Guanylin peptide family: history, interactions with ANP, and new pharmacological perspectives

Uroguanylin inhibits H-ATPase activity and surface expression in renal distal tubules by a PKG-dependent pathway

Cumulative evidence suggests that guanylin peptides play an important role on electrolyte homeostasis. We have previously reported that uroguanylin (UGN) inhibits bicarbonate reabsorption in a renal distal tubule. In the present study, we tested the hypothesis that the bicarbonaturic effect of UGN is at least in part attributable to inhibition of H(+)-ATPase-mediated hydrogen secretion in the distal nephron. By in vivo stationary microperfusion experiments, we were able to show that UGN inhibits H(+)-ATPase activity by a PKG-dependent pathway because KT5823 (PKG inhibitor) abolished the UGN effect on distal bicarbonate reabsorption and H89 (PKA inhibitor) was unable to prevent it. The in vivo results were confirmed by the in vitro experiments, where we used fluorescence microscopy to measure intracellular pH (pHi) recovery after an acid pulse with NH4Cl. By this technique, we observed that UGN and 8 bromoguanosine-cGMP (8Br-cGMP) inhibited H(+)-ATPase-dependent pHi recovery and that the UGN inhibitory effect was abolished in the presence of the PKG inhibitor. In addition, by using RT-PCR technique, we verified that Madin-Darby canine kidney (MDCK)-C11 cells express guanylate cyclase-C. Besides, UGN stimulated an increase of both cGMP content and PKG activity but was unable to increase the production of cellular cAMP content and PKA activity. Furthermore, we found that UGN reduced cell surface abundance of H+-ATPase B1 subunit in MDCK-C11 and that this effect was abolished by the PKG inhibitor. Taken together, our data suggest that UGN inhibits H(+)-ATPase activity and surface expression in renal distal cells by a cGMP/PKG-dependent pathway.

Pendrin, a novel transcriptional target of the uroguanylin system

Guanylin (GN) and uroguanylin (UGN) are low-molecular-weight peptide hormones produced mainly in the intestinal mucosa in response to oral salt load. GN and UGN (guanylin peptides) induce secretion of electrolytes and water in both intestine and kidney. Thought to act as "intestinal natriuretic factors", GN and UGN modulate renal salt secretion by both endocrine mechanisms (linking the digestive system and kidney) and paracrine/autocrine (intrarenal) mechanisms. The cellular function of GN and UGN in intestine and proximal tubule is mediated by guanylyl cyclase C (GC-C)-, cGMP-, and G protein-dependent pathways, whereas, in principal cells of the cortical collecting duct (CCD), these peptide hormones act via GC-C-independent signaling through phospholipase A2 (PLA2). The Cl(-)/HCO(-)3 exchanger pendrin (SLC26A4), encoded by the PDS gene, is expressed in non-α intercalated cells of the CCD. Pendrin is essential for CCD bicarbonate secretion and is also involved in NaCl balance and blood pressure regulation. Our recent studies have provided evidence that pendrin-mediated anion exchange in the CCD is regulated at the transcriptional level by UGN. UGN exerts an inhibitory effect on the pendrin gene promoter likely via heat shock factor 1 (HSF1) action at a defined heat shock element (HSE) site. Recent studies have unraveled novel roles for guanylin peptides in several organ systems including involvement in appetite regulation, olfactory function, cell proliferation and differentiation, inflammation, and reproductive function. Both the guanylin system and pendrin have also been implicated in airway function. Future molecular research into the receptors and signal transduction pathways involved in the action of guanylin peptides and the pendrin anion exchanger in the kidney and other organs, and into the links between them, may facilitate discovery of new therapies for hypertension, heart failure, hepatic failure and other fluid retention syndromes, as well as for diverse diseases such as obesity, asthma, and cancer.

Treatment of erectile dysfunction: new targets and strategies from recent research

In recent years, research on penile erection has increasingly been centered on the molecular mechanisms involved. Major progress has been made in the field and at present a whole number of neurotransmitters, chemical effectors, growth factors, second-messenger molecules, ions, intercellular proteins, and hormones have been characterized as components of the complex process of erection. This knowledge has led to the discovery of several new therapeutic targets and multiple medical approaches for the treatment of erectile dysfunction (ED). This review focuses on the progress made in this field within the last few years.

Guanylin and functional coupling proteins in the hepatobiliary system of rat and guinea pig

Guanylin, a bioactive intestinal peptide, is involved in the cystic fibrosis transmembrane conductance (CFTR)-regulated electrolyte/water secretion in various epithelia. In the present work we report on the expression and cellular localization of guanylin and its affiliated signaling and effector proteins, including guanylate cyclase C (Gucy2c), Proteinkinase GII (Pkrg2), CFTR and the solute carrier family 4, anion exchanger, member 2 (Slc4a2) in the hepatobiliary system of rat and guinea pig. Localization studies in the liver and the gallbladder revealed that guanylin is located in the secretory epithelial cells of bile ducts of the liver and of the gallbladder, while Gucy2c, Pkrg2, CFTR, and Slc4a2 are confined exclusively to the apical membrane of the same epithelial cells. Based on these findings, we assume that guanylin is synthesized as an intrinsic peptide in epithelial cells of the hepatobiliary system and released luminally into the hepatic and cystic bile to regulate electrolyte secretion by a paracrine/luminocrine signaling pathway.