Bilateral macronodular adrenal disease (BMAD), also referred to as primary bilateral macronodular adrenal hyperplasia (PBMAH), represents a rare etiology of subclinical or overt Cushing's syndrome (CS), characterized by the presence of multiple large nodules in both adrenal glands. Although historically considered a sporadic condition, familial cases of BMAD have become increasingly recognized in recent years. As early surgical intervention is typically chosen for these familial cases, evidence on the long-term effectiveness of conservative medical therapy remains scarce. Here, we report a Japanese parent-child pair with subclinical and overt CS with genetically confirmed BMAD in which both individuals harbored ARMC5 mutations and exhibited aberrant hormone responses and were managed with long-term metyrapone monotherapy. In both cases, sustained biochemical control of adrenocortical hyperfunction was achieved in more than 5 years. One patient developed progressive hypokalemia, eventually leading to unilateral adrenalectomy. These findings suggest that metyrapone monotherapy serves as an effective noninvasive treatment strategy for select familial BMAD patients, although close monitoring is warranted for potential complications.

Pancreatic islet cells continuously synthesize and secrete large quantities of peptide hormones, making them uniquely dependent on robust proteostasis networks to maintain cellular function. Traditionally, the unfolded protein response (UPR) is considered a stress-responsive pathway that protects cells from endoplasmic reticulum (ER) dysfunction or triggers apoptosis when ER stress is excessive. Here, we propose that proteostasis functions as an active physiological signaling network that governs islet cell adaptation, plasticity, and long-term homeostasis, extending beyond its conventional role in the response to cellular damage. In pancreatic β cells, glucose signaling suppresses the expression of the proapoptotic factor CHOP through both IRS2-dependent and IRS2-independent pathways, indicating that metabolic signaling directly remodels the ER stress response. In contrast, the CHOP-GADD34-eIF2α dephosphorylation axis constitutes a negative feedback mechanism that fine-tunes translational recovery and determines the balance between adaptation and cell death. Moreover, 4E-BP1-mediated inhibition of mRNA translation and modulation of mTOR signaling alleviate proteotoxic stress and promote β-cell survival under conditions of increased secretory demand. In addition to translational control, IGF2 receptor-mediated signaling has recently been implicated in the regulation of autophagy, further linking lysosomal quality control to β-cell proteostasis. Importantly, proteostasis also affects α-cell biology, where UPR signaling regulates glucagon secretion and contributes to α-to-β cell transdifferentiation, highlighting a previously unrecognized role of ER homeostasis in endocrine cell identity. Finally, recent findings indicate that progressive impairment of proteostasis is a hallmark of islet aging, integrating defects in protein folding, translation, autophagy, and stress adaptation into the pathogenesis of diabetes.

Pancreatic β cells maintain glucose homeostasis through insulin production, and their loss underlies both type 1 and type 2 diabetes. Among the signaling systems that govern β-cell biology, insulin and insulin-like growth factor (IGF) receptor pathways have long attracted attention as intrinsic modulators of β-cell growth, survival and secretory competence. However, the physiological and pathological relevance of these receptors in β cells remains uncertain, reflecting model-specific discrepancies and the complex interplay between local autocrine and systemic endocrine effects. Recent analyses have expanded this view, revealing the coexistence of insulin receptor-dependent and insulin receptor-independent regulatory modules that govern β-cell adaptation to metabolic stress. Furthermore, molecular regulators, including inceptor and IGF2R, reshape our understanding of insulin/IGF receptor signaling as a flexible, adaptive network. Together, these insights suggest that precise modulation of receptor networks may hold the key to unlocking endogenous β-cell regenerative capacity.

Glucose-stimulated insulin secretion (GSIS) in β cells depends critically on membrane depolarization-induced Ca2+ influx. Accordingly, the electrophysiological assessment of intact islets, where β cells act as functional syncytia, is essential for evaluating insulin secretory dynamics. Imeglimin, an oral agent used in treating type 2 diabetes, increases insulin secretion; however, its effects on β-cell electroactivity remain unclear. Here, we investigated extracellular and membrane potentials in imeglimin-treated mouse islets using microelectrode array (MEA) recordings and a plasma membrane potential indicator (PMPI). Imeglimin augmented first-phase insulin release and significantly increased the fraction of the plateau phase (FOPP), an MEA-derived parameter reflecting secretory competence, under 11.1 mM glucose. Consistent with these findings, the increase in PMPI fluorescence demonstrated enhanced membrane depolarization in response to imeglimin at high-glucose concentrations. These findings indicate that imeglimin potentiates β-cell electroactivity, thereby facilitating GSIS at the islet level.

Endoplasmic reticulum (ER) stress is a critical driver of pancreatic β-cell dysfunction and apoptosis. Although metformin, a drug used to treat type 2 diabetes, primarily decreases blood glucose levels by improving insulin sensitivity, its direct effects on β-cell survival remain unclear. Here, we investigated the effect of metformin on β-cell stress responses under ER stress conditions. Thapsigargin (Tg)-induced ER stress increased β-cell apoptosis in mouse islets, which was prevented by metformin in a dose-dependent manner. Treatment with metformin for 24 h suppressed the Tg-induced upregulation of unfolded protein response (UPR)-related genes, as confirmed by transcriptomic and pathway analyses. Quantitative proteomics revealed that Tg inhibited eIF2 signaling and protein translation, both of which were partially restored by metformin. Enrichment analysis further indicated the attenuation of apoptotic pathways in metformin-treated islets. Polysome profiling and puromycin incorporation assays demonstrated that metformin reduced protein translation independently of ER stress. Metformin promoted the dephosphorylation of 4E-BP1, a key initiator of cap-dependent protein translation that is activated by phosphorylation, and the antiapoptotic effect of metformin was abolished by 4E-BP1 knockdown in MIN6 cells. Phosphoproteomic analysis indicated that the activation of mTOR signaling, a kinase of 4E-BP1, in Tg-treated islets was mitigated by metformin. Taken together, these findings reveal a cytoprotective mechanism of metformin in β-cells, in which metformin suppresses ER stress-induced apoptosis through 4E-BP1-mediated inhibition of mRNA translation and modulation of mTOR signaling. This study highlights a β-cell-intrinsic action of metformin that may contribute to its long-term therapeutic benefits in diabetes management.

Vitiligo is a chronic autoimmune disease, that causes depigmented patches that impose psychosocial burden, with many patients responding poorly to current therapies[1]. Diabetes mellitus (DM) has been linked to vitiligo; however, data regarding type 2 DM remain limited and inconsistent [2]. Using UK Biobank data, we investigated associations between DM, glycemic measures, and vitiligo risk, and conducted Mendelian randomization to assess causality.

AIMS:Although metformin has antitumor effects, the detailed mechanism of action, particularly with respect to the cellular responses mediated through G protein-coupled receptors (GPCRs), remains unclear. METHODS AND RESULTS:Here, we assayed a panel of 200 GPCRs in cells treated with metformin and reported that signaling through several receptors, including lysophosphatidic acid (LPA) receptors, was suppressed. Metformin significantly attenuated LPA-induced intracellular Ca2+ mobilization in LPA receptor 1 (LPAR1)-, 2 (LPAR2)-, and 3 (LPAR3)-transfected rat hepatoma RH7777 cells. LPA treatment increased LPAR3-transfected RH7777 cell adhesion and migration. This response to LPA was attenuated by treatment with the Gq/11 inhibitor YM-254890 and metformin. In contrast, these inhibitors had minimal effects on the cell migration induced by epidermal growth factor. CONCLUSIONS:These results indicate that the inhibition of LPA receptor signaling by metformin, especially the consequent suppression of LPAR3-mediated cell migration, may contribute to the antitumor effects of metformin.

It is not easy to construct an accurate dysfunction model of human pancreatic islet cells under high glucose burden in in vitro culture because long-term culture of human pancreatic islet cells while retaining their function is difficult. We previously showed alginate encapsulation enabled human islet cells to maintain glucose responsiveness for long-term in vitro culture. Using this capsulation method, we cultured human islet cells for 4 weeks under normal or high glucose conditions. We confirmed that disruption of glucose responsiveness in human islet cells was elicited by high glucose charge, but not under normal glucose conditions. To investigate the mechanism of this disruption, we RNA sequenced cultured samples under normal or high glucose conditions using two different batches. We picked up common down- or up-regulation genes in two different batches under high glucose load and, compared them with those under normal glucose levels. The number of common down-regulation genes was 96, and that of common up-regulation genes was 174. We validated the changes of expression level of each candidate gene in beta cells using single-cell RNA sequencing data, and we further extracted 7 out of 96 common down-regulation genes and 8 out of 174 common up-regulation genes. These genes are putative causal genes for beta cell dysfunction. Moreover, we found that the proinsulin to C-peptide ratio increased, and mature insulin granules decreased under high glucose conditions, suggesting that impaired glucose responsiveness was caused to some extent by the abnormal status of insulin granules.

Dysregulated α cell function contributes to the development of diabetes. In this study, we find that treatment with imeglimin, an antidiabetic drug, prevents glucagon release and induces a loss of α cell identity through direct action on α cells. Mechanistically, imeglimin reduces Gsα expression to inhibit the exchange protein directly activated by cyclic adenosine monophosphate 2 (EPAC2)-mediated secretion of glucagon induced by low glucose, gastric inhibitory polypeptide (GIP), or adrenaline in an insulin-independent manner. Imeglimin also attenuates α cell Ca2+ oscillations. MafB expression is downregulated by imeglimin to induce α cell dedifferentiation. In addition, imeglimin upregulates C/EBP homologous protein (CHOP) expression, which partly contributes to the reduction in Gsα and MafB expression to reduce glucagon secretion and induce α cell reprogramming without altering protein translation. These pleiotropic effects of imeglimin on glucagon secretion and α cell identity can be recapitulated in mouse models of diabetes in vivo. These data suggest that the imeglimin-mediated regulation of α cell plasticity, particularly via glucagon suppression, may contribute to glucose homeostasis.

Vagal nerve stimulation has emerged as a promising modality for treating a wide range of chronic conditions, including metabolic disorders. However, the cellular and molecular pathways driving these clinical benefits remain largely obscure. Here, we demonstrate that fibroblast growth factor 3 (Fgf3) mRNA is upregulated in the mouse vagal ganglia under acute metabolic stress. Systemic and vagal sensory overexpression of Fgf3 enhanced glucose-stimulated insulin secretion (GSIS), improved glucose excursion, and increased energy expenditure and physical activity. Fgf3-elicited insulinotropic and glucose-lowering responses were recapitulated when overexpression of Fgf3 was restricted to the pancreas-projecting vagal sensory neurons. Genetic ablation of Fgf3 in pancreatic vagal afferents exacerbated high-fat diet-induced glucose intolerance and blunted GSIS. Finally, electrostimulation of the vagal afferents enhanced GSIS and glucose clearance independently of efferent outputs. Collectively, we demonstrate a direct role for the vagal afferent signaling in GSIS and identify Fgf3 as a vagal sensory-derived metabolic factor that controls pancreatic β-cell activity.

Introduction and Objective: Aging is associated with the declination of β-cell function in type 2 diabetes. However, the precise mechanisms underlying the functional changes in β cells due to aging remain unclear. In this study, we investigated the changes in β-cell functions associated with aging. Methods: We cultured islets from young (7 weeks of age) and aged (61 weeks of age) mice under low (3.9 mM) and high (11.1 mM) glucose conditions for 24 hours, then performed single-cell RNA-sequencing, histological evaluation, and qPCR. Results: In β cells from aged mice, 1344 genes were upregulated and 174 were downregulated under high glucose conditions. Pathway analysis for the differentially expressed genes in aged β cells manifested alterations in pathways associated with β-cell proliferation and apoptosis. Among these pathways, Nupr1 showed a marked 2.38-fold upregulation in aged β cells. In aged islets, β-cell proliferation significantly declined with a 98% reduction in EdU incorporation, and glucose-induced β-cell proliferation was absent. TUNEL staining showed a 4.7-fold increase in β-cell apoptosis in aged islets. Lipid droplets in β cells were highly accumulated in aged islets. qPCR confirmed elevated Nupr1 expression in aged islets, and immunofluorescence studies demonstrated a 2.2-fold increase in Nupr1 nuclear intensity in aged β cells under high glucose conditions. In young islets, glucose stimulation reduced Nupr1 expression, but this effect was absent in aged islets. Treatment with an Nupr1 inhibitor, ZZW-115, demonstrated a 1.45-fold increase in β-cell proliferation and a 55% decrease in β-cell apoptosis in non-aged islets under high glucose conditions. Conclusion: Aging reduced β-cell proliferation, exacerbated β-cell apoptosis, and increased Nupr1 expression in islets, with a loss of glucose responsiveness. Nupr1 inhibitor ameliorated β-cell proliferation and apoptosis, indicating the potential role of Nupr1 in senescence-associated β-cell dysfunctions. E. Ong Yajima: None. T. Tsuno: None. J. Shirakawa: None. JST FOREST Program ( JPMJFR234O)

Background and Aims Metabolic dysfunction-associated steatotic liver disease (MASLD) is a highly prevalent and increasingly chronic liver disorder with increasing global incidence, closely linked to prolonged high-fat diet (HFD)-induced metabolic impairment. Although imeglimin, an antidiabetic agent known to improve insulin resistance, has demonstrated therapeutic potential in metabolic diseases, its effects and underlying molecular mechanism in MASLD remain unclear. Approach and results In this study, we employed a long-term (48-week) high-fat diet-induced murine model of MASLD to recapitulate human disease progression, then treated those mice with imeglimin for 6 months to investigate its therapeutic effects. Imeglimin treatment improved insulin resistance, restored liver function, attenuated hepatic inflammation, and promoted hepatocyte viability. PEN2, a component of the γ-secretase complex, is identified as the key target of imeglimin. The therapeutic effects of imeglimin are abrogated in liver-specific Pen2-deficient mice or upon pharmacologic inhibition of AMP-activated protein kinase (AMPK), indicating that activation of PEN2-AMPK signaling is required for its beneficial effects. Furthermore, we found that imeglimin also protected human pluripotent stem cell (hPSC)-derived hepatocyte-like cells from free fatty acid (FFA)-induced lipid accumulation. Conclusion Collectively, our findings indicate that imeglimin ameliorates hepatic lipotoxicity by targeting PEN2 to activate AMPK axis, suggesting its potential as a new drug for MASLD treatment in the near future.

Insulin-like growth factor -2 receptor (IGF2R), also known as cation-independent mannose-6-phosphate receptor (CI-MPR), is localized in cytosolic vesicles and is unique in its ability to transport enzymes to the lysosome and to clear IGF2 from the cell surface by acting as a scavenger receptor. To evaluate the direct role of IGF2R in β-cell biology we undertook complementary in vitro knockdown and in vivo knockout approaches. A β-cell line with a stable knockdown of IGF2R (IGF2RKD), exhibited decreased glucose-induced insulin secretion, and enhanced cell proliferation. Tamoxifen-inducible β-cell-specific IGF2R knockout mice exhibited impaired glucose tolerance and blunted insulin secretion after high-fat diet-loading that was likely secondary to reduced β-cell mass due to attenuated proliferation. β-cells with IGF2RKD exhibited decreased autophagosomes following starvation, which was accompanied by a reduced expression of p62, LC3B, and ULK1. Aged mice also showed impaired autophagy in βIGF2R-deficient β-cells. Reduced IGF2R function and m6A methylation were observed in islets from both mouse and human type 2 diabetes. Taken together, these data point to IGF2R as an important regulator of insulin secretion, cell proliferation and autophagy in mammalian β-cells.

ARTICLE HIGHLIGHTS:Although imeglimin promotes β-cell proliferation and ameliorates β-cell apoptosis, the detailed metabolic changes induced by imeglimin in β-cells are unknown. Imeglimin increases adenylosuccinate (S-AMP), which is produced by adenylosuccinate synthase (ADSS) from inosine monophosphate and aspartate, and imeglimin also increases amino acid content, including aspartate, in mouse islets. Inhibition of S-AMP production by an ADSS inhibitor reduces the ability of imeglimin to increase β-cell proliferation and ameliorate β-cell apoptosis in mouse islets, human islets, porcine islets, and human pluripotent stem cell-derived β-cells. Imeglimin increases S-AMP to promote β-cell proliferation and ameliorate β-cell apoptosis.

The matricellular protein Fibulin-5 (Fbln5) is a secreted protein that is essential for elastic fiber formation, and pancreatic islets are usually surrounded by the extracellular matrix (ECM), which includes elastic fibers. However, much uncertainty remains regarding the function of the ECM and its components in β-cells. Here, we describe the role of Fbln5 in β-cell replication. Fbln5 expression was increased upon glucose stimulation in β-cells of mouse and human islets. β-Cell-specific Fbln5-knockout (βFbln5KO) mice exhibit significantly reduced β-cell proliferation in vivo but not in vitro. Secreted extracellular Fbln5 enhances β-cell replication. Fbln5-deficient β-cells exhibit the downregulated expression of the gene encoding Polo-like kinase 1 (PLK1), which is accompanied by ERK-mediated FoxM1 nuclear export. These data suggest that Fbln5 is secreted from β-cells in response to glucose and plays important roles in the appropriate maintenance of β-cell functions in an autocrine or paracrine manner.

Semaphorins were initially identified as axon guidance molecules that were widely expressed and involved in divergent functions in various organs, including neuronal development and immunological processes. Collapsin response mediator proteins (CRMPs) are involved in the intracellular signaling of semaphorin 3A (Sema3a) and are highly expressed in the nervous system. However, the participation of semaphorins or their receptors plexins and CRMPs in the regulation of islet function remains unknown. In this study, we measured the expression of semaphorin, plexin, and CRMP families in mouse islets, and their expression levels were altered by treatment with high glucose or a glucokinase activator (GKA). The expression and phosphorylation of CRMP-2 in islets were upregulated in high-fat diet (HF)-fed obese mice, and the expression of CRMP-2 was downregulated in islets from db/db mice. HF-fed CRMP-2 knockout mice exhibited impaired glucose tolerance. These results indicated that the semaphorin/plexin/CRMP families in mouse islets might be involved in glucose metabolism partly through glucose/glucokinase.