Verapamil Prevents Decline of IGF-I in Subjects With Type 1 Diabetes and Promotes ß-Cell IGF-I Signaling.

Verapamil promotes functional ß-cell mass and improves glucose homeostasis in diabetic mice and humans with type 1 diabetes (T1D). Now, our global proteomics analysis of serum from subjects with T1D at baseline and after 1 year of receiving verapamil or placebo revealed IGF-I as a protein with significantly changed abundance over time. IGF-I, which promotes ß-cell survival and insulin secretion, decreased during disease progression, and this decline was blunted by verapamil. In addition, we found that verapamil reduces ß-cell expression of IGF-binding protein 3 (IGFBP3), whereas IGFBP3 was increased in human islets exposed to T1D-associated cytokines and in diabetic NOD mouse islets. IGFBP3 binds IGF-I and blocks its downstream signaling, which has been associated with increased ß-cell apoptosis and impaired glucose homeostasis. Consistent with the downregulation of IGFBP3, we have now discovered that verapamil increases ß-cell IGF-I signaling and phosphorylation/activation of the IGF-I receptor (IGF1R). Moreover, we found that thioredoxin-interacting protein (TXNIP), a proapoptotic factor downregulated by verapamil, promotes IGFBP3 expression and inhibits the phosphorylation/activation of IGF1R. Thus, our results reveal IGF-I signaling as yet another previously unappreciated pathway affected by verapamil and TXNIP that may contribute to the beneficial verapamil effects in the context of T1D. ARTICLE HIGHLIGHTS: Verapamil prevents the decline of IGF-I in subjects with type 1 diabetes (T1D). Verapamil decreases the expression of ß-cell IGF-binding protein 3 (IGFBP3), whereas IGFBP3 is increased in human and mouse islets under T1D conditions. Verapamil promotes ß-cell IGF-I signaling by increasing phosphorylation of IGF-I receptor and its downstream effector AKT. Thioredoxin-interacting protein (TXNIP) increases IGFBP3 expression and inhibits the phosphorylation/activation of IGF1R in ß-cells. Regulation of IGFBP3 and IGF-I signaling by verapamil and TXNIP may contribute to the beneficial verapamil effects in the context of T1D.

Expanding bifactor models of psychological traits to account for multiple sources of measurement error.

Over the last decade, applications of bifactor modeling within clinical settings have increased markedly but typically rely on data collected on single occasions. A shortcoming of such research is that reliability coefficients are likely inflated because key sources of measurement error are inadequately modeled and/or confounded with construct variance. We address these problems using three variations of multi-occasion bifactor models with Bayesian-derived parameter estimates to separate systematic variance into general and group factor effects and measurement error into three subcomponents (transient, specific-factor, and random-response). Collectively, these models produce indices of reliability and validity aligned with both standard confirmatory factor models and generalizability designs that extend interpretations of results to the broader domains from which items and occasions are sampled. We demonstrate how these techniques can provide new insights into psychometric properties of scores using Negative Emotionality domain and facet scales from the newly updated Big Five Inventory (BFI-2; Soto & John, 2017). Overall, the two-occasion congeneric bifactor model provided the best fit to the data and most informative indices for revising measures, examining dimensionality of composite and subscale scores, and evaluating the viability of those scores. We include code in R for analyzing all models in our extended online Supplemental Material. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Alpha Cell Thioredoxin-interacting Protein Deletion Improves Diabetes-associated Hyperglycemia and Hyperglucagonemia.

Thioredoxin-interacting protein (TXNIP) has emerged as a key factor in pancreatic beta cell biology, and its upregulation by glucose and diabetes contributes to the impairment in functional beta cell mass and glucose homeostasis. In addition, beta cell deletion of TXNIP protects against diabetes in different mouse models. However, while TXNIP is ubiquitously expressed, its role in pancreatic alpha cells has remained elusive. We generated an alpha cell TXNIP knockout (aTKO) mouse and assessed the effects on glucose homeostasis. While no significant changes were observed on regular chow, after a 30-week high-fat diet, aTKO animals showed improvement in glucose tolerance and lower blood glucose levels compared to their control littermates. Moreover, in the context of streptozotocin (STZ)-induced diabetes, aTKO mice showed significantly lower blood glucose levels compared to controls. While serum insulin levels were reduced in both control and aTKO mice, STZ-induced diabetes significantly increased glucagon levels in control mice, but this effect was blunted in aTKO mice. Moreover, glucagon secretion from aTKO islets was >2-fold lower than from control islets, while insulin secretion was unchanged in aTKO islets. At the same time, no change in alpha cell or beta cell numbers or mass was observed, and glucagon and insulin expression and content were comparable in isolated islets from aTKO and control mice. Thus together the current studies suggest that downregulation of alpha cell TXNIP is associated with reduced glucagon secretion and that this may contribute to the glucose-lowering effects observed in diabetic aTKO mice.

Exploratory study reveals far reaching systemic and cellular effects of verapamil treatment in subjects with type 1 diabetes.

Currently, no oral medications are available for type 1 diabetes (T1D). While our recent randomized placebo-controlled T1D trial revealed that oral verapamil had short-term beneficial effects, their duration and underlying mechanisms remained elusive. Now, our global T1D serum proteomics analysis identified chromogranin A (CHGA), a T1D-autoantigen, as the top protein altered by verapamil and as a potential therapeutic marker and revealed that verapamil normalizes serum CHGA levels and reverses T1D-induced elevations in circulating proinflammatory T-follicular-helper cell markers. RNA-sequencing further confirmed that verapamil regulates the thioredoxin system and promotes an anti-oxidative, anti-apoptotic and immunomodulatory gene expression profile in human islets. Moreover, continuous use of oral verapamil delayed T1D progression, promoted endogenous beta-cell function and lowered insulin requirements and serum CHGA levels for at least 2 years and these benefits were lost upon discontinuation. Thus, the current studies provide crucial mechanistic and clinical insight into the beneficial effects of verapamil in T1D.

Deletion of Gdf15 Reduces ER Stress-induced Beta-cell Apoptosis and Diabetes.

Endoplasmic reticulum (ER) stress contributes to pancreatic beta-cell apoptosis in diabetes, but the factors involved are still not fully elucidated. Growth differentiation factor 15 (GDF15) is a stress response gene and has been reported to be increased and play an important role in various diseases. However, the role of GDF15 in beta cells in the context of ER stress and diabetes is still unclear. In this study, we have discovered that GDF15 promotes ER stress-induced beta-cell apoptosis and that downregulation of GDF15 has beneficial effects on beta-cell survival in diabetes. Specifically, we found that GDF15 is induced by ER stress in beta cells and human islets, and that the transcription factor C/EBPß is involved in this process. Interestingly, ER stress-induced apoptosis was significantly reduced in INS-1 cells with Gdf15 knockdown and in isolated Gdf15 knockout mouse islets. In vivo, we found that Gdf15 deletion attenuates streptozotocin-induced diabetes by preserving beta cells and insulin levels. Moreover, deletion of Gdf15 significantly delayed diabetes development in spontaneous ER stress-prone Akita mice. Thus, our findings suggest that GDF15 contributes to ER stress-induced beta-cell apoptosis and that inhibition of GDF15 may represent a novel strategy to promote beta-cell survival and treat diabetes.

Using Parallel Splits with Self-Report and Other Measures to Enhance Precision in Generalizability Theory Analyses.

Although generalizability theory (G-theory) provides indices of reliability that take multiple sources of measurement error into account, those indices are typically conservative in nature because they reflect random rather than classical parallelism. One way to address these shortcomings is to use parallel splits rather than items as the unit of analysis in G-theory designs. In this article, we provide the most extensive treatment to date in how to effectively integrate parallel splits into an extended set of G-theory designs using data from the newly developed version of the Big Five Inventory (BFI-2; Soto & John). Results revealed that properly designed splits approximated classical parallelism while improving overall score consistency and reducing key components of measurement error. Variance components within appropriately chosen G-theory designs also provided effective means to evaluate the quality of splits and determine the best ways to improve score consistency and reduce specific sources of measurement error. To help readers in applying these techniques, we provide a comprehensive instructional supplement with code in R for creating parallel splits, analyzing all illustrated designs, and modifying those designs for other objectively or subjectively scored measures.

Interrelationships between latent state-trait theory and generalizability theory within a structural equation modeling framework.

Over recent years, latent state-trait theory (LST) and generalizability theory (GT) have been applied to a wide variety of situations in numerous disciplines to enhance understanding of the reliability and validity of assessment data. Both methodologies involve partitioning of observed score variation into systematic and measurement error components. LST theory is focused on separating state, trait, error, and sometimes method effects, whereas generalizability theory is concerned with distinguishing universe score effects from multiple sources of measurement error. Despite these fundamental differences in focus, LST and GT share much in common. In this article, we use data from a widely used personality measure to illustrate similarities and differences between these two frameworks and show how the same data can be readily interpreted from both perspectives. We also provide comprehensive instructional online supplemental materials to demonstrate how to analyze data using the R package for all LST models and GT designs discussed. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Human Glucagon Expression Is under the Control of miR-320a.

Increased glucagon is a hallmark of diabetes and leads to worsening of the hyperglycemia, but the molecular mechanisms causing it are still unknown. We therefore investigated the possibility that microRNAs might be involved in the regulation of glucagon. Indeed, analysis of the glucagon 3' untranslated region (UTR) revealed potential binding sites for miR-320a, and using luciferase reporter assays we found that miR-320a directly targets the 3' UTRs of human and rodent glucagon. In addition, endogenous glucagon mRNA and protein expression as well as glucagon secretion were reduced in response to miR-320a overexpression, whereas inhibition of miR-320a upregulated glucagon expression. Interestingly, miR-320a expression was decreased by high glucose, and this was associated with an increase in glucagon expression in human islets and mouse αTC1-6 cells. Moreover, miR-320a overexpression completely blunted these effects. Importantly, miR-320a was also significantly downregulated in human islets of subjects with type 2 diabetes and this was accompanied by increased glucagon expression. Thus, our data suggest that glucose-induced downregulation of miR-320a may contribute to the paradoxical increase in glucagon observed in type 2 diabetes and reveal for the first time that glucagon expression is under the control by a microRNA providing novel insight into the abnormal regulation of glucagon in diabetes.

Expanding G-Theory Models to Incorporate Congeneric Relationships: Illustrations Using the Big Five Inventory.

We used structural equation modeling techniques to expand traditional generalizability theory (G-theory) models to allow for congeneric relationships among item responses while accounting for the primary sources of measurement error that affect results from objectively scored, self-report measures. Data came from 919 respondents who completed the Agreeableness, Conscientiousness, Extraversion, Neuroticism, and Openness subscales of the Big Five Inventory (BFI; John et al., 1991) on two occasions. When compared to traditional and factor-based essential tau-equivalent G-theory models, congeneric models on average yielded superior fit statistics, higher estimates of reliability, and lower estimates of transient and specific-factor measurement error. Essential tau-equivalent and congeneric factor models also were configured to allow for simultaneous partitioning of systematic and measurement error variance at both total score and individual item levels. We provide detailed guidelines, examples, and computer code in R for all models discussed in an extended online supplement to enable readers to apply the demonstrated techniques.

Identification of an Anti-diabetic, Orally Available Small Molecule that Regulates TXNIP Expression and Glucagon Action.

Diabetes is characterized by hyperglycemia, loss of functional islet beta cell mass, deficiency of glucose-lowering insulin, and persistent alpha cell secretion of gluconeogenic glucagon. Still, no therapies that target these underlying processes are available. We therefore performed high-throughput screening of 300,000 compounds and extensive medicinal chemistry optimization and here report the discovery of SRI-37330, an orally bioavailable, non-toxic small molecule, which effectively rescued mice from streptozotocin- and obesity-induced (db/db) diabetes. Interestingly, in rat cells and in mouse and human islets, SRI-37330 inhibited expression and signaling of thioredoxin-interacting protein, which we have previously found to be elevated in diabetes and to have detrimental effects on islet function. In addition, SRI-37330 treatment inhibited glucagon secretion and function, reduced hepatic glucose production, and reversed hepatic steatosis. Thus, these studies describe a newly designed chemical compound that, compared to currently available therapies, may provide a distinct and effective approach to treating diabetes.

Serum miR-204 is an early biomarker of type 1 diabetes-associated pancreatic beta-cell loss.

Pancreatic beta-cell death is a major factor in the pathogenesis of type 1 diabetes (T1D), but straightforward methods to measure beta-cell loss in humans are lacking, underlining the need for novel biomarkers. Using studies in INS-1 cells, human islets, diabetic mice, and serum samples of subjects with T1D at different stages, we have identified serum miR-204 as an early biomarker of T1D-associated beta-cell loss in humans. MiR-204 is a highly enriched microRNA in human beta-cells, and we found that it is released from dying beta-cells and detectable in human serum. We further discovered that serum miR-204 was elevated in children and adults with T1D and in autoantibody-positive at-risk subjects but not in type 2 diabetes or other autoimmune diseases and was inversely correlated with remaining beta-cell function in recent-onset T1D. Thus, serum miR-204 may provide a much needed novel approach to assess early T1D-associated human beta-cell loss even before onset of overt disease.

Verapamil and beta cell function in adults with recent-onset type 1 diabetes.

Pancreatic beta cell loss is a key factor in the pathogenesis of type 1 diabetes (T1D), but therapies to halt this process are lacking. We previously reported that the approved antihypertensive calcium-channel blocker verapamil, by decreasing the expression of thioredoxin-interacting protein, promotes the survival of insulin-producing beta cells and reverses diabetes in mouse models1. To translate these findings into humans, we conducted a randomized double-blind placebo-controlled phase 2 clinical trial ( NCT02372253 ) to assess the efficacy and safety of oral verapamil added for 12 months to a standard insulin regimen in adult subjects with recent-onset T1D. Verapamil treatment, compared with placebo was well tolerated and associated with an improved mixed-meal-stimulated C-peptide area under the curve, a measure of endogenous beta cell function, at 3 and 12 months (prespecified primary endpoint), as well as with a lower increase in insulin requirements, fewer hypoglycemic events and on-target glycemic control (secondary endpoints). Thus, addition of once-daily oral verapamil may be a safe and effective novel approach to promote endogenous beta cell function and reduce insulin requirements and hypoglycemic episodes in adult individuals with recent-onset T1D.

miR-204 Controls Glucagon-Like Peptide 1 Receptor Expression and Agonist Function.

Glucagon-like peptide 1 receptor (GLP1R) agonists are widely used to treat diabetes. However, their function is dependent on adequate GLP1R expression, which is downregulated in diabetes. GLP1R is highly expressed on pancreatic ß-cells, and activation by endogenous incretin or GLP1R agonists increases cAMP generation, which stimulates glucose-induced ß-cell insulin secretion and helps maintain glucose homeostasis. We now have discovered that the highly ß-cell-enriched microRNA, miR-204, directly targets the 3' UTR of GLP1R and thereby downregulates its expression in the ß-cell-derived rat INS-1 cell line and primary mouse and human islets. Furthermore, in vivo deletion of miR-204 promoted islet GLP1R expression and enhanced responsiveness to GLP1R agonists, resulting in improved glucose tolerance, cAMP production, and insulin secretion as well as protection against diabetes. Since we recently identified thioredoxin-interacting protein (TXNIP) as an upstream regulator of miR-204, we also assessed whether in vivo deletion of TXNIP could mimic that of miR-204. Indeed, it also enhanced islet GLP1R expression and GLP1R agonist-induced insulin secretion and glucose tolerance. Thus, the present studies show for the first time that GLP1R is under the control of a microRNA, miR-204, and uncover a previously unappreciated link between TXNIP and incretin action.

Islet ChREBP-ß is increased in diabetes and controls ChREBP-α and glucose-induced gene expression via a negative feedback loop.

OBJECTIVE: Carbohydrate-response element-binding protein (ChREBP) is the major transcription factor conferring glucose-induced gene expression in pancreatic islets, liver and adipose tissue. Recently, a novel ChREBP isoform, ChREBP-ß, was identified in adipose tissue and found to be also expressed in islets and involved in glucose-induced beta cell proliferation. However, the physiological function of this less abundant ß-isoform in the islet, and in diabetes, is largely unknown. The aims of the present study, therefore, were to determine how diabetes affects ChREBP-ß and elucidate its physiological role in pancreatic beta cells. METHODS: Non-obese diabetic and obese, diabetic ob/ob mice were used as models of T1D and T2D and human islets and the rat INS-1 beta cell line were exposed to low/high glucose and used for ChREBP isoform-specific gain-and-loss-of-function experiments. Changes in ChREBP-ß and ChREBP-α were assessed by qRT-PCR, immunoblotting, promoter luciferase, and chromatin immunoprecipitation studies. RESULTS: Expression of the ChREBP-ß isoform was highly induced in diabetes and by glucose, whereas ChREBP-α was downregulated. Interestingly, ChREBP-ß gain-of-function experiments further revealed that it was ChREBP-ß that downregulated ChREBP-α through a negative feedback loop. On the other hand, ChREBP-ß knockdown led to unabated ChREBP-α activity and glucose-induced expression of target genes, suggesting that one of the physiological roles of this novel ß-isoform is to help keep glucose-induced and ChREBP-α-mediated gene expression under control. CONCLUSIONS: We have identified a previously unappreciated negative feedback loop by which glucose-induced ChREBP-ß downregulates ChREBP-α-signaling providing new insight into the physiological role of islet ChREBP-ß and into the regulation of glucose-induced gene expression.

miR-204 Targets PERK and Regulates UPR Signaling and ß-Cell Apoptosis.

Endoplasmic reticulum (ER) stress plays an important role in the pathogenesis of diabetes and the associated ß-cell apoptosis. Although microRNAs (miRNAs) have been widely studied in various diseases including diabetes, the role of miRNAs in ER stress and ß-cell apoptosis has only started to be elucidated. We recently showed that diabetes increases ß-cell miR-204 and have now discovered that miR-204 directly targets the 3'untranslated region of protein kinase R-like ER kinase (PERK), 1 of the 3 ER transmembrane sensors and a key factor of the unfolded protein response (UPR). In addition, by using primary human islets, mouse islets, and INS-1 ß-cells, we found that miR-204 decreased PERK expression as well as its downstream factors, activating transcription factor 4 and CCAAT enhancer-binding protein homologous protein, whereas it had no effect on the other 2 ER transmembrane sensors, activating transcription factor 6 and inositol-requiring enzyme-1α. Interestingly, we discovered that miR-204 also inhibited PERK signaling in the context of ER stress, and this exacerbated ER stress-induced ß-cell apoptosis. This effect could be mimicked by PERK inhibitors supporting the notion that the miR-204-mediated inhibition of PERK and UPR signaling was conferring these detrimental effects on cell survival. Taken together, we have identified PERK as a novel target of miR-204 and show that miR-204 inhibits PERK signaling and increases ER stress-induced cell death, revealing for the first time a link between this miRNA and UPR.

Cytokines Regulate ß-Cell Thioredoxin-interacting Protein (TXNIP) via Distinct Mechanisms and Pathways.

Thioredoxin-interacting protein (TXNIP) is a key regulator of diabetic ß-cell apoptosis and dysfunction, and TXNIP inhibition prevents diabetes in mouse models of type 1 and type 2 diabetes. Although we have previously shown that TXNIP is strongly induced by glucose, any regulation by the proinflammatory cytokines tumor necrosis factor α (TNFα), interleukin-1ß (IL-1ß), and interferon γ (IFNγ) has remained largely unexplored. Moreover, even though this three-cytokine mixture is widely used to mimic type 1 diabetes in vitro, the mechanisms involved are not fully understood. Interestingly, we have now found that this cytokine mixture increases ß-cell TXNIP expression; however, although TNFα had no effect, IL-1ß surprisingly down-regulated TXNIP transcription, whereas IFNγ increased TXNIP levels in INS-1 ß-cells and primary islets. Human TXNIP promoter analyses and chromatin immunoprecipitation studies revealed that the IL-1ß effect was mediated by inhibition of carbohydrate response element binding protein activity. In contrast, IFNγ increased pro-apoptotic TXNIP post-transcriptionally via induction of endoplasmic reticulum stress, activation of inositol-requiring enzyme 1α (IRE1α), and suppression of miR-17, a microRNA that targets and down-regulates TXNIP. In fact, miR-17 knockdown was able to mimic the IFNγ effects on TXNIP, whereas miR-17 overexpression blunted the cytokine effect. Thus, our results demonstrate for the first time that the proinflammatory cytokines TNFα, IL-1ß, and IFNγ each have distinct and in part opposing effects on ß-cell TXNIP expression. These findings thereby provide new mechanistic insight into the regulation of TXNIP and ß-cell biology and reveal novel links between proinflammatory cytokines, carbohydrate response element binding protein-mediated transcription, and microRNA signaling.

MicroRNA-200 is induced by thioredoxin-interacting protein and regulates Zeb1 protein signaling and beta cell apoptosis.

Small noncoding microRNAs have emerged as important regulators of cellular processes, but their role in pancreatic beta cells has only started to be elucidated. Loss of pancreatic beta cells is a key factor in the pathogenesis of diabetes, and we have demonstrated that beta cell expression of thioredoxin-interacting protein (TXNIP) is increased in diabetes and causes beta cell apoptosis, whereas TXNIP deficiency is protective against diabetes. Recently, we found that TXNIP also impairs beta cell function by inducing microRNA (miR)-204. Interestingly, using INS-1 beta cells and primary islets, we have now discovered that expression of another microRNA, miR-200, is induced by TXNIP and by diabetes. Furthermore, we found that miR-200 targeted and decreased Zeb1 (zinc finger E-box-binding homeobox 1) and promoted beta cell apoptosis as measured by cleaved caspase-3 levels, Bax/Bcl2 ratio, and TUNEL. In addition, Zeb1 knockdown mimicked the miR-200 effects on beta cell apoptosis, suggesting that Zeb1 plays an important role in mediating miR-200 effects. Moreover, miR-200 increased beta cell expression of the epithelial marker E-cadherin, consistent with inhibition of epithelial-mesenchymal transition, a process thought to be involved in beta cell expansion. Thus, we have identified a novel TXNIP/miR-200/Zeb1/E-cadherin signaling pathway that, for the first time, links miR-200 to beta cell apoptosis and diabetes and also beta cell TXNIP to epithelial-mesenchymal transition. In addition, our results shed new light on the regulation and function of miR-200 in beta cells and show that TXNIP-induced microRNAs control various processes of beta cell biology.

Thioredoxin-interacting protein stimulates its own expression via a positive feedback loop.

Thioredoxin-interacting protein (TXNIP) has emerged as a key regulator of important cellular processes including redox state, inflammation, and apoptosis and plays a particularly critical role in pancreatic ß-cell biology and diabetes development. High glucose and diabetes induce TXNIP expression, whereas inhibition of TXNIP expression or TXNIP deficiency protects against pancreatic ß-cell apoptosis and diabetes. We now have discovered that TXNIP stimulates its own expression by promoting dephosphorylation and nuclear translocation of its transcription factor, carbohydrate response element-binding protein (ChREBP), resulting in a positive feedback loop as well as regulation of other ChREBP target genes playing important roles in glucose and lipid metabolism. Considering the detrimental effects of elevated TXNIP in ß-cell biology, this novel pathway sheds new light onto the vicious cycle of increased TXNIP, leading to even more TXNIP expression, oxidative stress, inflammation, ß-cell apoptosis, and diabetes progression. Moreover, the results demonstrate, for the first time, that TXNIP modulates ChREBP activity and thereby uncover a previously unappreciated link between TXNIP signaling and cell metabolism.

Thioredoxin-interacting protein promotes islet amyloid polypeptide expression through miR-124a and FoxA2.

Thioredoxin-interacting protein (TXNIP) is up-regulated by glucose and diabetes and plays a critical role in glucotoxicity, inflammation, and beta-cell apoptosis, whereas we have found that TXNIP deficiency protects against diabetes. Interestingly, human islet amyloid polypeptide (IAPP) is also induced by glucose, aggregates into insoluble amyloid fibrils found in islets of most individuals with type 2 diabetes and promotes inflammation and beta-cell cytotoxicity. However, so far no connection between TXNIP and IAPP signaling had been reported. Using TXNIP gain and loss of function experiments, INS-1 beta-cells and beta-cell-specific Txnip knock-out mice, we now found that TXNIP regulates IAPP expression. Promoter analyses and chromatin-immunoprecipitation assays further demonstrated that TXNIP increases IAPP expression at the transcriptional level, and we discovered that TXNIP-induced FoxA2 (forkhead box A2) transcription factor expression was conferring this effect by promoting FoxA2 enrichment at the proximal FoxA2 site in the IAPP promoter. Moreover, we found that TXNIP down-regulates miR-124a expression, a microRNA known to directly target FoxA2. Indeed, miR-124a overexpression led to decreased FoxA2 expression and IAPP promoter occupancy and to a significant reduction in IAPP mRNA and protein expression and also effectively inhibited TXNIP-induced IAPP expression. Thus, our studies have identified a novel TXNIP/miR-124a/FoxA2/IAPP signaling cascade linking the critical beta-cell signaling pathways of TXNIP and IAPP and thereby provide new mechanistic insight into an important aspect of transcriptional regulation and beta-cell biology.

Thioredoxin-interacting protein regulates insulin transcription through microRNA-204.

Beta-cell dysfunction and impaired insulin production are hallmarks of diabetes, but despite the growing diabetes epidemic, the molecular mechanisms underlying this disease have remained unclear. We identified thioredoxin-interacting protein (TXNIP), a cellular redox regulator, as a crucial factor in beta-cell biology and show that beta-cell TXNIP is upregulated in diabetes, whereas TXNIP deficiency protects against diabetes by preventing beta-cell apoptosis. Here we show that TXNIP and diabetes induce beta-cell expression of a specific microRNA, miR-204, which in turn blocks insulin production by directly targeting and downregulating MAFA, a known insulin transcription factor. In particular, we first discovered the regulation of miR-204 by TXNIP by microarray analysis, followed by validation studies in INS-1 beta cells, islets of Txnip-deficient mice, diabetic mouse models and primary human islets. We then further found that TXNIP induces miR-204 by inhibiting the activity of signal transducer and activator of transcription 3 (STAT3), a transcription factor that is involved in miR-204 regulation. We also identified MAFA as a target that is downregulated by miR-204. Taken together, our results demonstrate that TXNIP controls microRNA expression and insulin production and that miR-204 is involved in beta-cell function. The newly identified TXNIP-miR-204-MAFA-insulin pathway may contribute to diabetes progression and provides new insight into TXNIP function and microRNA biology in health and disease.