Increasing brain angiotensin converting enzyme 2 activity decreases anxiety-like behavior in male mice by activating central Mas receptors

Abstract

Over-activation of brain renin-angiotensin system (RAS) has been implicated in the etiology of anxiety disorders. Angiotensin converting enzyme (ACE2) inhibits RAS activity by converting angiotensin II, the effector peptide of RAS, to angiotensin-(1-7), which activates Mas receptors (MasR). Whether increasing brain ACE2 activity reduces anxiety by stimulating central MasR is unknown. To test the hypothesis that increasing brain ACE2 activity reduces anxiety-like behavior via central MasR stimulation, we generated male mice overexpressing ACE2 (ACE2 KI mice) and wild type littermate controls (WT). ACE2 KI mice explored the open arms of the elevated plus maze (EPM) significantly more than WT, suggesting increasing ACE2 activity is anxiolytic. Central delivery of diminazene aceturate, an ACE2 activator, to C57BL/6 mice also reduced anxiety-like behavior in the EPM, but centrally administering ACE2 KI mice A-779, a MasR antagonist, abolished their anxiolytic phenotype, suggesting that ACE2 reduces anxiety-like behavior by activating central MasR. To identify the brain circuits mediating these effects, we measured Fos, a marker of neuronal activation, subsequent to EPM exposure and found that ACE2 KI mice had decreased Fos in the bed nucleus of stria terminalis but had increased Fos in the basolateral amygdala (BLA). Within the BLA, we determined that ~62% of GABAergic neurons contained MasR mRNA and expression of MasR mRNA was upregulated by ACE2 overexpression, suggesting that ACE2 may influence GABA neurotransmission within the BLA via MasR activation. Indeed, ACE2 overexpression was associated with increased frequency of spontaneous inhibitory postsynaptic currents (indicative of presynaptic release of GABA) onto BLA pyramidal neurons and central infusion of A-779 eliminated this effect. Collectively, these results suggest that ACE2 may reduce anxiety-like behavior by activating central MasR that facilitate GABA release onto pyramidal neurons within the BLA.

The intricacies of the renin-angiotensin-system in metabolic regulation

“…Consistent with a role for this protective axis in the neural regulation of energy balance, ACE2 has been localized to many relevant brain regions such as the PVN, arcuate and NTS [140]. Similarly, immunohistochemical and in situ hybridization studies have localized the MasR to many such brain regions [141–143] and we have detected MasR mRNA in the basolateral amygdala [138]. …”

“…Second, ACE2 also elevates Ang-(1-7) levels which can then activate the MasR in various brain regions. This Ang-(1-7)/MasR pathway has been implicated in various brain functions, including anxiety-like behavior, the neural regulation of cardiovascular function and neuroendocrine secretion, among many others [138, 139]. Consistent with a role for this protective axis in the neural regulation of energy balance, ACE2 has been localized to many relevant brain regions such as the PVN, arcuate and NTS [140].…”

Angiotensin Type-2 Receptors Influence the Activity of Vasopressin Neurons in the Paraventricular Nucleus of the Hypothalamus in Male Mice

“…ALZET osmotic minipumps and Brain Infusion Kits (DURECT Corporation, Cupertino, CA) for the chronic delivery of C21 (7.5 ng/kg/h for one week) or aCSF control into the lateral cerebral ventricle (icv) were prepared according to the manufacturer's instructions. After allowing the pumps to prime, by incubating them in a 37°C water bath for a minimum of 48 hours, pumps and infusion kits were implanted using a Kopf stereotaxic device as described (29).…”

Significance of angiotensin 1–7 coupling with MAS1 receptor and other GPCRs to the renin‐angiotensin system: IUPHAR Review 22

“…The overexpression of ACE2 in the brain was found to activate central MAS1‐induced spontaneous postsynaptic inhibitory currents, indicative of presynaptic GABA release onto pyramidal neurons, which reduced anxiety‐like behaviour in mice; the MAS1 antagonist A‐779 eliminated this effect. Furthermore, centrally administering A‐779 abolished the anxiolytic phenotype in ACE2‐null mice (Oscar et al, ; Fontes et al, ; Wang et al, ). Indeed, activation of the brain Ang(1–7)/MAS1 axis in hypertensive transgenic (mRen2)27 rats lowered BP and attenuated cardiac remodelling by improving the autonomic balance (Kangussu et al, ).…”

“…Central Ang(1–7) treatment of hypertensive (mRen2)27 transgenic rats attenuates the anxiety and depression‐like behaviour in these animals (Almeida‐Santos et al, ; Wang et al, ). In a chronic constriction injury rat model, intrathecal administration of Ang(1–7) relieves, whereas A‐779 aggravates injury‐induced neuropathic pain (Zhao et al, ).…”