Abstract 160: Angiotensin-(1-7) Decreases the Pro-inflammatory Effects of Prorenin in Hypothalamic Microglia

Abstract

The chronic hypertensive action of angiotensin II (Ang II) mediated within central cardiovascular control centers includes a pro-inflammatory effect and induction of microglial activation in the paraventricular nucleus (PVN) of the hypothalamus. The objective here was to investigate whether angiotensin-(1-7), a protective arm of the renin-angiotensin system (RAS), can exert anti-inflammatory effects in hypothalamic microglia. The presence of Mas, the receptor for Ang-(1-7), within the PVN and other cardiovascular control centers of normotensive (SD; Sprague Dawley) rats was demonstrated by quantitative real time PCR analyses. Mas was maintained in microglial cultures prepared from the hypothalamus of SD rat pups based on immunostaining and PCR. Treatment of microglial cultures with Ang-(1-7) (100nM, 3 -12h) elicited time-dependent significant (P<0.05) decreases in the basal levels of mRNAs for the pro-inflammatory cytokines interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor-necrosis factor α (TNFα), and in the microglial-macrophage marker CD11b. For example, the levels of IL-1β mRNA (normalized to GAPDH) within control and Ang-(1-7) treated cells were 1.0±0.09, 0.70±0.06, 0.40±0.04, and 0.48±0.07 (n=6). There was no significant effect of Ang-(1-7) on basal IL-1β mRNA at 10 nM (6h), and 1000 nM Ang-(1-7) produced no greater effect than 100 nM of this peptide. Treatment of cultures with the RAS component prorenin (PRO; 10, 20 or 50 nM; 6h) elicited highly significant (P<0.001) increases in IL-1β mRNA (4.2±0.10, 7.4±0.35, 16.7±0.46, respectively, n=6) when compared with controls (0.78±0.06), effects that far exceeded the ~2.0 fold increase in IL-1β mRNA elicited by Ang II (100 nM). Similar stimulatory effects of PRO on TNFα, IL-6 and CD11b mRNAs were also observed. The stimulatory action of PRO (10 nM) on IL-1β and TNFα mRNAs, but not CD11b mRNA, was attenuated by co-treatment with Ang-(1-7) (100 nM). For example, levels of IL-1β mRNA in PRO and Ang-(1-7)/PRO treated cells were 34.1±1.3 and 24.4±1.1 respectively (n=6), a reduction of ~29% (P<0.001). Collectively, these data suggest that Ang-(1-7) exerts a direct anti-inflammatory action at hypothalamic microglia, and inhibits PRO-induced pro-inflammatory effects.