Abstract P2048: Epigenetic Modification By Angiotensin II Mediates Augmentation Of Intrarenal Angiotensinogen Expression

Abstract

Inappropriately activated intrarenal renin-angiotensin system, including proximal tubular angiotensinogen (AGT) augmentation, contributes to the progression of hypertension and associated kidney injury. It has been demonstrated that interleukin 6 (IL-6) is required for angiotensin II (Ang II)-induced AGT augmentation in renal proximal tubular cells (PTC). However, molecular mechanisms remain unelucidated. Recent studies suggest that Ang II downregulates cardiac class II histone deacetylases (HDAC), which exhibit protective effects against hypertension related tissue injury. Furthermore, HDAC9 (a class II HDAC) has been shown to act as an epigenetic repressor of proximal tubular AGT. Accordingly, the present study investigated the hypothesis that Ang II decreases HDAC9 levels, thereby enabling IL-6 to promote AGT expression in PTC. Ang II (400 ng/kg/min) was chronically perfused to male mice (N=7) for 14 days to investigate the regulation of intrarenal HDAC9. Moreover, cultured human PTC (hPTC) were used to create wild-type, HDAC9 overexpression, and HDAC9 knockdown by shRNA models and were treated with 100 nM Ang II, 10 ng/ml IL-6, or both for 24 hours. Chronic Ang II infusion elevated blood pressure and suppressed renal cortical HDAC9 levels. A decrease in HDAC9 was also observed in Ang II-treated hPTC. Treatment of hPTC with both Ang II and IL-6 increased AGT mRNA levels (1.50±0.10, ratio to the control, N=6), whereas individual treatments with Ang II or IL-6 did not alter AGT expression levels as previously demonstrated. This upregulation of AGT expression by Ang II and IL-6 co-stimulation was attenuated by the overexpression of HDAC9 in hPTC (1.10±0.08, ratio to the control). Importantly, AGT expression was enhanced by IL-6 without Ang II (2.31±0.08 by IL-6 and 2.27±0.15 by Ang II+IL-6, ratio to the control) in cells receiving the HDAC9 gene knockdown, suggesting that HDAC9 down-regulation mediates IL-6-induced AGT upregulation in hPTC. These results indicate that Ang II-induced epigenetic modification, such as the suppression of intrarenal HDAC9, results in increased accessibility of IL-6-derived transcription factors to the AGT promoter and consequent augmentation of intrarenal AGT expression in Ang II-dependent hypertension.