-perturbed molecular pathways is needed to identify targets with potential to lead to improved treatment. In a murine AKI model, the authors used single-cell RNA sequencing, single-moleculein situhybridization, and protein expression analyses to create the first comprehensive renal cell type–specific transcriptional profiles for multiple AKI stages. Their findings revealed a marked nephrogenic signature and surprising mixed-identity cells (expressing markers of different cell types) in the injured renal tubules. Moreover, the authors identified potential pathologic epithelial-to-stromal crosstalk and several novel genes not previously implicated in AKI, and demonstrated that older onset age exacerbates the AKI outcome. This work provides a rich resource for examining the molecular genetics of AKI.BackgroundCurrent management of AKI, a potentially fatal disorder that can also initiate or exacerbate CKD, is merely supportive. Therefore, deeper understanding of the molecular pathways perturbed in AKI is needed to identify targets with potential to lead to improved treatment.MethodsWe performed single-cell RNA sequencing (scRNA-seq) with the clinically relevant unilateral ischemia-reperfusion murine model of AKI at days 1, 2, 4, 7, 11, and 14 after AKI onset. Using real-time quantitative PCR, immunofluorescence, Western blotting, and both chromogenic and single-moleculein situhybridizations, we validated AKI signatures in multiple experiments.ResultsOur findings show the time course of changing gene expression patterns for multiple AKI stages and all renal cell types. We observed elevated expression of crucial injury response factors—including kidney injury molecule-1 (Kim1), lipocalin 2 (Lcn2), and keratin 8 (Krt8)—and of several novel genes (Ahnak,Sh3bgrl3, andCol18a1) not previously examined in kidney pathologies. AKI induced proximal tubule dedifferentiation, with a pronounced nephrogenic signature represented bySox4andCd24a. Moreover, AKI caused the formation of “mixed-identity cells” (expressing markers of different renal cell types) that are normally seen only during early kidney development. The injured tubules acquired a proinflammatory and profibrotic phenotype; moreover, AKI dramatically modified ligand-receptor crosstalk, with potential pathologic epithelial-to-stromal interactions. Advancing age in AKI onset was associated with maladaptive response and kidney fibrosis.ConclusionsThe scRNA-seq, comprehensive, cell-specific profiles provide a valuable resource for examining molecular pathways that are perturbed in AKI. The results fully define AKI-associated dedifferentiation programs, potential pathologic ligand-receptor crosstalk, novel genes, and the improved injury response in younger mice, and highlight potential targets of kidney injury.