Regulation Of Β-cell Function Research Articles

9366 The Rnf20 Histone Modifier Is A Crucial Mediator Of Pancreatic Beta Cell Identity And Function

Abstract Disclosure: T.H. Pierre: None. Y. Liu: None. M.M. Bethea: None. K. Coutinho: None. C. Hunter: None. Diabetes is characterized by the loss of pancreatic β-cell mass. As diabetes incidence continues to elevate, it is critical that we develop a better understanding of the factors that define functional β-cells in order to improve current therapeutics. One approach is through the study of transcription factors (TFs), which are essential for β-cell development and function. Prior work from our lab and others has examined Islet-1 (Isl1) a LIM-homeodomain TF that is required for the maturation of the endocrine pancreas and adult β-cell function. We have also extensively characterized several Isl1-interacting co-regulators (e.g., Ldb1 and SSBP3) that facilitate its roles in maintaining glucose homeostasis. Most recently, we have identified that Isl1 interacts with the ubiquitin ligases Ring Finger 20 (Rnf20) and Rnf40, whose histone H2B monoubiquitation (H2Bub1) activity support the gene regulatory functions of Isl1. With in vitro experiments, we demonstrated that Rnf20 and Rnf40 are important for glucose stimulated insulin secretion (GSIS) and mediate the expression of β-cell identity genes. Based on these findings, we hypothesize that Isl1-Rnf complexes modify histones to regulate β-cell gene expression and function. To address this hypothesis in vivo, we developed an adult inducible β-cell knockout of Rnf20 (Rnf20Δβ-cell). Rnf20Δβ-cell mice display fasting hyperglycemia and severe glucose intolerance that is driven by impaired GSIS, reduced insulin content, and the dysregulation of critical β-cell genes including Ins1, Ucn3, and Slc2a2. Additionally, loss of Rnf20 perturbs insulin processing and overall β-cell maturation as observed by measurement of proinsulin:insulin ratios, C-peptide levels, and whole islet RNA-seq. Phenotypes exhibited by Rnf20Δβ-cell mice are similar to those observed in Isl1 β-cell knockout mice, and comparative transcriptomics revealed an overlap of 570 genes involved in metabolism, zinc homeostasis, and islet proliferation including Slc30a8 and Matn2, both of which we found are occupied by Isl1 and Rnf20. Collectively, our findings demonstrate the importance of the Rnf20 histone modifier in regulating β-cell function and expand our understanding of the Isl1 regulatory network. Presentation: 6/2/2024

High-Fat Diets Fed during Pregnancy Cause Changes to Pancreatic Tissue DNA Methylation and Protein Expression in the Offspring: A Multi-Omics Approach.

Maternal obesity, caused by diets rich in fats and sugars during pregnancy, can predispose offspring to metabolic diseases such as diabetes. We hypothesized that obesity during pregnancy leads to increased DNA methylation and reduced protein expression in factors regulating β-cell function and apoptosis. Female C57BL/6J mice were fed a high-fat diet (HFD; 42% fat content; n = 3) or a control diet (CON; 16% fat content; n = 3) for fourteen weeks before and during pregnancy. Offspring were euthanized at 8 weeks and pancreatic tissue was collected. Isolated DNA was analyzed using whole-genome bisulfite sequencing. Protein expression was quantified using LC-MS. No significant differences in body weight were observed between HFD and control pups (p = 0.10). Whole-genome bisulfite sequencing identified 91,703 and 88,415 differentially methylated regions (DMRs) in CON vs. HFD male and female offspring. A total of 34 and 4 proteins were determined to have changes in expression that correlated with changes in DNA methylation in CON vs. HFD males and females, respectively. The majority of these factors were grouped into the metabolic function category via pathway analyses. This study illustrates the complex relationship between epigenetics, diet, and sex-specific responses, therefore offering insights into potential therapeutic targets and areas for further research.

MicroRNA 29 modulates β-cell mitochondrial metabolism and insulin secretion via underlying miR-29-OXPHOS complex pathways.

MicroRNAs (miRNAs) regulate β-cell function, and β-cell mitochondria and insulin secretion are perturbed in diabetes. We aimed to identify key miRNAs regulating β-cell mitochondrial metabolism and novel β-cell miRNA-mitochondrial pathways. TargetScan (http://www.targetscan.org/) was used to predict if 16 miRNAs implicated in β-cell function target 27 cis-eGenes implicated in mitochondrial activity. The expression of candidate miRNAs and insulin secretion after 24 and 1 h pre-incubation in 2.8, 11.1- and 16.7-mM glucose was measured in clonal INS-1 832/13 β-cells. MiR-29 silenced INS-1 832/13 cells were assessed for insulin secretion (glucose, pyruvate, and K+), target cis-eGene expression (Ndufv3 and Ndufa10 components of mitochondrial complex I (CI)), OXPHOS (CI-V) protein expression, and mitochondrial OXPHOS respiration/activity. The expression of differentially expressed miR-29 miRNAs was evaluated in Goto-Kakizaki (GK) rat, db/db mouse and type 2 diabetic (T2D) human islets, as well as NMRI mouse islets cultured under glucolipotoxic conditions. MiR-29, miR-15 and miR-124 were predicted to regulate ~20 cis-eGenes, while miR-29 alone was predicted to regulate ≥12 of these in rat and human species. MiR-29 expression and insulin secretion were reduced in INS-1 832/13 cells after 24 h in elevated glucose. MiR-29 knockdown increased all tested insulin secretory responses, Nudfv3, Ndufa10, complex I and II expression, and cellular mitochondrial OXPHOS. MiR-29 expression was reduced in db/db islets but increased in GK rat and T2D human islets. We conclude miR-29 is a key miRNA in regulating β-cell mitochondrial metabolism and insulin secretion via underlying miR-29-OXPHOS complex pathways. Furthermore, we infer reduced miR-29 expression compensatorily enhances insulin secretion under glucotoxicity.

Regulation of B-cell function and expression of CD11c, T-bet, and FcRL5 in response to different activation signals.

CD11c, FcRL5, or T-bet are commonly expressed by B cells expanding during inflammation, where they can make up >30% of mature B cells. However, the association between the proteins and differentiation and function in the host response remains largely unclear. We have assessed the co-expression of CD11c, T-bet, and FcRL5 in an in vitro B-cell culture system to determine how stimulation via the BCR, toll-like receptor 9 (TLR9), and different cytokines influence CD11c, T-bet, and FcRL5 expression. We observed different expression dynamics for all markers, but a largely overlapping regulation of CD11c and FcRL5 in response to BCR and TLR9 activation, while T-bet was strongly dependent on IFN-γ signaling. Investigating plasma cell differentiation and APC functions, there was no association between marker expression and antibody secretion or T-cell help. Rather the functions were associated with TLR9-signalling and B-cell-derived IL-6 production, respectively. These results suggest that the expression of CD11c, FcRL5, and T-bet and plasma cell differentiation and improved APC functions occur in parallel and are regulated by similar activation signals, but they are not interdependent.

The prostaglandin E2 EP3 receptor has disparate effects on islet insulin secretion and content in β-cells in a high-fat diet-induced mouse model of obesity.

Signaling through prostaglandin E2 EP3 receptor (EP3) actively contributes to the β-cell dysfunction of type 2 diabetes (T2D). In T2D models, full-body EP3 knockout mice have a significantly worse metabolic phenotype than wild-type controls due to hyperphagia and severe insulin resistance resulting from loss of EP3 in extra-pancreatic tissues, masking any potential beneficial effects of EP3 loss in the β cell. We hypothesized β-cell-specific EP3 knockout (EP3 βKO) mice would be protected from high-fat diet (HFD)-induced glucose intolerance, phenocopying mice lacking the EP3 effector, Gαz, which is much more limited in its tissue distribution. When fed a HFD for 16 wk, though, EP3 βKO mice were partially, but not fully, protected from glucose intolerance. In addition, exendin-4, an analog of the incretin hormone, glucagon-like peptide 1, more strongly potentiated glucose-stimulated insulin secretion in islets from both control diet- and HFD-fed EP3 βKO mice as compared with wild-type controls, with no effect of β-cell-specific EP3 loss on islet insulin content or markers of replication and survival. However, after 26 wk of diet feeding, islets from both control diet- and HFD-fed EP3 βKO mice secreted significantly less insulin as a percent of content in response to stimulatory glucose, with or without exendin-4, with elevated total insulin content unrelated to markers of β-cell replication and survival, revealing severe β-cell dysfunction. Our results suggest that EP3 serves a critical role in temporally regulating β-cell function along the progression to T2D and that there exist Gαz-independent mechanisms behind its effects.NEW & NOTEWORTHY The EP3 receptor is a strong inhibitor of β-cell function and replication, suggesting it as a potential therapeutic target for the disease. Yet, EP3 has protective roles in extrapancreatic tissues. To address this, we designed β-cell-specific EP3 knockout mice and subjected them to high-fat diet feeding to induce glucose intolerance. The negative metabolic phenotype of full-body knockout mice was ablated, and EP3 loss improved glucose tolerance, with converse effects on islet insulin secretion and content.

Unraveling the significance of PPP1R1A gene in pancreatic β-cell function: A study in INS-1 cells and human pancreatic islets

Background and aimsThe protein phosphatase 1 regulatory inhibitor subunit 1A (PPP1R1A) has been linked with insulin secretion and diabetes mellitus. Yet, its full significance in pancreatic β-cell function remains unclear. This study aims to elucidate the role of the PPP1R1A gene in β-cell biology using human pancreatic islets and rat INS-1 (832/13) cells. ResultsDisruption of Ppp1r1a in INS-1 cells was associated with reduced insulin secretion and impaired glucose uptake; however, cell viability, ROS, apoptosis or proliferation were intact. A significant downregulation of crucial β-cell function genes such as Ins1, Ins2, Pcsk1, Cpe, Pdx1, Mafa, Isl1, Glut2, Snap25, Vamp2, Syt5, Cacna1a, Cacna1d and Cacnb3, was observed upon Ppp1r1a disruption. Furthermore, silencing Pdx1 in INS-1 cells altered PPP1R1A expression, indicating that PPP1R1A is a target gene for PDX1. Treatment with rosiglitazone increased Ppp1r1a expression, while metformin and insulin showed no effect. RNA-seq analysis of human islets revealed high PPP1R1A expression, with α-cells showing the highest levels compared to other endocrine cells. Muscle tissues exhibited greater PPP1R1A expression than pancreatic islets, liver, or adipose tissues. Co-expression analysis revealed significant correlations between PPP1R1A and genes associated with insulin biosynthesis, exocytosis machinery, and intracellular calcium transport. Overexpression of PPP1R1A in human islets augmented insulin secretion and upregulated protein expression of Insulin, MAFA, PDX1, and GLUT1, while silencing of PPP1R1A reduced Insulin, MAFA, and GLUT1 protein levels. ConclusionThis study provides valuable insights into the role of PPP1R1A in regulating β-cell function and glucose homeostasis. PPP1R1A presents a promising opportunity for future therapeutic interventions.

Prmt5 deficient mouse B cells display RNA processing complexity and slower colorectal tumor progression.

Protein arginine methyltransferase 5 (Prmt5) is essential for normal B-cell development; however, the roles of Prmt5 in tumor-infiltrating B cells in tumor therapy have not been well elucidated. Here, we revealed that CD19-cre-Prmt5fl/fl (Prmt5cko) mice showed smaller tumor weights and volumes in the colorectal cancer mouse model; B cells expressed higher levels of Ccl22 and Il12a, which attracted T cells to the tumor site. Furthermore, we used direct RNA sequencing to comprehensively profile RNA processes in Prmt5 deletion B cells to explore underline mechanisms. We found significantly differentially expressed isoforms, mRNA splicing, poly(A) tail lengths, and m6A modification changes between the Prmt5cko and control groups. Cd74 isoform expressions might be regulated by mRNA splicing; the expression of two novel Cd74 isoforms was decreased, while one isoform was elevated in the Prmt5cko group, but the Cd74 gene expression showed no changes. We observed Ccl22, Ighg1, and Il12a expression was significantly increased in the Prmt5cko group, whereas Jak3 and Stat5b expression was decreased. Ccl22 and Ighg1 expression might be associated with poly(A) tail length, Jak3, Stat5b, and Il12a expression might be modulated by m6A modification. Our study demonstrated that Prmt5 regulates B-cell function through different mechanisms and supported the development of Prmt5-targeted antitumor treatments.

1751-P: SERCA2 Regulates ER Lipid Composition and Proinsulin Processing

Endoplasmic reticulum calcium (ER Ca2+) levels are primarily maintained through the sarco-ER Ca2+ ATPase (SERCA) pump. We have demonstrated reduced SERCA2 expression in islets from human cadaveric donors with Type 2 Diabetes (T2D) compared to normoglycemic controls and linked β-cell specific deletion of SERCA2 with impaired proinsulin processing. To test mechanisms of how reduced ER Ca2+ and SERCA2 deficiency regulate proinsulin processing, a SNAP-tagged human proinsulin adenovirus (SNAP-proinsulin) was overexpressed in rat insulinoma β-cells where SERCA2 had been deleted (S2KO INS-1) using CRISPR/Cas9 and in islets from C57BL/6 mice with SERCA2 haploinsufficiency fed a high fat diet or treated ex vivo with glucolipotoxicity (GLT). Immunoblotting SNAP-tagged cleavage products showed reduced proinsulin processing in SERCA2 deficient models compared to wildtype (WT), these defects were exacerbated by GLT treatment. To determine whether reduced processing could be related to impaired trafficking of proinsulin within the β-cell secretory pathway, SNAP-proinsulin was fluorescently labelled in C57BL/6 mouse islets treated with GLT. The colocalization of SNAP-proinsulin with Golgi immuno-marker, Giantin, suggested an accumulation in this compartment. The ER is the main site of lipid synthesis and lipid remodeling is known to regulate β-cell function. Preliminary mass spectrometry data revealed that loss of SERCA2 increases ER levels of phosphatidylcholine and decreases ceramide and sphingomyelin in S2KO INS-1 cells compared to WT cells. Taken together, these results demonstrate that ER Ca2+ deficiency changes ER lipid composition, which may affect proinsulin processing and trafficking. Characterizing this novel mechanism could provide valuable insight into β-cell dysfunction in T2D. Disclosure M.Hartley: Employee; Eli Lilly and Company. M.J.Pearson: None. F.Syed: None. H.Bui: None. T.Kono: None. K.D.Roth: Employee; Eli Lilly and Company. C.Evans-molina: Advisory Panel; Provention Bio, Inc., DiogenX, Avotres Inc., Neurodon, MaiCell Therapeutics, Other Relationship; Isla Technology, Bristol-Myers Squibb Company, Nimbus Therapeutics, Research Support; Lilly, Astellas Pharma Inc. Funding National Institute of Diabetes and Digestive and Kidney Diseases (R01DK093954, R01DK127308, R01DK127236)

MiRNAs in the beta cell - friends or foes?

Type-2 diabetes (T2D) develops due to insulin resistance and an inability of the pancreatic β-cells to increase secretion of insulin and reduce elevated blood glucose levels. Diminished β-cell function and mass have been implicated in impaired β-cell secretory capacity and several microRNAs (miRNAs) have been reported to be involved in regulating β-cell processes. We believe miRNAs are nodes in important miRNA-mRNA networks regulating β-cell function and that miRNAs therefore can be targets for the treatment of T2D. MiRNAs are short (≈19-23nt) endogenous non-coding RNAs which regulate gene expression by directly binding to the mRNA of their target genes. Under normal circumstances miRNAs act as rheostats to keep expression of their gene targets at optimal levels for different β-cell outputs. In T2D, levels of some miRNAs are altered as part of the compensatory mechanism to improve insulin secretion. Other miRNAs are differentially expressed as part of the process of T2D pathogenesis, which results in reduced insulin secretion and increased blood glucose. In this review we present recent findings concerning miRNAs in islets and in insulin-secreting cells, and their differential expression in diabetes, with a specific focus on miRNAs involved in β-cell apoptosis/proliferation and glucose-stimulated insulin secretion. We present thoughts around miRNA-mRNA networks, and miRNAs as both therapeutic targets to improve insulin secretion and as circulating biomarkers of diabetes. Overall, we hope to convince you that miRNAs in β-cells are essential for regulating their function and can in the future be of clinical use in treatment and/or prevention of diabetes.

Hydrogen peroxide detoxification through the peroxiredoxin/thioredoxin antioxidant system: A look at the pancreatic β-cell oxidant defense.

Reactive oxygen species (ROS), such as hydrogen peroxide, are formed when molecular oxygen obtains additional electrons, increasing its reactivity. While low concentrations of hydrogen peroxide are necessary for regulation of normal cellular signaling events, high concentrations can be toxic. To maintain this balance between beneficial and deleterious concentrations of hydrogen peroxide, cells utilize antioxidants. Our recent work supports a primary role for peroxiredoxin, thioredoxin, and thioredoxin reductase as the oxidant defense pathway used by insulin-producing pancreatic β-cells. These three players work in an antioxidant cycle based on disulfide exchange, with oxidized targets ultimately being reduced using electrons provided by NADPH. Peroxiredoxins also participate in hydrogen peroxide-based signaling through disulfide exchange with redox-regulated target proteins. This chapter will describe the catalytic mechanisms of thioredoxin, thioredoxin reductase, and peroxiredoxin and provide an in-depth look at the roles these enzymes play in antioxidant defense pathways of insulin-secreting β-cells. Finally, we will evaluate the physiological relevance of peroxiredoxin-mediated hydrogen peroxide signaling as a regulator of β-cell function.

Highlights from Recent Cancer Literature

Breaking Insights| December 02 2022 Highlights from Recent Cancer Literature Author & Article Information Online ISSN: 1538-7445 Print ISSN: 0008-5472 ©2022 American Association for Cancer Research2022American Association for Cancer Research Cancer Res (2022) 82 (23): 4301–4302. https://doi.org/10.1158/0008-5472.CAN-82-23-BI Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Cite Icon Cite Search Site Article Versions Icon Versions Version of Record December 2 2022 Citation Highlights from Recent Cancer Literature. Cancer Res 1 December 2022; 82 (23): 4301–4302. https://doi.org/10.1158/0008-5472.CAN-82-23-BI Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest Search Advanced Search Stimulator of interferon genes (STING) agonists rapidly moved into clinical trials with great optimism but have only shown mediocre therapeutic efficacy in patients. Li and colleagues revealed that STING activation in B cells drives immunosuppression that counteracts the stimulatory activity of these drugs, and that blocking regulatory B-cell function can improve STING-based cancer immunotherapy. Using specific deletion of STING (TMEM173) in B cells, they first showed that systemic delivery of STING agonists is more effective in controlling multiple cancer models, most importantly pancreatic ductal adenocarcinomas (PDAC). Next, they found that in response to STING activation, B cells take on a regulatory phenotype and produce two suppressive cytokines, IL35 and IL10. They found that IL35 production is essential for their suppressive nature, acting to suppress natural killer (NK) cell antitumor responses specifically in response to STING agonists. Finally, they showed that a combination of blocking anti-IL35 antibodies in combination... You do not currently have access to this content.

Downregulation of the m6A reader protein YTHDC1 leads to islet β-cell failure and diabetes

N6-methyladenosine (m6A) methyltransferase writer proteins (METTL3/METTL14) have been shown to regulate β-cell function and diabetes. However, whether and which m6A reader proteins regulate β-cell function and the pathogenesis of diabetes are largely unknown. In this study, we showed that YTHDC1 (YTH domain-containing protein 1), a key m6A nuclear reader protein, plays an essential role in maintaining β-cell function. YTHDC1 is downregulated in islet β cells in type 2 diabetes, which is due to lipotoxicity and chronic inflammation. β-Cell specific deletion of Ythdc1 results in β-cell failure and diabetes, which is likely due to the decreased expression of β-cell specific transcription factors and insulin secretion-related genes. Taken together, YTHDC1 is required for maintaining β-cell function, and the downregulation of YTHDC1 leads to β-cell failure and diabetes.

Metformin inhibits the pathogenic functions of AChR-specific B and Th17 cells by targeting miR-146a

Myasthenia gravis (MG) is characterized by fatigable skeletal muscle weakness with a fluctuating and unpredictable disease course and is caused by circulating autoantibodies and pathological T helper cells. Regulation of B-cell function and the T-cell network may be a potential therapeutic strategy for MG. MicroRNAs (miRNAs) have emerged as potential biomarkers in immune disorders due to their critical roles in various immune cells and multiple inflammatory diseases. Aberrant miR-146a signal activation has been reported in autoimmune diseases, but a detailed exploration of the relationship between miR-146a and MG is still necessary. Using an experimental autoimmune myasthenia gravis (EAMG) rat model, we observed that miR-146a was highly expressed in the spleen but expressed at low levels in the thymus and lymph nodes in EAMG rats. Additionally, miR-146a expression in T and B cells was also quite different. EAMG-specific Th17 and Treg cells had lower miR-146a levels, while EAMG-specific B cells had higher miR-146a levels, indicating that targeted intervention against miR-146a might have diametrically opposite effects. Metformin, a drug that was recently demonstrated to alleviate EAMG, may rescue the functions of both Th17 cells and B cells by reversing the expression of miR-146a. We also investigated the downstream target genes of miR-146a in both T and B cells using bioinformatics screening and qPCR. Taken together, our study identifies a complex role of miR-146a in the EAMG rat model, suggesting that more caution should be paid in targeting miR-146a for the treatment of MG.

Glucose mediates upregulation of Cck expression independent of cAMP signaling

Cholecystokinin (CCK) is a gut peptide hormone that is also produced by pancreatic β‐cells under conditions of metabolic stress and obesity. Treatment with exogenous CCK can alleviate obesity‐related diabetes in animal models without significant side effects. We have established that CCK is expressed primarily in the pancreatic β‐cell and that CCK is highly upregulated in ob/ob mice. We have also shown that elevated cellular cAMP stimulates β‐cell CCK expression and secretion. However, the specific islet cell types that express CCK and the regulation of Cck transcription in the islet has not been thoroughly explored. A more recent study from our lab showed that high glucose concentrations can upregulate Cck expression in mouse islets and human islets. We hypothesize that Cck expression is upregulated in response to various diabetogenic conditions and that CCK upregulation by glucose can occur independent of cAMP activation.Islets from 16‐week‐old C57BL/6J mice were harvested for use in a dose‐dependent 24‐hour study using different glucose concentrations: No glucose, 2.5mM, 7mM, 11mM & 25mM. After 24‐hour treatment, islets were collected for RNA isolation and cDNA synthesis to identify changes in Cck mRNA expression after incubation with different glucose concentrations. Cck mRNA levels were elevated 4‐8 fold in islets treated with 25 mM glucose compared to islets treated with 0 to 11mM glucose. Notably, the hypoglycemic treatment of no glucose and 2.5mM showed a 4‐fold increase when compared to the 7mM and 11mM treatments. Following this experiment, we wanted to determine if high glucose would still increase Cck mRNA expression after inhibiting cAMP. Islets were pre‐incubated for 45 minutes with 10nM sulprostone, which activated prostaglandin E3 (EP3) receptor and inhibits adenylate cyclase. After inhibition of cAMP, we incubated the islets at 2.5mM and 25mM glucose concentrations like the prior experiment and observed changes in Cck mRNA expression. After treatment with sulprostone, we are still able to see a significant increase in Cck mRNA expression in islets treated with 25mM glucose compared to those treated with 2.5mM glucose, even with cAMP inhibition.This data suggests that there are alternative pathways that could lead to CCK upregulation in the pancreatic islet independent of cAMP. It also shows that hypoglycemia may also increase Cckexpression, which suggests that CCK is upregulated in response to several forms of metabolic stress. We can further explore the effectiveness of glucose to increase CCK expression by treating islets with cycloheximide and deoxyglucose to determine if glucose metabolism is required for upregulation of Cck.This information will help with our general understanding of how CCK functions in pancreatic islet and how Cck transcription is regulated through signaling pathways and transcriptional networks that regulate β‐cell function and identity under diabetogenic conditions.

Carbon monoxide and β-cell function: Implications for type 2 diabetes mellitus

Carbon monoxide (CO), a member of the multifunctional gasotransmitters family produced by heme oxygenases (i.e., HO-1 and HO-2), has received significant attention because of its involvement in carbohydrate metabolism. Experimental evidence indicates that both HO-2- and HO-1-derived CO stimulate insulin secretion, but the latter mainly acts as a compensatory response in pre-diabetes conditions. CO protects pancreatic β-cell against cytokine- and hypoxia-induced apoptosis and promotes β-cell regeneration. CO cross-talks with nitric oxide (NO) and hydrogen sulfide (H2S), other important gasotransmitters in carbohydrate metabolism, in regulating β-cell function and insulin secretion. These data speak in favor of the potential therapeutic application of CO in type 2 diabetes mellitus (T2DM) and preventing the progression of pre-diabetes to diabetes. Either CO (as both gaseous form and CO-releasing molecule) or pharmacological formulations made of natural HO inducers (i.e., bioactive components originating from plant-based foods) are potential candidates for developing CO-based therapeutics in T2DM. Future studies are needed to assess the safety/efficacy and potential therapeutic applications of CO in T2DM.

Glycerol-3-phosphate phosphatase operates a glycerol shunt in pancreatic β-cells that controls insulin secretion and metabolic stress

ObjectiveThe recently identified glycerol-3-phosphate (Gro3P) phosphatase (G3PP) in mammalian cells, encoded by the PGP gene, was shown to regulate glucose, lipid and energy metabolism by hydrolyzing Gro3P and to control glucose-stimulated insulin secretion (GSIS) in β-cells, in vitro. However, whether G3PP regulates β-cell function and insulin secretion in vivo is not known. MethodsWe now examined the role of G3PP in the control of insulin secretion in vivo, β-cell function and glucotoxicity in inducible β-cell specific G3PP-KO (BKO) mice. Inducible BKO mice were generated by crossing floxed-G3PP mice with Mip-Cre-ERT (MCre) mice. All the in vivo studies were done using BKO and control mice fed normal diet and the ex vivo studies were done using pancreatic islets from these mice. ResultsBKO mice, compared to MCre controls, showed increased body weight, adiposity, fed insulinemia, enhanced in vivo GSIS, reduced plasma triglycerides and mild glucose intolerance. Isolated BKO mouse islets incubated at high (16.7 mM), but not at low or intermediate glucose (3 and 8 mM), showed elevated GSIS, Gro3P content as well as increased levels of metabolites and signaling coupling factors known to reflect β-cell activation for insulin secretion. BKO islets also showed reduced glycerol release and increased O2 consumption and ATP production at high glucose only. BKO islets chronically exposed to elevated glucose levels showed increased apoptosis, reduced insulin content and decreased mRNA expression of β-cell differentiation markers, Pdx-1, MafA and Ins-2. ConclusionsThe results demonstrate that β-cells are endowed with a “glycerol shunt”, operated by G3PP that regulates β-cell metabolism, signaling and insulin secretion in vivo, primarily at elevated glucose concentrations. We propose that the glycerol shunt plays a role in preventing insulin hypersecretion and excess body weight gain and contributes to β-cell mass preservation in the face of hyperglycemia.

Lipid Droplets' Role in the Regulation of β-Cell Function and β-Cell Demise in Type 2 Diabetes.

During development of type 2 diabetes (T2D), excessive nutritional load is thought to expose pancreatic islets to toxic effects of lipids and reduce β-cell function and mass. However, lipids also play a positive role in cellular metabolism and function. Thus, proper trafficking of lipids is critical for β cells to maximize the beneficial effects of these molecules while preventing their toxic effects. Lipid droplets (LDs) are organelles that play an important role in the storage and trafficking of lipids. In this review, we summarize the discovery of LDs in pancreatic β cells, LD lifecycle, and the effect of LD catabolism on β-cell insulin secretion. We discuss factors affecting LD formation such as age, cell type, species, and nutrient availability. We then outline published studies targeting critical LD regulators, primarily in rat and human β-cell models, to understand the molecular effect of LD formation and degradation on β-cell function and health. Furthermore, based on the abnormal LD accumulation observed in human T2D islets, we discuss the possible role of LDs during the development of β-cell failure in T2D. Current knowledge indicates that proper formation and clearance of LDs are critical to normal insulin secretion, endoplasmic reticulum homeostasis, and mitochondrial integrity in β cells. However, it remains unclear whether LDs positively or negatively affect human β-cell demise in T2D. Thus, we discuss possible research directions to address the knowledge gap regarding the role of LDs in β-cell failure.

Tissue-specific responses that constrain glucose oxidation and increase lactate production with the severity of hypoxemia in fetal sheep.

Fetal hypoxemia decreases insulin and increases cortisol and norepinephrine concentrations and may restrict growth by decreasing glucose utilization and altering substrate oxidation. Specifically, we hypothesized that hypoxemia would decrease fetal glucose oxidation and increase lactate and pyruvate production. We tested this by measuring whole body glucose oxidation and lactate production, and molecular pathways in liver, muscle, adipose, and pancreas tissues of fetuses exposed to maternal hypoxemia for 9 days (HOX) compared with control fetal sheep (CON) in late gestation. Fetuses with more severe hypoxemia had lower whole body glucose oxidation rates, and HOX fetuses had increased lactate production from glucose. In muscle and adipose tissue, expression of the glucose transporter GLUT4 was decreased. In muscle, pyruvate kinase (PKM) and lactate dehydrogenase B (LDHB) expression was decreased. In adipose tissue, LDHA and lactate transporter (MCT1) expression was increased. In liver, there was decreased gene expression of PKLR and MPC2 and phosphorylation of PDH, and increased LDHA gene and LDH protein abundance. LDH activity, however, was decreased only in HOX skeletal muscle. There were no differences in basal insulin signaling across tissues, nor differences in pancreatic tissue insulin content, β-cell area, or genes regulating β-cell function. Collectively, these results demonstrate coordinated metabolic responses across tissues in the hypoxemic fetus that limit glucose oxidation and increase lactate and pyruvate production. These responses may be mediated by hypoxemia-induced endocrine responses including increased norepinephrine and cortisol, which inhibit pancreatic insulin secretion resulting in lower insulin concentrations and decreased stimulation of glucose utilization.NEW & NOTEWORTHY Hypoxemia lowered fetal glucose oxidation rates, based on severity of hypoxemia, and increased lactate production. This was supported by tissue-specific metabolic responses that may result from increased norepinephrine and cortisol concentrations, which decrease pancreatic insulin secretion and insulin concentrations and decrease glucose utilization. This highlights the vulnerability of metabolic pathways in the fetus and demonstrates that constrained glucose oxidation may represent an early event in response to sustained hypoxemia and fetal growth restriction.

Cathepsin C Regulates Cytokine-Induced Apoptosis in β-Cell Model Systems.

Emerging evidence suggests that several of the lysosomal cathepsin proteases are genetically associated with type 1 diabetes (T1D) and participate in immune-mediated destruction of the pancreatic β cells. We previously reported that the T1D candidate gene cathepsin H is downregulated by pro-inflammatory cytokines in human pancreatic islets and regulates β-cell function, apoptosis, and disease progression in children with new-onset T1D. In the present study, the objective was to investigate the expression patterns of all 15 known cathepsins in β-cell model systems and examine their role in the regulation of cytokine-induced apoptosis. Real-time qPCR screening of the cathepsins in human islets, 1.1B4 and INS-1E β-cell models identified several cathepsins that were expressed and regulated by pro-inflammatory cytokines. Using small interfering RNAs to knock down (KD) the cytokine-regulated cathepsins, we identified an anti-apoptotic function of cathepsin C as KD increased cytokine-induced apoptosis. KD of cathepsin C correlated with increased phosphorylation of JNK and p38 mitogen-activated protein kinases, and elevated chemokine CXCL10/IP-10 expression. This study suggests that cathepsin C is a modulator of β-cell survival, and that immune modulation of cathepsin expression in islets may contribute to immune-mediated β-cell destruction in T1D.

Targeting CD22 for the Treatment of B-Cell Malignancies.

Immunotherapeutic agents play an increasingly important role in the treatment of B-cell malignancies. CD19 and CD20 are common targets for lymphoid malignancies, though patients who relapse have few therapeutic options remaining. CD22 is a cell surface sialoglycoprotein uniquely present on B-cells and regulates B-cell function and proliferation. Thus, it is an appealing therapeutic target for autoimmune disorders and B-cell malignancies. A variety of therapies targeting CD22 have been developed, including monoclonal antibodies, antibody-drug conjugates, radioimmunoconjugates, chimeric antigen receptor T cells, and bispecific antibodies. Here, we review the biology of CD22 and key therapies targeting CD22 in lymphoid malignancies.