Altered metabolism distinguishes high-risk from stable carotid atherosclerotic plaques.

Aims: Identification and treatment of the rupture prone atherosclerotic plaque remains a challenge for reducing the burden of cardiovascular disease. The interconnection of metabolic and inflammatory processes in rupture prone plaques is poorly understood. Herein, we investigate associations between metabolite profiles, inflammatory mediators and vulnerability in carotid atherosclerotic plaques. Methods and results: We collected 159 carotid plaques from patients undergoing endarterectomy and measured 165 different metabolites in a targeted metabolomics approach. We identified a metabolite profile in carotid plaques that associated with histologically evaluated vulnerability and inflammatory mediators, as well as presence of symptoms in patients. The distinct metabolite profiles identified in high-risk and stable plaques were in line with different transcription levels of metabolic enzymes in the two groups, suggesting an altered metabolism in high-risk plaques. The altered metabolic signature in high-risk plaques was consistent with a change to increased glycolysis, elevated amino acid utilization and decreased fatty acid oxidation, similar to what is found in activated leucocytes and cancer cells. Conclusion: These results highlight a possible key role of cellular metabolism to support inflammation and a high-risk phenotype of atherosclerotic plaques. Targeting the metabolism of atherosclerotic plaques with novel metabolic radiotracers or inhibitors might therefore be valid future approaches to identify and treat the high-risk atherosclerotic plaque.

Sphingolipids Contribute to Human Atherosclerotic Plaque Inflammation.

OBJECTIVE: Lipids are central to the development of atherosclerotic plaques. Specifically, which lipids are culprits remains controversial, and promising targets have failed in clinical studies. Sphingolipids are bioactive lipids present in atherosclerotic plaques, and they have been suggested to have both proatherogenic and antiatherogenic. However, the biological effects of these lipids remain unknown in the human atherosclerotic plaque. The aim of this study was to assess plaque levels of sphingolipids and investigate their potential association with and contribution to plaque vulnerability. APPROACH AND RESULTS: Glucosylceramide, lactosylceramide, ceramide, dihydroceramide, sphingomyelin, and sphingosine-1-phosphate were analyzed in homogenates from 200 human carotid plaques using mass spectrometry. Inflammatory activity was determined by analyzing plaque levels of cytokines and plaque histology. Caspase-3 was analyzed by ELISA technique. Expression of regulatory enzymes was analyzed with RNA sequencing. Human coronary artery smooth muscle cells were used to analyze the potential role of the 6 sphingolipids as inducers of plaque inflammation and cellular apoptosis in vitro. All sphingolipids were increased in plaques associated with symptoms and correlated with inflammatory cytokines. All sphingolipids, except sphingosine-1-phosphate, also correlated with histological markers of plaque instability. Lactosylceramide, ceramide, sphingomyelin, and sphingosine-1-phosphate correlated with caspase-3 activity. In vitro experiments revealed that glucosylceramide, lactosylceramide, and ceramide induced cellular apoptosis. All analyzed sphingolipids induced an inflammatory response in human coronary artery smooth muscle cells. CONCLUSIONS: This study shows for the first time that sphingolipids and particularly glucosylceramide are associated with and are possible inducers of plaque inflammation and instability, pointing to sphingolipid metabolic pathways as possible novel therapeutic targets.

Serotonin (5-HT) receptor 2b activation augments glucose-stimulated insulin secretion in human and mouse islets of Langerhans.

AIMS/HYPOTHESIS: The Gq-coupled 5-hydroxytryptamine 2B (5-HT2B) receptor is known to regulate the proliferation of islet beta cells during pregnancy. However, the role of serotonin in the control of insulin release is still controversial. The aim of the present study was to explore the role of the 5-HT2B receptor in the regulation of insulin secretion in mouse and human islets, as well as in clonal INS-1(832/13) cells. METHODS: Expression of HTR2B mRNA and 5-HT2B protein was examined with quantitative real-time PCR, RNA sequencing and immunohistochemistry. α-Methyl serotonin maleate salt (AMS), a serotonin receptor agonist, was employed for robust 5-HT2B receptor activation. Htr2b was silenced with small interfering RNA in INS-1(832/13) cells. Insulin secretion, Ca(2+) response and oxygen consumption rate were determined. RESULTS: Immunohistochemistry revealed that 5-HT2B is expressed in human and mouse islet beta cells. Activation of 5-HT2B receptors by AMS enhanced glucose-stimulated insulin secretion (GSIS) in human and mouse islets as well as in INS-1(832/13) cells. Silencing Htr2b in INS-1(832/13) cells led to a 30% reduction in GSIS. 5-HT2B receptor activation produced robust, regular and sustained Ca(2+) oscillations in mouse islets with an increase in both peak distance (period) and time in the active phase as compared with control. Enhanced insulin secretion and Ca(2+) changes induced by AMS coincided with an increase in oxygen consumption in INS-1(832/13) cells. CONCLUSIONS/INTERPRETATION: Activation of 5-HT2B receptors stimulates GSIS in beta cells by triggering downstream changes in cellular Ca(2+) flux that enhance mitochondrial metabolism. Our findings suggest that serotonin and the 5-HT2B receptor stimulate insulin release.

miR-184 Regulates Pancreatic ß-Cell Function According to Glucose Metabolism.

In response to fasting or hyperglycemia, the pancreatic ß-cell alters its output of secreted insulin; however, the pathways governing this adaptive response are not entirely established. Although the precise role of microRNAs (miRNAs) is also unclear, a recurring theme emphasizes their function in cellular stress responses. We recently showed that miR-184, an abundant miRNA in the ß-cell, regulates compensatory proliferation and secretion during insulin resistance. Consistent with previous studies showing miR-184 suppresses insulin release, expression of this miRNA was increased in islets after fasting, demonstrating an active role in the ß-cell as glucose levels lower and the insulin demand ceases. Additionally, miR-184 was negatively regulated upon the administration of a sucrose-rich diet in Drosophila, demonstrating strong conservation of this pathway through evolution. Furthermore, miR-184 and its target Argonaute2 remained inversely correlated as concentrations of extracellular glucose increased, underlining a functional relationship between this miRNA and its targets. Lastly, restoration of Argonaute2 in the presence of miR-184 rescued suppression of miR-375-targeted genes, suggesting these genes act in a coordinated manner during changes in the metabolic context. Together, these results highlight the adaptive role of miR-184 according to glucose metabolism and suggest the regulatory role of this miRNA in energy homeostasis is highly conserved.

DNA methylation dynamics in human carotid plaques after cerebrovascular events.

OBJECTIVE: To understand whether cerebrovascular events, a major complication of atherosclerosis, are associated with any specific DNA methylation changes in the carotid plaque. APPROACH AND RESULTS: We profiled the DNA methylomes of human symptomatic carotid plaques obtained from patients who had cerebrovascular events (n=19) and asymptomatic counterparts (n=19) with a high-density microarray (≈485 000 CpG sites, Illumina), and crossed DNA methylation data with RNAseq-based expression data from an independent symptomatic carotid plaque set (n=8). Few (30) CpGs showed a significant (P<0.05; absolute Delta-Beta, >0.20) differential methylation between the 2 groups. Within symptomatic carotid plaques, DNA methylation correlated significantly with postcerebrovascular event time (range, 3-45 days; r-value range, -0.926 to 0.857; P<0.05) for ≈45 000 CpGs, the vast majority of which became hypomethylated with increasing postcerebrovascular event time. Hypomethylation was not due to erasure of the gene-body and CG-poor region hypermethylation that accompany the progression of stable lesions, but rather targeted promoters and CpG islands. Noticeably, promoter hypomethylation and increased expression of genes involved in the inhibition of the inflammatory response, defense against oxidative stress, and active DNA demethylation were observed with increasing postcerebrovascular event time. Concomitantly, histological changes consistent with phagocyte-driven plaque healing were observed. CONCLUSIONS: Weak changes in the DNA methylome distinguish symptomatic from asymptomatic plaques, but a widespread demethylation resulting in permissive transcriptional marks at atheroprotective gene promoters is established in plaques after a cerebrovascular event, thus mirroring previous observations that ruptured plaques tend to revert to a stable structure. The identified loci are candidate targets to accelerate the pace of carotid plaque stabilization.

Bone morphogenetic protein 4 inhibits insulin secretion from rodent beta cells through regulation of calbindin1 expression and reduced voltage-dependent calcium currents.

AIMS/HYPOTHESIS: Type 2 diabetes is characterised by progressive loss of pancreatic beta cell mass and function. Therefore, it is of therapeutic interest to identify factors with the potential to improve beta cell proliferation and insulin secretion. Bone morphogenetic protein 4 (BMP4) expression is increased in diabetic animals and BMP4 reduces glucose-stimulated insulin secretion (GSIS). Here, we investigate the molecular mechanism behind this inhibition. METHODS: BMP4-mediated inhibition of GSIS was investigated in detail using single cell electrophysiological measurements and live cell Ca(2+) imaging. BMP4-mediated gene expression changes were investigated by microarray profiling, quantitative PCR and western blotting. RESULTS: Prolonged exposure to BMP4 reduced GSIS from rodent pancreatic islets. This inhibition was associated with decreased exocytosis due to a reduced Ca(2+) current through voltage-dependent Ca(2+) channels. To identify proteins involved in the inhibition of GSIS, we investigated global gene expression changes induced by BMP4 in neonatal rat pancreatic islets. Expression of the Ca(2+)-binding protein calbindin1 was significantly induced by BMP4. Overexpression of calbindin1 in primary islet cells reduced GSIS, and the effect of BMP4 on GSIS was lost in islets from calbindin1 (Calb1) knockout mice. CONCLUSIONS/INTERPRETATION: We found BMP4 treatment to markedly inhibit GSIS from rodent pancreatic islets in a calbindin1-dependent manner. Calbindin1 is suggested to mediate the effect of BMP4 by buffering Ca(2+) and decreasing Ca(2+) channel activity, resulting in diminished insulin exocytosis. Both BMP4 and calbindin1 are potential pharmacological targets for the treatment of beta cell dysfunction.

Impaired fibrous repair: a possible contributor to atherosclerotic plaque vulnerability in patients with type II diabetes.

OBJECTIVE: Diabetes mellitus (DM) type II is increasing rapidly worldwide. Patients with DM II have a greater atherosclerotic burden and higher risk of developing cardiovascular complications. Inflammation has been proposed as the main cause for the high risk of atherosclerotic disease in DM II. In this study, we compared markers of inflammation and fibrous repair in plaques from subjects with and without DM II. APPROACH AND RESULTS: Carotid endarterectomy specimens were obtained from 63 patients with and 131 without DM. Plaque structure, connective tissue proteins, inflammatory cells, and markers were analyzed by immunohistochemistry, ELISA, Mesoscale, and Luminex technology. Carotid plaques from diabetics had lower levels of extracellular matrix proteins, elastin, and collagen, which are critical for plaque stability. Plaques from diabetics had reduced levels of platelet-derived growth factor and matrix metalloproteinase-2, both important for tissue repair. No differences were observed in inflammatory markers in plaques from diabetic and nondiabetic patients. CONCLUSION: This study suggests that atherosclerotic plaques in subjects with DM II are more prone to rupture because of impaired repair responses rather than to increased vascular inflammation. Although this study did not have a mechanistic design, our findings suggest that targeting impaired repair responses in carotid plaques may help to increase our understanding of atherosclerotic plaque development and vulnerability in patients with DM II.

Confluence does not affect the expression of miR-375 and its direct targets in rat and human insulin-secreting cell lines.

MicroRNAs are small non-coding RNAs, which negatively regulate the expression of target genes. They have emerged as important modulators in beta cell compensation upon increased metabolic demand, failure of which leads to reduced insulin secretion and type 2 diabetes. To elucidate the function of miRNAs in beta cells, insulin-secreting cell lines, such as the rat insulinoma INS-1 832/13 and the human EndoC-ßH1, are widely used. Previous studies in the cancer field have suggested that miRNA expression is influenced by confluency of adherent cells. We therefore aimed to investigate whether one of the most enriched miRNAs in the pancreatic endocrine cells, miR-375, and two of its validated targets in mouse, Cav1 and Aifm1, were differentially-expressed in cell cultures with different confluences. Additionally, we measured the expression of other miRNAs, such as miR-152, miR-130a, miR-132, miR-212 and miR-200a, with known roles in beta cell function. We did not see any significant expression changes of miR-375 nor any of the two targets, in both the rat and human beta cell lines at different confluences. Interestingly, among the other miRNAs measured, the expression of miR-132 and miR-212 positively correlated with confluence, but only in the INS-1 832/13 cells. Our results show that the expression of miR-375 and other miRNAs with known roles in beta cell function is independent of, or at least minimally influenced by the density of proliferating adherent cells, especially within the confluence range optimal for functional assays to elucidate miRNA-dependent regulatory mechanisms in the beta cell.

Osteopontin Affects Insulin Vesicle Localization and Ca2+ Homeostasis in Pancreatic Beta Cells from Female Mice.

Type 2 diabetic patients suffer from insulin resistance and reduced insulin secretion. Osteopontin (OPN), a versatile protein expressed in several tissues throughout the body including the islets of Langerhans, has previously been implicated in the development of insulin resistance. Here we have investigated the role of OPN in insulin secretion using an OPN knock out mouse model (OPN-/-). Ultra-structural analyzes of islets from OPN-/- and WT mice indicated weaker cell-cell connections between the islet cells in the OPN-/- mouse compared to WT. Analysis of the insulin granule distribution in the beta cells showed that although OPN-/- and WT beta cells have the same number of insulin granules OPN-/- beta cells have significantly fewer docked granules. Both OPN-/- and WT islets displayed synchronized Ca2+ oscillations indicative of an intact beta cell communication. OPN-/- islets displayed higher intracellular Ca2+ concentrations when stimulated with 16.7 mM glucose than WT islets and the initial dip upon elevated glucose concentrations (which is associated with Ca2+ uptake into ER) was significantly lower in these islets. Glucose-induced insulin secretion was similar in OPN-/- and WT islets. Likewise, non-fasted blood glucose levels were the same in both groups. In summary, deletion of OPN results in several minor beta-cell defects that can be compensated for in a healthy system.

Mitochondrial transcription factor B2 is essential for mitochondrial and cellular function in pancreatic ß-cells.

OBJECTIVE: Insulin release from pancreatic ß-cells is controlled by plasma glucose levels via mitochondrial fuel metabolism. Therefore, insulin secretion is critically dependent on mitochondrial DNA (mtDNA) and the genes it encodes. Mitochondrial transcription factor B2 (TFB2M) controls transcription of mitochondrial-encoded genes. However, its precise role in mitochondrial metabolism in pancreatic ß-cells and, consequently, in insulin secretion remains unknown. METHODS: To elucidate the role of TFB2M in mitochondrial function and insulin secretion in vitro and in vivo, mice with a ß-cell specific homozygous or heterozygous knockout of Tfb2m and rat clonal insulin-producing cells in which the gene was silenced were examined with an array of metabolic and functional assays. RESULTS: There was an effect of gene dosage on Tfb2m expression and function. Loss of Tfb2m led to diabetes due to disrupted transcription of mitochondrial DNA (mtDNA) and reduced mtDNA content. The ensuing mitochondrial dysfunction activated compensatory mechanisms aiming to limit cellular dysfunction and damage of ß-cells. These processes included the mitochondrial unfolded protein response, mitophagy, and autophagy. Ultimately, however, these cell-protective systems were overridden, leading to mitochondrial dysfunction and activation of mitochondrial-dependent apoptotic pathways. In this way, ß-cell function and mass were reduced. Together, these perturbations resulted in impaired insulin secretion, progressive hyperglycemia, and, ultimately, development of diabetes. CONCLUSIONS: Loss of Tfb2m in pancreatic ß-cells results in progressive mitochondrial dysfunction. Consequently, insulin secretion in response to metabolic stimuli is impaired and ß-cell mass reduced. Our findings indicate that TFB2M plays an important functional role in pancreatic ß-cells. Perturbations of its actions may lead to loss of functional ß-cell mass, a hallmark of T2D.

Optogenetic Control of Pancreatic Islets.

In light of the emerging diabetes epidemic, new experimental approaches in islet research are needed to elucidate the mechanisms behind pancreatic islet dysfunction and to facilitate the development of more effective therapies. Optogenetics has created numerous new experimental tools enabling us to gain insights into processes little was known about before. The spatial and temporal precision that it can achieve is also attractive for studying the cells of the pancreatic islet and we set out to explore the possibilities of this technology for our purposes. We here describe how to use the islets of an "optogenetic beta-cell" mouse line in islet batch incubations and Ca(2+) imaging experiments. This protocol enables light-induced insulin release and provides an all-optical solution to control and measure intracellular Ca(2+) levels in pancreatic beta-cells. The technique is easy to set up and provides a useful tool for controlling the activity of distinct islet cell populations.

Several type 2 diabetes-associated variants in genes annotated to WNT signaling interact with dietary fiber in relation to incidence of type 2 diabetes.

BACKGROUND: TCF7L2 is a central transcription factor in the canonical wingless-type MMTV integration site (WNT) signaling pathway, and genetic variants in TCF7L2 have been found to interact with dietary fiber intake on type 2 diabetes risk. Here, we investigate whether other type 2 diabetes genes could be involved in the WNT signaling pathway and whether variants in such genes might interact with dietary fiber on type 2 diabetes incidence. RESULTS: We included 26,905 individuals without diabetes from the Malmö Diet and Cancer Study cohort. Diet data was collected at baseline using a food frequency questionnaire, a 7-day food record, and an interview. Altogether, 51 gene loci were analyzed for putative links to WNT signaling. Over a mean follow-up period of 14.7 years, 3132 incident cases of type 2 diabetes were recorded. Seven genes (nine single nucleotide polymorphisms (SNPs)) were annotated as involved in WNT signaling including TCF7L2 (rs7903146 and rs12255372), HHEX (rs1111875), HNF1A (rs7957197), NOTCH2 (rs10923931), TLE4 (rs13292136), ZBED3 (rs4457053), and PPARG (rs1801282 and rs13081389). SNPs in TCF7L2, NOTCH2, and ZBED3 showed significant interactions with fiber intake on type 2 diabetes incidence (P interaction = 0.034, 0.005, 0.017, and 0.002, respectively). The magnitude of the association between the TCF7L2 risk allele and incident type 2 diabetes increased from the lowest to the highest quintiles of fiber intake. Higher fiber associated with lower type 2 diabetes risk only among risk allele carriers of the NOTCH2 variant and homozygotes of the risk allele of the ZBED3 variant. CONCLUSIONS: Our results suggest that several type 2 diabetes susceptibility SNPs in genes involved in WNT signaling may interact with dietary fiber intake on type 2 diabetes incidence.

Transcriptional regulation of the miR-212/miR-132 cluster in insulin-secreting ß-cells by cAMP-regulated transcriptional co-activator 1 and salt-inducible kinases.

MicroRNAs are central players in the control of insulin secretion, but their transcriptional regulation is poorly understood. Our aim was to investigate cAMP-mediated transcriptional regulation of the miR-212/miR-132 cluster and involvement of further upstream proteins in insulin secreting ß-cells. cAMP induced by forskolin+IBMX or GLP-1 caused increased expression of miR-212/miR-132, and elevated phosphorylation of cAMP-response-element-binding-protein (CREB)/Activating-transcription-factor-1 (ATF1) and Salt-Inducible-Kinases (SIKs). CyclicAMP-Regulated Transcriptional Co-activator-1 (CRTC1) was concomitantly dephosphorylated and translocated to the nucleus. Silencing of miR-212/miR-132 reduced, and overexpression of miR-212 increased, glucose-stimulated insulin secretion. Silencing of CRTC1 expression resulted in decreased insulin secretion and miR-212/miR-132 expression, while silencing or inhibition of SIKs was associated with increased expression of the microRNAs and dephosphorylation of CRTC1. CRTC1 protein levels were reduced after silencing of miR-132, suggesting feed-back regulation. Our data propose cAMP-dependent co-regulation of miR-212/miR-132, in part mediated through SIK-regulated CRTC1, as an important factor for fine-tuned regulation of insulin secretion.

Identification of Shared and Unique Serum Lipid Profiles in Diabetes Mellitus and Myocardial Infarction.

BACKGROUND: Diabetes mellitus (DM) and cardiovascular disease are associated with dyslipidemia, but the detailed lipid molecular pattern in both diseases remains unknown. METHODS AND RESULTS: We used shotgun mass spectrometry to determine serum levels of 255 molecular lipids in 316 controls, 171 DM, and 99 myocardial infarction (MI) events from a cohort derived from the Malmö Diet and Cancer study. Orthogonal projections to latent structures analyses were conducted between the lipids and clinical parameters describing DM or MI. Fatty acid desaturases (FADS) and elongation of very long chain fatty acid protein 5 (ELOVL5) activities were estimated by calculating product to precursor ratios of polyunsaturated fatty acids in complex lipids. FADS genotypes encoding these desaturases were then tested for association with lipid levels and ratios. Differences in the levels of lipids belonging to the phosphatidylcholine and triacylglyceride (TAG) classes contributed the most to separating DM from controls. TAGs also played a dominating role in discriminating MI from controls. Levels of C18:2 fatty acids in complex lipids were lower both in DM and MI versus controls (DM, P=0.004; MI, P=6.0E-06) at least due to an acceleration in the metabolic flux from C18:2 to C20:4 (eg, increased estimated ELOVL5: DM, P=0.02; MI, P=0.04, and combined elongase-desaturase activities: DM, P=3.0E-06; MI, P=2.0E-06). Minor allele carriers of FADS genotypes were associated with increased levels of C18:2 (P≤0.007) and lower desaturase activity (P≤0.002). CONCLUSIONS: We demonstrate a possible relationship between decreased levels of C18:2 in complex lipids and DM or MI. We thereby highlight the importance of molecular lipids in the pathogenesis of both diseases.

Low Dose Iron Treatments Induce a DNA Damage Response in Human Endothelial Cells within Minutes.

BACKGROUND: Spontaneous reports from patients able to report vascular sequelae in real time, and recognition that serum non transferrin bound iron may reach or exceed 10µmol/L in the blood stream after iron tablets or infusions, led us to hypothesize that conventional iron treatments may provoke acute vascular injury. This prompted us to examine whether a phenotype could be observed in normal human endothelial cells treated with low dose iron. METHODOLOGY: Confluent primary human endothelial cells (EC) were treated with filter-sterilized iron (II) citrate or fresh media for RNA sequencing and validation studies. RNA transcript profiles were evaluated using directional RNA sequencing with no pre-specification of target sequences. Alignments were counted for exons and junctions of the gene strand only, blinded to treatment types. PRINCIPAL FINDINGS: Rapid changes in RNA transcript profiles were observed in endothelial cells treated with 10µmol/L iron (II) citrate, compared to media-treated cells. Clustering for Gene Ontology (GO) performed on all differentially expressed genes revealed significant differences in biological process terms between iron and media-treated EC, whereas 10 sets of an equivalent number of randomly selected genes from the respective EC gene datasets showed no significant differences in any GO terms. After 1 hour, differentially expressed genes clustered to vesicle mediated transport, protein catabolism, and cell cycle (Benjamini p = 0.0016, 0.0024 and 0.0032 respectively), and by 6 hours, to cellular response to DNA damage stimulus most significantly through DNA repair genes FANCG, BLM, and H2AFX. Comet assays demonstrated that 10µM iron treatment elicited DNA damage within 1 hour. This was accompanied by a brisk DNA damage response pulse, as ascertained by the development of DNA damage response (DDR) foci, and p53 stabilization. SIGNIFICANCE: These data suggest that low dose iron treatments are sufficient to modify the vascular endothelium, and induce a DNA damage response.

Dual Effect of Rosuvastatin on Glucose Homeostasis Through Improved Insulin Sensitivity and Reduced Insulin Secretion.

Statins are beneficial in the treatment of cardiovascular disease (CVD), but these lipid-lowering drugs are associated with increased incidence of new on-set diabetes. The cellular mechanisms behind the development of diabetes by statins are elusive. Here we have treated mice on normal diet (ND) and high fat diet (HFD) with rosuvastatin. Under ND rosuvastatin lowered blood glucose through improved insulin sensitivity and increased glucose uptake in adipose tissue. In vitro rosuvastatin reduced insulin secretion and insulin content in islets. In the beta cell Ca(2+) signaling was impaired and the density of granules at the plasma membrane was increased by rosuvastatin treatment. HFD mice developed insulin resistance and increased insulin secretion prior to administration of rosuvastatin. Treatment with rosuvastatin decreased the compensatory insulin secretion and increased glucose uptake. In conclusion, our data shows dual effects on glucose homeostasis by rosuvastatin where insulin sensitivity is improved, but beta cell function is impaired.

Regulation of Pancreatic Beta Cell Stimulus-Secretion Coupling by microRNAs.

Increased blood glucose after a meal is countered by the subsequent increased release of the hypoglycemic hormone insulin from the pancreatic beta cells. The cascade of molecular events encompassing the initial sensing and transport of glucose into the beta cell, culminating with the exocytosis of the insulin large dense core granules (LDCVs) is termed "stimulus-secretion coupling." Impairment in any of the relevant processes leads to insufficient insulin release, which contributes to the development of type 2 diabetes (T2D). The fate of the beta cell, when exposed to environmental triggers of the disease, is determined by the possibility to adapt to the new situation by regulation of gene expression. As established factors of post-transcriptional regulation, microRNAs (miRNAs) are well-recognized mediators of beta cell plasticity and adaptation. Here, we put focus on the importance of comprehending the transcriptional regulation of miRNAs, and how miRNAs are implicated in stimulus-secretion coupling, specifically those influencing the late stages of insulin secretion. We suggest that efficient beta cell adaptation requires an optimal balance between transcriptional regulation of miRNAs themselves, and miRNA-dependent gene regulation. The increased knowledge of the beta cell transcriptional network inclusive of non-coding RNAs such as miRNAs is essential in identifying novel targets for the treatment of T2D.

Optogenetic control of insulin secretion in intact pancreatic islets with ß-cell-specific expression of Channelrhodopsin-2.

Insulin is secreted from the pancreatic ß-cells in response to elevated glucose. In intact islets the capacity for insulin release is determined by a complex interplay between different cell types. This has made it difficult to specifically assess the role of ß-cell defects to the insulin secretory impairment in type 2 diabetes. Here we describe a new approach, based on optogenetics, that enables specific investigation of ß-cells in intact islets. We used transgenic mice expressing the light-sensitive cation channel Channelrhodopsin-2 (ChR2) under control of the insulin promoter. Glucose tolerance in vivo was assessed using intraperitoneal glucose tolerance tests, and glucose-induced insulin release was measured from static batch incubations. ChR2 localization was determined by fluorescence confocal microscopy. The effect of ChR2 stimulation with blue LED light was assessed using Ca(2+) imaging and static islet incubations. Light stimulation of islets from transgenic ChR2 mice triggered prompt increases in intracellular Ca(2+). Moreover, light stimulation enhanced insulin secretion in batch-incubated islets at low and intermediate but not at high glucose concentrations. Glucagon release was not affected. Beta-cells from mice rendered diabetic on a high-fat diet exhibited a 3.5-fold increase in light-induced Ca(2+) influx compared with mice on a control diet. Furthermore, light enhanced insulin release also at high glucose in these mice, suggesting that high-fat feeding leads to a compensatory potentiation of the Ca(2+) response in ß-cells. The results demonstrate the usefulness and versatility of optogenetics for studying mechanisms of perturbed hormone secretion in diabetes with high time-resolution and cell-specificity.

Endothelial cell processing and alternatively spliced transcripts of factor VIII: potential implications for coagulation cascades and pulmonary hypertension.

BACKGROUND: Coagulation factor VIII (FVIII) deficiency leads to haemophilia A. Conversely, elevated plasma levels are a strong predictor of recurrent venous thromboemboli and pulmonary hypertension phenotypes in which in situ thromboses are implicated. Extrahepatic sources of plasma FVIII are implicated, but have remained elusive. METHODOLOGY/PRINCIPAL FINDINGS: Immunohistochemistry of normal human lung tissue, and confocal microscopy, flow cytometry, and ELISA quantification of conditioned media from normal primary endothelial cells were used to examine endothelial expression of FVIII and coexpression with von Willebrand Factor (vWF), which protects secreted FVIII heavy chain from rapid proteloysis. FVIII transcripts predicted from database mining were identified by RT-PCR and sequencing. FVIII mAb-reactive material was demonstrated in CD31+ endothelial cells in normal human lung tissue, and in primary pulmonary artery, pulmonary microvascular, and dermal microvascular endothelial cells. In pulmonary endothelial cells, this protein occasionally colocalized with vWF, centered on Weibel Palade bodies. Pulmonary artery and pulmonary microvascular endothelial cells secreted low levels of FVIII and vWF to conditioned media, and demonstrated cell surface expression of FVIII and vWF Ab-reacting proteins compared to an isotype control. Four endothelial splice isoforms were identified. Two utilize transcription start sites in alternate 5' exons within the int22h-1 repeat responsible for intron 22 inversions in 40% of severe haemophiliacs. A reciprocal relationship between the presence of short isoforms and full-length FVIII transcript suggested potential splice-switching mechanisms. CONCLUSIONS/SIGNIFICANCE: The pulmonary endothelium is confirmed as a site of FVIII secretion, with evidence of synthesis, cell surface expression, and coexpression with vWF. There is complex alternate transcription initiation from the FVIII gene. These findings provide a framework for future research on the regulation and perturbation of FVIII synthesis, and of potential relevance to haemophilia, thromboses, and pulmonary hypertensive states.