Abstract: TH-PO413

RhoA Effector mDia1 Contributes to Kidney Injury in the Early Stage of High-Fat Diet Induced Obesity

Session Information

Category: Nutrition, Inflammation, and Metabolism

  • 1401 Nutrition, Inflammation, Metabolism

Authors

  • Naitoh, Makiko, Keio university, Tokyo, Japan
  • Tokuyama, Hirobumi, Internal Medicine, Keio University, Tokyo, Japan
  • Wakino, Shu, Keio University , Tokyo, Japan
  • Itoh, Hiroshi, Keio University School of Medicine, Tokyo, Japan
Background

Obesity is a critical contributor to kidney damages that are reported to be structurally characterized by glomerulomegaly, tubular hypertrophy and renal hypertrophy. We have previously demonstrated that proximal tubular (PT) hypertrophy occurred in obese mice fed with high-fat diet (HFD) for twelve weeks, which activated RhoA/ROCK signaling leading to inflammatory reaction. However, the early changes which precede this renal tubular cell change and RhoA activation was unclear.

Methods

We used male C57Bl/6J mice with overexpressed dominant negative RhoA genes selectively expressed in the PT (dnRhoATg/Tg) to suppress RhoA activation. Morphological and biochemical changes were compared between dnRhoATg/Tg mice and their wild-type littermates (WT) fed with HFD or low-fat diet (LFD) for 2 weeks. To investigate the molecular mechanism, we utilized tissue culture system with human kidney-2 (HK-2) cells.

Results

Although the body weight, serum insulin and lipid levels were increased in HFD-fed WT mice, fasting glucose levels were not altered as compared with LFD-fed WT mice. HFD-fed WT mice showed no significant renal morphological changes except increased tubular proliferation even two weeks after the initiation of HFD as assessed by Ki67 staining. Although urinary albumin excretion was not altered, the excretion of NGAL was increased in HFD-fed WT mice. Immunoblot analysis revealed increased expression level of one of the RhoA effectors, Diaphanous-related formin-1 (mDia1) and decreased expression level of negative cell cycle regulator p27 in HFD-fed WT mice, while the activity of another RhoA downstream target ROCK was unaltered. Compared with WT on HFD, RhoATg/Tg on HFD exhibited less tubular cell proliferation and NGAL excretion. The upregulation of mDia1 and the downregulation of p27 in HFD-fed mice was restored in HFD-fed RhoATg/Tg mice. In cultured HK-2 cells, treatment with insulin upregulated mDia1 and downregulated p27, which were ameliorated by siRNA-mediated knockdown of mDia1.

Conclusion

The activation of RhoA/mDia1 pathway in PT promotes PT proliferation in early stage of obesity probably through insulin stimulation. The early activation of RhoA/mDia1 pathway may precede the activation of RhoA/ROCK pathway and may play a critical roles in the initiation process of obesity-induced renal damages.