Chronic changes in cardiac load can cause the vertebrate heart to remodel. For ectotherms, ambient temperature can directly alter cardiac load. Therefore, long-term ambient temperature change can initiate a dynamic cardiac remodelling response to preserve cardiac function. The aims of my PhD thesis were to study the effects of chronic temperature change on the ectothermic heart and cardiovascular system, using the cold-active rainbow trout and the cold-dormant freshwater turtle. In contrast to the majority of previous studies, my experiments focused on the passive, rather than active, properties of the heart. In results chapters 3, 4, 5 and 6, I studied the effects of thermal remodelling on the rainbow trout heart. Chronic cold caused a global increase in chamber stiffness, both at the whole chamber and micromechanical level, with an associated myocardial fibrosis. In the ventricle and atrium there was an up-regulation of collagen promoting genes. In the ventricle, I found cold-induced hypertrophy of the spongy myocardium with an up-regulation of hypertrophic growth factors, which was associated with an increase in tissue lipid suggesting an increase in fatty acid oxidation (FAO). In the atrium, there was no hypertrophy, but there was an increase in extra-bundular sinus, suggesting chronic dilation. Chronic warming initiated an opposite response, with increased cardiac compliance associated with an up-regulation of collagen degrading genes in the ventricle and atrium. In the outflow tract (OFT) and atrium, this increased activity of matrix metalloproteinase (MMPs) and in the OFT abundance of MMPs was increased. The warmed ventricle showed atrophy of the spongy myocardium with a decrease in lipid and an increase in glycogen suggesting a switch in cellular energetics from FAO to glycolytic pathways. In chapters 7, 8 and 9, I studied the effects of thermal remodelling on the freshwater turtle heart. I found an in vivo decrease in systemic resistance causing an increased right to left cardiac shunt flow, associated with an increased elastin content of the major outflow vessels. Cold acclimation increased cardiac sensitivity to preload as well as whole chamber passive stiffness and micromechanical stiffness of tissue sections, associated ventricular fibrosis and increased collagen coherency. In addition, chronic cold decreased the gelatinase activity of MMPs and increased mRNA expression of a tissue inhibitor of MMPs. Furthermore, chronic cold was associated with a decrease in tissue lipid and phosphates, but an increase in tissue protein, glycogen and lactate. These changes in tissue biochemistry suggest a switch in cellular energetics from FAO to glycolytic pathways, likely due to the decreased oxygen availability associated with winter inactivity. Overall, the chambers of the ectothermic heart show distinct remodelling phenotypes, which likely reflect their in cardiac function. Thermal remodelling of the fish ventricle serves both cardio-protection, from the haemodynamic strain of changes in cardiac preload and afterload, as well as compensation for the direct effects of temperature. In the turtle, changes in compliance and cellular energetics of the ventricle suggest a cardio-protective mechanism preparing the heart for increased haemodynamic stress and hypoxic or anoxic conditions during inactive winter hibernation.

The estuarine sheepshead minnow (Cyprinodon variegatus) is the most eurythermic fish species, with a thermal tolerance window between 0.6°C and 45.1°C. However, little is known about the physiological mechanisms that allow this species to survive this temperature range. In order to understand how sheepshead minnow physiology is affected by temperature acclimation and acute changes in temperature, I conducted research on this species using a multi-level approach. I began at the organismal level, and examined the effects of these temperature changes on the sheepshead minnow's metabolic rate and swimming performance. The next chapter investigated the effects of changing temperatures on cardiac function (i.e., tissue/organ specific effects). In the final chapter, I conducted research at the sub-cellular level, and determined how mitochondrial bioenergetics / function is impacted by changing temperatures. This research shows that while sheepshead minnows are able to sustain heart function and mitochondrial respiration over a broad range of temperatures; they also display a plastic temperature response which is associated with the downregulation of standard metabolic rate and cardiac remodeling to maintain force generation. Collectively, these physiological responses may contribute to the sheepshead minnow's ability to maintain physiological and organismal function across a large temperature range.

No description available.

Le réchauffement climatique constitue une problématique d'actualité très préoccupante en raison de ses effets potentiels sur la biodiversité et le secteur agricole. Mieux comprendre l'adaptation des plantes face à ce phénomène récent représente donc un intérêt majeur pour la science et la société. L'étude de populations naturelles provenant d'un gradient d'altitude permet de corréler l'impact d'un ensemble de conditions climatiques (température, humidité, radiation, etc.) à des traits phénotypiques. Ces différentes populations sont dites adaptées à leurs conditions climatiques in natura. En cultivant ces plantes dans des conditions standardisées de laboratoire (intensité lumineuse, substrat, température, arrosage, etc...), la variabilité phénotypique observée, est alors due essentiellement à la variabilité génétique intrinsèque à chaque plante, donc à son génotype. La mise en culture de ces mêmes plantes en changeant une seule variable, par exemple la température, permet de mettre en évidence un phénotype caractéristique. Ce phénotype observé peut être une réponse d'acclimatation d'un génome adapté. Le projet WallOmics vise à caractériser l'adaptation des plantes à l'altitude par l'étude de populations naturelles d'Arabidopsis thaliana provenant des Pyrénées. Les acteurs moléculaires de l'adaptation des plantes au climat sont encore mal connus mais il apparaît que la paroi des cellules végétales pourrait avoir un rôle important dans ce processus. En effet, celle-ci représente le squelette des plantes et leur confère une rigidité tout en représentant une barrière externe sensible et dynamique face aux changements environnementaux. Sa structure et sa composition peuvent être modifiées à tout moment. Il est d'ailleurs possible de dire que cette paroi végétale donne la forme générale de la plante (taille, forme, densité, etc...), son phénotype observable. Ce projet se consacrera principalement à l'étude des parois des cellules végétales. Les nouvelles technologies ont permis l'émergence des données dites "omiques", c'est-à-dire de vastes ensembles de données provenant de niveaux biologiques multiples, comme des données écologiques, de phénotypages, biochimiques, protéomiques, transcriptomiques et génomiques. L'étude et la mise en relation de ces données ont favorisé le développement d'approches globales qui visent à établir une réponse à plusieurs échelles. C'est justement par ce type d'approche non mécanistique que le projet WallOmics a contribué à établir les bases moléculaires des modifications des parois face aux changements climatiques. / Global warming is a current issue of great concern because of its potential effects on biodiversity and the agricultural sector. Better understanding the adaptation of plants to this recent phenomenon is therefore a major interest for science and society. The study of natural populations from an altitude gradient allows correlating a set of climatic conditions (temperature, humidity, radiation, etc...) with phenotypic traits. These different populations are considered as adapted to their climatic conditions in natura. By cultivating these plants under standardized laboratory conditions (light intensity, substrate, temperature, watering, etc.), the observed phenotypic variability, is essentially due to the genetic variability intrinsic to each genotype. The growth of these same plants by changing a single variable, for example temperature, makes possible to highlight a characteristic phenotype. This phenotype may be an acclimation response of a relevant genome. The WallOmics project aims at characterizing the adaptation of plants to altitude by studying natural populations of Arabidopsis thaliana from the Pyrenees. The molecular actors of the adaptation of plants are still poorly described, but it appears that the plant cell wall could play an important role in this process. Indeed, it represents the skeleton of plants and gives them rigidity while representing a dynamic and sensitive external barrier to environmental changes. Its structure and composition can be modified at any time. It is also possible to say that the plant cell wall gives the general shape of the plant (size, shape, density, etc.), that is its observable phenotype. This project will focus mainly on the study of the plant cell wall. New technologies have enabled the emergence of the so-called "omics" data, large sets of data at multiple biological levels, such as ecological, phenotypic, metabolomic, proteomic, transcriptomic and genomic data. The study and the links between these data have favoured the development of integrative approaches aimed at establishing a response at several scales. It is precisely by this type of non- mechanistic approach that the WallOmics project has contributed to establish the molecular players of plant cell wall modifications in the global warming context.