The vestibular evoked myogenic potential (VEMP) has been shown to be clinically useful in providing diagnostic information regarding the function of the otolith receptors, inferior vestibular nerve, and vestibulospinal pathways. The VEMP is a biphasic response elicited by loud clicks or tone bursts and recorded from the tonically contracted sternocleidomastoid (SCM) muscle. Because the VEMP is an inhibitory response, it is important to investigate stimulus and parameter characteristics in order to determine the optimal test protocol and maximize clinical usefulness. The aims of this study were 1) to evaluate the effects of 4 different methods of SCM muscle activation and the effect of visual biofeedback on VEMP latency, amplitude, asymmetry ratio, mean rectified EMG level, and difficulty ratings, and 2) to determine the influence of SCM muscle activation pattern and visual biofeedback level on test-retest reliability. Forty-eight healthy volunteers between the ages of 18 and 50 underwent VEMP testing using each of the following muscle activation patterns: supine with the head raised (SE), supine with the head turned away from the test ear (SR), supine with the head raised and turned away from the test ear (SER), and sitting with the head turned away from the test ear (SitR). Testing subjects with the SER method yielded the most robust amplitude response and sternocleidomastoid EMG activity. No statistically significant differences were found in interaural asymmetry ratios among the 4 methods of SCM activation. Subjects rated the SE and SER methods as more difficult than the SE and SitR methods at each of the 3 target levels. Test-retest reliability was high for P1/N1 amplitude and mean rectified EMG levels when subjects were provided visual biofeedback to monitor the level of tonic SCM muscle activity. The study demonstrates the importance of providing patients a means of monitoring and maintaining the amplitude of the rectified EMG at a constant target level during SCM muscle activation. Although no evidence to reject or strongly favor a specific method was found, monaural-ipsilateral recording with the SitR method was found to be advantageous for individuals with weakness or decreased endurance for sustained muscle contraction.

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Vasomotor tone is largely maintained by sympathetic nerves, myogenic reactivity and key local and circulating hormones. Acting together, these factors ensure moment-to-moment adjustments of net vascular tone required to maintain hemodynamic stability. In rat mesenteric small veins (MSV) and arteries (MSA), we investigated the contribution of the endothelium, L-type voltage operated calcium channels (L-VOCCs), PKC and Rho kinase to myogenic reactivity. The interaction of myogenic reactivity with norepinephrine (NE), endothelin-1 (ET-1), and sympathetic nerve activation was also investigated under conditions of changing transmural distending pressure. We also evaluated the relative contribution of alpha adrenergic (α-A) and endothelinergic receptors to NE and ET-1 contractile responses, respectively. Additionally, the effects of changing transmural pressure on endothelial dilator function of MSV were examined. Myogenic reactivity was not altered by nitric oxide synthase (NOS) inhibition or endothelium removal in both vessels. L-VOCCs blockade completely abolished arterial tone, while only partially reducing venous tone. PKC and Rho kinase inhibitors largely abolished venous and arterial myogenic reactivity. Increasing transmural pressure did not alter NE, ET-1, and bradykinin responses, but it significantly reduced neurogenic contractions. MSV were more sensitive to NE, ET-1 and sympathetic nerve activation compared with corresponding arteries. α-A and ET-1 receptor agonist and antagonist application revealed the participation of α1-A and ETA receptors in NE and ET-1 contractile responses, respectively. α2-A and ETB receptors appeared to mediate NE and ET-1 responses in MSV, respectively. Bradykinin induced-vasodilation was mainly reduced by NOS inhibition, and BKCa and SkCa blockade. These results suggest that myogenic factors are important contributors to net venous tone in MSV; PKC and Rho kinase activation are important to myogenic reactivity in both vessels, while L-VOCCs play a limited role in the veins versus the arteries; mesenteric veins maintain an enhanced sensitivity to NE, ET-1 and sympathetic nerve activation compared to the arteries with neurogenic contractions being affected by transmural pressure elevations; α1-ARs and ETA are the predominant receptors mediating contractile responses to NE and ET-1, respectively, with functional evidence indicating the presence of α2-ARs and ETB receptors in MSV; and venous endothelial dilator function is not affected by an elevation of transmural pressure. / Natural Sciences and Engineering Research Council of Canada (NSERC). Libyan Ministry of Education and Scientific Research.

Les protéines SREBP-1, Sterol Response Element Binding Proteins, sont des régulateurs clés du métabolisme des lipides et du cholestérol. A ce titre, ils ont été largement étudiés dans le foie et le tissu adipeux. Les facteurs SREBP-1 sont également exprimés dans le muscle squelettique au sein duquel ils sont les principaux médiateurs des effets géniques de l’insuline.Les travaux de thèse présentés dans ce manuscrit ont eu pour but de définir le rôle spécifique de SREBP-1 dans le muscle squelettique. L’étude transcriptomique de cellules musculaires humaines révèle plus de1500 gènes régulés par SREBP-1 dans le muscle squelettique humain, dont la moitié est réprimée. L’analyse fonctionnelle de ces gènes révèle l’implication de SREBP-1 dans des fonctions musculaires dépassant la cadre du métabolisme glucido-lipidique. Ainsi, SREBP-1 inhibe l’expression de plusieurs gènes impliqués dans la différenciation et le maintien du phénotype musculaire. En conséquence, la sur expression de SREBP-1 bloque la différenciation myogénique in vitro et induit une atrophie marquée in vitro, sur des myotubes différenciés et in Vivo, dans le muscle squelettique de souris.En parallèle, deux répresseurs transcriptionnels : BHLHB2 et BHLHB3 apparaissent, après étude de leur promoteur, comme deux nouvelles cibles directes de SREBP-1. Ainsi, 20% des gènes inhibés par SREBP-1sont des cibles de BHLHB2 et BHLHB3, de nombreux gènes muscle-spécifiques y compris. De plus, BHLHB2 apparaît, de la même façon que SREBP-1, comme un acteur essentiel dans l’action de l’insuline sur le muscle squelettique, et dans le développement de l’insulino-résistance musculaire chez les patients diabétiques de type2.Le blocage de la différenciation myogénique et l’atrophie induite par SREBP-1 in vitro étant reversées par l’inhibition de l’expression de BHLHB2 et BHLHB3, nous concluons que BHLHB2 et BHLHB3 sont responsables de l’effet répressif de SREBP-1 sur le phénotype musculaire.Ces résultats mettent donc en évidence un nouveau rôle pour les facteurs SREBP-1 dans la régulation de la myogenèse et le maintien de la masse musculaire. SREBP-1 intègrent ainsi la régulation métabolique au contrôle du phénotype musculaire / Transcription factors SREBP-1, Sterol Response Element Binding Proteins, are key regulators of lipid and cholesterol homeostasis. Their function has been largely studied in liver and adipose tissue, but they are also well expressed in skeletal muscle where they mediate insulin transcriptional effects.This work aims to define the muscle specific role of SREBP-1. Microarray analysis of human myotubes over-expressing SREBP-1 identifies more than 1500 SREBP-1 target genes in human skeletal muscle, including number of repressed genes. Gene ontology analysis reveals the involvement of SREBP-1 in a large variety of biological functions in muscle cells. In fact, SREBP-1 represses expression of a number of muscle-specific genes and markers of muscle differentiation. As a result, SREBP-1 over-expression leads to blockage of in vitro myogenic differentiation and marked atrophy in vitro as in Vivo.In the same time, we identified the transcriptional repressors BHLHB2 and BHLHB3 as new direct target genes of SREBP-1, by promoter analysis. 20% of SREBP-1 repressed genes are also target genes of BHLHB2 and BHLHB3. Furthermore, BHLHB2, like SREBP-1, is involved in insulin action on skeletal muscle and muscular insulin-resistance in type 2 diabetic patients.As SREBP-1 effects on atrophy and myogenic differentiation inhibition are reversed by silencing BHLHB2 and BHLHB3 expression, we can conclude that BHLHB2 and BHLHB3 mediate negative SREBP-1action on muscular phenotype.These results confer a new role for SREBP-1 in the regulation of muscle mass and muscle cell differentiation, thus linking the control of muscle mass to metabolic pathways

Traumatic brain injury (TBI) is the most frequent cause of death in children and young adults in the United States. Besides emergency neurosurgical procedures, there are few medical treatment options to improve recovery in people who have experienced a TBI. Management of patients who survive TBI is complicated by both central nervous system and peripheral systemic effects. The pathophysiology of systemic inflammation and coagulopathy following TBI has been attributed to trauma-induced endothelial cell dysfunction; however, there is little knowledge of the mechanisms by which trauma might impact the functions of the vascular endothelium at sites remote from the injury. The endothelium lining these small vessels normally produces nitric oxide (NO), arachidonic acid metabolites, and endothelial-dependent hyperpolarizing factors to relax the surrounding vascular smooth muscle. For this research study we investigated the effects of fluid-percussion-induced TBI on endothelial-dependent vasodilatory functions in a remote tissue bed (the mesenteric circulation) 24 hours after injury. We hypothesized that TBI causes changes in the mesenteric artery endothelium that result in a loss of endothelial-dependent vasodilation. We found that vasodilations induced by the muscarinic-receptor agonist, acetylcholine, are attenuated following TBI. While the endothelial-derived hyperpolarizing component of vasodilation was preserved, the NO component was severely impaired. Therefore, we tested whether the loss of NO component was due to a decrease in bioavailablity of the NO synthase (NOS) cofactor BH4, the NOS substrate L-arginine, or to changes in expression/activity of the enzyme arginase, which competes with NOS for L-arginine. We found that supplementation of L-arginine and inhibition of the enzyme arginase rescues endothelial-dependent vasodilations in TBI arteries. This study demonstrates that there are pathological systemic effects outside the point of injury following TBI leading to a dysfunctional endothelial vasodilatory pathway. These data provide insight into the pathophysiology of endothelial dysfunction after trauma and may lead to new potential targets for drug therapy.

Les ARN hélicases DDX5 et DDX17 sont des protéines « multi-tâches », elles sont impliquées dans de nombreuses étapes de la régulation du métabolisme des ARNs dont la transcription, l’épissage et la dégradation des ARNs. Lors de processus biologiques complexes tels que la myogénèse, les programmes d’expression génique sont profondément modifiés. Durant mon travail de thèse, j’ai contribué à montrer que DDX5 et DDX17 sont des protéines orchestratrices de la différenciation en coordonnant de manière directe et dynamique plusieurs niveaux de régulation génique. DDX5 et DDX17 contrôlent l’activité du facteur de transcription MyoD, régulateur majeur de la myogénèse ainsi que des microARNs spécifiques du muscle miR-1 et miR-206. Ceux-ci ciblent et régulent en retour l’expression de DDX5 et DDX17 mettant en place une boucle de rétro-contrôle négative induisant la diminution d’expression de ces deux protéines au cours de la différenciation. Enfin, cette diminution d’expression permet la mise en place d’un programme d’épissage participant à l’acquisition de phénotypes morphologiques des cellules différenciées. D’un point de vue mécanistique, il apparaît qu’un sous-groupe des événements d’épissage régulés durant la différenciation est contrôlé par la coopération de DDX5 et DDX17 avec le facteur d’épissage hnRNP H/F. D’autre part, DDX5 a aussi été impliqué dans un contexte pathologique du muscle. Cette hélicase interagit avec la mutation responsable de la Dystrophie Myotonique de type 1 (DM1). Durant ma thèse, j’ai produit des résultats préliminaires suggérant un rôle de DDX5 dans la mise en place des défauts d’épissage observés dans cette pathologie / RNA helicases DDX5 and DDX17 are “multi-tasks” proteins involved in nearly all aspects of RNA metabolism such as transcription, splicing and RNA degradation. During complex biological processes like myogenesis, gene expression programs are deeply modified. During my PhD, I contributed to show that DDX5 and DDX17 are orchestrators of differentiation by dynamically and directly orchestrating several layers of gene expression. DDX5 and DDX17 control the activity of the transcription factor MyoD, master regulator of myogenesis, as well as the expression of miR1/206, muscle-specific micro-RNAs. During myogenesis, these miRNAs downregulate the protein expression of DDX5 and DDX17 in a negative feedback loop, contributing to the switch of splicing programs observed in differenciated cells. Mechanistically, this splicing subprogram appear to be in part regulated by DDX5 and DDX17 in cooperation with hnRNP H/F splicing factors. Moreover DDX5 has been involved in a pathological muscular pathology : Myotonic Dystrophy type 1 (DM1). This helicase interact with the DM1 pathological mutation. During my PhD, I produced preliminary results suggesting a role for DDX5 in the establishment of the splicing defects observed in DM1

A disfunção cardiovascular induzida pelo consumo crônico de etanol esta associada à formação de espécies reativas de oxigênio (ERO). A angiotensina II, via receptores AT1, é um importante formador de ERO no sistema cardiovascular. O objetivo foi avaliar a participação dos receptores AT1 nas disfunções cardiovasculares induzidas pelo consumo crônico de etanol. Ratos Wistar foram divididos em quatro grupos: Controle: recebeu água \"ad libitum\"; Etanol: recebeu solução de etanol 20% (vol./vol.); Controle+Losartan: recebeu água \"ad libitum\" e losartan (10 mg/kg) diariamente por gavagem; Etanol+Losartan: recebeu solução de etanol 20% e losartan. Foram realizadas aferições semanais da pressão arterial e freqüência cardíaca dos animais. Foram realizadas as dosagens para determinar: o nível de etanol no sangue; os níveis plasmáticos e teciduais (aorta e leito arterial mesentérico) de angiotensina I (ANG I) e ANG II; a atividade plasmática da renina; atividade plasmática e tecidual da enzima conversora de angiotensina (ECA); níveis plasmáticos de aldosterona; níveis plasmáticos do peptídeo natriurético atrial (ANP), vasopressina (AVP) e ocitocina (OT); a osmolaridade e o sódio plasmático; nitrato plasmático e tecidual; espécies reativas ao ácido tiobarbitútico (TBARS); a formação tecidual de ânion superóxido; a capacidade antioxidante total; além de verificar a expressão gênica e protéica (aorta) da via das MAPKs, via do óxido nítrico (NO), das ciclooxigenases (COX), além dos componentes do sistema renina angiontensina (SRA). A artéria aorta torácica foi isolada e foram obtidas curvas concentração-resposta para fenilefrina, acetilcolina (Ach) e nitroprussiato de sódio (NPS). O tratamento crônico de etanol aumentou a pressão arterial sistólica, diastólica e média dos animais, sem afetar a freqüência cardíaca; induziu o aumento da atividade plasmática da renina, aumento da atividade da ECA e dos níveis plasmáticos de ANG I e ANG II, sendo que tais efeitos não foram prevenidos pela administração de losartan. Não houve alteração dos níveis teciduais de ANG I e ANG II. O tratamento com etanol não alterou a osmolaridade ou os níveis plasmáticos de sódio e de aldosterona. Nos animais tratados cronicamente com etanol houve redução plasmática de AVP, OT e aumento de ANP. O losartan não preveniu estes efeitos induzidos pelo etanol. O etanol promoveu aumento dos níveis plasmáticos de TBARS, os níveis teciduais de ânion superóxido, e o tratamento com losartan preveniu tais respostas. O tratamento com etanol não alterou os níveis plasmáticos de peróxido de hidrogênio e da atividade plasmática da SOD. Houve redução dos níveis plasmáticos e teciduais do NO, alteração da capacidade antioxidante plasmática total e o tratamento com losartan preveniu esses efeitos. O consumo etanol potencializou a resposta vasoconstritora induzida pela fenilefrina em anéis de aorta com e sem endotélio. O losartan preveniu tal resposta contrátil. No entanto, o tratamento com etanol não alterou a resposta de relaxamento induzida pela Ach e pelo NPS em anéis de aorta. O etanol foi capaz de alterar a expressão gênica e protéica da via das MAPKs, via do NO-AKT, das COX, e os componentes do SRA. Portanto, conclui-se que o consumo crônico de etanol ativa o SRA sistêmico, induz estresse oxidativo sistêmico e vascular, altera a reatividade vascular, reduz os níveis plasmáticos de NO, altera a expressão gênica e protéica da via das MAPKs, do NO, das COX e os componentes do SRA, e promove alterações neuro-humorais que, em conjunto, contribuem para a elevação da pressão arterial sistêmica e alterações cardiovasculares pela ação da ANG II via receptor AT1. / The cardiovascular dysfunction induced by chronic ethanol consumption is associated with the formation of reactive oxygen species (ROS). Angiotensin II via AT1 receptors is a major maker of ROS in the cardiovascular system. To evaluate the role of AT1 receptors in the cardiovascular dysfunction induced by chronic ethanol consumption. Male Wistar rats were divided into four groups: Control: received water \"ad libitum\"; Ethanol: received ethanol solution 20% (vol./vol.); Control+Losartan: received water \"ad libitum\" and losartan (10 mg/kg) daily by gavage; Losartan+Ethanol: received 20% ethanol solution and losartan. The measurements were performed to determine: the level of ethanol in blood, plasma and tissue levels (aorta and mesenteric arterial bed) of angiotensin I (ANG I) to ANG II, plasma renin activity, plasma and tissue activity of angiotensin converting enzyme (ACE), plasma aldosterone levels, plasma levels of atrial natriuretic peptide (ANP), vasopressin (AVP) and oxytocin (OT); osmolality and sodium, plasma and tissue nitrate (NO); tiobarbitútico reactive to acid species (TBARS); tissue formation superoxide anion, total antioxidant capacity, besides verifying the gene and protein expression of MAPK pathway, the nitric oxide (NO), the cyclooxygenase (COX), in addition to the components of the renin angiotensin (RAS). The thoracic aorta was isolated and concentration-response curves for phenylephrine, acetylcholine and sodium nitroprusside were obtained. Chronic ethanol treatment increased systolic blood pressure, diastolic and mean animals, without affecting heart rate; induced increase in plasma renin activity, increased plasma and tissue levels of ACE and plasma levels of ANG I and ANG II, and these effects were prevented by administration of losartan. There were no changes in tissue levels of ANG I and ANG II. The treatment with ethanol did not alter osmolarity and plasma levels of sodium and aldosterone. In animals chronically treated with ethanol was reduced plasma AVP, OT and ANP increase. Losartan did not prevent these effects induced by ethanol. Ethanol promoted increased plasma levels of TBARS, tissue levels of superoxide anion, and treatment with losartan prevented these responses. The ethanol treatment did not alter plasma levels of hydrogen peroxide and plasma activity of SOD. There was a reduction in plasma and tissue levels of NO, alteration in total plasma antioxidant capacity and treatment with losartan prevented these effects. The consumption ethanol potentiated the pressor response induced by phenylephrine in aortic rings with and without endothelium. The losartan prevented this contractile response. However, treatment with ethanol did not alter the response of relaxation induced by Ach and SNP in aortic rings. The ethanol was able to alter the gene and protein expression via the MAPK, via the NOAKT, the COX, and the components of the RAS. Therefore, it is concluded that chronic consumption of ethanol activates the systemic RAS, induces systemic oxidative stress and vascular change vascular reactivity, reduces plasma levels of NO, alters gene and protein expression via the MAPK, NO, the COX and RAS components, and promotes neurohumoral changes that, together, contribute to the elevation of blood pressure and cardiovascular changes by the action of ANG II via AT1 receptor.

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