Glucose and Several Mitogenic Agents Modulate the Glucagon-Like Peptide-2 Receptor Expression in Cultured Rat Astrocytes

Background

Glucagon-like peptide-2 (GLP-2) is an intestinal trophic factor that induces astrocyte proliferation through its own receptor (GLP-2R), but the control of its expression is not well known.

Objective

To study the effects of glucose and of different mitogenic agents on the control of GLP-2R expression in cultured rat astrocytes.

Methods

GLP-2R mRNA content was measured by quantitative RT-PCR.

Results

GLP-2R expression was higher in proliferating than in resting cells. The expression was dependent of glucose concentration both in the absence and in the presence of GLP-2. In the presence of a high glucose concentration, GLP-2, PDGF, and PDGF plus GLP-2 presented opposite effects depending on the incubation time. However, insulin, IGF-1, and EGF alone, and plus GLP-2 had no effect. IGF-2, but not IGF-2 plus GLP-2, increased the expression. On the contrary, NGF decreased the GLP-2R expression, but NGF plus GLP-2 increased it even until values similar to those obtained with GLP-2 alone. Interestingly, in the presence of a low glucose concentration, leptin and NPY produced a significant reduction of GLP-2R expression.

Conclusion

Astrocytes are distributed throughout the brain, where GLP-2 appears to have important functions. Since these cells express the GLP-2R, the results of this study could be considered of interest to advance the knowledge of the role of GLP-2 signaling in the CNS, which should lead a better understanding of the events that occur under normal and pathophysiological conditions.

Catch-up growth in intrauterine growth-restricted piglets associated with the restore of pancreatic and intestinal functions via porcine glucagon-like peptide-2 microspheres

Intrauterine growth restriction (IUGR) results in abnormal morphology and gastrointestinal function, such as reduced villi height and crypt depth, thinner mucosa and muscle layers, and reduced brush border enzyme activities, delayed gastric emptying, increased stress response. As a gastrointestinal growth factor, the manner by which the porcine glucagon-like peptide-2 (pGLP-2) microsphere administration restored the gastrointestinal function and growth performance of IUGR piglets was investigated. Fourteen newborn Duroc × (Yorkshire × Landrace) IUGR piglets (0.92 ± 0.113 kg) were assigned into the IUGR (negative control group) and pGLP-2 microsphere groups. The piglets in group pGLP-2 were intraperitoneally administered with 100 mg pGLP-2 microspheres on day 1 after birth. From days 15 to 26 of trial, the body weight of the pGLP-2 group was significantly higher than that of the control. IUGR piglets of group pGLP-2 showed a significantly increased pancreas weight, serum insulin content and activity of lipase and amylase. Injection of pGLP-2 microspheres restored the intestinal absorptive capacity by significantly increasing the mRNA expression of the sodium-glucose cotransporter 1 in the jejunum and the peptide transporter 1 in the jejunum. It also restored the redox balance by increasing the catalase mRNA expression and decreasing the heat shock protein 70 mRNA expression. In addition, this improvement was associated with the significant increase in gut diameter, length and weight. Therefore, it was concluded that the injection of pGLP-2 microspheres was a suitable therapeutic strategy for compensatory growth in low birth weight IUGR piglets.

Effects of butyrate supplementation on blood glucagon-like peptide-2 concentration and gastrointestinal functions of lactating dairy cows fed diets differing in starch content

The objective of this study was to evaluate effects of butyrate supplementation on plasma concentration of glucagon-like peptide-2 (GLP-2), apparent total-tract digestibility, and responses to a grain challenge of lactating dairy cows fed diets differing in starch content. Eight Holstein cows averaging 58.6 ± 9.96 d in milk (4 primiparous cows fitted with rumen cannula and 4 multiparous intact cows) were blocked by parity and assigned to one of two 4 × 4 Latin squares balanced for carryover effects with a 2 × 2 factorial arrangement of treatments. Treatments were dietary starch content [20.6 vs. 27.5%, respectively, for low starch (LS) and high starch (HS)] and butyrate supplementation (butyrate vs. control) with 21-d periods. Butyrate was provided as Gustor BP70 WS (Norel, S.A., Madrid, Spain), containing 70% sodium butyrate and 30% fatty acid mixture, at 2% of dietary dry matter (providing butyrate at 1.1% of dietary dry matter), and control premix contained 70% wheat bran and 30% fatty acid mixture. Feeds, orts, and fecal samples were collected from d 17 to 19 to determine apparent total-tract nutrient digestibility. Blood and rumen fluid samples were collected on d 19. The baseline of dry matter intake (DMI) was determined as average DMI from d 17 to 19 for each cow, and cows were feed-restricted at 60% of the baseline DMI on d 20, and a grain challenge was conducted by providing steam-flaked corn grain at 0.6% of body weight, on an as-fed basis, in addition to each treatment diet on d 21, and blood and ruminal fluid samples were collected. The interaction of dietary starch content by butyrate supplementation was significant for plasma GLP-2 concentration, being greater for cows fed butyrate with the HS diet than those fed the other 3 diets. Cows fed butyrate increased n-butyrate concentration in the ruminal fluid and tended to increase dry matter and organic matter digestibility compared with the control. During the grain challenge, rumen endotoxin concentration increased over time and was higher for cows fed the HS diets compared with those fed LS diets. However, response variables related to inflammation were not affected by the grain challenge. However, serum haptoglobin, lipopolysaccharide-binding protein, and serum amyloid-A concentrations were greater for cows fed butyrate with the LS diet, but not for those fed the HS diet. These results indicate that butyrate supplementation may increase plasma GLP-2 concentration for cows fed HS diets, and total-tract digestibility regardless of dietary starch content. However, butyrate supplementation did not mitigate inflammation in this study.

Glucagon-Like Peptide-2 Improve Intestinal Mucosal Barrier Function in Aged Rats

Glucagon-like peptide-2 (GLP-2) plays a major role in repairing impaired intestinal mucosa, but its mechanism in the improvement of intestinal barrier function during the aging process remains unclear. In this study, 26-month-old male Sprague-Dawley rats were randomized to control group and GLP-2 group treated with a dose of 250 μg•kg-1•d-1 by intraperitoneal injection. After 14 days of treatment, intestinal mucosal morphometric changes were observed by light microscopy and transmission electron microscopy (TEM). Small intestinal permeability was evaluated by fluorescein isothiocyanate (FITC)-labeled dextran. The mRNA and protein expression of Zonula Occludens-1 (ZO-1), occludin, claudin-1 and the GLP-2 receptor (GLP-2R) were detected by Real-time PCR and Western blot. Our results showed that GLP-2 administration significantly improved the age-related atrophy of intestinal mucosa and villi and increased small intestinal permeability. The mRNA and protein expression of ZO-1and occludin in ileum were up regulated in the GLP-2-treated old rats. In addition, the serum GLP-2 levels were negatively correlated with small intestinal permeability measured by FITC-dextran levels (r=-0.610, P<0.01). Taking all these data together, it is concluded that GLP-2 improved small intestinal epithelial barrier function in aged rats mainly by facilitating intestinal mucosa growth, alleviating the increased small intestinal permeability and increasing ZO-1 and occludin expression. Our observations provide evidence for the clinical significance of GLP-2 in preventing the intestinal epithelial barrier dysfunction during aging.