La mélatonine est une neuro-hormone secrétée par la glande pinéale pour réguler les rythmes circadiens, le sommeil, la physiologie de la rétine, la reproduction saisonnière et diverses fonctions neuronales. La mélatonine exerce ses fonctions en se liant à deux récepteurs membranaires appelés MT1 et MT2 qui appartiennent à la famille des récepteurs couplés aux protéines G (RCPG). Les RCPG sont connus pour former des homo- et hétérodimères mais la pertinence physiologique de ces complexes reste à démontrer. Plusieurs études montrent que la fonction de ces complexes ne se limite pas à la régulation des protéines G hétérotrimériques, mais inclue également la régulation d'autres protéines comme les transporteurs et les canaux ioniques. Dans ce travail, nous rapportons la formation d'hétérodimères MT1/MT2 dans les photorécepteurs de la rétine de souris et nous montrons que l’augmentation de la sensibilité de ces cellules à la lumière par la mélatonine requiert l'activation de la voie Gq/PLC/PKC qui est spécifique de l’hétéromère. Cette étude confirme alors la pertinence physiologique de l’hétérodimérisation des récepteurs de la mélatonine.Nous avons ensuite cherché à identifier de nouveaux partenaires de MT1 et MT2 en effectuant plusieurs cribles protéomiques et génétiques et un interactome de 378 protéines a pu être construit. L'analyse bioinformatique a révélé la présence de plusieurs protéines présynaptiques (canaux calciques voltage-dépendants Cav2.2, SNAP25, Synapsin et Munc-18) dans l'interactome MT1. Parmi ces partenaires, nous avons montré dans les cellules CHO que le récepteur MT1 interagit avec la protéine Cav2.2 et inhibe l’entrée du calcium d'une manière indépendante de la stimulation par l’agoniste, ce qui suggère un rôle régulateur de MT1 dans la libération des neurotransmetteurs.Un autre partenaire caractérisé est le transporteur de la dopamine DAT. L'interaction physique de DAT avec les récepteurs de la mélatonine diminue l’expression de DAT à la surface cellulaire et diminue l'absorption de la dopamine dans les cellules HEK293. La pertinence physiologique de ces observations a été appuyée par l’augmentation de la recapture de la dopamine dans les synaptosomes du striatum de souris knock-out pour les récepteurs de la mélatonine. En conclusion, ce rapport montre que la construction des interactomes des RCPG offre de nouvelles perspectives pour la découverte de nouvelles fonctions de ces récepteurs, comme les fonctions rétiniennes et neuronales des récepteurs de la mélatonine dans notre étude. La formation de complexes RCPG/RCPG, RCPG/canaux ioniques et RCPG/transporteurs peut avoir un effet fonctionnel réciproque au niveau de l’activité du récepteur et de ces partenaires, mettant ainsi en évidence de nouveaux mécanismes moléculaires de cross-talk cellulaire. / Melatonin is a neurohormone secreated by the pineal gland in a circadian manner. This hormone is involved in the regulation of circadian rhythms, sleep, retinal physiology, seasonal reproduction and various neuronal functions. Melatonin exerts its effects through two G protein-coupled receptors (GPCR) called MT1 and MT2. GPCRs are known to form homo- and heterodimers, but the physiological relevance of these complexes remains a matter of debate. An increasing number of reports show that the function of these GPCR complexes is not restricted to the regulation of heterotrimeric G proteins but include also the regulation of other proteins like transporters and ion channels. Here, we report the formation of MT1/MT2 heterodimers in mouse retinal rod photoreceptors and show that the enhancing effect of melatonin on light sensitivity in these cells requires the activation of the heteromer-specific Gq/PLC/PKC signaling pathway. This study demonstrates the physiological relevance of GPCR heterodimerization.We next searched for new MT1 and MT2 interacting proteins in an unbiased manner by performing several proteomic and genetic screens. An interactome of 378 proteins was built. Bioinformatic analysis revealed the presence of several presynaptic proteins (voltage-gated calcium channel Cav2.2, SNAP25, Synapsin and Munc-18) in the MT1 interactome. Presynaptic localization of MT1 and spatial proximity with presynaptic proteins was confirmed in mouse and rat brains. Among these potential partners, we show that MT1 physically interacts with Cav2.2 in CHO cell line and inhibits Cav2.2-promoted Ca2+ entry in an agonist-independent manner suggesting a regulatory role of MT1 in neurotransmitter release.Another proteins identified in the screens was the dopamine transporter DAT. Physical interaction of DAT with melatonin receptors decreased DAT cell surface expression and diminished dopamine uptake in HEK293 cell. Supporting this result we found using the in vivo model of melatonin receptors knockout mice a respective increase of dopamine uptake in synaptosomal preparations of the striatum of supporting the physiological relevance of these GPCR/transporter complexes. In conclusion, this report shows that GPCR interactome building provides new insights into receptor function, like retinal and neuronal functions of melatonin receptors in our case. Formation of GPCR/GPCR, GPCR/ion channel and GPCR/transporter complexes may have a reciprocal functional impact, on the activity of the receptor and interacting partners thus elucidating new molecular mechanisms cellular cross-talk.

Yim, Po Yee Annie. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 166-219). / Abstracts in English and Chinese. / Acknowledgements --- p.ii / Abstract --- p.iv / Abbreviations --- p.xi / Table of Content --- p.xiii / List of Figures --- p.xviii / List of Tables --- p.xxi / Major Conference Presentations --- p.xxiii / Publication in Preparation --- p.xxvi / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- General Overview of Adolescent Idiopathic Scoliosis (AIS) --- p.2 / Chapter 1.2 --- Natural History --- p.3 / Chapter 1.3 --- Current Treatments --- p.5 / Chapter 1.3.1 --- Non-operative Treatments --- p.5 / Chapter 1.3.2 --- Surgical Treatments --- p.6 / Chapter 1.4 --- Current Hypothesis on the Etiology of AIS --- p.8 / Chapter 1.4.1 --- Genetic Factors --- p.8 / Chapter 1.4.2 --- Neuromuscular Impairment --- p.10 / Chapter 1.4.3 --- Abnormalities in Skeletal Development --- p.11 / Chapter 1.4.4 --- Metabolic Dysfunction --- p.12 / Chapter 1.4.4.1 --- Lower Bone Mineral Density --- p.12 / Chapter 1.4.4.2 --- Delayed Sexual Maturity --- p.14 / Chapter 1.4.4.3 --- Hormonal Dysfunction --- p.14 / Chapter 1.5 --- Skeletal arid Spinal Growth in AIS --- p.16 / Chapter 1.5.1 --- Abnormal Growth during Puberty --- p.16 / Chapter 1.5.2 --- Growth Pattern --- p.17 / Chapter 1.5.3 --- Disproportional Growth in AIS --- p.18 / Chapter 1.5.4 --- Asymmetric Growth --- p.20 / Chapter 1.6 --- Melatonin and its Receptor --- p.22 / Chapter 1.6.1 --- Introduction --- p.22 / Chapter 1.6.2 --- Melatonin Receptor --- p.24 / Chapter 1.6.3 --- Melatonin's Role in t h e Skeletal System --- p.25 / Chapter 1.6.4 --- Melatonin-Deficient Scoliotic Animal Model --- p.27 / Chapter 1.6.5 --- Melatonin and AIS --- p.29 / Chapter 1.6.5.1 --- Melatonin Level in AIS --- p.30 / Chapter 1.6.5.2 --- Melatonin Receptor in AIS --- p.30 / Chapter Chapter 2 --- Hypothesis and Objectives --- p.39 / Chapter 2.1 --- Study Hypothesis --- p.40 / Chapter 2.2 --- Objectives --- p.41 / Chapter Chapter 3 --- Abnormal skeletal growth patterns in adolescent idiopathic scoliosis - A longitudinal study till skeletal maturity --- p.42 / Chapter 3.1 --- Introduction --- p.43 / Chapter 3.2 --- Methodology --- p.44 / Chapter 3.2.1 --- Recruitments of Subjects --- p.44 / Chapter 3.2.1.1 --- Patients with AIS --- p.44 / Chapter 3.2.1.2 --- Normal Controls --- p.44 / Chapter 3.2.1.3 --- Patients Consents --- p.45 / Chapter 3.2.2 --- Anthropometric Measurements --- p.45 / Chapter 3.2.3 --- Data Analysis --- p.46 / Chapter 3.2.3.1 --- Cross-sectional Study --- p.46 / Chapter 3.2.3.2 --- Longitudinal Study --- p.46 / Chapter 3.3 --- Results --- p.47 / Chapter 3.3.1 --- Cross-sectional Study of Anthropometric Measurements --- p.47 / Chapter 3.3.2 --- Longitudinal Study of Anthropometric Measurements --- p.48 / Chapter 3.3.2.1 --- Comparison Adjusted for Chronological Age --- p.49 / Chapter 3.3.2.2 --- Comparison Along Year Since Menarche (YSM) --- p.49 / Chapter 3.4 --- Discussion --- p.51 / Chapter Chapter 4 --- Establishment of a Melatonin-Deficierit Induced Scoliotic Model with Locally Bred Chicken --- p.63 / Chapter 4.1 --- Introduction --- p.64 / Chapter 4.2 --- Methodology --- p.67 / Chapter 4.2.1 --- Animals --- p.67 / Chapter 4.2.2 --- Materials and Reagents --- p.67 / Chapter 4.2.3 --- Pinealectomy --- p.68 / Chapter 4.2.4 --- Confirmation of Pineal Gland Removal --- p.69 / Chapter 4.2.5 --- Development of Scoliosis --- p.69 / Chapter 4.2.6 --- Measurement of Long Bone Growth --- p.70 / Chapter 4.2.7 --- Measurement of Weight --- p.71 / Chapter 4.2.8 --- Measurement of Bone Mineral Density (BMD) --- p.71 / Chapter 4.2.8.1 --- Micro Computed Tomography (MicroCT) --- p.71 / Chapter 4.2.8.2 --- Image Processing and Evaluation of BMD --- p.71 / Chapter 4.2.9 --- Data Analysis --- p.72 / Chapter 4.2.9.1 --- Measurements of Long Bone Growth and Weight --- p.72 / Chapter 4.2.9.2 --- Bone Mineral Density --- p.72 / Chapter 4.3 --- Results --- p.73 / Chapter 4.3.1 --- Confirmation of Pineal Gland Removal --- p.73 / Chapter 4.3.2 --- Occurrence of Scoliosis --- p.73 / Chapter 4.3.3 --- Measurements of Long Bone and Weight --- p.74 / Chapter 4.3.4 --- Measurement of Bone Mineral Density --- p.75 / Chapter 4.4 --- Discussion --- p.76 / Chapter Chapter 5 --- Expression of Melatonin Receptor in AIS and Control --- p.102 / Chapter 5.1 --- Introduction --- p.103 / Chapter 5.2 --- Methodology --- p.105 / Chapter 5.2.1 --- Subjects Recruitments --- p.105 / Chapter 5.2.2 --- Cell Isolation --- p.106 / Chapter 5.2.2.1 --- Bone Biopsies for Osteoblasts Isolation --- p.106 / Chapter 5.2.2.2 --- Materials and Reagents --- p.106 / Chapter 5.2.2.3 --- Isolation of Osteoblasts from Bone Biopsies --- p.107 / Chapter 5.2.3 --- Expression Level and Pattern of Melatonin Receptors 1A and IB --- p.108 / Chapter 5.2.3.1 --- Materials and Reagents --- p.108 / Chapter 5.2.3.2 --- Validation of Specificities of Antibodies by Co-immunoprecipitation --- p.113 / Chapter 5.2.3.3 --- Quantification of Protein Expression of Melatonin Receptors in Osteoblasts --- p.115 / Chapter 5.2.3.4 --- Quantification of mRNA Expression of Melatonin Receptor in Osteoblast --- p.117 / Chapter 5.2.3.5 --- Localization of Melatonin Receptor 1A and IB by Immunofluorescence Staining --- p.119 / Chapter 5.2.4 --- Evaluation and Correlation of Clinical Phenotypes with Melatonin Receptor Expression --- p.120 / Chapter 5.2.5 --- Data Analysis --- p.120 / Chapter 5.3 --- Results --- p.121 / Chapter 5.3.1 --- Protein Expression of Melatonin Receptor 1A and IB --- p.121 / Chapter 5.3.2 --- mRNA Expression of Melatonin Receptor 1A and IB --- p.121 / Chapter 5.3.3 --- Localization of Melatonin Receptors 1A and IB --- p.122 / Chapter 5.3.4 --- Evaluation and Correlation of Clinical Phenotypes with Melatonin Receptor Expression --- p.123 / Chapter 5.4 --- Discussion --- p.124 / Chapter Chapter 6 --- Summary and Overall Discussion --- p.152 / Chapter 6.1 --- Study Flowchart --- p.153 / Chapter 6.2 --- Summary and Discussion --- p.159 / Chapter 6.3 --- Limitations and Further Studies --- p.163 / Bibliography --- p.166

Man, Chi Wai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 141-184). / Abstract also in Chinese. / Acknowledgements --- p.ii / Abstract --- p.iv / Abbreviations --- p.xi / List of Tables --- p.xviii / List of Figures --- p.xx / Major Conference Presentations --- p.xxii / Publications in Preparation --- p.xxiv / Study Flowchart --- p.xxv / Chapter Chapter 1 --- Study Background --- p.1 / Chapter 1. --- Introduction --- p.2 / Chapter 1.1. --- General Overview of Adolescent Idiopathic Scoliosis (AIS) --- p.2 / Chapter 1.2. --- Natural History --- p.3 / Chapter 1.3. --- Current Treatments --- p.5 / Chapter 1.4. --- Additional Phenotypes Abnormalities --- p.9 / Chapter 1.5. --- Bone Modeling and Remodeling in Adolescents --- p.14 / Chapter 1.6. --- Bone Development --- p.15 / Chapter 1.7. --- Bone (re)modeling by osteoclasts and osteoblasts --- p.17 / Chapter 1.8. --- Factors Affecting Osteoblasts Regulation --- p.19 / Chapter 1.9. --- Current Hypothesis on the Etiology of AIS --- p.21 / Chapter 1.10. --- Melatonin --- p.26 / Chapter Chapter 2 --- Hypothesis and Objectives --- p.47 / Chapter 2. --- Hypothesis and Objectives --- p.48 / Chapter 2.1. --- Study Hypothesis --- p.48 / Chapter 2.2. --- Objectives --- p.48 / Chapter Chapter 3 --- Study on the Anthropometric Parameters and Bone Geometry of Girls with Severe AIS --- p.49 / Chapter 3.1. --- Introduction --- p.50 / Chapter 3.2. --- Methodology --- p.51 / Chapter 3.2.1. --- Recruitment of Subjects --- p.51 / Chapter 3.2.2. --- Evaluation of Curve Severity of Scoliosis --- p.52 / Chapter 3.2.3. --- Anthropometric Measurements --- p.53 / Chapter 3.2.4. --- Measurements of BMD --- p.53 / Chapter 3.2.5. --- Data Analysis --- p.54 / Chapter 3.3. --- Results --- p.55 / Chapter 3.3.1. --- Anthropometry --- p.55 / Chapter 3.3.2. --- BMD of Femoral Neck and Midshaft of Radius --- p.56 / Chapter 3.4. --- Discussion --- p.57 / Chapter Chapter 4 --- Response of Osteoblasts to Melatonin in AIS Girls In vitro Study --- p.69 / Chapter 4.1. --- Introduction --- p.70 / Chapter 4.2. --- Methodology --- p.72 / Chapter 4.2.1. --- Subjects Recruitments --- p.72 / Chapter 4.2.2. --- Cell Isolation --- p.73 / Chapter 4.2.3. --- Effect of Melatonin on Proliferation and Differentiation of AIS Osteoblasts --- p.76 / Chapter 4.2.4. --- Data Analysis --- p.79 / Chapter 4.3. --- Results --- p.80 / Chapter 4.3.1. --- Isolated Osteoblasts from Normal Human and AIS Patients --- p.80 / Chapter 4.3.2. --- Effect of Melatonin on Osteoblasts Proliferation --- p.80 / Chapter 4.3.3. --- Effect of Melatonin on Cell Differentiation --- p.81 / Chapter 4.4. --- Discussion --- p.83 / Chapter Chapter 5 --- Expression of MT1 and MT2 receptors in AIS Osteoblasts --- p.101 / Chapter 5.1. --- Introduction --- p.102 / Chapter 5.2. --- Methodology --- p.104 / Chapter 5.2.1. --- Osteoblast Samples --- p.104 / Chapter 5.2.2. --- Protein Expression of Melatonin Receptors in AIS Osteoblasts. --- p.105 / Chapter 5.2.3. --- Genotyping of MT2 receptors by Restriction Fragment Length Polymorphism (RFLP) --- p.109 / Chapter 5.2.4. --- Clinical Evaluations of the AIS Patients --- p.110 / Chapter 5.2.5. --- Data Analysis --- p.110 / Chapter 5.3. --- Results --- p.111 / Chapter 5.3.1. --- Semi quantification of Melatonin Receptors in AIS Osteoblasts 111 --- p.111 / Chapter 5.3.2. --- RFLP --- p.112 / Chapter 5.3.3. --- Functional Response Between the Different AIS Groups --- p.112 / Chapter 5.3.4. --- Correlation of the Clinical Phenotypes with the Different AIS Subgroups --- p.114 / Chapter 5.4. --- Discussion --- p.115 / Chapter Chapter 6 --- Summary and Conclusion --- p.132 / Chapter 6.1. --- Summary and Discussion --- p.133 / Chapter 6.2. --- Limitations and Further Studies --- p.136 / Chapter 6.3. --- Conclusion --- p.138 / Bibliography --- p.141 / Appendix I --- p.185 / Appendix II --- p.186 / Appeddix III --- p.187 / Appendix IV --- p.188 / Appendix V --- p.189 / Appendix VI --- p.190

Diss. (sammanfattning) Linköping : Univ., 2001. / Härtill 4 uppsatser.

On the basis of clinical studies, some researchers have advocated that the neurohormone and antioxidant melatonin, shown to possess intrinsic anticancer properties, be used as co-therapy in cancer patients being treated with the antineoplastic agent 5-fluorouracil, as increased patient survival times and enhanced quality of life have been observed. The focus of this research was thus to investigate the mechanisms of this seemingly beneficial drug interaction between 5-fluorouracil and melatonin. Metabolism studies were undertaken, in which it was established that there is no hepatic metabolic drug interaction between these agents by cytochrome P450, and that neither agent alters the activity of this enzyme system. Co-therapy with melatonin is thus unlikely to alter plasma levels of 5-fluorouracil by this mechanism. Novel mechanisms by which 5-fluorouracil is toxic were elucidated, such as the induction of lipid peroxidation, due to the formation of reactive oxygen species; decreases in brain serotonin, dopamine and norepinephrine levels, possibly leading to depression; hippocampal shrinkage and morphological alterations and lysis of hippocampal cells, which may underlie cognitive impairment; and a reduction in the nociceptive threshold when administered acutely. All these deleterious effects are attenuated by the co-administration of melatonin, suggesting that the agent exhibits antidepressive and analgesic properties, in addition to its known antioxidative and free radical-scavenging abilities. This suggests that melatonin cotherapy can significantly decrease 5-fluorouracil-induced toxicity, but this may also exert a protective effect on cancer cells and thus compromise the anticancer efficacy of 5-fluorouracil. It was, furthermore, found that stimulation of indoleamine 2,3-dioxygenase activity, mediated by increases in superoxide anion and interferon-γ levels, may underlie resistance to 5-fluorouracil therapy. Melatonin was shown to increase superoxide anion levels in vivo, and this is believed to be by conversion to the metabolite and known oxidant 6- hydroxymelatonin. This highlights that the possible deleterious effects of melatonin metabolites should be studied further. Serum corticosterone levels and cytokine profiles are unaltered by both 5-FU and melatonin, suggesting that these agents may be used by HIV infected individuals without promoting the progression to AIDS. It can thus be concluded that melatonin co-therapy is potentially useful in countering 5-fluorouracil toxicity.

Use of Melatonin Derivatives as Spin Traps for Hydroxyl Radicals: A Computational Studies. Aaron Teye Caesar and Dr. Scott Jeffery Kirkby, Department of Chemistry, College of Arts and Sciences, East Tennessee State University, Johnson City, TN. Free radicals, especially reactive oxygen species, have been implicated in several deleterious processes which result in degenerative and cardiovascular diseases. Melatonin (N-acetyl-5-methoxytryptamin, MLT) is a naturally occurring antioxidant which has shown some potential for use as a spin trap. Spin traps react with short lived radicals such as hydroxy (.OH) or superoxide (O2-) to produce more stable products called spin adducts which may be characterized by electron paramagnetic resonance spectroscopy. This work examines whether MLT derivatives show improved spin adduct stability which may enhance their spin trapping characteristics. Electronic structure calculations of MLT, selected derivatives and 2-OH radical products were performed at the HF/6-31G(d), cc-pVDZ and DFT/B3LYP/6-31G(d) and cc-pVDZ levels of theory using NWChem. The stabilization energy was calculated using; ∆Estabilization = Espin adduct – (Espin trap + Ehydroxy radical). In units of hartrees, the results of 2-OHMLT, 2-OHMLT-Me and 2-OHMLT-CN are -0.43738, -1.60054, -1.60380 for HF/6-31G(d); -1.46071, -1.44788 and -1.46173 for DFT/6-31G(d) respectively. Also, HF/cc-pVDZ and DFTB3LYP/cc-pVDZ respectively gave -1.61268, -1.60233, -1.61409 and -1.44929, -0.26318, -1.45521.

Melatonin (N-acetyl-5-methoxytryptamin, MLT) is a naturally occurring antioxidant which has shown some potential for use as a spin trap. Spin traps react with short lived hydroxyl radicals (HO·) to produce more stable products called spin adducts which may be characterized by electron paramagnetic resonance spectroscopy. However, the relative stability of hydroxyl spin adducts of melatonin derivatives (MLTD) compared to 2-hydroxymelatonin (HO-MLT) has not been examined computationally. Computational studies have been done on four selected MLTD; methylmelatonin (Me-MLT), chloromelatonin (Cl-MLT), cyanomelatonin (CN-MLT), and nitromelatonin (NO2-MLT). Geometry of the structures were optimized at the HF/6-31G(d), cc-pVXZ, (X=D and T) and DFT/B3LYP/6-31G(d), cc-pVDZ and cc-pVTZ levels of theory and extrapolated to the complete basis set limit using cc-pVXZ (X=D, T) basis sets. The lowest relative energy was found to be a mix of results for 2-OH-MLT-Me at HF and 2-OH-MLT-NO2 at DFT.

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy