Beta Cell Dysfunction in Youth- and Adult-Onset Type 2 Diabetes: An Extensive Narrative Review with a Special Focus on the Role of Nutrients.

Traditionally a disease of adults, type 2 diabetes (T2D) has been increasingly diagnosed in youth, particularly among adolescents and young adults of minority ethnic groups. Especially, during the recent COVID-19 pandemic, obesity and prediabetes have surged not only in minority ethnic groups but also in the general population, further raising T2D risk. Regarding its pathogenesis, a gradually increasing insulin resistance due to central adiposity combined with a progressively defective ß-cell function are the main culprits. Especially in youth-onset T2D, a rapid ß-cell activity decline has been observed, leading to higher treatment failure rates, and early complications. In addition, it is well established that both the quantity and quality of food ingested by individuals play a key role in T2D pathogenesis. A chronic imbalance between caloric intake and expenditure together with impaired micronutrient intake can lead to obesity and insulin resistance on one hand, and ß-cell failure and defective insulin production on the other. This review summarizes our evolving understanding of the pathophysiological mechanisms involved in defective insulin secretion by the pancreatic islets in youth- and adult-onset T2D and, further, of the role various micronutrients play in these pathomechanisms. This knowledge is essential if we are to curtail the serious long-term complications of T2D both in pediatric and adult populations.

Nutrient-dependent regulation of ß-cell proinsulin content.

Insulin is made from proinsulin, but the extent to which fasting/feeding controls the homeostatically regulated proinsulin pool in pancreatic ß-cells remains largely unknown. Here, we first examined ß-cell lines (INS1E and Min6, which proliferate slowly and are routinely fed fresh medium every 2-3 days) and found that the proinsulin pool size responds to each feeding within 1 to 2 h, affected both by the quantity of fresh nutrients and the frequency with which they are provided. We observed no effect of nutrient feeding on the overall rate of proinsulin turnover as quantified from cycloheximide-chase experiments. We show that nutrient feeding is primarily linked to rapid dephosphorylation of translation initiation factor eIF2α, presaging increased proinsulin levels (and thereafter, insulin levels), followed by its rephosphorylation during the ensuing hours that correspond to a fall in proinsulin levels. The decline of proinsulin levels is blunted by the integrated stress response inhibitor, ISRIB, or by inhibition of eIF2α rephosphorylation with a general control nonderepressible 2 (not PERK) kinase inhibitor. In addition, we demonstrate that amino acids contribute importantly to the proinsulin pool; mass spectrometry shows that ß-cells avidly consume extracellular glutamine, serine, and cysteine. Finally, we show that in both rodent and human pancreatic islets, fresh nutrient availability dynamically increases preproinsulin, which can be quantified without pulse-labeling. Thus, the proinsulin available for insulin biosynthesis is rhythmically controlled by fasting/feeding cycles.

miR-200b-3p Induces the Formation of Insulin-Producing Cells from Umbilical Cord Mesenchymal Stem Cells by Targeting ZEB2.

Studies have reported that miRNAs regulate ß-cell differentiation, pancreatic development, and insulin secretion. However, the biological function of miRNAs during the formation of insulin-producing cells (IPCs) from umbilical cord-derived mesenchymal stem cells (UCMSCs) is poorly understood. Herein, the role and mechanism of miR-200b-3p during UCMSC differentiation into IPCs were investigated. UCMSCs were induced for IPC differentiation. An animal model was established by transplanting UCMSC-derived IPCs into streptozotocin-induced diabetic mice. Cell surface markers of undifferentiated UCMSCs and the expression of proinsulin and Pdx-1 in UCMSC-derived IPCs were measured by flow cytometry analysis. The interaction between miR-200b-3p and zinc finger E-box binding homeobox 2 (ZEB2) 3' untranslated region (UTR) was confirmed by luciferase reporter assay. Insulin secretion in UCMSC-derived IPCs was measured by enzyme-linked immunosorbent assay (ELISA). Islet marker (insulin and Pdx-1) levels were evaluated using immunofluorescence staining. In this study, undifferentiated UCMSCs had MSC phenotype and the potential for osteogenesis and adipogenesis. UCMSC-derived IPCs displayed glucose responsive insulin secretion and expressed insulin, Pdx-1 and proinsulin. miR-200b-3p was overexpressed in UCMSC-derived IPCs. Mechanically, miR-200b-3p targeted ZEB2. ZEB2 knockdown reversed the inhibitory effect of miR-200b-3p downregulation on IPC differentiation from UCMSCs in vitro. Moreover, miR-200b-3p silencing inhibited the anti-hypoglycemic effects and insulinogenesis of UCMSC-derived IPCs grafts in the kidney capsule of diabetic mice. Overall, miR-200b-3p induces the formation of IPCs from UCMSCs by targeting ZEB2.

Chicken ovalbumin upstream promoter transcription factor type II interacts and functionally cooperates with GATA4 to regulate anti-Müllerian hormone receptor type 2 transcription in mouse MA-10 Leydig cells.

BACKGROUND: Leydig cells produce testosterone and insulin-like 3, two hormones essential for male sex differentiation and reproductive function. The orphan nuclear receptor, chicken ovalbumin upstream promoter transcription factor type II (COUP-TFII), and the zinc finger factor GATA4 are two transcription factors involved in Leydig cell differentiation, gene expression, and function. OBJECTIVES: Several Leydig cell gene promoters contain binding motifs for both GATA factors and nuclear receptors. The goal of the present study is to determine whether GATA4 and COUP-TFII cooperate to regulate gene expression in Leydig cells. MATERIALS AND METHODS: The transcriptomes from GATA4- and COUP-TFII-depleted MA-10 Leydig cells were analyzed using bioinformatic tools. Functional cooperation between GATA4 and COUP-TFII, and other related family members, was assessed by transient transfections in Leydig (MA-10 and MLTC-1) and fibroblast (CV-1) cell lines on several gene promoters. Recruitment of GATA4 and COUP-TFII to gene promoters was investigated by chromatin immunoprecipitation. Co-immunoprecipitation was used to determine whether GATA4 and COUP-TFII interact in MA-10 Leydig cells. RESULTS: Transcriptomic analyses of GATA4- and COUP-TFII-depleted MA-10 Leydig cells revealed 44 commonly regulated genes including the anti-Müllerian hormone receptor type (Amhr2) gene. GATA4 and COUP-TFII independently activated the Amhr2 promoter, and their combination led to a stronger activation. A GC-rich element, located in the proximal Amhr2 promoter was found to be essential for GATA4- and COUP-TFII-dependent activation as well as for the COUP-TFII/GATA4 cooperation. COUP-TFII and GATA4 directly interacted in MA-10 Leydig cell extracts. Chromatin immunoprecipitation revealed that GATA4 and COUP-TFII are recruited to the proximal Amhr2 promoter, which contains binding sites for both factors in addition to the GC-rich element. Cooperation between COUP-TFII and GATA6, but not GATA1 and GATA3, was also observed. DISCUSSION AND CONCLUSION: Our results establish the importance of physical and functional cooperation between COUP-TFII/GATA4 in the regulation of gene expression in MA-10 Leydig cells, and more specifically the Amhr2 gene.

A chemoenzymatic strategy for site-selective functionalization of native peptides and proteins.

The emergence of new therapeutic modalities requires complementary tools for their efficient syntheses. Availability of methodologies for site-selective modification of biomolecules remains a long-standing challenge, given the inherent complexity and the presence of repeating residues that bear functional groups with similar reactivity profiles. We describe a bioconjugation strategy for modification of native peptides relying on high site selectivity conveyed by enzymes. We engineered penicillin G acylases to distinguish among free amino moieties of insulin (two at amino termini and an internal lysine) and manipulate cleavable phenylacetamide groups in a programmable manner to form protected insulin derivatives. This enables selective and specific chemical ligation to synthesize homogeneous bioconjugates, improving yield and purity compared to the existing methods, and generally opens avenues in the functionalization of native proteins to access biological probes or drugs.

IGF-1R/YAP signaling pathway is involved in collagen V-induced insulin biosynthesis and secretion in rat islet INS-1 cells.

PURPOSE: Type V collagen (collagen V) is one of the important components of extracellular matrix (ECM) in pancreas. We previously reported that pre-coating collagen V on the culture dishes enhanced insulin production in INS-1 rat pancreatic ß cells. In this study, we investigate the underlying mechanism. RESULTS: Insulin biosynthesis and secretion are both increased in INS-1 cells cultured on collagen V-coated dishes, accompanied by the reduced nuclear translocation of Yes-associated protein (YAP), a transcriptional co-activator. YAP, the downstream effector of Hippo signaling pathway, plays an important role in the development and function of pancreas. Inhibition of YAP activation by verteporfin further up-regulates insulin biosynthesis and secretion. Silencing large tumor suppressor (LATS), a core component of Hippo pathway which inhibits activity of YAP by phosphorylation, by siRNA transfection inhibits both insulin biosynthesis and secretion. In the present study, the protein level of insulin-like growth factor 1 receptor (IGF-1 R), detected as the upstream molecule of YAP, is reduced in the INS-1 cells cultured on the dishes coated with collagen V. The silencing of IGF-1 R by siRNA transfection further enhances insulin biosynthesis and secretion. IGF-1 treatment reduces collagen V-induced up-regulation of insulin biosynthesis and secretion, accompanying the increased nuclear YAP. CONCLUSION: Inhibition of IGF-1 R/YAP signal pathway is involved in collagen V-induced insulin biosynthesis and secretion in INS-1 cells.

Serum Orosomucoid Is Associated with Serum Adiponectin, Adipose Tissue Insulin Resistance Index, and a Family History of Type 2 Diabetes in Young Normal Weight Japanese Women.

INTRODUCTION: Adipose tissue (AT) expandability may be facilitated by adiponectin and suppressed by orosomucoid, and reduced AT expandability may be associated with first-degree relatives of type 2 diabetes. We tested the hypothesis that orosomucoid may be associated not only with adiponectin and adipose tissue insulin resistance but also with a family history of type 2 diabetes (FHD). Research Design and Methods. Anthropometric and metabolic variables, adipokines, and measures of inflammatory and insulin resistance were cross-sectionally investigated in 153 young normal weight Japanese women. Stepwise multivariate linear regression analyses were used to identify the most important determinants of orosomucoid. RESULTS: Orosomucoid was higher in women with positive (n = 57) compared to women with negative FHD and was associated positively with FHD (both p = 0.01). Orosomucoid also showed positive associations with fasting glucose (p < 0.001), free fatty acids (p = 0.001), and HbA1c (p = 0.007), whereas there was no association with fasting insulin and serum lipids. In addition, orosomucoid was associated inversely with adiponectin (p = 0.02) and positively with adipose tissue-insulin resistance index (AT-IR, the product of fasting insulin and free fatty acids; p = 0.001) but not with homeostasis model assessment-insulin resistance, leptin, and high-sensitivity C-reactive protein. In multivariate analyses, AT-IR (standardized ß, 0.22; p = 0.003), serum adiponectin (standardized ß, -0.163; p = 0.032), FHD+ (standardized ß, 0.178; p = 0.029), and HbA1c (standardized ß, 0.213; p = 0.005) emerged as independent determinants of orosomucoid and explained 15.2% of its variability. CONCLUSIONS: These results are the first to demonstrate that orosomucoid is associated not only with adipose tissue-insulin resistance and adiponectin but also with FHD.

The CLOCK protein regulates insulin secretion related with L-type calcium channels in rat pancreatic beta cells.

BACKGROUND: Circadian locomotor output cycles kaput protein (CLOCK) plays a crucial role in glucose homeostasis and controlling insulin secretion. However, the mechanism of the CLOCK regulating rhythmic insulin secretion has not been fully understood. METHODS: Rhythmic expression of the CLOCK in rat pancreatic beta cell was detected. INS-1 cells were transfected with siRNAs to knockdown the CLOCK before the cells were incubated with different concentrations of glucose. Insulin secretion was analyzed by ELISA method. Expression of the L-type calcium channel protein (Cav1.2, Cacna1c) was determined both in the CLOCK-knockdown cells and the control cells. Calcium influx was probed by fluorescent. Chromatin immunoprecipitation (ChIP) test and dual-luciferase reporter gene experiments were applied to verify the relationship between the CLOCK and Cav1.2. RESULTS: The CLOCK is abundantly expressed in rat pancreatic beta cells. Transcription level of the CLOCK showed rhythmicity in the beta cells. Compared to the control group, insulin release was significantly impaired with 25 mM glucose incubation in the CLOCK-knockdown group, but not showed with 2.5 mM glucose incubation. The expression of Cav1.2 and the influx of calcium were significantly decreased in the CLOCK-knockdown group with 25 mM glucose incubation. ChIP test indicted that the CLOCK bound to -444∼-454 region of the Cacna1c promoter of the INS-1 cells, but the binding was significantly reduced following the CLOCK-knockdown. Luciferase experiment was in accordance with the finding of ChIP. CONCLUSIONS: The CLOCK mediating Cav1.2 expression may point out a potential pathway of circadian rhythm affecting insulin secretion.

Effect of Mori ramulus on the postprandial blood glucose levels and inflammatory responses of healthy subjects subjected to an oral high-fat/sucrose challenge: A double-blind, randomized, crossover clinical trial.

Blood glucose is inadequately controlled in diabetes mellitus, causing various inflammation-related complications. This study aimed to investigate responses to an oral sucrose/lipid challenge in the context of glucose metabolism after consumption of Mori ramulus (MR) extract. In this study on healthy subjects, the optimal dose and safety of MR were confirmed in a preliminary pilot trial (n = 24), meanwhile, blood glucose, insulin, and inflammatory marker levels were detected via an oral sucrose/lipid tolerance test in the main trial (n = 36). In the main study, the blood glucose response was significantly decreased after 240 min in the MR group. Compared to the placebo group, the treatment group exhibited plasma insulin levels that were significantly increased at 120 min and decreased at 240 min. In conclusion, a single MR extract dose protects against inflammation induced by high-fat/sugar to maintain normal insulin secretion and thus helps to maintain postprandial blood glucose levels via an inflammatory mechanism.

Adhesion GPCR GPR56 Expression Profiling in Human Tissues.

Despite the immense functional relevance of GPR56 (gene ADGRG1) in highly diverse (patho)physiological processes such as tumorigenesis, immune regulation, and brain development, little is known about its exact tissue localization. Here, we validated antibodies for GPR56-specific binding using cells with tagged GPR56 or eliminated ADGRG1 in immunotechniques. Using the most suitable antibody, we then established the human GPR56 tissue expression profile. Overall, ADGRG1 RNA-sequencing data of human tissues and GPR56 protein expression correlate very well. In the adult brain especially, microglia are GPR56-positive. Outside the central nervous system, GPR56 is frequently expressed in cuboidal or highly prismatic secreting epithelia. High ADGRG1 mRNA, present in the thyroid, kidney, and placenta is related to elevated GPR56 in thyrocytes, kidney tubules, and the syncytiotrophoblast, respectively. GPR56 often appears in association with secreted proteins such as pepsinogen A in gastric chief cells and insulin in islet ß-cells. In summary, GPR56 shows a broad, not cell-type restricted expression in humans.

Schisandrin C Affects Glucose-Stimulated Insulin Secretion in Pancreatic ß-Cells and Glucose Uptake in Skeletal Muscle Cells.

The aim of our study was to investigate the effect of three lignans (schisandrol A, schisandrol B, and schisandrin C) on insulin secretion in rat INS-1 pancreatic ß-cells and glucose uptake in mouse C2C12 skeletal muscle cells. Schisandrol A and schisandrin C enhanced insulin secretion in response to high glucose levels with no toxic effects on INS-1 cells. The effect of schisandrin C was superior to that of gliclazide (positive control), a drug commonly used to treat type 2 diabetes (T2D). In addition, western blot analysis showed that the expression of associated proteins, including peroxisome proliferator-activated receptor γ (PPARγ), pancreatic and duodenal homeobox 1 (PDX-1), phosphatidylinositol 3-kinase (PI3K), Akt, and insulin receptor substrate-2 (IRS-2), was increased in INS-1 cells after treatment with schisandrin C. In addition, insulin secretion effect of schisandrin C were enhanced by the Bay K 8644 (L-type Ca2+ channel agonist) and glibenclamide (K+ channel blocker), were abolished by the nifedipine (L-type Ca2+ channel blocker) and diazoxide (K+ channel activator). Moreover, schisandrin C enhanced glucose uptake with no toxic effects on C2C12 cells. Western blot analysis showed that the expression of associated proteins, including insulin receptor substrate-1 (IRS-1), AMP-activated protein kinase (AMPK), PI3K, Akt, glucose transporter type 4 (GLUT-4), was increased in C2C12 cells after treatment with schisandrin C. Schisandrin C may improve hyperglycemia by enhancing insulin secretion in pancreatic ß-cells and improving glucose uptake into skeletal muscle cells. Our findings may provide evidence that schisandrin C may be beneficial in devising novel anti-T2D strategies.

Regulatory Effects of N-3 PUFAs on Pancreatic ß-cells and Insulin-sensitive Tissues.

The N-3 polyunsaturated fatty acids (PUFAs) have a wide range of health benefits, including antiinflammatory effects, improvements in lipids metabolism and promoting insulin secretion, as well as reduction of cancer risk. Numerous studies support that N-3 PUFAs have the potentials to improve many metabolic diseases, such as diabetes, nonalcoholic fatty liver disease and obesity, which are attributable to N-3 PUFAs mediated enhancement of insulin secretion by pancreatic ß-cells and improvements in insulin sensitivity and metabolic disorders in peripheral insulin-sensitive tissues such as liver, muscles, and adipose tissue. In this review, we summarized the up-to-date clinical and basic studies on the regulatory effects and molecular mechanisms of N-3 PUFAs mediated benefits on pancreatic ß-cells, adipose tissue, liver, and muscles in the context of glucose and/or lipid metabolic disorders. We also discussed the potential factors involved in the inconsistent results from different clinical researches of N-3 PUFAs.

Systolic Dysfunction of the Heart in Type 1 Diabetes Mellitus.

Impaired insulin synthesis is accompanied by hyperglycemia and the development of diabetic cardiomyopathy. Echocardiography and left-ventricular catheterization were employed for studying the contractile function of the left ventricle in 2 weeks after administration of streptozotocin (60 mg/kg). The results obtained by both methods were similar and indicated the development of systolic dysfunction with a 27% decrease in cardiac output. The invasive study showed that the maximum rate of left-ventricular pressure development, the contractility index, and systolic left-ventricular pressure were within the normal range, but the peak ejection rate was reduced by 28%. BP was normal, but the vascular stiffness index was increased by about 1.5 times and inversely correlated with the peak ejection rate (r=-0.69). The results showed that systolic dysfunction in type 1 diabetes model was due to reduced ejection from the left ventricle at normal rate of left-ventricular pressure development.

Exploring Insulin Production Following Alveolar Islet Transplantation (AIT).

Recent studies have demonstrated the feasibility of islet implantation into the alveoli. However, until today, there are no data on islet behavior and morphology at their transplant site. This study is the first to investigate islet distribution as well insulin production at the implant site. Using an ex vivo postmortem swine model, porcine pancreatic islets were isolated and aerosolized into the lung using an endoscopic spray-catheter. Lung tissue was explanted and bronchial airways were surgically isolated and connected to a perfusor. Correct implantation was confirmed via histology. The purpose of using this new lung perfusion model was to measure static as well as dynamic insulin excretions following glucose stimulation. Alveolar islet implantation was confirmed after aerosolization. Over 82% of islets were correctly implanted into the intra-alveolar space. The medium contact area to the alveolar surface was estimated at 60 +/- 3% of the total islet surface. The new constructed lung perfusion model was technically feasible. Following static glucose stimulation, insulin secretion was detected, and dynamic glucose stimulation revealed a biphasic insulin secretion capacity during perfusion. Our data indicate that islets secrete insulin following implantation into the alveoli and display an adapted response to dynamic changes in glucose. These preliminary results are encouraging and mark a first step toward endoscopically assisted islet implantation in the lung.

Pharmacological Inhibition of Inositol-Requiring Enzyme 1α RNase Activity Protects Pancreatic Beta Cell and Improves Diabetic Condition in Insulin Mutation-Induced Diabetes.

ß-cell ER stress plays an important role in ß-cell dysfunction and death during the pathogenesis of diabetes. Proinsulin misfolding is regarded as one of the primary initiating factors of ER stress and unfolded protein response (UPR) activation in ß-cells. Here, we found that the ER stress sensor inositol-requiring enzyme 1α (IRE1α) was activated in the Akita mice, a mouse model of mutant insulin gene-induced diabetes of youth (MIDY), a monogenic diabetes. Normalization of IRE1α RNase hyperactivity by pharmacological inhibitors significantly ameliorated the hyperglycemic conditions and increased serum insulin levels in Akita mice. These benefits were accompanied by a concomitant protection of functional ß-cell mass, as shown by the suppression of ß-cell apoptosis, increase in mature insulin production and reduction of proinsulin level. At the molecular level, we observed that the expression of genes associated with ß-cell identity and function was significantly up-regulated and ER stress and its associated inflammation and oxidative stress were suppressed in islets from Akita mice treated with IRE1α RNase inhibitors. This study provides the evidence of the in vivo efficacy of IRE1α RNase inhibitors in Akita mice, pointing to the possibility of targeting IRE1α RNase as a therapeutic direction for the treatment of diabetes.

Carbon monoxide enhances calcium transients and glucose-stimulated insulin secretion from pancreatic ß-cells by activating Phospholipase C signal pathway in diabetic mice.

In early stage of diabetes, insulin secretion from pancreatic ß-cells is increased to deal with the elevated blood glucose. Previous studies have reported that islet-produced carbon monoxide (CO) is associated with increased glucose-stimulated insulin secretion from ß-cells. However, this compensatory mechanism by which CO may act to enhance ß-cell function remain unclear. In this study, we revealed that CO promoted intracellular calcium ([Ca2+]i) elevation and glucose-stimulated insulin secretion (GSIS) from pancreatic ß-cells in leptin receptor deficient db/db mice but not in C57 mice. The stimulatory effects of CO on ß-cell function in db/db mice was blocked by inhibition of Phospholipase C (PLC) signaling pathway. We further demonstrated that CO triggered [Ca2+]i transients and enhanced GSIS in C57 islets when ß-cells overexpressed with PLCγ1 and PLCδ1, but not PLCß1. On the other hand, reducing PLCγ1 and PLCδ1 expressions in db/db islets dramatically attenuated the stimulatory effects of CO on ß-cell function, whereas interfering PLCß1 expression had no effects on CO-induced ß-cell function enhancement. Our findings showing that CO elevated [Ca2+]i and enhanced GSIS by activating PLC signaling through PLCγ1 and PLCδ1 isoforms in db/db pancreatic ß-cells may suggest an important mechanism by which CO promotes ß-cell function to prevent hyperglycemia. Our study may also provide new insights into the therapy for type II diabetes and offer a potential target for therapeutic applications of CO.

Structural Lessons From the Mutant Proinsulin Syndrome.

Insight into folding mechanisms of proinsulin has been provided by analysis of dominant diabetes-associated mutations in the human insulin gene (INS). Such mutations cause pancreatic ß-cell dysfunction due to toxic misfolding of a mutant proinsulin and impairment in trans of wild-type insulin secretion. Anticipated by the "Akita" mouse (a classical model of monogenic diabetes mellitus; DM), this syndrome illustrates the paradigm endoreticulum (ER) stress leading to intracellular proteotoxicity. Diverse clinical mutations directly or indirectly perturb native disulfide pairing leading to protein misfolding and aberrant aggregation. Although most introduce or remove a cysteine (Cys; leading in either case to an unpaired thiol group), non-Cys-related mutations identify key determinants of folding efficiency. Studies of such mutations suggest that the hormone's evolution has been constrained not only by structure-function relationships, but also by the susceptibility of its single-chain precursor to impaired foldability. An intriguing hypothesis posits that INS overexpression in response to peripheral insulin resistance likewise leads to chronic ER stress and ß-cell dysfunction in the natural history of non-syndromic Type 2 DM. Cryptic contributions of conserved residues to folding efficiency, as uncovered by rare genetic variants, define molecular links between biophysical principles and the emerging paradigm of Darwinian medicine: Biosynthesis of proinsulin at the edge of non-foldability provides a key determinant of "diabesity" as a pandemic disease of civilization.

Collagen type I enhances cell growth and insulin biosynthesis in rat pancreatic cells.

Type I collagen (collagen I) is the most abundant component of the extracellular matrix (ECM) in the pancreas. We previously reported that collagen I-coated culture dishes enhanced proliferation of rat pancreatic ß cell line, INS-1 cells, via up-regulation of ß-catenin nuclear translocation. In this study, we further investigated the effects of collagen I on insulin production of INS-1 cells. The results indicate that insulin synthesis as well as cell proliferation is increased in the INS-1 cells cultured on the dishes coated with collagen I. Up-regulation of insulin-like growth factor 1 receptor (IGF-1R) on the INS-1 cells cultured on the collagen-coated dishes is involved in up-regulation of cell proliferation and increase of insulin biosynthesis; however, up-regulation of insulin secretion in the INS-1 cells on collagen I-coated dishes was further enhanced by inhibition of IGF-1R. Autophagy of INS-1 cells on collagen I-coated dishes was repressed via IGF-1R upregulation, and inhibition of autophagy with 3MA further enhanced cell proliferation and insulin biosynthesis but did not affect insulin secretion. E-cadherin/ß-catenin adherent junction complexes are stabilized by autophagy. That is, autophagy negatively regulates the nuclear translocation of ß-catenin that leads to insulin biosynthesis and cell proliferation. In conclusion, IGF-1R/downregulation of autophagy/nuclear translocation of ß-catenin is involved in collagen I-induced INS-1 cell proliferation and insulin synthesis.

Pancreatic Ppy-expressing γ-cells display mixed phenotypic traits and the adaptive plasticity to engage insulin production.

The cellular identity of pancreatic polypeptide (Ppy)-expressing γ-cells, one of the rarest pancreatic islet cell-type, remains elusive. Within islets, glucagon and somatostatin, released respectively from α- and δ-cells, modulate the secretion of insulin by ß-cells. Dysregulation of insulin production raises blood glucose levels, leading to diabetes onset. Here, we present the genetic signature of human and mouse γ-cells. Using different approaches, we identified a set of genes and pathways defining their functional identity. We found that the γ-cell population is heterogeneous, with subsets of cells producing another hormone in addition to Ppy. These bihormonal cells share identity markers typical of the other islet cell-types. In mice, Ppy gene inactivation or conditional γ-cell ablation did not alter glycemia nor body weight. Interestingly, upon ß-cell injury induction, γ-cells exhibited gene expression changes and some of them engaged insulin production, like α- and δ-cells. In conclusion, we provide a comprehensive characterization of γ-cells and highlight their plasticity and therapeutic potential.