Mercury contamination and life history traits of Allis shad <Emphasis Type="Italic">Alosa alosa</Emphasis> (Linnaeus, 1758) and Twaite shad <Emphasis Type="Italic">Alosa fallax</Emphasis> (Lacépède, 1803) in the Gironde estuary (South West France)

Mercury concentration [Hg] was assessed in 20 adult Allis shad Alosa alosa (54–59 cm) and 20 adult Twaite shad Alosa fallax (36–44 cm) collected during their spawning migration in the Dordogne and the Garonne rivers (France). [Hg] was measured in the gills, dorsal muscle, liver and kidney. Twaite shad exhibited higher [Hg] than Allis shad. Median [Hg] values were [Hg]_Gills = 0.33 μg g⁻¹ (dw), [Hg]_Muscle = 1.22 μg g⁻¹, [Hg]_Liver = 1.99 μg g⁻¹, [Hg]_Kidney = 1.93 μg g⁻¹ for Twaite shad and [Hg]_Gills = 0.06 μg g⁻¹, [Hg]_Muscle = 0.20 μg g⁻¹, [Hg]_Liver = 1.18 μg g⁻¹, [Hg]_Kidney = 1.08 μg g⁻¹ for Allis shad. In order to understand such differences, we investigated some life history traits of the two species: migratory history, age (3–6 years), size at age (an expression of growth) and the number of spawning events (0–2 events). The difference in estuarine residence time between the juveniles of both species, which was assumed to influence [Hg], was investigated using otolith Sr:Ca ratio. The microchemical analysis revealed a significant difference in the residence time of juveniles in the estuary (medians are 21 d and 10 d for Twaite shad and Allis shad, respectively) but this residence time seems too short to influence [Hg] (Allis shad: r _spearman < 0.128; Twaite shad: r _spearman < −0.340). As both species show the same age structure, the influence of age on [Hg] was negligible. The literature shows that the differences in growth and in the number of spawning events reported in our study are in favour of a higher [Hg] for Twaite shad than for Allis shad. Although trophic status was not investigated here, the literature reveals that it is another factor that could produce higher [Hg] in Twaite shad, since its diet includes higher trophic levels than Allis shad. Guest editors: S. Dufour, E. Prévost, E. Rochard & P. Williot Fish and diadromy in Europe (ecology, management, conservation)     

Alcohol‐mediated miR‐34a modulates hepatocyte growth and apoptosis

MicroRNAs (miRs) have been recently shown to be heavily involved in the development of alcoholic liver disease (ALD) and suggested as a potential therapeutic target in ALD. The miR‐34a was consistently reported to be significantly elevated in several ALD rodent models, but it remains unclear how miR‐34a modulates the cellular behaviours of hepatocytes in ALD development and progression. This study aims to characterize alcohol‐induced miR‐34a impact on hepatocytes growth and apoptosis. The miRNA array was performed to assess changes in miRNA after chronic alcohol feeding. Liver and blood samples were used to examine ALD progression. The miR‐34a was overexpressed in human hepatocytes to evaluate its impact on cell growth and apoptosis. Real‐time quantitative PCR and Western blot were used to determine the growth and apoptosis molecular signalling pathways associated with miR‐34a. Alcohol feeding significantly promoted fatty liver progression, serum ALT levels, apoptosis and miR‐34a expression in rat liver. Overexpression of miR‐34a in human hepatocytes suppressed cell growth signallings, including c‐Met, cyclin D1 and cyclin‐dependent kinase 6 (CDK6). The miR‐34a might also inhibit the expression of sirtuin 1 (Sirt1) and its target, B‐cell lymphoma 2. Interestingly, the expression of miR‐34a reverses the suppressive effects of ethanol on cell growth. But, miR‐34a promotes hepatocyte senescence and apoptosis. Although the miR‐34a‐mediated down‐regulation of cell growth‐associated genes may contribute to cell growth retardation, other miR‐34a targets, such as Sirt1, may reverse this phenotype. Future studies will be needed to clarify the role of miR‐34a in ALD progression.     

INFLUENCE OF VIRAL REPLICATION MECHANISMS ON WITHIN‐HOST EVOLUTIONARY DYNAMICS

Viruses replicate their genomes using a variety of mechanisms, leading to different distributions of mutations among their progeny. Yet, models of viral evolution often only consider the mean mutation rate. To investigate when and how replication mechanisms impact viral evolution, we analyze the early dynamics of within‐host infection for two idealized cases: when all offspring virions from an infected cell carry the same genotype, mutated or not; and when mutations occur independently across offspring virions. Other replication life histories fall between these extremes. Using branching process models, we study the probability that viral infection becomes established when mutations are lethal, and in the more general case of two strains of different fitness. For a given mean mutation rate, we show that a lineage of viruses with correlated mutations is less likely to survive than with independent mutations, but when it survives, the viral population grows faster. While this holds true for all parameter regimes, replication life history has a quantitatively significant influence on viral dynamics when stochastic effects are important and when mutations are crucial for survival—conditions typical of evolutionary escape situations.     

Constraints on the use of lifespan-shortening Wolbachia to control dengue fever

Dengue fever, a viral disease spread by the mosquito Aedes aegypti, affects 50–100 million people a year in many tropical countries. Because the virus must incubate within mosquito hosts for two weeks before being able to transmit the infection, shortening the lifespan of mosquitoes may curtail dengue transmission. We developed a continuous time reaction-diffusion model of the spatial spread of Wolbachia through a population of A. aegypti. This model incorporates the lifespan-shortening effects of Wolbachia on infected A. aegypti and the fitness advantage to infected females due to cytoplasmic incompatibility (CI). We found that local establishment of the Wolbachia infection can occur if the fitness advantage due to CI exceeds the fitness reduction due to lifespan-shortening effects, in accordance with earlier results concerning fecundity reduction. However, spatial spread is possible only if the fitness advantage due to CI is twice as great as the fitness reduction due to lifespan shortening effects. Moreover, lifespan-shortening and fecundity-reduction can have different effects on the speed of wave-retreat. Using data from the literature, we estimated all demographic parameters for infected and uninfected mosquitoes and computed the velocities of spread of infection. Our most optimistic estimates suggest that the spatial spread of lifespan-shortening Wolbachia may be so slow that efficient spatial spread would require a prohibitively large number of point releases. However, as these estimates of demographic parameters may not accurately reflect natural conditions, further research is necessary to corroborate these predictions.     

Identification of active site residues of the adeno-associated virus type 2 Rep endonuclease

Adeno-associated virus type 2 Rep endonuclease activity is necessary for both viral DNA replication and site-specific integration of the viral genome into human chromosome 19. The biochemical activities required for site-specific endonuclease activity (namely specific DNA binding and transesterification activity) have been mapped to the amino-terminal domain of the AAV2 Rep protein. The amino-terminal 208 amino acids are alone sufficient for site-specific endonuclease activity, and nicking by this domain is metal-dependent. To identify this metal-binding site, we have employed a cysteine mutagenesis approach that targets conserved acidic amino acids. By using this technique, we provide functional biochemical data supporting a role for glutamate 83 in the coordination of metal ions in the context of Rep endonuclease activity. In addition, our biochemical data suggest that glutamate 164, although not involved in the coordination of metal ions, is closely associated with the active site. Thus, in lieu of a crystal structure for the AAV type 2 amino-terminal domain, our data corroborate the recently published structural studies of the AAV type 5 endonuclease and suggest that although the two enzymes are not highly conserved with respect to the AAV family, their active sites are highly conserved.     

Amelioration of age‐related brain function decline by Bruton's tyrosine kinase inhibition

One of the hallmarks of aging is the progressive accumulation of senescent cells in organisms, which has been proposed to be a contributing factor to age‐dependent organ dysfunction. We recently reported that Bruton's tyrosine kinase (BTK) is an upstream component of the p53 responses to DNA damage. BTK binds to and phosphorylates p53 and MDM2, which results in increased p53 activity. Consistent with this, blocking BTK impairs p53‐induced senescence. This suggests that sustained BTK inhibition could have an effect on organismal aging by reducing the presence of senescent cells in tissues. Here, we show that ibrutinib, a clinically approved covalent inhibitor of BTK, prolonged the maximum lifespan of a Zmpste24^?/? progeroid mice, which also showed a reduction in general age‐related fitness loss. Importantly, we found that certain brain functions were preserved, as seen by reduced anxiety‐like behaviour and better long‐term spatial memory. This was concomitant to a decrease in the expression of specific markers of senescence in the brain, which confirms a lower accumulation of senescent cells after BTK inhibition. Our data show that blocking BTK has a modest increase in lifespan in Zmpste24^?/? mice and protects them from a decline in brain performance. This suggests that specific inhibitors could be used in humans to treat progeroid syndromes and prevent the age‐related degeneration of organs such as the brain.     

Peyer’s Patches and Mesenteric Lymph Nodes Cooperatively Promote Enteropathy in a Mouse Model of Food Allergy

Background and Objective

To improve the efficacy and safety of tolerance induction for food allergies, identifying the tissues responsible for inducing intestinal inflammation and subsequent oral tolerance is important. We used OVA23-3 mice, which express an ovalbumin-specific T-cell receptor, to elucidate the roles of local and systemic immune tissues in intestinal inflammation.

Methods and Results

OVA23-3 mice developed marked enteropathy after consuming a diet containing egg white (EW diet) for 10 days but overcame the enteropathy (despite continued moderate inflammation) after receiving EW diet for a total of 28 days. Injecting mice with anti-IL-4 antibody or cyclosporine A confirmed the involvement of Th2 cells in the development of the enteropathy. To assess the individual contributions of Peyer’s patches (PPs), mesenteric lymph nodes (MLNs), and the spleen to the generation of effector CD4⁺ T-cells, we analyzed the IL-4 production, proliferation in response to ovalbumin, and CD4⁺ T-cell numbers of these tissues. EW feeding for 10 days induced significant IL-4 production in PPs, the infiltration of numerous CD4⁺ T-cells into MLNs, and a decrease in CD4⁺ T-cell numbers in spleen. On day 28, CD4⁺ T-cells from all tissues had attenuated responses to ovalbumin, suggesting tolerance acquisition, although MLN CD4⁺ T-cells still maintained IL-4 production with proliferation. In addition, removal of MLNs but not the spleen decreased the severity of enteropathy and PP-disrupted mice showed delayed onset of EW-induced inflammatory responses. Disruption of peripheral lymphoid tissues or of both PPs and MLNs almost completely prevented the enteropathy.

Conclusions

PPs and MLNs coordinately promote enteropathy by generating effector T-cells during the initial and exacerbated phases, respectively; the spleen is dispensable for enteropathy and shows tolerogenic responses throughout EW-feeding. The regulation of PPs may suppress the initiation of intestinal inflammation, subsequently restricting MLNs and inhibiting the progression of food-allergic enteropathy.     

Polycyclic aromatic hydrocarbons and heavy metals in Kostrena coastal area

The aim of this study was to determine pollution by polycyclic aromatic hydrocarbons (PAH) and heavy metals in seawater and sediment in Kostrena coastal area, as well as their toxicity using bioluminescence based tests. Total PAH concentration in seawater ranged 1.7-155.3 ng/L. The share of carcinogenetic PAH was relatively high, ranging 22-48.3%. Nickel concentrations in seawater were beyond detection limits (< 0.1 microg/L), vanadium concentrations ranged 0.66-1.96 microg/L, chrome concentrations were beyond detection limits, and copper concentrations were also beyond detection limits or extremely low (up to 0.32 microg/L). EC50 values in seawater ranged 23.80-90.90 ng/L. Correlation between total PAH concentration and toxicity of seawater showed strong connection between them (r = 0.9579). Total PAH concentration in marine sediment ranged 58.02-1116 microg/kg dry weight (d.w.). The share of carcinogenetic PAH was extremely high ranging 10-53%. Nickel concentrations in marine sediment ranged 8-24 mg/kg d.w., vanadium concentrations ranged 24-42 mg/kg d.w., chrome concentrations ranged 11-19 mg/kg d.w., and copper concentrations ranged 7-25 mg/kg d.w. EC50 values in marine sediment ranged 818-4596 microg/kg d.w. Correlation between total PAH concentration and toxicity of marine sediment showed weak connection between them (r = 0.2590). Previous studies of seawater samples from areas of the Adriatic sea under the direct influence of oil industry did not include concentrations of heavy metals, which makes our study the first to present such comprehensive results. Our results point out the need for further evaluations and following of marine environment pollution and its consequences on living organisms and marine ecosystem in whole.     

Biotransformation of methyl tert-butyl ether by human cytochrome P450 2A6

Methyl tert-butyl ether (MTBE) is widely used as gasoline oxygenate and octane number enhancer for more complete combustion in order to reduce the air pollution caused by motor vehicle exhaust. The possible adverse effects of MTBE on human health are of major public concern. However, information on the metabolism of MTBE in human tissues is scarce. The present study demonstrates that human cytochrome P450 2A6 is able to metabolize MTBE to tert-butyl alcohol (TBA), a major circulating metabolite and marker for exposure to MTBE. As CYP2A6 is known to be constitutively expressed in human livers, we infer that it may play a significant role in metabolism of gasoline ethers in liver tissue.