Differential expression of neuronal ACE2 in transgenic mice with overexpression of the brain renin-angiotensin system

Abstract

Angiotensin-converting enzyme 2 (ACE2) is a newly discovered carboxy-peptidase responsible for the formation of vasodilatory peptides such as angiotensin-(1-7). We hypothesized that ACE2 is part of the brain renin-angiotensin system, and its expression is regulated by the other elements of this system. ACE2 immunostaining was performed in transgenic mouse brain sections from neuron-specific enolase-AT(1A) (overexpressing AT(1A) receptors), R(+)A(+) (overexpressing angiotensinogen and renin), and control (nontransgenic littermates) mice. Results show that ACE2 staining is widely distributed throughout the brain. Using cell-type-specific antibodies, we observed that ACE2 staining is present in the cytoplasm of neuronal cell bodies but not in glial cells. In the subfornical organ, an area lacking the blood-brain barrier and sensitive to blood-borne angiotensin II, ACE2 was significantly increased in transgenic mice. Interestingly, ACE2 mRNA and protein expression were inversely correlated in the nucleus of tractus solitarius/dorsal motor nucleus of the vagus and the ventrolateral medulla, when comparing transgenic to nontransgenic mice. These results suggest that ACE2 is localized to the cytoplasm of neuronal cells in the brain and that ACE2 levels appear highly regulated by other components of the renin-angiotensin system, confirming its involvement in this system. Moreover, ACE2 expression in brain structures involved in the control of cardiovascular function suggests that the carboxypeptidase may have a role in the central regulation of blood pressure and diseases involving the autonomic nervous system, such as hypertension.

Overexpression of Angiotensin-Converting Enzyme 2 in the Rostral Ventrolateral Medulla Causes Long-Term Decrease in Blood Pressure in the Spontaneously Hypertensive Rats

“…The staining was primarily localized in the neuronal cell body but was not restricted to it, because axonal processes of some neurons were also stained. This distribution was consistent with the distribution of ACE2 in mouse brain reported by Doobay et al 14 They demonstrated the presence of ACE2 immunoreactivity in neurons of subfornical organ, the paraventricular nucleus, the area postrema, the dorsal motor nucleus of the vagus, the nucleus tractus solitarius (NTS), the nucleus ambiguus, and the RVLM. Localization of ACE2 in these discrete cardiovascular-regulatory nuclei was our initial indication that this enzyme may play a critical role in BP control and hypertension.…”

“…12 In addition, ACE2 gene transfer both lowers blood pressure (BP) and improves cardiac pathology in the SHR. 13 In spite of these dramatic beneficial effects of ACE2 in the peripheral system and the observation that ACE2 is present in various cardiovascular regulatory brain areas, 14,15 the role of this enzyme in neural control of BP has not been delineated. These observations, coupled with the importance of the RVLM in central cardiovascular regulation, led us to propose the following hypothesis: ACE2 expression is decreased in the RVLM in hyper-tensive rats, and, thus, its overexpression would lead to beneficial effects on BP.…”

Angiotensin II regulates ACE and ACE2 in neurons through p38 mitogen-activated protein kinase and extracellular signal-regulated kinase 1/2 signaling

“…In the present study, we demonstrated that ACE and ACE2 are expressed in the cell membrane and cytoplasm of CATH.a neurons and that ANG II modulates these two enzymes in opposite directions. The subcellular localization of ACE2 agrees with previous in vitro studies (8,13); however, it is not clear if ACE is localized in the cytoplasm as well as in the membrane. The increase in the ratio of ACE to ACE2 correlates with results in animal models of heart failure or hypertension (1,13).…”

“…For this reason, ACE and ACE2 expression in neurons and glial cells inside the blood-brain barrier is important. On the other hand, ACE2 is also present in brain centers that control cardiovascular function and is associated with AT 1 R expression (8,16). In the present study, we demonstrated that ACE and ACE2 are expressed in the cell membrane and cytoplasm of CATH.a neurons and that ANG II modulates these two enzymes in opposite directions.…”

Characterization of Carboxypeptidase A6, an Extracellular Matrix Peptidase

“…A possibility in the production of angiotensin II exists in which angiotensin-converting enzyme-2 (ACE2) removes Leu 10 of angiotensin I followed by the removal of His 9 by CPA6. ACE2 is widely distributed throughout the brain, including the olfactory bulb, but is incapable of removing His 9 to produce angiotensin II (46). The function of angiotensin within the brain is in the regulation of water and sodium intake and the control of sympathoadrenal systems (47).…”