Brain-Targeted Angiotensin-Converting Enzyme 2 Overexpression Attenuates Neurogenic Hypertension by Inhibiting Cyclooxygenase-Mediated Inflammation

Abstract

Overactivity of the renin angiotensin system (RAS), oxidative stress, and cyclooxygenases (COX) in the brain are implicated in the pathogenesis of hypertension. We previously reported that Angiotensin-Converting Enzyme 2 (ACE2) overexpression in the brain attenuates the development of DOCA-salt hypertension, a neurogenic hypertension model with enhanced brain RAS and sympathetic activity. To elucidate the mechanisms involved, we investigated whether oxidative stress, mitogen activated protein kinase signaling and cyclooxygenase (COX) activation in the brain are modulated by ACE2 in neurogenic hypertension. DOCA-salt hypertension significantly increased expression of Nox-2 (+61 ±5 %), Nox-4 (+50 ±13 %) and nitrotyrosine (+89 ±32 %) and reduced activity of the antioxidant enzymes, catalase (−29 ±4 %) and SOD (−31 ±7 %), indicating increased oxidative stress in the brain of non-transgenic mice. This increased oxidative stress was attenuated in transgenic mice overexpressing ACE2 in the brain. DOCA-salt-induced reduction of nNOS expression (−26 ±7 %) and phosphorylated eNOS/total eNOS (−30 ±3 %), and enhanced phosphorylation of Akt and ERK1/2 in the paraventricular nucleus (PVN), were reversed by ACE2 overexpression. In addition, ACE2 overexpression blunted the hypertension-mediated increase in gene and protein expression of COX-1 and COX-2 in the PVN. Furthermore, gene silencing of either COX-1 or COX-2 in the brain, reduced microglial activation and accompanied neuro-inflammation, ultimately attenuating DOCA-salt hypertension. Together, these data provide evidence that brain ACE2 overexpression reduces oxidative stress and COX-mediated neuro-inflammation, improves anti-oxidant and nitric oxide signaling, and thereby attenuates the development of neurogenic hypertension.

Kinin B1 Receptor Promotes Neurogenic Hypertension Through Activation of Centrally Mediated Mechanisms

“…Previous findings have emphasized the role of inflammatory cytokines in the PVN in mediating sympatho-excitation and autonomic function during various cardiovascular diseases, including hypertension. 4, 5, 30 In our study, we found that B1R gene deletion reversed the DOCA-salt hypertension-induced autonomic dysfunction and sympatho-excitation, and improved baroreflex sensitivity, suggesting a central role for B1R activation during neurogenic hypertension.…”

“…5 To assess the effects of B1R deletion on baroreflex function, we determined spontaneous baroreflex sensitivity (SBRS) using the sequence method. SBRS was significantly reduced in WT+DOCA mice compared to sham (Figure 2F).…”

“…5 Notably, we investigated the gene and protein expression of Nox2, a catalytic subunit of NADPH Oxidase and iNOS in the PVN. Real time RT-PCR analysis showed significant increases in Nox2 and iNOS gene expression in the PVN of WT+DOCA mice but not in B1RKO+DOCA mice (Supplemental Figure S5).…”

“…Recent studies from our group and others demonstrate a link between inflammation and activated renin angiotensin system in neurogenic hypertension. 3–5, 30 Inflammation in the brain involves primarily the activation of microglia. We have previously shown that neurogenic hypertension involves activation of microglia in the PVN and indeed inhibition of PVN microglia activation fully abolishes Ang-II-induced hypertension.…”

“…4, 5 ASK1 was identified as a ROS-sensitive MAPK kinase kinase, which activates the c-jun-terminal kinase (JNK) and p44/42 MAPK (ERK1/2) cascade. 33 Activation of kinin B1R with a selective agonist either in vitro or in vivo enhanced aortic superoxide anion production through activation of NADPH oxidase, which was abolished by apocynin, a selective inhibitor of NADPH oxidase.…”