Secretin stimulates biliary cell proliferation by regulating expression of microRNA 125b and microRNA let7a in mice.

BACKGROUND & AIMS: Proliferating cholangiocytes secrete and respond to neuroendocrine hormones, including secretin. We investigated whether secretin secreted by S cells and cholangiocytes stimulates biliary proliferation in mice. METHODS: Cholestasis was induced in secretin knockout (Sct(-/-)) and wild-type (control) mice by bile duct ligation (BDL). At days 3 and 7 after BDL, control and Sct(-/-) mice received tail-vein injections of morpholinos against microRNA 125b or let7a. One week later, liver tissues and cholangiocytes were collected. Immunohistochemical, immunoblot, luciferase reporter, and real-time polymerase chain reaction assays were performed. Intrahepatic bile duct mass (IBDM) and proliferation were measured. Secretin secretion was measured in conditioned media from cholangiocytes and S cells and in serum and bile. RESULTS: Secretin secretion was increased in supernatants from cholangiocytes and S cells and in serum and bile after BDL in control mice. BDL Sct(-/-) mice had lower IBDM, reduced proliferation, and reduced production of vascular endothelial growth factor (VEGF) A and nerve growth factor (NGF) compared with BDL control. BDL and control mice given morpholinos against microRNA 125b or let7a had increased IBDM. Livers of mice given morpholinos against microRNA 125b had increased expression of VEGFA, and those treated with morpholinos against microRNA let7a had increased expression of NGF. Secretin regulated VEGF and NGF expression that negatively correlated with microRNA 125b and let7a levels in liver tissue. CONCLUSIONS: After liver injury, secretin produced by cholangiocytes and S cells reduces microRNA 125b and let7a levels, resulting in up-regulation of VEGF and NGF. Modulation of cholangiocyte expression of secretin could be a therapeutic approach for biliary diseases.

Lipolytic actions of secretin in mouse adipocytes.

Secretin (Sct), a classical gut hormone, is now known to play pleiotropic functions in the body including osmoregulation, digestion, and feeding control. As Sct has long been implicated to regulate metabolism, in this report, we have investigated a potential lipolytic action of Sct. In our preliminary studies, both Sct levels in circulation and Sct receptor (SctR) transcripts in adipose tissue were upregulated during fasting, suggesting a potential physiological relevance of Sct in regulating lipolysis. Using SctR knockout and Sct knockout mice as controls, we show that Sct is able to stimulate lipolysis in vitro in isolated adipocytes dose- and time-dependently, as well as acute lipolysis in vivo. H-89, a protein kinase A (PKA) inhibitor, was found to attenuate lipolytic effects of 1 µM Sct in vitro, while a significant increase in PKA activity upon Sct injection was observed in the adipose tissue in vivo. Sct was also found to stimulate phosphorylation at 660(ser) of hormone sensitive lipase (HSL) and to bring about the translocation of HSL from cytosol to the lipid droplet. In summary, our data demonstrate for the first time the in vivo and in vitro lipolytic effects of Sct, and that this function is mediated by PKA and HSL.

Secretin deficiency causes impairment in survival of neural progenitor cells in mice.

Hippocampal neurogenesis is the lifelong production of new neurons in the central nervous system (CNS), and affects many physiological and pathophysiological conditions, including neurobehavioral disorders. The early postnatal stage is the most prominent neurogenesis period; however, the functional role of neurogenesis in this developing stage has not been well characterized. To understand the role of hippocampal neurogenesis in the postnatal developing period, we analyzed secretin, a neuropeptide, which is expressed significantly higher in the development stage. Secretin is a pleiotropic neuropeptide hormone that belongs to the secretin/VIP/glucagon peptide family. Although secretin was originally isolated in the gastrointestinal system, it has been found that secretin itself acts as a neuropeptide in the CNS. Here, we report a new function of secretin as a survival factor for neural progenitor cells in the hippocampus. We found that secretin-deficient mice exhibit decreased numbers of BrdU-labeled new neurons and dramatically increased apoptosis of doublecortin-positive neural progenitor cells in the subgranular zone of the dentate gyrus (DG) during the early postnatal period. Furthermore, we found that reduced survival of neural progenitor cells leads to decreased volume of DG, reduced long-term potentiation and impaired spatial learning ability in adults. Our studies demonstrate that secretin has important implications for neurogenesis in postnatal development, and affects neurobehavioral function in the adult mouse.

Loss of secretin results in systemic and pulmonary hypertension with cardiopulmonary pathologies in mice.

More than 1 billion people globally are suffering from hypertension, which is a long-term incurable medical condition that can further lead to dangerous complications and death if left untreated. In earlier studies, the brain-gut peptide secretin (SCT) was found to be able to control blood pressure by its cardiovascular and pulmonary effects. For example, serum SCT in patients with congestive heart failure was one-third of the normal level. These observations strongly suggest that SCT has a causal role in blood pressure control, and in this report, we used constitutive SCT knockout (SCT-/-) mice and control C57BL/6N mice to investigate differences in the morphology, function, underlying mechanisms and response to SCT treatment. We found that SCT-/- mice suffer from systemic and pulmonary hypertension with increased fibrosis in the lungs and heart. Small airway remodelling and pulmonary inflammation were also found in SCT-/- mice. Serum NO and VEGF levels were reduced and plasma aldosterone levels were increased in SCT-/- mice. Elevated cardiac aldosterone and decreased VEGF in the lungs were observed in the SCT-/- mice. More interestingly, SCT replacement in SCT-/- mice could prevent the development of heart and lung pathologies compared to the untreated group. Taken together, we comprehensively demonstrated the critical role of SCT in the cardiovascular and pulmonary systems and provide new insight into the potential role of SCT in the pathological development of cardiopulmonary and cardiovascular diseases.

Peptic ulceration may be a hormonal deficiency disease.

Evidence is reviewed that Helicobacter pylori infection may cause a deficiency of the hormone secretin that allows peptic ulcer disease to develop by impairing the body's defenses to gastric acid. Secretin is released into the circulation from the S-cells of the duodenal crypts in response to gastric acid entering the duodenum. Once in the circulation, secretin has five well-documented effects that protect the upper intestine from gastric acid: it stimulates secretion of bicarbonate rich exocrine pancreatic juice; it stimulates secretion of alkaline bile; it stimulates secretion of alkaline mucus from the duodenal submucosal glands of Brunner; it inhibits the humoral phase of gastric secretion; and it inhibits gastric motility, thereby delaying gastric emptying. Impaired secretin release and reduced duodenal S-cells have been documented in peptic ulcer patients compared with control patients. Clinical evidence that patients with H. pylori infection and peptic ulceration have increased gastric secretion and motility and decreased duodenal bicarbonate response to gastric acid, all of which normalize after eradication of the infection, could be explained by reversible impairment of the secretin mechanism. Gastric metaplasia in the duodenum with H. pylori infection is known to reduce the S-cell population. The fact that not all patients with H. pylori infection develop peptic ulceration suggests that degree of secretin deficiency determined by extent of the infection must reach a critical level for peptic ulceration to occur. Peptic ulceration may be a hormonal deficiency disease, a result of secretin deficiency caused by H. pylori infection. It may be the first example of a specific hormonal deficiency disease caused by a specific bacterial infection.

[Secretin and peptic ulcer]. / Sekretin i iazvennaia bolezn'.

Eighty patients with peptic ulcer were examined by the microprecipitation test according to Hoigne. Skin tests were made in 63 and the leukocytolysis test with secretin in 39 patients who were also examined for the effect of secretin on peripheral blood cellular composition, pH of gastric juice, and for therapeutic action of the hormone. Sixty-six per cent of peptic ulcer patients showed secretin antibodies and positive skin tests, whereas 59% of patients the positive leukocytolysis test with secretin. The endogenous hormone provoked a reduction in the leukocyte, lymphocyte and neutrophil counts, raised pH of gastric juice and exerted a beneficial therapeutic action. Secretin antibodies are likely to bind the hormone and give rise to secretin deficiency. Administration of secretin has a good therapeutic effect in duodenal ulcer patients.

Central and peripheral administration of secretin inhibits food intake in mice through the activation of the melanocortin system.

Secretin (Sct) is released into the circulation postprandially from the duodenal S-cells. The major functions of Sct originated from the gastrointestinal system are to delay gastric emptying, stimulate fluid secretion from pancreas and liver, and hence optimize the digestion process. In recent years, Sct and its receptor (Sctr) have been identified in discrete nuclei of the hypothalamus, including the paraventricular nucleus (PVN) and the arcuate nucleus (Arc). These nuclei are the primary brain sites that are engaged in regulating body energy homeostasis, thus providing anatomical evidence to support a functional role of Sct in appetite control. In this study, the effect of Sct on feeding behavior was investigated using wild-type (wt), Sct(-/-), and secretin receptor-deficient (Sctr(-/-)) mice. We found that both central and peripheral administration of Sct could induce Fos expression in the PVN and Arc, suggesting the activation of hypothalamic feeding centers by this peptide. Consistent with this notion, Sct was found to increase thyrotropin-releasing hormone and melanocortin-4 receptor (Mc4r) transcripts in the PVN, and augment proopiomelanocortin, but reduces agouti-related protein mRNA expression in the Arc. Injection of Sct was able to suppress food intake in wt mice, but not in Sctr(-/-) mice, and that this effect was abolished upon pretreatment with SHU9119, an antagonist for Mc4r. In summary, our data suggest for the first time that Sct is an anorectic peptide, and that this function is mediated by the melanocortin system.

Impaired hippocampal synaptic function in secretin deficient mice.

Secretin is a gut peptide hormone that is also expressed in the CNS. To explore the potential neuroactive role of secretin in the brain, we have generated secretin deficient mice. Secretin deficient mice demonstrated impairment in synaptic plasticity (significant reduction in long term potentiation (LTP) induction and LTP maintenance) in the CA1 area of the hippocampus. Using a beta-galactosidase (lacZ) reporter in the targeted allele and secretin antibody staining, we have detected secretin gene expression in the hippocampus, cerebellum, and the brain stem in adult mouse brain. In the hippocampus, secretin was expressed in the dentate gyrus, the hilus, and the molecular layer. These findings suggest that secretin is involved in synaptic function in the adult brain.