Insulin Secretion In Pancreatic Β-cells Research Articles

Hyperglycemia from Diabetes Potentiates Uncarboxylated Osteocalcin-Stimulated Insulin Secretion in Rat INS-1 Pancreatic β-Cells

Hyperglycemia from Diabetes Potentiates Uncarboxylated Osteocalcin-Stimulated Insulin Secretion in Rat INS-1 Pancreatic β-Cells

Diabetes current and future translatable therapies.

Diabetes is one of the major diseases and concerns of public health systems that affects over 200 million patients worldwide. It is estimated that 90% of these patients suffer from diabetes type 2, while 10% present diabetes type 1. This type of diabetes and certain types of diabetes type 2, are characterized by dysregulation of blood glycemic levels due to the total or partial depletion of insulin-secreting pancreatic β-cells. Different approaches have been proposed for long-term treatment of insulin-dependent patients; amongst them, cell-based approaches have been the subject of basic and clinical research since they allow blood glucose level sensing and in situ insulin secretion. The current gold standard for insulin-dependent patients is on-demand exogenous insulin application; cell-based therapies aim to remove this burden from the patient and caregivers. In recent years, protocols to isolate and implant pancreatic islets from diseased donors have been developed and tested in clinical trials. Nevertheless, the shortage of donors, along with the need of immunosuppressive companion therapies, have pushed researchers to focus their attention and efforts to overcome these disadvantages and develop alternative strategies. This review discusses current tested clinical approaches and future potential alternatives for diabetes type 1, and some diabetes type 2, insulin-dependent patients. Additionally, advantages and disadvantages of these discussed methods.

Structure of an open KATP channel reveals tandem PIP2 binding sites mediating the Kir6.2 and SUR1 regulatory interface

ATP-sensitive potassium (KATP) channels, composed of four pore-lining Kir6.2 subunits and four regulatory sulfonylurea receptor 1 (SUR1) subunits, control insulin secretion in pancreatic β-cells. KATP channel opening is stimulated by PIP2 and inhibited by ATP. Mutations that increase channel opening by PIP2 reduce ATP inhibition and cause neonatal diabetes. Although considerable evidence has implicated a role for PIP2 in KATP channel function, previously solved open-channel structures have lacked bound PIP2, and mechanisms by which PIP2 regulates KATP channels remain unresolved. Here, we report the cryoEM structure of a KATP channel harboring the neonatal diabetes mutation Kir6.2-Q52R, in the open conformation, bound to amphipathic molecules consistent with natural C18:0/C20:4 long-chain PI(4,5)P2 at two adjacent binding sites between SUR1 and Kir6.2. The canonical PIP2 binding site is conserved among PIP2-gated Kir channels. The non-canonical PIP2 binding site forms at the interface of Kir6.2 and SUR1. Functional studies demonstrate both binding sites determine channel activity. Kir6.2 pore opening is associated with a twist of the Kir6.2 cytoplasmic domain and a rotation of the N-terminal transmembrane domain of SUR1, which widens the inhibitory ATP binding pocket to disfavor ATP binding. The open conformation is particularly stabilized by the Kir6.2-Q52R residue through cation-π bonding with SUR1-W51. Together, these results uncover the cooperation between SUR1 and Kir6.2 in PIP2 binding and gating, explain the antagonistic regulation of KATP channels by PIP2 and ATP, and provide a putative mechanism by which Kir6.2-Q52R stabilizes an open channel to cause neonatal diabetes.

KCNH6 channel promotes insulin exocytosis via interaction with Munc18-1 independent of electrophysiological processes

Glucose-stimulated insulin secretion (GSIS) in pancreatic islet β-cells primarily relies on electrophysiological processes. Previous research highlighted the regulatory role of KCNH6, a member of the Kv channel family, in governing GSIS through its influence on β-cell electrophysiology. In this study, we unveil a novel facet of KCNH6's function concerning insulin granule exocytosis, independent of its conventional electrical role. Young mice with β-cell-specific KCNH6 knockout (βKO) exhibited impaired glucose tolerance and reduced insulin secretion, a phenomenon not explained by electrophysiological processes alone. Consistently, islets from KCNH6-βKO mice exhibited reduced insulin secretion, conversely, the overexpression of KCNH6 in murine pancreatic islets significantly enhanced insulin release. Moreover, insulin granules lacking KCNH6 demonstrated compromised docking capabilities and a reduced fusion response upon glucose stimulation. Crucially, our investigation unveiled a significant interaction between KCNH6 and the SNARE protein regulator, Munc18-1, a key mediator of insulin granule exocytosis. These findings underscore the critical role of KCNH6 in the regulation of insulin secretion through its interaction with Munc18-1, providing a promising and novel avenue for enhancing our understanding of the Kv channel in diabetes mechanisms.

In situ structure of actin remodeling during glucose-stimulated insulin secretion using cryo-electron tomography

Actin mediates insulin secretion in pancreatic β-cells through remodeling. Hampered by limited resolution, previous studies have offered an ambiguous depiction as depolymerization and repolymerization. We report the in situ structure of actin remodeling in INS-1E β-cells during glucose-stimulated insulin secretion at nanoscale resolution. After remodeling, the actin filament network at the cell periphery exhibits three marked differences: 12% of actin filaments reorient quasi-orthogonally to the ventral membrane; the filament network mainly remains as cell-stabilizing bundles but partially reconfigures into a less compact arrangement; actin filaments anchored to the ventral membrane reorganize from a “netlike” to a “blooming” architecture. Furthermore, the density of actin filaments and microtubules around insulin secretory granules decreases, while actin filaments and microtubules become more densely packed. The actin filament network after remodeling potentially precedes the transport and release of insulin secretory granules. These findings advance our understanding of actin remodeling and its role in glucose-stimulated insulin secretion.

Serum albumin adjusted calcium and fluoride among type 2 diabetes mellitus patients.

The regulation of glucose-dependent insulin secretion in pancreatic β-cells relies on calcium concentration, making it a calcium-dependent process. Disruptions in calcium homeostasis may contribute to insulin dysfunction and disturbances in glucose homeostasis, potentially playing a role in the development of type 2 diabetes mellitus (T2DM). In T2DM patients, there may be changes in fluoride metabolism due to impaired renal function. Measurement of serum albumin-adjusted calcium and is crucial since changes in albumin levels can impact the accurate estimation of true calcium.

Trace Amine-Associated Receptors and Monoamine-Mediated Regulation of Insulin Secretion in Pancreatic Islets.

Currently, metabolic syndrome treatment includes predominantly pharmacological symptom relief and complex lifestyle changes. Trace amines and their receptor systems modulate signaling pathways of dopamine, norepinephrine, and serotonin, which are involved in the pathogenesis of this disorder. Trace amine-associated receptor 1 (TAAR1) is expressed in endocrine organs, and it was revealed that TAAR1 may regulate insulin secretion in pancreatic islet β-cells. For instance, accumulating data demonstrate the positive effect of TAAR1 agonists on the dynamics of metabolic syndrome progression and MetS-associated disease development. The role of other TAARs (TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9) in the islet's function is much less studied. In this review, we summarize the evidence of TAARs' contribution to the metabolic syndrome pathogenesis and regulation of insulin secretion in pancreatic islets. Additionally, by the analysis of public transcriptomic data, we demonstrate that TAAR1 and other TAAR receptors are expressed in the pancreatic islets. We also explore associations between the expression of TAARs mRNA and other genes in studied samples and demonstrate the deregulation of TAARs' functional associations in patients with metabolic diseases compared to healthy donors.

Exosomes; a Potential Source of Biomarkers, Therapy, and Cure for Type-1 Diabetes.

The scourge of type-1 diabetes (T1D) is the morbidity and mortality it and its complications cause at a younger age. This propels the constant search for better diagnostic, treatment, and management strategies, with the ultimate quest being a cure for T1D. Recently, the therapeutic potential of exosomes has generated a lot of interest. Among the characteristics of exosomes of particular interest are (a) their regenerative capacity, which depends on their "origin", and (b) their "content", which determines the cell communication and crosstalk they influence. Other functional capacities, including paracrine and endocrine homeostatic regulation, pathogenic response ability resulting in insulin secretory defects or β-cell death under normal metabolic conditions, immunomodulation, and promotion of regeneration, have also garnered significant interest. Exosome "specificity" makes them suitable as biomarkers or predictors, and their "mobility" and "content" lend credence to drug delivery and therapeutic suitability. This review aims to highlight the functional capacities of exosomes and their established as well as novel contributions at various pathways in the onset and progression of T1D. The pathogenesis of T1D involves a complex crosstalk between insulin-secreting pancreatic β-cells and immune cells, which is partially mediated by exosomes. We also examine the potential implications for type 2 diabetes (T2D), as the link in T2D has guided T1D exploration. The collective landscape presented is expected to help identify how a deeper understanding of exosomes (and their cargo) can provide a framework for actionable solutions to prevent, halt, or change the very course of T1D and its complications.

Glucocorticoid receptor-NECAB1 axis can negatively regulate insulin secretion in pancreatic β-cells

The mechanisms of impaired glucose-induced insulin secretion from the pancreatic β-cells in obesity have not yet been completely elucidated. Here, we aimed to assess the effects of adipocyte-derived factors on the functioning of pancreatic β-cells. We prepared a conditioned medium using 3T3-L1 cell culture supernatant collected at day eight (D8CM) and then exposed the rat pancreatic β-cell line, INS-1D. We found that D8CM suppressed insulin secretion in INS-1D cells due to reduced intracellular calcium levels. This was mediated by the induction of a negative regulator of insulin secretion—NECAB1. LC–MS/MS analysis results revealed that D8CM possessed steroid hormones (cortisol, corticosterone, and cortisone). INS-1D cell exposure to cortisol or corticosterone increased Necab1 mRNA expression and significantly reduced insulin secretion. The increased expression of Necab1 and reduced insulin secretion effects from exposure to these hormones were completely abolished by inhibition of the glucocorticoid receptor (GR). NECAB1 expression was also increased in the pancreatic islets of db/db mice. We demonstrated that the upregulation of NECAB1 was dependent on GR activation, and that binding of the GR to the upstream regions of Necab1 was essential for this effect. NECAB1 may play a novel role in the adipoinsular axis and could be potentially involved in the pathophysiology of obesity-related diabetes mellitus.

Metformin Preserves Insulin Secretion in Pancreatic β-cells through FGF21/Akt Pathway In vitro and In vivo.

In our previous studies, it was found that metformin can elevate the expression of FGF21 in the peripheral blood of type 2 diabetic rats and improve insulin sensitivity in diabetic rats. However, whether this effect is mediated by increased FGF21 expression in pancreatic islet β-cells is still unknown. Therefore, this study focuses on the effect of metformin on insulin secretion in pancreatic β-cells. Metformin can effectivly improve insulin resistance. Metformin influencing pancreatic βcell function is inclusive. In this study, we sought to analyze possible variations in insulin secretion and possible signaling mechanisms after metformin intervention. The study employed an in vivo model of a high-fat diet in streptozocin-induced diabetic rats and an in vitro model of rat pancreatic β-cells (INS-1 cells) that were subjected to damage caused by hyperglycemia and hyperlipidemia. After treating INS-1 cells in normal, high-glucose, and high-glucose+metformin, we measured insulin secretion by glucose-stimulated insulin secretion (GSIS). Insulin was measured using an enzyme-linked immunosorbent assay. FGF21 expression was detected by RT-PCR and Western blot, as well as that p-Akt and t-Akt expression were detected by Western blot in INS-1 cells and diabetic rat islets. Finally, to verify the regulation of the FGF21 /Akt axis in metformin administration, additional experiments were carried out in metformin-stimulated INS-1 cells. High-glucose could significantly stimulate insulin secretion while metformin preserved insulin secretion. Expression of FGF21 and p-Akt was decreased in high-glucose, however, metformin could reverse this effect in INS-1 cells and diabetic rat islets. Our results demonstrate a protective role of metformin in preserving insulin secretion through FGF21/Akt signaling in T2DM.

IL-33 promotes pancreatic β-cell survival and insulin secretion under diabetogenic conditions through PPARγ

Pancreatic β-cell dysfunction plays a vital role in the development of diabetes. IL-33 exerts anti-diabetic effects via its anti-inflammatory properties and has been demonstrated to increase insulin secretion in animal models. However, IL-33, as a pleiotropic cytokine, may also exert a deleterious effect on β-cells, which has not been rigorously studied. In the present study, we found that IL-33 promoted cell survival and insulin secretion in MIN6 (a mouse pancreatic β-cell line) cells under diabetogenic conditions. IL-33 increased the expression of its receptor ST2 and the transcription factor PPARγ, whereas PPARγ inhibition impaired IL-33-mediated β-cell survival and insulin release. IL-33 did not repress the expression of pro-inflammatory mediators, including Tf, Icam1, Cxcl10, and Il1b, whereas it significantly reduced the expression of Ccl2. IL-33 decreased TNF-α secretion and increased IL-10 secretion; these effects were completely reversed by PPARγ inhibition. IL-33 increased glucose uptake and expression of Glut2. It upregulated the expression of glycolytic enzyme genes, namely, Pkm2, Hk2, Gpi1, and Tpi, and downregulated the expression of Gck, Ldha, and Mct4. However, it did not alter hexokinase activity. Moreover, IL-33 increased the number and activity of mitochondria, accompanied by increased ATP production and reduced accumulation of ROS. IL-33 upregulated the expression of PGC-1α and cytochrome c, and mitochondrial fission- and fusion-associated genes, including Mfn1, Mfn2, and Dnm1l. IL-33-mediated mitochondrial homeostasis was partially reversed by PPARγ inhibition. Altogether, IL-33 protects β-cell survival and insulin secretion that could be partially driven via PPARγ, which regulates glucose uptake and promotes mitochondrial function and anti-inflammatory responses.

Pitfalls of Mitochondrial Redox Signaling Research.

Redox signaling from mitochondria (mt) to the cytosol and plasma membrane (PM) has been scarcely reported, such as in the case of hypoxic cell adaptation or (2-oxo-) 2-keto-isocaproate (KIC) β-like-oxidation stimulating insulin secretion in pancreatic β-cells. Mutual redox state influence between mitochondrial major compartments, the matrix and the intracristal space, and the cytosol is therefore derived theoretically in this article to predict possible conditions, when mt-to-cytosol and mt-to-PM signals may occur, as well as conditions in which the cytosolic redox signaling is not overwhelmed by the mitochondrial antioxidant capacity. Possible peroxiredoxin 3 participation in mt-to-cytosol redox signaling is discussed, as well as another specific case, whereby mitochondrial superoxide release is diminished, whereas the matrix MnSOD is activated. As a result, the enhanced conversion to H2O2 allows H2O2 diffusion into the cytosol, where it could be a predominant component of the H2O2 release. In both of these ways, mt-to-cytosol and mt-to-PM signals may be realized. Finally, the use of redox-sensitive probes is discussed, which disturb redox equilibria, and hence add a surplus redox-buffering to the compartment, where they are localized. Specifically, when attempts to quantify net H2O2 fluxes are to be made, this should be taken into account.

The role of peripheral β-amyloid in insulin resistance, insulin secretion, and prediabetes: in vitro and population-based studies.

Previous experimental studies have shown that mice overexpressing amyloid precursor protein, in which β-amyloid (Aβ) is overproduced, exhibit peripheral insulin resistance, pancreatic impairment, and hyperglycemia. We aimed to explore the effects of Aβ on insulin action and insulin secretion in vitro and the association of plasma Aβ with prediabetes in human. We examined the effects of Aβ40 and Aβ42 on insulin-inhibited glucose production in HepG2 cells, insulin-promoted glucose uptake in C2C12 myotubes, and insulin secretion in INS-1 cells. Furthermore, we conducted a case-control study (N = 1142) and a nested case-control study (N = 300) within the prospective Tongji-Ezhou cohort. Odds ratios (ORs) and 95% confidence intervals (CIs) for prediabetes were estimated by using conditional logistic regression analyses. In the in vitro studies, Aβ40 and Aβ42 dose-dependently attenuated insulin-inhibited glucose production in HepG2 cells, insulin-promoted glucose uptake in C2C12 myotubes, and basal and glucose-stimulated insulin secretion in INS-1 cells. In the case-control study, plasma Aβ40 (adjusted OR: 2.00; 95% CI: 1.34, 3.01) and Aβ42 (adjusted OR: 1.94; 95% CI: 1.33, 2.83) were positively associated with prediabetes risk when comparing the extreme quartiles. In the nested case-control study, compared to the lowest quartile, the highest quartile of plasma Aβ40 and Aβ42 were associated with 3.51-fold (95% CI: 1.61, 7.62) and 2.75-fold (95% CI: 1.21, 6.22) greater odds of prediabetes, respectively. Elevated plasma Aβ40 and Aβ42 levels were associated with increased risk of prediabetes in human subjects, which may be through impairing insulin sensitivity in hepatocytes and myotubes and insulin secretion in pancreatic β-cells.

295-LB: Pancreatic Peroxisomes Are Required for Physiological Regulation of Insulin Secretion and Maintenance of Normal Glucose Tolerance in Male Mice

The regulation of glucose-stimulated insulin secretion (GSIS) is central to maintenance of glucose disposal. The role of lipid storage and lipid oxidation to regulate pancreatic islet β-cell insulin secretion is not completely understood. Peroxisomes are enriched in insulin-producing β-cells, but their contribution to β-cell function and maturity is lacking. Therefore, we generated a novel model of peroxisomal dysfunction to test the hypothesis that peroxisomal lipid metabolism is required to prevent a hyperlipidemic environment that interferes with β-cell function and maturity. Pex5 plays a critical role in importing the majority of peroxisomal proteins into the peroxisomal matrix; thus, deletion of the Pex5 gene creates a cellular environment with reductions in function of this organelle. In this study, we bred Pex5 mice on a C57BL/6J background containing ‘floxed’ alleles to Pdx1-cre mice to generate offspring with a pancreas-wide deficiency in Pex5 expression and abundance. Glucose tolerance was impaired by 12 weeks in male mice (n=20; AUC p<0.05). Surprisingly, GSIS was elevated in Pex5Pdx1-/- mice compared to littermate controls both in vivo (n=15; AUC p<0.05) and ex vivo in isolated islets as measured by perifusion analysis (n=12; AUC p<0.01). We further found that a subset of β-cells from Pex5Pdx1-/- mice expressed the de-differentiation marker Aldh1a3, while a subset of β-cells showed reductions in MafA and Nkx6.1 staining compared to controls. Perilipin-1 staining showed increased presence of lipid droplets in pancreatic tissue of Pex5Pdx1-/- mice versus controls. Thus, pancreatic deletion of peroxisomal function results in increased lipid storage in pancreatic tissue that is correlated with exaggerated insulin secretion. Collectively, these data are in support of a model whereby peroxisomal function supports β-cell insulin secretion and maintenance of the fully differentiated state. Disclosure S. Burke: None. S. Ghosh: None. D. Burk: None. R. Noland: None. J. Collier: None.

Disrupting of family with sequence similarity 105, member A (Fam105a) deteriorates pancreatic β-cell physiology and insulin secretion in INS-1 cells

The role of “Family with sequence similarity 105, member A” (FAM105A) in pancreatic β-cell function in relation to type 2 diabetes mellitus (T2D) is not fully understood. To address this issue, various molecular and functional experiments were conducted on primary human islets and INS-1 cells. RNA-seq expression analysis showed that FAM105A is highly expressed in human islets and its expression is reduced in diabetic islets compared to healthy islets. FAM105A expression correlated negatively with HbA1c levels and body mass index (BMI). Co-expression analysis showed a significant correlation between FAM105A with PDX1, GCK, GLUT1 and INSR, but not the INS gene. Silencing of Fam105a impaired insulin release, content, glucose uptake, and mitochondria ATP content but did not affect cell viability, reactive oxygen species (ROS) or apoptosis levels. Silencing of Fam105a was associated with reduced Pdx1 and Glut2 expression at mRNA and protein levels. RNA-seq analysis of dysregulated genes in Fam105a-silenced cells showed an overall downregulation of gene expression in β-cells and insulin secretion pathway. Disrupting Pdx1 did not affect Fam105a expression in INS-1 cells. Overall, the results suggest that FAM105A plays an important role in pancreatic β-cells biology and may be involved in the development of T2D.

Parkin-mediated mitophagy is negatively regulated by FOXO3A, which inhibits Plk3-mediated mitochondrial ROS generation in STZ diabetic stress-treated pancreatic β cells.

Diabetes mellitus (DM) is one of the most researched metabolic diseases worldwide. It leads to extensive complications such as cardiovascular disease, nephropathy, retinopathy, and peripheral and central nervous system through an inability to produce or respond to insulin. Although oxidative stress-mediated mitophagy has been reported to play an important role in the pathogenesis of DM, specific studies are still lacking as well as remain highly controversial. Here, we found that Parkin-mediated mitophagy in pancreatic β cells under streptozotocin (STZ)-diabetic stress was induced by Polo-like kinase 3 (Plk3) and inhibited by the transcription factor Forkhead Box O3A (FOXO3A). STZ stress induces mitochondrial recruitment of Parkin through Plk3-mediated mitochondrial reactive oxygen species (ROS) generation, which causes pancreatic cell damage. Conversely, FOXO3A acts as negative feedback to prevent diabetic stress by inhibiting Plk3. Meanwhile, antioxidants including N-acetylcysteine (NAC) and natural COA water scientifically block these mitochondrial ROS and mitochondrial recruitment of Parkin by inhibiting Plk3. Through a 3D organoid ex vivo model, we confirmed that not only ROS inhibitors but also mitophagy inhibitory factors such as 3-MA or Parkin deletion can compensate for pancreatic cell growth and insulin secretion under STZ diabetic stress. These findings suggest that the Plk3-mtROS-PINK1-Parkin axis is a novel mitophagy process that inhibits pancreatic β-cell growth and insulin secretion and FOXO3A and antioxidants may provide new alternatives for effective diabetes treatment strategies in the future.

Small molecule glucagon release inhibitors with activity in human islets.

Type 1 diabetes (T1D) accounts for an estimated 5% of all diabetes in the United States, afflicting over 1.25 million individuals. Maintaining long-term blood glucose control is the major goal for individuals with T1D. In T1D, insulin-secreting pancreatic islet β-cells are destroyed by the immune system, but glucagon-secreting islet α-cells survive. These remaining α-cells no longer respond properly to fluctuating blood glucose concentrations. Dysregulated α-cell function contributes to hyper- and hypoglycemia which can lead to macrovascular and microvascular complications. To this end, we sought to discover small molecules that suppress α-cell function for their potential as preclinical candidate compounds. Prior high-throughput screening identified a set of glucagon-suppressing compounds using a rodent α-cell line model, but these compounds were not validated in human systems. Here, we dissociated and replated primary human islet cells and exposed them to 24 h treatment with this set of candidate glucagon-suppressing compounds. Glucagon accumulation in the medium was measured and we determined that compounds SW049164 and SW088799 exhibited significant activity. Candidate compounds were also counter-screened in our InsGLuc-MIN6 β-cell insulin secretion reporter assay. SW049164 and SW088799 had minimal impact on insulin release after a 24 h exposure. To further validate these hits, we treated intact human islets with a selection of the top candidates for 24 h. SW049164 and SW088799 significantly inhibited glucagon release into the medium without significantly altering whole islet glucagon or insulin content. In concentration-response curves SW088799 exhibited significant inhibition of glucagon release with an IC50 of 1.26 µM. Given the set of tested candidates were all top hits from the primary screen in rodent α-cells, this suggests some conservation of mechanism of action between human and rodents, at least for SW088799. Future structure-activity relationship studies of SW088799 may aid in elucidating its protein target(s) or enable its use as a tool compound to suppress α-cell activity in vitro.

Chemical Constituents from the Roots of Angelica reflexa That Improve Glucose-Stimulated Insulin Secretion by Regulating Pancreatic β-Cell Metabolism.

The aim of this study was to discover bioactive constituents of Angelica reflexa that improve glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells. Herein, three new compounds, namely, koseonolin A (1), koseonolin B (2), and isohydroxylomatin (3), along with 28 compounds (4-31) were isolated from the roots of A. reflexa by chromatographic methods. The chemical structures of new compounds (1-3) were elucidated through spectroscopic/spectrometric methods such as NMR and HRESIMS. In particular, the absolute configuration of the new compounds (1 and 3) was performed by electronic circular dichroism (ECD) studies. The effects of the root extract of A. reflexa (KH2E) and isolated compounds (1-31) on GSIS were detected by GSIS assay, ADP/ATP ratio assay, and Western blot assay. We observed that KH2E enhanced GSIS. Among the compounds 1-31, isohydroxylomatin (3), (-)-marmesin (17), and marmesinin (19) increased GSIS. In particular, marmesinin (19) was the most effective; this effect was superior to treatment with gliclazide. GSI values were: 13.21 ± 0.12 and 7.02 ± 0.32 for marmesinin (19) and gliclazide at a same concentration of 10 μM, respectively. Gliclazide is often performed in patients with type 2 diabetes (T2D). KH2E and marmesinin (19) enhanced the protein expressions associated with pancreatic β-cell metabolism such as peroxisome proliferator-activated receptor γ, pancreatic and duodenal homeobox 1, and insulin receptor substrate-2. The effect of marmesinin (19) on GSIS was improved by an L-type Ca2+ channel agonist and K+ channel blocker and was inhibited by an L-type Ca2+ channel blocker and K+ channel activator. Marmesinin (19) may improve hyperglycemia by enhancing GSIS in pancreatic β-cells. Thus, marmesinin (19) may have potential use in developing novel anti-T2D therapy. These findings promote the potential application of marmesinin (19) toward the management of hyperglycemia in T2D.

Apigenin Alleviates Endoplasmic Reticulum Stress-Mediated Apoptosis in INS-1 β-Cells.

The improvement of type 2 diabetes mellitus induced by naturally occurring polyphenols, known as flavonoids, has received considerable attention. However, there is a dearth of information regarding the effect of the trihydroxyflavone apigenin on pancreatic β-cell function. In the present study, the anti-diabetic effect of apigenin on pancreatic β-cell insulin secretion, apoptosis, and the mechanism underlying its anti-diabetic effects, were investigated in the INS-ID β-cell line. The results showed that apigenin concentration-dependently facilitated 11.1-mM glucose-induced insulin secretion, which peaked at 30 µM. Apigenin also concentration-dependently inhibited the expression of endoplasmic reticulum (ER) stress signaling proteins, CCAAT/enhancer binding protein (C/EBP) homologous protein (CHOP) and cleaved caspase-3, which was elevated by thapsigargin in INS-1D cells, with peak suppression at 30 µM. This was strongly correlated with the results of flow cytometric analysis of annexin V/propidium iodide (PI) staining and DNA fragmentation analysis. Moreover, the increased expression of thioredoxin-interacting protein (TXNIP) induced by thapsigargin was remarkably reduced by apigenin in a concentration-dependent manner. These results suggest that apigenin is an attractive candidate with remarkable and potent anti-diabetic effects on β-cells, which are mediated by facilitating glucose-stimulated insulin secretion and preventing ER stress-mediated β-cell apoptosis, the latter of which may be possibly mediated by reduced expression of CHOP and TXNIP, thereby promoting β-cell survival and function.

Glucocorticoid-mediated induction of ZBTB16 affects insulin secretion in human islets and EndoC-βH1 β-cells

Glucocorticoid use is associated with steroid-induced diabetes mellitus and impaired pancreatic β-cell insulin secretion. Here, the glucocorticoid-mediated transcriptomic changes in human pancreatic islets and the human insulin-secreting EndoC-βH1 cells were investigated to uncover genes involved in β-cell steroid stress-response processes. Bioinformatics analysis revealed glucocorticoids to exert their effects mainly on enhancer genomic regions in collaboration with auxiliary transcription factor families including AP-1, ETS/TEAD, and FOX. Remarkably, we identified the transcription factor ZBTB16 as a highly confident direct glucocorticoid target. Glucocorticoid-mediated induction of ZBTB16 was time- and dose-dependent. Manipulation of ZBTB16 expression in EndoC-βH1 cells combined with dexamethasone treatment demonstrated its protective role against glucocorticoid-induced reduction of insulin secretion and mitochondrial function impairment. In conclusion, we determine the molecular impact of glucocorticoids on human islets and insulin-secreting cells and investigate the effects of glucocorticoid targets on β-cell function. Our findings can pave the way for therapies against steroid-induced diabetes mellitus.