Human Transcriptomic Validation of a Proximal Tubule–Fibrogenic Interstitial Pyrimidinergic Axis in Kidney Disease

Background: Kidney fibrosis develops through sustained communication between injured tubular epithelial cells and surrounding interstitial populations. In our recent mechanistic study, we identified a pyrimidinergic pathway linking injury-associated proximal tubule metabolism to P2Y6-mediated fibroblast activation. Here, we sought to determine whether this biological axis is also detectable in human kidney disease transcriptomes. Methods: We analyzed publicly available human kidney single-cell RNA-sequencing (sc-RNA-seq) data spanning healthy reference tissue, acute kidney injury (AKI), and diabetic kidney disease (DKD). We quantified proximal tubule (PT) pyrimidine metabolism at the subject level and examined the abundance, P2RY6 expression, and subtype distribution of fibrogenic interstitial cells. We also evaluated calcium signaling and extracellular matrix (ECM)-related associations across compartments. Results: PT pyrimidine metabolism was significantly increased in diseased kidneys, with the strongest elevation observed in AKI. P2RY6 expression was elevated in the stromal compartment in both AKI and DKD, with the strongest signal in ACTA2+ myofibroblasts. The fibrogenic interstitial compartment expanded in disease and showed a significant increase in P2RY6 expression in DKD. Fibrogenic interstitial cells from AKI and DKD kidneys also displayed increased calcium signaling activity. At the subject level, higher PT pyrimidine module score was associated with stronger interstitial calcium signaling (rho = 0.395, p = 0.011), while greater abundance of P2RY6-positive fibrogenic interstitial cells correlated with ECM remodeling (rho = 0.434, p = 0.005). Conclusions: These findings provide human transcriptomic validation of a proximal tubule–fibrogenic interstitial pyrimidinergic axis in kidney disease. By extending our prior mechanistic observations into human single-cell data, this study strengthens the translational relevance of P2Y6-linked epithelial–interstitial communication as a candidate pathway in fibrogenic kidney remodeling.