Expression Of Galanin-like Peptide Research Articles

Epigenetic upregulation of galanin-like peptide mediates deoxynivalenol induced-growth inhibition in pituitary cells

Deoxynivalenol (DON) is an unavoidable contaminant in human food, animal feeds, and agricultural products. Growth retardation in children caused by extensive DON pollution has become a global problem that cannot be ignored. Previous studies have shown that DON causes stunting in children through intestinal dysfunction, insulin-like growth factor-1 (IGF-1) axis disorder and peptide YY (PYY). Galanin-like peptide (GALP) is an important growth regulator, but its role in DON-induced growth retardation is unclear. In this study, we report the important role of GALP during DON-induced growth inhibition in the rat pituitary tumour cell line GH3. DON was found to increase the expression of GALP through hypomethylationin the promoter region of the GALP gene and upregulate the expression of proinflammatory factors, while downregulate the expression of growth hormone (GH). Furthermore, GALP overexpression promoted proinflammatory cytokines, including TNF-α, IL-1β, IL-11 and IL-6, and further reduced cell viability and cell proliferation, while the inhibitory effect of GALP was the opposite. The expression of GALP and insulin like growth factor binding protein acid labile subunit (IGFALS) showed the opposite trend, which was the potential reason for the regulation of cell proliferation by GALP. In addition, GALP has anti-apoptotic effects, which could not eliminate the inflammatory damage of cells, thus aggravating cell growth inhibition. The present findings provide new mechanistic insights into the toxicity of DON-induced growth retardation and suggest a therapeutic potential of GALP in DON-related diseases.

Galanin-like peptide (GALP) neurone-specific phosphoinositide 3-kinase signalling regulates GALP mRNA levels in the hypothalamus of males and luteinising hormone levels in both sexes.

Galanin-like peptide (GALP) neurones participate in the metabolic control of reproduction and are targets of insulin and leptin regulation. Phosphoinositide 3-kinase (PI3K) is common to the signalling pathways utilised by both insulin and leptin. Therefore, we investigated whether PI3K signalling in neurones expressing GALP plays a role in the transcriptional regulation of the GALP gene and in the metabolic control of luteinising hormone (LH) release. Accordingly, we deleted PI3K catalytic subunits p110α and p110β via conditional gene targeting (cKO) in mice (GALP-p110α/β cKO). To monitor PI3K signalling in GALP neurones, these animals were also crossed with Cre-dependent FoxO1GFP reporter mice. Compared to insulin-infused control animals, the PI3K-Akt-dependent FoxO1GFP nuclear exclusion in GALP neurones was abolished in GALP-p110α/β cKO mice. We next used food deprivation to investigate whether the GALP-neurone specific ablation of PI3K activity affected the susceptibility of the gonadotrophic axis to negative energy balance. Treatment did not affect LH levels in either sex. However, a significant genotype effect on LH levels was observed in females. By contrast, no genotype effect on LH levels was observed in males. A sex-specific genotype effect on hypothalamic GALP mRNA was observed, with fed and fasted GALP-p110α/β cKO males having lower GALP mRNA expression compared to wild-type fed males. Finally, the effects of gonadectomy and steroid hormone replacement on GALP mRNA levels were investigated. Compared to vehicle-treated mice, steroid hormone replacement reduced mediobasal hypothalamus GALP expression in wild-type and GALP-p110α/β cKO animals. In addition, within the castrated and vehicle-treated group and compared to wild-type mice, LH levels were lower in GALP-p110α/β cKO males. Double immunofluorescence using GALP-Cre/R26-YFP mice showed androgen and oestrogen receptor co-localisation within GALP neurones. Our data demonstrate that GALP neurones are direct targets of steroid hormones and that PI3K signalling regulates hypothalamic GALP mRNA expression and LH levels in a sex-specific fashion.

Oestrogen‐Dependent Stimulation of Luteinising Hormone Release by Galanin‐Like Peptide in Female Rats

Galanin-like peptide (GALP), a ligand for three types of galanin receptor, is reported to have a role in regulating luteinising hormone (LH) release in male rodents and primates, but its role in LH release in female rodents remains controversial. The present study was conducted to test whether GALP has a stimulatory role in regulating LH secretion in female rats. The effect of i.c.v. infusion of GALP (5 nmol) on pulsatile LH release was investigated in Wistar-Imamichi strain female rats, or lean and obese Zucker rats. In oestradiol-17beta (oestradiol)-primed ovariectomised (OVX) Wistar-Imamichi female rats, i.c.v. infusion of GALP caused a gradual increase in LH release for the first 1.5 h after the infusion followed by an increased LH pulse frequency during the next 1.5 h, resulting in a significant increase in the mean LH concentrations and baseline levels of LH pulses throughout the sampling period and in the frequency of LH pulses at the last half of the period compared to vehicle-treated controls. The stimulatory effect of GALP was oestrogen-dependent because the same GALP treatment did not affect LH release in OVX rats in the absence of oestradiol. In lean Zucker rats, LH pulses were found in oestradiol-primed OVX individuals and central GALP infusion increased mean LH concentrations in the last half of the period. By contrast, few LH pulses were found in oestradiol-primed OVX obese Zucker rats reportedly with lower hypothalamic GALP expression. Central GALP infusion caused an apparent but transient increase in LH release, resulting in the significant increase in all pulse parameters of LH pulses compared to vehicle-treated controls in the first half of the sampling period. These results suggest that hypothalamic GALP is likely involved in stimulating GnRH/LH release, and that the stimulatory effect of GALP on LH release is oestrogen-dependent in female rats.

Central Insulin-Like Growth Factor 1 Receptors Play Distinct Roles in the Control of Reproduction, Food Intake, and Body Weight in Female Rats1

Estradiol and progesterone induction of the LH surge in ovariectomized female rats requires concurrent activation of brain insulin-like growth factor 1 (IGF1) receptors. The present study determined whether brain IGF1 receptor signaling is required for estrous cyclicity in gonadally intact female rats. A selective IGF1 receptor antagonist (JB-1) or vehicle was continuously administered into the third ventricle by osmotic minipumps. Following surgical placement of the minipumps, all rats temporarily reduced food intake, lost weight, and suspended estrous cycles. Control rats resumed cycles within a few days and exhibited compensatory hyperphagia until they returned to presurgical body weight. Animals receiving JB-1 had severely delayed or absent estrous cycles, failed to show rebound feeding, and regained body weight more slowly. Vehicle-infused animals pair fed to JB-1-treated rats had even lower body weights but resumed estrous cycles sooner than those given drug alone. Chronic infusion of IGF1 alone had no effect on any of these parameters, but coinfusion of IGF1 with the antagonist completely reversed JB-1 effects on food intake and estrous cyclicity and partially reversed the effects on body weight. There were no significant differences in the expression of galanin-like peptide (Galp) or Kiss1 mRNA in the arcuate or periventricular hypothalamic area of control and JB-1-treated animals at a time point when food intake and estrous cycles were different between controls and JB-1-treated rats. These data suggest that brain IGF1 signaling is necessary for normal estrous cycles as well as compensatory hyperphagia and that IGF1 modulation of the reproductive axis is not secondary to reduced food intake.

Postnatal developmental change of the gene expression of galanin-like peptide in rat hypothalamus

Postnatal developmental change of the gene expression of galanin-like peptide in rat hypothalamus

Galanin-Like Peptide Rescues Reproductive Function in the Diabetic Rat

Galanin-like peptide (GALP) is expressed in the hypothalamic arcuate nucleus and is regulated by leptin and insulin. Centrally administered GALP stimulates gonadotropin secretion and sexual behavior in the rat. Type 1 diabetes is associated with reduced expression of GALP, as well as an overall decline in reproductive function. We postulated that tonic activity of GALP in the brain is required to sustain normal reproductive activity. To test this hypothesis, we examined whether central (intracerebroventricular) immunoblockade of GALP would reduce sexual behaviors and serum levels of luteinizing hormone (LH) in normal adult male rats. We found that GALP antibody reversibly reduced serum levels of LH and abolished male sexual behaviors (P < 0.05 and 0.001, respectively). Second, we tested whether intracerebroventricular GALP could restore normal plasma LH levels and sexual behavior in diabetic animals. We compared groups of diabetic rats that received intracerebroventricular GALP or vehicle and found that GALP increased serum levels of LH and sexual behavior. Third, we examined whether intracerebroventricular administration of affinity-purified GALP antibody could block the effect of insulin and leptin in reversing the effects of diabetes on LH and sexual behavior. We found that treatment of diabetic animals with insulin and leptin nearly normalized LH levels and sexual behaviors; however, this effect was attenuated by intracerebroventricular administration of GALP antibody (P < 0.05). These observations demonstrate that endogenous GALP provides trophic support to the neuroendocrine reproductive axis, including sexual behavior.

Galanin-Like Peptide mRNA Alterations in Arcuate Nucleus and Neural Lobe of Streptozotocin-Diabetic and Obese Zucker Rats

Galanin-like peptide (GALP) is a 60-amino-acid peptide with structural similarities to galanin and a high affinity for galanin receptors. GALP is expressed by a discrete population of neurons in the arcuate nucleus (ARC) and median eminence of the hypothalamus of several species, including the rat. GALP neurons express leptin receptors and GALP mRNA levels are decreased slightly in fasted rats and stimulated significantly by acute leptin treatment in combination with fasting. In studies to further explore the leptin dependence of GALP expression, we examined GALP mRNA levels in the hypothalamus of obese Zucker and streptozotocin-induced diabetic (STZ-DM) rats. In leptin receptor-deficient obese Zucker rats, with 75% higher body weight than lean littermates, GALP mRNA levels in the ARC were decreased by 75%, while neuropeptide Y (NPY) mRNA levels were increased 7-fold (n = 5, p < 0.001), consistent with earlier reports. In hypoleptinemic diabetic rats with 4.5-fold higher blood glucose and 15% lower body weight than controls, GALP mRNA levels in the ARC were decreased by 90%, while NPY mRNA levels were increased 9-fold (n = 5, p < 0.001). GALP is also expressed by pituicytes in the neural lobe of the rat pituitary gland and GALP expression is increased by osmotic stimulation such as dehydration and salt loading. Thus, in STZ-DM rats that are in a hyperosmotic state with elevated plasma vasopressin levels, GALP mRNA levels were increased by ∼20-fold in the neural lobe relative to control (n = 4, p < 0.001). The current findings are consistent with a strong tonic influence of leptin receptor signalling on hypothalamic GALP expression under normal conditions, and possible abnormalities in GALP neuronal signalling and their putative targets, thyrotropin-releasing hormone and gonadotropin hormone-releasing hormone neurons, under pathophysiological conditions such as diabetes and obesity. Our data in STZ-DM rats also clearly demonstrate that GALP gene expression is differentially regulated in neurons and pituicytes.

Effects of diabetes and insulin on the expression of galanin-like peptide in the hypothalamus of the rat.

Galanin-like peptide (GALP) is produced in a small population of neurons in the arcuate nucleus of the hypothalamus, and leptin stimulates the hypothalamic expression of GALP mRNA. Because insulin and leptin share common signaling pathways in the brain, we reasoned that GALP neurons might also be responsive to changes in circulating concentrations of insulin. To test this hypothesis, we first studied the effect of insulin deficiency on the expression of GALP by comparing levels of GALP mRNA between normal and diabetic animals. Streptozotocin-induced diabetes was associated with a significant reduction in the expression of GALP mRNA, which was reversed by treatment with either insulin or leptin. Second, we examined the effect of insulin administered directly into the brain on the expression of GALP mRNA in fasted rats. Hypothalamic levels of GALP mRNA were lower in animals after a 48-h fast, and central treatment with insulin reversed this effect. These results suggest that GALP neurons are direct targets for regulation by insulin and implicate these cells for a role in the metabolic and behavioral sequelae of type 1 diabetes.

Galanin-like peptide (GALP) is a target for regulation by leptin in the hypothalamus of the rat.

Galanin-like peptide (GALP), which was recently isolated from the porcine hypothalamus, shares sequence homology with galanin and binds with high affinity to galanin receptors. To study the distribution and regulation of GALP-expressing cells in the brain, we cloned a 120 base-pair cDNA fragment of rat GALP and produced an antisense riboprobe. In situ hybridization for GALP mRNA was then performed on tissue sections throughout the forebrain of adult ovariectomized female rats. We found GALP mRNA-containing cells in the arcuate nucleus (Arc), caudal dorsomedial nucleus, median eminence and the pituitary. Because GALP mRNA in the Arc appeared to overlap with the known distribution of leptin receptor mRNA, we tested the hypothesis that GALP expression is regulated by leptin. Using in situ hybridization, we compared the number of GALP mRNA-containing cells among groups of rats that were fed ad lib or fasted for 48 h and treated with either leptin or vehicle. Fasting reduced the number of identifiable cells containing GALP mRNA in the Arc, whereas the treatment of fasted animals with leptin produced a 4-fold increase in the number of cells expressing GALP message. The presence of GALP mRNA in the hypothalamus and pituitary and its regulation by leptin suggests that GALP may have important neuroendocrine functions, including the physiological regulation of feeding, metabolism, and reproduction.