Heterozygous inactivation of plasma membrane Ca(2+)-ATPase in mice increases glucose-induced insulin release and beta cell proliferation, mass and viability

Multiple-Tissue and Multilevel Analysis on Differentially Expressed Genes and Differentially Correlated Gene Pairs for HFpEF

Heart failure with preserved ejection fraction (HFpEF) is a complex disease characterized by dysfunctions in the heart, adipose tissue, and cerebral arteries. The elucidation of the interactions between these three tissues in HFpEF will improve our understanding of the mechanism of HFpEF. In this study, we propose a multilevel comparative framework based on differentially expressed genes (DEGs) and differentially correlated gene pairs (DCGs) to investigate the shared and unique pathological features among the three tissues in HFpEF. At the network level, functional enrichment analysis revealed that the networks of the heart, adipose tissue, and cerebral arteries were enriched in the cell cycle and immune response. The networks of the heart and adipose tissues were enriched in hemostasis, G-protein coupled receptor (GPCR) ligand, and cancer-related pathway. The heart-specific networks were enriched in the inflammatory response and cardiac hypertrophy, while the adipose-tissue-specific networks were enriched in the response to peptides and regulation of cell adhesion. The cerebral-artery-specific networks were enriched in gene expression (transcription). At the module and gene levels, 5 housekeeping DEGs, 2 housekeeping DCGs, 6 modules of merged protein–protein interaction network, 5 tissue-specific hub genes, and 20 shared hub genes were identified through comparative analysis of tissue pairs. Furthermore, the therapeutic drugs for HFpEF-targeting these genes were examined using molecular docking. The combination of multitissue and multilevel comparative frameworks is a potential strategy for the discovery of effective therapy and personalized medicine for HFpEF.

Calcium Signaling in ß-cell Physiology and Pathology: A Revisit

Pancreatic beta (β) cell dysfunction results in compromised insulin release and, thus, failed regulation of blood glucose levels. This forms the backbone of the development of diabetes mellitus (DM), a disease that affects a significant portion of the global adult population. Physiological calcium (Ca²⁺) signaling has been found to be vital for the proper insulin-releasing function of β-cells. Calcium dysregulation events can have a dramatic effect on the proper functioning of the pancreatic β-cells. The current review discusses the role of calcium signaling in health and disease in pancreatic β-cells and provides an in-depth look into the potential role of alterations in β-cell Ca²⁺ homeostasis and signaling in the development of diabetes and highlights recent work that introduced the current theories on the connection between calcium and the onset of diabetes.

Targeted Derivation of Organotypic Glucose- and GLP-1-Responsive β Cells Prior to Transplantation into Diabetic Recipients

Generation of functional β cells from pluripotent sources would accelerate diagnostic and therapeutic applications for diabetes research and therapy. However, it has been challenging to generate competent β cells with dynamic insulin-secretory capacity to glucose and incretin stimulations. We introduced transcription factors, critical for β-cell development and function, in differentiating human induced pluripotent stem cells (PSCs) and assessed the impact on the functionality of derived β-cell (psBC) progeny. A perifusion system revealed stepwise transduction of the PDX1, NEUROG3, and MAFA triad (PNM) enabled in vitro generation of psBCs with glucose and GLP-1 responsiveness within 3 weeks. PNM transduction upregulated genes associated with glucose sensing, insulin secretion, and β-cell maturation. In recipient diabetic mice, PNM-transduced psBCs showed glucose-responsive insulin secretion as early as 1 week post transplantation. Thus, enhanced pre-emptive β-cell specification of PSCs by PNM drives generation of glucose- and incretin-responsive psBCs in vitro, offering a competent tissue-primed biotherapy.

MicroRNA Sequencing Reveals the Effect of Different Levels of Non-Fibrous Carbohydrate/Neutral Detergent Fiber on Rumen Development in Calves

Rumen development in calves is affected by many factors, including dietary composition. MicroRNAs (miRNAs) are known to function in the development of the rumen in cattle, what is not known is how these miRNAs function in rumen development of calves fed with high and low ratios of non-fibrous carbohydrate (NFC)/neutral detergent fiber (NDF). A total of six healthy Charolais hybrids bull calves of similar weight were divided into two groups; three calves were fed a mixed diet with NFC/NDF = 1.35 (H group), and three were fed a mixed diet with NFC/NDF = 0.80 (L group). After 105 days on the diet, calves were sacrificed and rumen tissues were collected. Tissues were subjected to histological observation and miRNA expression analysis. Functional enrichment analysis was conducted on the target genes of the miRNAs. Targeting and regulatory relationships were verified by luciferase reporter assay and quantitative PCR (qPCR). We found that the length of rumen papilla in the L group was significantly greater than that in the H group, while the width of rumen papilla in H group was significantly greater than that that in L group. We identified 896 miRNAs; 540 known miRNAs, and 356 novel predicted miRNAs. After statistical testing, we identified 24 differentially expressed miRNAs (DEmiRNAs). miRNA-mRNA-cluster network analysis and literature reviews revealed that cell proliferation, differentiation, physical and nutrient stimuli processes participate in rumen development under different NFC/NDF levels. The regulatory relationships between three DEmiRNAs and five target genes were verified by examining the levels of expression. The binding sites on bta-miR-128 for the peroxisome proliferator activated receptor gamma (PPARG) and solute carrier family 16 member 1 (SLC16A1) genes were investigated using a dual luciferase assay. The results of this study provide insight into the role of miRNAs in rumen development in calves under different NFC/NDF levels.

Na+/Ca2+ Exchanger a Druggable Target to Promote β-Cell Proliferation and Function

An important feature of type 2 diabetes is a decrease in β-cell mass. Therefore, it is essential to find new approaches to stimulate β-cell proliferation. We have previously shown that heterozygous inactivation of the Na+/Ca2+ exchanger (isoform 1; NCX1), a protein responsible for Ca2+ extrusion from cells, increases β-cell proliferation, mass, and function in mice. Here, we show that Ncx1 inactivation also increases β-cell proliferation in 2-year-old mice and that NCX1 inhibition in adult mice by four small molecules of the benzoxyphenyl family stimulates β-cell proliferation both in vitro and in vivo. NCX1 inhibition by small interfering RNA or small molecules activates the calcineurin/nuclear factor of activated T cells (NFAT) pathway and inhibits apoptosis induced by the immunosuppressors cyclosporine A (CsA) and tacrolimus in insulin-producing cell. Moreover, NCX1 inhibition increases the expression of β-cell-specific genes, such as Ins1, Ins2, and Pdx1, and inactivates/downregulates the tumor suppressors retinoblastoma protein (pRb) and miR-193a and the cell cycle inhibitor p53. Our data show that Na+/Ca2+ exchange is a druggable target to stimulate β-cell function and proliferation. Specific β-cell inhibition of Na+/Ca2+ exchange by phenoxybenzamyl derivatives may represent an innovative approach to promote β-cell regeneration in diabetes and improve the efficiency of pancreatic islet transplantation for the treatment of the disease.

Loureirin B promotes insulin secretion through inhibition of KATP channel and influx of intracellular calcium

The development of new diabetes drugs continues to be explored. Loureirin B, a flavonoid, extracted from Dracaena cochinchinensis, has been confirmed to increase insulin secretion and decrease blood glucose levels. For searching the promotion of insulin secretion with the treatment of loureirin B, experiments were employed based on cell experiments and computational methods. First, promotion of insulin secretion was dependent on extracellular glucose concentration. At the genetic level, loureirin B enhanced the relative mRNA level of Pdx-1 and MafA. Meanwhile the intracellular level of ATP increased due to the continuous absorption of glucose. Further experiments showed that the currents of K_ATP channel on Ins-1 cells were inhibited and the voltage-dependent calcium channels were subsequently activated. The increase of Cx43 protein expression might mediate the Ca²⁺ to the intracellular. Through computational simulation, we hypothesized that loureirin B might interact with K_ATP channels to promote insulin secretion. In conclusion, it could be concluded that loureirin B promoted insulin secretion mainly through increasing mRNA level of Pdx-1, MafA, intracellular ATP level, inhibiting the K_ATP current, influx of Ca²⁺ to the intracellular.

Local and regional control of calcium dynamics in the pancreatic islet

Ca²⁺ is the key intracellular regulator of insulin secretion, acting in the β-cell as the ultimate trigger for exocytosis. In response to high glucose, ATP-sensitive K⁺ channel closure and plasma membrane depolarization engage a sophisticated machinery to drive pulsatile cytosolic Ca²⁺ changes. Voltage-gated Ca²⁺ channels, Ca²⁺ -activated K⁺ channels and Na⁺ /Ca²⁺ exchange all play important roles. The use of targeted Ca²⁺ probes has revealed that during each cytosolic Ca²⁺ pulse, uptake of Ca²⁺ by mitochondria, endoplasmic reticulum (ER), secretory granules and lysosomes fine-tune cytosolic Ca²⁺ dynamics and control organellar function. For example, changes in the expression of the Ca²⁺ -binding protein Sorcin appear to provide a link between ER Ca²⁺ levels and ER stress, affecting β-cell function and survival. Across the islet, intercellular communication between highly interconnected "hubs," which act as pacemaker β-cells, and subservient "followers," ensures efficient insulin secretion. Loss of connectivity is seen after the deletion of genes associated with type 2 diabetes (T2D) and follows metabolic and inflammatory insults that characterize this disease. Hubs, which typically comprise ~1%-10% of total β-cells, are repurposed for their specialized role by expression of high glucokinase (Gck) but lower Pdx1 and Nkx6.1 levels. Single cell-omics are poised to provide a deeper understanding of the nature of these cells and of the networks through which they communicate. New insights into the control of both the intra- and intercellular Ca²⁺ dynamics may thus shed light on T2D pathology and provide novel opportunities for therapy.

The Plasma Membrane Calcium ATPases and Their Role as Major New Players in Human Disease

The Ca²⁺ extrusion function of the four mammalian isoforms of the plasma membrane calcium ATPases (PMCAs) is well established. There is also ever-increasing detail known of their roles in global and local Ca²⁺ homeostasis and intracellular Ca²⁺ signaling in a wide variety of cell types and tissues. It is becoming clear that the spatiotemporal patterns of expression of the PMCAs and the fact that their abundances and relative expression levels vary from cell type to cell type both reflect and impact on their specific functions in these cells. Over recent years it has become increasingly apparent that these genes have potentially significant roles in human health and disease, with PMCAs1-4 being associated with cardiovascular diseases, deafness, autism, ataxia, adenoma, and malarial resistance. This review will bring together evidence of the variety of tissue-specific functions of PMCAs and will highlight the roles these genes play in regulating normal physiological functions and the considerable impact the genes have on human disease.

The Na+/Ca2+ exchanger and the Plasma Membrane Ca2+-ATPase in β-cell function and diabetes

The rat pancreatic β-cell expresses 6 splice variants of the Plasma Membrane Ca²⁺-ATPase (PMCA) and two splice variants of the Na⁺/Ca²⁺ exchanger 1 (NCX1). In the β-cell Na⁺/Ca²⁺ exchange displays a high capacity, contributes to both Ca²⁺ outflow and influx and participates to the control of insulin release. Gain of function studies show that overexpression of PMCA2 or NCX1 leads to endoplasmic reticulum (ER) Ca²⁺ depletion with subsequent ER stress, decrease in β-cell proliferation and β-cell death by apoptosis. Loss of function studies show, on the contrary, that heterozygous inactivation of NCX1 (Ncx1^+/-) leads to an increase in β-cell function and a 5 fold increase in both β-cell mass and proliferation. The mutation also increases β-cell resistance to hypoxia, and Ncx1^+/- islets show a 2-4 times higher rate of diabetes cure than Ncx1^+/+ islets when transplanted in diabetic animals. Thus, down-regulation of the Na⁺/Ca²⁺ exchanger leads to various changes in β-cell function that are opposite to the major abnormalities seen in diabetes. In addition, the β-cell includes the mutually exclusive exon B in the alternative splicing region of NCX1, which confers a high sensitivity of its NCX splice variants (NCX1.3 & 1.7) to the inhibitory action of compounds like KBR-7943. Heterozygous inactivation of PMCA2 leads to apparented, though not completely similar results.These provide 2 unique models for the prevention and treatment of β-cell dysfunction in diabetes and following islet transplantation.

Glucagon-Like Peptide 1 Protects Pancreatic β-Cells From Death by Increasing Autophagic Flux and Restoring Lysosomal Function

Studies in animal models of type 2 diabetes have shown that glucagon-like peptide 1 (GLP-1) receptor agonists prevent β-cell loss. Whether GLP-1 mediates β-cell survival via the key lysosomal-mediated process of autophagy is unknown. In this study, we report that treatment of INS-1E β-cells and primary islets with glucolipotoxicity (0.5 mmol/L palmitate and 25 mmol/L glucose) increases LC3 II, a marker of autophagy. Further analysis indicates a blockage in autophagic flux associated with lysosomal dysfunction. Accumulation of defective lysosomes leads to lysosomal membrane permeabilization and release of cathepsin D, which contributes to cell death. Our data further demonstrated defects in autophagic flux and lysosomal staining in human samples of type 2 diabetes. Cotreatment with the GLP-1 receptor agonist exendin-4 reversed the lysosomal dysfunction, relieving the impairment in autophagic flux and further stimulated autophagy. Small interfering RNA knockdown showed the restoration of autophagic flux is also essential for the protective effects of exendin-4. Collectively, our data highlight lysosomal dysfunction as a critical mediator of β-cell loss and shows that exendin-4 improves cell survival via restoration of lysosomal function and autophagic flux. Modulation of autophagy/lysosomal homeostasis may thus define a novel therapeutic strategy for type 2 diabetes, with the GLP-1 signaling pathway as a potential focus.

BRD4 regulates fructose-inducible lipid accumulation-related genes in the mouse liver

OBJECTIVE

Fructose intake induces hepatic steatosis by activating fat synthesis. In this study, we searched for genes that showed acute induction in the livers of mice force-fed with fructose, and examined how this induction is regulated.

MATERIALS/METHODS

We identified genes induced at 6h after the fructose force-feeding using a microarray and quantitative real-time RT-PCR. Histone acetylation and an acetylated histone binding protein bromodomain containing (BRD)4 binding around the fructose-inducible genes were examined using a chromatin immunoprecipitation assay. We examined whether (+)-JQ1, an inhibitor of the binding between the BRD4 and acetylated histones, inhibited the expressions of fructose-inducible genes, histone acetylation and BRD4 binding around the genes.

RESULTS

We identified upregulated genes related to lipid accumulation, such as Cyp8b1, Dak and Plin5, in mice force-fed with fructose compared with those force-fed with glucose. Acetylation of histones H3 and H4, and BRD4 binding around the transcribed region of those fructose-inducible genes, were enhanced by fructose force-feeding. Meanwhile, (+)-JQ1 treatment reduced expressions of fructose-inducible genes, histone acetylation and BRD4 binding around these genes.

CONCLUSIONS

Acute induction of genes related to lipid accumulation in the livers of mice force-fed with fructose is associated with the induction of histone acetylation and BRD4 binding around these genes.