A subset of cyclophilins have been implicated in mechanisms of neuroinflammation and neurodegeneration that contributes to the pathogenesis of Multiple Sclerosis. Mitochondrial dysfunction leading to mitochondrial permeability transition plays a pivotal role in axonal damage and disease progression in Multiple Sclerosis. Cyclophilin D (CypD) is a crucial regulatory component of the mitochondrial permeability transition pore and it was demonstrated that the cyclophilin D knockout animals showed reduced experimental allergic encephalomyelitis (EAE) clinical disease severity and axonal injury. We investigated the effect of N-methyl-4-isoleucine-cyclosporin (NIM811), a non-immunosuppressive and non-selective cyclophilin inhibitor, on the course and severity of EAE. EAE mice treated with NIM811 showed a significant reduction in clinical disease severity compared to vehicle treated mice. FACS analysis performed with the dissociated thoracolumbar spine showed that NIM811 treatment was associated with a reduction in CNS macrophages but does not alter T-helper lineage frequencies. In addition, we demonstrated NIM811’s effect on crude mitochondrial fraction obtained from brain and liver homogenates of both wild type and CypD knockout mice in order to determine drug specificity. Benefits observed from the pharmacological inhibition of cyclophilin may lead to a novel MS therapy but NIM811’s exact mechanism of action has yet to be elucidated.

Phenylarsine oxide (PAO) is a membrane-permeable trivalent arsenic compounds, which interfere the biochemical activity of intracellular enzymes or proteins through reacting specifically with sulfhydryl and vicinal dithiol groups in the protein structure. Although the deleterious effects of arsenic compounds in bioorganisms have been extensively studied, however its role in the synaptogenesis is still obscure. Here we test the role of PAO on the synaptic activity at developing Xenopus neuromuscular synapse by using whole-cell patch clamp recording. Bath application of PAO dose-dependently increases the frequency of spontaneous synaptic currents (SSC frequency) and reaches its maximal effect at 10 £gM. The SSC frequency is robustly facilitated in 10~15 minutes after PAO application and then the release of neurotransmitter were abruptly ceased due to the degenerative collapse of the presynaptic motoneuron. Pretreatment of the culture with Ca2+ chelator BAPTA-AM significantly blunted the SSC frequency facilitation induced by PAO, suggesting a rise in Ca2+ in presynaptic motoneuron is a prerequisite. The PAO-induced SSC frequency facilitation is unaffected even that Ca2+ is eliminated from culture medium or addition of pharmacological Ca2+ channel inhibitor cadmium, indicating the influx of extracellular Ca2+ is not needed for the rise of [Ca2+]i. Depletion of endoplasmic reticulum Ca2+ pool with thapsigargin effectively hampered the PAO-induced SSC frequency facilitation. Pretreatment of ryanodine receptor inhibitor TMB-8 but not IP3 receptor inhibitor XeC significantly occluded the increase of SSC frequency elicited by PAO. Furthermore, bath application of the culture with either mitochondria oxidative phosphorylation uncoupler FCCP or mitochondrial permeability transition pore inhibitor cyclosporin A significantly abolished the SSC facilitating effect of PAO. Pretreatment the culture with TMB-8 and cyclosporin A have no addictive effects on the occlusion of PAO-induced SSC frequency facilitation, suggesting a consecutively released Ca2+ from internal store through ryanodine receptor and mitochondria is responsible for PAO-induced SSC frequency facilitation. The synaptic facilitating effect of PAO is eliminated while incubated with free radical scavenger n-acetylcysteine. Furthermore, treating cultures with complex III of electron transport chain (ETC) inhibitor antimycin A, but not complex I inhibitor rotenone, abolished PAO-induced facilitation of synaptic transmission. PAO elicited no facilitation effects on SSC frequency when pretreatment the culture with either thiol-modifying agent NEM or thiol-reducing agent DTT. Overall, results from our current study provide evidences that reactive oxygen species derived from PAO inhibition on complex III of ETC induce the open of MPT pore in mitochondria, the accompanied Ca2+ leak from mitochondria and Ca2+-induced Ca2+ release from endoplasmic reticulum resulted in a robustly release of neurotransmitter and a destructive damage on the neuron.

There is a large body of clinical and experimental evidence linking heart disease with impairment of myocardial energetics, particularly the creatine kinase (CK) system. The goal of the experiments described in this thesis was to develop and study models of increased CK phosphotransfer, by overexpressing the CK isoenzymes and/or augmenting intracellular creatine stores. Pilot experiments were performed in cultured cells, which were used to (a) study the effects of CK overexpression in vitro, and (b) validate constructs prior to generation of transgenic mice. Expression was verified at the protein level for all constructs in HL-1 and HEK293 cells, and enzymatic activity was confirmed. Mitochondrial CK (CKmt) was expressed in the mitochondria, as expected, and CKmt overexpression was associated with a significant reduction in cell death in a model of ischemia/reperfusion injury (68.1 ± 7.1% of control, p≤0.05). Transgenic mice overexpressing CKmt in the heart were generated by a targeted approach, using PhiC31 integration at the ROSA26 locus. Transgene expression was confirmed in vitro in embryonic stem cells, and in vivo at the mRNA and protein levels. There was only a modest increase in CKmt activity; therefore, homozygous transgenic mice were generated to increase expression levels, and had 27% higher CKmt activity than wild-types (p≤0.01). Mitochondrial localization of CKmt was confirmed by electron microscopy. Citrate synthase activity, a marker of mitochondrial volume, was ~10% lower in transgenic mice (p≤0.05). Baseline phenotyping studies found that CKmt-overexpressing mice have normal cardiac structure and function. These mice are currently being backcrossed onto a pure C57BL/6 background for further studies in models of heart disease. In addition to CKmt, transgenic mice overexpressing the cytosolic CK isoenzymes, CK-M and CK-B, were generated. Due to the modest level of expression observed at ROSA26, random-integration transgenesis was used, and multiple lines were generated for each construct (carrying 2 or 6 transgene copies in the CK-M line; 2, 3, or ~30 in CK-B). Transgene expression was validated at the mRNA, protein, and activity levels. These lines are currently being expanded for further validation and phenotyping studies. Previous experiments in our group have demonstrated that increasing intracellular creatine (Cr) reduces ischemia/reperfusion injury, and a series of in vitro experiments was performed to determine whether this effect may be mediated by inhibition of the mitochondrial permeability transition pore (mPTP). The mPTP plays a significant role in ischemia/reperfusion, and there is evidence linking the CK system to regulation of the mPTP. Therefore, a model was developed to test whether Cr affects mPTP opening in cardiac-derived HL-1 cells, as this mechanism may contribute to the protective effect observed in vivo. Cr incubation conditions were determined empirically, and 24-hour incubation with 5mM or 10mM Cr was found to significantly delay mPTP opening, to a similar degree to the established mPTP inhibitor, cyclosporin A. This provides evidence that Cr may exert protective effects in the heart by a variety of mechanisms, in addition to its traditional role in energy metabolism. In summary, the experiments conducted in this thesis have produced a range of tools for studying augmentation of the creatine kinase system as a therapeutic target in heart disease. The results of in vitro assays indicate that mitochondrial CK may be a particularly promising target, and that inhibition of the mitochondrial permeability transition pore may contribute to the cardioprotective effect of creatine. Finally, the transgenic models generated and validated over the course of this project will allow for a wide range of future studies into the potential benefits of CK overexpression in the mammalian heart.

Cell swelling may contribute to acute cell injury subsequent to ischemia/reperfusion. The potential role of mitochondrial uncoupling and the resultant mitochondrial swelling, due to opening of the mitochondrial permeability transition pore (MPTP), were examined in an in vitro ischemically pelleted isolated rabbit cardiomyocyte model using the protonophore, carbonyl cyanide m-chlorophenylhydrazone (CCCP) to uncouple mitochondria. Cyclosporin A (CsA) was employed to inhibit MPTP opening. Cell volume was determined by a cell-flotation, density-gradient assay, using bromododecane. Cell viability, subsequent to an osmotic stress, was determined by trypan blue permeability. Ischemic preconditioning (IPC) facilitated volume regulation following an osmotic stress. Ischemic-cell swelling was reduced by IPC. IPC protected ischemically pelleted cells, but CsA had no significant effects on injury or IPC protection. CCCP ischemia accelerated rates of ischemic contracture and injury, and abolished IPC protection. IPC protection was restored by CsA. In CCCP-ischemic-uncoupled cells, subjected to a reduced (170 mOsm) osmotic stress, CsA and IPC afforded independent and additive protection. Chelerythrine and 5-hydroxydecanoate (5-HD) blocked IPC, but did not reduce CsA protection. Electron microscopy confirmed that CCCP ischemia induced mitochondrial matrix swelling that was reduced by CsA. Cardioprotection by IPC and CsA was accompanied by proportional reductions in cell swelling. Morphometric analysis of the electron photomicrographs demonstrated that the mitochondrial volume fractions were significantly reduced in the CsA/CCCP (29.8 ± 2.3%, P < 0.004) and IPC/CsA/CCCP (31.5 ± 1.7%, P < 0.0008) groups as compared to the CCCP-ischemic group (40.5 ± 1.7%) The IPC/CCCP group (39.5 ± 4.2%) was not significantly different from the CCCP-ischemic group. NIM 811, a CsA analogue MPTP blocker with no calcineurin inhibitory activity, afforded protection similar to CsA. The results suggest that CsA protection may, in part, be mediated by reduction of mitochondrial swelling.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Tamarindus indica L. é um componente natural amplamente consumido por humanos, apresentando propriedade antiinflamatória, antidiabética e antihepatotóxica. Além disso, como nós demonstramos previamente, o extrato apresenta atividade hipolipêmica e antioxidante. Neste trabalho, nós demonstramos o efeito do extrato de T. indica sobre mitocôndrias isoladas de fígado de rato. Na presença de Ca2+, o extrato causou um inchamento osmótico mitocondrial concentração-dependente, associado ao aumento da velocidade basal (V4), dissipação do potencial de membrana e liberação do Ca2+ pré-acumulado, os quais foram inibidos por ciclosporina A (CsA) e assim atribuídos a transição de permeabilidade da membrana mitocondrial (TPMM). A indução do inchamento osmótico mitocondrial foi prevenida por EGTA e vermelho de rutênio, indicando a dependência da TPMM de Ca2+. A oxidação de proteínas tiol mitocondrial, um mecanismo bem estabelecido como causador da TPMM, foi detectado. Entretanto, nenhuma alteração significante foi observada no estado redox de GSH. A oxidação de NAD(P)H e o acúmulo de espécies reativas de oxigênio produzidas pela mitocôndria foram observadas, em ambos os casos, foram prevenidas por CsA e/ou EGTA, indicando que são conseqüências da TPMM induzida pelo extrato de T. indica. Portanto, sem aparente envolvimento do estresse oxidativo no processo, sugerindo uma interação direta de compostos do extrato com grupos tiólicos de proteínas da membrana. O extrato de T. indica induziu uma depleção de ATP associada à TPMM, mostrando assim potencial para causar a morte celular por apoptose ou necrose, resultante da indução da TPMM por si ou pela depleção do ATP via TPMM. In vitro, o extrato apresentou capacidade scavenger de radicais livres, verificado pelo ensaio do DPPH, radical superóxido e radical hidroxil; e ainda foi capaz de diminuir a lipoperoxidação mitocondrial. Além disso, em baixas concentrações, o extrato mostrou uma propriedade quelante de Fe2+. / Tamarindus indica L. is a natural dietary component widely consumed by humans, presenting well established anti-inflammatory, anti-diabetic and anti-hepatotoxic properties. In addition, as we have previously demonstrated, extract presents hypolipemic and antioxidant activities. We show here the effects of T. indica extract on isolated rat liver mitochondria. In the presence of Ca2+, the extract caused mitochondrial concentration-dependent swelling, associated to, resting respiration increase (V4), membrane potential dissipation and release of pre-accumulated Ca2+, inhibited by cyclosporine A (CsA) and thus ascribable to mitochondrial permeability transition (MPT). This swelling induction was prevented by EGTA and ruthenium red, indicating strict dependence of MPT on Ca2+. Oxidation of mitochondrial membrane protein thiols, a well established mechanism causing MPT was detected. However, no significant change was observed in the GSH redox state, and the NADPH oxidation and accumulation of mitochondria-generated reactive oxygen species that was observed, were prevented by CsA and/or EGTA, indicating that they are consequence of the MPT induced by T. indica extract. Therefore, no apparent oxidative stress condition is involved as cause of this process suggesting that direct interaction with membrane protein thiol groups of the compounds responsible for MPT induction occurs. T. indica extract led to MPTassociated ATP depletion, thus showing the potential to cause cell death by apoptosis or necrosis resulting from MPT induction per se or from ATP depletion by MPT. In vitro, the extract presented free radical scavenging ability, as assessed by the 2,2-diphenyl-1- picrylhydrazyl (DPPH), superoxide radicals and radical hydroxyl assays, and led to decreased lipid peroxidation in mitochondria, as assessed by the thiobarbituric acid reactive substances (TBARS) assay. In addition, the extract showed an iron chelanting property in low concentrations.

L'ischémie-reperfusion (IR) rénale entraîne des lésions de nécrose tubulaire aigue, nécessitant parfois une épuration extra rénale transitoire voir définitive. La mitochondrie joue un rôle important dans la physiopathologie de ces lésions d'IR en entrainant la mort cellulaire. L'étude de l'IR dans la cellule cardiaque a permis de mettre en évidence le rôle central du pore de transition de perméabilité mitochondriale (mPTP) dans le déclenchement de cette mort cellulaire. La ciclosporine (CsA) a été proposée comme thérapeutique pour protéger la cellule des lésions d'IR en retardant l'ouverture de ce mPTP. Cependant la CsA a des effets rénaux vasoconstricteurs aigus, nécessitant une validation expérimentale de sa protection dans l'IR rénale. Au cours de ce travail de thèse, nous avons mis au point un modèle murin d'IR rénale. Ensuite nous avons montré que le post-conditionnement à la CsA, ainsi que le post-conditionnement ischémique, permettent d'améliorer la fonction rénale avec un retard à l'ouverture du mPTP. Dans un deuxième travail, nous montrons que le pré conditionnement à la CsA est dose et temps dépendant, et médié en partie par l'augmentation d'expression d'une protéine chaperonne, l'Heat Shock Protéine 70 (HSP70). L'injection en bolus de CsA permet également d'améliorer la fonction rénale dans ce modèle d'IR avec un retard à l'ouverture du mPTP. Nos résultats ouvrent de nouvelles perspectives dans la protection rénale, notamment dans la réduction des épisodes d'insuffisance rénale aigue après chirurgie aortique ou en transplantation rénale / Ischemia-reperfusion (IR) is a situation encountered in transplantation or during aortic surgery, which can result in renal damages, requiring sometimes transient or definitive dialysis. Mitochondria play a crucial role in the pathophysiology of IR causing cell death. Previous studies of cardiac IR highlighted the role of mitochondrial permeability transition pore (mPTP). Cyclosporin A (CsA) has been proposed as a treatment to protect the kidney from IR by the delay of the opening of the mPTP. However, CsA has acute renal hemodynamic effects and a long-term toxicity, requiring an experimental validation of its protection in the renal IR. In this work, we developed a mouse model of renal IR. In a first study, we showed that the post-conditioning with CsA and ischemic postconditioning improve renal function with a delay of the opening of the mPTP. In a second study, we showed that a high dose of CsA injected just before the ischemia improves renal function and leads to the delay of the opening of mPTP mediated by an increase of HSP70. Our results open new perspectives in renal protection, especially for reducing episodes of acute renal failure in aortic surgery or in renal transplantation

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal