Photoswitchable diacylglycerols enable optical control of protein kinase C.

Increased levels of the second messenger lipid diacylglycerol (DAG) induce downstream signaling events including the translocation of C1-domain-containing proteins toward the plasma membrane. Here, we introduce three light-sensitive DAGs, termed PhoDAGs, which feature a photoswitchable acyl chain. The PhoDAGs are inactive in the dark and promote the translocation of proteins that feature C1 domains toward the plasma membrane upon a flash of UV-A light. This effect is quickly reversed after the termination of photostimulation or by irradiation with blue light, permitting the generation of oscillation patterns. Both protein kinase C and Munc13 can thus be put under optical control. PhoDAGs control vesicle release in excitable cells, such as mouse pancreatic islets and hippocampal neurons, and modulate synaptic transmission in Caenorhabditis elegans. As such, the PhoDAGs afford an unprecedented degree of spatiotemporal control and are broadly applicable tools to study DAG signaling

Proteasomal degradation of the histone acetyl transferase p300 contributes to beta-cell injury in a diabetes environment

In type 2 diabetes, amyloid oligomers, chronic hyperglycemia, lipotoxicity, and pro-inflammatory cytokines are detrimental to beta-cells, causing apoptosis and impaired insulin secretion. The histone acetyl transferase p300, involved in remodeling of chromatin structure by epigenetic mechanisms, is a key ubiquitous activator of the transcriptional machinery. In this study, we report that loss of p300 acetyl transferase activity and expression leads to beta-cell apoptosis, and most importantly, that stress situations known to be associated with diabetes alter p300 levels and functional integrity. We found that proteasomal degradation is the mechanism subserving p300 loss in beta-cells exposed to hyperglycemia or pro-inflammatory cytokines. We also report that melatonin, a hormone produced in the pineal gland and known to play key roles in beta-cell health, preserves p300 levels altered by these toxic conditions. Collectively, these data imply an important role for p300 in the pathophysiology of diabetes

Ground based detection and study of Saturn Electrostatic Discharges

Geophysical Research Abstracts EGU2008-A-09350EGU General Assemblyjournal articl

Ground-based study of Saturn lightning discharges

EPSC AbstractsEuropean Planetary Science Congressjournal articl

Ground-based study of Saturn lightning

Geophysical Research AbstractsEGU2009-9410EGU General Assemblyjournal articl

Glucose- and Hormone-Induced cAMP Oscillations in α- and β-Cells Within Intact Pancreatic Islets

OBJECTIVEcAMP is a critical messenger for insulin and glucagon secretion from pancreatic beta- and alpha-cells, respectively. Dispersed beta-cells show cAMP oscillations, but the signaling kinetics in cells within intact islets of Langerhans is unknown.RESEARCH DESIGN AND METHODSThe subplasma-membrane cAMP concentration ([cAMP](pm)) was recorded in alpha-and beta-cells in the mantle of intact mouse pancreatic islets using total internal reflection microscopy and a fluorescent translocation biosensor. Cell identification was based on the opposite effects of adrenaline on cAMP in alpha- and beta-cells.RESULTSIn islets exposed to 3 mmol/L glucose, [cAMP](pm) was low and stable. Glucagon and glucagon-like peptide-1(7-36)-amide (GLP-1) induced dose-dependent elevation of [cAMP](pm), often with oscillations synchronized among beta-cells. Whereas glucagon also induced [cAMP](pm) oscillations in most alpha-cells, &lt; 20% of the alpha-cells responded to GLP-1. Elevation of the glucose concentration to 11-30 mmol/L in the absence of hormones induced slow [cAMP](pm) oscillations in both alpha- and beta-cells. These cAMP oscillations were coordinated with those of the cytoplasmic Ca2+ concentration ([Ca2+](i)) in the beta-cells but not caused by the changes in [Ca2+](i) . The transmembrane adenylyl cyclase (AC) inhibitor 2'5'-dideoxyadenosine suppressed the glucose- and hormone-induced [cAMP](pm) elevations, whereas the preferential inhibitors of soluble AC, KH7, and 1,3,5(10)-estratrien-2,3,17-beta-triol perturbed cell metabolism and lacked effect, respectively.CONCLUSIONSOscillatory [cAMP](pm) signaling in secretagogue-stimulated beta-cells is maintained within intact islets and depends on transmembrane AC activity. The discovery of glucose- and glucagon-induced [cAMP](pm) oscillations in alpha-cells indicates the involvement of cAMP in the regulation of pulsatile glucagon secretion.</p

Inhibitory Effects of Leptin on Pancreatic α-Cell Function

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)OBJECTIVE-Leptin released from adipocytes plays a key role in the control of food intake, energy balance, and glucose homeostasis. In addition to its central action, leptin directly affects pancreatic beta-cells, inhibiting insulin secretion, and, thus, modulating glucose homeostasis. However, despite the importance of glucagon secretion in glucose homeostasis, the role of leptin in a-cell function has not been studied in detail. In the present study, we have investigated this functional interaction. RESEARCH DESIGN AND METHODS-The presence of leptin receptors (ObR) was demonstrated by RT-PCR analysis, Western blot, and immunocytochemistry. Electrical activity was analyzed by patch-clamp and Ca(2+) signals by confocal microscopy. Exocytosis and glucagon secretion were assessed using fluorescence methods and radioimmunoassay, respectively. RESULTS-The expression of several ObR isoforms (a-e) was detected in glucagon-secreting alpha TC1-9 cells. ObRb, the main isoform involved in leptin signaling, was identified at the protein level in alpha TC1-9 cells as well as in mouse and human alpha-cells. The application of leptin (6.25 nmol/l) hyperpolarized the alpha-cell membrane potential, suppressing the electrical activity induced by 0.5 mmol/l glucose. Additionally, leptin inhibited Ca(2+) signaling in alpha TC1-9 cells and in mouse and human alpha-cells within intact islets. A similar result occurred with 0.625 nmol/l leptin. These effects were accompanied by a decrease in glucagon secretion from mouse islets and were counteracted by the phosphatidylinositol 3-kinase inhibitor, wortmannin, suggesting the involvement of this pathway in leptin action. CONCLUSIONS-These results demonstrate that leptin inhibits alpha-cell function, and, thus, these cells are involved in the adipo-insular communication. Diabetes 58:1616-1624, 200958716161624Ministerio de Educacion y Ciencia [BFU2007-67607, PCI2005-A7-0131, BFU2008-01492, SAF2006-07382]Ministerio de Ciencia a InnovacionFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Ministerio de Educacion y Ciencia [BFU2007-67607, PCI2005-A7-0131, BFU2008-01492, SAF2006-07382]FAPESP [2008/53811-8

Colocalization of connexin 36 and corticotropin-releasing hormone in the mouse brain

<p>Abstract</p> <p>Background</p> <p>Gap junction proteins, connexins, are expressed in most endocrine and exocrine glands in the body and are at least in some glands crucial for the hormonal secretion. To what extent connexins are expressed in neurons releasing hormones or neuropeptides from or within the central nervous system is, however, unknown. Previous studies provide indirect evidence for gap junction coupling between subsets of neuropeptide-containing neurons in the paraventricular nucleus (PVN) of the hypothalamus. Here we employ double labeling and retrograde tracing methods to investigate to what extent neuroendocrine and neuropeptide-containing neurons of the hypothalamus and brainstem express the neuronal gap junction protein connexin 36.</p> <p>Results</p> <p>Western blot analysis showed that connexin 36 is expressed in the PVN. In bacterial artificial chromosome transgenic mice, which specifically express the reporter gene Enhanced Green Fluorescent Protein (EGFP) under the control of the connexin 36 gene promoter, EGFP expression was detected in magnocellular (neuroendocrine) and in parvocellular neurons of the PVN. Although no EGFP/connexin36 expression was seen in neurons containing oxytocin or vasopressin, EGFP/connexin36 was found in subsets of PVN neurons containing corticotropin-releasing hormone (CRH), and in somatostatin neurons located along the third ventricle. Moreover, CRH neurons in brainstem areas, including the lateral parabrachial nucleus, also expressed EGFP/connexin 36.</p> <p>Conclusion</p> <p>Our data indicate that connexin 36 is expressed in subsets of neuroendocrine and CRH neurons in specific nuclei of the hypothalamus and brainstem.</p