Schizophrenia susceptibility pathway neuregulin 1-ErbB4 suppresses Src upregulation of NMDA receptors

Hypofunction of the N-methyl D-aspartate subtype of glutamate receptor (NMDAR) is hypothesized to be a mechanism underlying cognitive dysfunction in individuals with schizophrenia. For the schizophrenia-linked genes NRG1 and ERBB4, NMDAR hypofunction is thus considered a key detrimental consequence of the excessive NRG1-ErbB4 signaling found in people with schizophrenia. However, we show here that neuregulin 1β-ErbB4 (NRG1β-ErbB4) signaling does not cause general hypofunction of NMDARs. Rather, we find that, in the hippocampus and prefrontal cortex, NRG1β-ErbB4 signaling suppresses the enhancement of synaptic NMDAR currents by the nonreceptor tyrosine kinase Src. NRG1β-ErbB4 signaling prevented induction of long-term potentiation at hippocampal Schaffer collateral-CA1 synapses and suppressed Src-dependent enhancement of NMDAR responses during theta-burst stimulation. Moreover, NRG1β-ErbB4 signaling prevented theta burst-induced phosphorylation of GluN2B by inhibiting Src kinase activity. We propose that NRG1-ErbB4 signaling participates in cognitive dysfunction in schizophrenia by aberrantly suppressing Src-mediated enhancement of synaptic NMDAR function.     

Chikungunya virus neutralization antigens and direct cell-to-cell transmission are revealed by human antibody-escape mutants

Chikungunya virus (CHIKV) is an alphavirus responsible for numerous epidemics throughout Africa and Asia, causing infectious arthritis and reportedly linked with fatal infections in newborns and elderly. Previous studies in animal models indicate that humoral immunity can protect against CHIKV infection, but despite the potential efficacy of B-cell-driven intervention strategies, there are no virus-specific vaccines or therapies currently available. In addition, CHIKV has been reported to elicit long-lasting virus-specific IgM in humans, and to establish long-term persistence in non-human primates, suggesting that the virus might evade immune defenses to establish chronic infections in man. However, the mechanisms of immune evasion potentially employed by CHIKV remain uncharacterized. We previously described two human monoclonal antibodies that potently neutralize CHIKV infection. In the current report, we have characterized CHIKV mutants that escape antibody-dependent neutralization to identify the CHIKV E2 domain B and fusion loop "groove" as the primary determinants of CHIKV interaction with these antibodies. Furthermore, for the first time, we have also demonstrated direct CHIKV cell-to-cell transmission, as a mechanism that involves the E2 domain A and that is associated with viral resistance to antibody-dependent neutralization. Identification of CHIKV sub-domains that are associated with human protective immunity, will pave the way for the development of CHIKV-specific sub-domain vaccination strategies. Moreover, the clear demonstration of CHIKV cell-to-cell transmission and its possible role in the establishment of CHIKV persistence, will also inform the development of future anti-viral interventions. These data shed new light on CHIKV-host interactions that will help to combat human CHIKV infection and inform future studies of CHIKV pathogenesis.     

Antioxidative and free radical scavenging activities of selected medicinal herbs

The antioxidative and superoxide- and hydroxyl radical-scavenging activities and pro-oxidant effect of twelve selected medicinal herbs were studied. The aqueous extracts of Coptis chinensis, Paeonia suffruticosa, Prunella vulgaris and Senecio scandens exhibited the highest potency in inhibiting rat erythrocyte hemolysis and lipid peroxidation in rat kidney and brain homogenates. The aforementioned four herbs also demonstrated strong superoxide- and hydroxyl radical-scavenging activity, but exerted only a slight pro-oxidant effect.     

Habitat Preference, Reproduction and Diet of the Earthworm Eel, Chendol keelini (Teleostei: Chaudhuriidae)

The ecology of the earthworm eel, Chendol keelini, was studied in the field over a period of nine months. In addition this information was supplemented by aquarium observations. The species was most abundant in pools where it was associated with leaf litter and mats of fine tree roots along the banks. It fed on benthic invertebrates, especially chironomid and ephemeropteran larvae. C. keelini is sexually dimorphic; adult males develop a headhump and grow to a larger size than females. Reproduction was seasonal; the reproductive phase coincided with the wet season and lasted for several months. Fecundity was around 40 eggs per clutch. The eggs were spherical, between 1.2 and 1.5mm in diameter, and possessed a pair of long filaments for adhesion to the substrate. Females probably spawned more than once during the breeding season. The length frequency distributions and juvenile growth suggest that C. keelini is a short-lived species that matures during the first year with few individuals surviving to the second breeding season.     

Insights into interactions between the alpha-helical region of the salmon calcitonin antagonists and the human calcitonin receptor using photoaffinity labeling

Fish-like calcitonins (CTs), such as salmon CT (sCT), are widely used clinically in the treatment of bone-related disorders; however, the molecular basis for CT binding to its receptor, a class II G protein-coupled receptor, is not well defined. In this study we have used photoaffinity labeling to identify proximity sites between CT and its receptor. Two analogues of the antagonist sCT(8-32) containing a single photolabile p-benzoyl-l-phenylalanine (Bpa) residue in position 8 or 19 were used. Both analogues retained high affinity for the CT receptor and potently inhibited agonist-induced cAMP production. The [Bpa(19)]sCT(8-32) analogue cross-linked to the receptor at or near the equivalent cross-linking site of the full-length peptide, within the fragment Cys(134)-Lys(141) (within the amino terminus of the receptor, adjacent to transmembrane 1) (Pham, V., Wade, J. D., Purdue, B. W., and Sexton, P. M. (2004) J. Biol. Chem. 279, 6720-6729). In contrast, proteolytic mapping and mutational analysis identified Met(49) as the cross-linking site for [Bpa(8)]sCT(8-32). This site differed from the previously identified cross-linking site of the agonist [Bpa(8)]human CT (Dong, M., Pinon, D. I., Cox, R. F., and Miller, L. J. (2004) J. Biol. Chem. 279, 31177-31182) and may provide evidence for conformational differences between interaction with active and inactive state receptors. Molecular modeling suggests that the difference in cross-linking between the two Bpa(8) analogues can be accounted for by a relatively small change in peptide orientation. The model was also consistent with cooperative interaction between the receptor amino terminus and the receptor core.     

phrA, the major photoreactivating factor in the cyanobacterium Synechocystis sp. strain PCC 6803 codes for a cyclobutane-pyrimidine-dimer-specific DNA photolyase

A new broad-host-range plasmid, pSL1211, was constructed for the over-expression of genes in Synechocystis sp. strain PCC 6803. The plasmid was derived from RSF1010 and an Escherichia coli over-expression plasmid, pTrcHisC. Over-expressed protein is made with a removable N-terminal histidine tag. The plasmid was used to over-express the phrA gene and purify the gene product from Synechocystis sp. strain PCC 6803. PhrA is the major ultraviolet-light-resistant factor in the cyanobacterium. The purified PhrA protein exhibited an optical absorption spectrum similar to that of the cyclobutane pyrimidine dimer (CPD) DNA photolyase from Synechocuccus sp. strain PCC 6301 (Anacystis nidulans). Mass spectrometry analysis of PhrA indicated that the protein contains 8-hydroxy-5-deazariboflavin and flavin adenine dinucleotide (FADH2) as cofactors. PhrA repairs only cyclobutane pyrimidine dimer but not pyrimidine (6-4) pyrimidinone photoproducts. On the basis of these results, the PhrA protein is classified as a class I, HDF-type, CPD DNA photolyase.     

Age-dependent choice of sexual partners and the transmission dynamics of HIV in Sub-Saharan Africa.

A mathematical model of the transmission of HIV-1 within heterosexual populations in Sub-Saharan Africa is described and its properties analysed. The model incorporates epidemiological and demographic processes and extends previous work in this area via the inclusion of age and sex dependency in rates of sexual partner change, and sexual partner choice dependent on age. Parameter assignments are made on the basis of current data on the transmission dynamics of HIV-1 and the demography of human populations in Africa. Both age-dependent rates of sexual activity and the sexual contact of males with females younger than themselves act to enhance the predicted demographic impact. With realistic parameter values, the model suggests AIDS is able to reverse the sign of population growth rates from positive to negative values over a timescale of a few decades. The sensitivity of this prediction is examined in relation to changes in the pattern of sexual contact between different age classes of females and males, different patterns of change in the age-dependent rate of sexual partner change, different assumptions concerning the doubling time of the epidemic in its early stages, and the relative efficiencies of viral transmission between men and women, and vice versa. The impact AIDS is predicted to have on the number of young and elderly persons as a fraction of the number of productive adults (the dependancy ratio) is examined under various assumptions concerning the weighting to be applied to mirror the burden imposed by the care of those with AIDS. The paper includes an assessment of the influence of the timing of changes in sexual behaviour, or the promotion of the use of condoms, on the predicted course of the epidemic. The paper concludes with a discussion of data needs and the model refinements required to more accurately mirror current understanding of the epidemiology of HIV-1.     

A Truncated Fragment of Src Protein Kinase Generated by Calpain-mediated Cleavage Is a Mediator of Neuronal Death in Excitotoxicity

Excitotoxicity resulting from overstimulation of glutamate receptors is a major cause of neuronal death in cerebral ischemic stroke. The overstimulated ionotropic glutamate receptors exert their neurotoxic effects in part by overactivation of calpains, which induce neuronal death by catalyzing limited proteolysis of specific cellular proteins. Here, we report that in cultured cortical neurons and in vivo in a rat model of focal ischemic stroke, the tyrosine kinase Src is cleaved by calpains at a site in the N-terminal unique domain. This generates a truncated Src fragment of ∼52 kDa, which we localized predominantly to the cytosol. A cell membrane-permeable fusion peptide derived from the unique domain of Src prevents calpain from cleaving Src in neurons and protects against excitotoxic neuronal death. To explore the role of the truncated Src fragment in neuronal death, we expressed a recombinant truncated Src fragment in cultured neurons and examined how it affects neuronal survival. Expression of this fragment, which lacks the myristoylation motif and unique domain, was sufficient to induce neuronal death. Furthermore, inactivation of the prosurvival kinase Akt is a key step in its neurotoxic signaling pathway. Because Src maintains neuronal survival, our results implicate calpain cleavage as a molecular switch converting Src from a promoter of cell survival to a mediator of neuronal death in excitotoxicity. Besides unveiling a new pathological action of Src, our discovery of the neurotoxic action of the truncated Src fragment suggests new therapeutic strategies with the potential to minimize brain damage in ischemic stroke.