The putative (pro)renin receptor blocker HRP fails to prevent (pro)renin signaling

Abstract

The prorenin/renin receptor is a recently discovered component of the renin-angiotensin system. The effects of aliskiren, a direct inhibitor of human renin, were compared with the handle region decoy peptide (HRP), which blocks the prorenin/renin receptor, in double-transgenic rats overexpressing the human renin and angiotensinogen genes. After 7 wk, all aliskiren-treated rats were alive, whereas mortality was 40% in vehicle-treated and 58% in HRP-treated rats. Aliskiren but not the HRP reduced BP and normalized albuminuria, cystatin C, and neutrophil gelatinase-associated lipocalin, a marker of renal tubular damage, to the levels of nontransgenic controls. In vitro, human renin and prorenin induced extracellular signal-regulated kinase 1/2 phosphorylation, independent of angiotensin II (AngII), in vascular smooth muscle cells. Preincubation with the HRP or aliskiren did not prevent renin- and prorenin-induced extracellular signal-regulated kinase 1/2 phosphorylation, whereas the MAP kinase kinase (MEK1/2) inhibitor PD98059 prevented both. In conclusion, renin inhibition but not treatment with the HRP protects against AngII-induced renal damage in double-transgenic rats. In addition, the in vitro data do not support the use of the HRP to block AngII-independent prorenin- or renin-mediated effects.

Figure 1.

Effect of aliskiren and HRP on mortality (A) and systolic BP (B). Data are means ± SEM. *P < 0.05 versus vehicle-treated dTGR and HRP-treated dTGR.

Figure 2.

Effect of aliskiren and HRP on albuminuria (A), cystatin C (B), and NGAL (C). All three markers demonstrated that aliskiren but not HRP improved renal damage. Data are means ± SEM. *P < 0.05 versus vehicle-treated dTGR and HRP-treated dTGR.

Figure 3.

(P)RR mRNA expression in the kidney. Vehicle-treated dTGR showed lower renal (P)RR expression compared with aliskiren-treated dTGR and SD rats. HRP and SD rat (P)RR expressions were not different. Data are means ± SEM. *P < 0.05 versus aliskiren-treated dTGR and SD rats. AU, arbitrary units.

Figure 4.

(A and B) Time-course analysis of renin-induced (10 nM; A) and prorenin-induces (2 nM; B) ERK1/2 phosphorylation (p-ERK1/2) in human VSMC (top) with unphosphorylated ERK as loading control (bottom). (C) Renin and prorenin (10 min) also induced p-ERK1/2 in AT1_A receptor–deficient VSMC. (D through F) Effects of 10 μM aliskiren (D), 1 μM HRP (E), and MEK1/2 inhibitor (PD98059; 100 nM; F) on renin- and prorenin-induced (both 10 min) p-ERK1/2 in human VSMC (top) with unphosphorylated ERK as loading control (bottom). All experiments were performed after 24-h serum starvation in the presence of losartan (Los) and the AT2 receptor blocker (PD123319).