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-beta I, collagen type I and nuclear factor-kappa B (NF-kappa B) 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-beta I, collagen type 1, NF-kappa B and I kappa B-alpha, and the results showed that ANP, TGF-beta I, collagen type I and NF-kappa B significantly increased in untransfected cells, and the transfection of ANP significantly attenuated high glucose-activated TGF-beta I, collagen I and NF-kappa B expression. ANP siRNA knocked-down ANP but significantly increased TGF-beta I and collagen I under normal glucose conditions; ANP siRNA decreased I kappa B-alpha but strongly enhanced high glucose-activated TGF-beta I, collagen type I and NF-kappa B. In contrast, medium from ANP-transfected cells attenuated high glucose-activated TGF-beta I and collagen type I expression in NRK-52E cells transfected with siANP. In conclusion, our results demonstrated that siANP increased activation of TGF-beta I, collagen type I and NF-kappa B in NRK-52E cells under high glucose conditions, and medium from ANP-transfected cells attenuated high glucose-activated TGF-beta I 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-beta I and NF-kappa B expression. J. Cell. Physiol. 219: 776-786, 2009. (C) 2009 Wiley-Liss, Inc.