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Articles by T. Niwa
Total Records ( 2 ) for T. Niwa
  G Muteliefu , A Enomoto , P Jiang , M Takahashi and T. Niwa

Background. Previously, we demonstrated that indoxyl sulphate (IS), a uraemic toxin, induced aortic calcification in hypertensive rats. This study aimed to determine if IS induces the production of reactive oxygen species (ROS) and the expression of osteoblast-specific proteins in human aortic smooth muscle cells (HASMCs).

Methods. In order to achieve these goals, HASMCs were incubated with IS. ROS were detected using probes with a fluorescence detector. The expression of alkaline phosphatase (ALP), osteopontin and organic anion transporters (OAT1, OAT3) was studied by western blotting. The expression of core binding factor 1 (Cbfa1), ALP, osteopontin and NADPH oxidases (Nox1, Nox2 and Nox4) was analysed by reverse transcription-polymerase chain reaction (RT-PCR). Knockdown of Nox4 was performed by RNA interference (RNAi).

Results. IS induced ROS generation and the expression of Nox4, Cbfa1, ALP and osteopontin in HASMCs. A NADPH oxidase inhibitor and antioxidants inhibited IS-induced ROS production and mRNA expression of Cbfa1 and ALP. Knockdown of Nox4 using small interfering RNA (siRNA) inhibited IS-induced ROS production and mRNA expression of Cbfa1, ALP and osteopontin. OAT3 was expressed in HASMCs.

Conclusions. IS induces ROS generation by upregulating Nox4, and the expression of osteoblast-specific proteins such as Cbfa1, ALP and osteopontin in HASMCs.

  H Shimizu , D Bolati , A Adijiang , A Enomoto , F Nishijima , M Dateki and T. Niwa

Various uremic toxins accumulate in patients with chronic renal failure (CRF) and one of them is indoxyl sulfate, which accelerates the progression of CRF through unknown mechanisms. The present study investigates how indoxyl sulfate promotes CRF using the proximal tubular cell line HK-2 and CRF rats. Indoxyl sulfate inhibited serum-induced cell proliferation and promoted the activation of senescence-associated β-galactosidase, a marker of cellular senescence, and the expression of -smooth muscle actin (-SMA), a marker of fibrosis, through inducing p53 expression and phosphorylation. Pifithrin-, p-nitro, a p53 inhibitor, blocked these effects. Indoxyl sulfate evoked reactive oxygen species (ROS), and the antioxidant N-acetylcysteine inhibited indoxyl sulfate-induced p53 expression and phosphorylation, as well as indoxyl sulfate-induced -SMA expression. We previously demonstrated that although cellular senescence and fibrosis are detectable in the kidneys of CRF rats, the oral adsorbent AST-120 repressed these effects. Here, we found that β-galactosidase, p53 and -SMA were expressed and colocalized in the renal tubules of CRF rats, whereas AST-120 decreased the expression of these genes. Taken together, these findings indicate that indoxyl sulfate induces the expression and phosphorylation of p53 though ROS production, thus inhibiting cell proliferation and promoting cellular senescence and renal fibrosis.

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