Angiotensinogen, a prohormone, is synthesized and secreted mainly by the liver but also from other tissues (reviewed in Fyhrquist and Saijonmaa 2008, Cat and Touyz 2011). Renin, an aspartyl protease specific for angiotensinogen, is secreted into the bloodstream by juxtaglomerular cells of the kidney in response to a drop in blood pressure. Renin cleaves angiotensinogen to yield a decapaptide, angiotensin I (angiotensin-1, angiotensin-(1-10)). Circulating renin can also bind the membrane-localized (pro)renin receptor (ATP6AP2) which increases its catalytic activity. After cleavage of angiotensinogen to angiotensin I by renin, two C-terminal amino acid residues of angiotensin I are removed by angiotensin-converting enzyme (ACE), located on the surface of endothelial cells, to yield angiotensin II (angiotensin-2, angiotensin-(1-8)), the active peptide that causes vasoconstriction, resorption of sodium and chloride, excretion of potassium, water retention, and aldosterone secretion.
More recently other, more tissue-localized pathways leading to angiotensin II and alternative derivatives of angiotensinogen have been identified (reviewed in Kramkowski et al. 2006, Kumar et al. 2007, Fyhrquist and Saijonmaa 2008, Becari et al. 2011). Chymase, cathepsin G, and cathepsin X (cathepsin Z) can each cleave angiotensin I to yield angiotensin II. Angiotensin-converting enzyme 2 (ACE2) cleaves 1 amino acid residue from angiotensin I (angiotensin-(1-10)) to yield angiotensin-(1-9), which can be cleaved by ACE to yield angiotensin-(1-7). ACE2 can also cleave angiotensin II to yield angiotensin-(1-7). Neprilysin can cleave either angiotensin-(1-9) or angiotensin I to yield angiotensin-(1-7). Angiotensin-(1-7) binds the MAS receptor (MAS1, MAS proto-oncogene) and, interestingly, produces effects opposite to those produced by angiotensin II.
Aminopeptidase A (APA, ENPEP) cleaves angiotensin II to yield angiotensin III (angiotensin-(2-8)), which is then cleaved by aminopeptidase N (APN, ANPEP) yielding angiotensin IV (angiotensin-(3-8)). Angiotensin IV binds the AT4 receptor (AT4R, IRAP, LNPEP, oxytocinase).
Inhibitors of renin (e.g. aliskiren) and ACE (e.g. lisinopril, ramipril) are currently used to treat hypertension (reviewed in Gerc et al. 2009, Verdecchia et al. 2010, Alreja and Joseph 2011).