Direct evidence for the spontaneous conversion of residual intact tubules within injured kidney tissue into proinflammatory failed-repair proximal tubular cells.

Recent studies have revealed that proinflammatory failed-repair proximal tubular cells (FR-PTCs) emerge during the chronic phase following kidney injury and play a crucial role in the transition from acute kidney injury (AKI) to chronic kidney disease (CKD). These cells, also known as VCAM1-positive tubular cells, are characterized by the persistent expression of inflammatory and profibrotic molecules, which sustain tissue injury and ultimately lead to renal function decline. Interestingly, FR-PTCs have also been detected in the kidneys of CKD patients without prior AKI, suggesting that they may arise through mechanisms independent of acute injury. We hypothesized that residual normal tubular cells surviving within injured kidneys could spontaneously convert into FR-PTCs, even in the absence of new injury, as a result of compensatory overload that imposes metabolic stress on remaining nephrons.

To test this hypothesis, we conducted lineage tracing of residual healthy proximal tubules in injured kidneys using Slc34a1^GCE/R26^tdTomato mice carrying a tamoxifen-inducible tdTomato reporter specific to proximal tubules. Kidney injury was induced by unilateral ischemia–reperfusion injury (IRI), and contralateral nephrectomy was performed to impose functional overload on the injured kidney. Tamoxifen was administered 28 days after IRI to label surviving tubular cells during recovery. The fate and phenotype of labeled cells were examined two months later under steady conditions without further injury. Additionally, RNA sequencing of isolated tdTomato⁺ tubules was performed to identify molecular pathways and metabolic alterations associated with phenotypic transition.

At 28 days after IRI, tdTomato⁺ cells were LTL-positive, KIM1-negative, and VCAM1-negative, confirming accurate labeling of residual normal tubules. After two months (day 84), a subset of these cells newly expressed VCAM1, indicating spontaneous conversion into FR-PTCs. Transcriptomic analysis revealed upregulation of genes related to fatty acid metabolism, suggesting increased energy demand in residual tubules. Immunostaining and ELISA demonstrated elevated levels of the lipid peroxidation product 4-hydroxynonenal (4HNE) in residual tubules. In cultured tubular cells, exposure to 4HNE induced DNA damage, G2/M arrest, and VCAM1 expression. Together, these findings indicate that surviving tubular cells after AKI undergo metabolic stress, where lipid peroxidation and DNA damage drive their conversion into FR-PTCs.

Lineage tracing demonstrated that normal tubular cells in injured kidneys can spontaneously convert into FR-PTCs during the chronic phase, even without additional injury. This suggests that some VCAM1-positive tubular cells observed in the chronic stage are not derived from those formed during the initial AKI. The conversion appears driven by enhanced fatty acid metabolism and accumulation of lipid peroxidation products, which induce tubular injury and promote FR-PTC formation. Limiting metabolic overload and protecting residual tubules may thus represent a promising therapeutic strategy to preserve renal structure and delay CKD progression. This abstract was also submitted for the ASN kidney week 2025 congress.