BACKGROUND: Kidney fibrosis is a common mechanism of progressive kidney diseases including diabetic kidney disease (DKD). We have revealed that palladin, an actin-associated protein, drives kidney fibrosis through actin dynamics. However, it has not been elucidated whether palladin is related to the pathogenesis of DKD. In this study, we investigated whether palladin is associated with kidney dysfunction, fibrosis, and prognosis in DKD.; METHODS: We conducted a retrospective cohort study of Japanese patients diagnosed with DKD by kidney biopsy between 2000 and 2020. Palladin expression was quantified as the percentage of positive area on immunohistochemistry and log2-transformed (log2 palladin). We assessed its correlation with baseline clinical characteristics and pathological findings. Event-free survival for the initiation of renal replacement therapy (RRT) or all-cause death was analyzed by Kaplan-Meier analysis and Cox proportional hazards regression.; RESULTS: A total of 38 patients were enrolled with a mean age of 57.4years (10 women). Median follow-up was 2.6years (range 0.01-19.9), during which 12 patients experienced the composite outcome. On immunohistochemistry, palladin is expressed in myofibroblasts in kidneys from patients with DKD. Log2 palladin was independently associated with lower baseline eGFR (B=-12.3mL/min/1.73 m2 per doubling; 95% CI-20.1 to-4.54; p=0.003). Higher palladin was associated with poorer event-free survival (log-rank p=0.003). In Cox analysis, doubling of palladin-positive area was associated with increased risk of RRT initiation or death (age-adjusted HR 2.70; 95% CI 1.36 to 6.33; p=0.004).; CONCLUSION: Interstitial palladin expression may serve as a histopathological prognostic marker in patients with DKD. © 2026. The Author(s), under exclusive licence to Japanese Society of Nephrology.

Acute kidney injury (AKI) remains a significant clinical challenge with limited therapeutic options. While d-alanine shows promise in AKI treatment, its formulation requires l-alanine co-inclusion for pharmaceutical stabilization through racemization. This study investigated the biological activity of synthetic d-alanine compounds in the human proximal tubular epithelial cell line (HK-2). We synthesized d-alanine hydrochloride, a dipeptide, and a tripeptide and evaluated their effects on cell viability under normal and hypoxic conditions. d-Alanine hydrochloride (10M) and dipeptide (10M) significantly enhanced cell viability compared with the controls, with d-alanine hydrochloride demonstrating superior efficacy under hypoxic conditions. Gene expression analysis revealed that these compounds promoted cell cycle progression and increased cyclin B1 expression under hypoxic conditions. Notably, these synthetic forms maintained therapeutic efficacy without requiring l-alanine co-inclusion. Although limited to in vitro experiments, our findings suggest that d-alanine hydrochloride and dipeptide forms are promising therapeutic candidates for AKI treatment. © 2025 Wiley‐VHCA AG, Zurich, Switzerland.

Fibrosis is a common end-stage pathway of progressive chronic kidney diseases. Previously we demonstrated that myocardin-related transcription factor (MRTF)-serum response factor (SRF) signaling drives the expression of fibrosis-related molecules through actin cytoskeleton dynamics in renal fibroblasts. However, it has not been elucidated whether actin-associated proteins relate to the pathogenesis of fibrosis. Here, we reveal that the actin cytoskeleton-regulating pathway is significantly correlated with estimated glomerular filtration rate (eGFR) and collagen type 1 alpha 1 expression in human proteome analysis. We found that palladin was one of the TGF-beta1-dependent actin-associated proteins in renal fibroblasts. Our mechanistic studies demonstrated that palladin activates MRTF-SRF signaling via actin cytoskeleton rearrangement upon TGF-beta1 stimulation. In addition, palladin expression itself was enhanced by MRTF-SRF signaling, indicating a positive feedback loop. In vitro, genetic silencing of the palladin-MRTF-SRF axis suppressed extracellular matrix production and myofibroblast differentiation. In preclinical models in vivo, fibroblast-specific palladin-deficient mice (palladiniFBKO) were protected from kidney dysfunction and fibrosis that developed in adenine-induced nephropathy, which was associated with reduced numbers of myofibroblasts compared to wild type (palladinF/F) mice. In patients with renal disease, palladin was significantly upregulated in the renal interstitium of patients with low eGFR and kidney fibrosis. Moreover, upregulation of the palladin-MRTF-SRF axis correlated with kidney function and fibrosis in patients with various kidney diseases, including IgA nephropathy, diabetic nephropathy, and nephrosclerosis. Taken together, we consider palladin to be a novel regulator of actin cytoskeleton signaling in fibrotic fibroblasts and represents a novel therapeutic target for the treatment of progressive kidney diseases. © 2025 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland. © 2025 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.