Particulate Guanylyl Cyclase A/cGMP Signaling Pathway in the Kidney: Physiologic and Therapeutic Indications

Abstract

The particulate guanylyl cyclase A (pGC-A)/cGMP pathway plays important roles in regulating renal physiological function and as well as in counteracting pathophysiological conditions. Naturally occurring peptide pGC-A activators consist of atrial natriuretic peptide (ANP), b-type NP (BNP), and urodilatin (URO). These activators bind and activate pGC-A, generating the second messenger cyclic 3',5' guanosine monophosphate (cGMP). Cyclic GMP binds to downstream pathway effector molecules including protein kinase G (PKG), cGMP-gated ion channels, and phosphodiesterases (PDEs). These mediators result in a variety of physiological actions in the kidney, including diuresis, natriuresis, increased glomerular filtration rate (GFR) and organ protection, thus, opposing renal cellular injury and remodeling. Downstream proteins regulated by PKG include collagen 1 (Col-1), transforming growth factor beta (TGF-β) and apoptosis-related proteins. In addition to their physiological regulatory effects, pGC-A/cGMP signaling is critical for preserving renal homeostasis in different renal diseases such as acute kidney injury (AKI). Regarding therapeutic options, native pGC-A activators have short half-lives and their activity can be further enhanced by advances in innovative peptide engineering. Thus, novel designer peptide pGC-A activators with enhanced renal activity are under development.

Keywords: acute kidney injury; cGMP; natriuretic peptide; particulate guanylyl cyclase A; protein kinase G; renal.

Figure 1

Particulate GC-A signaling pathway and renal actions overview. ANP/BNP/URO/CRRL269 activate pGC-A receptor, generating second messenger cGMP, which binds to protein kinase G (PKG), cGMP-gated ion channels, and phosphodiesterases (PDEs). Cyclic GMP induces pluripotent biological actions, including diuresis, natriuresis, anti-inflammation, anti-fibrosis, anti-apoptosis, and GFR increase.

Figure 2

CRRL269 as an enhanced pGC-A activator. (A) CRRL269 structure; (B) CRRL269 implicated as a potential drug for AKI due to GFR increase, diuresis, natriuresis, and less hypotension.

Figure 3

CRRL269 possesses enhanced pGC-A activator in vitro in human renal cells. CRRL269 generated significantly higher cGMP in HEK293 cells overexpressing pGC-A receptors (HEK pGC-A) and human renal proximal tubular cells (RPTC) compared to BNP or URO. Cells were treated with Hank’s balanced salt solution (HBSS, as negative control, neg ctrl), BNP, URO or CRRL269 for 10 min and cell lysates were collected for cGMP radioimmunoassay. * p < 0.05, versus neg ctrl, ^† p < 0.05, versus BNP, ^# p < 0.05, versus URO. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology [27].

Figure 4

CRRL269 as an enhanced pGC-A activator in vivo in normal canines (n = 5). CRRL269 induced significantly higher and sustained diuresis (urine output, UV), natriuresis (urinary sodium excretion, UNaV), GFR, and lower blood pressure (mean arterial pressure, MAP) compared to BNP or URO. Acute studies were performed with intravenous infusion of low dose 2 pmol/kg/min and high dose 33 pmol/kg/min BNP, URO or CRRL269 in normal canines. Data are calculated from the difference from baseline. BL = baseline; Low = infusion of low dose 2 pmoL/kg/min BNP, URO or CRRL269; High = infusion of high dose 33 pmoL/kg/min; Wo = washout (0–30 min post-infusion); Rec1 = recovery 1, 30–60 min post-infusion; Rec2 = recovery 2, 60–90 min post-infusion. * p < 0.05, versus baseline (1-way ANOVA and Dunnett post-tests), ^† p < 0.05, versus BNP, ^# p < 0.05, versus URO (2-way ANOVA and Bonferroni post-hoc tests). American Journal of Physiology-Regulatory, Integrative and Comparative Physiology [27].