Contribution of different mechanisms to pancreatic beta-cell hyper-secretion in non-obese diabetic (NOD) mice during pre-diabetes

Disrupted Endoplasmic Reticulum Ca2+ Handling: A Harβinger of β-Cell Failure

The β-cell workload increases in the setting of insulin resistance and reduced β-cell mass, which occurs in type 2 and type 1 diabetes, respectively. The prolonged elevation of insulin production and secretion during the pathogenesis of diabetes results in β-cell ER stress. The depletion of β-cell Ca2+ER during ER stress activates the unfolded protein response, leading to β-cell dysfunction. Ca2+ER is involved in many pathways that are critical to β-cell function, such as protein processing, tuning organelle and cytosolic Ca2+ handling, and modulating lipid homeostasis. Mutations that promote β-cell ER stress and deplete Ca2+ER stores are associated with or cause diabetes (e.g., mutations in ryanodine receptors and insulin). Thus, improving β-cell Ca2+ER handling and reducing ER stress under diabetogenic conditions could preserve β-cell function and delay or prevent the onset of diabetes. This review focuses on how mechanisms that control β-cell Ca2+ER are perturbed during the pathogenesis of diabetes and contribute to β-cell failure.

Beta cell specific cannabinoid 1 receptor deletion counteracts progression to hyperglycemia in non-obese diabetic mice

OBJECTIVE

Type 1 diabetes (T1D) occurs because of islet infiltration by autoreactive immune cells leading to destruction of beta cells and it is becoming evident that beta cell dysfunction partakes in this process. We previously reported that genetic deletion and pharmacological antagonism of the cannabinoid 1 receptor (CB1) in mice improves insulin synthesis and secretion, upregulates glucose sensing machinery, favors beta cell survival by reducing apoptosis, and enhances beta cell proliferation. Moreover, beta cell specific deletion of CB1 protected mice fed a high fat high sugar diet against islet inflammation and beta cell dysfunction. Therefore, we hypothesized that it would mitigate the dysfunction of beta cells in the precipitating events leading to T1D.

METHODS

We genetically deleted CB1 specifically from beta cells in non-obese diabetic (NOD; NOD RIP Cre+ Cnr1fl/fl) mice. We evaluated female NOD RIP Cre+ Cnr1fl/fl mice and their NOD RIP Cre-Cnr1fl/fl and NOD RIP Cre+ Cnr1Wt/Wt littermates for onset of hyperglycemia over 26 weeks. We also examined islet morphology, islet infiltration by immune cells and beta cell function and proliferation.

RESULTS

Beta cell specific deletion of CB1 in NOD mice significantly reduced the incidence of hyperglycemia by preserving beta cell function and mass. Deletion also prevented beta cell apoptosis and aggressive insulitis in NOD RIP Cre+ Cnr1fl/fl mice compared to wild-type littermates. NOD RIP Cre+ Cnr1fl/fl islets maintained normal morphology with no evidence of beta cell dedifferentiation or appearance of extra islet beta cells, indicating that protection from autoimmunity is inherent to genetic deletion of beta cell CB1. Pancreatic lymph node Treg cells were significantly higher in NOD RIP Cre+ Cnr1fl/flvs NOD RIP Cre-Cnr1fl/fl.

CONCLUSIONS

Collectively these data demonstrate how protection of beta cells from metabolic stress during the active phase of T1D can ameliorate destructive insulitis and provides evidence for CB1 as a potential pharmacologic target in T1D.

Inferior Colliculus Transcriptome After Status Epilepticus in the Genetically Audiogenic Seizure-Prone Hamster GASH/Sal

The Genetic Audiogenic Seizure Hamster from Salamanca (GASH/Sal), an animal model of reflex epilepsy, exhibits generalized tonic–clonic seizures in response to loud sound with the epileptogenic focus localized in the inferior colliculus (IC). Ictal events in seizure-prone strains cause gene deregulation in the epileptogenic focus, which can provide insights into the epileptogenic mechanisms. Thus, the present study aimed to determine the expression profile of key genes in the IC of the GASH/Sal after the status epilepticus. For such purpose, we used RNA-Seq to perform a comparative study between the IC transcriptome of GASH/Sal and that of control hamsters both subjected to loud sound stimulation. After filtering for normalization and gene selection, a total of 36 genes were declared differentially expressed from the RNA-seq analysis in the IC. A set of differentially expressed genes were validated by RT-qPCR showing significant differentially expression between GASH/Sal hamsters and Syrian control hamsters. The confirmed differentially expressed genes were classified on ontological categories associated with epileptogenic events similar to those produced by generalized tonic seizures in humans. Subsequently, based on the result of metabolomics, we found the interleukin-4 and 13-signaling, and nucleoside transport as presumably altered routes in the GASH/Sal model. This research suggests that seizures in GASH/Sal hamsters are generated by multiple molecular substrates, which activate biological processes, molecular processes, cellular components and metabolic pathways associated with epileptogenic events similar to those produced by tonic seizures in humans. Therefore, our study supports the use of the GASH/Sal as a valuable animal model for epilepsy research, toward establishing correlations with human epilepsy and searching new biomarkers of epileptogenesis.

Deficiency of PRKD2 triggers hyperinsulinemia and metabolic disorders

Hyperinsulinemia is the earliest symptom of insulin resistance (IR), but a causal relationship between the two remains to be established. Here we show that a protein kinase D2 (PRKD2) nonsense mutation (K410X) in two rhesus monkeys with extreme hyperinsulinemia along with IR and metabolic defects by using extreme phenotype sampling and deep sequencing analyses. This mutation reduces PRKD2 at both the mRNA and the protein levels. Taking advantage of a PRKD2-KO mouse model, we demonstrate that PRKD2 deletion triggers hyperinsulinemia which precedes to IR and metabolic disorders in the PRKD2 ablation mice. PRKD2 deficiency promotes β-cell insulin secretion by increasing the expression and activity of L-type Ca²⁺ channels and subsequently augmenting high glucose- and membrane depolarization-induced Ca²⁺ influx. Altogether, these results indicate that down-regulation of PRKD2 is involved in the pathogenesis of hyperinsulinemia which, in turn, results in IR and metabolic disorders.

Hyperinsulinemia can precede the development of insulin resistance. Here the authors identify a PKD2 mutation that leads to hyperinsulinemia and insulin resistance in Rhesus monkey and show that PKD2 deficiency promotes beta cell insulin secretion by activating L-type Ca2+ channels.

Contrasting Frustrated Lewis Pair Reactivity with Selenium- and Boron-Based Lewis Acids

The activation of π-bonds in diynyl esters has been investigated by using soft and hard Lewis acids. In the case of the soft selenium Lewis acid PhSeCl, sequential activation of the alkyne bonds leads initially to an isocoumarin (1 equiv PhSeCl) and then to a tetracyclic conjugated structure with the isocoumarin subunit fused to a benzoselenopyran (3 equiv PhSeCl). Conversely, the reaction with the hard Lewis acidic borane B(C6 F5 )3 initiates a cascade reaction to yield a complex π-conjugated system containing phthalide and indene subunits.

Chemical constituents from the tubers of Scirpus yagara and their anti-inflammatory activities

A new natural compound, dehydrophyllodulcin (1) was isolated from the tubers of Scirpus yagara, together with 11 known compounds. Among them, compounds 2, 5-8, and 10-12 were isolated from this plant for the first time. (1)H NMR, (13)C NMR, and 2D NMR data of compound 1 are first reported in this article, though it was synthesized in 1996. The structures of all compounds were determined by comprehensive analyses of their spectroscopic data and compared with literature information. Moreover, the anti-inflammatory effects of compounds 1, 3, 4, 6, and 9 against inflammatory cytokines production in Lipopolysaccharide - or Pam3csk4-stimulated macrophage RAW264.7 cells were evaluated by Enzyme-linked immunosorbent assay. And these compounds significantly inhibited the tumor necrosis factor (TNF)-α, interleukin (IL)-6 productions in RAW264.7 cells, with IC50 values less than 20 μM.

Diacylglycerol Guides the Hopping of Clathrin-Coated Pits along Microtubules for Exo-Endocytosis Coupling

Many receptor-mediated endocytic processes are mediated by constitutive budding of clathrin-coated pits (CCPs) at spatially randomized sites before slowly pinching off from the plasma membrane (60-100 s). In contrast, clathrin-mediated endocytosis (CME) coupled with regulated exocytosis in excitable cells occurs at peri-exocytic sites shortly after vesicle fusion (∼10 s). The molecular mechanism underlying this spatiotemporal coupling remains elusive. We show that coupled endocytosis makes use of pre-formed CCPs, which hop to nascent fusion sites nearby following vesicle exocytosis. A dynamic cortical microtubular network, anchored at the cell surface by the cytoplasmic linker-associated protein on microtubules and the LL5β/ELKS complex on the plasma membrane, provides the track for CCP hopping. Local diacylglycerol gradients generated upon exocytosis guide the direction of hopping. Overall, the CCP-cytoskeleton-lipid interaction demonstrated here mediates exocytosis-coupled fast recycling of both plasma membrane and vesicular proteins, and it is required for the sustained exocytosis during repetitive stimulations.

Alterations of the Ca²⁺ signaling pathway in pancreatic beta-cells isolated from db/db mice

Upon glucose elevation, pancreatic beta-cells secrete insulin in a Ca²⁺-dependent manner. In diabetic animal models, different aspects of the calcium signaling pathway in beta-cells are altered, but there is no consensus regarding their relative contributions to the development of beta-cell dysfunction. In this study, we compared the increase in cytosolic Ca²⁺ ([Ca²⁺]_i) via Ca²⁺ influx, Ca²⁺ mobilization from endoplasmic reticulum (ER) calcium stores, and the removal of Ca²⁺ via multiple mechanisms in beta-cells from both diabetic db/db mice and non-diabetic C57BL/6J mice. We refined our previous quantitative model to describe the slow [Ca²⁺]_i recovery after depolarization in beta-cells from db/db mice. According to the model, the activity levels of the two subtypes of the sarco-endoplasmic reticulum Ca²⁺-ATPase (SERCA) pump, SERCA2 and SERCA3, were severely down-regulated in diabetic cells to 65% and 0% of the levels in normal cells. This down-regulation may lead to a reduction in the Ca²⁺ concentration in the ER, a compensatory up-regulation of the plasma membrane Na⁺/Ca²⁺ exchanger (NCX) and a reduction in depolarization-evoked Ca²⁺ influx. As a result, the patterns of glucose-stimulated calcium oscillations were significantly different in db/db diabetic beta-cells compared with normal cells. Overall, quantifying the changes in the calcium signaling pathway in db/db diabetic beta-cells will aid in the development of a disease model that could provide insight into the adaptive transformations of beta-cell function during diabetes development.

Imaging beta-cell mass and function in situ and in vivo

Glucose-stimulated insulin secretion (GSIS) from pancreatic beta-cells is critical to the maintenance of blood glucose homeostasis in animals. Both decrease in pancreatic beta-cell mass and defects in beta-cell function contribute to the onset of diabetes, although the underlying mechanisms remain largely unknown. Molecular imaging techniques can help beta-cell study in a number of ways. High-resolution fluorescence imaging techniques provide novel insights into the fundamental mechanisms underlying GSIS in isolated beta-cells or in situ in pancreatic islets, and dynamic changes of beta-cell mass and function can be noninvasively monitored in vivo by imaging techniques such as positron emission tomography and single-photon emission computed tomography. All these techniques will contribute to the better understanding of the progression of diabetes and the search for the optimized therapeutic measures that reverse deficits in beta-cell mass and function.

Investigation of secreted protein transcripts as early biomarkers for type 1 diabetes in the mouse model

Type 1 diabetes (T1D) represents a serious health burden in the world, complicated by the fact that disease onset can be preceded by a long time period without evident clinical signs. It would be then of critical importance to detect the disease in its early stages. In this direction, we seek here to identify early preinflammatory markers for autoimmune diabetes, mining our previously reported transcriptome data relevant to distinct early sub-phenotypes in the NOD mouse, associated with early insulin autoantibodies (E-IAA). More specifically we focus on secreted or transmembrane protein transcripts, identifying in this category 71 differentially expressed transcripts which are regulated at the early preinflammatory stages of T1D in the pancreatic lymph nodes (PLN). Following the expression patterns of these 71 transcripts, correspondence analysis (a multivariate analysis method) reveals a clear-cut segregation of the individual samples according to the early subphenotype used. Thus the 71 transcripts coding for secreted proteins constitute a candidate-set of predictive biomarkers for the development of autoimmune damage of the β cells of the pancreas. The majority of these genes have human orthologs and accordingly they represent potential candidate biomarkers for the human disease. In addition, for predictive purposes, the analysis reveals the possibility to reduce significantly the size of the candidate-set in practice, with various genes displaying identical expression profiles.

Bulk-like endocytosis plays an important role in the recycling of insulin granules in pancreatic beta cells

Although bulk endocytosis has been found in a number of neuronal and endocrine cells, the molecular mechanism and physiological function of bulk endocytosis remain elusive. In pancreatic beta cells, we have observed bulk-like endocytosis evoked both by flash photolysis and trains of depolarization. Bulk-like endocytosis is a clathrin-independent process that is facilitated by enhanced extracellular Ca(2+) entry and suppressed by the inhibition of dynamin function. Moreover, defects in bulk-like endocytosis are accompanied by hyperinsulinemia in primary beta cells dissociated from diabetic KKAy mice, which suggests that bulk-like endocytosis plays an important role in maintaining the exo-endocytosis balance and beta cell secretory capability.