Wang Lei, de Kloet Annette D, Pati Dipanwita, Hiller Helmut, Smith Justin A, Pioquinto David J, Ludin Jacob A, Oh S Paul, Katovich Michael J, Frazier Charles J, Raizada Mohan K, Krause Eric G
Department of Pharmacodynamics, College of Pharmacy, University of Florida, 32611, USA.
Department of Physiology and Functional Genomics, College of Medicine, University of Florida, 32611, USA.
Neuropharmacology. 2016 Jun;105:114-123. doi: 10.1016/j.neuropharm.2015.12.026. Epub 2016 Jan 6.
Over-activation of the brain renin-angiotensin system (RAS) has been implicated in the etiology of anxiety disorders. Angiotensin converting enzyme 2 (ACE2) inhibits RAS activity by converting angiotensin-II, the effector peptide of RAS, to angiotensin-(1-7), which activates the Mas receptor (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.
大脑肾素-血管紧张素系统（RAS）的过度激活与焦虑症的病因有关。血管紧张素转换酶2（ACE2）通过将RAS的效应肽血管紧张素-II转化为血管紧张素-（1-7）来抑制RAS活性，血管紧张素-（1-7）可激活Mas受体（MasR）。增加大脑ACE2活性是否通过刺激中枢MasR来减轻焦虑尚不清楚。为了验证增加大脑ACE2活性通过中枢MasR刺激减少焦虑样行为的假设，我们培育了过表达ACE2的雄性小鼠（ACE2基因敲入小鼠）和野生型同窝对照小鼠（WT）。ACE2基因敲入小鼠在高架十字迷宫（EPM）开放臂中的探索次数显著多于WT，表明增加ACE2活性具有抗焦虑作用。向C57BL/6小鼠脑内注射乙酰氨基阿维菌素（一种ACE2激活剂）也减少了EPM中的焦虑样行为，但向ACE2基因敲入小鼠脑内注射MasR拮抗剂A-779消除了它们的抗焦虑表型，这表明ACE2通过激活中枢MasR来减少焦虑样行为。为了确定介导这些效应的脑回路，我们在EPM暴露后测量了神经元激活标记物Fos，发现ACE基因敲入小鼠终纹床核中的Fos减少，但基底外侧杏仁核（BLA）中的Fos增加。在BLA内，我们确定约62%的γ-氨基丁酸能神经元含有MasR mRNA，并且MasR mRNA的表达通过ACE2过表达而上调，这表明ACE2可能通过MasR激活影响BLA内的γ-氨基丁酸能神经传递。事实上，ACE2过表达与BLA锥体神经元上自发抑制性突触后电流频率增加（表明γ-氨基丁酸的突触前释放）有关，而脑内注射A-779消除了这种效应。总的来说，这些结果表明ACE2可能通过激活中枢MasR来减少焦虑样行为，中枢MasR促进γ-氨基丁酸释放到BLA内的锥体神经元上。
