Importance de l'exposition trophique à un effluent municipal majeur dans l'induction d'effets physiologiques chez deux espèces de poissons mobiles et piscivores

Ce projet de maîtrise s'insère dans le cadre des travaux menés sur le fleuveSaint-Laurent par le Centre de recherche sur les interactions bassins versants -écosystèmes aquatiques (RIVE) en collaboration avec le Groupe de rechercheinteruniversitaire en limnologie et en environnement aquatique (GRIL) et le ministèredes Forêts, de la Faune et des Parcs du Québec (MFFP). Ces travaux s' intéressent àl'état du fleuve en relation avec l'effluent de la station d'épuration des eaux usées de lacommunauté urbaine de Montréal (CUM). La station de la CUM est la troisième plusiinportante station d'épuration au monde et constitue le plus important apport en matièreorganique particulaire provenant des égouts (MOPPE) et en contaminants tels que lesBPCs et les HAPs dans le fleuve Saint-Laurent (Ville de Montréal, 2012; Pham et al. ,1999).La MOPPE se compose d'un mélange de détritus organiques et de microorganismesauxquels peuvent être liés de nombreux contaminants. La MOPPE, qui constitue unesource de nourriture de haute qualité pour les organismes benthiques, représente parconséquent un important vecteur de transfert de contaminants dans le réseau trophiqueaquatique (Costello et Read, 1994). Les deux principales voies d'exposition des poissonsaux contaminants sont: (1) la voie directe (dans l'eau) et (2) la voie trophique (vial' alimentation). La voie trophique constitue par ailleurs la principale voie d'expositionpour de nombreux contaminants persistants et bioaccumulés (Persic, 2004; Loizeauet al., 2001). De nombreux travaux ont démontré qu' il est possible de suivrel'incorporation de la MOPPE, dans le réseau trophique aquatique du milieu récepteur, aumoyen des isotopes stables de l'azote (δ15N) (deBruyn et al., 2003; deBruyn etRasmussen, 2002; Tucker et al. , 1999). Ceci s'explique par le fait que la MOPPE, quiest d'origine terrestre, présente typiquement un δ15N plus faible que la matière organiqueparticulaire autochtone au milieu aquatique, dû à l'usage d'engrais synthétisés à based'azote atmosphérique présentant un δ15N très faible (≈ 0 ‰) (Michener et Lathja,2007).Bien que l' effet des rejets d' effluents contaminés dans le milieu aquatique ait étéabondamment étudié chez les espèces de poissons de petite taille ou chez des organismesen cages, l' évaluation des impacts sur les grandes espèces de poissons plus mobiles estproblématique puisque leur durée d'exposition réelle aux contaminants est difficilementquantifiable. Néanmoins, certaines grandes espèces sont d'un grand intérêt puisque cesont les espèces faisant l'objet de pêche récréative et/ou commerciale et qui sont doncles plus consommées. À cet égard, puisque ces grandes espèces se situent fréquemment àdes niveaux trophiques élevés, le phénomène de bioamplification des contaminants estégalement préoccupant pour la santé humaine (Gobas et al. , 1999). En l'occurrence,puisque l' exposition directe des espèces de poissons mobiles est difficilementquantifiable et considérant que la voie trophique constitue une voie majeure d'expositionaux contaminants et de transfert de ceux-ci à travers le réseau trophique aquatique,l'exposition trophique apparait utile afm de quantifier l'exposition des poissons mobilesaux contaminants provenant de l' effluent de la CUM. En effet, la signature isotopiquedes tissus des animaux est étroitement liée à la composition isotopique de leur diète.Ainsi, suivant une modification de la composition isotopique de sa diète, un organismeverra ses tissus devenir progressivement en équilibre isotopique avec la nouvelle diète(Phillips et Eldridge, 2006).L'objectif de cette étude était d'évaluer la possibilité de tracer des impactsphysiologiques chez deux espèces de poissons mobiles et piscivores exposées àl'effluent de la station d'épuration de la CUM à l'aide de l'exposition trophique telle quedéterminée par la signature isotopique de l'azote (δ15N) des tissus des poissons. Pour cefaire, le Ô15N a été mesuré dans le foie de dorés jaunes (Sander vitre us) et de dorés noirs(Sander canadensis) capturés dans le fleuve Saint-Laurent, sur un tronçon d'environ200 km, incluant le point de rejet de la CUM, de même des sites situés en amont et enaval de ce dernier. Chez ces mêmes individus, l'activité de l'éthoxyrésorufme-Odééthylase(EROD) et les cassures des brins d'ADN ont été mesurées commebiomarqueurs de défense et de dommages respectivement, afm de témoigner des impactsphysiologiques induits par l'exposition à l'effluent de la CUM.Nos résultats ont démontré que chez chacune des deux espèces cibles, les valeursmoyennes de δ15N mesurées dans le foie étaient systématiquement plus faibles àl' effluent qu'à tous les autres sites, indiquant un fort lien trophique avec la MOPPE de laCUM. Nos résultats ont également démontré une relation négative claire entre l'activitéEROD et le δ15N, ce qui suggère que l'induction de l' activité EROD reflète l'expositiontrophique des poissons à différents niveaux de contaminants associés à la MOPPE.Toutefois, aucune relation n'a pu être établie entre l' activité EROD et la distance du sitede capture du poisson par rapport au point de rejet de l' effluent. Cela suggère que lessites de capture des individus ne sont pas nécessairement représentatifs des sitesd'alimentation et conséquemment des niveaux d' activité EROD tels qu'induits parl'ingestion de proies trophiquement liées à la MOPPE. En ce qui a trait aux cassures desbrins d'ADN, seule une relation avec la distance du site de capture du poisson parrapport au point de rejet de l'effluent a pu être établie, ce qui suggère que l'expositiondirecte des poissons à la contamination serait plus importante que la voie trophique pourinduire des dommages à l'ADN.Cette étude constitue une première démonstration que le réseau trophique du fleuveSaint-Laurent, entre Beauharnois et le lac Saint-Pierre, est largement influencé par laMOPPE provenant de l'effluent de la CUM, et ce, à l'apex du réseau trophique, chez desindividus adultes, de deux grandes espèces de poissons mobiles et piscivores. Égalementnos résultats ont démontré pour la première fois qu' il est possible de tracer des effetsphysiologiques de l'exposition trophique aux contaminants, chez des grandes espèces depoissons mobiles et piscivores à l' aide de la signature isotopique de l'azote (δ15N)

IN SITU CHONDROCYTE VISCOELASTICITY FOLLOWING STATIC AND DYNAMIC COMPRESSIONS

INTRODUCTION Articular Cartilage (AC) is a thin layer of connective tissue covering bony surfaces of joints [1]. AC allows joints to move smoothly during load transmissions, and plays an essential part in the joints overall health [2]. Chondrocytes maintain AC extracellular matrix, the integrity of which depends largely on compressions applied to the tissue. Past studies used strain control protocols to apply static or short term dynamic compressions to AC and observe changes in chondrocyte morphology [1]. However, there is a lack of studies investigating chondrocyte cell behaviour under long-term cyclic compressions at different frequencies. The purpose of this study was to use three different loading protocols in order to see how chondrocyte cell behaviour undergoing static loading compare to cyclic loading at walking and running frequencies. METHODS Patellae from New Zealand white rabbits (N=12) were isolated and randomly assigned to one of three loading protocols [2]; (i) static loading with a constant strain level of 10 %,  (ii) dynamic sinusoidal loading oscillating at 1 Hz (walking frequency) and an average strain magnitude of 10%, (iii) dynamic sinusoidal loading oscillating at 2 Hz (running frequency) and the same average strain level. Compressive strain was applied for 45 min, followed by 15 min recovery. Cells were stained and tracked by Zeiss laser scanning microscopy during the loading protocol; time points were taken at 5min, 15min, and 30min during loading and at 2min, 5min, and 15min during recovery. RESULTS For the loading period, cellular width and depth (perpendicular  to the tissue thickness axis) for static loading increased on average by 10%, while cellular height (along the tissue thickness axis) decreased by approximately 20% with respect to the unloaded state (Figure 1a). Similar results were observed for width and depth for dynamic loading at 1 Hz frequency. However, unlike static loading, cellular height did not fully recover to its original state for all of the cells (Figure 1b). For the loading period of dynamic loading at 2 Hz, an increase was observed in cellular depth by approximately 15% along with an average increase in cellular width by 20%, while cellular height was decreased by almost 25% (Figure 1c).DISCUSSION AND CONCLUSIONS The lack of variation between static and dynamic compressions at 1 Hz suggests that the cellular mechanical response is similar when an individual walks or stands. The cellular mechanical response for 2 Hz frequency is different from static and 1 Hz loading protocols, thus suggesting that greater changes in cellular morphologies compensate the increase in frequency. In the future, more studies can be conducted to evaluate how cells respond at the same frequencies but under various strain levels

The Effect of Altering the Mechanical Loading Environment on the Expression of Bone Regenerating Molecules in Cases of Distraction Osteogenesis

Distraction osteogenesis (DO) is a surgical technique where gradual and controlled separation of two bony fragments following an osteotomy leads to the induction of new bone formation in the distracted gap. DO is used for limb lengthening, correction of bony deformities, and the replacement of bone loss secondary to infection, trauma, and tumors. Although DO gives satisfactory results in most cases, one major drawback of this technique is the prolonged period of time the external fixator has to be kept on until the newly formed bone consolidates thus leading to numerous complications. Numerous attempts at accelerating bone formation during DO have been reported. One specific approach is manipulation of the mechanical environment during DO by applying changes in the standard protocol of distraction. Attempts at changing this mechanical environment led to mixed results. Increasing the rate or applying acute distraction, led to poor bone formation in the distracted zone. On the other hand, the addition of compressive forces (such as weight bearing, alternating distraction with compression or by over-lengthening, and then shortening) has been reported to increase bone formation. It still remains unclear why these alterations may lead to changes in bone formation. While the cellular and molecular changes occurring during the standard DO protocol, specifically increased expression of transforming growth factor-beta 1, platelet-derived growth factor, insulin-like growth factor, basic fibroblast growth factor, vascular endothelial growth factor, and bone morphogenic proteins have been extensively investigated, the literature is sparse on the changes occurring when this protocol is altered. It is the purpose of this article to review the pertinent literature on the changes in the expression of various proteins and molecules as a result of changes in the mechanical loading technique in DO and try to define potential future research directions

High impact exercise improves bone microstructure and strength in growing rats

Physical activity is beneficial for skeletal development. However, impact sports during adolescence, leading to bone growth retardation and/or bone quality improvement, remains unexplained. This study investigated the effects of in vivo low (LI), medium (MI), and high (HI) impact loadings applied during puberty on bone growth, morphometry and biomechanics using a rat model. 4-week old rats (n = 30) were divided into control, sham, LI, MI, and HI groups. The impact was applied on the right tibiae, 5 days/week for 8 weeks mimicking walking (450 microepsilon), uphill running (850 microepsilon) and jumping (1250 microepsilon) conditions. Trabecular and cortical parameters were determined by micro-CT, bone growth rate by calcein labeling and toluidine blue staining followed by histomorphometry. Bio-mechanical properties were evaluated from bending tests. HI group reduced rat body weight and food consumption compared to shams. Bone growth rate also decreased in MI and HI groups despite developing thicker hypertrophic and proliferative zone heights. HI group showed significant increment in bone mineral density, trabecular thickness, cortical and total surface area. Ultimate load and stiffness were also increased in MI and HI groups. We conclude that impact loading during adolescence reduces bone growth moderately but improves bone quality and biomechanics at the end of the growing period

Clinical Study The Accordion Maneuver: A Noninvasive Strategy for Absent or Delayed Callus Formation in Cases of Limb Lengthening

The distraction osteogenesis (DO) technique has been used worldwide to treat many orthopaedic conditions. Although successful, absent or delayed callus formation in the distraction gap can lead to significant morbidities. An alternate cycle of distractioncompression (accordion maneuver) is one approach to accelerate bone regeneration. The primary aim of our study is to report our experience with the accordion maneuver during DO and to provide a detailed description of this technique, as performed in our center. The secondary aim is to present a review of the literature regarding the use of accordion maneuver. We reviewed the database of all patients undergoing limb lengthening from the year of 1997 to 2012. Four patients (6.15%) out of 65 showed poor bone regenerate in their tibiae and therefore accordion maneuver was applied for a mean of 6.75 weeks. Of these, three patients have had successful outcome with this technique. The literature showed that this technique is successful approach to trigger bone healing. However, details of how and when to apply this combination of distraction-compression forces were lacking. In conclusion, the accordion technique is safe noninvasive approach to promote bone formation, thus avoiding more invasive surgical procedures in cases of poor callus formation in limb lengthening

Biomechanical simulations of the scoliotic deformation process in the pinealectomized chicken: a preliminary study

<p>Abstract</p> <p>Background</p> <p>The basic mechanisms whereby mechanical factors modulate the metabolism of the growing spine remain poorly understood, especially the role of growth adaptation in spinal disorders like in adolescent idiopathic scoliosis (AIS). This paper presents a finite element model (FEM) that was developed to simulate early stages of scoliotic deformities progression using a pinealectomized chicken as animal model.</p> <p>Methods</p> <p>The FEM includes basic growth and growth modulation created by the muscle force imbalance. The experimental data were used to adapt a FEM previously developed to simulate the scoliosis deformation process in human. The simulations of the spine deformation process are compared with the results of an experimental study including a group of pinealectomized chickens.</p> <p>Results</p> <p>The comparison of the simulation results of the spine deformation process (Cobb angle of 37°) is in agreement with experimental scoliotic deformities of two representative cases (Cobb angle of 41° and 30°). For the vertebral wedging, a good agreement is also observed between the calculated (28°) and the observed (25° – 30°) values.</p> <p>Conclusion</p> <p>The proposed biomechanical model presents a novel approach to realistically simulate the scoliotic deformation process in pinealectomized chickens and investigate different parameters influencing the progression of scoliosis.</p

Biomechanical analysis and modeling of different vertebral growth patterns in adolescent idiopathic scoliosis and healthy subjects

<p>Abstract</p> <p>Background</p> <p>The etiology of AIS remains unclear, thus various hypotheses concerning its pathomechanism have been proposed. To date, biomechanical modeling has not been used to thoroughly study the influence of the abnormal growth profile (i.e., the growth rate of the vertebral body during the growth period) on the pathomechanism of curve progression in AIS. This study investigated the hypothesis that AIS progression is associated with the abnormal growth profiles of the anterior column of the spine.</p> <p>Methods</p> <p>A finite element model of the spinal column including growth dynamics was utilized. The initial geometric models were constructed from the bi-planar radiographs of a normal subject. Based on this model, five other geometric models were generated to emulate different coronal and sagittal curves. The detailed modeling integrated vertebral body growth plates and growth modulation spinal biomechanics. Ten years of spinal growth was simulated using AIS and normal growth profiles. Sequential measures of spinal alignments were compared.</p> <p>Results</p> <p>(1) Given the initial lateral deformity, the AIS growth profile induced a significant Cobb angle increase, which was roughly between three to five times larger compared to measures utilizing a normal growth profile. (2) Lateral deformities were absent in the models containing no initial coronal curvature. (3) The presence of a smaller kyphosis did not produce an increase lateral deformity on its own. (4) Significant reduction of the kyphosis was found in simulation results of AIS but not when using the growth profile of normal subjects.</p> <p>Conclusion</p> <p>Results from this analysis suggest that accelerated growth profiles may encourage supplementary scoliotic progression and, thus, may pose as a progressive risk factor.</p

EMSY overexpression disrupts the BRCA2/RAD51 pathway in the DNA-damage response: implications for chromosomal instability/recombination syndromes as checkpoint diseases

EMSY links the BRCA2 pathway to sporadic breast/ovarian cancer. It encodes a nuclear protein that binds to the BRCA2 N-terminal domain implicated in chromatin/transcription regulation, but when sporadically amplified/overexpressed, increased EMSY level represses BRCA2 transactivation potential and induces chromosomal instability, mimicking the activity of BRCA2 mutations in the development of hereditary breast/ovarian cancer. In addition to chromatin/transcription regulation, EMSY may also play a role in the DNA-damage response, suggested by its ability to localize at chromatin sites of DNA damage/repair. This implies that EMSY overexpression may also repress BRCA2 in DNA-damage replication/checkpoint and recombination/repair, coordinated processes that also require its interacting proteins: PALB2, the partner and localizer of BRCA2; RPA, replication/checkpoint protein A; and RAD51, the inseparable recombination/repair enzyme. Here, using a well-characterized recombination/repair assay system, we demonstrate that a slight increase in EMSY level can indeed repress these two processes independently of transcriptional interference/repression. Since EMSY, RPA and PALB2 all bind to the same BRCA2 region, these findings further support a scenario wherein: (a) EMSY amplification may mimic BRCA2 deficiency, at least by overriding RPA and PALB2, crippling the BRCA2/RAD51 complex at DNA-damage and replication/transcription sites; and (b) BRCA2/RAD51 may coordinate these processes by employing at least EMSY, PALB2 and RPA. We extensively discuss the molecular details of how this can happen to ascertain its implications for a novel recombination mechanism apparently conceived as checkpoint rather than a DNA repair system for cell division, survival, death, and human diseases, including the tissue specificity of cancer predisposition, which may renew our thinking about targeted therapy and prevention