Variation de l’expression et de l’activité des 11β-hydroxystéroïde déshydrogénases rénales, cardiaques et placentaires au cours de la gestation de la rate

L’activation du système rénine-angiotensine-aldostérone peut entraîner le développement d’une hypertension artérielle et de la fibrose cardiaque. Toutefois, au cours de la grossesse, malgré une hausse substantielle des niveaux d’aldostérone, ces effets délétères ne sont pas observés. L’aldostérone exerce ses effets via les récepteurs des minéralocorticoïdes, les MR, qui peuvent également lier le cortisol avec une affinité similaire. La régulation des niveaux locaux de ce glucocorticoïde par les 11β-hydroxystéroïde déshydrogénases (11β-HSD) est donc essentielle pour éviter une stimulation inappropriée des MR. Nous suggérons que, durant la grossesse, ces enzymes sont impliquées dans la protection de la mère et du foetus contre les niveaux élevés d’aldostérone et de cortisol. Notre hypothèse de travail est que les mécanismes d’adaptation qui prennent place au cours de la grossesse nécessitent des changements d’expression (ARNm et protéine) et d’activité des 11β-HSD spécifiques selon le tissu. Des rates Sprague-Dawley ont été sacrifiées aux jours 14, 17, 19 et 22 de gestation (terme = jour 23) et leurs organes ont été collectés. Dans le rein, les niveaux protéiques des 11β-HSD sont diminués en fin de gestation. Dans le placenta, on observe une importante chute de l’expression génique et protéique de la 11β-HSD1 au jour 17 tandis que la 11β-HSD2 y est augmentée. L’expression et l’activité de la 11β-HSD2 sont par la suite diminuées jusqu’à terme. Aucune différence significative n’est retrouvée dans le ventricule gauche cardiaque. En conclusion, nos résultats démontrent que la gestation est accompagnée d’importants changements dans le placenta, possiblement pour assurer un développement foetal adéquat, tandis que le rein et le coeur sont peu ou pas affectés. Des études plus approfondies sur l’expression des MR dans ces tissus nous aideront à mieux comprendre l’implication des 11β-HSD au fil de la gestation.The activation of the renin-angiotensin-aldosterone system can lead to hypertension and cardiac fibrosis. However, despite a substantial elevation of aldosterone during pregnancy, those adverse effects are not observed. Aldosterone acts via the mineralocorticoid receptors (MR) which can also bind cortisol with a similar affinity. Regulation of the local levels of this glucocorticoid by the 11β-hydroxysteroid dehydrogenases (11β-HSD) is thus crucial to avoid overstimulation of MRs. We believe that these enzymes are involved in the maternal and fetal protections against the high levels of aldosterone and cortisol observed during pregnancy. We propose that the adaptative mechanisms occurring during normal pregnancy involve tissue-specific changes in the expression (mRNA and protein) and activity of both 11β-HSDs. Pregnant Sprague-Dawley rats were sacrified on day 14, 17, 19 or 22 of gestation (term = day 23) and their organs were collected. In the kidney, our results have shown that 11β-HSDs protein levels decrease in late gestation. In the placenta, a dramatic decrease of 11β-HSD1 mRNA and protein expressions is observed on day 17 while 11β-HSD2 levels are increased. Expression and activity of the 11β-HSD2 are then decreased up to day 22. No significant differences were detected in the left cardiac ventricle. In conclusion, our results demonstrate that gestation is associated with important modifications in the placenta, possibly to ensure a normal fetal growth, while expression in the kidney and the heart is barely changed. More studies on MR expression in those tissues will be required to better characterise the function of the 11β-HSDs throughout pregnancy

Naturalness assessment performed using forestry maps to validate forest management sustainability

One-quarter of forest areas worldwide are managed for forestry purposes. Depending upon the type of practice and intensity of management, forestry may alter forests to various degrees and raise sustainability issues. To mitigate the alteration of natural forests by forestry and to promote sustainability, ecosystem management has been implemented widely over the past quarter century. A need remains for the development of comprehensive and operational assessment approaches to validate its effectiveness. Naturalness assessment could be used to validate effectiveness of ecosystem management since this concept relates to the degree to which a natural state has been altered. We developed an approach that integrates stand- and landscape- scale traits of naturalness into a single comprehensive assessment that can be performed using only forestry maps. To illustrate our approach, we assessed naturalness in four managed forest landscapes (2184 km2), representing a management gradient of increasing intensity from passive restoration to plantation forestry. We defined four naturalness classes, i.e., natural, semi-natural, altered and artificial. Assessment was performed in two steps. At step one, we attributed a class to each managed stand by comparing its current composition with natural stand compositions of its potential natural vegetation. At the landscape scale, certain developmental stages or forest types could be in excess in managed forest landscapes compared with natural forest landscapes. At step two, we transferred numbers of stages or types in excess from the natural class to more altered classes. We demonstrated that naturalness decreased as management intensity increased. Passive restoration and extensive management generated a landscape where semi-natural forests predominated in mixtures with a lower abundance of natural forests. Intensive management generated a largely semi-natural forest landscape. Plantation forestry generated a landscape where semi-natural and altered forests predominated. In conclusion, it should now be possible to validate the effectiveness of different practices and intensity of ecosystem management in promoting sustainability, by performing our assessment approach periodically following every update of forestry maps. Our approach could also allow for more comprehensive assessment of forest management strategies developed to mitigate global change by putting into better perspective their potential effects upon forest alteration of various forestry practices that have been implemented to sequester carbon

On the dynamics of the adenylate energy system: homeorhesis vs homeostasis.

Biochemical energy is the fundamental element that maintains both the adequate turnover of the biomolecular structures and the functional metabolic viability of unicellular organisms. The levels of ATP, ADP and AMP reflect roughly the energetic status of the cell, and a precise ratio relating them was proposed by Atkinson as the adenylate energy charge (AEC). Under growth-phase conditions, cells maintain the AEC within narrow physiological values, despite extremely large fluctuations in the adenine nucleotides concentration. Intensive experimental studies have shown that these AEC values are preserved in a wide variety of organisms, both eukaryotes and prokaryotes. Here, to understand some of the functional elements involved in the cellular energy status, we present a computational model conformed by some key essential parts of the adenylate energy system. Specifically, we have considered (I) the main synthesis process of ATP from ADP, (II) the main catalyzed phosphotransfer reaction for interconversion of ATP, ADP and AMP, (III) the enzymatic hydrolysis of ATP yielding ADP, and (IV) the enzymatic hydrolysis of ATP providing AMP. This leads to a dynamic metabolic model (with the form of a delayed differential system) in which the enzymatic rate equations and all the physiological kinetic parameters have been explicitly considered and experimentally tested in vitro. Our central hypothesis is that cells are characterized by changing energy dynamics (homeorhesis). The results show that the AEC presents stable transitions between steady states and periodic oscillations and, in agreement with experimental data these oscillations range within the narrow AEC window. Furthermore, the model shows sustained oscillations in the Gibbs free energy and in the total nucleotide pool. The present study provides a step forward towards the understanding of the fundamental principles and quantitative laws governing the adenylate energy system, which is a fundamental element for unveiling the dynamics of cellular life

Degraded Trees from Spruce Budworm Epidemics as Bioenergy Feedstock: A Profitability Analysis of Forest Operations

Natural disturbances are common in Canadian boreal managed forests. For example, during and after insect epidemics, foresters must deal with significant amounts of degraded or dead wood that cannot be processed into sawn timber or pulp. Bioenergy could be an alternative pathway for this wood. A case study in Quebec (Canada) was used to evaluate the profitability of pellet production for bioenergy using degraded trees from insect epidemics. A bioenergy scenario was simulated in which degraded trees were harvested for bioenergy alongside sound wood for timber and pulp. This scenario was compared to a reference scenario in which degraded trees were left on cutovers. Using wood pellets as a case study, the results showed that at current market prices, harvesting degraded trees for pellet production is not as profitable as leaving them in the forest. Nevertheless, the overall forest operations for procuring wood for timber and pulp were still profitable, even with very high degradation levels. Procuring degraded trees reduced the overall fixed costs per harvested m3 and allowed average savings of C$2.83/harvested m3. The silvicultural savings associated with lower site preparation needs following procurement of degraded trees ranged from C$0/ha to C$500/ha, resulting in average savings of C$2.31/harvested m3. Depending on the stand conditions, the distribution of fixed costs and silvicultural savings of biomass procurement could be either low or significant