The role of epithelial cell injury in kidney transplant outcomes - a cross-sectional study.

We defined injury-induced transcriptome states in 4502 kidney transplant biopsies taken 1 day to 45 years post-transplant using genome-wide microarrays. Injury was measured by injury-induced gene sets and classifiers previously developed in transplants. In principal component analysis, PC1 correlated with both acute and chronic kidney injury and related inflammation, and PC2 with time post-transplant. PC3 was a novel dimension that correlated with epithelial remodeling pathways. Both PC1 and PC3 correlated with reduced survival, PC1 effects strongly increasing with time whereas PC3 effects being time-independent. In this model, we studied the expression of genes annotated in native kidneys in epithelial cells with failed repair: 12 "New" gene sets previously defined in single nucleus RNA sequencing of native kidneys with AKI (Genome Med.14(1):103). The "New4" gene sets reflecting epithelial-mesenchymal transition (EMT) correlated with injury PC1, lower eGFR, higher donor age, and future failure as strongly as any gene sets previously derived in transplants, independent of nephron segment of origin and graft rejection. These results suggest that there are two distinct dimensions in kidney transplant response to injury: PC1, AKI-induced changes, failed repair, and inflammation; and PC3, a response involving epithelial remodeling without inflammation. Increasing kidney age amplifies PC1 and particularly PC3.