Human apolipoprotein C-I expression in mice impairs learning and memory functions

The H2 allele of APOC1, giving rise to increased gene expression of apolipoprotein C-I (apoC-I), is in genetic disequilibrium with the APOE4 allele and may provide a major risk factor for Alzheimer's disease (AD). We found that apoC-I protein is present in astrocytes and endothelial cells within hippocampal regions in both human control and AD brains. Interestingly, apoC-I colocalized with beta-amyloid (Abeta) in plaques in AD brains, and in vitro experiments revealed that aggregation of Abeta was delayed in the presence of apoC-I. Moreover, apoC-I was found to exacerbate the soluble Abeta oligomer-induced neuronal death. To establish a potential role for apoC-I in cognitive functions, we used human (h) APOC1(+/0) transgenic mice that express APOC1 mRNA throughout their brains and apoC-I protein in astrocytes and endothelial cells. The hAPOC1(+/0) mice displayed impaired hippocampal-dependent learning and memory functions compared with their wild-type littermates, as judged from their performance in the object recognition task (P = 0.012) and in the Morris water maze task (P = 0.010). ApoC-I may affect learning as a result of its inhibitory properties toward apoE-dependent lipid metabolism. However, no differences in brain mRNA or protein levels of endogenous apoE were detected between transgenic and wild-type mice. In conclusion, human apoC-I expression impairs cognitive functions in mice independent of apoE expression, which supports the potential of a modulatory role for apoC-I during the development of AD.     

Influence of temperature,oxygen and food availability on the migrational activity of bathyal benthic foraminifera: evidence by microcosm experiments

Foraminifera are a dominant group of amoeboid protists in the deep-sea and play possibly a significant role in decomposition processes of incoming organic matter. In order to study the poorly known ecology of these protozoans, microcosm experiments with living bathyal benthic foraminifera have been conducted. Foraminifera from 2880 m and shallower water depths were successfully maintained and their movement patterns investigated. By video documentation, high mean migration speed of 20,02 (N = 22) and 24,48 m min^-1 (N = 10) at 4 °C were found for species such as Hoeglundina elegans and Quinqueloculina seminula from 1847 m and 1921 m water depth, respectively. The results demonstrate that some bathyal foraminifera have migration speeds comparable to those of shallow water species. Environmental factors such as temperature, food concentration and oxygen content showed a marked influence on the migration of some species. An increase in temperature from 10 °C to 15 °C resulted in an increase of 35% in the migration speed of Allogromia spp. However, other species reacted differently. Higher food concentration resulted in a decrease in speed of some species. While in Quinqueloculina lamarckiana speed was not greatly affected by a low oxygen content in the sediment, other foraminifera responded to oxygen depletion by migration to the surface layers. Observations of benthic foraminifera in the laboratory microcosms are discussed in relation to microhabitats and the fate of organic matter on the sea floor and in the sediment.     

Identification of a bifunctional enzyme MnmC involved in the biosynthesis of a hypermodified uridine in the wobble position of tRNA

The gene encoding the bifunctional enzyme MnmC that catalyzes the two last steps in the biosynthesis of 5-methylaminomethyl-2-thiouridine (mnm5s2U) in tRNA has been previously mapped at about 50 min on the Escherichia coli K12 chromosome, but to date the identity of the corresponding enzyme has not been correlated with any of the known open reading frames (ORFs). Using the protein fold-recognition approach, we predicted that the 74-kDa product of the yfcK ORF located at 52.6 min and annotated as "putative peptidase" comprises a methyltransferase domain and a FAD-dependent oxidoreductase domain. We have cloned, expressed, and purified the YfcK protein and demonstrated that it catalyzes the formation of mnm5s2U in tRNA. Thus, we suggest to rename YfcK as MnmC.     

Differences in basal and stress-induced HPA regulation of wild house mice selected for high and low aggression

Male wild house mice, selected for short (SAL) and long (LAL) attack latency, show distinctly different behavioral strategies in coping with environmental challenges. In this study, we tested the hypothesis that this difference in coping style is associated with a differential stress responsiveness of the hypothalamic-pituitary-adrenal (HPA) system. SAL rather than LAL mice showed a clear fluctuation in circulating corticosterone concentrations around the circadian peak with significantly higher levels in the late light phase. LAL mice showed lower basal ACTH levels and higher thymic and spleen weights compared to SAL. Under basal conditions, glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) mRNA in the hippocampus and corticotropin-releasing hormone (CRH) mRNA in the paraventricular nucleus of the hypothalamus were not different between the two lines. Forced swimming for 5 min induced high immobility behavior in LAL mice which was associated with an enhanced and prolonged corticosterone response as compared to SAL, while absolute ACTH levels did not differ. In addition, LAL mice showed an increase in hippocampal MR mRNA (but not GR) and hypothalamic CRH mRNA at 24 h after forced swimming. In conclusion, a genetic trait in coping style of wild house mice is associated with an idiosyncratic pattern of HPA activity, and greater responsiveness of physiological and molecular stress markers in LAL mice. In view of the profound differences in behavioral traits and stress system reactivity, these mouse lines genetically selected for attack latency present an interesting model for studying the mechanism underlying individual variation in susceptibility to stress-related psychopathology.     

Arabidopsis RecQI4A suppresses homologous recombination and modulates DNA damage responses

The DNA damage response and DNA recombination are two interrelated mechanisms involved in maintaining the integrity of the genome, but in plants they are poorly understood. RecQ is a family of genes with conserved roles in the regulation of DNA recombination in eukaryotes; there are seven members in Arabidopsis. Here we report on the functional analysis of the Arabidopsis RecQl4A gene. Ectopic expression of Arabidopsis RecQl4A in yeast RecQ-deficient cells suppressed their hypersensitivity to the DNA-damaging drug methyl methanesulfonate (MMS) and enhanced their rate of homologous recombination (HR). Analysis of three recQl4A mutant alleles revealed no obvious developmental defects or telomere deregulation in plants grown under standard growth conditions. Compared with wild-type Arabidopsis, the recQl4A mutant seedlings were found to be hypersensitive to UV light and MMS, and more resistant to mitomycin C. The average frequency of intrachromosomal HR in recQl4A mutant plants was increased 7.5-fold over that observed in wild-type plants. The data reveal roles for Arabidopsis RecQl4A in maintenance of genome stability by modulation of the DNA damage response and suppression of HR.     

EPR characterisation of the triplet state in photosystem II reaction centers with singly reduced primary acceptor Q(A)

The triplet states of photosystem II core particles from spinach were studied using time-resolved cw EPR technique at different reduction states of the iron--quinone complex of the reaction center primary electron acceptor. With doubly reduced primary acceptor, the well-known photosystem II triplet state characterised by zero-field splitting parameters |D|=0.0286 cm(-1), |E|=0.0044 cm(-1) was detected. When the primary acceptor was singly reduced either chemically or photochemically, a triplet state of a different spectral shape was observed, bearing the same D and E values and characteristic spin polarization pattern arising from RC radical pair recombination. The latter triplet state was strongly temperature dependent disappearing at T=100 K, and had a much faster decay than the former one. Based on its properties, this triplet state was also ascribed to the photosystem II reaction center. A sequence of electron-transfer events in the reaction centers is proposed that explains the dependence of the triplet state properties on the reduction state of the iron--quinone primary acceptor complex.     

Sensitization to apoptosis underlies KrasD12-dependent oncolysis of murine C26 colorectal carcinoma cells by reovirus T3D

Reovirus T3D is an oncolytic agent that preferentially targets tumor cells expressing an activated Ras oncogene. Ras signaling interferes with the cellular stress response that inhibits translation of reovirus RNAs. Murine C26 colorectal carcinoma cells express a mutant KrasD12 gene. Reovirus T3D efficiently kills C26 cells, but not C26 cells in which the KrasD12 mRNA is stably repressed by expression of KrasD12-directed short-hairpin RNAs. Surprisingly, neither reovirus T3D protein synthesis nor T3D virus yields were suppressed by deletion of KrasD12. Rather, reovirus-induced tumor cell apoptosis was completely abrogated as a result of Kras knockdown. We conclude that sensitization of C26 tumor cells to reovirus-induced apoptosis underlies the Ras dependency of reovirus T3D oncolysis.     

Hepatocyte growth factor triggers signaling cascades mediating vascular smooth muscle cell migration

A key event in neointima formation and atherogenesis is the migration of vascular smooth muscle cells (VSMCs) into the intima. This is controlled by cytokines and extracellular matix (ECM) components within the microenvironment of the diseased vessel wall. At present, these signals have only been partially identified. In this study, we demonstrate that Met, the receptor tyrosine kinase for hepatocyte growth factor (HGF), is expressed on VSMCs isolated from the intima of atherosclerotic plaques of carotid arteries. Stimulation with HGF led to activation of Met as well as to activation of PI3-K, PKB/Akt, MEK, and the MAP kinases Erk1 and -2. Moreover, HGF induced lamellipodia formation, a characteristic feature of motile cells, and promoted VSMC migration across fibronectin-coated filters. The HGF-induced cell migration was mediated by beta1 integrins and required PI3-K activation. Our results suggest a role for the HGF-Met signaling pathway in the pathogenesis of atherosclerosis and restenosis.