Calcineurin/NFAT signalling regulates pancreatic beta-cell growth and function

Ca2+ signaling and metabolic stress-induced pancreatic β-cell failure

Early in the development of Type 2 diabetes (T2D), metabolic stress brought on by insulin resistance and nutrient overload causes β-cell hyperstimulation. Herein we summarize recent studies that have explored the premise that an increase in the intracellular Ca2+ concentration ([Ca2+]i), brought on by persistent metabolic stimulation of β-cells, causes β-cell dysfunction and failure by adversely affecting β-cell function, structure, and identity. This mini-review builds on several recent reviews that also describe how excess [Ca2+]i impairs β-cell function.

An update review of post-transplant diabetes mellitus: Concept, risk factors, clinical implications and management

OBJECTIVE

Kidney transplantation is the gold standard therapeutic alternative for patients with end-stage renal disease; nevertheless, it is not without potential complications leading to considerable morbidity and mortality such as post-transplant diabetes mellitus (PTDM). This narrative review aims to comprehensively evaluate PTDM in terms of its diagnostic approach, underlying pathophysiological pathways, epidemiological data, and management strategies.

METHODS

Articles were retrieved from electronic databases using predefined search terms. Inclusion criteria encompassed studies investigating PTDM diagnosis, pathophysiology, epidemiology, and management strategies.

RESULTS

PTDM emerges as a significant complication following kidney transplantation, influenced by various pathophysiological factors including peripheral insulin resistance, immunosuppressive medications, infections, and proinflammatory pathways. Despite discrepancies in prevalence estimates, PTDM poses substantial challenges to transplant. Diagnostic approaches, including traditional criteria such as fasting plasma glucose (FPG) and HbA1c, are limited in their ability to capture early PTDM manifestations. Oral glucose tolerance test (OGTT) emerges as a valuable tool, particularly in the early post-transplant period. Management strategies for PTDM remain unclear, within sufficient evidence from large-scale randomized clinical trials to guide optimal interventions. Nevertheless, glucose-lowering agents and life style modifications constitute primary modalities for managing hyperglycemia in transplant recipients.

DISCUSSION

The complex interplay between PTDM and the transplant process necessitates individualized diagnostic and management approaches. While early recognition and intervention are paramount, modifications to maintenance immunosuppressive regimens based solely on PTDM risk are not warranted, given the potential adverse consequences such as increased rejection risk. Further research is essential to refine management strategies and enhance outcomes for transplant recipients.

Human Menstrual Blood-Derived Stem Cells Protect against Tacrolimus-Induced Islet Dysfunction via Cystathionine β-Synthase Mediated IL-6/STAT3 Inactivation

Diabetes imposes a huge burden worldwide. Islet transplantation is an alternative therapy for diabetes. However, tacrolimus, a kind of immunosuppressant after organ transplantation, is closely related to post-transplant diabetes mellitus. Mesenchymal stem cells (MSCs) have attracted interest for their potential to alleviate diabetes. In vivo experiments revealed that human menstrual blood-derived stem cells (MenSCs) treatment improved tacrolimus-induced blood glucose, body weight, and glucose tolerance disorders in mice. RNA sequencing was used to analyze the potential therapeutic targets of MenSCs. In this study, we illustrated that cystathionine β-synthase (CBS) contributed to tacrolimus -induced islet dysfunction. Using β-cell lines (MIN6, β-TC-6), we demonstrated that MenSCs ameliorated tacrolimus-induced islet dysfunction in vitro. Moreover, MenSC reduced the tacrolimus-induced elevation of CBS levels and significantly enhanced the viability, anti-apoptotic ability, glucose-stimulated insulin secretion (GSIS), and glycolytic flux of β-cells. We further revealed that MenSCs exerted their therapeutic effects by inhibiting CBS expression to activate the IL6/JAK2/STAT3 pathway. In conclusion, we showed that MenSCs may be a potential strategy to improve tacrolimus-induced islet dysfunction.

Zinc-chelating BET bromodomain inhibitors equally target islet endocrine cell types

Inhibition of the bromodomain and extraterminal domain (BET) protein family is a potential strategy to prevent and treat diabetes; however, the clinical use of BET bromodomain inhibitors (BETis) is associated with adverse effects. Here, we explore a strategy for targeting BETis to β cells by exploiting the high-zinc (Zn2+) concentration in β cells relative to other cell types. We report the synthesis of a novel, Zn2+-chelating derivative of the pan-BETi (+)-JQ1, (+)-JQ1-DPA, in which (+)-JQ1 was conjugated to dipicolyl amine (DPA). As controls, we synthesized (+)-JQ1-DBA, a non-Zn2+-chelating derivative, and (-)-JQ1-DPA, an inactive enantiomer that chelates Zn2+. Molecular modeling and biophysical assays showed that (+)-JQ1-DPA and (+)-JQ1-DBA retain potent binding to BET bromodomains in vitro. Cellular assays demonstrated (+)-JQ1-DPA attenuated NF-ĸB target gene expression in β cells stimulated with the proinflammatory cytokine interleukin 1β. To assess β-cell selectivity, we isolated islets from a mouse model that expresses green fluorescent protein in insulin-positive β cells and mTomato in insulin-negative cells (non-β cells). Surprisingly, Zn2+ chelation did not confer β-cell selectivity as (+)-JQ1-DPA was equally effective in both β and α cells; however, (+)-JQ1-DPA was less effective in macrophages, a nonendocrine islet cell type. Intriguingly, the non-Zn2+-chelating derivative (+)-JQ1-DBA displayed the opposite selectivity, with greater effect in macrophages compared with (+)-JQ1-DPA, suggesting potential as a macrophage-targeting molecule. These findings suggest that Zn2+-chelating small molecules confer endocrine cell selectivity rather than β-cell selectivity in pancreatic islets and provide valuable insights and techniques to assess Zn2+ chelation as an approach to selectively target small molecules to pancreatic β cells.NEW & NOTEWORTHY Inhibition of BET bromodomains is a novel potential strategy to prevent and treat diabetes mellitus. However, BET inhibitors have negative side effects. We synthesized a BET inhibitor expected to exploit the high zinc concentration in β cells to accumulate in β cells. We show our inhibitor targeted pancreatic endocrine cells; however, it was less effective in immune cells. A control inhibitor showed the opposite effect. These findings help us understand how to target specific cells in diabetes treatment.

The evolving roles of Wnt signaling in stem cell proliferation and differentiation, the development of human diseases, and therapeutic opportunities

The evolutionarily conserved Wnt signaling pathway plays a central role in development and adult tissue homeostasis across species. Wnt proteins are secreted, lipid-modified signaling molecules that activate the canonical (β-catenin dependent) and non-canonical (β-catenin independent) Wnt signaling pathways. Cellular behaviors such as proliferation, differentiation, maturation, and proper body-axis specification are carried out by the canonical pathway, which is the best characterized of the known Wnt signaling paths. Wnt signaling has emerged as an important factor in stem cell biology and is known to affect the self-renewal of stem cells in various tissues. This includes but is not limited to embryonic, hematopoietic, mesenchymal, gut, neural, and epidermal stem cells. Wnt signaling has also been implicated in tumor cells that exhibit stem cell-like properties. Wnt signaling is crucial for bone formation and presents a potential target for the development of therapeutics for bone disorders. Not surprisingly, aberrant Wnt signaling is also associated with a wide variety of diseases, including cancer. Mutations of Wnt pathway members in cancer can lead to unchecked cell proliferation, epithelial-mesenchymal transition, and metastasis. Altogether, advances in the understanding of dysregulated Wnt signaling in disease have paved the way for the development of novel therapeutics that target components of the Wnt pathway. Beginning with a brief overview of the mechanisms of canonical and non-canonical Wnt, this review aims to summarize the current knowledge of Wnt signaling in stem cells, aberrations to the Wnt pathway associated with diseases, and novel therapeutics targeting the Wnt pathway in preclinical and clinical studies.

Diabetes and the fabkin complex: A dual-edged sword

The Fabkin complex, composed of FABP4, ADK, and NDPKs, emerges as a novel regulator of insulin-producing beta cells, offering promising prospects for diabetes treatment. Our approach, which combines literature review and database analysis, sets the stage for future research. These findings hold significant implications for both diabetes treatment and research, as they present potential therapeutic targets for personalized treatment, leading to enhanced patient outcomes and a deeper comprehension of the disease. The multifaceted role of the Fabkin complex in glucose metabolism, insulin resistance, anti-inflammation, beta cell proliferation, and vascular function underscores its therapeutic potential, reshaping diabetes management and propelling advancements in the field.

Genetic and Epigenetic Associations with Post-Transplant Diabetes Mellitus

Post-transplant diabetes mellitus (PTDM) is a common complication of solid organ transplantation. PTDM prevalence varies due to different diabetes definitions. Consensus guidelines for the diagnosis of PTDM have been published based on random blood glucose levels, glycated hemoglobin (HbA1c), and oral glucose tolerance test (OGTT). The task of diagnosing PTDM continues to pose challenges, given the potential for diabetes to manifest at different time points after transplantation, thus demanding constant clinical vigilance and repeated testing. Interpreting HbA1c levels can be challenging after renal transplantation. Pre-transplant risk factors for PTDM include obesity, sedentary lifestyle, family history of diabetes, ethnicity (e.g., African-Caribbean or South Asian ancestry), and genetic risk factors. Risk factors for PTDM include immunosuppressive drugs, weight gain, hepatitis C, and cytomegalovirus infection. There is also emerging evidence that genetic and epigenetic variation in the organ transplant recipient may influence the risk of developing PTDM. This review outlines many known risk factors for PTDM and details some of the pathways, genetic variants, and epigenetic features associated with PTDM. Improved understanding of established and emerging risk factors may help identify people at risk of developing PTDM and may reduce the risk of developing PTDM or improve the management of this complication of organ transplantation.

Impact of varied immunosuppressive agents and posttransplant diabetes mellitus on prognosis among diverse transplant recipients (Experimental studies)

The success of solid organ transplantation (SOT) and the use of immunosuppressive agents offer hope to patients with end-stage diseases. However, the impact of posttransplant diabetes mellitus (PTDM) on SOT patients has become increasingly evident. In our study, we utilized the Scientific Registry of Transplant Recipients (SRTR) database to investigate the association between PTDM and patient survival in various types of organ transplantations, including liver, kidney, intestinal, heart, lung, and combined heart-lung transplantations (all P<0.001). Our findings revealed a negative effect of PTDM on the survival of these patients. Furthermore, we examined the effects of both generic and innovator immunosuppressive agents on the development of PTDM and the overall survival of different SOT populations. Interestingly, the results were inconsistent, indicating that the impact of these agents may vary depending on the specific type of transplantation and patient population. Overall, our study provides a comprehensive and systematic assessment of the effects of different immunosuppressive agents on prognosis, as well as the impact of PTDM on the survival of patients undergoing various types of SOT. These findings emphasize the need for further research and highlight the importance of optimizing immunosuppressive regimens and managing PTDM in SOT patients to improve their long-term outcomes.

Metabolic Disorders in Liver Transplant Recipients: The State of the Art

Liver transplantation represents a chief therapeutic approach for acute liver failure, end-stage liver disease and hepatocellular carcinoma. Despite witnessing advancements in short- and medium-term survival over recent decades, attributed to refinements in surgical techniques and immunosuppressive protocols, long-term mortality remains impervious to modification. Notably, cardiovascular disease emerges as a predominant cause of mortality among liver transplant recipients. This trend is accentuated by the increasing prominence of non-alcoholic steatohepatitis-related cirrhosis as an indication for liver transplantation. Moreover, the administration of immunosuppressive agents is intricately linked to the degradation of the metabolic profile in liver transplant recipients, thereby contributing to the initiation or exacerbation of cardiovascular risk factors, such as hypertension, diabetes, and dyslipidaemia. In addition, the post-liver transplantation period is marked by a decline in lifestyle quality and a failure to acknowledge the psychological distress experienced by patients throughout the transplant process. These factors can precipitate a deterioration in the patient's metabolic profile, exacerbated by suboptimal therapeutic compliance. This narrative review aims to comprehensively address the principal metabolic disorders intricately associated with liver transplantation.

Canonical and noncanonical Wnt signaling: Multilayered mediators, signaling mechanisms and major signaling crosstalk

Wnt signaling plays a major role in regulating cell proliferation and differentiation. The Wnt ligands are a family of 19 secreted glycoproteins that mediate their signaling effects via binding to Frizzled receptors and LRP5/6 coreceptors and transducing the signal either through β-catenin in the canonical pathway or through a series of other proteins in the noncanonical pathway. Many of the individual components of both canonical and noncanonical Wnt signaling have additional functions throughout the body, establishing the complex interplay between Wnt signaling and other signaling pathways. This crosstalk between Wnt signaling and other pathways gives Wnt signaling a vital role in many cellular and organ processes. Dysregulation of this system has been implicated in many diseases affecting a wide array of organ systems, including cancer and embryological defects, and can even cause embryonic lethality. The complexity of this system and its interacting proteins have made Wnt signaling a target for many therapeutic treatments. However, both stimulatory and inhibitory treatments come with potential risks that need to be addressed. This review synthesized much of the current knowledge on the Wnt signaling pathway, beginning with the history of Wnt signaling. It thoroughly described the different variants of Wnt signaling, including canonical, noncanonical Wnt/PCP, and the noncanonical Wnt/Ca2+ pathway. Further description involved each of its components and their involvement in other cellular processes. Finally, this review explained the various other pathways and processes that crosstalk with Wnt signaling.

Posttransplant Diabetes Mellitus: Recent Developments in Pharmacological Management of Hyperglycemia

CONTEXT

The management of solid-organ transplantation is rapidly evolving, and posttransplant diabetes mellitus (PTDM), which is increasingly common, is a barrier to transplant success, adversely impacting infection rates, allograft survival, cardiovascular disease, quality of life, and overall mortality. Currently, the management of PTDM relies primarily on intensified insulin therapy. However, emerging studies report that several noninsulin glucose-lowering agents are safe and effective in improving metabolic control and enhancing treatment adherence. More importantly, their use in PTDM can potentially transform the long-term management of these complex patients, as some glucose-lowering agents may provide benefits beyond glycemic control. For instance, glucagon-like peptide 1 receptor agonists (GLP-1 RA) and sodium-glucose cotransporter 2 (SGLT-2) inhibitors may offer cardiorenal protection, and pioglitazone may treat nonalcoholic fatty liver disease (NAFLD). This review will focus on the pharmacological management of PTDM and the emerging evidence for noninsulin glucose-lowering agents in this population.

EVIDENCE ACQUISITION

Evidence from observational studies, randomized controlled trials, and meta-analyses.

EVIDENCE SYNTHESIS

PTDM adversely affects the outcomes of infection, organ survival, cardiovascular events, and mortality. Insulin therapy has been the drug of choice but is associated with weight gain and hypoglycemia. In contrast, noninsulin agents appear safe and may provide additional benefits, such as cardiorenal protection with SGLT-2 inhibitors and GLP-1 RA, and cardiometabolic benefits with pioglitazone, in patients undergoing solid-organ transplantation.

CONCLUSIONS

Optimal care of patients with PTDM requires close monitoring and the early involvement of the endocrinologist as part of a multidisciplinary team. Noninsulin glucose-lowering agents will likely play an increasing role as more long-term, controlled studies become available in this setting.

Tacrolimus and Diabetes in Kidney Transplantation: The Impact of Cyp3a5 Gene Polymorphism

BACKGROUND

To explore the correlation between single nucleotide polymorphisms (SNPs) of CYP3A4 rs2740574 and CYP3A5 rs776746 and post-transplant diabetes mellitus (PTDM) in Chinese renal allograft recipients treated with tacrolimus.

METHODS

A total of 244 patients treated with tacrolimus were included in this study, wherein DNA sequencing was detected through fluorescence in situ hybridization, and SNP genotyping was performed.

RESULTS

Among the 244 patients, 44 (18%) developed PTDM. The PTDM group exhibited higher preoperative body mass index and fasting plasma glucose levels, with higher creatinine values one year after surgery. The CYP3A4 rs2740574 genotype was found to be unique in its homozygous AA form. For CYP3A5 rs776746, the genotypes were distributed as follows: 28 (11.5%) cases with AA, 101 (41.4%) cases with AG, and 115 (47.1%) cases with GG, respectively (P = .042). The AA genotype showed a statistically significant difference from both AG and GG genotypes. Furthermore, the A allele of CYP3A5 rs776746 was found to be associated with an increased risk for PTDM development.

CONCLUSIONS

The occurrence of tacrolimus-related PTDM is associated with body mass index, fasting plasma glucose levels, and CYP3A5 genotype before renal transplantation. Post-transplant diabetes mellitus is correlated with unfavorable long-term renal graft function, whereas the expression of the CYP3A5 rs776746 gene is linked to an elevated risk of PTDM.

Function and therapeutic value of astrocytes in diabetic cognitive impairment

Diabetic cognitive impairment (DCI) is a complex complication of diabetes in the central nervous system, and its pathological mechanism is still being explored. Astrocytes are abundant glial cells in central nervous system that perform diverse functions in health and disease. Accumulating excellent research has identified astrocyte dysfunction in many neurodegenerative diseases (such as Alzheimer's disease, aging and Parkinson's disease), and summarized and discussed its pathological mechanisms and potential therapeutic value. However, the contribution of astrocytes to DCI has been largely overlooked. In this review, we first systematically summarized the effects and mechanisms of diabetes on brain astrocytes, and found that the diabetic environment (such as hyperglycemia, advanced glycation end products and cerebral insulin resistance) mediated brain reactive astrogliosis, which was specifically reflected in the changes of cell morphology and the remodeling of signature molecules. Secondly, we emphasized the contribution and potential targets of reactive astrogliosis to DCI, and found that reactive astrogliosis-induced increased blood-brain barrier permeability, glymphatic system dysfunction, neuroinflammation, abnormal cell communication and cholesterol metabolism dysregulation worsened cognitive function. In addition, we summarized effective strategies for treating DCI by targeting astrocytes. Finally, we discuss the application of new techniques in astrocytes, including single-cell transcriptome, in situ sequencing, and prospected new functions, new subsets and new targets of astrocytes in DCI.

Evolving challenges with long-term care of liver transplant recipients

The number of liver transplants (LT) performed worldwide continues to rise, and LT recipients are living longer post-transplant. This has led to an increasing number of LT recipients requiring lifelong care. Optimal care post-LT requires careful attention to both the allograft and systemic issues that are more common after organ transplantation. Common causes of allograft dysfunction include rejection, biliary complications, and primary disease recurrence. While immunosuppression prevents rejection and reduces incidences of some primary disease recurrence, it has detrimental systemic effects. Most commonly, these include increased incidences of metabolic syndrome, various malignancies, and infections. Therefore, it is of utmost importance to optimize immunosuppression regimens to prevent allograft dysfunction while also decreasing the risk of systemic complications. Institutional protocols to screen for systemic disease and heightened clinical suspicion also play an important role in providing optimal long-term post-LT care. In this review, we discuss these common complications of LT as well as unique considerations when caring for LT recipients in the years after transplant.

Transcriptional signature of islet neogenesis-associated protein peptide-treated rat pancreatic islets reveals induction of novel long non-coding RNAs

Background

Diabetes mellitus is characterized by chronic hyperglycemia with loss of β-cell function and mass. An attractive therapeutic approach to treat patients with diabetes in a non-invasive way is to harness the innate regenerative potential of the pancreas. The Islet Neogenesis-Associated Protein pentadecapeptide (INGAP-PP) has been shown to induce β-cell regeneration and improve their function in rodents. To investigate its possible mechanism of action, we report here the global transcriptional effects induced by the short-term INGAP-PP in vitro treatment of adult rat pancreatic islets.

Methods and findings

Rat pancreatic islets were cultured in vitro in the presence of INGAP-PP for 4 days, and RNA-seq was generated from triplicate treated and control islet samples. We performed a de novo rat gene annotation based on the alignment of RNA-seq reads. The list of INGAP-PP-regulated genes was integrated with epigenomic data. Using the new gene annotation generated in this work, we quantified RNA-seq data profiled in INS-1 cells treated with IL1β, IL1β+Calcipotriol (a vitamin D agonist) or vehicle, and single-cell RNA-seq data profiled in rat pancreatic islets. We found 1,669 differentially expressed genes by INGAP-PP treatment, including dozens of previously unannotated rat transcripts. Genes differentially expressed by the INGAP-PP treatment included a subset of upregulated transcripts that are associated with vitamin D receptor activation. Supported by epigenomic and single-cell RNA-seq data, we identified 9 previously unannotated long noncoding RNAs (lncRNAs) upregulated by INGAP-PP, some of which are also differentially regulated by IL1β and vitamin D in β-cells. These include Ri-lnc1, which is enriched in mature β-cells.

Conclusions

Our results reveal the transcriptional program that could explain the enhancement of INGAP-PP-mediated physiological effects on β-cell mass and function. We identified novel lncRNAs that are induced by INGAP-PP in rat islets, some of which are selectively expressed in pancreatic β-cells and downregulated by IL1β treatment of INS-1 cells. Our results suggest a relevant function for Ri-lnc1 in β-cells. These findings are expected to provide the basis for a deeper understanding of islet translational results from rodents to humans, with the ultimate goal of designing new therapies for people with diabetes.

Early retinal neurovascular findings in post-transplant diabetes mellitus patients without clinical signs of diabetic retinopathy

BACKGROUND

Post-transplant diabetes mellitus (PTDM) is a specific subtype of diabetes with an uncertain impact on mortality and morbidity in post-transplant patients. Diabetic retinopathy is the most common microvascular complication of diabetes mellitus, but the long-term clinical progression in PTDM is unknown. New technologies are being used to assess pre-clinical signs of retinal changes, such as swept-source optical coherence tomography (OCT) and OCT-angiography. The aim of this study was to detect pre-clinical structural and vascular changes in the retina using swept-source-OCT and OCT-angiography in patients with PTDM.

METHODS

In this retrospective cohort study, post-kidney transplant patients were divided into PTDM and non-PTDM (control) groups. Both eyes of eligible PTDM patients and controls were included in this study. Inner retinal layer thickness was measured with swept-source-OCT. Retinal capillary density and the foveal avascular zone were measured with OCT-angiography.

RESULTS

In the PTDM group, reduced thickness was found in the inferior ganglion cell layer plus inner plexiform layer (95% CI -8.76 to -0.68; p = 0.022) and the temporal inferior segment (95% CI -10.23 to -0.76; p = 0.024) of the inner retina, as well as in the retinal nerve fiber layer in the temporal (95% CI -34.78 to -9.28 p = 0.001) and temporal inferior segments (95% CI -33.26 to -5.03 p = 0.008). No significant differences were found in the vascular capillary plexus between groups at all depths, segments, or foveal avascular zone (p = 0.088).

CONCLUSIONS

According to OCT-angiography, PTDM patients had reduced inner neurosensory retinal layers but no significant change in vascular density, which suggests that early neuroretinal degeneration might occur prior to vascular changes secondary to PTDM. Prospective studies could help elucidate the clinical course of retinal neuropathy and microvascular pathology in PTDM and provide a better understanding of PTDM complications.

Calcineurin regulates aldosterone production via dephosphorylation of NFATC4

The mineralocorticoid aldosterone, secreted by the adrenal zona glomerulosa (ZG), is critical for life, maintaining ion homeostasis and blood pressure. Therapeutic inhibition of protein phosphatase 3 (calcineurin, Cn) results in inappropriately low plasma aldosterone levels despite concomitant hyperkalemia and hyperreninemia. We tested the hypothesis that Cn participates in the signal transduction pathway regulating aldosterone synthesis. Inhibition of Cn with tacrolimus abolished the potassium-stimulated (K+-stimulated) expression of aldosterone synthase, encoded by CYP11B2, in the NCI-H295R human adrenocortical cell line as well as ex vivo in mouse and human adrenal tissue. ZG-specific deletion of the regulatory Cn subunit CnB1 diminished Cyp11b2 expression in vivo and disrupted K+-mediated aldosterone synthesis. Phosphoproteomics analysis identified nuclear factor of activated T cells, cytoplasmic 4 (NFATC4), as a target for Cn-mediated dephosphorylation. Deletion of NFATC4 impaired K+-dependent stimulation of CYP11B2 expression and aldosterone production while expression of a constitutively active form of NFATC4 increased expression of CYP11B2 in NCI-H295R cells. Chromatin immunoprecipitation revealed NFATC4 directly regulated CYP11B2 expression. Thus, Cn controls aldosterone production via the Cn/NFATC4 pathway. Inhibition of Cn/NFATC4 signaling may explain low plasma aldosterone levels and hyperkalemia in patients treated with tacrolimus, and the Cn/NFATC4 pathway may provide novel molecular targets to treat primary aldosteronism.

What the BTBR/J mouse has taught us about diabetes and diabetic complications

Human and mouse genetics have delivered numerous diabetogenic loci, but it is mainly through the use of animal models that the pathophysiological basis for their contribution to diabetes has been investigated. More than 20 years ago, we serendipidously identified a mouse strain that could serve as a model of obesity-prone type 2 diabetes, the BTBR (Black and Tan Brachyury) mouse (BTBR T+ Itpr3tf/J, 2018) carrying the Lepob mutation. We went on to discover that the BTBR-Lepob mouse is an excellent model of diabetic nephropathy and is now widely used by nephrologists in academia and the pharmaceutical industry. In this review, we describe the motivation for developing this animal model, the many genes identified and the insights about diabetes and diabetes complications derived from >100 studies conducted in this remarkable animal model.

SIRT3-and FAK-mediated acetylation-phosphorylation crosstalk of NFATc1 regulates Nε-carboxymethyl-lysine-induced vascular calcification in diabetes mellitus

BACKGROUND AND AIMS

Arterial calcification is the predictor of cardiovascular risk in diabetic patients. N^ε-carboxymethyl-lysine (CML), a toxic metabolite, is associated with accelerated vascular calcification in diabetes mellitus (DM). However, the mechanism remains elusive. This study aims to explore the key regulators involved in CML-induced vascular calcification in DM.

METHODS

We used Western blot and immuno-staining to test the expression and localization of nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) in human samples, a diabetic apolipoprotein E-deficient (ApoE^-/-) mouse model, and a vascular smooth muscle cells (VSMC) model. Further, we confirmed the regulator of NFATc1 phosphorylation and acetylation induced by CML. The role of NFATc1 in VSMCs calcification and osteogenic differentiation was explored in vivo and in vitro.

RESULTS

In diabetic patients, CML and NFATc1 levels increased in the severe calcified anterior tibial arteries. CML significantly promoted NFATc1 expression and nuclear translocation in VSMCs and mouse aorta. Knockdown of NFATc1 significantly inhibited CML-induced calcification. CML promoted NFATc1 acetylation at K549 by downregulating sirtuin 3 (SIRT3), which antagonized the focal adhesion kinase (FAK) induced NFATc1 phosphorylation at the Y270 site. FAK and SIRT3 affected the nuclear translocation of NFATc1 by regulating the acetylation-phosphorylation crosstalk. NFATc1 dephosphorylation mutant Y270F and deacetylation mutant K549R had opposite effects on VSMC calcification. SIRT3 overexpression and FAK inhibitor could reverse CML-promoted VSMC calcification.

CONCLUSIONS

CML enhances vascular calcification in DM through NFATc1. In this process, CML increases NFATc1 acetylation by downregulating SIRT3 to antagonize FAK-induced NFATc1 phosphorylation.

Signaling pathways and intervention for therapy of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents one of the fastest growing epidemic metabolic disorders worldwide and is a strong contributor for a broad range of comorbidities, including vascular, visual, neurological, kidney, and liver diseases. Moreover, recent data suggest a mutual interplay between T2DM and Corona Virus Disease 2019 (COVID-19). T2DM is characterized by insulin resistance (IR) and pancreatic β cell dysfunction. Pioneering discoveries throughout the past few decades have established notable links between signaling pathways and T2DM pathogenesis and therapy. Importantly, a number of signaling pathways substantially control the advancement of core pathological changes in T2DM, including IR and β cell dysfunction, as well as additional pathogenic disturbances. Accordingly, an improved understanding of these signaling pathways sheds light on tractable targets and strategies for developing and repurposing critical therapies to treat T2DM and its complications. In this review, we provide a brief overview of the history of T2DM and signaling pathways, and offer a systematic update on the role and mechanism of key signaling pathways underlying the onset, development, and progression of T2DM. In this content, we also summarize current therapeutic drugs/agents associated with signaling pathways for the treatment of T2DM and its complications, and discuss some implications and directions to the future of this field.

Ca2+-Mediated Signaling Pathways: A Promising Target for the Successful Generation of Mature and Functional Stem Cell-Derived Pancreatic Beta Cells In Vitro

Diabetes mellitus is a chronic disease affecting over 500 million adults globally and is mainly categorized as type 1 diabetes mellitus (T1DM), where pancreatic beta cells are destroyed, and type 2 diabetes mellitus (T2DM), characterized by beta cell dysfunction. This review highlights the importance of the divalent cation calcium (Ca²⁺) and its associated signaling pathways in the proper functioning of beta cells and underlines the effects of Ca²⁺ dysfunction on beta cell function and its implications for the onset of diabetes. Great interest and promise are held by human pluripotent stem cell (hPSC) technology to generate functional pancreatic beta cells from diabetic patient-derived stem cells to replace the dysfunctional cells, thereby compensating for insulin deficiency and reducing the comorbidities of the disease and its associated financial and social burden on the patient and society. Beta-like cells generated by most current differentiation protocols have blunted functionality compared to their adult human counterparts. The Ca²⁺ dynamics in stem cell-derived beta-like cells and adult beta cells are summarized in this review, revealing the importance of proper Ca²⁺ homeostasis in beta-cell function. Consequently, the importance of targeting Ca²⁺ function in differentiation protocols is suggested to improve current strategies to use hPSCs to generate mature and functional beta-like cells with a comparable glucose-stimulated insulin secretion (GSIS) profile to adult beta cells.

mTOR-inhibitors and post-transplant diabetes mellitus: a link still debated in kidney transplantation

The mammalian target of rapamycin inhibitors (mTOR-Is, Sirolimus, and Everolimus) are immunosuppressive drugs widely employed in kidney transplantation. Their main mechanism of action includes the inhibition of a serine/threonine kinase with a pivotal role in cellular metabolism and in various eukaryotic biological functions (including proteins and lipids synthesis, autophagy, cell survival, cytoskeleton organization, lipogenesis, and gluconeogenesis). Moreover, as well described, the inhibition of the mTOR pathway may also contribute to the development of the post-transplant diabetes mellitus (PTDM), a major clinical complication that may dramatically impact allograft survival (by accelerating the development of the chronic allograft damage) and increase the risk of severe systemic comorbidities. Several factors may contribute to this condition, but the reduction of the beta-cell mass, the impairment of the insulin secretion and resistance, and the induction of glucose intolerance may play a pivotal role. However, although the results of several in vitro and in animal models, the real impact of mTOR-Is on PTDM is still debated and the entire biological machinery is poorly recognized. Therefore, to better elucidate the impact of the mTOR-Is on the risk of PTDM in kidney transplant recipients and to potentially uncover future research topics (particularly for the clinical translational research), we decided to review the available literature evidence regarding this important clinical association. In our opinion, based on the published reports, we cannot draw any conclusion and PTDM remains a challenge. However, also in this case, the administration of the lowest possible dose of mTOR-I should also be recommended.

Deciphering the multifunctional role of dual leucine zipper kinase (DLK) and its therapeutic potential in disease

Dual leucine zipper kinase (DLK, MAP3K12), a serine/threonine protein kinase, plays a key role in neuronal development, as it regulates axon regeneration and degeneration through its downstream kinase. Importantly, DLK is closely related to the pathogenesis of numerous neurodegenerative diseases and the induction of β-cell apoptosis that leads to diabetes. In this review, we summarize the current understanding of DLK function, and then discuss the role of DLK signaling in human diseases. Furthermore, various types of small molecule inhibitors of DLK that have been published so far are described in detail in this paper, providing some strategies for the design of DLK small molecule inhibitors in the future.

SLC25A46 promotes mitochondrial fission and mediates resistance to lipotoxic stress in INS-1E insulin-secreting cells

Glucose sensing in pancreatic β-cells depends on oxidative phosphorylation and mitochondria-derived signals that promote insulin secretion. Using mass spectrometry-based phosphoproteomics to search for downstream effectors of glucose-dependent signal transduction in INS-1E insulinoma cells, we identified the outer mitochondrial membrane protein SLC25A46. Under resting glucose concentrations, SLC25A46 was phosphorylated on a pair of threonine residues (T44/T45) and was dephosphorylated in response to glucose-induced Ca2+ signals. Overexpression of SLC25A46 in INS-1E cells caused complete mitochondrial fragmentation, resulting in a mild mitochondrial defect associated with lowered glucose-induced insulin secretion. In contrast, inactivation of the Slc25a46 gene resulted in dramatic mitochondrial hyperfusion, without affecting respiratory activity or insulin secretion. Consequently, SLC25A46 is not essential for metabolism-secretion coupling under normal nutrient conditions. Importantly, insulin-secreting cells lacking SLC25A46 had an exacerbated sensitivity to lipotoxic conditions, undergoing massive apoptosis when exposed to palmitate. Therefore, in addition to its role in mitochondrial dynamics, SLC25A46 plays a role in preventing mitochondria-induced apoptosis in INS-E cells exposed to nutrient stress. By protecting mitochondria, SLC25A46 might help to maintain β-cell mass essential for blood glucose control.

No Time to Die-How Islets Meet Their Demise in Transplantation

Islet transplantation represents an effective treatment for patients with type 1 diabetes mellitus (T1DM) and severe hypoglycaemia unawareness, capable of circumventing impaired counterregulatory pathways that no longer provide protection against low blood glucose levels. The additional beneficial effect of normalizing metabolic glycaemic control is the minimisation of further complications related to T1DM and insulin administration. However, patients require allogeneic islets from up to three donors, and the long-term insulin independence is inferior to that achieved with solid organ (whole pancreas) transplantation. This is likely due to the fragility of islets caused by the isolation process, innate immune responses following portal infusion, auto- and allo-immune-mediated destruction and β-cell exhaustion following transplantation. This review covers the specific challenges related to islet vulnerability and dysfunction that affect long-term cell survival following transplantation.

Progress of new-onset diabetes after liver and kidney transplantation

Organ transplantation is currently the most effective treatment for end-stage organ failure. Post transplantation diabetes mellitus (PTDM) is a severe complication after organ transplantation that seriously affects the short-term and long-term survival of recipients. However, PTDM is often overlooked or poorly managed in its early stage. This article provides an overview of the incidence, and pathogenesis of and risk factors for PTDM, aiming to gain a deeper understanding of PTDM and improve the quality of life of recipients.

Bariatric Surgery: Targeting pancreatic β cells to treat type II diabetes

Pancreatic β-cell function impairment and insulin resistance are central to the development of obesity-related type 2 diabetes mellitus (T2DM). Bariatric surgery (BS) is a practical treatment approach to treat morbid obesity and achieve lasting T2DM remission. Traditionally, sustained postoperative glycemic control was considered a direct result of decreased nutrient intake and weight loss. However, mounting evidence in recent years implicated a weight-independent mechanism that involves pancreatic islet reconstruction and improved β-cell function. In this article, we summarize the role of β-cell in the pathogenesis of T2DM, review recent research progress focusing on the impact of Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG) on pancreatic β-cell pathophysiology, and finally discuss therapeutics that have the potential to assist in the treatment effect of surgery and prevent T2D relapse.

Impact of Chronic Immunosuppression on Short-, Mid-, and Long-Term Bariatric Surgery Outcomes

INTRODUCTION

Bariatric surgical outcomes depend heavily on proper healing of gastrointestinal anatomy, metabolic alterations, and patient lifestyle modifications which are all negatively impacted by immunosuppression and underlying inflammatory diseases. There is a lack of literature exploring how patients with diseases requiring immunosuppression respond to bariatric surgical intervention in the long term.

METHODS

A retrospective analysis of chronically immunosuppressed patients who underwent primary bariatric surgeries at Mayo Clinic was conducted (2008-2020). Data collected included patient demographics, BMI, underlying disease, and immunosuppression regimen and complications at 3, 6, 12, 24, and 60 months.

RESULTS

We identified a total of 89 (RYGB = 49, SG = 34, BPD/DS = 6) patients on chronic immunosuppression who underwent bariatric surgery at our center. RYGB (N = 49), 38.2% had a SG (N = 34) and 6.7% had a BPD/DS (N = 6). Rheumatoid arthritis and renal transplantation were the most underlying condition at 20.22% each (N = 18). There were a total of 2 (2.25%) intraoperative complications. In the immediate post-operative period, there were 15 (16.5%) minor complications. In follow-up, 6.1% of RYGB patients experienced marginal ulcerations, while no gastrointestinal leaks occurred. The mean pre-surgical BMI was 48.29 kg/m² (SD = 18.41). Percent total weight loss (%TWL) and BMI reduction were 30.89% and 14.83 kg/m² (SD = 9.07) at 12 months and 29.48% and 14.43 kg/m² (SD = 13.46) at 60 months, respectively. The mean follow-up time was 30.49 months.

CONCLUSIONS

Bariatric surgery remains safe and effective therapy for chronically immunosuppressed patients with excellent long-term outcomes for patients with moderate to severe obesity.

Modeling type 2 diabetes in rats by administering tacrolimus

The prevalence of diabetes is rapidly increasing. The current number of diagnosed cases is ~422 million, expected to reach ~640 million by 2040. Type 2 diabetes, which constitutes ~95% of the cases, is characterized by insulin resistance and a progressive loss of β-cell function. Despite intense research efforts, no treatments are yet able to cure the disease or halt its progression. Since all existing animal models of type 2 diabetes have serious drawbacks, one is needed that represents the complete pathogenesis, is low cost and non-obese, and can be developed relatively quickly. The aim of this study was to evaluate a low-cost, non-obese model of type 2 diabetes engendered by administering a daily high dose of tacrolimus (an immunosuppressant) to Wistar rats for 4 weeks. The biochemical and antioxidant markers were measured at basal and after the 4-week tacrolimus treatment. At week 4, the values of these parameters closely resembled those observed in human type 2 diabetes, including fasting blood glucose at 141.5 mg/dL, blood glucose greater than 200 mg/dL at 120 min of the glucose tolerance test, blood glucose at varied levels in the insulin tolerance test, and elevated levels of cholesterol and triglyceride. The tacrolimus treatment produced hypoinsulinemia and sustained hyperglycemia, probably explained by the alteration found in pancreatic β-cell function and morphology. This model should certainly be instrumental for evaluating possible type 2 diabetes treatments, and for designing new immunosuppressants that do not cause pancreatic damage, type 2 diabetes, or new-onset diabetes after transplantation (NODAT).

NFATc1 signaling drives chronic ER stress responses to promote NAFLD progression

OBJECTIVES

Non-alcoholic fatty liver disease (NAFLD) can persist in the stage of simple hepatic steatosis or progress to steatohepatitis (NASH) with an increased risk for cirrhosis and cancer. We examined the mechanisms controlling the progression to severe NASH in order to develop future treatment strategies for this disease.

DESIGN

NFATc1 activation and regulation was examined in livers from patients with NAFLD, cultured and primary hepatocytes and in transgenic mice with differential hepatocyte-specific expression of the transcription factor (Alb-cre, NFATc1^c.a . and NFATc1^Δ/Δ ). Animals were fed with high-fat western diet (WD) alone or in combination with tauroursodeoxycholic acid (TUDCA), a candidate drug for NAFLD treatment. NFATc1-dependent ER stress-responses, NLRP3 inflammasome activation and disease progression were assessed both in vitro and in vivo.

RESULTS

NFATc1 expression was weak in healthy livers but strongly induced in advanced NAFLD stages, where it correlates with liver enzyme values as well as hepatic inflammation and fibrosis. Moreover, high-fat WD increased NFATc1 expression, nuclear localisation and activation to promote NAFLD progression, whereas hepatocyte-specific depletion of the transcription factor can prevent mice from disease acceleration. Mechanistically, NFATc1 drives liver cell damage and inflammation through ER stress sensing and activation of the PERK-CHOP unfolded protein response (UPR). Finally, NFATc1-induced disease progression towards NASH can be blocked by TUDCA administration.

CONCLUSION

NFATc1 stimulates NAFLD progression through chronic ER stress sensing and subsequent activation of terminal UPR signalling in hepatocytes. Interfering with ER stress-responses, for example, by TUDCA, protects fatty livers from progression towards manifest NASH.

Interventions Against Posttransplantation Diabetes: A Scientific Rationale for Treatment Hierarchy Based on Literature Review

Posttransplant diabetes (PTD) is a common medical complication after solid organ transplantation. Because of adverse outcomes associated with its development and detrimental impact on long-term survival, strategies to prevent or manage PTD are critically important but remain underresearched. Treatment hierarchies of antidiabetic therapies in the general population are currently being revolutionized based on cardiovascular outcome trials, providing evidence-based rationale for optimization of medical management. However, opportunities for improving medical management of PTD are challenged by 2 important considerations: (1) translating clinical evidence data from the general population to underresearched solid organ transplant cohorts and (2) targeting treatment based on primary underlying PTD pathophysiology. In this article, the aim is to provide an overview of PTD treatment options from a new angle. Rationalized by a consideration of underlying PTD pathophysiological defects, which are heterogeneous among diverse transplant patient cohorts, a critical appraisal of the published literature and summary of current research in progress will be reviewed. The aim is to update transplant professionals regarding medical management of PTD from a new perspective tailored therapeutic intervention based on individualized characteristics. As the gap in clinical evidence between management of PTD versus type 2 diabetes widens, it is imperative for the transplant community to bridge this gap with targeted clinical trials to ensure we optimize outcomes for solid organ transplant recipients who are at risk or develop PTD. This necessary clinical research should help efforts to improve long-term outcomes for solid transplant patients from both a patient and graft survival perspective.

BefA, a microbiota-secreted membrane disrupter, disseminates to the pancreas and increases β cell mass

Microbiome dysbiosis is a feature of diabetes, but how microbial products influence insulin production is poorly understood. We report the mechanism of BefA, a microbiome-derived protein that increases proliferation of insulin-producing β cells during development in gnotobiotic zebrafish and mice. BefA disseminates systemically by multiple anatomic routes to act directly on pancreatic islets. We detail BefA's atomic structure, containing a lipid-binding SYLF domain, and demonstrate that it permeabilizes synthetic liposomes and bacterial membranes. A BefA mutant impaired in membrane disruption fails to expand β cells, whereas the pore-forming host defense protein, Reg3, stimulates β cell proliferation. Our work demonstrates that membrane permeabilization by microbiome-derived and host defense proteins is necessary and sufficient for β cell expansion during pancreas development, potentially connecting microbiome composition with diabetes risk.

Wnt4 is heterogeneously activated in maturing β-cells to control calcium signaling, metabolism and function

Diabetes is a multifactorial disorder characterized by loss or dysfunction of pancreatic β-cells. β-cells are heterogeneous, exhibiting different glucose sensing, insulin secretion and gene expression. They communicate with other endocrine cell types via paracrine signals and between β-cells via gap junctions. Here, we identify the importance of signaling between β-cells via the extracellular signal WNT4. We show heterogeneity in Wnt4 expression, most strikingly in the postnatal maturation period, Wnt4-positive cells, being more mature while Wnt4-negative cells are more proliferative. Knock-out in adult β-cells shows that WNT4 controls the activation of calcium signaling in response to a glucose challenge, as well as metabolic pathways converging to lower ATP/ADP ratios, thereby reducing insulin secretion. These results reveal that paracrine signaling between β-cells is important in addition to gap junctions in controling insulin secretion. Together with previous reports of WNT4 up-regulation in obesity our observations suggest an adaptive insulin response coordinating β-cells.

Regeneration of β-cells of the islet apparatus of the pancreas. Literature review

Diabetes of both type 1 and type 2 is characterized by a progressive loss of β-cell mass, which contributes to the disruption of glucose homeostasis. The optimal antidiabetic therapy would be simple replacement of lost cells, but at present, many researchers have shown that the pancreas (PZ) of adults has a limited regenerative potential. In this regard, significant efforts of researchers are directed to methods of inducing the proliferation of β-cells, stimulating the formation of β-cells from alternative endogenous sources and/or the generation of β-cells from pluripotent stem cells. Factors that regulate β-cell regeneration under physiological or pathological conditions, such as mediators, transcription factors, signaling pathways and potential pharmaceuticals, are also being intensively studied. In this review, we consider recent scientific studies carried out in the field of studying the development and regeneration of insulin-producing cells obtained from exogenous and endogenous sources and their use in the treatment of diabetes. The literature search while writing this review was carried out using the databases of the RSIC, CyberLeninka, Scopus, Web of Science, MedLine, PubMed for the period from 2005 to 2021. using the following keywords: diabetes mellitus, pancreas, regeneration, β-cells, stem cells, diabetes therapy.

Fast Tacrolimus Metabolism Does Not Promote Post-Transplant Diabetes Mellitus after Kidney Transplantation

Post-transplant diabetes mellitus (PTDM) after kidney transplantation induced by tacrolimus is an important issue. Fast tacrolimus metabolism, which can be estimated by concentration-to-dose (C/D) ratio, is associated with increased nephrotoxicity and unfavorable outcomes after kidney transplantation. Herein, we elucidate whether fast tacrolimus metabolism also increases the risk for PTDM. Data from 596 non-diabetic patients treated with tacrolimus-based immunosuppression at the time of kidney transplantation between 2007 and 2015 were retrospectively analyzed. The median follow-up time after kidney transplantation was 4.7 years (IQR 4.2 years). Our analysis was complemented by experimental modeling of fast and slow tacrolimus metabolism kinetics in cultured insulin-producing pancreatic cells (INS-1 cells). During the follow-up period, 117 (19.6%) patients developed PTDM. Of all patients, 210 (35.2%) were classified as fast metabolizers (C/D ratio < 1.05 ng/mL × 1/mg). Fast tacrolimus metabolizers did not have a higher incidence of PTDM than slow tacrolimus metabolizers (p = 0.496). Consistent with this, insulin secretion and the viability of tacrolimus-treated INS-1 cells exposed to 12 h of tacrolimus concentrations analogous to the serum profiles of fast or slow tacrolimus metabolizers or to continuous exposure did not differ (p = 0.286). In conclusion, fast tacrolimus metabolism is not associated with increased incidence of PTDM after kidney transplantation, either in vitro or in vivo. A short period of incubation of INS-1 cells with tacrolimus using different concentration profiles led to comparable effects on cell viability and insulin secretion in vitro. Consistent with this, in our patient, collective fast Tac metabolizers did not show a higher PTDM incidence compared to slow metabolizers.

The Ldb1 transcriptional co-regulator is required for establishment and maintenance of the pancreatic endocrine lineage

Pancreatic islet cell development is regulated by transcription factors (TFs) that mediate embryonic progenitor differentiation toward mature endocrine cells. Prior studies from our lab and others showed that the islet-enriched TF, Islet-1 (Isl1), interacts with the broadly-expressed transcriptional co-regulator, Ldb1, to regulate islet cell maturation and postnhyperatal function (by embryonic day (E)18.5). However, Ldb1 is expressed in the developing pancreas prior to Isl1 expression, notably in multipotent progenitor cells (MPCs) marked by Pdx1 and endocrine progenitors (EPs) expressing Neurogenin-3 (Ngn3). MPCs give rise to the endocrine and exocrine pancreas, while Ngn3⁺ EPs specify pancreatic islet endocrine cells. We hypothesized that Ldb1 is required for progenitor identity in MPC and EP populations during development to impact islet appearance and function. To test this, we generated a whole-pancreas Ldb1 knockout, termed Ldb1^ΔPanc , and observed severe developmental and postnatal pancreas defects including disorganized progenitor pools, a significant reduction of Ngn3-expressing EPs, Pdx1^HI β-cells, and early hormone⁺ cells. Ldb1^ΔPanc neonates presented with severe hyperglycemia, hypoinsulinemia, and drastically reduced hormone expression in islets, yet no change in total pancreas mass. This supports the endocrine-specific actions of Ldb1. Considering this, we also developed an endocrine-enriched model of Ldb1 loss, termed Ldb1^ΔEndo . We observed similar dysglycemia in this model, as well as a loss of islet identity markers. Through in vitro and in vivo chromatin immunoprecipitation experiments, we found that Ldb1 occupies key Pdx1 and Ngn3 promoter domains. Our findings provide insight into novel regulation of endocrine cell differentiation that may be vital toward improving cell-based diabetes therapies.

Disrupting the DREAM complex enables proliferation of adult human pancreatic β cells

Resistance to regeneration of insulin-producing pancreatic β cells is a fundamental challenge for type 1 and type 2 diabetes. Recently, small molecule inhibitors of the kinase DYRK1A have proven effective in inducing adult human β cells to proliferate, but their detailed mechanism of action is incompletely understood. We interrogated our human insulinoma and β cell transcriptomic databases seeking to understand why β cells in insulinomas proliferate, while normal β cells do not. This search reveals the DREAM complex as a central regulator of quiescence in human β cells. The DREAM complex consists of a module of transcriptionally repressive proteins that assemble in response to DYRK1A kinase activity, thereby inducing and maintaining cellular quiescence. In the absence of DYRK1A, DREAM subunits reassemble into the pro-proliferative MMB complex. Here, we demonstrate that small molecule DYRK1A inhibitors induce human β cells to replicate by converting the repressive DREAM complex to its pro-proliferative MMB conformation.

Calcineurin/NFATc2 and PI3K/AKT signaling maintains β-cell identity and function during metabolic and inflammatory stress

Pancreatic islets respond to metabolic and inflammatory stress by producing hormones and other factors that induce adaptive cellular and systemic responses. Here we show that intracellular Ca2+ ([Ca2+]i) and ROS signals generated by high glucose and cytokine-induced ER stress activate calcineurin (CN)/NFATc2 and PI3K/AKT to maintain β-cell identity and function. This was attributed in part by direct induction of the endocrine differentiation gene RFX6 and suppression of several β-cell "disallowed" genes, including MCT1. CN/NFATc2 targeted p300 and HDAC1 to RFX6 and MCT1 promoters to induce and suppress gene transcription, respectively. In contrast, prolonged exposure to stress, hyperstimulated [Ca2+]i, or perturbation of CN/NFATc2 resulted in downregulation of RFX6 and induction of MCT1. These findings reveal that CN/NFATc2 and PI3K/AKT maintain β-cell function during acute stress, but β-cells dedifferentiate to a dysfunctional state upon loss or exhaustion of Ca2+/CN/NFATc2 signaling. They further demonstrate the utility of targeting CN/NFATc2 to restore β-cell function.

Cardiometabolic and Kidney Protection in Kidney Transplant Recipients With Diabetes: Mechanisms, Clinical Applications, and Summary of Clinical Trials

Kidney transplantation is the therapy of choice for patients with end-stage renal disease. Preexisting diabetes is highly prevalent in kidney transplant recipients (KTR), and the development of posttransplant diabetes is common because of a number of transplant-specific risk factors such as the use of diabetogenic immunosuppressive medications and posttransplant weight gain. The presence of pretransplant and posttransplant diabetes in KTR significantly and variably affect the risk of graft failure, cardiovascular disease (CVD), and death. Among the many available therapies for diabetes, there are little data to determine the glucose-lowering agent(s) of choice in KTR. Furthermore, despite the high burden of graft loss and CVD among KTR with diabetes, evidence for strategies offering cardiovascular and kidney protection is lacking. Recent accumulating evidence convincingly shows glucose-independent cardiorenal protective effects in non-KTR with glucose-lowering agents, such as sodium-glucose cotransporter-2 inhibitors and glucagon-like peptide-1 receptor agonists. Therefore, our aim was to review cardiorenal protective strategies, including the evidence, mechanisms, and rationale for the use of these glucose-lowering agents in KTR with diabetes.

New-Onset Diabetes Mellitus (NODM) After Liver Transplantation (LT): The Ultimate Non-diabetogenic Immunosuppressive Therapy

New-onset diabetes mellitus (NODM) is a common long-term complication after liver transplantation (LT). It is thought to be drug-induced in most cases, no matter the underlying disease that cause liver failure and indicated transplantation. Standard post-transplantation (PT) immunosuppressive regimens include prolonged use of calcineurin inhibitors (CNIs), namely tacrolimus (TAC), alongside corticosteroids to avoid acute and chronic graft rejection. This combination is well known for its diabetogenicity. Significant differences between the applied regimens stand out concerning the duration and dosages to prevent the metabolic side effects of these drugs in the long run without compromising the graft's survival. Studies were collected after an extensive research of PubMed database for this very specific topic using the following MeSH keywords in multiple combinations: "Liver Transplantation," "Diabetes Mellitus," "NODM," "Tacrolimus," "Cyclosporine A," and "Steroids." In addition, we used the same keywords for regular searches in Google Scholar. Only the relevant English human studies between 2010 and 2020 were collected except for review articles. Duplicates were eliminated using Mendeley software. Twelve relevant studies directly related to the targeted topic were collected and discussed, including five retrospective cohorts, four prospective cohorts, one clinical trial, one prospective pilot, and one case report. Their topics included primarily the factors increasing the risk of new-onset diabetes mellitus after liver transplantation (NODALT), TAC-based immunosuppression and its relative blood levels affecting the possible development of NODALT, the role of cyclosporine in substituting TAC regimen, and the effect of different steroids-avoiding protocols on the prevention of NODALT. The reviewed studies suggested that lowering the serum concentration of tacrolimus (cTAC) throughout the PT period and eliminating the corticosteroids regimen as early as possible, among other measures, can significantly impact the rate of emergence of NODM. This traditional review tackles the most recent studies about NODALT to establish a comprehensive view on this issue and guide clinicians and researchers for the safest immunosuppressive regimen to date, while maintaining a balanced metabolic profile.

Parathyroid Hormone Promotes Human Umbilical Vein Endothelial Cell Migration and Proliferation Through Orai1-Mediated Calcium Signaling

Parathyroid hormone is the main endocrine regulator of extracellular calcium and phosphorus levels. Secondary hyperparathyroidism–induced endothelial dysfunction may be related to calcium homeostasis disorders. Here, we investigated the effects of parathyroid hormone on human umbilical vein endothelial cells (HUVECs) and characterized the involvement of store-operated Ca²⁺ entry (SOCE) and the nuclear factor of activated T cells (NFAT) signaling pathway. We used immunoblot experiments to find that parathyroid hormone significantly enhanced the expression of the Orai1 channel, a type of channel mediating SOCE, SOCE activity, and Orai1-mediated proliferation of HUVECs but did not increase Orai2 and Orai3. RNA-seq was utilized to identify 1,655 differentially expressed genes (823 upregulated and 832 downregulated) in parathyroid hormone–treated HUVECs as well as enhanced focal adhesion signaling and expression levels of two key genes, namely, COL1A1 and NFATC1. Increased protein and mRNA expression levels of COL1A1 and NFATC1 were confirmed by immunoblotting and quantitative RT-PCR, respectively. Cytosol and nuclei fractionation experiments and immunofluorescence methods were used to show that parathyroid hormone treatment increased NFATC1 nuclear translocation, which was inhibited by a calcineurin inhibitor (CsA), a selective calmodulin antagonist (W7), an Orai channel inhibitor (BTP2), or Orai1 small interfering RNA (siRNA) transfection. Parathyroid hormone also increased COL1A1 expression, cell migration, and proliferation of HUVECs. The PTH-induced increase in HUVEC migration and proliferation were inhibited by CsA, W7, BTP2, or COL1A1 siRNA transfection. These findings indicated that PTH increased Orai1 expression and Orai1-mediated SOCE, causing the nuclear translocation of NFATC1 to increase COL1A1 expression and COL1A1-mediated HUVEC migration and proliferation. These results suggest potential key therapeutic targets of Orai1 and the downstream calmodulin/calcineurin/NFATC1/COL1A1 signaling pathway in parathyroid hormone–induced endothelial dysfunction and shed light on underlying mechanisms that may be altered to prevent or treat secondary hyperparathyroidism–associated cardiovascular disease.

Dynamic changes in β-cell [Ca2+] regulate NFAT activation, gene transcription, and islet gap junction communication

OBJECTIVE

Diabetes occurs because of insufficient insulin secretion due to β-cell dysfunction within the islet of Langerhans. Elevated glucose levels trigger β-cell membrane depolarization, action potential generation, and slow sustained free-Ca2+ ([Ca2+]) oscillations, which trigger insulin release. Nuclear factor of activated T-cell (NFAT) is a transcription factor, which is regulated by the increases in [Ca2+] and calceineurin (CaN) activation. NFAT regulation links cell activity with gene transcription in many systems and regulates proliferation and insulin granule biogenesis within the β-cell. However, the link between the regulation of β-cell electrical activity and oscillatory [Ca2+] dynamics with NFAT activation and downstream transcription is poorly understood. Here, we tested whether dynamic changes to β-cell electrical activity and [Ca2+] regulate NFAT activation and downstream transcription.

METHODS

In cell lines, mouse islets, and human islets, including those from donors with type 2 diabetes, we applied both agonists/antagonists of ion channels together with optogenetics to modulate β-cell electrical activity. We measured the dynamics of [Ca2+] and NFAT activation as well as performed whole transcriptome and functional analyses.

RESULTS

Both glucose-induced membrane depolarization and optogenetic stimulation triggered NFAT activation as well as increased the transcription of NFAT targets and intermediate early genes (IEGs). Importantly, slow, sustained [Ca2+] oscillation conditions led to NFAT activation and downstream transcription. In contrast, in human islets from donors with type2 diabetes, NFAT activation by glucose was diminished, but rescued upon pharmacological stimulation of electrical activity. NFAT activation regulated GJD2 expression and increased Cx36 gap junction permeability upon elevated oscillatory [Ca2+] dynamics. However, it is unclear if NFAT directly binds the GJD2 gene to regulate expression.

CONCLUSIONS

This study provides an insight into the specific patterns of electrical activity that regulate NFAT activation, gene transcription, and islet function. In addition, it provides information on how these factors are disrupted in diabetes.

Gypenoside A attenuates dysfunction of pancreatic β cells by activating PDX1 signal transduction via the inhibition of miR-150-3p both in vivo and in vitro

Saponin gypenoside A (GP) has shown its potential to handle diabetes mellitus. MicroRNA-150-3p (miR-150-3p) is closely related to the dysfunction of pancreatic β cells by targeting PDX1. Given the function of GP is related to its regulation on different miRs, the current study assessed the role of miR-150-3p as a therapeutic target for the hypoglycemic effects of GP. Pancreatic β cell dysfunction was induced in mice using the high-fatty diet (HFD) method and then handled with GP. Changes in insulin release and resistance and the activity of the miR-150-3p/PDX1 axis were detected. The expression of miR-150-3p was induced to confirm its central in the effects of GP. The results of in vivo tests were then validated with in vitro assays. HFD administration suppressed glucose tolerance, delayed insulin release, and induced insulin resistance and pancreas apoptosis in mice, which was indicative of the dysfunction of β pancreatic cells. Changes in pancreatic β function were associated with the increased expression of miR-150-3p and suppressed expression of PDX1. After the administration of GP, the impairments of the pancreas were alleviated and the expression of miR-150-3p was inhibited, contributing to the restored level of PDX1. The injection of miR-150-3p agomir counteracted the protective effects of GP. In in vitro assays, the pretransfection of miR-150-3p mimetics also counteracted the protective effects of GP on pancreatic β cells against palmitic acid. Collectively, miR-150-3p played a key role in the protective effects of GP against pancreatic β cell dysfunction by inhibiting PDX1 expression.

Dysregulation of β-Cell Proliferation in Diabetes: Possibilities of Combination Therapy in the Development of a Comprehensive Treatment

Diabetes mellitus (DM) is a metabolic disorder characterized by chronic hyperglycemia as a result of insufficient insulin levels and/or impaired function as a result of autoimmune destruction or insulin resistance. While Type 1 DM (T1DM) and Type 2 DM (T2DM) occur through different pathological processes, both result in β-cell destruction and/or dysfunction, which ultimately lead to insufficient β-cell mass to maintain normoglycemia. Therefore, therapeutic agents capable of inducing β-cell proliferation is crucial in treating and reversing diabetes; unfortunately, adult human β-cell proliferation has been shown to be very limited (~0.2% of β-cells/24 h) and poorly responsive to many mitogens. Furthermore, diabetogenic insults result in damage to β cells, making it ever more difficult to induce proliferation. In this review, we discuss β-cell mass/proliferation pathways dysregulated in diabetes and current therapeutic agents studied to induce β-cell proliferation. Furthermore, we discuss possible combination therapies of proliferation agents with immunosuppressants and antioxidative therapy to improve overall long-term outcomes of diabetes.

Heme oxygenase-1 gene delivery for altering high mobility group box-1 protein in pancreatic islet

Pancreatic islet transplantation is a promising strategy for the treatment of type I diabetes. High-mobility group box-1 (HMGB1), highly expressed in islet cells, is a potent immune stimulator in immune rejection. Heme oxygenase-1 (HO1) gene therapy can modulate the release of HMGB1 by altering intracellular molecules for successful cell transplantation. After delivery of the heme oxygenase-1 (HO1) gene to islet cells using an adeno-associated viral vector (AAV), it was evaluated the changes in cytoplasmic Ca²⁺ ions and calcineurin activity as well as histone acetyltransferase (HAT) and Poly(ADP) ribose polymerase-1 (PARP-1). Inhibition of HMGB1 release was evaluated through altering these intracellular molecules. Then, after transplantation of HO1-transduced islets, the therapeutic effect of them was evaluated through measuring blood glucose level to diabetic mice and through immunohistochemical analysis. The transduced HO1 gene significantly inhibited HMGB1 release in islets that was under the cell damage by hypoxia exposure. It was confirmed that this result was initially due to the decrease in cytoplasmic Ca²⁺ ion concentration and calcineurin activity. In addition, the delivered HO1 gene simultaneously reduced the activity of HAT and PARP-1, which are involved in the translocation of HMGB1 from the nucleus to the cytoplasm. As a result, when the HO1 gene-transduced islets were transplanted into diabetic mice, the treatment efficiency of diabetes was effectively improved by increasing the survival rate of the islets. Collectively, these results suggest that HO1 gene transfer can be used for successful islet transplantation by altering the activity of intracellular signal molecules and reducing HMGB1 release.

Posttransplant Diabetes Mellitus and Immunosuppression Selection in Older and Obese Kidney Recipients

Rationale & Objective

Posttransplant diabetes mellitus (DM) after kidney transplantation increases morbidity and mortality, particularly in older and obese recipients. We aimed to examine the impact of immunosuppression selection on the risk of posttransplant DM among both older and obese kidney transplant recipients.

Study Design

Retrospective database study.

Setting & Participants

Kidney-only transplant recipients aged ≥18 years from 2005 to 2016 in the United States from US Renal Data System records, which integrate Organ Procurement and Transplantation Network/United Network for Organ Sharing records with Medicare billing claims.

Exposures

Various immunosuppression regimens in the first 3 months after transplant.

Outcomes

Development of DM >3 months-to-1 year posttransplant.

Analytical Approach

We used multivariable Cox regression to compare the incidence of posttransplant DM by immunosuppression regimen with the reference regimen of thymoglobulin (TMG) or alemtuzumab (ALEM) with tacrolimus + mycophenolic acid + prednisone using inverse propensity weighting.

Results

12.7% of kidney transplant recipients developed posttransplant DM with higher incidences in older (≥55 years vs <55 years: 16.7% vs 10.1%) and obese (body mass index [BMI] ≥ 30 kg/m² vs BMI < 30 kg/m²: 17.1% vs 10.9%) patients. The incidence of posttransplant DM was lower with steroid avoidance [TMG/ALEM + no prednisone (8.4%) and IL2rAb + no prednisone (9.7%)] than TMG/ALEM with triple therapy (13.1%). After adjustment for donor and recipient characteristics, TMG/ALEM with steroid avoidance was beneficial for all groups [age < 55 years: adjusted HR (aHR), 0.63 (95% confidence interval [CI], 0.54-0.72); age ≥ 55 years: aHR, 0.69 (95% CI, 0.60-0.79); BMI < 30 kg/m²: aHR, 0.69 (95% CI, 0.60-0.78); BMI ≥ 30 kg/m²: aHR, 0.67 (95% CI, 0.57-0.79)]. However, IL2rAb with steroid avoidance was beneficial only for older patients (aHR, 0.76; 95% CI, 0.58-0.99) and for those with BMI < 30 kg/m² (aHR, 0.63; 95% CI, 0.46-0.87).

Limitations

Retrospective study and lacked data on immunosuppression levels.

Conclusions

The beneficial impact of steroid avoidance using tacrolimus on posttransplant DM appears to differ by patient age and induction regimen.

Protein phosphatase 2A in the healthy and failing heart: New insights and therapeutic opportunities

Protein phosphatases have emerged as critical regulators of phosphoprotein homeostasis in settings of health and disease. Protein phosphatase 2A (PP2A) encompasses a large subfamily of enzymes that remove phosphate groups from serine/threonine residues within phosphoproteins. The heterogeneity in PP2A structure, which arises from the grouping of different catalytic, scaffolding and regulatory subunit isoforms, creates distinct populations of catalytically active enzymes (i.e. holoenzymes) that localise to different parts of the cell. This structural complexity, combined with other regulatory mechanisms, such as interaction of PP2A heterotrimers with accessory proteins and post-translational modification of the catalytic and/or regulatory subunits, enables PP2A holoenzymes to target phosphoprotein substrates in a highly specific manner. In this review, we summarise the roles of PP2A in cardiac physiology and disease. PP2A modulates numerous processes that are vital for heart function including calcium handling, contractility, β-adrenergic signalling, metabolism and transcription. Dysregulation of PP2A has been observed in human cardiac disease settings, including heart failure and atrial fibrillation. Efforts are underway, particularly in the cancer field, to develop therapeutics targeting PP2A activity. The development of small molecule activators of PP2A (SMAPs) and other compounds that selectively target specific PP2A holoenzymes (e.g. PP2A/B56α and PP2A/B56ε) will improve understanding of the function of different PP2A species in the heart, and may lead to the development of therapeutics for normalising aberrant protein phosphorylation in settings of cardiac remodelling and dysfunction.

The Pancreatic ß-cell Response to Secretory Demands and Adaption to Stress

Pancreatic β cells dedicate much of their protein translation capacity to producing insulin to maintain glucose homeostasis. In response to increased secretory demand, β cells can compensate by increasing insulin production capability even in the face of protracted peripheral insulin resistance. The ability to amplify insulin secretion in response to hyperglycemia is a critical facet of β-cell function, and the exact mechanisms by which this occurs have been studied for decades. To adapt to the constant and fast-changing demands for insulin production, β cells use the unfolded protein response of the endoplasmic reticulum. Failure of these compensatory mechanisms contributes to both type 1 and 2 diabetes. Additionally, studies in which β cells are "rested" by reducing endogenous insulin demand have shown promise as a therapeutic strategy that could be applied more broadly. Here, we review recent findings in β cells pertaining to the metabolic amplifying pathway, the unfolded protein response, and potential advances in therapeutics based on β-cell rest.

Identification of direct transcriptional targets of NFATC2 that promote β cell proliferation

The transcription factor NFATC2 induces β cell proliferation in mouse and human islets. However, the genomic targets that mediate these effects have not been identified. We expressed active forms of Nfatc2 and Nfatc1 in human islets. By integrating changes in gene expression with genomic binding sites for NFATC2, we identified approximately 2200 transcriptional targets of NFATC2. Genes induced by NFATC2 were enriched for transcripts that regulate the cell cycle and for DNA motifs associated with the transcription factor FOXP. Islets from an endocrine-specific Foxp1, Foxp2, and Foxp4 triple-knockout mouse were less responsive to NFATC2-induced β cell proliferation, suggesting the FOXP family works to regulate β cell proliferation in concert with NFATC2. NFATC2 induced β cell proliferation in both mouse and human islets, whereas NFATC1 did so only in human islets. Exploiting this species difference, we identified approximately 250 direct transcriptional targets of NFAT in human islets. This gene set enriches for cell cycle-associated transcripts and includes Nr4a1. Deletion of Nr4a1 reduced the capacity of NFATC2 to induce β cell proliferation, suggesting that much of the effect of NFATC2 occurs through its induction of Nr4a1. Integration of noncoding RNA expression, chromatin accessibility, and NFATC2 binding sites enabled us to identify NFATC2-dependent enhancer loci that mediate β cell proliferation.

Diabetes in Kidney Transplantation

Diabetes mellitus (DM) is one of the most common complications after kidney transplantation and is associated with unfavorable outcomes including death. DM can be present before transplant but post-transplant DM (PTDM) refers to diabetes that is diagnosed after solid organ transplantation. Despite its high prevalence, optimal treatment to prevent complications of PTDM is unknown. Medical therapy of pre-existent DM or PTDM after transplant is challenging because of frequent interactions between antidiabetic and immunosuppressive agents. There is also frequent need for medication dose adjustments due to residual kidney disease and a higher risk of medication side effects in patients treated with immunosuppressive agents. Sodium-glucose cotransporter 2 inhibitors have demonstrated a favorable cardio-renal profile in patients with DM without a transplant and hence hold great promise in this patient population although there is concern about the higher risk of urinary tract infections. The significant gaps in our understanding of the pathophysiology, diagnosis, and management of DM after kidney transplantation need to be urgently addressed.