Local action of endogenous renal tubular atrial natriuretic peptide

Up‐regulation of atrial natriuretic peptide (ANP) mRNA in the kidneys in several disorders has been demonstrated; however, evidence that ANP synthesized by the kidney exerts a local function has never been produced. Therefore, we investigated whether endogenous ANP could modulate high glucose‐stimulated TGF‐β1, collagen type I and nuclear factor‐κB (NF‐κB) in NRK‐52E cells using transfection of ANP and ANP small interfering RNA (siANP). NRK‐52E cells were grown with or without transfection with ANP plasmid; cells were also transfected with ANP siRNA or control siRNA. These cells were then stimulated with a high glucose concentration to modulate ANP, TGF‐β1, collagen type I, NF‐κB and IκB‐α, and the results showed that ANP, TGF‐β1, collagen type I and NF‐κB significantly increased in untransfected cells, and the transfection of ANP significantly attenuated high glucose‐activated TGF‐β1, collagen I and NF‐κB expression. ANP siRNA knocked‐down ANP but significantly increased TGF‐β1 and collagen I under normal glucose conditions; ANP siRNA decreased IκB‐α but strongly enhanced high glucose‐activated TGF‐β1, collagen type I and NF‐κB. In contrast, medium from ANP‐transfected cells attenuated high glucose‐activated TGF‐β1 and collagen type I expression in NRK‐52E cells transfected with siANP. In conclusion, our results demonstrated that siANP increased activation of TGF‐β1, collagen type I and NF‐κB in NRK‐52E cells under high glucose conditions, and medium from ANP‐transfected cells attenuated high glucose‐activated TGF‐β1 and collagen type I. This is the first study to demonstrate the auto/paracrine action of endogenous ANP in renal tubular cells on the attenuation of hyperglycemia‐activated TGF‐β1 and NF‐κB expression. J. Cell. Physiol. 219: 776–786, 2009. © 2009 Wiley‐Liss, Inc.