Prediction of Tuberculosis From Lung Tissue Images of Diversity Outbred Mice Using Jump Knowledge Based Cell Graph Neural Network.

Tuberculosis (TB), primarily affecting the lungs, is caused by the bacterium Mycobacterium tuberculosis and poses a significant health risk. Detecting acid-fast bacilli (AFB) in stained samples is critical for TB diagnosis. Whole Slide (WS) Imaging allows for digitally examining these stained samples. However, current deep-learning approaches to analyzing large-sized whole slide images (WSIs) often employ patch-wise analysis, potentially missing the complex spatial patterns observed in the granuloma essential for accurate TB classification. To address this limitation, we propose an approach that models cell characteristics and interactions as a graph, capturing both cell-level information and the overall tissue micro-architecture. This method differs from the strategies in related cell graph-based works that rely on edge thresholds based on sparsity/density in cell graph construction, emphasizing a biologically informed threshold determination instead. We introduce a cell graph-based jumping knowledge neural network (CG-JKNN) that operates on the cell graphs where the edge thresholds are selected based on the length of the mycobacteria's cords and the activated macrophage nucleus's size to reflect the actual biological interactions observed in the tissue. The primary process involves training a Convolutional Neural Network (CNN) to segment AFBs and macrophage nuclei, followed by converting large (42831*41159 pixels) lung histology images into cell graphs where an activated macrophage nucleus/AFB represents each node within the graph and their interactions are denoted as edges. To enhance the interpretability of our model, we employ Integrated Gradients and Shapely Additive Explanations (SHAP). Our analysis incorporated a combination of 33 graph metrics and 20 cell morphology features. In terms of traditional machine learning models, Extreme Gradient Boosting (XGBoost) was the best performer, achieving an F1 score of 0.9813 and an Area under the Precision-Recall Curve (AUPRC) of 0.9848 on the test set. Among graph-based models, our CG-JKNN was the top performer, attaining an F1 score of 0.9549 and an AUPRC of 0.9846 on the held-out test set. The integration of graph-based and morphological features proved highly effective, with CG-JKNN and XGBoost showing promising results in classifying instances into AFB and activated macrophage nucleus. The features identified as significant by our models closely align with the criteria used by pathologists in practice, highlighting the clinical applicability of our approach. Future work will explore knowledge distillation techniques and graph-level classification into distinct TB progression categories.

Toward Continuous-Flow Hyperpolarisation of Metabolites via Heterogenous Catalysis, Side-Arm-Hydrogenation, and Membrane Dissolution of Parahydrogen.

Side-arm hydrogenation (SAH) by homogeneous catalysis has extended the reach of the parahydrogen enhanced NMR technique to key metabolites such as pyruvate. However, homogeneous hydrogenation requires rapid separation of the dissolved catalyst and purification of the hyperpolarised species with a purity sufficient for safe in-vivo use. An alternate approach is to employ heterogeneous hydrogenation in a continuous-flow reactor, where separation from the solid catalysts is straightforward. Using a TiO2 -nanorod supported Rh catalyst, we demonstrate continuous-flow parahydrogen enhanced NMR by heterogeneous hydrogenation of a model SAH precursor, propargyl acetate, at a flow rate of 1.5 mL/min. Parahydrogen gas was introduced into the flowing solution phase using a novel tube-in-tube membrane dissolution device. Without much optimization, proton NMR signal enhancements of up to 297 (relative to the thermal equilibrium signals) at 9.4 Tesla were shown to be feasible on allyl-acetate at a continuous total yield of 33 %. The results are compared to those obtained with the standard batch-mode technique of parahydrogen bubbling through a suspension of the same catalyst.

Ultra-Low Loading Pt/CeO2 Catalysts: Ceria Facet Effect Affords Improved Pairwise Selectivity for Parahydrogen Enhanced NMR Spectroscopy.

Oxide supports with well-defined shapes enable investigations on the effects of surface structure on metal-support interactions and correlations to catalytic activity and selectivity. Here, a modified atomic layer deposition technique was developed to achieve ultra-low loadings (8-16 ppm) of Pt on shaped ceria nanocrystals. Using octahedra and cubes, which expose exclusively (111) and (100) surfaces, respectively, the effect of CeO2 surface facet on Pt-CeO2 interactions under reducing conditions was revealed. Strong electronic interactions result in electron-deficient Pt species on CeO2 (111) after reduction, which increased the stability of the atomically dispersed Pt. This afforded significantly higher NMR signal enhancement in parahydrogen-induced polarization experiments compared with the electron-rich platinum on CeO2 (100), and a factor of two higher pairwise selectivity (6.1 %) in the hydrogenation of propene than any previously reported monometallic heterogeneous Pt catalyst.

Author Correction: Succinate promotes stem cell migration through the GPR91-dependent regulation of DRP1-mediated mitochondrial fission.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Succinate promotes stem cell migration through the GPR91-dependent regulation of DRP1-mediated mitochondrial fission.

The role of metabolites produced from stem cell metabolism has been emerged as signaling molecules to regulate stem cell behaviors such as migration. The mitochondrial morphology is closely associated with the metabolic balance and stem cell function. However, the physiological role of succinate on human mesenchymal stem cell (hMSC) migration by regulating the mitochondrial morphology remains unclear. Here, we investigate the effect of succinate on hMSC migration via regulation of mitochondrial dynamics and its related signaling pathway. Succinate (50 µM) significantly accelerates hMSC migration. Succinate increases phosphorylation of pan-PKC, especially the atypical PKCζ level which was blocked by the knockdown of Gαq and Gα12. Activated PKCζ subsequently phosphorylates p38 MAPK. Cytosolic DRP1 is phosphorylated by p38 MAPK and results in DRP1 translocation to the mitochondria outer membrane, eventually inducing mitochondrial fragmentation. Mitochondrial fission-induced mitochondrial function elevates mitochondrial ROS (mtROS) levels and activates Rho GTPases, which then induces F-actin formation. Furthermore, in a skin excisional wound model, we found the effects of succinate-pretreated hMSC enhanced wound closure, vascularization and re-epithelialization and confirmed that DRP1 has a vital role in injured tissue regeneration. Overall, succinate promotes DRP1-mediated mitochondrial fission via GPR91, consequently stimulating the hMSC migration through mtROS-induced F-actin formation.

Photoreduction of Graphene Oxide and Photochemical Synthesis of Graphene-Metal Nanoparticle Hybrids by Ketyl Radicals.

The photoreduction of graphene oxide (GO) using ketyl radicals is demonstrated for the first time. The use of photochemical reduction through ketyl radicals generated by I-2959 or (1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one) is interesting because it affords spatial and temporal control of the reduction process. Graphene-metal nanoparticle hybrids of Ag, Au, and Pd were also photochemically fabricated in a one-pot procedure. Comprehensive spectroscopic and imaging techniques were carried out to fully characterize the materials. The nanoparticle hybrids showed promising action for the catalytic degradation of model environmental pollutants, namely, 4-nitrophenol, Rose Bengal, and Methyl Orange. The process described can be extended to polymer nanocomposites that can be photopatterned and could be potentially extended to fabricating plastic electronic devices.

Reduction in new-onset diabetes mellitus after renal transplant with erythropoietin-stimulating agents: a retrospective cohort study.

BACKGROUND: Studies have shown that erythropoietin-stimulating agents (ESAs) protect mice against the development of diabetes through direct effects on pancreatic ß cells. However, the effect of ESAs on the incidence of diabetes in humans has not been well studied. It is unknown whether exposure to ESAs is associated with a reduced incidence of new-onset diabetes after transplant (NODAT). OBJECTIVE: The objective of this study is to examine the relationship between ESA exposure post-renal transplant and the development of NODAT. DESIGN: We performed a single center, retrospective cohort analysis. PATIENTS: We compared patients who received a first live or deceased donor renal allograft, with any exposure to an ESA vs. those without such exposure and who developed NODAT and who did not. Patients with a prior history of diabetes mellitus or multi-organ transplant, including a second renal transplant were excluded. MEASUREMENTS AND METHODS: NODAT was defined based on the 2008 Canadian Diabetes Association criteria. Multivariate logistic regression analysis was performed to determine factors independently associated with NODAT. RESULTS: One hundred thirty-two (29 %) patients were exposed to an ESA, four of which developed NODAT compared to 128 who did not develop NODAT (p < 0.0001). Of those not exposed to an ESA, 15 % (48/319) developed NODAT. By Fisher's exact test, exposure to an ESA at any time post-transplant reduced the risk of developing NODAT; odds ratio (OR) = 0.08, 95 % confidence interval (CI) (0.018-0.352), p = 0.0008. Older age; OR = 1.41, 95 % CI (1.036-1.933), p < 0.02, higher random blood sugar at discharge; OR = 1.30, 95 % CI (1.077-1.57), p < 0.006 and deceased donor; OR 2.18 CI (1.009-4.729), p = 0.04 were associated with an increased risk of NODAT. LIMITATIONS: The limitations of this study include its retrospective nature, single center, and homogenous population; thus, generalizability of the results must be approached with caution. CONCLUSION: ESA exposure may be associated with a reduced incidence of NODAT in the post-renal transplant population. The role of ESA in preventing NODAT requires further investigation.

MISE EN CONTEXTE: Des études ont démontré que les agents stimulant l'érythropoïèse (ASE) protègent les souris contre le développement du diabète par leur action directe sur les cellules bêta du pancréas. Toutefois, l'effet des ASE sur l'incidence du diabète chez l'humain n'a pas fait l'objet d'études approfondies. On ignore toujours si l'exposition aux ASE est associée à une réduction de l'incidence de l'apparition du diabète sucré post-transplantation (DSPT). OBJECTIFS DE L'ÉTUDE: Cette étude visait à évaluer la relation entre l'exposition aux ASE à la suite d'une greffe de rein et la survenue du DSPT. MODÈLE D'ÉTUDE: Il s'agit d'une étude de cohorte rétrospective qui s'est tenue dans un seul centre. PARTICIPANTS: Nous avons comparé les cas de patients qui recevaient une première allogreffe de rein, d'un donneur vivant ou décédé. Les comparaisons ont porté sur la présence ou l'absence d'une exposition aux ASE à la suite de la transplantation et sur le fait de développer ou non un DSPT conséquemment. Les patients ayant un historique de diabète sucré ou ayant subi une transplantation multiorganes dans le passé, y compris une deuxième greffe de rein, ont été exclus de l'étude. MÉTHODOLOGIE: La manifestation d'un DSPT a été déterminée selon des critères établis par l'Association Canadienne du Diabète en 2008. L'analyse par régression logistique multivariée a été utilisée pour déterminer les facteurs indépendamment liés au DSPT. RÉSULTATS: Sur les 132 patients (29 %) exposés aux ASE à la suite de la greffe, seuls quatre ont développé un DSPT (p < 0,000 1). Des patients qui n'avaient pas été exposés aux ASE, 15 % (48/319) ont développé un DSPT. Selon le test exact de Fisher, l'exposition à un ASE, peu importe le moment après la transplantation, a eu pour effet de réduire le risque de développer un DSPT [rapport de cote (RC) = 0,08 ; intervalle de confiance (IC) à 95 % (0,018-0,352), p = 0, 000 8]. Parmi les facteurs associés à un risque élevé de développer un DSPT, on note l'âge avancé du patient [RC = 1,41 ; IC à 95 % (1,036-1,933), p < 0,02], une glycémie aléatoire plus élevée à la sortie de l'hôpital [RC = 1,30 ; IC à 95 % (1,077-1,57), p < 0,006] et la transplantation d'un greffon provenant d'un donneur cadavérique [RC = 2,18 ; IC à 95 % (1,009-4,729), p = 0.04]. LIMITES DE L'ÉTUDE: Cette étude est limitée par sa nature rétrospective et par le fait qu'elle ait été menée à l'intérieur d'un seul centre et au sein d'une population homogène. Par conséquent, la généralisabilité des résultats doit être abordée avec prudence. CONCLUSIONS: L'exposition aux ASE pourrait être associée à une réduction de l'incidence du DSPT au sein de la population des receveurs d'une greffe de rein. Le rôle des ASE dans la prévention du DSPT exige des recherches plus poussées.

Differences in the clinical characteristics of ethnic minority groups with heart failure managed in specialized heart failure clinics.

OBJECTIVES: The purpose of our study was to compare the clinical features of Chinese and South Asians, the 2 largest minority populations in Canada, with non-Chinese/non-South Asian (NCH/NSA) patients managed in common social macroenvironments and healthcare systems. BACKGROUND: Heart failure is an increasingly prevalent condition. Although ethnic minorities comprise a growing proportion of the population in Western countries, the clinical profiles of ethnic minorities with heart failure are largely unknown. METHODS: We analyzed records of patients with heart failure managed in 2 specialized clinics in Ontario, Canada. Of the 1,671 patients, 181 (11%) were identified as Chinese and 215 (13%) as South Asian. RESULTS: Our analyses showed that fewer Chinese patients were found to have a history of myocardial infarction (MI) (30% vs. 52%), 3 occluded/stenosed coronary vessels on angiogram (47% vs. 51%), grade 3 or worse left ventricular dysfunction (22% vs. 42%), and a prescription of angiotensin-converting enzyme inhibitors (42% vs. 63%) compared with their NCH/NSA counterparts. In contrast, South Asian patients more frequently had a past history of an MI (70% vs. 52%), 3 occluded/stenosed coronary vessels on angiogram (68% vs. 51%), and treatment with coronary revascularizations (55% vs. 40%) compared with NCH/NSA patients. CONCLUSIONS: Our study demonstrates important differences in comorbid conditions, clinical characteristics, and treatment patterns among Chinese and South Asian patients compared with NCH/NSA patients with heart failure. Awareness of these differences will help to develop differential strategies necessary to prevent and manage heart failure among ethnic minority groups.

In vivo knockdown of adipocyte erythropoietin receptor does not alter glucose or energy homeostasis.

The growing prevalence of obesity and diabetes necessitate a better understanding of the role of adipocyte biology in metabolism. Increasingly, erythropoietin (EPO) has been shown to have extraerythropoietic and cytoprotective roles. Exogenous administration has recently been shown to have beneficial effects on obesity and diabetes in mouse models and EPO can modulate adipogenesis and insulin signaling in 3T3-L1 adipocytes. However, its physiological role in adipocytes has not been identified. Using male and female mice with adipose tissue-specific knockdown of the EPO receptor, we determine that adipocyte EPO signaling is not essential for the maintenance of energy homeostasis or glucose metabolism. Adipose tissue-specific disruption of EPO receptor did not alter adipose tissue expansion, adipocyte morphology, insulin resistance, inflammation, or angiogenesis in vivo. In contrast to the pharmacological effects of EPO, we demonstrate that EPO signaling at physiological levels is not essential for adipose tissue regulation of metabolism.

Dual role of VAMP8 in regulating insulin exocytosis and islet ß cell growth.

Optimal insulin secretion required to maintain glucose homeostasis is the summation of total pancreatic islet ß cell mass and intrinsic secretory capacity of individual ß cells, which are regulated by distinct mechanisms that could be amplified by glucagon-like-peptide-1 (GLP-1). Because of these actions of GLP-1 on islet ß cells, GLP-1 has been deployed to treat diabetes. We employed SNARE protein VAMP8-null mice to demonstrate that VAMP8 mediates insulin granule recruitment to the plasma membrane, which partly accounts for GLP-1 potentiation of glucose-stimulated insulin secretion. VAMP8-null mice also exhibited increased islet ß cell mass from increased ß cell mitosis, with ß cell proliferative activity greatly amplified by GLP-1. Thus, despite the ß cell exocytotic defect, VAMP8-null mice have an increased total insulin secretory capacity, which improved glucose homeostasis. We conclude that these VAMP8-mediated events partly underlie the therapeutic actions of GLP-1 on insulin secretion and ß cell growth.

In vivo role of focal adhesion kinase in regulating pancreatic ß-cell mass and function through insulin signaling, actin dynamics, and granule trafficking.

Focal adhesion kinase (FAK) acts as an adaptor at the focal contacts serving as a junction between the extracellular matrix and actin cytoskeleton. Actin dynamics is known as a determinant step in insulin secretion. Additionally, FAK has been shown to regulate insulin signaling. To investigate the essential physiological role of FAK in pancreatic ß-cells in vivo, we generated a transgenic mouse model using rat insulin promoter (RIP)-driven Cre-loxP recombination system to specifically delete FAK in pancreatic ß-cells. These RIPcre(+)fak(fl/fl) mice exhibited glucose intolerance without changes in insulin sensitivity. Reduced ß-cell viability and proliferation resulting in decreased ß-cell mass was observed in these mice, which was associated with attenuated insulin/Akt (also known as protein kinase B) and extracellular signal-related kinase 1/2 signaling and increased caspase 3 activation. FAK-deficient ß-cells exhibited impaired insulin secretion with normal glucose sensing and preserved Ca(2+) influx in response to glucose, but a reduced number of docked insulin granules and insulin exocytosis were found, which was associated with a decrease in focal proteins, paxillin and talin, and an impairment in actin depolymerization. This study is the first to show in vivo that FAK is critical for pancreatic ß-cell viability and function through regulation in insulin signaling, actin dynamics, and granule trafficking.

Hepatocyte-specific deletion of Janus kinase 2 (JAK2) protects against diet-induced steatohepatitis and glucose intolerance.

Non-alcoholic fatty liver disease (NAFLD) is becoming the leading cause of chronic liver disease and is now considered to be the hepatic manifestation of the metabolic syndrome. However, the role of steatosis per se and the precise factors required in the progression to steatohepatitis or insulin resistance remain elusive. The JAK-STAT pathway is critical in mediating signaling of a wide variety of cytokines and growth factors. Mice with hepatocyte-specific deletion of Janus kinase 2 (L-JAK2 KO mice) develop spontaneous steatosis as early as 2 weeks of age. In this study, we investigated the metabolic consequences of jak2 deletion in response to diet-induced metabolic stress. To our surprise, despite the profound hepatosteatosis, deletion of hepatic jak2 did not sensitize the liver to accelerated inflammatory injury on a prolonged high fat diet (HFD). This was accompanied by complete protection against HFD-induced whole-body insulin resistance and glucose intolerance. Improved glucose-stimulated insulin secretion and an increase in ß-cell mass were also present in these mice. Moreover, L-JAK2 KO mice had progressively reduced adiposity in association with blunted hepatic growth hormone signaling. These mice also exhibited increased resting energy expenditure on both chow and high fat diet. In conclusion, our findings indicate a key role of hepatic JAK2 in metabolism such that its absence completely arrests steatohepatitis development and confers protection against diet-induced systemic insulin resistance and glucose intolerance.

The redundant role of JAK2 in regulating pancreatic ß-cell mass.

Janus kinase (JAK) 2 is a non-receptor tyrosine kinase that mediates the downstream effects of various growth factors, including growth hormone, prolactin, placental lactogen, and erythropoietin (EPO). EPO is a hematopoietic growth factor that is largely known for its role in promoting proliferation, differentiation and survival of cells in the erythroid lineage. Global loss of the EPO receptor (EPO-R) has been shown to be embryonically lethal in mice due to anemia attributed to defects in erythropoiesis. Interesting, mice with global deficiency of JAK2 share a similar developmental phenotype as the EPO-R knockout mice, demonstrating that JAK2 is essential in eliciting the biological effects of EPO, particularly in erythrocytosis. Recent studies from our group have shown that exogenous EPO protects mice against diabetes through direct effects on pancreatic ß-cells, and these protective effects are dependent on the presence of JAK2 in the ß-cells. Here, we briefly highlight the cytoprotective effects of exogenous EPO in the pancreatic ß-cells as well as our new findings on the redundant role of JAK2 in ß-cell expansion after high-fat feeding in mice.

Redundant role of the cytochrome c-mediated intrinsic apoptotic pathway in pancreatic ß-cells.

Cytochrome c is one of the central mediators of the mitochondrial or the intrinsic apoptotic pathway. Mice harboring a 'knock-in' mutation of cytochrome c, impairing only its apoptotic function, have permitted studies on the essential role of cytochrome c-mediated apoptosis in various tissue homeostasis. To this end, we examined the role of cytochrome c in pancreatic ß-cells under homeostatic conditions and in diabetes models, including those induced by streptozotocin (STZ) and c-Myc. Previous studies have shown that both STZ- and c-Myc-induced ß-cell apoptosis is mediated through caspase-3 activation; however, the precise mechanism in these modes of cell death was not characterized. The results of our study show that lack of functional cytochrome c does not affect glucose homeostasis or pancreatic ß-cell mass under basal conditions. Moreover, the cytochrome c-mediated intrinsic apoptotic pathway is required for neither STZ- nor c-Myc-induced ß-cell death. We also observed that the extrinsic apoptotic pathway mediated through caspase-8 was not essential in c-Myc-induced ß-cell destruction. These findings suggest that cytochrome c is not required for STZ-induced ß-cell apoptosis and, together with the caspase-8-mediated extrinsic pathway, plays a redundant role in c-Myc-induced ß-cell apoptosis.

The extra-hematopoietic role of erythropoietin in diabetes mellitus.

Diabetes mellitus is a complex metabolic disorder characterized by chronic hyperglycemia and vascular complications, leading to significant morbidity and mortality. All forms of diabetes are ultimately related to insufficient functional pancreatic ß-cell mass to maintain euglycemia. In this context, the promotion of ß-cell survival and function is a fundamental issue of direct relevance to diabetes prevention and treatment. Although first identified as a hematopoietic factor that promotes erythropoiesis and erythrocyte survival, an accumulating body of evidence suggests that erythropoietin (EPO) may also exert cytoprotective effects on non-erythroid tissues, including the brain, kidney, blood vessels, and pancreatic ß cells. Recent reports have demonstrated the biological effects of EPO on the pancreatic ß cells and its potential preventative and therapeutic role in diabetes. This review will focus on the emerging extra-hematopoietic roles of EPO and its potential protective role in diabetes.

Vhl is required for normal pancreatic ß cell function and the maintenance of ß cell mass with age in mice.

Type 2 diabetes is hallmarked by insulin resistance and insufficient ß-cell function. Islets of type 2 diabetes patients have been shown to have decreased hypoxia-inducible factor (HIF)-1α/ß expression. Target genes of the HIF pathway are involved in angiogenesis, survival, proliferation, and energy metabolism, and von Hippel-Lindau protein (VHL) is a negative regulator of this pathway. We hypothesized that increased HIF-mediated gene transcription by VHL deletion in the ß-cells would increase ß-cell mass and function. We generated ß-cell-specific VHL-knockout mice using the Cre-loxP recombination system driven by the rat insulin promoter to assess the role of VHL in glucose homeostasis and ß-cell function. VHL deletion in the pancreatic ß-cells led to impaired glucose tolerance due to defects in glucose-stimulated insulin secretion and ß-cell mass with age. VHL-knockout islets had decreased GLUT2, but increased glucose transporter 1 and vascular endothelial growth factor expression. Furthermore, there were significant aberrations in islet morphology in the VHL-knockout mice, likely due to increased islet vasculature. Given that erythropoietin (EPO) is a target gene of the HIF pathway, which is not expressed in islets, we tested whether activating EPO signaling by systemic administration with recombinant human EPO (rHuEPO) can overcome the ß-cell defects that occurred with VHL loss. We observed improved glucose tolerance and restoration of GLUT2 expression in VHL-deficient ß-cells in response to rHuEPO. Contrary to our hypothesis, loss of VHL and increased transcription of HIF-target genes resulted in impaired ß-cell function and mass, which can be overcome with exogenous EPO. Our results indicate a critical role for VHL in ß-cell function and mass, and that EPO administration improved ß-cell function making it a potential strategy for diabetes treatment.

Erythropoietin protects against diabetes through direct effects on pancreatic beta cells.

A common feature among all forms of diabetes mellitus is a functional ß-cell mass insufficient to maintain euglycemia; therefore, the promotion of ß-cell growth and survival is a fundamental goal for diabetes prevention and treatment. Evidence has suggested that erythropoietin (EPO) exerts cytoprotective effects on nonerythroid cells. However, the influence of EPO on pancreatic ß cells and diabetes has not been evaluated to date. In this study, we report that recombinant human EPO treatment can protect against diabetes development in streptozotocin-induced and db/db mouse models of type 1 and type 2 diabetes, respectively. EPO exerts antiapoptotic, proliferative, antiinflammatory, and angiogenic effects within the islets. Using ß-cell-specific EPO receptor and JAK2 knockout mice, we show that these effects of EPO result from direct biological effects on ß cells and that JAK2 is an essential intracellular mediator. Thus, promotion of EPO signaling in ß cells may be a novel therapeutic strategy for diabetes prevention and treatment.

Executioners of apoptosis in pancreatic {beta}-cells: not just for cell death.

Pancreatic beta-cell mass is dynamic and is regulated by beta-cell proliferation, neogenesis, and apoptosis. Under physiological conditions, apoptosis is tightly regulated with a slow, net rise in beta-cell mass over time. Excessive beta-cell apoptosis is an important contributor to both type 1 and type 2 diabetes development. Therefore, much effort has been given recently to better understand the mechanisms of apoptosis that occur both during physiological homeostasis and during the course of both types of diabetes. Caspases are the executioners of apoptosis that ultimately result in cell suicide. In mammals, there are 14 caspases, of which many participate in the apoptotic pathways. Genetic mouse models have been important tools for elucidation of the specific apoptotic pathways that play an essential role in beta-cell apoptosis under physiological and pathological conditions. This review focuses on the diverse roles of each of the specific caspases and their regulators, unveiling both the classical apoptotic roles as well as emerging nonapoptotic roles.

Deletion of Fas in the pancreatic beta-cells leads to enhanced insulin secretion.

Fas/Fas ligand belongs to the tumor necrosis factor superfamily of receptors/ligands and is best known for its role in apoptosis. However, recent evidence supports its role in other cellular responses, including proliferation and survival. Although Fas has been implicated as an essential mediator of beta-cell death in the pathogenesis of type 1 diabetes, the essential role of Fas specifically in pancreatic beta-cells has been found to be controversial. Moreover, the role of Fas on beta-cell homeostasis and function is not clear. The objective of this study is to determine the role of Fas specifically in beta-cells under both physiological and diabetes models. Mice with Fas deletion specifically in the beta-cells were generated using the Cre-loxP system. Cre-mediated Fas deletion was under the control of the rat insulin promoter. Absence of Fas in beta-cells leads to complete protection against FasL-induced cell death. However, Fas is not essential in determining beta-cell mass or susceptibility to streptozotocin- or HFD-induced diabetes. Importantly, Fas deletion in beta-cells leads to increased p65 expression, enhanced glucose tolerance, and glucose-stimulated insulin secretion, with increased exocytosis as manifested by increased changes in membrane capacitance and increased expression of Syntaxin1A, VAMP2, and munc18a. Together, our study shows that Fas in the beta-cells indeed plays an essential role in the canonical death receptor-mediated apoptosis but is not essential in regulating beta-cell mass or diabetes development. However, beta-cell Fas is critical in the regulation of glucose homeostasis through regulation of the exocytosis machinery.

Absence of caspase-3 protects pancreatic {beta}-cells from c-Myc-induced apoptosis without leading to tumor formation.

c-Myc is a powerful trigger of beta-cell apoptosis, proliferation, and dedifferentiation in rodent islets in vivo. In a transgenic mouse model, c-Myc induction causes rapid beta-cell apoptosis and overt diabetes. When suppression of apoptosis is achieved by overexpression of Bcl-x(L) in an inducible model of c-Myc activation, a full spectrum of tumor development, including distant metastasis, occurs. Caspase-3 is a key pro-apoptotic protein involved in the execution phase of multiple apoptotic pathways. To test whether caspase-3 is an essential mediator of apoptosis in this model of tumorigenesis, we generated caspase-3 knock-out mice containing the inducible c-myc transgene (c-Myc(+)Casp3(-/-)). In contrast to Bcl-x(L)-overexpressing c-Myc(+) mice, c-Myc(+)Casp3(-/-) mice remained euglycemic for up to 30 days of c-Myc activation, and there was no evidence of tumor formation. Interestingly, caspase-3 deletion also led to the suppression of proliferation, perhaps through regulation of the cell cycle inhibitory protein p27, suggesting a possible mechanism for maintaining a balance between suppression of apoptosis and excessive proliferation in the context of c-Myc activation. Additionally, c-Myc-activated Casp3(-/-) mice were protected from streptozotocin-induced diabetes. Our studies demonstrate that caspase-3 deletion confers protection from c-Myc-induced apoptosis and diabetes development without unwanted tumorigenic effects. These results may lead to further elucidation of the mechanisms of c-Myc biology relevant to beta-cells, which may result in novel therapeutic strategies for diabetes.