Abstract
The two axes of the renin–angiotensin system include the classical ACE/Ang II/AT1 axis and the counter-regulatory ACE2/Ang-(1-7)/Mas1 axis. ACE2 is a multifunctional monocarboxypeptidase responsible for generating Ang-(1-7) from Ang II. ACE2 is important in the vascular system where it is found in arterial and venous endothelial cells and arterial smooth muscle cells in many vascular beds. Among the best characterized functions of ACE2 is its role in regulating vascular tone. ACE2 through its effector peptide Ang-(1-7) and receptor Mas1 induces vasodilation and attenuates Ang II-induced vasoconstriction. In endothelial cells activation of the ACE2/Ang-(1-7)/Mas1 axis increases production of the vasodilator’s nitric oxide and prostacyclin’s and in vascular smooth muscle cells it inhibits pro-contractile and pro-inflammatory signaling. Endothelial ACE2 is cleaved by proteases, shed into the circulation and measured as soluble ACE2. Plasma ACE2 activity is increased in cardiovascular disease and may have prognostic significance in disease severity. In addition to its enzymatic function, ACE2 is the receptor for severe acute respiratory syndrome (SARS)-coronavirus (CoV) and SARS-Cov-2, which cause SARS and coronavirus disease-19 (COVID-19) respectively. ACE-2 is thus a double-edged sword: it promotes cardiovascular health while also facilitating the devastations caused by coronaviruses. COVID-19 is associated with cardiovascular disease as a risk factor and as a complication. Mechanisms linking COVID-19 and cardiovascular disease are unclear, but vascular ACE2 may be important. This review focuses on the vascular biology and (patho)physiology of ACE2 in cardiovascular health and disease and briefly discusses the role of vascular ACE2 as a potential mediator of vascular injury in COVID-19.
Highlights
The renin–angiotensin system (RAS) plays a pivotal role in the regulation of blood pressure, electrolyte and water homeostasis, vascular tone and cardiovascular and renal health [1]
Activation is initiated with the release of liver-derived angiotensinogen into the circulation, where it is cleaved by kidney-derived renin into angiotensin I (Ang I) [3], which undergoes further cleavage to angiotensin II (Ang II) by angiotensin-converting enzyme (ACE), expressed mainly in pulmonary endothelial cells (Figure 1)
Clinical studies demonstrated increased expression of ACE2 in cardiomyocytes and vascular cells in hearts from patients who were treated with ACE inhibitors (ACEi) compared with those treated with angiotensin receptor blockers (ARB) [59]
Summary
The renin–angiotensin system (RAS) plays a pivotal role in the regulation of blood pressure, electrolyte and water homeostasis, vascular tone and cardiovascular and renal health [1]. It has been proposed that physiological stretch up-regulates vascular smooth muscle cell ACE2, which inhibits proliferation and migration, likely through increased Ang-(1-7)/Mas1 signalling [57]. Clinical studies demonstrated increased expression of ACE2 in cardiomyocytes and vascular cells in hearts from patients who were treated with ACE inhibitors (ACEi) compared with those treated with angiotensin receptor blockers (ARB) [59].
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