The (pro)renin receptor is cleaved by ADAM19 in the Golgi leading to its secretion into extracellular space

(Pro)renin receptor is associated with angiogenic activity in proliferative diabetic retinopathy

AIMS/HYPOTHESIS

The renin-angiotensin system (RAS) potentially has a role in the development of end-organ damage, and tissue RAS activation has been suggested as a risk factor for diabetic retinopathy. We have recently shown significant involvement of (pro)renin receptor ([P]RR) in retinal inflammation in a rodent model of early diabetes. In this study we aim to elucidate the (P)RR-associated pathogenesis of fibrovascular proliferation, a late-stage angiogenic complication in human diabetic retinopathy.

METHODS

Vitreous fluids from 23 eyes of patients with proliferative diabetic retinopathy (PDR) and 16 eyes of controls with non-diabetic, idiopathic macular diseases (macular hole and epiretinal membrane) were collected. Protein levels of soluble (P)RR were measured by ELISA, and immunofluorescence was performed to assess the localisation of (P)RR and related molecules in fibrovascular tissues from PDR eyes.

RESULTS

(P)RR immunoreactivity was detected in neovascular endothelial cells, colocalised with prorenin, phosphorylated extracellular signal-regulated kinase (ERK) and vascular endothelial growth factor (VEGF). Prorenin application to human retinal microvascular endothelial cells significantly upregulated mRNA expression of VEGF, especially the VEGF165 isoform, which was abolished by (P)RR or ERK signalling blockade. Proteases known to cleave (P)RR, including furin, were positive in endothelial cells in fibrovascular tissues. Protein levels of soluble (P)RR in vitreous fluids were higher in PDR eyes than in non-diabetic control eyes, and correlated significantly with vitreous prorenin and VEGF levels and the vascular density of fibrovascular tissues.

CONCLUSIONS/INTERPRETATION

Our data using human samples provide the first evidence that (P)RR is associated with angiogenic activity in PDR.

Soluble (pro)renin receptor and blood pressure during pregnancy: a prospective cohort study

The renin-angiotensin system is believed to influence blood pressure (BP) during pregnancy, but the associations between BP during pregnancy and the soluble form of the (pro)renin receptor (s[P]RR), a new component of the tissue renin-angiotensin system, remain undetermined. In this prospective cohort study of 437 pregnant women with normal BP (systolic <140 mm Hg and diastolic <90 mm Hg) during early pregnancy (<16 weeks of gestation) regression analysis was performed to examine the associations between plasma s(P)RR concentrations and BP in 3 gestational stages (20-24, 28-32, and 36-40 weeks of gestation) and logistic regression analysis to evaluate the incidence of preeclampsia. Plasma s(P)RR concentrations at early, middle (16-28 weeks), and late pregnancy (>28 weeks) and at delivery averaged 29.7 ± 10.0, 31.3 ± 12.0, 39.2 ± 8.9, and 40.4 ± 10.2 ng/mL (mean ± SD), respectively. A 1-ng/mL increase in plasma s(P)RR concentration in early pregnancy predicted systolic/diastolic BP elevation in the later 3 gestational stages: 0.11 (95% CI, 0.014-0.20)/0.093 (0.027-0.16) mm Hg for 20 to 24 weeks, 0.11 (0.029-0.19)/0.088 (0.027-0.15) mm Hg for 28 to 32 weeks, and 0.16 (0.058-0.26)/0.12 (0.043-0.19]) mm Hg for 36 to 40 weeks, respectively. Plasma s(P)RR concentrations in middle and late pregnancy were not associated with BP. Adjusted models revealed that women with plasma s(P)RR concentrations above the 75th percentile at delivery had a significantly increased risk of preeclampsia (odds ratio, 22.5 [95% CI, 1.8-279.9]). In conclusion, high circulating levels of s(P)RR at early pregnancy predicted a subsequent elevation in BP, and high concentrations at delivery were significantly associated with preeclampsia.

The (pro)renin receptor ((P)RR) can act as a repressor of Wnt signalling

The (pro)renin receptor ((P)RR) and Wnt signalling are both involved in different diseases ranging from cardiac and renal end-organ damage to cancer. (P)RR function involves signalling via the transcription factor promyelocytic leukemia zinc finger protein (PLZF) as well as the furin-mediated generation of vacuolar proton-translocating ATPase (V-ATPase)-associated and soluble (P)RR isoforms. Recently, the (P)RR was described as adaptor protein of Wnt (co)receptors. The aim of this study was to analyse the contribution of these distinct (P)RR functions to Wnt signalling. Using Tcf/Lef reporter gene systems in HEK293T and HepG2 cells and quantification of endogenous axin2 mRNA and protein levels in HEK293T cells we were able to demonstrate that full-length (P)RR acts as a repressor of Wnt signalling in a system preactivated either by Wnt3a stimulation or by constitutively active β-catenin. These repressive effects are mediated by Dvl but are independent of the mutation status of β-catenin. Furthermore, the V-ATPase complex, but not PLZF translocation or renin enzymatic activity, is necessary for the induction of Tcf/Lef-responsive genes by Wnt3a. Our data indicate interference of (P)RR and Wnt cascades, a fact that has to be considered concerning pathophysiology of cardio-renal and oncological entities as well as in drug development programs targeting (P)RR or Wnt pathways.

The (pro)renin receptor. A decade of research: what have we learned?

The discovery of a (pro)renin receptor ((P)RR) in 2002 provided a long-sought explanation for tissue renin–angiotensin system (RAS) activity and a function for circulating prorenin, the inactive precursor of renin, in end-organ damage. Binding of renin and prorenin (referred to as (pro)renin) to the (P)RR increases angiotensin I formation and induces intracellular signalling, resulting in the production of profibrotic factors. However, the (pro)renin concentrations required for intracellular signalling in vitro are several orders of magnitude above (patho)physiological plasma levels. Moreover, the phenotype of prorenin-overexpressing animals could be completely attributed to angiotensin generation, possibly even without the need for a receptor. The efficacy of the only available putative (pro)renin receptor blocker handle region peptide remains doubtful, leading to inconclusive results. The fact that, in contrast to other RAS components, (P)RR knock-outs, even tissue-specific, are lethal, points to an important, (pro)renin-independent, function of the (P)RR. Indeed, recent research has highlighted ancillary functions of the (P)RR as an essential accessory protein of the vacuolar-type H⁺-ATPase (V-ATPase), and in this role, it acts as an intermediate in Wnt signalling independent of (pro)renin. In conclusion, (pro)renin-dependent signalling is unlikely in non-(pro)renin synthesizing organs, and the (P)RR role in V-ATPase integrity and Wnt signalling may explain some, if not all of the phenotypes previously associated with (pro)renin-(P)RR interaction.

(Pro)renin and its receptors: pathophysiological implications

Tissue angiotensin generation depends on the uptake of circulating (kidney-derived) renin and/or its precursor prorenin [together denoted as (pro)renin]. Since tissue renin levels are usually somewhat higher than expected based upon the amount of (renin-containing) blood in tissue, an active uptake mechanism has been proposed. Several candidates have been evaluated in the past three decades, including a renin-binding protein, the mannose 6-phosphate/insulin-like growth factor II receptor and the (pro)renin receptor. Although the latter seemed the most promising, its nanomolar affinity for renin and prorenin is several orders of magnitude above their actual (picomolar) levels in blood, raising doubt on whether (pro)renin–(pro)renin receptor interaction will ever occur in vivo. A wide range of in vitro studies have now demonstrated (pro)renin-receptor-induced effects at nanomolar renin and prorenin concentrations, resulting in a profibrotic phenotype. In addition, beneficial in vivo effects of the putative (pro)renin receptor blocker HRP (handle region peptide) have been observed, particularly in diabetic animal models. Despite these encouraging results, many other studies have reported either no or even contrasting effects of HRP, and (pro)renin-receptor-knockout studies revealed lethal consequences that are (pro)renin-independent, most probably due to the fact that the (pro)renin receptor co-localizes with vacuolar H+-ATPase and possibly determines the stability of this vital enzyme. The present review summarizes all of the recent findings on the (pro)renin receptor and its blockade, and critically compares it with the other candidates that have been proposed to mediate (pro)renin uptake from blood. It ends with the conclusion that the (pro)renin–(pro)renin receptor interaction, if it occurs in vivo, is limited to (pro)renin-synthesizing organs such as the kidney.

Current knowledge of (pro)renin receptor as an accessory protein of vacuolar H+-ATPase

The (pro)renin receptor (P)RR is a receptor for renin and prorenin, not only allowing local production of angiotensin I from angiotensinogen, but also inducing intracellular signaling. Intriguingly, (P)RR is also called ATP6AP2 because a (P)RR fragment was demonstrated to be associated with vacuolar-type H+-ATPase (V-ATPase), which is of importance for the maintenance of intracellular pH. Recent studies implicate that deletion of (P)RR results in the dysfunction of V-ATPase, suggesting that the (P)RR is essential for its role as a proton pump. Furthermore, the novel function of (P)RR as an adaptor protein between the Wnt receptor complex and the V-ATPase was discovered. Thus, (P)RR is a multi-functional molecule with functions beyond renin and prorenin. This review focuses on the current knowledge and issues of (P)RR and V-ATPase.

The role of ADAM-mediated shedding in vascular biology

Within the vasculature the disintegrins and metalloproteinases (ADAMs) 8, 9, 10, 12, 15, 17, 19, 28 and 33 are expressed on endothelial cells, smooth muscle cells and on leukocytes. As surface-expressed proteases they mediate cleavage of vascular surface molecules at an extracellular site close to the membrane. This process is termed shedding and leads to the release of a soluble substrate ectodomain thereby critically modulating the biological function of the substrate. In the vasculature several surface molecules undergo ADAM-mediated shedding including tumour necrosis factor (TNF) α, interleukin (IL) 6 receptor α, L-selectin, vascular endothelial (VE)-cadherin, the transmembrane CX3C-chemokine ligand (CX3CL) 1, Notch, transforming growth factor (TGF) and heparin-binding epidermal growth factor (HB-EGF). These substrates play distinct roles in vascular biology by promoting inflammation, permeability changes, leukocyte recruitment, resolution of inflammation, regeneration and/or neovascularisation. Especially ADAM17 and ADAM10 are capable of cleaving many substrates with diverse function within the vasculature, whereas other ADAMs have a more restricted substrate range. Therefore, targeting ADAM17 or ADAM10 by pharmacologic inhibition or gene knockout not only attenuates the inflammatory response in animal models but also affects tissue regeneration and neovascularisation. Recent discoveries indicate that other ADAMs (e.g. ADAM8 and 9) also play important roles in vascular biology but appear to have more selective effects on vascular responses (e.g. on neovascularisation only). Although, targeting of ADAM17 and ADAM10 in inflammatory diseases is still a promising approach, temporal and spatial as well as substrate-specific inhibition approaches are required to minimise undesired side effects on vascular cells.