Mutational Landscape of the Proglucagon-Derived Peptides

Strong efforts have been placed on understanding the physiological roles and therapeutic potential of the proglucagon peptide hormones including glucagon, GLP-1 and GLP-2. However, little is known about the extent and magnitude of variability in the amino acid composition of the proglucagon precursor and its mature peptides. Here, we identified 184 unique missense variants in the human proglucagon gene GCG obtained from exome and whole-genome sequencing of more than 450,000 individuals across diverse sub-populations. This provides an unprecedented source of population-wide genetic variation data on missense mutations and insights into the evolutionary constraint spectrum of proglucagon-derived peptides. We show that the stereotypical peptides glucagon, GLP-1 and GLP-2 display fewer evolutionary alterations and are more likely to be functionally affected by genetic variation compared to the rest of the gene products. Elucidating the spectrum of genetic variations and estimating the impact of how a peptide variant may influence human physiology and pathophysiology through changes in ligand binding and/or receptor signalling, are vital and serve as the first important step in understanding variability in glucose homeostasis, amino acid metabolism, intestinal epithelial growth, bone strength, appetite regulation, and other key physiological parameters controlled by these hormones.

GLP-2 Prevents Neuronal and Glial Changes in the Distal Colon of Mice Chronically Treated with Cisplatin

Cisplatin is a chemotherapeutic agent widely used for the treatment of solid cancers. Its administration is commonly associated with acute and chronic gastrointestinal dysfunctions, likely related to mucosal and enteric nervous system (ENS) injuries, respectively. Glucagon-like peptide-2 (GLP-2) is a pleiotropic hormone exerting trophic/reparative activities on the intestine, via antiapoptotic and pro-proliferating pathways, to guarantee mucosal integrity, energy absorption and motility. Further, it possesses anti-inflammatory properties. Presently, cisplatin acute and chronic damages and GLP-2 protective effects were investigated in the mouse distal colon using histological, immunohistochemical and biochemical techniques. The mice received cisplatin and the degradation-resistant GLP-2 analog ([Gly2]GLP-2) for 4 weeks. Cisplatin-treated mice showed mucosal damage, inflammation, IL-1β and IL-10 increase; decreased number of total neurons, ChAT- and nNOS-immunoreactive (IR) neurons; loss of SOX-10-IR cells and reduced expression of GFAP- and S100β-glial markers in the myenteric plexus. [Gly2]GLP-2 co-treatment partially prevented mucosal damage and counteracted the increase in cytokines and the loss of nNOS-IR and SOX-10-IR cells but not that of ChAT-IR neurons. Our data demonstrate that cisplatin causes mucosal injuries, neuropathy and gliopathy and that [Gly2]GLP-2 prevents these injuries, partially reducing mucosal inflammation and inducing ENS remodeling. Hence, this analog could represent an effective strategy to overcome colonic injures induced by cisplatin.

Differential expression of glucagon-like peptide-2 (GLP-2) is involved in pancreatic islet cell adaptations to stress and beta-cell survival

Recent studies have confirmed that locally released proglucagon derived gene products, other than glucagon, have a major influence on pancreatic endocrine function. We assessed the impact of glucagon-like peptide-2 (GLP-2) on beta-cell secretory function, proliferation and apoptosis, as well as glucose tolerance, feeding behaviour and islet adaptions to chemically-induced insulin deficiency and resistance. The GLP-2 receptor was evidenced on cultured rodent and human beta-cells, rodent alpha-cells and isolated mouse islets. GLP-2 had no effect on insulin secretion from beta-cells, or isolated mouse islets. In vivo, GLP-2 administration significantly (P<0.05 to P<0.01) decreased food intake in mice. Conversely, GLP-2 had no discernible effects on glucose disposal or insulin secretion. As expected, streptozotocin treatment decreased and hydrocortisone increased beta-cell mass in mice. GLP-2 was visualised in mouse islets and intestinal L-cells. Islet GLP-2 co-localisation with glucagon was significantly decreased (P<0.01) by both streptozotocin and hydrocortisone. In contrast, both interventions increased (P<0.05) co-localisation of GLP-2 with somatostatin. Interestingly, GLP-2 positive cells were reduced (P<0.05) in the intestines of streptozotocin, but not hydrocortisone, treated mice. Further in vitro investigations revealed that GLP-2 protected rodent and human 1.1B4 beta-cells against streptozotocin induced DNA damage. Furthermore, GLP-2 augmented (P<0.05) BRIN BD11 beta-cell proliferation, but was less efficacious in 1.1B4 cells. These data highlight the involvement of GLP-2 receptor signalling in the adaptations to pancreatic islet cell stress.

Neonatal oxytocin administration and supplemental milk ameliorate the weaning transition and alter hormonal expression in the gastrointestinal tract in pigs

The aim of this study was to investigate the influences of milk supplementation during lactation, over 1 wk after weaning, and oxytocin administration for the first 14 d of life on the pigs' response to weaning. Pigs from 20 litters were allocated to each of these 3 treatments in a randomized factorial design. Oxytocin was administered subcutaneously daily from 0 to 14 d of age at a rate of 10 I.U. per kg. The milk supplement consisted of a mixture of 25% skim milk powder offered either during lactation between 10 and 20 d of age or for the first week after weaning as a transitional diet along with dry pellets. Pigs were weaned at 21 d of age. Growth rate was measured from birth to slaughter at 140 d of age and feed intake of supplemental milk or feed from 10 to 56 d of age. Organ weights (heart, liver, stomach, and kidneys) and the gene expression of ghrelin, leptin, and glucagon-like peptides (glucagon-like peptide-1 and glucagon-like peptide-2) were measured in the stomach, ileum, and duodenum at 10, 21, and 28 d of age. Milk supplementation after weaning resulted in immediate feed intake and partially alleviated the depression in growth rate over the first 7 d postweaning (P < 0.001), but milk supplementation during lactation had no effects (P > 0.1). However, effects were only transient and disappeared once the milk liquid diet was removed. Neonatal oxytocin administration reduced weight loss over the first 2 d after weaning (P = 0.03), without affecting feed intake (P > 0.1), hence possibly reducing weaning stress. Seven days after weaning, oxytocin-treated pigs had greater stomach ghrelin and leptin expression (both P = 0.02), and pigs supplemented with milk after weaning had greater stomach leptin and glucagon-like peptide-2 expression (P = 0.02 and P = 0.05, respectively). Hence, neonatal oxytocin administration or postweaning milk supplementation are both effective means of enhancing gastric leptin expression and reducing weight loss at weaning, likely improving gut health during this critical period.

Combined effects of oligofructose and Bifidobacterium animalis on gut microbiota and glycemia in obese rats

OBJECTIVE

Prebiotics and probiotics may be able to modify an obesity-associated gut microbiota. The aim of this study was to examine the individual and combined effects of the prebiotic oligofructose (OFS) and the probiotic Bifidobacterium animalis subsp. lactis BB-12 (BB-12) on gut microbiota and host metabolism in obese rats.

METHODS

Adult male, diet-induced obese Sprague Dawley rats were randomized to: (1) Control (C); (2) 10% OFS; (3) BB-12; (4) OFS + BB-12 for 8 weeks (n = 9-10 rats/group). Body composition, glycemia, gut permeability, satiety hormones, cytokines, and gut microbiota were examined.

RESULTS

Prebiotic, but not probiotic reduced energy intake, weight gain, and fat mass (P < 0.01). OFS, BB-12, and the combined OFS + BB-12 improved glycemia (P < 0.05). Individually, OFS and BB-12 reduced insulin levels (P < 0.05). Portal GLP-1 was increased with OFS, whereas probiotic increased GLP-2 (P < 0.05). There was a marked increase in bifidobacteria and lactobacilli (P < 0.01) with OFS that was not observed with probiotic alone.

CONCLUSIONS

The impact of prebiotic intake on body composition and gut microbiota was of greater magnitude than the probiotic BB-12. Despite this, an improvement in glucose AUC with both prebiotic or probiotic demonstrates the beneficial role of each of these "biotic" agents in glycemic control.

[Transfection and identification of the cloned strain that stably expressing glucagon like peptide-2 receptor in CaCO2 cell lines]

OBJECTIVE

To establish Caco2 cell line with stable expression of glucagon like peptide-2 receptor( GLP-2R) , in order to establish an in vitro model for the study of protective mechanism of GLP-2 of the intestinal tract.

METHODS

The GLP-2R/pcDNA3. 1 ( + ) plasmid was verified by restriction endonuclease and sequencing , and then it was transfected into Caco2 cells with lipofectamine. After G418 selection, the clones with stable expression of GLP-2R were obtained by limited dilution cloning and expanding. The mRNA and protein expression of GLP-2R in normal human intestine, Caco2 cells, HER293, VE cells, as well as in transfected Caco2 cells were determined with RT-PCR and Western blot.

RESULTS

The sequence of GLP-2R/pcDNA 3. 1 plasmid was correct. No expression of GLP-2R mRNA and protein was found in HER293 and VE cells, but weak expression were found in Caco2 cells, and strong expression was found in normal human intestines. The expression of GLP-2R mRNA and protein expression in Caco2/GLP-2R ( + ) cells were obviously increased after transfection.

CONCLUSION

GLP-2R has special distribution. The expression of GLP-2R is weak in normal Caco2 cells. The establishment of Caco2/GLP-2R ( + ) cellular model is beneficial for the further research of the mechanism of action of GLP-2.