Abstract 564: Differential Expression and Regulation of Angiotensinogen in Renal Proximal Tubule Cells From S1, S2 and S3 Segments

Abstract

In angiotensin II (Ang II)-dependent hypertension, intrarenal angiotensinogen (AGT) augmentation induced by Ang II and associated pathogenic factors including interleukin 6 (IL-6) cause further elevation of intratubular Ang II production, leading to the progression of hypertension and kidney injury. Recent studies have suggested that renal proximal straight tubules (S3 segment) are the main source of intrarenal AGT and that S1 and S2 segments do not express AGT mRNA under normal conditions. However, AGT expression and its regulation by Ang II and/or IL-6 in each proximal tubule segment have not been demonstrated an in vitro setting. The availability of specific cell lines derived from mouse S1, S2 and S3 segments provided an opportunity to decisively determine each segments’ capability to express AGT and respond to stimuli. Thus, this study was performed to determine AGT expression and its response to stimulation with Ang II and IL-6 in S1, S2 and S3 cell line. Basal AGT mRNA and protein levels were detected by RT-PCR and western blot analysis. Basal levels of Ang II type 1 receptor (AT1R) and STAT3, which is a transcription factor in IL-6 signaling pathway, were also measured. In addition, the cells were incubated with 100 nM Ang II and/or 400 nM IL-6 for 24 h. Basal AGT levels in S1 and S3 cells were lower than in mouse whole kidney (0.09-fold and 0.33-fold compared with mouse whole kidney). S2 cells exhibited the highest basal AGT levels (4.15-fold) among these cells. In S1 cells, AGT expression was stimulated by IL-6 (1.89 ± 0.32, ratio to control) and co-stimulation with Ang II and IL-6 (1.85 ± 0.28) although Ang II alone did not alter AGT levels. In S2 cells, only the co-stimulation increased AGT expression (1.35 ± 0.01). No changes were observed by similar treatments in S3 cells. Basal AT1R levels were lower in S3 than in S1 and S2 cells (0.97 ± 0.09 in S2, 0.32 ± 0.07 in S3, ratio to S1). S1 cells showed the highest basal levels of STAT3. Basal STAT3 levels in S3 cells were lower than that in S1 and S2 cells. These results indicate that S2 cells are main source of intrarenal AGT which can be augmented by Ang II and IL-6 during the development of Ang II-dependent hypertension. Furthermore, low basal levels of AT1R and STAT3 in S3 cells explain why these cells do not respond to Ang II and IL-6.