The RAS (renin-angiotensin system) is composed of two arms: the pressor arm containing AngII (angiotensin II)/ACE (angiotensin-converting enzyme)/AT1Rs (AngII type 1 receptors), and the depressor arm represented by Ang-(1-7) [angiotensin-(1-7)]/ACE2/Mas receptors. All of the components of the RAS are present in the brain. Within the brain, Ang-(1-7) contributes to the regulation of BP (blood pressure) by acting at regions that control cardiovascular function such that, when Ang-(1-7) is injected into the nucleus of the solitary tract, caudal ventrolateral medulla, paraventricular nucleus or anterior hypothalamic area, a reduction in BP occurs; however, when injected into the rostral ventrolateral medulla, Ang-(1-7) stimulates an increase in BP. In contrast with AngII, Ang-(1-7) improves baroreflex sensitivity and has an inhibitory neuromodulatory role in hypothalamic noradrenergic neurotransmission. Ang-(1-7) not only exerts effects related to BP regulation, but also acts as a cerebroprotective component of the RAS by reducing cerebral infarct size and neuronal apoptosis. In the present review, we provide an overview of effects elicited by Ang-(1-7) in the brain, which suggest a potential role for Ang-(1-7) in controlling the central development of hypertension.

Ang-(1-7) [angiotensin-(1-7)] constitutes an important functional end-product of the RAS (renin-angiotensin system) endogenously formed from AngI (angiotensin I) or AngII (angiotensin II) through the catalytic activity of ACE2 (angiotensin-converting enzyme 2), prolyl carboxypeptidase, neutral endopeptidase or other endopeptidases. Ang-(1-7) lacks the pressor, dipsogenic or stimulatory effect on aldosterone release characteristic of AngII. In contrast, it produces vasodilation, natriuresis and diuresis, and inhibits angiogenesis and cell growth. At the central level, Ang-(1-7) acts at sites involved in the control of cardiovascular function, thus contributing to blood pressure regulation. This action may result from its inhibitory neuromodulatory action on NE [noradrenaline (norepinephrine)] levels at the synaptic cleft, i.e. Ang-(1-7) reduces NE release and synthesis, whereas it causes an increase in NE transporter expression, contributing in this way to central NE neuromodulation. Thus, by selective neurotransmitter release, Ang-(1-7) may contribute to the overall central cardiovascular effects. In the present review, we summarize the central effects of Ang-(1-7) and the mechanism by which the peptide modulates NE levels in the synaptic cleft. We also provide new evidences of its cerebroprotective role.

Aberrations in the ubiquitin-proteasome system (UPS) are implicated in the pathogenesis of various diseases. Tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamines biosynthesis, is involved in hypertension development. In this study we investigated whether UPS regulated TH turnover in PC12 cells and hypothalamic and brainstem neurons from spontaneously hypertensive rats (SHR) and whether this system was impaired in hypertension. PC12 cells were exposed to proteasome or lysosome inhibitors and TH protein level evaluated by Western blot. Lactacystin, a proteasome inhibitor, induced an increase of 86±15% in TH levels after 30 min of incubation, then it started to decrease up to 6 h to reach control levels and finally it rose up to 35.2±8.5% after 24 h. Bafilomycin, a lysosome inhibitor, did not alter TH protein levels during short times, but it increased TH by 92±22% above basal after 6 h treatment. Before degradation proteasome substrates are labeled by conjugation with ubiquitin. Efficacy of proteasome inhibition on TH turnover was evidenced by accumulation of ubiquitinylated TH after 30 min. Further, the inhibition of proteasome increased the quantity of TH phosphorylated at Ser40, which is essential for TH activity, by 2.7±0.3 fold above basal. TH protein level was upregulated in neurons from hypothalami and brainstem of SHR when the proteasome was inhibited during 30 min, supporting that neuronal TH is also short-term regulated by the proteasome. Since the increased TH levels reported in hypertension may result from proteasome dysfunction, we evaluate proteasme activity. Proteasome activity was significantly reduced by 67±4% in hypothalamic and brainstem neurons from SHR while its protein levels did not change. Present findings show that TH is regulated by the UPS. The impairment in proteasome activity observed in SHR neurons may be one of the causes of the increased TH protein levels reported in hypertension.

The MAS1 receptor (R) exerts protective effects in the brain, heart, vessels and kidney. R trafficking plays a critical function in signal termination and propagation and in R resensitization. We examined MAS1R internalization and trafficking upon agonist stimulation and the role of β-arrestin2 in the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and Akt following MAS1R stimulation. Human embryonic kidney 293T cells were transfected with the coding sequence for MAS1R-YFP. MAS1R internalization was evaluated by measuring the MAS1R present in the plasma membrane after agonist stimulation using a ligand-binding assay. MAS1R trafficking was evaluated by its colocalization with trafficking markers. MAS1R internalization was blocked in the presence of shRNAcaveolin-1 and with dominant negatives for Eps15 (a protein involved in endocytosed Rs by clathrin-coated pits (CCP)) and for dynamin. After stimulation, MAS1R colocalized with Rab11, a slow recycling vesicle marker, and not with Rab4, a fast recycling vesicle marker, or LysoTracker, a lysosome marker. Cells transfected with MAS1R showed an increase in Akt and ERK1/2 activation upon Ang-(1-7) stimulation, which was blocked when the CCP pathway was blocked. Suppression of β-arrestin2 by shRNA reduced the Ang-(1-7)-induced ERK1/2 activation, while Akt activation was not modified. We conclude that upon agonist stimulation, MAS1R is internalized through CCP and caveolae in a dynamin-dependent manner and is then slowly recycled back to the plasma membrane. MAS1R induced Akt and ERK1/2 activation from early endosomes, and the activation of ERK1/2 was mediated by β-arrestin2. Thus, MAS1R activity and density may be tightly controlled by the cell.

Shiga toxin 2 (Stx2) from enterohemorrhagic Escherichia coli (EHEC) produces hemorrhagic colitis, hemolytic uremic syndrome (HUS) and acute encephalopathy. The mortality rate in HUS increases significantly when the central nervous system (CNS) is involved. Besides, EHEC also releases lipopolysaccharide (LPS). Many reports have described cognitive dysfunctions in HUS patients, the hippocampus being one of the brain areas targeted by EHEC infection. In this context, a translational murine model of encephalopathy was employed to establish the deleterious effects of Stx2 and the contribution of LPS in the hippocampus. Results demonstrate that systemic administration of a sublethal dose of Stx2 reduced memory index and produced depression like behavior, pro-inflammatory cytokine release and NF-kB activation independent of the ERK 1/2 signaling pathway. On the other hand, LPS activated NF-kB dependent on ERK 1/2 signaling pathway. Cotreatment of Stx2 with LPS aggravated the pathologic state, while dexamethasone treatment succeeded in preventing behavioral alterations. Our present work suggests that the use of drugs such as corticosteroids or NF-kB signaling inhibitors may serve as neuroprotectors from EHEC infection.

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