Uroguanylin

Guanylin, uroguanylin, and the bacterial heat-stable enterotoxin (ST) peptides comprise a new family of cyclic guanosine 3'-5' monophosphate (cGMP)-regulating agonists. The discovery of guanylin and uroguanylin peptides stems from studies of cellular mechanisms underlying a form of secretory diarrhea caused by enteric bacteria. Guanylin, uroguanylin, and microbial ST peptides activate a common apical membrane receptor-guanylate cyclase (R-GC) that elicits large increases in the intestinal secretion of chloride and bicarbonate via the intracellular second messenger, cGMP. Guanylin and uroguanylin were isolated from rat jejunum and opossum urine, respectively. These peptides are endogenous peptide hormones that physiologically regulate R-GC signaling proteins in target cells. Physiological roles for these peptides include the regulation of epithelial cell balance in the intestinal epithelium and modulation of sodium balance through actions in the kidney. The guanylin-uroguanylin-ST peptides are candidate therapeutic agents targeting receptors in the intestine, kidney, and other epithelia. For example, uroguanylin has anti-tumor actions in an animal model for human colon cancer. The ST peptides can be used as diagnostic agents to detect secondary colon cancers by single photon-emitting computed tomography (SPECT) imaging, thus localizing metastatic forms of colon cancer. Other examples of potential therapeutic applications for the guanylin family of cGMP-regulating agonists are: (1) the irritable bowel syndrome (IBS) with constipation, (2) salt-dependent forms of high blood pressure, (3) liver regeneration and repair, and (4) respiratory diseases such as asthma. Competitive pharmacological antagonists of bacterial ST peptides offer a means for treating the diarrhea caused by ST-secreting strains of enteric bacteria.

Uroguanylin is a 16 amino acid peptide that constitutes a key component of the gut- brain axis with special relevance in body weight regulation. In childhood and adolescence, periods of life with notable metabolic changes; limited data exist, with measurements of pro-uroguanylin in adolescence but not in prepubertal children. This study investigates pro-uroguanylin circulating levels in children with obesity and its relationship with obesity, sex and pubertal development. We analyzed circulating prouroguanylin levels in 117 children (62) and adolescents (55), including 73 with obesity and 44 with normal weight. The pro-uroguanylin concentration is higher in lean girls during pre-puberty versus lean boys (1111 vs 635, p < 0.001). During puberty, pro-uroguanylin levels are higher in lean males with respect to lean females (1060 vs 698, p < 0.01). In girls, a negative correlation exists between pro-uroguanylin and age, Tanner stage, weight, height, BMI (body mass index), waist circumference and plasma levels of leptin and testosterone; a positive correlation was found between pro-uroguanylin and free triiodothyronine. In boys, a positive correlation was found between pro-uroguanylin and BMI and waist circumference and a negative correlation was found with high density lipoprotein-cholesterol. We conclude that a sexual dimorphism exists in circulating pro-uroguanylin levels with respect to BMI. Uroguanylin presents also an opposed circulating pattern during puberty in both sexes.

Aim:To investigate the cyclic guanosine monophosphate (cGMP)/guanylate cyclase C (GC-C)-independent signaling pathway in astrocytes, which are a suitable model due to their lack of GC-C expression.Methods:Patch clamp was performed and intracellular Ca2+ concentrations and pH were measured in primary astrocyte cultures and brain slices of wild type (WT) and GC-C knockout (KO) mice. The function of GC-C-independent signaling pathway in the cerebellum was determined by behavior tests in uroguanylin (UGN) KO and GC-C KO mice.Results:We showed for the first time that UGN changed intracellular Ca2+ levels in different brain regions of the mouse. In addition to the midbrain and hypothalamus, GC-C was expressed in the cerebral and cerebellar cortex. The presence of two signaling pathways in the cerebellum (UGN hyperpolarized Purkinje cells via GC-C and increased intracellular Ca2+ concentration in astrocytes) led to a different motoric function in GC-C KO and UGN KO mice, probably via different regulation of intracellular pH in astrocytes.Conclusion:The UGN effects on astrocytes via a Ca2+-dependent signaling pathway could be involved in the modulation of neuronal activity.