Angiotensin-(1-7) regulates tyrosine hydroxylase and norepinephrine transporter expression in neuronal cultures from spontaneously hypertensive rats

M. A. LOPEZ VERRILLI, M. M. GIRONACCI

Berlín, Alemania

Congreso; 22nd Scientific Meeting of the International Society of Hypertension,; 2008

Objectives: Angiotensin (Ang) (1-7) is an antihypertensive peptide of the renin-angiotensin system that exerts opposite effects to Ang II on central sympathetic activity. Since Ang-(1-7) decreases hypothalamic norepinephrine (NE) release (Hypertension 2004;44:783-7) we hypothesize that Ang-(1-7) may decrease NE biosynthesis modulating tyrosine hydroxylase (TH), the rate-limiting step enzyme in NE biosynthesis, or stimulate NE uptake through NE transporter (NET). Our aim was to investigate the effect of Ang-(1-7) on NET and TH expression at the central level in spontaneously hypertensive rats (SHR). Methods: Neuronal cells in primary culture from hypothalamus-brainstem of SHR were used to determine TH and NET expression by western blot. One-way ANOVA was used to perform statistical analysis. Results: Endogenous TH levels were 1.7-fold greater in neuronal cultures from SHR than in those from normotensive Wistar-Kyoto (WKY) rats. Treatment of SHR neuronal cultures with 100 nM Ang-(1-7) during 30 min caused a decrease in TH endogenous expression of 31±3%, and this effect was blocked by an AT2 receptor antagonist. No change was observed with longer time exposure. Since the ubiquitin-proteasome system is the major pathway for protein degradation, we examined the involvement of the proteasomal pathway in the Ang-(1-7)-induced decrease in TH expression. MG132, a selective proteasome inhibitor, blocked the Ang-(1-7)-mediated TH downregulation, suggesting a proteasome-dependent TH degradation. Basal NET expression was 3-fold higher in neuronal cultures from SHR than in WKY. Incubation of SHR neuronal cultures with 10 or 100 nM Ang-(1-7) during 3 h caused an increase in NET endogenous levels of 70±18% and 60±11%, respectively. Conclusion: Together with the fact that the peptide induces a decrease in NE release, our study supports a negative neuromodulator role for Ang-(1-7) on NE central sympathetic nervous activity.