Neuronal over-expression of ACE2 protects brain from ischemia-induced damage

Abstract

Angiotensin (Ang) II exaggerates cerebral injury in ischemic damage. Angiotensin-converting enzyme type 2 (ACE2) converts Ang II into Ang (1–7) and thus, may protect against the effects of Ang II. We hypothesized that neuronal ACE2 over-expression decreases ischemic stroke in mice with Ang II overproduction. Human renin and angiotensinogen double transgenic (RA) mice and RA mice with neuronal over-expression of ACE2 (SARA) were used for the study. The mean arterial pressure (MAP) was calculated from telemetry-recorded blood pressure (BP). SARA mice were infused peripherally with Norepinephrine to “clamp” the BP, or intracerebroventricularly-infused with a Mas receptor antagonist (A-779). Middle cerebral artery occlusion (MCAO) surgery was performed to induce permanent focal ischemic stroke. Cerebral blood flow (CBF) and neurological function were determined. Two days after surgery, brain samples were collected for various analyses. Results showed: 1) When compared to chronically hypertensive RA mice, SARA mice had lower basal MAP, less MCAO-induced infarct volume, and increased CBF, neurological function and cerebral microvascular density in the peri-infarct area; 2) These changes in SARA mice were not altered after MAP “clamping”, but partially reversed by brain infusion of A-779; 3) Ang (1–7)/Ang II ratio, angiogenic factors, endothelial nitric oxide synthase (eNOS) expression and nitric oxide production were increased, whereas, NADPH oxidase subunits and reactive oxygen species were decreased in the brain of SARA mice. ACE2 protects brain from ischemic injury via the regulation of NADPH oxidase/eNOS pathways by changing Ang (1–7)/Ang II ratio, independently of MAP changes.

Angiotensin-(1–7) counteracts the effects of Ang II on vascular smooth muscle cells, vascular remodeling and hemorrhagic stroke: Role of the NFкB inflammatory pathway

“…After 24 hrs, mice were euthanized under an overdose of pentobarbital (150 mg/kg i.p). The doses used for Ang II (42 μg/kg/h), Ang-(1-7) (24 μg/kg/h) and A-779 (200 ng/kg/min) were based on previous studies [5, 18, 19]. …”

“…A radiotelemetry system (TA11PA-C10, Data Science International) was used for recording arterial BP under anesthesia by inhaling 2.5% isoflurane as we reported previously [5]. The telemetric probes were implanted in the left carotid artery.…”

“…To keep the sections from the similar level in each animal, the brains sections (20 μm) were sequentially put into six separate wells of a 6-well plate containing 2 ml of phosphate-buffered saline as we reported before [5, 24]. In total, three slices (sequentially from each well) of each brain were used for HE staining to present the data of MCA remodeling for each brain.…”

“…Centrally administered Ang-(1-7) increases the survival of stroke-prone spontaneously hypertensive rats (SHRSP) [4]. Our recent study demonstrated that neuron angiotensin converting enzyme 2 (ACE2) over-expression, which catalyzes Ang II into Ang-(1-7), protects brain from ischemic stroke injury [5]. However, it is unknown whether Ang-(1-7) might provide vascular protective effects on ICH by counteracting the deleterious effects of Ang II and ultimately possess great potential for the prevention and treatment of ICH.…”

Activation of the Neuroprotective Angiotensin-Converting Enzyme 2 in Rat Ischemic Stroke

“…The ACE2/Ang-(1-7)/Mas pathway has been highlighted as a promising target for induction of stroke neuroprotection 4 , and has proven efficacy in reducing infarct size and improving neurological function in preclinical models of ischemic 5-11 and hemorrhagic stroke 12 . Stroke neuroprotection has been demonstrated in both young 5, 6 and aged 10 animals, and methods for activating the axis have included direct intracerebroventricular administration of Ang-(1-7) 5, 7, 11 , delivery of ACE2-primed endothelial progenitor cells 8 , and neuronal ACE2 overexpression 9 . Pharmacological activation of this axis has recently become more feasible with the identification of diminazene aceturate, trade name Berenil®, as an activator of ACE2 13 .…”