Sex-Dependent Alterations in Social Behaviour and Cortical Synaptic Activity Coincide at Different Ages in a Model of Alzheimer’s Disease

Besides memory deficits, Alzheimer’s disease (AD) patients suffer from neuropsychiatric symptoms, including alterations in social interactions, which are subject of a growing number of investigations in transgenic models of AD. Yet the biological mechanisms underlying these behavioural alterations are poorly understood. Here, a social interaction paradigm was used to assess social dysfunction in the triple-transgenic mouse model of AD (3xTg-AD). We observed that transgenic mice displayed dimorphic behavioural abnormalities at different ages. Social disinhibition was observed in 18 months old 3xTg-AD males compared to age and sex-matched control mice. In 3xTg-AD females, social disinhibition was present at 12 months followed by reduced social interactions at 18 months. These dimorphic behavioural alterations were not associated with alterations in AD neuropathological markers such as Aβ or tau levels in the frontal cortex. However, patch-clamp recordings revealed that enhanced social interactions coincided temporally with an increase in both excitatory and inhibitory basal synaptic inputs to layer 2–3 pyramidal neurons in the prefrontal cortex. These findings uncover a novel pattern of occurrence of psychiatric-like symptoms between sexes in an AD model. Our results also reveal that functional alterations in synapse activity appear as a potentially significant substrate underlying behavioural correlates of AD.     

The cold-inducible RNA-binding protein migrates from the nucleus to cytoplasmic stress granules by a methylation-dependent mechanism and acts as a translational repressor

The cold-inducible RNA-binding protein (CIRP) is a nuclear 18-kDa protein consisting of an amino-terminal RNA Recognition Motif (RRM) and a carboxyl-terminal domain containing several RGG motifs. First characterized for its overexpression upon cold shock, CIRP is also induced by stresses such as UV irradiation and hypoxia. Here, we investigated the expression as well as the subcellular localization of CIRP in response to other stress conditions. We demonstrate that oxidative stress leads to the migration of CIRP to stress granules (SGs) without alteration of expression. Stress granules are dynamic cytoplasmic foci at which stalled translation initiation complexes accumulate in cells subjected to environmental stress. Relocalization of CIRP into SGs also occurs upon other cytoplasmic stresses (osmotic pressure or heat shock) as well as in response to stresses of the endoplasmic reticulum. CIRP migration into SGs is independent from TIA-1 which has been previously reported to be a general mediator of SG formation, thereby suggesting the existence of multiple pathways leading to SG formation. Moreover, deletion mutants revealed that both RGG and RRM domains can independently promote CIRP migration into SGs. However, the methylation of arginine residues in the RGG domain is necessary for CIRP to exit the nucleus to be further recruited into SGs. By RNA-tethering experiments, we also show that CIRP down-regulates mRNA translation and that this activity is carried by the carboxyl-terminal RG-enriched domain. Altogether, our findings further reveal the diversity of mechanisms by which CIRP is regulated by environmental stresses and provide new insights into CIRP cytoplasmic function.     

An inquiry into the selective protection of glycine during the radiolysis of glycine-alanine mixtures in aqueous solutions and its implications to the preservation of optically active amino acids in the early earth

Akaboshi et al. (1990) has found an unexpected protection of the achiral amino acid, glycine, towards ionizing radiation at the expense of the selective destruction of the chiral amino acids, alanine and aspartic acid. The present work examines the mechanism of this protection for the case of alanine. We have developed a computer model for the radiolysis of glycine, alanine and glycine-alanine mixtures in aqueous solution. It is established that this protection is due in part to the reaction of the α-radical of glycine with alanine to regenerate a more stable α-radical, according to the following reaction, $$ \cdot CH(NH_3^ + )CO_2^ - + CH_3 CH(NH_3^ + )CO_2^ - \to CH_2 (NH_3^ + )CO_2^ - + CH_3 \dot C(NH_3^ + )CO_2^ -$$ The rate constant of this reaction was estimated to be ≤10⁴M^-1s^-1. The implications for this selective protection of glycine are considered for a hypothetical case in which there would be an enrichment of about 10% ofL-alanine in the primitive ocean and taking the glycine/alanine ratios obtained in CH₄-and CO₂- dominated atmospheres using electric discharge experiments. It is predicted that alanine would be rapidly destroyed and radioracemized in spite of the fact that the concentration of alanine is equal or significantly lower than that of glycine. Assuming that chiral amino acids were a prerequisite for the origin of life, it can be deduced that life could have appeared in a relatively short period of time unless there was a constant supply of optical amino acids from extraterrestrial sources.     

Purification and properties of malate dehydrogenase from the extreme thermophileBacillus caldolyticus

The enzyme malate dehydrogenase (EC 1.1.1.37) from an extreme thermophileB. Caldolyticus was purified to about 91% homogeneity. The molar mass of the enzyme was determined as 73 000 daltons and it is composed of two subunits, each with a molar mass of 37 000. Initial velocity studies with oxaloacetic acid and NADH as substrates at pH 8.1, over a range of temperatures, indicate that the enzyme operates via a sequential type mechanism. Van't Hoff plots of the kinetic parameters displayed sharp changes in slope at characteristic temperatures, whereas the Arrhenius plot exhibited no such breaks over the temperature interval investigated. The enzyme was found to be stable at 41°C and lower temperatures. At 51°C and 59°C an almost immediate 20% reduction in activity was obtained, but no further inactivation occurred during the 60 min of incubation. At 59°C the enzyme lost 50% of its initial activity in about 38 s. High concentration of NADH was observed to greatly stabilize the enzyme at that temperature.It is suggested that the slope changes in the Van't Hoff plots and the stability profies at 51°C and 59°C are representative of a temperature induced conformational change in the enzyme.Proceedings of the Fourth College Park Colloquium on Chemical Evolution:Limits of Life, University of Maryland, College Park, 18–20 October 1978.     

Both Genome Segments Contribute to the Pathogenicity of Very Virulent Infectious Bursal Disease Virus

Infectious bursal disease virus (IBDV) causes an economically significant disease of chickens worldwide. Very virulent IBDV (vvIBDV) strains have emerged and induce as much as 60% mortality. The molecular basis for vvIBDV pathogenicity is not understood, and the relative contributions of the two genome segments, A and B, to this phenomenon are not known. Isolate 94432 has been shown previously to be genetically related to vvIBDVs but exhibits atypical antigenicity and does not cause mortality. Here the full-length genome of 94432 was determined, and a reverse genetics system was established. The molecular clone was rescued and exhibited the same antigenicity and reduced pathogenicity as isolate 94432. Genetically modified viruses derived from 94432, whose vvIBDV consensus nucleotide sequence was restored in segment A and/or B, were produced, and their pathogenicity was assessed in specific-pathogen-free chickens. We found that a valine (position 321) that modifies the most exposed part of the capsid protein VP2 critically modified the antigenicity and partially reduced the pathogenicity of 94432. However, a threonine (position 276) located in the finger domain of the virus polymerase (VP1) contributed even more significantly to attenuation. This threonine is partially exposed in a hydrophobic groove on the VP1 surface, suggesting possible interactions between VP1 and another, as yet unidentified molecule at this amino acid position. The restored vvIBDV-like pathogenicity was associated with increased replication and lesions in the thymus and spleen. These results demonstrate that both genome segments influence vvIBDV pathogenicity and may provide new targets for the attenuation of vvIBDVs.     

Substrate specificity, inhibition and enzymological analysis of recombinant human glutamate carboxypeptidase II

Glutamate carboxypeptidase II (GCPII, EC 3.4.17.21) is a membrane peptidase expressed in a number of tissues such as kidney, prostate and brain. The brain form of GCPII (also known as NAALADase) cleaves N-acetyl-aspartyl glutamate to yield free glutamate. Animal model experiments show that inhibition of GCPII prevents neuronal cell death during experimental ischaemia. GCPII thus represents an important target for the treatment of neuronal damage caused by excess glutamate. In this paper we report expression of an extracellular portion of human glutamate carboxypeptidase II (amino acids 44-750) in Drosophila Schneider's cells and its purification to homogeneity. A novel assay for hydrolytic activity of recombinant human GCPII (rhGCPII), based on fluorimetric detection of released alpha-amino groups was established, and used for its enzymological characterization. rhGCPII does not show dipeptidylpeptidase IV-like activity assigned to the native form of the enzyme previously. Using a complete set of protected dipeptides, substrate specificity of rhGCPII was elucidated. In addition to the previously described substrates, four novel compounds, Ac-Glu-Met, Ac-Asp-Met and, surprisingly, Ac-Ala-Glu and Ac-Ala-Met were identified as substrates for GCPII, and their respective kinetic constants determined. The glycosylation of rhGCPII was found indispensable for the enzymatic activity.     

The inhibitor thiomandelic acid binds to both metal ions in metallo-beta-lactamase and induces positive cooperativity in metal binding

Thiomandelic acid is a simple, broad spectrum, and reasonably potent inhibitor of metallo-beta-lactamases, enzymes that mediate resistance to beta-lactam antibiotics. We report studies by NMR and perturbed angular correlation (PAC) spectroscopy of the mode of binding of the R and S enantiomers of thiomandelic acid, focusing on their interaction with the two metal ions in cadmium-substituted Bacillus cereus metallo-beta-lactamase. The 113Cd resonances are specifically assigned to the metals in the two individual sites on the protein by using 113Cd-edited 1H NMR spectra. Each enantiomer of thiomandelate produces large downfield shifts of both 113Cd resonances and changes in the PAC spectra, which indicate that they bind such that the thiol of the inhibitor bridges between the two metals. For R-thiomandelate, this is unambiguously confirmed by the observation of scalar coupling between Halpha of the inhibitor and both cadmium ions. The NMR and PAC spectra reveal that the two chiral forms of the inhibitor differ in the details of their coordination geometry. The complex with R-thiomandelate, but not that with the S-enantiomer, shows evidence in the PAC spectra of a dynamic process in the nanosecond time regime, the possible nature of which is discussed. The thiomandelate complex of the mononuclear enzyme can be detected only at low metal to enzyme stoichiometry; the relative populations of mononuclear and binuclear enzyme as a function of cadmium concentration provide clear evidence for positive cooperativity in metal ion binding in the presence of the inhibitor, in contrast to the negative cooperativity observed in the free enzyme.     

Contrasting effects of climate change in continental vs. oceanic environments on population persistence and microevolution of Atlantic salmon

Facing climate change (CC), species are prone to multiple modifications in their environment that can lead to extinction, migration or adaptation. Identifying the role and interplay of different potential stressors becomes a key question. Anadromous fishes will be exposed to both river and oceanic habitat changes. For Atlantic salmon, the river water temperature, river flow and oceanic growth conditions appear as three main stressing factors. They could act on population dynamics or as selective forces on life‐history pathways. Using an individual‐based demo‐genetic model, we assessed the effects of these factors (1) to compare risks of extinction resulting from CC in river and ocean, and (2) to assess CC effects on life‐history pathways including the evolution of underlying genetic control of phenotypic plasticity. We focused on Atlantic salmon populations from Southern Europe for a time horizon of three decades. We showed that CC in river alone should not lead to extinction of Southern European salmon populations. In contrast, the reduced oceanic growth appeared as a significant threat for population persistence. An increase in river flow amplitude increased the risk of local extinction in synergy with the oceanic effects, but river temperature rise reduced this risk. In terms of life‐history modifications, the reduced oceanic growth increased the age of return of individuals through plastic and genetic responses. The river temperature rise increased the proportion of sexually mature parr, but the genetic evolution of the maturation threshold lowered the maturation rate of male parr. This was identified as a case of environmentally driven plastic response that masked an underlying evolutionary response of plasticity going in the opposite direction. We concluded that to counteract oceanic effects, river flow management represented the sole potential force to reduce the extinction probability of Atlantic salmon populations in Southern Europe, although this might not impede changes in migration life history.