Polymorphisms at the F12 and KLKB1 loci have significant trait association with activation of the renin-angiotensin system

BACKGROUND: Plasma coagulation Factor XIIa (Hageman factor; encoded by F12) and kallikrein (KAL or Fletcher factor; encoded by KLKB1) are proteases of the kallikerin-kinin system involved in converting the inactive circulating prorenin to renin. Renin is a key enzyme in the formation of angiotensin II, which regulates blood pressure, fluid and electrolyte balance and is a biomarker for cardiovascular, metabolic and renal function. The renin-angiotensin system is implicated in extinction learning in posttraumatic stress disorder. METHODS & RESULTS: Active plasma renin was measured from two independent cohorts- civilian twins and siblings, as well as U.S. Marines, for a total of 1,180 subjects. Genotyping these subjects revealed that the carriers of the minor alleles at the two loci- F12 and KLKB1 had a significant association with reduced levels of active plasma renin. Meta-analyses confirmed the association across cohorts. In vitro studies verified digestion of human recombinant pro-renin by kallikrein (KAL) to generate active renin. Subsequently, the active renin was able to digest the synthetic substrate angiotensinogen to angiotensin-I. Examination of mouse juxtaglomerular cell line and mouse kidney sections showed co-localization of KAL with renin. Expression of either REN or KLKB1 was regulated in cell line and rodent models of hypertension in response to oxidative stress, interleukin or arterial blood pressure changes. CONCLUSIONS: The functional variants of KLKB1 (rs3733402) and F12 (rs1801020) disrupted the cascade of enzymatic events, resulting in diminished formation of active renin. Using genetic, cellular and molecular approaches we found that conversion of zymogen prorenin to renin was influenced by these polymorphisms. The study suggests that the variant version of protease factor XIIa due to the amino acid substitution had reduced ability to activate prekallikrein to KAL. As a result KAL has reduced efficacy in converting prorenin to renin and this step of the pathway leading to activation of renin affords a potential therapeutic target

Transendothelial transport of renin-angiotensin system components

BACKGROUND: Vascular (interstitial) angiotensin (ANG) II production depends on circulating renin-angiotensin system (RAS) components. Mannose 6-phosphate (man-6-P) receptors and angiotensin II type 1 (AT(1)) receptors, via binding and internalization of (pro)renin and ANG II, respectively, could contribute to the transportation of these components across the endothelium. OBJECTIVE: To investigate the mechanism(s) contributing to transendothelial RAS component transport. METHODS: Human umbilical vein endothelial cells were cultured on transwell polycarbonate filters, and incubated with RAS components in the absence or presence of man-6-P, eprosartan or PD123319, to block man-6-P, AT(1) and angiotensin II type 2 (AT(2)) receptors, respectively. RESULTS: Apically applied (pro)renin and angiotensinogen slowly entered the basolateral compartment, in a similar manner as horseradish peroxidase, a molecule of comparable size that reaches the interstitium via diffusion only. Prorenin transport was unaffected by man-6-P. Apical ANG I and ANG II rapidly reached the basolateral fluid independent of AT(1) and AT(2) receptors. Basolateral ANG II during apical ANG I application was as high as apical ANG II, whereas during apical ANG II application it was lower. During basolateral ANG I application, ANG II generation occurred basolaterally only, in an angiotensin-converting enzyme (ACE)-dependent manner. CONCLUSIONS: Circulating (pro)renin, angiotensinogen, ANG I and ANG II enter the interstitium via diffusion, and interstitial ANG II generation is mediated, at least in part, by basolaterally located endothelial ACE