Single-cell analysis to promote kidney repair

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Summary Acute kidney injury (AKI) has a wide spectrum of outcomes from recovery to a long-term transition to chronic kidney disease (CKD). Between 2000 and 2014, AKI hospitalizations have increased from 3.5 to 11.7 per 1000 persons. Medicare patients aged 66 years and older hospitalized for AKI have a 35% cumulative probability of a recurrent AKI hospitalization within one year and 28% will be diagnosed with CKD in the same time frame. Men have a higher risk of AKI, and of developing progressive CKD, although the mechanisms are poorly understood. In the mouse, males also show a heightened vulnerability to AKI. Recent single cell RNA-seq studies from the McMahon and Kim groups have highlighted marked differences in gene expression between the sexes in proximal tubule segments, the region of the nephron most susceptible to AKI. Preliminary studies in the Humphreys and McMahon laboratories using single nuclear sequencing identified a cell type resulting from failed repair of proximal tubule cells (FR-PTC) following mild to severe AKI with a pro-inflammatory, pro- fibrotic signature. FR-PTCs are hypothesized to drive progressive kidney disease following AKI. This proposal centers on the postulates that an understanding of sex differences in response to AKI, and the application of genetic approaches to target proinflammatory properties of FR-PTCs and to eliminate FR-PTCs following renal repair, will be effective routes to ultimately benefit patient outcomes post AKI. To this end, we have assembled a complementary team, with prior collaborative experience: Humphreys (Washington University), Kim (University of Pennsylvannia) and McMahon (University of Southern California). All team members have participated in the ReBuilding a Kidney Consortium. In Specific Aim 1: we will characterize successful versus failed proximal tubule repair with single nucleus transcriptomics (snRNA-seq) and single nuclear chromatin accessibility studies (scATAC-seq) in male and female mouse models examining key findings in human kidney biopsies. In Specific Aim 2: we will harmonize multimodal datasets generated in Specific Aim1 to facilitate viewing and interrogation of these data by the broad research community. Mining of these data by the group will focus on defining the regulatory logic of repair strategies and outcomes in the male and female kidney. In Specific Aim 3: we will examine the hypothesis that adverse outcomes in the male kidney following AKI are driven by NF-kB pathway components Nfkb1 and TNIK in FR-PTCs, genetically eliminating the action of these genes. We will generate and validate a new transgenic mouse resource for the community, enabling genetic modification and elimination of FR-PTCs. We will determine whether FR-PTC removal has a favorable outcome, as we predict, on progressive kidney disease following AKI.