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OBJECTIVE: To explore the synergistic effect of deoxyribonuclease I (DNase I) knockdown combined with Schizandrin A (Sch A) in protecting islet beta-cells (ß-cells) from apoptosis under high-glucose (HG) conditions. METHODS: The concentration of Sch A was detected by Cell Counting Kit-8 (CCK-8). High glucose-cultured rat insulinoma beta cell line (RIN-M5F) cells were treated with Sch A and transfected with DNase I small interfering RNA (siRNA). Cell apoptosis rate and apoptosis-related protein level were examined by flow cytometry and Western blot method respectively. In addition, Na-K-adenosine triphosphatease (Na-K-ATPase) and Ca-Mg-ATPase activity, cell membrane potential, and intracellular Ca concentration was also examined respectively. RESULTS: Our study revealed that HG stimulation can cause a significant increase in DNase I level and cell apoptosis rate. However, Sch A combined with DNase I knockdown can significantly decrease the cell apoptosis rate and apoptosis-related protein levels such as BAX ( 0.05) and Caspase-3 ( 0.01). In addition, we also found that the combination of Sch A and DNase I knockdown can dramatically increase cell membrane potential level, Na-K-ATPase, and Ca-Mg-ATPase activity. Meanwhile, intracellular Ca concentration was also found to be significantly decreased by the synergistic effect of Sch A and DNase I knockdown. CONCLUSION: Overall, our study reveals a synergistic effect of Sch A and DNase I knockdown in protecting ß-cells from HG-induced apoptosis.

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The pharmacological potential of industrial hemp (Cannabis sativa) has been widely studied. However, the majority of studies have focused on cannabidiol, isolated from the inflorescence and leaf of the plant. In the present study, we evaluated the anti-diabetic potential of hemp root water (HWE) and ethanol extracts (HEE) in streptozotocin (STZ)-induced insulin-deficient diabetic mice. The administration of HWE and HEE ameliorated hyperglycemia and improved glucose homeostasis and islet function in STZ-treated mice (p < 0.05). HWE and HEE suppressed ß-cell apoptosis and cytokine-induced inflammatory signaling in the pancreas (p < 0.05). Moreover, HWE and HEE normalized insulin-signaling defects in skeletal muscles and apoptotic response in the liver and kidney induced by STZ (p < 0.05). Gas chromatography-mass spectrometry analysis of HWE and HEE showed possible active compounds which might be responsible for the observed anti-diabetic potential. These findings indicate the possible mechanisms by which hemp root extracts protect mice against insulin-deficient diabetes, and support the need for further studies geared towards the application of hemp root as a novel bioactive material.

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Pancreatic ß-cell apoptosis is a key feature of diabetes and can be induced by chronic exposure to saturated fatty acids (FAs). However, the underlying mechanisms remain poorly understood. We presently evaluated the role of Mcl-1 and mTOR in mice fed with high-fat-diet (HFD) and ß-cells exposed to the overloaded palmitic acid (PA). Compared with normal-chow-diet (NCD)-fed mice, HFD group showed impaired glucose tolerance after two months. Along with the diabetes progression, pancreatic islets first became hypertrophic and then atrophic, the ratio of ß-cell:α-cell increased in the islets of four months HFD-fed mice while decreased after six months. This process was accompanied by significantly increased ß-cell apoptosis and AMPK activity, and decreased Mcl-1 expression and mTOR activity. Consistently, glucose-induced insulin secretion dropped. In terms of mechanism, PA with lipotoxic dose could activate AMPK, which in turn inhibited ERK-stimulated Mcl-1Thr163 phosphorylation. Meanwhile, AMPK blocked Akt activity to release Akt inhibition on GSK3ß, followed by GSK3ß-initiated Mcl-1Ser159 phosphorylation. The context of Mcl-1 phosphorylation finally led to its degradation by ubiquitination. Also, AMPK inhibited the activity of mTORC1, resulting in a lower level of Mcl-1. Suppression of mTORC1 activity and Mcl-1 expression positively related to ß-cell failure. Alteration of Mcl-1 or mTOR expression rendered different tolerance of ß-cell to different dose of PA. In conclusion, lipid oversupply-induced dual modulation of mTORC1 and Mcl-1 finally led to ß-cell apoptosis and impaired insulin secretion. The study may help further understand the pathogenesis of ß-cell dysfunction in case of dyslipidemia, and provide promising therapeutic targets for diabetes.

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Methionine restriction (MR) improves glucose metabolism. In skeletal muscle, H19 is a key regulator of insulin sensitivity and glucose metabolism. Therefore, this study aims to reveal the underlying mechanism of H19 upon MR on glucose metabolism in skeletal muscle. Middle-aged mice were fed MR diet for 25 weeks. Mouse islets ß cell line ß-TC6 cells and mouse myoblast cell line C2C12 cells were used to establish the apoptosis or insulin resistance model. Our findings showed that MR increased B-cell lymphoma-2 (Bcl-2) expression, deceased Bcl-2 associated X protein (Bax), cleaved cysteinyl aspartate-specific proteinase-3 (Caspase-3) expression in pancreas, and promoted insulin secretion of ß-TC6 cells. Meanwhile, MR increased H19 expression, insulin Receptor Substrate-1/insulin Receptor Substrate-2 (IRS-1/IRS-2) value, protein Kinase B (Akt) phosphorylation, glycogen synthase kinase-3ß (GSK3ß) phosphorylation, and hexokinase 2 (HK2) expression in gastrocnemius muscle and promoted glucose uptake in C2C12 cells. But these results were reversed after H19 knockdown in C2C12 cells. In conclusion, MR alleviates pancreatic apoptosis and promotes insulin secretion. And MR enhances gastrocnemius muscle insulin-dependent glucose uptake and utilization via the H19/IRS-1/Akt pathway, thereby ameliorating blood glucose disorders and insulin resistance in high-fat-diet (HFD) middle-aged mice.

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Purpose: Deep sea water (DSW) is a natural resource rich in minerals, which participates in biological processes such as energy metabolism, regulates serum glucose and lipids levels, and has a certain protective effect on endocrine and metabolism-related diseases. Studies have shown that the improvement of glucose tolerance in diabetic mice by DSW may be associated with the protective effect on the structure and function of pancreatic islets, and the specific mechanism is still unclear. Other studies have shown that long-term exposure to high concentrations of fatty acids can lead to apoptosis and dysfunction of pancreatic ß-cell, increasing the risk of type 2 diabetes mellitus (T2DM). Down-regulation of plasma fatty acid levels may reduce pancreatic ß-cell dysfunction, thereby improving glucose homeostasis. Understanding the specific mechanism of DSW regulating blood glucose is of great significance for its clinical application. Methods: In the present study we used db/db mice as a T2DM model and treated mice with deep ocean mineral concentration (DOMC, a commercial product of DSW) for 4 and 12 weeks. Basic information, serum biochemical indicators, and pathological tissues were gathered for exploration. Results: The db/db mice treated with 4 weeks' DOMC (db/db+DOMC) showed decreased plasma cholesterol and triglyceride levels. Tests implied that in adipose tissues, the db/db+DOMC group's lipolysis process was inhibited, and the ß-fatty acid oxidation process was promoted. Besides, DOMC reduced lipogenesis and encouraged ß-oxidation in the liver, as a result, improved fatty liver in db/db mice. Further measurements showed DOMC improved glucose homeostasis slightly in db/db animals after a 12-week treatment by preventing pancreatic ß-cell apoptosis. Conclusion: DOMC inhibited pancreatic ß-cell apoptosis and regulated glucose homeostasis in db/db mice by lowering the lipid levels via regulation of fatty acid ß-oxidation, lipolysis, and lipogenesis processes.

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BACKGROUND: Albumin is the most abundant protein in serum and serves as a transporter of free fatty acids (FFA) in blood vessels. In type 2 diabetes mellitus (T2DM) patients, the reduced serum albumin level is a risk factor for T2DM development and progression, although this conclusion is controversial. Moreover, there is no study on the effects and mechanisms of albumin administration to relieve T2DM. We examined whether the administration of young and undamaged recombinant albumin can alleviate T2DM in mice. METHODS: The serum albumin levels and metabolic phenotypes including fasting blood glucose, glucose tolerance tests, and glucose-stimulated insulin secretion were studied in db/db mice or diet-induced obesity mice treated with saline or young, undamaged, and ultrapure rMSA. Apoptosis assays were performed at tissue and cell levels to determine the function of rMSA on islet ß cell protection. Metabolic flux and glucose uptake assays were employed to investigate metabolic changes in saline-treated or rMSA-treated mouse hepatocytes and compared their sensitivity to insulin treatments. RESULTS: In this study, treatment of T2DM mice with young, undamaged, and ultrapure recombinant mouse serum albumin (rMSA) increased their serum albumin levels, which resulted in a reversal of the disease including reduced fasting blood glucose levels, improved glucose tolerance, increased glucose-stimulated insulin secretion, and alleviated islet atrophy. At the cellular level, rMSA improved glucose uptake and glycolysis in hepatocytes. Mechanistically, rMSA reduced the binding between CAV1 and EGFR to increase EGFR activation leading to PI3K-AKT activation. Furthermore, rMSA extracellularly reduced the rate of fatty acid uptake by islet ß-cells, which relieved the accumulation of intracellular ceramide, endoplasmic reticulum stress, and apoptosis. This study provided the first clear demonstration that injections of rMSA can alleviate T2DM in mice. CONCLUSION: Our study demonstrates that increasing serum albumin levels can promote glucose homeostasis and protect islet ß cells, which alleviates T2DM.

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The loss of function or dysfunction of ß-cells in the pancreas, attributed to the development of diabetes, involve alterations in genetic and epigenetic signatures. Recent evidences highlight the pathophysiological role of histone deacetylases (HDACs) in type 1 and type 2 diabetes. Indeed, most HDAC members have been linked to critical pathogenic events in diabetes, including redox imbalance, endoplasmic reticulum (ER) homeostasis perturbation, onset of oxidative stress and inflammation, which ultimately deteriorate ß-cell function. Accumulating evidence highlights the inhibition of HDACs as a prospective therapeutic strategy. Several chemically synthesized small molecules have been investigated for their specific ability to inhibit HDACs (reffered as HDAC inibitors) in various experimental studies. This review provides insights into the critical pathways involved in regulating different classes of HDACs. Further, the intricate signaling networks between HDACs and the stress mediators in diabetes are also explored. We exhaustively sum up the inferences from various investigations on the efficiency of HDAC inhibitors in managing diabetes and its associated complications.

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AIMS: Pancreatic ß-cell apoptosis may be involved in the onset and progression of type 2 diabetes mellitus, although its mechanism remains unclear. We previously demonstrated that macrophage-derived interferon (IFN) ß induced X-linked inhibitor of apoptosis-associated factor 1 (XAF1) expression in ß-cells and accelerated ß-cell apoptosis in vitro. Here, we explored the effects of XAF1 on ß-cell function and progression of diabetes in vivo. METHODS: Pancreatic ß-cell-selective XAF1 overexpressing (Xaf1 Tg) mice were generated. Xaf1 Tg mice and their wild-type (WT) littermates were fed either a normal diet or a 40% or 60% high-fat diet (HFD). The effects of ß-cell XAF1 on ß-cell apoptosis and exacerbation of diabetes were investigated. RESULTS: Palmitic acid induced IFNß expression in macrophages, and HFD intake promoted macrophage infiltration in pancreatic islets, both of which cooperatively upregulated XAF1 expression in mouse islets. Furthermore, HFD-fed Xaf1 Tg mice demonstrated increased ß-cell apoptosis, lowered insulin expression, and impaired glucose tolerance compared with WT mice fed the same diet. These effects were more pronounced in the 60%HFD group than in the 40%HFD group. CONCLUSIONS: Pancreatic ß-cell XAF1 expression was enhanced via HFD-induced, macrophage-derived IFNß, which promoted ß-cell apoptosis and led to a reduction in insulin secretion and progression of diabetes. To our knowledge, this is the first report to demonstrate an association between pancreatic ß-cell XAF1 overexpression and exacerbation of diabetes, thus providing insight into the mechanism of ß-cell mass reduction in diabetes.

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It has been shown that citrus flavanone naringenin and its prenyl derivative 8-prenylnaringenin (8-PN) possess various pharmacological activities in in vitro and in vivo models. Interestingly, it has been proposed that prenylation can enhance biological potentials, including the estrogen-like activities of flavonoids. The objective of this study was to investigate the anti-diabetic potential and molecular mechanism of 8-PN in streptozotocin (STZ)-induced insulin-deficient diabetic mice in comparison with naringenin reported to exhibit hypoglycemic effects. The oral administration of naringenin and 8-PN ameliorated impaired glucose homeostasis and islet dysfunction induced by STZ treatment. These protective effects were associated with the suppression of pancreatic ß-cell apoptosis and inflammatory responses in mice. Moreover, both naringenin and 8-PN normalized STZ-induced insulin-signaling defects in skeletal muscles and apoptotic protein expression in the liver. Importantly, 8-PN increased the protein expression levels of estrogen receptor-α (ERα) in the pancreas and liver and of fibroblast growth factor 21 in the liver, suggesting that 8-PN could act as an ERα agonist in the regulation of glucose homeostasis. This study provides novel insights into the mechanisms underlying preventive effects of naringenin and 8-PN on the impairment of glucose homeostasis in insulin-deficient diabetic mice.

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Quercetin, a natural flavonoid, has been reported to prevent pancreatic ß-cell apoptosis in animal models of diabetes. However, the underlying mechanism remains unclear. We investigated the mechanisms through which quercetin protects ß cells from palmitate-induced apoptosis and determined whether autophagy is involved in this process. We found that quercetin treatment partially reduced palmitate-induced ß-cell apoptosis. This protective effect was abolished by pharmacologic inhibition of autophagy and by silencing a key autophagy gene. Further analysis revealed that palmitate treatment promoted the expression of LC3 II, a marker of autophagosomes, but resulted in the blockade of autophagic flux due to lysosome dysfunction. Defective lysosome accumulation can cause lysosomal membrane permeabilization and the release of cathepsins from lysosome into the cytosol that triggers apoptosis. Treatment with quercetin reversed lysosomal dysfunction and promoted autophagosome-lysosome fusion, which restored defective autophagic flux and provoked autophagy. Overall, our results indicate that lysosomal dysfunction is a major factor that contributes to ß-cell apoptosis and demonstrates that quercetin improves cell survival by restoring lysosomal function and autophagic flux. This study provides new evidence regarding the anti-apoptotic mechanism of quercetin in the treatment of type 2 diabetes.

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Receptor of advanced glycation end products (RAGE) mediates diverse signal transduction following ligand stimulation and plays an important role in diabetes complications and aging associated disease. We have previously verified that advanced glycation end products (AGE) bind to RAGE to cause pancreatic ß-cell apoptosis through the mitochondrial pathway. However, the direct interacting protein(s) of RAGE in ß cells has never been appreciated. In the present study, we utilized GST pull-down assay combined with mass spectrometry to identify the interacting proteins of the RAGE intracellular domain (C-terminal 43 amino acid of RAGE). Overall four RAGE interacting proteins, including Rab31, were identified with scores over 160. Rab31 was detected in three ß-cell lines and confirmed to have interacted with RAGE via co-immunoprecipitation and immunostaining assays. This interaction was further enhanced by glycation-serum (GS) stimulation due to membrane distribution of Rab31 following treatment with GS. We further confirmed that Rab31 promoted RAGE endocytosis and inhibited GS-induced ß-cell apoptosis through the pAKT/BCL2 pathway. These findings reveal a new RAGE interaction protein Rab31 that prevents AGE/RAGE-induced pancreatic ß-cell apoptosis. Rab31 is therefore a promising therapeutic target for preserving functional ß cells under diabetes conditions.

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PURPOSE: Pancreatic ß-cell failure is a central hallmark of the pathogenesis of diabetes mellitus; however, the molecular basis underlying chronic inflammation-caused ß-cell failure remains unclear. This study reported here specifically assessed the association between miR-25/miR-92b family and ß-cell failure in diabetes. METHODS: IL-1ß and two additional ER stress activators, palmitate and tunicamycin were applied to evaluate the expression level miR-25 by Taqman® RT-PCR. Glucose- and potassium-stimulated insulin secretion assays were performed to assess ß-cell function. Dual-luciferase activity, and western blotting assays were utilized for miR-25 target gene verification. CCK-8 and TUNEL staining were used to evaluate ß-cell viability and apoptosis. RESULTS: miRNA ChIP identified the increased level of miR-25 in INS-1 cells by IL-1ß treatment. Expression levels of miR-25 were significantly upregulated with the treatment of IL-1ß, palmitate or tunicamycin in both INS-1 cells and human islets. Ectopic elevation of miR-25 recapitulated most featured ß-cell defects caused by IL-1ß, including inhibition of insulin biosynthesis and increased ß-cell apoptosis. These detrimental effects of miR-25 relied on its seed sequence recognition and repressed expression of its target genes Neurod1 and Mcl1. The miR-25/NEUROD1 axis reduced insulin biosynthesis via transcriptional regulation of ß-cell specific genes. The miR-25/MCL1 axis caused ß-cell apoptosis in a CASPASE-3/PARP1-dependent manner. Comparable impairments were generated by miR-92b and miR-25, emphasizing the redundant biological roles of miRNA family members with the same seed sequence. CONCLUSION: MiR-25/miR-92b family plays a major role in ß-cell failure occurring under inflammation and diabetes states.

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Islet amyloid, formed by aggregation of human islet amyloid polypeptide (hIAPP), contributes to ß-cell death in type 2 diabetes. We previously showed that extracellular hIAPP aggregates promote Fas-mediated ß-cell apoptosis. Here, we tested if hIAPP aggregates can trigger the mitochondrial apoptotic pathway (MAP). hIAPP aggregation in Ad-hIAPP transduced INS-1 and human islet ß-cells promoted cytochrome c release, caspase-9 activation and apoptosis, which were reduced by Bax inhibitor. Amyloid formation in hIAPP-expressing mouse islets during culture increased caspase-9 activation in ß-cells. Ad-hIAPP transduced islets from CytcKA/KA and BaxBak ßDKO mice (models of blocked MAP), had lower caspase-9-positive and apoptotic ß-cells than transduced wild-type islets, despite comparable amyloid formation. Blocking Fas (markedly) and Bax or caspase-9 (modestly) reduced ß-cell death induced by extracellular hIAPP aggregates. These findings suggest a role for MAP in amyloid-induced ß-cell death and a potential strategy to reduce intracellular amyloid ß-cell toxicity by blocking cytochrome c apoptotic function.

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Type 1 diabetes (T1D) is an autoimmune disease characterised by the destruction of the insulin-producing beta (ß)-cells within the pancreatic islets. We have previously identified a novel parasite-derived molecule, termed Fasciola hepatica helminth defence molecule 1 (FhHDM-1), that prevents T1D development in non-obese diabetic (NOD) mice. In this study, proteomic analyses of pancreas tissue from NOD mice suggested that FhHDM-1 activated the PI3K/Akt signalling pathway, which is associated with ß-cell metabolism, survival and proliferation. Consistent with this finding, FhHDM-1 preserved ß-cell mass in NOD mice. Examination of the biodistribution of FhHDM-1 after intraperitoneal administration in NOD mice revealed that the parasite peptide localised to the pancreas, suggesting that it exerted a direct effect on the survival/function of ß-cells. This was confirmed in vitro, as the interaction of FhHDM-1 with the NOD-derived ß-cell line, NIT-1, resulted in increased levels of phosphorylated Akt, increased NADH and NADPH and reduced activity of the NAD-dependent DNA nick sensor, poly(ADP-ribose) polymerase (PARP-1). As a consequence, ß-cell survival was enhanced and apoptosis was prevented in the presence of the pro-inflammatory cytokines that destroy ß-cells during T1D pathogenesis. Similarly, FhHDM-1 protected primary human islets from cytokine-induced apoptosis. Importantly, while FhHDM-1 promoted ß-cell survival, it did not induce proliferation. Collectively, these data indicate that FhHDM-1 has significant therapeutic applications to promote ß-cell survival, which is required for T1D and T2D prevention and islet transplantation. KEY MESSAGES: FhHDM-1 preserves ß-cell mass in NOD mice and prevents the development of T1D. FhHDM-1 enhances phosphorylation of Akt in mouse ß-cell lines. FhHDM-1 increases levels of NADH/NADPH in mouse ß-cell lines in vitro. FhHDM-1 prevents cytokine-induced cell death of mouse ß-cell lines and primary human ß-cells in vitro via activation of the PI3K/Akt pathway.

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Monogenetic forms of diabetes represent 1%-5% of all diabetes cases and are caused by mutations in a single gene. These mutations, that affect genes involved in pancreatic ß-cell development, function and survival, or insulin regulation, may be dominant or recessive, inherited or de novo. Most patients with monogenic diabetes are very commonly misdiagnosed as having type 1 or type 2 diabetes. The severity of their symptoms depends on the nature of the mutation, the function of the affected gene and, in some cases, the influence of additional genetic or environmental factors that modulate severity and penetrance. In some patients, diabetes is accompanied by other syndromic features such as deafness, blindness, microcephaly, liver and intestinal defects, among others. The age of diabetes onset may also vary from neonatal until early adulthood manifestations. Since the different mutations result in diverse clinical presentations, patients usually need different treatments that range from just diet and exercise, to the requirement of exogenous insulin or other hypoglycemic drugs, e.g., sulfonylureas or glucagon-like peptide 1 analogs to control their glycemia. As a consequence, awareness and correct diagnosis are crucial for the proper management and treatment of monogenic diabetes patients. In this chapter, we describe mutations causing different monogenic forms of diabetes associated with inadequate pancreas development or impaired ß-cell function and survival, and discuss the molecular mechanisms involved in ß-cell demise.

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The novel coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) was declared a pandemic by the WHO on 19 March 2020. This pandemic is associated with markedly elevated blood glucose levels and a remarkable degree of insulin resistance, which suggests pancreatic islet ß-cell dysfunction or apoptosis and insulin's inability to dispose of glucose into cellular tissues. Diabetes is known to be one of the top pre-existing co-morbidities associated with the severity of COVID-19 along with hypertension, cardiocerebrovascular disease, advanced age, male gender, and recently obesity. This review focuses on how COVID-19 may be responsible for the accelerated development of type 2 diabetes mellitus (T2DM) as one of its acute and suspected long-term complications. These observations implicate an active role of metabolic syndrome, systemic and tissue islet renin-angiotensin-aldosterone system, redox stress, inflammation, islet fibrosis, amyloid deposition along with ß-cell dysfunction and apoptosis in those who develop T2DM. Utilizing light and electron microscopy in preclinical rodent models and human islets may help to better understand how COVID-19 accelerates islet and ß-cell injury and remodeling to result in the long-term complications of T2DM.

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AIMS: Diabetes mellitus (DM) is a disorder of heterogeneous etiology marked by persistent hyperglycemia. Exogenous insulin is the only treatment for type 1 diabetes (T1D). Islet transplantation is a potential long cure for T1D but is disapproved due to the possibility of immune rejection in the later stage. The approaches used for treating type 2 diabetes (T2D) include diet restrictions, weight management and pharmacological interventions. These procedures have not been able to boost the quality of life for diabetic patients owing to the complexity of the disorder. DATA SYNTHESIS: Hence, research has embarked on permanent ways of managing, or even curing the disease. One of the possible approaches to restore the pancreas with new glucose-responsive ß-cells is by their regeneration. Regeneration of ß-cells include islet neogenesis, dedifferentiation, and trans-differentiation of the already differentiated cells. CONCLUSIONS: This review briefly describes the islet development, functions of ß-cells, mechanism and factors involved in ß-cell death. It further elaborates on the potential of the existing and possible therapeutic modalities involved in the in-vivo replenishment of ß-cells with a focus on exercise, diet, hormones, small molecules, and phytochemicals.

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Isoforms of protein kinase B (also known as AKT) play important roles in mediating insulin and growth factor signals. Previous studies have suggested that the AKT2 isoform is critical for insulin-regulated glucose metabolism, while the role of the AKT1 isoform remains less clear. This study focuses on the effects of AKT1 on the adaptive response of pancreatic ß cells. Using a mouse model with inducible ß-cell-specific deletion of the Akt1 gene (ßA1KO mice), we showed that AKT1 is involved in high-fat-diet (HFD)-induced growth and survival of ß cells but is unnecessary for them to maintain a population in the absence of metabolic stress. When unchallenged, ßA1KO mice presented the same metabolic profile and ß-cell phenotype as the control mice with an intact Akt1 gene. When metabolic stress was induced by HFD, ß cells in control mice with intact Akt1 proliferated as a compensatory mechanism for metabolic overload. Similar effects were not observed in ßA1KO mice. We further demonstrated that AKT1 protein deficiency caused endoplasmic reticulum (ER) stress and potentiated ß cells to undergo apoptosis. Our results revealed that AKT1 protein loss led to the induction of eukaryotic initiation factor 2 α subunit (eIF2α) signaling and ER stress markers under normal-chow-fed conditions, indicating chronic low-level ER stress. Together, these data established a role for AKT1 as a growth and survival factor for adaptive ß-cell response and suggest that ER stress induction is responsible for this effect of AKT1.

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BACKGROUND: Major alteration in lifestyle of human population has promoted Type 2 diabetes mellitus (T2DM) to the level of an epidemic. This metabolic disorder is characterized by insulin resistance and pancreatic ß-cell dysfunction and apoptosis, triggered by endoplasmic reticulum (ER) stress, oxidative stress and cytokines. Computational modeling is necessary to consolidate information from various sources in order to obtain a comprehensive understanding of the pathogenesis of T2DM and to investigate possible interventions by performing in silico simulations. RESULTS: In this paper, we propose a Boolean network model integrating the insulin resistance pathway with pancreatic ß-cell apoptosis pathway which are responsible for T2DM. The model has five input signals, i.e. ER stress, oxidative stress, tumor necrosis factor α (TNF α), Fas ligand (FasL), and interleukin-6 (IL-6). We performed dynamical simulations using random order asynchronous update and with different combinations of the input signals. From the results, we observed that the proposed model made predictions that closely resemble the expression levels of genes in T2DM as reported in the literature. CONCLUSION: The proposed model can make predictions about expression levels of genes in T2DM that are in concordance with literature. Although experimental validation of the model is beyond the scope of this study, the model can be useful for understanding the aetiology of T2DM and discovery of therapeutic intervention for this prevalent complex disease. The files of our model and results are available at https://github.com/JieZheng-ShanghaiTech/boolean-t2dm .

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Insulin resistance and ß-cell dysfunction are the main defects in Type 2 Diabetes Mellitus (T2DM), and ß-cell dysfunction and apoptosis is the critical determinant in the progression of T2DM. G-protein coupled receptor 55 (GPR55) is an orphan G-protein coupled receptor, which is activated by endocannabinoids and lipid transmitters. Recently, GPR55 was shown to regulate glucose and energy homeostasis, however its role in ß-cell apoptosis was not studied. Therefore, in this study, we investigated the novel effect of GPR55 agonists, O-1602 and abnormal cannabidiol (Abn-CBD), on endoplasmic reticulum (ER) stress-induced apoptosis in mouse pancreatic ß-cell lines, MIN6 and Beta-TC-6, and its underlying mechanisms. Our results showed that O-1602 and Abn-CBD reduced ER stress-induced apoptosis in MIN6 and Beta-TC-6 cells. This was through the phosphorylation of 3'-5'-cyclic adenosine monophosphate response element-binding protein (CREB) in ß-cells, hence activating CREB downstream anti-apoptotic genes, Bcl-2 and Bcl-xL. Moreover, O-1602 and Abn-CBD directly activated kinases, CaMKIV, Erk1/2 and PKA, to induce CREB phosphorylation. Therefore, our results indicated that GPR55 agonists protected from ß-cell apoptosis through CREB activation, thus up-regulating anti-apoptotic genes. In conclusion, our study provided a novel protective effect of GPR55 agonists on ER stress-induced apoptosis in ß-cells and its underlying mechanisms mediating this protection, therefore we suggested that GPR55 might be a therapeutic target for T2DM.

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