Disorganization and degeneration of liver sympathetic innervations in nonalcoholic fatty liver disease revealed by 3D imaging.

Hepatic nerves have a complex role in synchronizing liver metabolism. Here, we used three-dimensional (3D) immunoimaging to explore the integrity of the hepatic nervous system in experimental and human nonalcoholic fatty liver disease (NAFLD). We demonstrate parallel signs of mild degeneration and axonal sprouting of sympathetic innervations in early stages of experimental NAFLD and a collapse of sympathetic arborization in steatohepatitis.

Developmental Time Course of SNAP-25 Isoforms Regulate Hippocampal Long-Term Synaptic Plasticity and Hippocampus-Dependent Learning.

SNAP-25 is essential to activity-dependent vesicle fusion and neurotransmitter release in the nervous system. During early development and adulthood, SNAP-25 appears to have differential influences on short- and long-term synaptic plasticity. The involvement of SNAP-25 in these processes may be different at hippocampal and neocortical synapses because of the presence of two different splice variants, which are developmentally regulated.

Disabling Gβγ-SNAP-25 interaction in gene-targeted mice results in enhancement of long-term potentiation at Schaffer collateral-CA1 synapses in the hippocampus.

Three SNARE proteins, SNAP-25, syntaxin 1A, and VAMP2 or synaptobrevin 2, constitute the minimal functional machinery needed for the regulated secretion of neurotransmitters. Dynamic changes in the regulated release of neurotransmitters are associated with the induction of long-term plasticity at central synapses. In-vitro studies have validated the C-terminus of SNAP-25 as a target for inhibitory Gi/o-coupled G-protein coupled receptors at a number of synapses.

SNAP-25 isoforms differentially regulate synaptic transmission and long-term synaptic plasticity at central synapses.

SNAP-25 exists as two developmentally regulated alternatively spliced isoforms, SNAP-25a and SNAP-25b. We explored the function of SNAP-25a and SNAP-25b at Schaffer collateral-CA1 synapses in hippocampus using 4-week-old wild-type (WT) and SNAP-25b-deficient (MT) mice. Characterizing the protein expression of individual SNAP-25 isoforms revealed that WT females had higher levels of SNAP-25a than WT males, suggesting a sex-dependent delay of the alternative splicing switch from SNAP-25a to SNAP-25b.

SNAP-25 Puts SNAREs at Center Stage in Metabolic Disease.

Synaptosomal Associated Protein of 25 kD (SNAP-25) is an essential protein contributing 2 out of 4 α-helices in the formation of the core soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex which mediates regulated membrane fusion. Regulated exocytosis is a strictly controlled event in eukaryotic cells mediating important homeostatic processes and cellular communications. Altered release of neurotransmitters or hormones is usually considered as part of the progressing pathophysiology of central neurological or peripheral metabolic disorders.

SNAP-25a and SNAP-25b differently mediate interactions with Munc18-1 and Gβγ subunits.

SNAP-25 is a protein involved in regulated membrane fusion and part of the SNARE complex. It exists as two splicing variants, SNAP-25a and SNAP-25b, which differ in 9 out of 206 amino acids. SNAP-25 together with Syntaxin 1 and VAMP-2 forms the ternary SNARE complex essential for mediating activity-dependent release of hormones and neurotransmitters.

SNAP-25b-deficiency increases insulin secretion and changes spatiotemporal profile of Caoscillations in β cell networks.

SNAP-25 is a protein of the core SNARE complex mediating stimulus-dependent release of insulin from pancreatic β cells. The protein exists as two alternatively spliced isoforms, SNAP-25a and SNAP-25b, differing in 9 out of 206 amino acids, yet their specific roles in pancreatic β cells remain unclear. We explored the effect of SNAP-25b-deficiency on glucose-stimulated insulin release in islets and found increased secretion both in vivo and in vitro.

Minor differences in the molecular machinery mediating regulated membrane fusion has major impact on metabolic health.

The exocytosis of signaling molecules from neuronal, neuroendocrine and endocrine cells is regulated by membrane fusion involving SNAP-25 and associated SNARE proteins. The importance of this process for metabolic control recently became evident by studies of mouse mutants genetically engineered to only express one of 2 closely related, alternatively-spliced variants of SNAP-25. The results showed that even minor differences in the function of proteins regulating exocytosis are sufficient to provoke metabolic disease, including hyperglycaemia, liver steatosis, adipocyte hypertrophy and obesity.

Replacing SNAP-25b with SNAP-25a expression results in metabolic disease.

Synaptosomal-associated protein of 25 kDa (SNAP-25) is a key molecule in the soluble N-ethylmaleimide-sensitive factor attachment protein (SNARE) complex mediating fast Ca(2+)-triggered release of hormones and neurotransmitters, and both splice variants, SNAP-25a and SNAP-25b, can participate in this process. Here we explore the hypothesis that minor alterations in the machinery mediating regulated membrane fusion can increase the susceptibility for metabolic disease and precede obesity and type 2 diabetes. Thus, we used a mouse mutant engineered to express normal levels of SNAP-25 but only SNAP-25a.

Munc18-1 and Munc18-2 proteins modulate beta-cell Ca2+ sensitivity and kinetics of insulin exocytosis differently.

Fast neurotransmission and slower hormone release share the same core fusion machinery consisting of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins. In evoked neurotransmission, interactions between SNAREs and the Munc18-1 protein, a member of the Sec1/Munc18 (SM) protein family, are essential for exocytosis, whereas other SM proteins are dispensable. To address if the exclusivity of Munc18-1 demonstrated in neuroexocytosis also applied to fast insulin secretion, we characterized the presence and function of Munc18-1 and its closest homologue Munc18-2 in β-cell stimulus-secretion coupling.

Nephrin is expressed on the surface of insulin vesicles and facilitates glucose-stimulated insulin release.

Objective: Nephrin, an immunoglobulin-like protein essential for the function of the glomerular podocyte and regulated in diabetic nephropathy, is also expressed in pancreatic beta-cells, where its function remains unknown. The aim of this study was to investigate whether diabetes modulates nephrin expression in human pancreatic islets and to explore the role of nephrin in beta-cell function.

Research Design And Methods: Nephrin expression in human pancreas and in MIN6 insulinoma cells was studied by Western blot, PCR, confocal microscopy, subcellular fractionation, and immunogold labeling.

SNAP-25 and gene-targeted mouse mutants.

The evolutionary conserved soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) fusion machinery is the operational unit in the release of neurotransmitters and hormones from excitable cells. The SNARE core complex consists of three proteins named SNAP-25 (synaptosomal-associated protein of 25 kD), syntaxin 1, and VAMP (vesicle-associated membrane protein)/synaptobrevin. Syntaxin 1 is, together with SNAP-25, localized to the plasma membrane, whereas VAMP/synaptobrevin is a component of secretory vesicles.

An ancient duplication of exon 5 in the Snap25 gene is required for complex neuronal development/function.

Alternative splicing is an evolutionary innovation to create functionally diverse proteins from a limited number of genes. SNAP-25 plays a central role in neuroexocytosis by bridging synaptic vesicles to the plasma membrane during regulated exocytosis. The SNAP-25 polypeptide is encoded by a single copy gene, but in higher vertebrates a duplication of exon 5 has resulted in two mutually exclusive splice variants, SNAP-25a and SNAP-25b.

Heterogeneous expression of SNARE proteins SNAP-23, SNAP-25, Syntaxin1 and VAMP in human parathyroid tissue.

In regulated exocytosis synaptosomal-associated protein of 25kDa (SNAP-25) is one of the key-players in the formation of SNARE (soluble N-ethylmaleimide-sensitive fusion attachment protein receptor) complex and membrane fusion. SNARE proteins are essentially expressed in neurons, neuroendocrine and endocrine cells. Whether parathyroid cells express these proteins is not known.

Tomosyn is expressed in beta-cells and negatively regulates insulin exocytosis.

Tomosyn, a syntaxin-binding protein, is capable of dissociating mammalian homolog of the Caenorhabditis elegans unc-18 gene from syntaxin and is involved in the regulation of exocytosis. We have investigated the expression, cellular localization, and functional role of tomosyn in pancreatic beta-cells. Western blotting revealed a 130-kDa protein corresponding to tomosyn in insulin-secreting beta-cell lines.

Neuronal calcium sensor-1 potentiates glucose-dependent exocytosis in pancreatic beta cells through activation of phosphatidylinositol 4-kinase beta.

Cytosolic free Ca2+ plays an important role in the molecular mechanisms leading to regulated insulin secretion by the pancreatic beta cell. A number of Ca2+-binding proteins have been implicated in this process. Here, we define the role of the Ca2+-binding protein neuronal Ca2+ sensor-1 (NCS-1) in insulin secretion.

Cyclin-dependent kinase 5 activators p35 and p39 facilitate formation of functional synapses.

Cyclin-dependent kinase 5 (Cdk5) has emerged as a key coordinator of cell signaling in neurite outgrowth. Cdk5 needs to associate with one of the regulatory proteins p35 or p39 to be an active enzyme. To investigate if Cdk5 plays a role in the establishment of functional synapses, we have characterized the expression of Cdk5, p35, and p39 in the neuroblastoma-glioma cell line NG108-15, and recorded postsynaptic activity in myotubes in response to presynaptic overexpression of Cdk5, p35, and p39.

DARPP-32 and inhibitor-1 are expressed in pancreatic beta-cells.

Insulin secretion from pancreatic beta-cells has to be tightly regulated to ensure accurate glucose homeostasis. The capacity of beta-cells to respond to extracellular stimulation is determined by several signaling pathways. One important feature of these pathways is phosphorylation and subsequent dephosphorylation of a wide range of cellular substrates.

Developmentally regulated switch in alternatively spliced SNAP-25 isoforms alters facilitation of synaptic transmission.

Although the basic molecular components that promote regulated neurotransmitter release are well established, the contribution of these proteins as regulators of the plasticity of neurotransmission and refinement of synaptic connectivity during development is elaborated less fully. For example, during the period of synaptic growth and maturation in brain, the expression of synaptosomal protein 25 kDa (SNAP-25), a neuronal t-SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) essential for action potential-dependent neuroexocytosis, is altered through alternative splicing of pre-mRNA transcripts. We addressed the role of the two splice-variant isoforms of SNAP-25 with a targeted mouse mutation that impairs the shift from SNAP-25a to SNAP-25b.

Mint1, a Munc-18-interacting protein, is expressed in insulin-secreting beta-cells.

Munc-18-interacting (Mint) proteins are adaptors involved in regulation of synaptic vesicle exocytosis. We have investigated expression and cellular localization of Mint1 in pancreatic islets with special reference to insulin-secreting beta-cells. Western blotting showed that Mint1 was expressed in hamster (HIT-T15) and rat (RINm5F) beta-cell lines.

Cyclin-dependent kinase 5 associated with p39 promotes Munc18-1 phosphorylation and Ca(2+)-dependent exocytosis.

Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine/threonine protein kinase that requires association with a regulatory protein, p35 or p39, to form an active enzyme. Munc18-1 plays an essential role in membrane fusion, and its function is regulated by phosphorylation. We report here that both p35 and p39 were expressed in insulin-secreting beta-cells, where they exhibited individual subcellular distributions and associated with membranous organelles of different densities.