Vascular Endothelial Adrenomedullin-RAMP2 System Is Essential for Vascular Integrity and Organ Homeostasis

Abstract

Background-Revealing the mechanisms underlying the functional integrity of the vascular system could make available novel therapeutic approaches. We previously showed that knocking out the widely expressed peptide adrenomedullin (AM) or receptor activity-modifying protein 2 (RAMP2), an AM-receptor accessory protein, causes vascular abnormalities and is embryonically lethal. Our aim was to investigate the function of the vascular AM-RAMP2 system directly. Methods and Results-We generated endothelial cell-specific RAMP2 and AM knockout mice (E-RAMP2 −/− and E-AM−/− mice died perinatally. In surviving adults, vasculitis occurred spontaneously. With aging, E-RAMP2 −/− mice showed severe organ fibrosis with marked oxidative stress and accelerated vascular senescence. Later, liver cirrhosis, cardiac fibrosis, and hydronephrosis developed. We next used a line of drug-inducible E-RAMP2 −/− mice (DI-E-RAMP2 −/− ) to induce RAMP2 deletion in adults, which enabled us to analyze the initial causes of the aforementioned vascular and organ damage. Early after the induction, pronounced edema with enhanced vascular leakage occurred. In vitro analysis revealed the vascular leakage to be caused by actin disarrangement and detachment of endothelial cells. We found that the AM-RAMP2 system regulates the Rac1-GTP/RhoA-GTP ratio and cortical actin formation and that a defect in this system causes the disruption of actin formation, leading to vascular and organ damage at the chronic stage after the gene deletion. Conclusions -Our findings show that the AM-RAMP2 system is a key determinant of vascular integrity and homeostasis from prenatal stages through adulthood. Furthermore, our models demonstrate how endothelial cells regulate vascular integrity and how their dysregulation leads to organ damage. (Circulation. 2013;127:842-853.)

Functional differentiation of RAMP2 and RAMP3 in their regulation of the vascular system

“…We previously showed that RAMP2 is essential for angiogenesis and vascular homeostasis in both embryos and adults [17,18]. In the present study, we found that the phenotypes of RAMP2−/− and RAMP3−/− mice are strikingly different: whereas RAMP2−/− mice die in utero due to vascular abnormalities, RAMP3−/− mice are born normally with no blood vessel or lymphatic abnormalities.…”

“…More recently, we developed drug-inducible vascular endothelial cell-specific RAMP2−/− (DI-VE-RAMP2−/−) mice, with which we can induce RAMP2 gene deletion in adults. Using this model, we found that RAMP2 is essential for angiogenesis and vascular homeostasis in adults, as DI-VE-RAMP2−/ − mice exhibit vascular structural abnormalities and spontaneously develop vascular inflammation and organ fibrosis [18]. Collectively, these findings indicate that the AM-RAMP2 system is essential for angiogenesis and vascular homeostasis throughout a mouse's life, from embryo to adult.…”

Adrenomedullin regulates intestinal physiology and pathophysiology

“…And RAMP2 À/À embryos also die in utero at midgestation due to severe deformation, vascular fragility, severe edema, and hemorrhage [65]. Very recent studies with endothelial cell-specific RAMP2 KO mice have confirmed that the AM-RAMP2 system is a key determinant of vascular integrity and homeostasis from prenatal stages to adulthood [66]. Surprisingly, a complete absence of RAMP3 has no effect on survival [67].…”

“…Although AM is a vasodilator when injected peripherally, it acts as a vasoconstrictor when it is injected into the brain, through stimulation of sympathetic nervous system [74]. Moreover, AM and PAMP are well known for being potent angiogenic agents [75], they are necessary to maintain the integrity of the microvasculature [66] and promote a faster healing of epithelial wounds [76].…”

The Ins and Outs of Small GTPase Rac1 in the Vasculature

“…Ras homolog gene family, member A (RhoA), cell division control protein 42 (Cdc42), and protein superfamily of small GTPases (Ras)-related C3 botulinum toxin substrate 1 (Rac1)-the Rho GTPases-have been implicated in various vascular diseases, such as atherosclerosis, hypertension, diabetes, vascular leakage, angiogenesis, and aneurysm formation (Ferri et al, 2013;Jin et al, 2013;Khan et al, 2013;Koyama et al, 2013;Marinkovic et al, 2013;Nagase, 2013;Boissier and Huynh-Do, 2014;Liu et al, 2014;Sun et al, 2014;Varela et al, 2014). Rac1 is well recognized for its role in actin remodeling and the induction of membrane protrusions, but it also has several other downstream effects, such as activation of NADPH oxidases or cell-surface receptor-mediated signaling resulting in an inflammatory response (Ambriz-Pena et al, 2014;Cuadrado et al, 2014;D'Ambrosi et al, 2014;Marinkovic et al, 2014b).…”