The effects of somatostatin and some of its tetrapeptide fragments on ethanol-induced gastric mucosal erosion in rat

A study was made of the cytoprotective effects of somatostatin (SRIF) and its 3-6, 5-8, 7-10, 9-12 and 11-14 tetrapeptide fragments on absolute ethanol-induced haemorrhagic erosions in the stomach of rat. The SRIF molecule was found to prevent the gastric erosions induced by ethanol. The 7-10 and 11-14 fragments exhibited similar properties. There are two peaks in the cytoprotective dose-response curves. It is concluded that various fragments of SRIF can also exert cytoprotective effects.     

PhyloSim - Monte Carlo simulation of sequence evolution in the R statistical computing environment

Background  

The Monte Carlo simulation of sequence evolution is routinely used to assess the performance of phylogenetic inference methods and sequence alignment algorithms. Progress in the field of molecular evolution fuels the need for more realistic and hence more complex simulations, adapted to particular situations, yet current software makes unreasonable assumptions such as homogeneous substitution dynamics or a uniform distribution of indels across the simulated sequences. This calls for an extensible simulation framework written in a high-level functional language, offering new functionality and making it easy to incorporate further complexity.     

Protein array based interactome analysis of amyloid-β indicates an inhibition of protein translation

Oligomeric amyloid-β is currently of interest in amyloid-β mediated toxicity and the pathogenesis of Alzheimer's disease. Mapping the amyloid-β interaction partners could help to discover novel pathways in disease pathogenesis. To discover the amyloid-β interaction partners, we applied a protein array with more than 8100 unique recombinantly expressed human proteins. We identified 324 proteins as potential interactors of oligomeric amyloid-β. The Gene Ontology functional analysis of these proteins showed that oligomeric amyloid-β bound to multiple proteins with diverse functions both from extra and intracellular localizations. This undiscriminating binding phenotype indicates that multiple protein interactions mediate the toxicity of the oligomeric amyloid-β. The most highly impacted cellular system was the protein translation machinery. Oligomeric amyloid-β could bind to altogether 24 proteins involved in translation initiation and elongation. The binding of amyloid-β to purified rat hippocampal ribosomes validated the protein array results. More importantly, in vitro translation assays showed that the oligomeric amyloid-β had a concentration dependent inhibitory activity on translation. Our results indicate that the inhibited protein synthesis is one of the pathways that can be involved in the amyloid-beta induced neurotoxicity.     

Tianeptine potentiates AMPA receptors by activating CaMKII and PKA via the p38, p42/44 MAPK and JNK pathways

Impairments of cellular plasticity appear to underlie the pathophysiology of major depression. Recently, elevated levels of phosphorylated AMPA receptor were implicated in the antidepressant effect of various drugs. Here, we investigated the effects of an antidepressant, Tianeptine, on synaptic function and GluA1 phosphorylation using murine hippocampal slices and in vivo single-unit recordings. Tianeptine, but not imipramine, increased AMPA receptor-mediated neuronal responses both in vitro and in vivo, in a staurosporine-sensitive manner. Paired-pulse ratio was unaltered by Tianeptine, suggesting a postsynaptic site of action. Tianeptine, 10 μM, enhanced the GluA1-dependent initial phase of LTP, whereas 100 μM impaired the latter phases, indicating a critical role of GluA1 subunit phosphorylation in the excitation. Tianeptine rapidly increased the phosphorylation level of Ser⁸³¹-GluA1 and Ser⁸⁴⁵-GluA1. Using H-89 and KN-93, we show that the activation of both PKA and CaMKII is critical in the effect of Tianeptine on AMPA responses. Moreover, the phosphorylation states of Ser^217/221-MEK and Thr¹⁸³/Tyr¹⁸⁵-p42MAPK were increased by Tianeptine and specific kinase blockers of the MAPK pathways (PD 98095, SB 203580 and SP600125) prevented the effects of Tianeptine. Overall these data suggest that Tianeptine potentiates several signaling cascades associated with synaptic plasticity and provide further evidence that a major mechanism of action for Tianeptine is to act as an enhancer of glutamate neurotransmission via AMPA receptors.     

Effect of the beta-sheet-breaker peptide LPFFD on oriented network of amyloid β25-35 fibrils

Amyloid fibrils are self-associating filamentous structures deposited in extracellular tissue in various neurodegenerative and protein misfolding disorders. It has been shown that beta-sheet-breaker (BSB) peptides may interfere with amyloid fibril assembly. Although BSB peptides are prospective therapeutic agents in amyloidosis, there is ambiguity about the mechanisms and generality of their action. In the present work we analyzed the effect of the BSB peptide LPFFD on the growth kinetics, morphologic, and mechanical properties of amyloid β25-35 (Aβ25-35) fibrils assembled in an oriented array on mica surface. Aβ25-35 is thought to represent the biologically active, toxic fragment of the full-length Aβ peptide. Growth kinetics and morphologic features were analyzed using in situ atomic force microscopy in the presence of various concentrations of LPFFD. We found that the addition of LPFFD only slightly altered the assembly kinetics of Aβ25-35 fibrils. Already formed fibrils did not disassemble in the presence of high concentrations of LPFFD. The mechanical stability of the fibrils was explored with force spectroscopy methods. The nanomechanical behavior of Aβ25-35 fibrils is characterized by the appearance of force staircases which correspond to the force-driven unzipping and dissociation of several protofilaments. In the presence of LPFFD single-plateau force traces dominated. The effects of LPFFD on Aβ25-35 fibril assembly and stability suggest that inter-protofilament interactions were slightly weakened. Complete disassembly of fibrils, however, was not observed. Thus, under the conditions explored here, LPFFD may not be considered as a BSB peptide with generalized beta-sheet breaking properties.     

Cell types, circuits, computation

How does the connectivity of a neuronal circuit, together with the individual properties of the cell types that take part in it, result in a given computation? We examine this question in the context of retinal circuits. We suggest that the retina can be viewed as a parallel assemblage of many small computational devices, highly stereotypical and task-specific circuits afferent to a given ganglion cell type, and we discuss some rules that govern computation in these devices. Multi-device processing in retina poses conceptual problems when it is contrasted with cortical processing. We lay out open questions both on processing in retinal circuits and on implications for cortical processing of retinal inputs.     

Optogenetic approaches to restoring visual function in retinitis pigmentosa

Retinitis pigmentosa is a hereditary eye disease that affects photoreceptors and leads to blindness. The discovery of a microbial light-gated channel and the subsequent development of similar 'optogenetic' sensors have opened the door to creating artificial photoreceptors in the remaining retinal circuits of retinitis pigmentosa retinas via gene therapy. Here we review recent studies in animal models of retinitis pigmentosa that have combined knowledge of retinal cell types, circuits and computations with the ability to equip cell types with optogenetic sensors in order to restore visual activity. We also discuss the translational potential of this therapy.     

Novel mechanism of activation of NADPH oxidase 5. calcium sensitization via phosphorylation

In contrast to other Nox isoforms, the activity of Nox5 does not require the presence of accessory proteins and is entirely dependent on the elevation of intracellular calcium. Previous studies have shown that the EC(50) of Nox5 for calcium is relatively high and raises the question of whether Nox5 can be sufficiently activated in cells that do not experience extreme elevations of intracellular calcium. In the current study, we have identified a novel mechanism governing the activity of Nox5. Exposure of cells expressing Nox5 to phorbol 12-myristate 13-acetate (PMA) resulted in a slow and sustained increase in ROS, which was markedly different from the rapid response to ionomycin. PMA greatly potentiated the activity of Nox5 in response to low concentrations of ionomycin. The ability of PMA to increase Nox5 activity was abolished by calcium chelation and was a direct effect on enzyme activity, since PMA increased the calcium sensitivity of Nox5 in a cell-free assay. PMA stimulated the time-dependent phosphorylation of Nox5 on Thr(494) and Ser(498). Mutation of these residues to alanine abolished both PMA-dependent phosphorylation and calcium sensitization. Conversely, mutation of Thr(494) and Ser(498) to glutamic acid produced a gain of function mutant that had increased activity at low concentrations of ionomycin. Within the cell, Nox5 was detected in detergent-resistant microdomains of the endoplasmic reticulum. In summary, the phosphorylation of Nox5 at key residues facilitates enzyme activation at lower levels of intracellular calcium and may provide an avenue for enzyme activation in response to a greater variety of extracellular stimuli.