Claudin-1 Inhibitor PDS-0330 Ameliorates Diabetic Kidney Disease by Suppressing Src/Akt/mTOR Signaling Pathway in Podocytes

Introduction Recent studies have reported that claudin-1, which is reactively expressed in malignant tumors and inflammatory diseases, plays an important role in disease progression. In diabetic kidney disease (DKD), upregulated expression of claudin-1 in podocytes has also been shown to contribute to disease progression. However, it remains unclear whether claudin-1 itself could be a therapeutic target in DKD. In this study, we investigated whether the claudin-1 inhibitor PDS-0330 could ameliorate DKD. Methods Five-week-old male C57BL/6J mice were fed either a high-fat diet (HFD) or a normal diet (ND). At 15 weeks of age, PDS-0330 (Inh) or vehicle as control (Ctrl) was administered orally once per week for 4 weeks. At the end of the treatment period, blood, urine, and kidney samples were collected. In in vitro study, immortalized podocytes were treated with Inh or Ctrl and cultured for 48 hours in either normal glucose medium (5.5 mM; NG) or high glucose medium (25 mM; HG), after which proteins were extracted for analysis. Results Mice fed an HFD showed significant increases in body weight and serum glucose levels compared with ND mice, and these parameters were not significantly affected by Inh treatment. HFD mice treated with Ctrl (HFD-Ctrl) exhibited significantly higher urinary albumin excretion than ND mice treated with Ctrl (ND-Ctrl), whereas the Inh-treated HFD mice (HFD-Inh) showed a significant reduction. Transmission electron microscopy revealed foot process effacement in HFD-Ctrl podocytes, which was markedly improved in HFD-Inh mice. Immunofluorescence staining demonstrated claudin-1 expression in podocytes of HFD mice. Furthermore, phospho-mTOR staining in podocytes was significantly increased in HFD-Ctrl compared with ND-Ctrl and was significantly attenuated in HFD-Inh. Western blot analysis of kidney samples revealed activation of the Src/Akt/mTOR signaling pathway in HFD-Ctrl mice, which was significantly reduced in HFD-Inh mice. In in vitro study, Ctrl-treated podocytes cultured in HG (HG-Ctrl) showed significant activation of Src/Akt/mTOR signaling compared with those in NG (NG-Ctrl). This activation was significantly suppressed in Inh-treated podocytes (HG-Inh). Conclusion These findings suggest that podocyte claudin-1 could be a potential therapeutic target in DKD.