Submitted on January 27, 2008
Accepted on May 4, 2008
Co-stimulation with Angiotensin II and Interleukin 6 Augments Angiotensinogen Expression in Cultured Human Renal Proximal Tubular Cells
Ryousuke Satou1, Romer A. Gonzalez-Villalobos1, Kayoko Miyata1, Naro Ohashi1, Akemi Katsurada1, L. Gabriel Navar1, and Hiroyuki Kobori1*
1 Department of Physiology, and Hypertension and Renal Center of Excellence, Tulane University Health Sciences Center, New Orleans, Louisiana, United States
* To whom correspondence should be addressed. E-mail: hkobori{at}tulane.edu.
Augmented intrarenal Ang II stimulates IL-6 which contributes to renal injury. The expression of intrarenal angiotensinogen (AGT) is enhanced by increased intrarenal Ang II in human renin/human AGT double transgenic mice. Ang II also augments AGT expression in hepatocytes and cardiac myocytes. However, the mechanisms underlying AGT augmentation by Ang II and the contribution of IL-6 to this system are poorly understood. This study was performed in human renal proximal tubular epithelial cells (HRPTECs) to test the hypothesis that IL-6 contributes to the upregulation of AGT expression by Ang II. Human kidney-2 (HK-2) cells, immortalized HRPTECs, were incubated with 10-7 M Ang II and/or 10 ng/mL IL-6 up to 24 h. AGT mRNA and protein expressions were measured by real-time RT-PCR and ELISA, respectively. The activities of NF-
B and STAT3 were evaluated by western blot and EMSA. Stimulation with either Ang II or IL-6 did not significantly alter AGT mRNA or protein expression. In contrast, co-stimulation with Ang II and IL-6 significantly increased AGT mRNA and protein expressions (1.26 +/- 0.10 and 1.16 +/- 0.13 over control, respectively). Olmesartan, an Ang II type 1 receptor blocker, and an IL-6 receptor antibody individually inhibited this synergistic effect. NF-B was also activated by co-stimulation with Ang II and IL-6. Phosphorylation and activity of STAT3 were increased by stimulation with IL-6 alone and by co-stimulation. The present study indicates that IL-6 plays an important role in Ang II-mediated augmentation of AGT expression in human renal proximal tubular cells.
