Sensitivity to stress in the bivalve Macoma balthica from the most northern (Arctic) to the most southern (French) populations: low sensitivity in Arctic populations because of genetic adaptations?

The stress sensitivity, determined in copper exposureexperiments and in survival in air tests, and thegenetic structure, measured by means of isoenzymeelectrophoresis, were assessed in populations of theBaltic clam Macoma balthica (L.) from itssouthern to its northern distribution limit, in orderto test the hypotheses that near the distributionlimit the clams would be more stress sensitive andwould have a lower genetic variability. Thepopulations in west and north Europe show a stronggenetic resemblance. The populations in the sub-ArcticWhite Sea are genetically slightly different, and showa low stress sensitivity. The populations in theArctic Pechora Sea are genetically very distant fromthe other populations, and show the lowest stresssensitivity. Near the southern distribution limit, inagreement with the hypotheses, genetic variability islow and stress sensitivity high. On the other hand, incontrast to expectation, near the northerndistribution limit, in the populations of the PechoraSea, the genetic variability was higher, thus notreduced, and the stress sensitivity was low comparedto all other populations. Yet, it remains a questionif such is due to gradual physiologicalacclimatization (and ongoing differential selection)or to genetic adaptation.     

The respiratory performance and survival of the bivalve Macoma balthica (L.) at the southern limit of its distribution area: a translocation experiment

The hypothesis was tested that animals near their extreme Southern limits, due to high temperatures, have a high respiration rate, whereby they reach an extreme low weight-index and ultimately disappear. At estuarine stations the respiration rate of Macoma balthica (L.) (Baltic clam) did not show interseasonal changes, indicating seasonal acclimation, but within the season the respiration increased with increasing temperature, indicating the absence of short-term acclimation. In clams translocated from the Netherlands towards the Bidasoa estuary, 200 km South of their Southern distribution limit, their respiration rate was higher and weight-index lower than in specimens living in Dutch estuaries. Irrespective of an effect of the temperature, clams exposed in experiments to water from Bidasoa showed a higher respiration than clams exposed to water from the other stations. Moreover, at non-estuarine stations with a low food content, the clams showed reversed acclimation, i.e., the respiration rates in winter were much lower than summer rates, most probably a strategy to conserve energy by means of a depressed metabolism. A weight index of 5 mg DW/cm(3) and glycogen content of 2% DW are suggested as the minimal values below which the metabolic energy balance of Baltic clams becomes more negative and the clam population disappears. It was concluded that factors other than temperature influenced the respiration and weight-index of clams, and hence their presence or absence, e.g., food concentration, innate seasonal cycles, and possible pollutants in the water.     

Projected carbon stocks in the conterminous USA with land use and variable fire regimes

The dynamic global vegetation model (DGVM) MC2 was run over the conterminous USA at 30 arc sec (~800 m) to simulate the impacts of nine climate futures generated by 3GCMs (CSIRO, MIROC and CGCM3) using 3 emission scenarios (A2, A1B and B1) in the context of the LandCarbon national carbon sequestration assessment. It first simulated potential vegetation dynamics from coast to coast assuming no human impacts and naturally occurring wildfires. A moderate effect of increased atmospheric CO₂ on water use efficiency and growth enhanced carbon sequestration but did not greatly influence woody encroachment. The wildfires maintained prairie‐forest ecotones in the Great Plains. With simulated fire suppression, the number and impacts of wildfires was reduced as only catastrophic fires were allowed to escape. This greatly increased the expansion of forests and woodlands across the western USA and some of the ecotones disappeared. However, when fires did occur, their impacts (both extent and biomass consumed) were very large. We also evaluated the relative influence of human land use including forest and crop harvest by running the DGVM with land use (and fire suppression) and simple land management rules. From 2041 through 2060, carbon stocks (live biomass, soil and dead biomass) of US terrestrial ecosystems varied between 155 and 162 Pg C across the three emission scenarios when potential natural vegetation was simulated. With land use, periodic harvest of croplands and timberlands as well as the prevention of woody expansion across the West reduced carbon stocks to a range of 122–126 Pg C, while effective fire suppression reduced fire emissions by about 50%. Despite the simplicity of our approach, the differences between the size of the carbon stocks confirm other reports of the importance of land use on the carbon cycle over climate change.     

The inhibitory receptor IRp60 (CD300a) is expressed and functional on human mast cells

Mast cell-mediated responses are likely to be regulated by the cross talk between activatory and inhibitory signals. We have screened human cord blood mast cells for recently characterized inhibitory receptors expressed on NK cells. We found that IRp60, an Ig superfamily member, is expressed on human mast cells. On NK cells, IRp60 cross-linking leads to the inhibition of cytotoxic activity vs target cells in vitro. IRp60 is constitutively expressed on mast cells but is down-regulated in vitro by the eosinophil proteins major basic protein and eosinophil-derived neurotoxin. An immune complex-mediated cross-linking of IRp60 led to inhibition of IgE-induced degranulation and stem cell factor-mediated survival via a mechanism involving tyrosine phosphorylation, phosphatase recruitment, and termination of cellular calcium influx. To evaluate the role of IRp60 in regulation of allergic responses in vivo, a murine model of allergic peritonitis was used in which the murine homolog of IRp60, LMIR1, was neutralized in BALB/c mice by mAbs. This neutralization led to a significantly augmented release of inflammatory mediators and eosinophilic infiltration. These data demonstrate a novel pathway for the regulation of human mast cell function and allergic responses, indicating IRp60 as a candidate target for future treatment of allergic and mast cell-associated diseases.     

Hyperthermia assists survival of astrocytes from oxidative-mediated necrotic cell death.

In response to many stresses and pathologic states, including different models of nervous system injury, cells synthesize a variety of proteins, most notably the inducible 72 kDa heat shock protein 70 (Hsp70), which plays important roles in maintaining cellular integrity and viability. We report here that cultured astrocytes from rat diencephalon express high levels of Hsp70 upon exposure to elevated temperatures, and are less vulnerable to a subsequent oxidative stress. Complex oxidative stress was induced by exposure of astrocytes to an aqueous extract of tobacco smoke. This resulted in both glutathione and ATP depletion, along with cell death that proceeded through a necrotic pathway. Pretreatment of cultures with the glutathione replenishing agent, N-acetyl-L-cysteine, prevented glutathione and ATP loss as well as necrotic cell death. Thermal stress also protected astrocytes from necrotic cell death but without affecting glutathione or ATP levels. We propose that heat shock protects astrocytes from necrosis induced by oxidative stress, probably as a result of Hsp70 synthesis, through an antioxidant-ATP independent mechanism. As Hsp70 may transfer from glial to neuronal cells, its synthesis by astrocytes may represent an important survival mechanism by which astrocytes protect neurons against oxidative-mediated cell death.     

Cholecalciferol metabolites binding in porcine parathyroid glands.

We studied the cytoplasmic and nuclear binding of 25-hydroxychole-calciferol and 1alpha,25-dihydroxycholecalciferol inside porcine parathyroid glands. Both sterols bind to cytoplasmic components, but a specific nuclear uptake was demonstrated only for 1alpha,25-dihydroxycholecalciferol. These findings support the hypothesis that mammalian parathyroid glands are a target organ for some cholecalciferol metabolites.     

Recruitment and year-to-year variability in a population of Macoma balthica (L.)

Because of methodological problems, macrobenthic studies usually neglect the juvenile stages of invertebrate communities, due to the fact that appearance of recruits in samples is only detected some weeks or even months after their true recruitment. During this period, the temporary meiobenthos undergoes high rates of mortality. From year to year, juvenile survival rate is thus responsible for temporal patterns observed in adult population densities.The results presented here relate to the population dynamics of the tellinid bivalve Macoma balthica (L.). A study of temporary meiobenthos was conducted over two consecutive years in an intertidal Macoma-community located at the mouth of the Gironde Estuary in southwest France. Sampling of juvenile stages required short intervals (2 weeks) between successive samplings and a fine sieving mesh size (63 µm). Other population parameters, such as temporal patterns in density, reproductive cycle, and individual growth, were recorded.Recruitment processes showed a year-to-year variability, with regard to settlement density, settlement period, and survival rate. In 1983, recruitment was moderate and protracted over several months. Only one main recruitment period was detected in 1984, resulting in a high juvenile density. In a previous study (1977), by contrast, recruitment was almost non-existent.This variability is discussed as a function of climatic and sedimentological conditions which prevailed in the estuary throughout the study period. However, none of these physical factors appeared to underlie the recruitment fluctuation in Macoma balthica. It is suggested that biological interactions are of prime importance in regulating population densities in this community.     

Pyruvate reduces DNA damage during hypoxia and after reoxygenation in hepatocellular carcinoma cells

Pyruvate is located at a crucial crossroad of cellular metabolism between the aerobic and anaerobic pathways. Modulation of the fate of pyruvate, in one direction or another, can be important for adaptative response to hypoxia followed by reoxygenation. This could alter functioning of the antioxidant system and have protective effects against DNA damage induced by such stress. Transient hypoxia and alterations of pyruvate metabolism are observed in tumors. This could be advantageous for cancer cells in such stressful conditions. However, the effect of pyruvate in tumor cells is poorly documented during hypoxia/reoxygenation. In this study, we showed that cells had a greater need for pyruvate during hypoxia. Pyruvate decreased the number of DNA breaks, and might favor DNA repair. We demonstrated that pyruvate was a precursor for the biosynthesis of glutathione through oxidative metabolism in HepG2 cells. Therefore, glutathione decreased during hypoxia, but was restored after reoxygenation. Pyruvate had beneficial effects on glutathione depletion and DNA breaks induced after reoxygenation. Our results provide more evidence that the alpha-keto acid promotes the adaptive response to hypoxia followed by reoxygenation. Pyruvate might thus help to protect cancer cells under such stressful conditions, which might be harmful for patients with tumors.     

Modified natural porcine surfactant modulates tobacco smoke-induced stress response in human monocytes

Tobacco smoke (TS) is a potent source of oxidants and oxidative stress is an important mechanism by which TS exerts its toxicity in the lung. We have shown that TS induces heat shock (HS)/stress protein (HSP) synthesis in human monocytes. Pulmonary surfactant (PS) whose major physiological function is to confer mechanical stability to alveoli, also modulates oxidative metabolism and other pro-inflammatory functions of monocytes-macrophages. In order to determine whether PS alters the stress response induced by TS, we incubated human peripheral blood monocytes overnight with modified natural porcine surfactant (Curosurf) (1 mg/ml) before exposure to TS. Curosurf decreased TS-induced, but not HS-induced, expression of the major cytosolic, inducible 72 kD HSP (Hsp70). Furthermore, TS-generated superoxide anions production was significantly decreased by Curosurf in an acellular system, suggesting a direct scavenging effect of PS. We also examined the effects of TS and PS on monocytes ultrastructure. Monocytes incubated with Curosurf presented smoother cell membranes than control monocytes, while TS-induced monocyte vacuolization was, at least in part, prevented by Curosurf. Taken together, our data suggest that PS plays a protective role against oxygen radical-mediated, TS-induced cellular stress responses.     

Expression of the molecular chaperone Hsp70 in detergent-resistant microdomains correlates with its membrane delivery and release

Accumulating evidence suggests that some heat shock proteins (Hsps), in particular the 72-kDa inducible Hsp70, associate to the cell membrane and might be secreted through an unknown mechanism to exert important functions in the immune response and signal transduction. We speculated that specialized structures named lipid rafts, known as important platforms for the delivery of proteins to the cell membrane, might be involved in the unknown mechanism ensuring membrane association and secretion of Hsp70. Lipid rafts are sphingolipid-cholesterol-rich structures that have been mainly characterized in polarized epithelial cells and can be isolated as detergent-resistant microdomains (DRMs). Analysis of soluble and DRM fractions prepared from unstressed Caco-2 epithelial cells revealed that Hsp70, and to a lesser extent calnexin, were present in DRM fractions. Increased expression of Hsps, through heat shock or by using drugs acting on protein trafficking or intracellular calcium level, induced an efficient translocation to DRM. We also found that Hsp70 was released by epithelial Caco-2 cells, and this release dramatically increased after heat shock. Drugs known to block the classical secretory pathway were unable to reduce Hsp70 release. By contrast, release of the protein was affected by the raft-disrupting drug methyl-beta-cyclodextrin. Our data suggest that lipid rafts are part of a mechanism ensuring the correct functions of Hsps and provide a rational explanation for the observed membrane association and release of Hsp70.