Role of Islet Glucokinase, Glucose Metabolism, and Insulin Pathway in the Enhancing Effect of Islet Neogenesis-Associated Protein on Glucose-Induced Insulin Secretion

Structural modifications of INGAP-PP present in HTD4010 peptide potentiate its effect on rat islet gene expression and insulin secretion

Type 2 diabetes (T2D) is characterized by peripheral insulin resistance and altered insulin secretion due to a progressive loss of β-cell mass and function. Today, most antidiabetic agents are designed to resolve impaired insulin secretion and/or insulin resistance, and only GLP-1-based formulations contribute to stopping the decline in β-cell mass. HTD4010, a peptide carrying two modifications of the amino acid sequence of INGAP-PP (N-terminus acetylation and substitution of Asn13 by Ala) showed greater plasma stability and could be a good candidate for proposal as a drug that could improve β cell mass and function lost in T2D. In the present study, we showed that HTD4010 included in the culture media of normal rat islets at a dose 100 times lower than that used for INGAP-PP was able to modulate, in the same way as the original peptide, both insulin secretion in response to glucose and the expression of key genes related to insular function, insulin and leptin intracellular pathways, neogenesis, apoptosis, and inflammatory response. Our results confirm the positive effect of HTD4010 on β-cell function and gene expression of factors involved in the maintenance of β-cell mass. Although new assays in animal models of prediabetes and T2D must be performed to be conclusive, our results are very encouraging, and they suggest that the use of HTD4010 at a dose 100 times lower than that of INGAP-PP could minimize its side effects in a future clinical trial.

Transcriptional signature of islet neogenesis-associated protein peptide-treated rat pancreatic islets reveals induction of novel long non-coding RNAs

Background

Diabetes mellitus is characterized by chronic hyperglycemia with loss of β-cell function and mass. An attractive therapeutic approach to treat patients with diabetes in a non-invasive way is to harness the innate regenerative potential of the pancreas. The Islet Neogenesis-Associated Protein pentadecapeptide (INGAP-PP) has been shown to induce β-cell regeneration and improve their function in rodents. To investigate its possible mechanism of action, we report here the global transcriptional effects induced by the short-term INGAP-PP in vitro treatment of adult rat pancreatic islets.

Methods and findings

Rat pancreatic islets were cultured in vitro in the presence of INGAP-PP for 4 days, and RNA-seq was generated from triplicate treated and control islet samples. We performed a de novo rat gene annotation based on the alignment of RNA-seq reads. The list of INGAP-PP-regulated genes was integrated with epigenomic data. Using the new gene annotation generated in this work, we quantified RNA-seq data profiled in INS-1 cells treated with IL1β, IL1β+Calcipotriol (a vitamin D agonist) or vehicle, and single-cell RNA-seq data profiled in rat pancreatic islets. We found 1,669 differentially expressed genes by INGAP-PP treatment, including dozens of previously unannotated rat transcripts. Genes differentially expressed by the INGAP-PP treatment included a subset of upregulated transcripts that are associated with vitamin D receptor activation. Supported by epigenomic and single-cell RNA-seq data, we identified 9 previously unannotated long noncoding RNAs (lncRNAs) upregulated by INGAP-PP, some of which are also differentially regulated by IL1β and vitamin D in β-cells. These include Ri-lnc1, which is enriched in mature β-cells.

Conclusions

Our results reveal the transcriptional program that could explain the enhancement of INGAP-PP-mediated physiological effects on β-cell mass and function. We identified novel lncRNAs that are induced by INGAP-PP in rat islets, some of which are selectively expressed in pancreatic β-cells and downregulated by IL1β treatment of INS-1 cells. Our results suggest a relevant function for Ri-lnc1 in β-cells. These findings are expected to provide the basis for a deeper understanding of islet translational results from rodents to humans, with the ultimate goal of designing new therapies for people with diabetes.

Islet neogenesis associated protein (INGAP) protects pancreatic β cells from IL-1β and IFNγ-induced apoptosis

The goal of this study was to determine whether recombinant Islet NeoGenesis Associated Protein (rINGAP) and its active core, a pentadecapeptide INGAP104-118 (Ingap-p), protect β cells against cytokine-induced death. INGAP has been shown to induce islet neogenesis in diabetic animals, to stimulate β-cell proliferation and differentiation, and to improve islet survival and function. Importantly, Ingap-p has shown promising results in clinical trials for diabetes (phase I/II). However, the full potential of INGAP and its mechanisms of action remain poorly understood. Using rat insulinoma cells RINm5F and INS-1 treated with interleukin-1β (IL-1β) and interferon-gamma (IFN-γ), we demonstrate here that both rINGAP and Ingap-p inhibit apoptosis, Caspase-3 activation, inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production, and explore the related signaling pathways. As expected, IL-1β induced nuclear factor kappa B (NF-κB), p38, and JNK signaling, whereas interferon-gamma (IFN-γ) activated the JAK2/STAT1 pathway and potentiated the IL-1β effects. Both rINGAP and Ingap-p decreased phosphorylation of IKKα/β, IkBα, and p65, although p65 nuclear translocation was not inhibited. rINGAP, used for further analysis, also inhibited STAT3, p38, and JNK activation. Interestingly, all inhibitory effects of rINGAP were observed for the cytokine cocktail, not IL-1β alone, and were roughly equal to reversing the potentiating effects of INFγ. Furthermore, rINGAP had no effect on IL-1β/NF-κB-induced gene expression (e.g., Ccl2, Sod2) but downregulated several IFNγ-stimulated (Irf1, Socs1, Socs3) or IFNγ-potentiated (Nos2) genes. This, however, was observed again only for the cytokine cocktail, not IFNγ alone, and rINGAP did not inhibit the IFNγ-induced JAK2/STAT1 activation. Together, these intriguing results suggest that INGAP does not target either IL-1β or IFNγ individually but rather inhibits the signaling crosstalk between the two, the exact mechanism of which remains to be investigated. In summary, our study characterizes the anti-inflammatory effects of INGAP, both protein and peptide, and suggests a new therapeutic utility for INGAP in the treatment of diabetes.

p110γ deficiency protects against pancreatic carcinogenesis yet predisposes to diet-induced hepatotoxicity

Pancreatic ductal adenocarcinoma (PDAC) is notorious for its poor survival and resistance to conventional therapies. PI3K signaling is implicated in both disease initiation and progression, and specific inhibitors of selected PI3K p110 isoforms for managing solid tumors are emerging. We demonstrate that increased activation of PI3K signals cooperates with oncogenic Kras to promote aggressive PDAC in vivo. The p110γ isoform is overexpressed in tumor tissue and promotes carcinogenesis via canonical AKT signaling. Its selective blockade sensitizes tumor cells to gemcitabine in vitro, and genetic ablation of p110γ protects against Kras-induced tumorigenesis. Diet/obesity was identified as a crucial means of p110 subunit up-regulation, and in the setting of a high-fat diet, p110γ ablation failed to protect against tumor development, showing increased activation of pAKT and hepatic damage. These observations suggest that a careful and judicious approach should be considered when targeting p110γ for therapy, particularly in obese patients.

Effects of islet neogenesis associated protein depend on vascular endothelial growth factor gene expression modulated by hypoxia-inducible factor 1-alpha

BACKGROUND

Pharmacology has provided efficient tools to improve insulin effect/secretion but the decrease in β-cell mass remains elusive. INGAP-PP could provide a therapeutic alternative to meet that challenge.

AIM

To further understand the mechanism that links INGAP-PP effects upon β-cell mass and function with islet angiogenesis.

METHODOLOGY

Normal male Wistar rats were divided into 2 groups and injected with a single dose of 100 mg/Kg suramin or saline. Both groups were divided into 2 subgroups that received daily doses of 2 mg/kg INGAP-PP or saline for ten days. Plasma glucose, triacylglycerol, TBARS, and insulin levels were measured. Pancreas immunomorphometric analyses were also performed. Pancreatic islets were isolated to measure glucose-stimulated insulin secretion (GSIS). Specific islet mRNA levels were studied by qRT-PCR. Statistical analysis was done using ANOVA.

RESULTS

No differences were recorded in body weight, food intake, or any other plasma parameter measured in all groups. Islets from INGAP-PP-treated rats significantly increased GSIS, β-cell mass, and mRNA levels of Bcl-2, Ngn-3, VEGF-A, VEGF-R2, CD31, Ang1 and Ang2, Laminin β-1, and Integrin β-1, and decreased mRNA levels of Caspase-8, Bad, and Bax. Islets from suramin-treated rats showed significant opposite effects, but INGAPP-PP administration rescued most of the suramin effects in animals treated with both compounds.

CONCLUSION

Our results reinforce the concept that INGAP-PP enhances insulin secretion and β-cell mass, acting through PI3K/Akt/mTOR pathways and simultaneously activating angiogenesis through HIF-1α-mediated VEGF-A secretion. Therefore, INGAP-PP might be a suitable antidiabetic agent able to overcome two major alterations present in T2D.

INGAP-PP effects on β-cell mass and function are related to its positive effect on islet angiogenesis and VEGFA production

Our aim was to determine whether islet angiogenesis and VEGFA production/release participate in the mechanism by which INGAP-PP enhances β-cell function and mass. We used two models: a) in vivo (normal rats injected with INGAP-PP for 10 days) and b) in vitro (normal islets cultured for 4 days with INGAP-PP, VEGFA, Rapamycin, and the specific VEGF-Receptor inhibitor, SU5416). INGAP-PP administration enhanced insulin secretion, β-cell mass, islet vascularization, and angiogenesis without affecting glucose homeostasis. Normal islets cultured with INGAP-PP and VEGFA increased insulin and VEGFA secretion while apoptosis decreased. INGAP-PP-induced effects were prevented by both Rapamycin and SU5416. INGAP-PP effects on β-cell mass and function were significantly associated with a positive effect on islet angiogenesis and VEGFA production/release. VEGF-A possibly potentiates INGAP-PP effect through mTORC pathway.

Liver carbohydrates metabolism: A new islet-neogenesis associated protein peptide (INGAP-PP) target

Islet-Neogenesis Associated Protein-Pentadecapeptide (INGAP-PP) increases β-cell mass and enhances glucose and amino acids-induced insulin secretion. Our aim was to demonstrate its effect on liver metabolism. For that purpose, adult male Wistar rats were injected twice-daily (10 days) with saline solution or INGAP-PP (250 μg). Thereafter, serum glucose, triglyceride and insulin levels were measured and homeostasis model assessment (HOMA-IR) and hepatic insulin sensitivity (HIS) were determined. Liver glucokinase and glucose-6-phosphatase (G-6-Pase) expression and activity, phosphoenolpyruvate carboxykinase (PEPCK) expression, phosphofructokinase-2 (PFK-2) protein content, P-Akt/Akt and glycogen synthase kinase-3β (P-GSK3/GSK3) protein ratios and glycogen deposit were also determined. Additionally, glucokinase activity and G-6-Pase and PEPCK gene expression were also determined in isolated hepatocytes from normal rats incubated with INGAP-PP (5 μg/ml). INGAP-PP administration did not modify any of the serum parameters tested but significantly increased activity of liver glucokinase and the protein level of its cytosolic activator, PFK-2. Conversely, INGAP-PP treated rats decreased gene expression and enzyme activity of gluconeogenic enzymes, G-6-Pase and PEPCK. They also showed a higher glycogen deposit and P-GSK3/GSK3 and P-Akt/Akt ratio. In isolated hepatocytes, INGAP-PP increased GK activity and decreased G-6-Pase and PEPCK expression. These results demonstrate a direct effect of INGAP-PP on the liver acting through P-Akt signaling pathway. INGAP-PP enhances liver glucose metabolism and deposit and reduces its production/output, thereby contributing to maintain normal glucose homeostasis. These results reinforce the concept that INGAP-PP might become a useful tool to treat people with impaired islet/liver glucose metabolism as it occurs in T2D.

The adverse effects of perinatal exposure to nonylphenol on carbohydrate metabolism in male offspring rats

BACKGROUND

We sought to investigate the adverse effects of perinatal exposure to nonylphenol (NP) on carbohydrate metabolism of male offspring rats.

METHODS

Thirty-two healthy pregnant Sprague Dawley rats were randomly divided into four groups, control normal diet group (C), NP normal diet group (NPN), control high-energy diet group (CH), and NP high-energy diet group (NPH). Both of the control groups were received a gavage of corn oil and the NP-groups were received NP (200 mg/kg/day) from gestational days 6 to post-natal day (PND) 21. The concentrations of NP in pancreatic tissues were measured by high-performance liquid chromatography (HPLC). The key genes of glucose metabolism expression were detected by reverse transcription-polymerase chain reaction (RT-PCR). The pancreatic tissues were stained with hematoxylin/eosin (HE).

RESULTS

On PND 1, the body weights of male pups in the NPN and NPH groups were lower than those of the CH group (p = 0.012 and 0.001, respectively). On PND 30, the body weight of male pups from the NPH group was elevated compared with the C group (p = 0.019), while the body weights of male pups in the NPN and NPH groups were elevated compared to the CH group (p = 0.034 and 0.004, respectively). On PND 60, the body weights of NPN and NPH pups were higher than those in the C (p < 0.001) and CH groups (p < 0.001). The levels of fasting blood glucose (FBG) were increased significantly in the animals treated with NP compared to control animals (F = 29.14, p < 0.001). The FBG levels in the treatment groups are ranked as follows: NPH > NPN > CH > C (p < 0.05). The concentrations of NP in pancreas tissues in both the NPN (2045.0 ± 130.1 μg/L) and NPH groups (2038.0 ± 104.2 μg/L) were higher than those in the C (499.5 ± 27.4 μg/L) and CH groups (494.2 ± 22.4 μg/L; p < 0.05). Morphological examination of tissues from rats exposed to NP shown that the NP-treated groups appeared to have a higher degree of inflammatory injury, edema, and focal necrotic cells in the pancreatic tissues. Compared with C group, expression of glucokinase (GCK) was down-regulated, while Uncoupling protein-2 (UCP-2) was up-regulated in the NP-treated groups (F_GCK = 218.89, p < 0.001; F_UCP-2 = 18.82, p < 0.001).

CONCLUSIONS

Prenatal exposure to NP could induce glucose metabolism disorder in male F1 rats, which may be due to the fact that NP induces abnormal expression patterns of GCK and UCP-2.

Formononetin exhibits anti-hyperglycemic activity in alloxan-induced type 1 diabetic mice

The aim of this study was to investigate the anti-hyperglycemic activity and mechanism of formononetin in alloxan-induced type 1 diabetic mice by determining its effect on some diabetes-related indices as described below. Body weight, fasting blood glucose, hepatic glycogen, serum insulin, and serum glucagon were determined by electronic scales, glucometer, and ELISA kits. Fas, Caspase-3, pancreatic and duodenal homeobox-1 , insulin receptor substrate 2, glucokinase and glucose transporter 2, mRNA and proteins levels in pancreas tissue, and glucokinase and glucose-6-phosphatase mRNA, and proteins levels in liver tissue were detected by fluorogenic quantitative-polymerase chain reaction and Western blot assays. The results indicated that formononetin (5, 10, and 20 mg/kg; oral administration) reversed the alloxan-induced increase of some indices (fasting blood glucose level and Fas and Caspase-3 mRNA and proteins levels in pancreas tissue) and reduction of some indices (body weight gain, oral glucose tolerance, insulin activity, hepatic glycogen level, pancreatic and duodenal homeobox-1, insulin receptor substrate 2, glucokinase and glucose transporter 2, mRNA and proteins levels in pancreas tissue, and glucokinase mRNA and protein levels in liver tissue). The glucagon level and glucose-6-phosphatase mRNA and protein levels in liver tissue were not affected by the drugs administration. In conclusion, formononetin exhibited anti-hyperglycemic activity in alloxan-induced type 1 diabetic mice by inhibiting islet B cell apoptosis and promoting islet B cell regeneration, insulin secretion, hepatic glycogen synthesis, and hepatic glycolysis.