The Clinical Manifestations and Molecular Mechanisms of Mitochondrial Neuro-Ophthalmological Disorders Patrick Yu Wai Man BMedSci (Hons), MBBS (Hons), MRCOphth Published work submitted to Newcastle University for the degree of Doctor of Philosophy in the Faculty of Medical Sciences 2010 I To Mum, Dad and Cynthia I Table of Contents LIST OF TABLES.....................................................................................................VII LIST OF FIGURES..................................................................................................VIII ABSTRACT.................................................................................................................IX ACKNOWLEDGEMENTS.......................................................................................XII AUTHOR’S DECLARATION................................................................................XIV ABBREVIATIONS....................................................................................................XV CHAPTER 1 INTRODUCTION ................................................................................. 1 1.1 THE MITOCHONDRION ........................................................................................... 2 1.1.1 Evolutionary Origin ....................................................................................... 2 1.1.2 Mitochondrial Structure ................................................................................. 2 1.1.3 Oxidative Phosphorylation ............................................................................. 4 1.2 MITOCHONDRIAL GENETICS ................................................................................... 8 1.2.1 Mitochondrial DNA ....................................................................................... 8 1.2.2 Mitochondrial Haplogroups ........................................................................... 9 1.2.3 Mitochondrial DNA Mutations .................................................................... 11 1.2.4 Mitochondrial Heteroplasmy ....................................................................... 11 I 1.2.5 Threshold Effect ........................................................................................... 12 1.3 MITOCHONDRIAL INHERITANCE ........................................................................... 13 1.3.1 Maternal Transmission ................................................................................. 13 1.3.2 Mitochondrial Bottleneck ............................................................................ 13 1.4 MITOCHONDRIAL DNA MAINTENANCE ............................................................... 16 1.4.1 Mitochondrial Nucleoids ............................................................................. 16 1.4.2 Mitochondrial DNA Replication .................................................................. 17 1.4.3 Mitochondrial Nucleotide Pools .................................................................. 20 1.4.4 Regulation of MtDNA Copy Number .......................................................... 22 1.5 MITOCHONDRIAL TRANSCRIPTION ....................................................................... 23 1.6 MITOCHONDRIAL TRANSLATION .......................................................................... 24 1.7 SOMATIC MTDNA ABNORMALITIES .................................................................... 26 1.7.1 Ageing .......................................................................................................... 26 1.7.2 Polg Mouse Models ..................................................................................... 27 1.7.3 Cancer .......................................................................................................... 28 1.7.4 Nuclear Mitochondrial Disorders ................................................................ 29 1.8 MITOCHONDRIAL DNA DELETIONS ..................................................................... 31 1.8.1 Formation ..................................................................................................... 31 1.8.2 Clonal Expansion ......................................................................................... 34 1.9 MITOCHONDRIAL DYNAMICS ............................................................................... 36 1.9.1 Fusion and Fission ....................................................................................... 36 II 1.9.2 MFN1 and MFN2 ........................................................................................ 37 1.9.3 OPA1 ............................................................................................................ 39 1.9.4 DRP1 and hFIS1 .......................................................................................... 40 1.9.5 Mitochondrial Membrane Proteases ............................................................ 42 1.9.6 Reactive Oxygen Species ............................................................................. 43 1.9.7 Apoptosis ..................................................................................................... 44 1.10 MITOCHONDRIAL DISEASES ............................................................................... 47 1.10.1 Epidemiology ............................................................................................. 47 1.10.2 Classification .............................................................................................. 48 1.10.3 Clinical Manifestations .............................................................................. 52 1.10.4 Diagnostic Investigations ........................................................................... 54 1.10.5 Mitochondrial Histochemistry ................................................................... 54 1.10.6 Biochemical Studies ................................................................................... 59 1.10.7 Molecular Genetic Analysis ....................................................................... 60 1.11 GENETIC COUNSELLING ..................................................................................... 63 1.12 TREATMENTS FOR MITOCHONDRIAL DISEASE .................................................... 64 1.12.1 Supportive Measures .................................................................................. 64 1.12.2 Disease-Modifying Treatments .................................................................. 65 1.12.3 Gene Therapy ............................................................................................. 67 1.12.4 Preventing Transmission ............................................................................ 68 1.13 ANIMAL MODELS OF MITOCHONDRIAL DISEASE ............................................... 69 III 1.13.1 Autosomal Dominant Optic Atrophy ......................................................... 69 1.13.2 Leber Hereditary Optic Neuropathy .......................................................... 71 1.13.3 Chronic Progressive External Ophthalmoplegia ........................................ 72 CHAPTER 2 RESEARCH FOCUS .......................................................................... 74 2.1 AUTOSOMAL DOMINANT OPTIC ATROPHY ........................................................... 75 2.2 LEBER HEREDITARY OPTIC NEUROPATHY ........................................................... 76 2.3 CHRONIC PROGRESSIVE EXTERNAL OPHTHALMOPLEGIA ..................................... 76 CHAPTER 3 DOA – CLINICAL PHENOTYPE AND MUTATIONAL SPECTRUM ................................................................................................................ 77 3.1 OPA1 IN MULTIPLE MITOCHONDRIAL DNA DELETION DISORDERS ....................... 78 3.2 GENOMIC REARRANGEMENTS IN OPA1 ARE FREQUENT IN AUTOSOMAL DOMINANT OPTIC ATROPHY .......................................................................................................... 78 3.3 OPA1 INCREASES THE RISK OF NORMAL BUT NOT HIGH TENSION GLAUCOMA ...... 78 3.4 MULTI-SYSTEM NEUROLOGICAL DISEASE IS COMMON IN PATIENTS WITH OPA1 MUTATIONS ................................................................................................................ 79 3.5 THE PREVALENCE AND NATURAL HISTORY OF DOMINANT OPTIC ATROPHY DUE TO OPA1 MUTATIONS ..................................................................................................... 79 3.6 GENETIC SCREENING FOR OPA1 AND OPA3 MUTATIONS IN PATIENTS WITH SUSPECTED INHERITED OPTIC NEUROPATHIES .......................................................... 79 3.7 PATTERN OF RETINAL GANGLION CELL LOSS IN DOMINANT OPTIC ATROPHY DUE TO OPA1 MUTATIONS ..................................................................................................... 80 IV CHAPTER 4 DOA – ANIMAL MODELS AND DISEASE MECHANISMS ...... 81 4.1 SECONDARY MTDNA DEFECTS DO NOT CAUSE OPTIC NERVE DYSFUNCTION IN A MOUSE MODEL OF DOMINANT OPTIC ATROPHY ........................................................... 82 4.2 SUBTLE NEUROLOGICAL AND METABOLIC ABNORMALITIES IN AN OPA1 MOUSE MODEL OF AUTOSOMAL DOMINANT OPTIC ATROPHY .................................................. 82 4.3 OPA1 MUTATIONS CAUSE CYTOCHROME C OXIDASE DEFICIENCY DUE TO LOSS OF WILD-TYPE MTDNA MOLECULES. .............................................................................. 82 4.4 OPA1 MUTATIONS IMPAIR MITOCHONDRIAL FUNCTION IN BOTH PURE AND COMPLICATED DOMINANT OPTIC ATROPHY ................................................................ 83 CHAPTER 5 LEBER HEREDITARY OPTIC NEUROPATHY .........................