Involvement of the brain (pro)renin receptor in cardiovascular homeostasis

Abstract

Rationale: Despite overwhelming evidence of the importance of brain renin-angiotensin system (RAS), the very existence of intrinsic brain RAS remains controversial.

Objective: To investigate the hypothesis that the brain (pro)renin receptor (PRR) is physiologically important in the brain RAS regulation and cardiovascular functions.

Methods and results: PRR is broadly distributed within neurons of cardiovascular-relevant brain regions. The physiological functions of PRR were studied in the supraoptic nucleus (SON) because this brain region showed greater levels of PRR mRNA in the spontaneously hypertensive rats (SHR) compared with normotensive Wistar-Kyoto (WKY) rats. Adeno-associated virus (AAV)-mediated overexpression of human PRR in the SON of normal rats resulted in increases in plasma and urine vasopressin, and decreases in H(2)O intake and urine output without any effects on mean arterial pressure and heart rate. Knockdown of endogenous PRR by AAV-short hairpin RNA in the SON of SHRs attenuated age-dependent increases in mean arterial pressure and caused a decrease in heart rate and plasma vasopressin. Incubation of neuronal cells in culture with human prorenin and angiotensinogen resulted in increased generation of angiotensin I and II. Furthermore, renin treatment increased phosphorylation of extracellular signal-regulated kinase ½ in neurons from both WKY rats and SHRs; however, the stimulation was 50% greater in the SHR.

Conclusions: The study demonstrates that brain PRR is functional and plays a role in the neural control of cardiovascular functions. This may help resolve a long-held controversy concerning the existence of intrinsic and functional brain RAS.

Figure 1. PRR in the brain of WKY and SHR

a. PRR mRNA in WKY and SHR brains. PVN: paraventricular nucleus; MnPO: median preoptic nucleus; OVLT: organum vasculosum of lamina terminals; RVLM: rostral ventrolateral medulla. *P< 0.05 vs. WKY. b. Representative immunofluorescence micrographs using anti-PRR and anti-NeuN antibodies reveal co-localization of PRR with neurons in the SON. c. Representative immunofluorescence micrographs using anti-PRR and anti-GFAP antibodies reveal that PRR is little present on astroglia in the SON.

Figure 2. Overexpression of hPRR in the SON of SD rats

a. Representative fluorescence micrographs confirming AAV-mediated transduction of the SON with GFP. b. RT-PCR assay of AAV-mediated-hPRR transduction in the SON. M: DNA marker; 1-3, AAV-hPRR rats; 4-7, AAV-GFP rats; +, positive control. c. Quantitation of hPRR and rPRR mRNA from AAV-transduced SON. †, represents undetectable hPRR.

Figure 3. Effect of PRR overexpression in the SON of SD rats on fluid homeostasis

Twelve weeks following microinjection, H2O intake, urine excretion, urinary osmolality, plasma and urinary AVP of animals were measured. * P<0.05 vs. AAV2-GFP.

Figure 4. Effect of PRR knockdown in the SON of SHR on cardiovascular function

a. ΔMAP and ΔHR compared to baseline values following microinjection of either Sc-shRNA or PRR-shRNA into the SON. * P<0.05 vs. PRR-shRNA. b. Effects of PRR-shRNA on PRR mRNA and plasma AVP level. * P<0.05 vs. Sc-shRNA.