Poly-GLP-1, a novel long-lasting glucagon-like peptide-1 polymer, ameliorates hyperglycaemia by improving insulin sensitivity and increasing pancreatic beta-cell proliferation

Exendin-4 induces a novel extended effect of ischemic tolerance via crosstalk with IGF-1R

Glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) agonist exendin-4 (Ex-4), a drug that has been used in the clinical treatment of type 2 diabetes mellitus, also confers a neuroprotective effect against stroke. Although GLP-1 analogs were reported to induce sustained insulin secretion and glucose tolerance improved after cessation of treatment, no study has revealed whether Ex-4 exerts sustained neuroprotection against stroke and the underlying mechanism after treatment cessation. In this study, mice were pretreated with Ex-4 for 7 days, and middle cerebral artery occlusion (MCAO) was performed on different days after cessation of Ex-4 treatment. Ex-4 ameliorated neurological dysfunction and reduced the infarct volume induced by MCAO. These protective effects lasted for 6 days after the cessation of Ex-4 treatment and were associated with sustained upregulation of PI3K, AKT, mTOR, and HIF-1α levels, as well as HIF-1α downstream genes. Knockdown of GLP-1R or HIF-1α in the brain by short hairpin RNA abolished Ex-4 treatment-mediated neuroprotection. In normal mice, Ex-4 treatment led to instant upregulation of p-PI3K, p-AKT, p-mTOR, and HIF-1α expression levels, which quickly returned to normal after cessation of Ex-4 treatment, while the expression levels of insulin growth factor-1 receptor (IGF-1R) remained high for 6 days after Ex-4 cessation. Additionally, Ex-4 did not directly induce IGF-1 production, which was only induced by MCAO. Ex-4 induces extended cerebral ischemic tolerance. This neuroprotective effect is associated with activation of GLP-1R and upregulation of IGF-1R in the brain, and the latter then activates the PI3K/AKT/mTOR/HIF-1 signaling pathway via binding to IGF-1 secreted from the ischemic brain.

Identification of a prolonged action molecular GLP-1R agonist for the treatment of femoral defects

Poly-GLP-1 promotes angiogenesis to accelerate bone formationviaBMSC differentiation and M2 polarization.

The Glucagon-Like Peptide-1 Receptor Agonist Exendin-4 Inhibits Lipopolysaccharide-Induced Osteoclast Formation and Bone Resorption via Inhibition of TNF-α Expression in Macrophages

Glucagon-like peptide-1 (GLP-1) receptor agonists are an effective treatment approach for type 2 diabetes. Recently, anti-inflammatory effects of GLP-1 receptor agonists have also been reported. Lipopolysaccharide (LPS) induces inflammation and osteoclast formation. In this study, we investigated the effect of exendin-4, a widely used GLP-1 receptor agonist, in LPS-induced osteoclast formation and bone resorption. LPS with or without exendin-4 was administered on mouse calvariae by daily subcutaneous injection. The number of osteoclasts, the ratio of bone resorption pits, and the level of C-terminal cross-linked telopeptide of type I collagen (CTX) were significantly lower in LPS- and exendin-4-coadministered mice than in mice administered with LPS alone. RANKL and TNF-α mRNA expression levels were lower in the exendin-4- and LPS-coadministered group than in the LPS-administered group. Our in vitro results showed no direct effects of exendin-4 on RANKL-induced osteoclast formation, TNF-α-induced osteoclast formation, or LPS-induced RANKL expression in stromal cells. Conversely, TNF-α mRNA expression was inhibited in the exendin-4- and LPS-cotreated macrophages compared with cells treated with LPS alone. These results indicate that the GLP-1 receptor agonist exendin-4 may inhibit LPS-induced osteoclast formation and bone resorption by inhibiting LPS-induced TNF-α production in macrophages.

Bariatric surgery and obesity: influence on the incretins

The gut hormone incretins have an important physiological role in meal-related insulin release and post-prandial glucose control. In addition to weight loss, the incretin hormones have a role in glucose control after bariatric surgery. The release of incretins, and specifically of glucagon-like peptide (GLP)-1, in response to the ingestion of nutrients, is greatly enhanced after gastric bypass (RYGBP). The rapid transit of food from the gastric pouch to the distal ileum is responsible for the greater GLP-1 release after RYGBP. The incretin effect on insulin secretion, or the greater insulin response to oral glucose compared to an isoglycemic intravenous glucose challenge, is severely impaired in patients with type 2 diabetes, but is recovered rapidly after RYGBP. The improvement in insulin secretion rate and β-cell sensitivity to oral glucose after RYGBP is mediated by endogenous GLP-1, and is abolished by exendin 9-39, a specific GLP-1 receptor antagonist. While calorie restriction and weight loss have major effects on the rapid and sustained improvement of fasted glucose metabolism, the enhanced incretin effect is a key player in post-prandial glucose control after RYGBP.

Effect of Glucagon-like Peptide-1 on the Differentiation of Adipose-derived Stem Cells into Osteoblasts and Adipocytes

Objectives

Glucagon-like peptide-1 (GLP-1) is an intestinally secreted hormone and it plays an important role in the regulation of glucose homeostasis. However, the possible role of GLP-1 in the differentiation of adipose-derived stem cells (ADSCs) remains unknown. Therefore this study investigated the effect of GLP-1 on the differentiation of ADSCs into osteoblasts and adipocytes.

Methods

ADSCs were isolated from human adipose tissues of the abdomens, cultured and characterized by flow cytometry and multi-lineage potential assay. ADSCs were induced in osteogenic and adipogenic media treated with two different doses (10 and 100 nM) of GLP-1, and then the effect of GLP-1 on differentiation of ADSCs into osteoblast and adipocyte was examined. The signaling pathway involved in these processes was also examined.

Results

Isolated human ADSCs expressed mesenchymal stem cell (MSC) specific markers as well as GLP-1 receptor (GLP-1R) proteins. They also showed multiple-lineage potential of MSC. GLP-1 was upregulated the activity and mRNA expression of osteoblast-specific marker, alkaline phosphatase and the mineralization of calcium. In contrast, GLP-1 significantly suppressed the expression of adipocyte-specific markers, peroxisome proliferator-activated receptor gamma (PPAR-γ), lipoprotein lipase (LPL) and adipocyte protein 2 (AP2). This decreased expression of adipocyte specific markers caused by GLP-1 was significantly reversed by the treatment of extracellular signal-regulated kinase (ERK) inhibitor, PD98059 (P < 0.05).

Conclusion

This result demonstrates that GLP-1 stimulates osteoblast differentiation in ADSCs, whereas it inhibits adipocyte differentiation. The ERK signaling pathway seems to be involved in these differentiation processes mediated by GLP-1.

Exendin-4, a glucagon-like peptide-1 receptor agonist, prevents osteopenia by promoting bone formation and suppressing bone resorption in aged ovariectomized rats

Osteoporosis mainly affects postmenopausal women and older men. Gastrointestinal hormones released after meal ingestion, such as glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide (GLP)-2, have been shown to regulate bone turnover. However, whether GLP-1, another important gastrointestinal hormone, and its analogues also have antiosteoporotic effects, especially in aged postmenopausal situation, has not been confirmed. In the present study, we evaluated the effects of the GLP-1 receptor agonist exendin-4 on ovariectomy (OVX)-induced osteoporosis in old rats. Twelve-month-old female Sprague-Dawley rats were subjected to OVX, and exendin-4 was administrated 4 weeks after the surgery and lasted for 16 weeks. Bone characters and related serum and gene biomarkers were analyzed. Sixteen weeks of treatment with exendin-4 slowed down body weight gain by decreasing fat mass and prevented the loss of bone mass in old OVX rats. Exendin-4 also enhanced bone strength and prevented the deterioration of trabecular microarchitecture. Moreover, exendin-4 decreased the urinary deoxypyridinoline (DPD)/creatinine ratio and serum C-terminal cross-linked telopeptides of type I collagen (CTX-I) and increased serum alkaline phosphatase (ALP), osteocalcin (OC), and N-terminal propeptide of type 1 procollagen (P1NP) levels, key biochemical markers of bone turnover. Interestingly, gene expression results further showed that exendin-4 not only inhibited bone resorption by increasing the osteoprotegerin (OPG)/receptor activator of NF-κB ligand (RANKL) ratio, but also promoted bone formation by increasing the expression of OC, Col1, Runx2, and ALP, which exhibited dual regulatory effects on bone turnover as compared with previous antiosteoporotic agents. In conclusion, these findings demonstrated for the first time the antiosteoporotic effects of exendin-4 in old OVX rats and that it might be a potential candidate for treatment of aged postmenopausal osteoporosis.

Glucagon-like peptide 1 receptor plays an essential role in geniposide attenuating lipotoxicity-induced β-cell apoptosis

β-Cell apoptosis is considered to be a major cause of loss of β cells in diabetes. Geniposide could prevent oxidative stress-induced neuron apoptosis, and improved glucose stimulated insulin secretion by activating glucagon-like peptide 1 receptor (GLP-1R) in INS-1 cells. Here we have investigated whether geniposide can exert a direct effect against pancreatic β-cell lipoapoptosis. The results indicated that pretreatment pancreatic INS-1 cells with geniposide for 7h attenuated palmitate-induced β-cell apoptosis and active caspase-3 expression, but this effect was disappeared at 18 h. Long-term incubation with palmitate decreased GLP-1R expression in INS-1 cells, and exendin (9-39), an antagonist for GLP-1R, inhibited the effect of geniposide on palmitate-induced apoptosis in INS-1 cells. Moreover, geniposide also improved the impairment of GLP-1R signaling through enhancing the phosphorylation of Akt and Foxo1, and increased the expression of PDX-1 in palmitate-treated INS-1 cells. These results suggest that geniposide inhibits early stage of lipotoxicity-induced β-cell apoptosis, and GLP-1R plays a critical role in geniposide counteracting the action of lipotoxicity in INS-1 pancreatic β cells.

A highly parallel method for synthesizing DNA repeats enables the discovery of 'smart' protein polymers

Robust high-throughput synthesis methods are needed to expand the repertoire of repetitive protein-polymers for different applications. To address this need, we developed a new method, overlap extension rolling circle amplification (OERCA), for the highly parallel synthesis of genes encoding repetitive protein-polymers. OERCA involves a single PCR-type reaction for the rolling circle amplification of a circular DNA template and simultaneous overlap extension by thermal cycling. We characterized the variables that control OERCA and demonstrated its superiority over existing methods, its robustness, high-throughput and versatility by synthesizing variants of elastin-like polypeptides (ELPs) and protease-responsive polymers of glucagon-like peptide-1 analogues. Despite the GC-rich, highly repetitive sequences of ELPs, we synthesized remarkably large genes without recursive ligation. OERCA also enabled us to discover 'smart' biopolymers that exhibit fully reversible thermally responsive behaviour. This powerful strategy generates libraries of repetitive genes over a wide and tunable range of molecular weights in a 'one-pot' parallel format.

Gastrointestinal hormones and the regulation of β-cell mass

Type 2 diabetes occurs due to a relative deficit in β-cell mass or function. Glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), cholecystokinin (CCK), and gastrin are gastrointestinal hormones that are secreted in response to nutrient intake, regulating digestion, insulin secretion, satiety, and β-cell mass. In this review, we focus upon β-cell mass regulation. β-cell mass expands through β-cell proliferation and islet neogenesis; β-cell mass is lost via apoptosis. GLP-1 and GIP are well-studied gastrointestinal hormones and influence β-cell proliferation, apoptosis, and islet neogenesis. CCK regulates β-cell apoptosis and mitogenesis, and gastrin stimulates islet neogenesis. GLP-1 and GIP bind to G protein-coupled receptors and regulate β-cell mass via multiple signaling pathways. The protein kinase A pathway is central to this process because it directly regulates proliferative and anti-apoptotic genes and transactivates several signaling cascades, including Akt and mitogen-activated protein kinases. However, the signaling pathways downstream of G protein-coupled CCK receptors that influence β-cell mass remain unidentified. Gastrointestinal hormones integrate nutrient signals from the gut to the β-cell, regulating insulin secretion and β-cell mass adaptation.