ß-Cell miRNA-503-5p Induced by Hypomethylation and Inflammation Promotes Insulin Resistance and ß-Cell Decompensation.

Chronic inflammation promotes pancreatic ß-cell decompensation to insulin resistance because of local accumulation of supraphysiologic interleukin 1ß (IL-1ß) levels. However, the underlying molecular mechanisms remain elusive. We show that miR-503-5p is exclusively upregulated in islets from humans with type 2 diabetes and diabetic rodents because of its promoter hypomethylation and increased local IL-1ß levels. ß-Cell-specific miR-503 transgenic mice display mild or severe diabetes in a time- and expression-dependent manner. By contrast, deletion of the miR-503 cluster protects mice from high-fat diet-induced insulin resistance and glucose intolerance. Mechanistically, miR-503-5p represses c-Jun N-terminal kinase-interacting protein 2 (JIP2) translation to activate mitogen-activated protein kinase signaling cascades, thus inhibiting glucose-stimulated insulin secretion (GSIS) and compensatory ß-cell proliferation. In addition, ß-cell miR-503-5p is packaged in nanovesicles to dampen insulin signaling transduction in liver and adipose tissues by targeting insulin receptors. Notably, specifically blocking the miR-503 cluster in ß-cells effectively remits aging-associated diabetes through recovery of GSIS capacity and insulin sensitivity. Our findings demonstrate that ß-cell miR-503-5p is required for the development of insulin resistance and ß-cell decompensation, providing a potential therapeutic target against diabetes. ARTICLE HIGHLIGHTS: Promoter hypomethylation during natural aging permits miR-503-5p overexpression in islets under inflammation conditions, conserving from rodents to humans. Impaired ß-cells release nanovesicular miR-503-5p to accumulate in liver and adipose tissue, leading to their insulin resistance via the miR-503-5p/insulin receptor/phosphorylated AKT axis. Accumulated miR-503-5p in ß-cells impairs glucose-stimulated insulin secretion via the JIP2-coordinated mitogen-activated protein kinase signaling cascades. Specific blockage of ß-cell miR-503-5p improves ß-cell function and glucose tolerance in aging mice.

Genetic lineage tracing identifies adaptive mechanisms of pancreatic islet ß cells in various mouse models of diabetes with distinct age of initiation.

During the pathogenesis of type 1 diabetes (T1D) and type 2 diabetes (T2D), pancreatic islets, especially the ß cells, face significant challenges. These insulin-producing cells adopt a regeneration strategy to compensate for the shortage of insulin, but the exact mechanism needs to be defined. High-fat diet (HFD) and streptozotocin (STZ) treatment are well-established models to study islet damage in T2D and T1D respectively. Therefore, we applied these two diabetic mouse models, triggered at different ages, to pursue the cell fate transition of islet ß cells. Cre-LoxP systems were used to generate islet cell type-specific (α, ß, or δ) green fluorescent protein (GFP)-labeled mice for genetic lineage tracing, thereinto ß-cell GFP-labeled mice were tamoxifen induced. Single-cell RNA sequencing (scRNA-seq) was used to investigate the evolutionary trajectories and molecular mechanisms of the GFP-labeled ß cells in STZ-treated mice. STZ-induced diabetes caused extensive dedifferentiation of ß cells and some of which transdifferentiated into a or δ cells in both youth- and adulthood-initiated mice while this phenomenon was barely observed in HFD models. ß cells in HFD mice were expanded via self-replication rather than via transdifferentiation from α or δ cells, in contrast, α or δ cells were induced to transdifferentiate into ß cells in STZ-treated mice (both youth- and adulthood-initiated). In addition to the re-dedifferentiation of ß cells, it is also highly likely that these "α or δ" cells transdifferentiated from pre-existing ß cells could also re-trans-differentiate into insulin-producing ß cells and be beneficial to islet recovery. The analysis of ScRNA-seq revealed that several pathways including mitochondrial function, chromatin modification, and remodeling are crucial in the dynamic transition of ß cells. Our findings shed light on how islet ß cells overcome the deficit of insulin and the molecular mechanism of islet recovery in T1D and T2D pathogenesis.

Restored UBE2C expression in islets promotes ß-cell regeneration in mice by ubiquitinating PER1.

Insulin deficiency may be due to the reduced proliferation capacity of islet ß-cell, contributing to the onset of diabetes. It is therefore imperative to investigate the mechanism of the ß-cell regeneration in the islets. NKX6.1, one of the critical ß-cell transcription factors, is a pivotal element in ß-cell proliferation. The ubiquitin-binding enzyme 2C (UBE2C) was previously reported as one of the downstream molecules of NKX6.1 though the exact function and mechanism of UBE2C in ß-cell remain to be elucidated. Here, we determined a subpopulation of islet ß-cells highly expressing UBE2C, which proliferate actively. We also discovered that ß-cell compensatory proliferation was induced by UBE2C via the cell cycle renewal pathway in weaning and high-fat diet (HFD)-fed mice. Moreover, the reduction of ß-cell proliferation led to insulin deficiency in ßUbe2cKO mice and, therefore, developed type 2 diabetes. UBE2C was found to regulate PER1 degradation through the ubiquitin-proteasome pathway via its association with a ubiquitin ligase, CUL1. PER1 inhibition rescues UBE2C knockout-induced ß-cell growth inhibition both in vivo and in vitro. Notably, overexpression of UBE2C via lentiviral transduction in pancreatic islets was able to relaunch ß-cell proliferation in STZ-induced diabetic mice and therefore partially alleviated hyperglycaemia and glucose intolerance. This study indicates that UBE2C positively regulates ß-cell proliferation by promoting ubiquitination and degradation of the biological clock suppressor PER1. The beneficial effect of UBE2C on islet ß-cell regeneration suggests a promising application in treating diabetic patients with ß-cell deficiency.

BRSK2 in pancreatic ß cells promotes hyperinsulinemia-coupled insulin resistance and its genetic variants are associated with human type 2 diabetes.

Brain-specific serine/threonine-protein kinase 2 (BRSK2) plays critical roles in insulin secretion and ß-cell biology. However, whether BRSK2 is associated with human type 2 diabetes mellitus (T2DM) has not been determined. Here, we report that BRSK2 genetic variants are closely related to worsening glucose metabolism due to hyperinsulinemia and insulin resistance in the Chinese population. BRSK2 protein levels are significantly elevated in ß cells from T2DM patients and high-fat diet (HFD)-fed mice due to enhanced protein stability. Mice with inducible ß-cell-specific Brsk2 knockout (ßKO) exhibit normal metabolism with a high potential for insulin secretion under chow-diet conditions. Moreover, ßKO mice are protected from HFD-induced hyperinsulinemia, obesity, insulin resistance, and glucose intolerance. Conversely, gain-of-function BRSK2 in mature ß cells reversibly triggers hyperglycemia due to ß-cell hypersecretion-coupled insulin resistance. Mechanistically, BRSK2 senses lipid signals and induces basal insulin secretion in a kinase-dependent manner. The enhanced basal insulin secretion drives insulin resistance and ß-cell exhaustion and thus the onset of T2DM in mice fed an HFD or with gain-of-function BRSK2 in ß cells. These findings reveal that BRSK2 links hyperinsulinemia to systematic insulin resistance via interplay between ß cells and insulin-sensitive tissues in the populations carrying human genetic variants or under nutrient-overload conditions.

Single-cell RNA sequencing combined with single-cell proteomics identifies the metabolic adaptation of islet cell subpopulations to high-fat diet in mice.

AIMS/HYPOTHESIS: Islets have complex heterogeneity and subpopulations. Cell surface markers representing alpha, beta and delta cell subpopulations are urgently needed for investigations to explore the compositional changes of each subpopulation in obesity progress and diabetes onset, and the adaptation mechanism of islet metabolism induced by a high-fat diet (HFD). METHODS: Single-cell RNA sequencing (scRNA-seq) was applied to identify alpha, beta and delta cell subpopulation markers in an HFD-induced mouse model of glucose intolerance. Flow cytometry and immunostaining were used to sort and assess the proportion of each subpopulation. Single-cell proteomics was performed on sorted cells, and the functional status of each alpha, beta and delta cell subpopulation in glucose intolerance was deeply elucidated based on protein expression. RESULTS: A total of 33,999 cells were analysed by scRNA-seq and clustered into eight populations, including alpha, beta and delta cells. For alpha cells, scRNA-seq revealed that the Ace2low subpopulation had downregulated expression of genes related to alpha cell function and upregulated expression of genes associated with beta cell characteristics in comparison with the Ace2high subpopulation. The impaired function and increased fragility of ACE2low alpha cells exposure to HFD was further suggested by single-cell proteomics. As for beta cells, the CD81high subpopulation may indicate an immature signature of beta cells compared with the CD81low subpopulation, which had robust function. We also found differential expression of Slc2a2 in delta cells and a potentially stronger cellular function and metabolism in GLUT2low delta cells than GLUT2high delta cells. Moreover, an increased proportion of ACE2low alpha cells and CD81low beta cells, with a constant proportion of GLUT2low delta cells, were observed in HFD-induced glucose intolerance. CONCLUSIONS/INTERPRETATION: We identified ACE2, CD81 and GLUT2 as surface markers to distinguish, respectively, alpha, beta and delta cell subpopulations with heterogeneous maturation and function. The changes in the proportion and functional status of islet endocrine subpopulations reflect the metabolic adaptation of islets to high-fat stress, which weakened the function of alpha cells and enhanced the function of beta and delta cells to bring about glycaemic homeostasis. Our findings provide a fundamental resource for exploring the mechanisms maintaining each islet endocrine subpopulation's fate and function in health and disease. DATA AVAILABILITY: The scRNA-seq analysis datasets from the current study are available in the Gene Expression Omnibus (GEO) repository under the accession number GSE203376.

Rab31, a receptor of advanced glycation end products (RAGE) interacting protein, inhibits AGE induced pancreatic ß-cell apoptosis through the pAKT/BCL2 pathway.

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.

Protocol for in vivo and ex vivo assessments of glucose-stimulated insulin secretion in mouse islet ß cells.

Pancreatic islet ß cells secrete insulin in a biphasic manner when sensing high blood glucose level. This protocol describes the evaluation of different phases of insulin secretion, as well as basal, glucose-stimulated and total insulin secretion abilities, thereby enabling precise assessment of ß cell function both in vivo and ex vivo. The in vivo assay consists of intravenous tube imbedding surgery and hyperglycemic clamp. The ex vivo assay consists of islet isolation, dynamic perfusion and static immersion. For complete details on the use and execution of this protocol, please refer to Sun et al. (2021).

Expression of miRNA-29 in Pancreatic ß Cells Promotes Inflammation and Diabetes via TRAF3.

Type 2 diabetes mellitus (T2DM) is recognized as a chronic, low-grade inflammatory disease characterized by insulin resistance and pancreatic ß cell dysfunction; however, the underlying molecular mechanism remains unclear. Here, we report a key ß cell-macrophage crosstalk pathway mediated by the miRNA-29-TNF-receptor-associated factor 3 (TRAF3) axis. ß cell-specific transgenic miR-29a/b/c mice are predisposed to develop glucose intolerance and insulin resistance when fed a high-fat diet (HFD). The metabolic effect of ß cell miR-29 is largely mediated through macrophages because either depletion of macrophages or reconstitution with miR-29-signaling defective bone marrow improves metabolic parameters in the transgenic mice. Mechanistically, our data show that miR-29 promotes the recruitment and activation of circulating monocytes and macrophages and, hence, inflammation, via miR-29 exosomes in a TRAF3-dependent manner. Our results demonstrate the ability of ß cells to modulate the systemic inflammatory tone and glucose homeostasis via miR-29 in response to nutrient overload.

Inhibition of miR-153, an IL-1ß-responsive miRNA, prevents beta cell failure and inflammation-associated diabetes.

OBJECTIVE: Systemic levels of up-regulated IL-1ß and IL-1 receptors promote the pathogenesis of inflammation-associated diabetes. IL-1 receptor antagonist (IL-Ra) has shown slightly elevated beta cell function in patients with type 2 diabetes without significant improvement of hyperglycaemia. We investigated whether miR-153, an IL-1ß responsive miRNA, could mimic IL-1ß effects and whether its interruption would improve blood glucose control then offer an assistant curative approach to inflammation-associated diabetes. MATERIALS/METHODS: Antago-miR-153 and Ago-miR-153 were injected into the abdominal aorta of leptin receptor-mutant db/db mice and C57BL/6 J mice, respectively. Blood glucose levels, glucose tolerance tests, insulin tolerance tests and insulin levels were regularly checked. Proteomic profiling combined with unbiased bioinformatics analysis, as well as experimental techniques, were utilized to identify target genes of miR-153. Anti-miR-153 and plasmid-based recovery assays were also performed using primary mouse islets and beta cell lines. RESULTS: The miR-153 expression level was increased in IL-1ß-treated beta cells and primary islets from the diabetic rodents. Pancreas overexpression of miR-153 caused glucose intolerance in C57BL/6 J mice but no alterations in body weight or insulin sensitivity. The inhibition of miR-153 temporarily reduced hyperglycaemia of db/db mice due to enhanced insulin secretion. Antago-miR-153 treatment ameliorated glucose intolerance in db/db mice during our observation period but did not improve insulin sensitivity. Mechanistically, miR-153 targeted three members of SNAREs to disturb insulin granule docking, thereby decreasing basal insulin secretion. Overexpression of anti-miR-153 or SNARE rescued the IL-1ß-induced basal insulin secretion defect. Furthermore, miR-153 targeted beta cell-specific transcriptional factors and survival molecules to inhibit insulin biosynthesis and cell viability. CONCLUSIONS: The IL-1ß-responsive miR-153 targets SNAREs, beta cell specific TFs and other key factors to eventually causes beta cell failure. Inhibiting miR-153 with Antago-miR-153 prevents hyperglycaemia in db/db mice, indicating that miR-153 may be a promising therapeutic target for the treatment of inflammation-associated diabetes.

Ets1-Mediated Acetylation of FoxO1 Is Critical for Gluconeogenesis Regulation during Feed-Fast Cycles.

The homeostatic balance of hepatic glucose uptake and production is exquisitely controlled by hormonal signals during feed-fast cycles. FoxO1, a transcription factor that functions in the regulation of glucose homeostasis, undergoes posttranslational modifications, such as acetylation, in response to hormonal signals, yet the mechanism remains poorly elucidated. Through expression profiling of 324 co-factors of CBP, a well-known acetyl-transferase of FoxO1, we identify Ets1 as a modulator of FoxO1 acetylation that is highly associated with feed-fast cycles. Mechanistic assays suggest that Ets1 enhances FoxO1 acetylation through the formation of a complex with CBP, which further promotes FoxO1 nuclear exclusion and inhibits its binding to gluconeogenic promoters. Functional studies further reveal that Ets1 inhibits gluconeogenesis under physiological and diabetes statuses, while the hyperinsulinemic-euglycemic clamp assay suggests hepatocyte Ets1 knockout mice have enhanced hepatic glucose production. Our study identifies Ets1 as an enhancer of FoxO1 acetylation and a repressor of hepatic gluconeogenesis in response to hormonal signals.

MicroRNA-24 promotes pancreatic beta cells toward dedifferentiation to avoid endoplasmic reticulum stress-induced apoptosis.

Current research indicates that beta cell loss in type 2 diabetes may be attributed to beta cell dedifferentiation rather than apoptosis; however, the mechanisms by which this occurs remain poorly understood. Our previous study demonstrated that elevation of microRNA-24 (miR-24) in a diabetic setting caused beta cell dysfunction and replicative deficiency. In this study, we focused on the role of miR-24 in beta cell apoptosis and dedifferentiation under endoplasmic reticulum (ER) stress conditions. We found that miR-24 overabundance protected beta cells from thapsigargin-induced apoptosis at the cost of accelerating the impairment of glucose-stimulated insulin secretion (GSIS) and enhancing the presence of dedifferentiation markers. Ingenuity® Pathway Analysis (IPA) revealed that elevation of miR-24 had an inhibitory effect on XBP1 and ATF4, which are downstream effectors of two key branches of ER stress, by inhibiting its direct target, Ire1α. Notably, elevated miR-24 initiated another pathway that targeted Mafa and decreased GSIS function in surviving beta cells, thus guiding their dedifferentiation under ER stress conditions. Our results demonstrated that the elevated miR-24, to the utmost extent, preserves beta cell mass by inhibiting apoptosis and inducing dedifferentiation. This study not only provides a novel mechanism by which miR-24 dominates beta cell turnover under persistent metabolic stress but also offers a therapeutic consideration for treating diabetes by inducing dedifferentiated beta cells to re-differentiation.

Hepatic c-Jun regulates glucose metabolism via FGF21 and modulates body temperature through the neural signals.

OBJECTIVE: c-Jun, a prominent member of the activator protein 1 (AP-1) family, is involved in various physiology processes such as cell death and survival. However, a role of hepatic c-Jun in the whole-body metabolism is poorly understood. METHODS: We generated liver-specific c-Jun knock-out (c-jun△li) mice to investigate the effect of hepatic c-Jun on the whole-body physiology, particularly in blood glucose and body temperature. Primary hepatocytes were also used to explore a direct regulation of c-Jun in gluconeogenesis. RESULTS: c-jun△li mice showed higher hepatic gluconeogenic capacity compared with control mice, and similar results were obtained in vitro. In addition, fibroblast growth factor 21 (FGF21) expression was directly inhibited by c-Jun knockdown and adenovirus-mediated hepatic FGF21 over-expression blocked the effect of c-Jun on gluconeogenesis in c-jun△li mice. Interestingly, c-jun△li mice also exhibited higher body temperature, with induced thermogenesis and uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT). Furthermore, the body temperature became comparable between c-jun△li and control mice at thermoneutral temperature (30 °C). Moreover, the activity of sympathetic nervous system (SNS) was increased in c-jun△li mice and the higher body temperature was inhibited by beta-adrenergic receptor blocker injection. Finally, the activated SNS and increased body temperature in c-jun△li mice was most likely caused by the signals from the brain and hepatic vagus nerve, as the expression of c-Fos (the molecular marker of neuronal activation) was changed in several brain areas controlling body temperature and body temperature was decreased by selective hepatic vagotomy. CONCLUSIONS: These data demonstrate a novel function of hepatic c-Jun in the regulation of gluconeogenesis and body temperature via FGF21 and neural signals. Our results also provide novel insights into the organ crosstalk in the regulation of the whole-body physiology.

Glucolipotoxicity-Inhibited miR-299-5p Regulates Pancreatic ß-Cell Function and Survival.

Inhibition of microRNAs (miRNAs) essential for pancreatic ß-cell biology (e.g., miR-375) results in ß-cell failure and diabetes in rodent models. Whether the downregulation of miRNAs in pancreatic islets is involved in the development of human type 2 diabetes remains unclear. Here, with the use of an miRNA microarray, we identified a set of miRNAs that were differentially expressed in healthy human islets under glucolipotoxic conditions. A downregulated miRNA, miR-299-5p, was preferentially studied because its inhibition causes dramatic ß-cell dysfunction and apoptosis. Proteomic profiling and bioinformatics methods identified four target genes, including a Trp53 effector, Perp, that were further confirmed by luciferase reporter assays. We narrowed down the effector of miR-299-5p downregulation to PERP owing to its upregulation in islets from diabetic rodents. Indeed, Perp inhibition prevented the ß-cell impairment caused by either miR-299-5p reduction or glucolipotoxicity. Additional investigations confirmed the modulatory effect of PERP on insulin secretion. Collectively, miR-299-5p appears to be an essential regulator of ß-cell biology, and its downregulation links PERP enhancement to ß-cell dysfunction and apoptosis in glucolipotoxic settings. Our work demonstrates a novel mechanism of glucolipotoxicity-induced ß-cell failure mediated through miR-299-5p downregulation.

A Presenilin/Notch1 pathway regulated by miR-375, miR-30a, and miR-34a mediates glucotoxicity induced-pancreatic beta cell apoptosis.

The presenilin-mediated Notch1 cleavage pathway plays a critical role in controlling pancreatic beta cell fate and survival. The aim of the present study was to investigate the role of Notch1 activation in glucotoxicity-induced beta cell impairment and the contributions of miR-375, miR-30a, and miR-34a to this pathway. We found that the protein levels of presenilins (PSEN1 and PSEN2), and NOTCH1 were decreased in INS-1 cells after treatment with increased concentrations of glucose, whereas no significant alteration of mRNA level of Notch1 was observed. Targeting of miR-375, miR-30a, and miR-34a to the 3'utr of Psen1, Psen2, and Notch1, respectively, reduced the amounts of relevant proteins, thereby reducing NICD1 amounts and causing beta cell apoptosis. Overexpression of NICD1 blocked the effects of glucotoxicity as well as miRNA overabundance. Downregulating the expression of miR-375, miR-30a, and miR-34a restored PSEN1, PSEN2, and NICD1 production and prevented glucotoxicity-induced impairment of the beta cells. These patterns of miRNA regulation of the Notch1 cleavage pathway were reproduced in GK rats as well as in aged rats. Our findings demonstrated that miRNA-mediated suppression of NICD1 links the presenilin/Notch1 pathway to glucotoxicity in mature pancreatic beta cells.