Dissertação (mestrado) - Pontifícia Universidade Católica do Paraná, Curitiba, 2007 / Bibliografia: f. 121-129

Human histidyl-tRNA synthetase (HARS) is an aminoacyl-tRNA synthetase (AARS) that catalyzes the attachment of the amino acid histidine to histidyl-tRNA (tRNAHis) in a two-step reaction that is essential for protein translation. Currently, two human diseases, Usher Syndrome IIIB (USH3B) and an inherited peripheral neuropathy, Charcot Marie Tooth Syndrome (CMT), have been linked genetically to single point mutations in the HARS gene. The recessive HARS USH3B mutation encodes an Y454S substitution localized at the interface between the anticodon-binding domain and the catalytic domain of the opposing subunit. Patients with Usher Syndrome IIIB lose their sight and hearing during their second decade of life, and clinicians have observed that the onset of deafness and blindness may be episodic and correlate with febrile illness. Furthermore, some young USH3B patients present with a fatal form of acute respiratory distress. In addition to the single HARS mutation linked to Usher Syndrome, eight other mutations in the HARS gene are associated with CMT, an inherited peripheral neuropathy. Peripheral neuropathies are associated with progressive and length-dependent damage of the motor and sensory neurons that transmit information to the spinal cord. The age of onset and phenotypic severity of CMT linked to HARS is highly variable. When expressed in a yeast model system, the HARS variants are dominantly lethal, and confer defects in axonal guidance and locomotor deficiencies when expressed in C.elegans. Here, the biochemical characterization of the HARS USH3B and three peripheral neuropathy variants are described. The approaches included enzyme kinetic analysis with purified HARS enzymes to monitor catalytic deficiencies, differential scanning fluorimetry (DSF) to evaluate structural instability, and cellular models to detect physiological effects of axonal outgrowth by CMT variants. The results suggest that Usher Syndrome IIIB is unlikely to be a consequence of a simple loss of aminoacylation function, while HARS-linked peripheral neuropathy variants all share common catalytic defects in aminoacylation. The HARS system represents a notable example in which two different complex human diseases arise from distinct mutations in the same parent gene. By understanding the biochemical basis of these inherited mutations and their link to Usher Syndrome and CMT, it may be possible to develop mechanism-based therapies to improve the quality of life of patients afflicted with them.

Lower motor neuron diseases and peripheral neuropathies are two groups of diseases that include multiple rare disorders where many causes are unknown and definitive treatments are unavailable. Understanding the molecular etiology of these genetic diseases provides an opportunity for rapid diagnosis, preconception genetic counseling and, in a subset, direction for the development of future treatment options. The recent introduction of whole exome sequencing (WES) marks a new era in Mendelian genetic disease research as the majority of the coding region of the genome can be sequenced in a timely and cost-effective manner. In this study, WES was used to investigate the molecular etiology of a cohort of 37 patients presenting with lower motor neuron disease or peripheral neuropathy. A molecular diagnosis was determined for seven patients informing the diagnostic utility of WES. Novel phenotypes were found for three genes originally associated with a different disorder. Finally, the foundation has been laid, through the use of functional studies and large scale data-sharing, to identify novel disease-causing genes for lower motor neuron disease and peripheral neuropathy.

Charcot-Marie-Tooth Neuropathien sind die häufigsten hereditären Erkrankungen des peripheren Nervensystems und dennoch bis heute nicht therapierbar. Die Lebensqualität der Patienten ist durch motorische und sensorische Defizite der Extremitäten häufig stark eingeschränkt. Ursache können unter anderem Mutationen in Schwann-Zellen sein, die zu dem typischen Bild von Demyelinisierung und axonalem Schaden führen. In den letzten Jahren konnte in Mausmodellen das Immunsystem als wichtiger Mediator in der Pathogenese der CMT 1 Subtypen A, B und X identifiziert werden. Insbesondere Makrophagen spielen eine tragende Rolle bei dem Verlust der axonalen Integrität, bei der Schädigung der Myelinscheiden, sowie bei der Dedifferenzierung von Schwann-Zellen. Entscheidender Faktor für Proliferation und Aktivierung der Makrophagen ist hierbei das Zytokin CSF-1, dessen korrespondierender Rezeptor auf Makrophagen exprimiert wird. Der CSF-1/CSF1R Signalweg bietet somit einen vielversprechenden Angriffspunkt. In der vorliegenden Arbeit wurden Mausmodelle der CMT 1 Subtypen A, B und X mit einem niedermolekularen CSF-1-Rezeptor Inhibitor behandelt. Anschließend erfolgte eine funktionelle und strukturelle Auswertung der peripheren Nerven. Das beste Ansprechen auf die Therapie zeigten Cx32def Mutanten. Strukturell fielen ein verringerter axonaler Schaden und eine verbesserte axonale Regenerationsfähigkeit sowie erhaltene neuromuskuläre Synapsen auf. Funktionell äußerte sich dies in verbesserten elektrophysiologischen Parametern und einem Krafterhalt, welcher als klinischer Parameter die größte Relevanz für betroffene Patienten hat und somit besonders hervorzuheben ist. Auch P0het Mutanten zeigten Verbesserungen nach der CSF1RI Behandlung. Anders als bei Cx32def Tieren zeigte sich hier jedoch vor allem ein Erhalt der Myelinintegrität. Weiterhin wirkte sich die Therapie positiv auf elektrophysiologische Parameter und Krafttests aus. Vor allem besonders stark betroffene Individuen schienen hierbei von der CSF1RI Behandlung zu profitieren. Bei PMP22tg Mutanten hingegen konnten keine positiven Effekte der CSF1RI Behandlung nachgewiesen werden. Strukturelle und funktionelle Parameter behandelter Tiere unterschieden sich nicht von unbehandelten. Diese Ergebnisse unterstreichen die Relevanz der sekundären Entzündungsreaktion in CMT 1 Neuropathien als wichtigen Mediator in der Pathogenese. Weiterhin konnte gezeigt werden, dass eine Intervention im CSF-1/CSF1R Signalweg einen vielversprechenden möglichen Ansatz für die Therapie der bisher nicht behandelbaren CMT 1 Subypen X und B darstellt. Unausweichlich ist hierbei ein möglichst früher Therapiestart vor Ausprägung der ersten molekularen und histologischen Veränderungen. Im Hinblick auf die nicht die Lebenserwartung reduzierende Erkrankung muss ferner eine Minimierung der Nebenwirkungen der Therapie gewährleistet sein. Besonders hervorzuheben ist hier die Verwendung eines Inhibitors, welcher nicht in das zentrale Nervensystem vordringen kann und somit die Funktion der Mikroglia nicht beeinträchtigt. / Charcot-Marie-Tooth neuropathies are the most abundant inherited disorders of the peripheral nervous system, caused by a various number of mutations in schwann cell proteins which lead to the typical outcome with demyelination and axonal damage. Affected Patients suffer from motor and sensory deficits of the upper and lower extremities. To this day there is no specific therapy available. Within the last years the immune system has been identified as a mediator in the pathogenesis oft the CMT 1 subtypes A, B and X. It was shown that macrophages play a crucial role in demyelination, loss of axonal integrity and schwann cell dedifferentiation. As main factor for macrophage proliferation and differentiation cytokine CSF-1 has been identified which corresponding receptor is expressed on the outer surface oft he macrophages. Hence the CSF-1/CSF1R signalling pathway represent a promising target for pharmacological approaches. In this study we treated mouse models of CMT 1 subtypes A, B and X with a small-molecule CSF-1-receptor inhibitor, followed by histological and functional evaluation of peripheral nerves and muscles. The best response to the treatment was observed in Cx32def mutants. The treatment resulted in reduced axonal damage, improved axonal regeneration and preserved neuromuscular junctions. In addition we found improved functional parameters in grip strength testing and in electrophysiological studies. In contrast to Cx32def mutants, the characteristic feature observed in P0het mutants after CSF-1-receptor inhibitor treatment was preserved myelin integrity. Especially strongly affected individuals seemed to benefit from the treatment. PMP22tg mutants did not respond to CSF-1-receptor inhibitor treatment. The results of this study emphaize the importance of low-grade secondary inflammation as a desease amplifier in CMT 1 neuropathies. Furthermore we could show that targeting the CSF-1/CSF1RI signalling pathway might represent a promising treatment approach for CMT 1 subtypes X and B. It should be started preferably in early childhood before the developement of the typical histopathological alterations.

In her 1895 novel, Professor Hieronimus, Amalie Skram describes the struggle of Else Kant, a young mother and artist, against a tyrannical and apparently unfeeling doctor who keeps her at a Copenhagen asylum for more than a month against her will. Else feels terrorized by the constant surveillance to which she is subjected. This voyeuristic tendency in psychiatry is not only a reflection of Amalie Skram's own experience at a Copenhagen asylum, but is also indicative of a new psychiatric epistemology that understood visual observation as the key to ascertaining objective truth. Skram's novel is thus read against the backdrop of Jean-Martin Charcot's intensely visual treatment practices at the Salpêtrière hospital in Paris, with a specific focus on the photographs of hysterical women Charcot commissioned and published. This voyeuristic/exhibitionistic dynamic between doctor and patient is also cast in semiotic terms, showing how arguments made as early as Lessing's Laokoon provide a useful way of understanding the essential differences between verbal and visual art, and for understanding the tensions between doctor and the patient. W.J.T. Mitchell's notion of "ekphrastic fear" proves a useful concept for demonstrating how anxieties about the breaking down of the strict boundaries between visual and verbal art correspond neatly to similar anxieties that the doctor had about the transgressive potential of a patient who takes up language and describes her condition. These tensions between word and image also highlight the particular historical context in which Skram's novel appeared. Professor Hieronimus was published the same year as Freud and Breuer's Studies on Hysteria, which many consider the founding document of Freudian psychoanalysis. Although writing for completely different audiences, both Freud and Skram argue for the value of the patient's verbal utterances at a time when the patient was seen as little more than a visual specimen whose disorders could only be accurately ascertained by the acute vision of a doctor. In his promotion of the "talking cure," Freud diverged sharply with his mentor, Charcot, and this turning point in psychiatric history from a visual to a verbal epistemological model highlights the timeliness and importance of Skram's novel.

<p> Comprehensive mastery of modern genetics involves a myriad of data processing and analytic techniques; these approaches vary because some genetic conditions are the result of single gene mutations that alter protein function, while other more complex diseases and traits are influenced by many genes. This dissertation will undertake investigation of the heritability and genetic risk of cranial cruciate ligament rupture in Labrador Retrievers, a congenital hypomyelinating polyneuropathy in four Golden Retrievers, and the potential usage of telomere length as a biomarker of welfare in dogs housed in commercial breeding facilities. </p> <p>In the first disease studied, 333 Labrador Retrievers with known torn or healthy cranial cruciate ligament(s) were genotyped via SNP array. Heritability of this polygenic trait was calculated using a variety of programs and including different fixed effects. Overall, heritability was high, ranging from 0.550 to 0.893, with sex and sterilization at a young age (≤12 months) strongly influencing risk of cranial cruciate ligament rupture. Neither genome-wide association analyses using this novel dataset of 333 Labrador Retrievers, nor additional analyses combining this data with publicly-available data, identified any significantly associated SNPs. However, the most associated SNPs were located near biologically relevant genes, such as <em>COL1A2</em> (a collagen gene) and <em>ITGA11</em> (a protein that binds to collagen), as well as genes encoding sex hormone receptors, such as <em>FSHR </em>and <em>LHCCGR</em>. Splitting the data in an attempt to predict phenotypes based on genotype was unsuccessful. Future work focused on parsing out genetic influencers of cranial cruciate ligament rupture risk should continue to collect sex, sterilization status, and age at sterilization data, and larger collaborations and use of publicly-available data will be required to increase the data robustness.</p> <p>For the second study, DNA from four unrelated Golden Retrievers diagnosed with congenital hypomyelinating polyneuropathy via neurological examination, electrodiagnostic evaluation, and peripheral nerve pathology were explored for genetic causes. Whole-genome sequencing was performed on all four dogs to identify potential causative variants. When compared to WGS from >1,000 other dogs who were presumably unaffected by this rare disease, likely causative variants were identified in all four dogs. Two cases shared a homozygous <em>MTMR2 </em>splice donor site variant, with a stop codon introduced within six codons following the inclusion of the intron. One case had a heterozygous <em>MPZ</em> missense mutation leading to an isoleucine to threonine substitution. The last case had a homozygous <em>SH3TC2</em> nonsense variant predicted to truncate approximately one-half of the protein. Haplotype analyses using 524 Golden Retrievers indicated that these variants emerged recently. Each of these variants occurred in genes that are associated with the human Charcot-Marie-Tooth group of heterogeneous peripheral nervous system diseases. Testing a population of unrelated Golden Retrievers (n > 200) did not identify any other dogs with these variants, though breeders should be cautious to avoid propagating these alleles.</p> <p>Finally, the last study within this dissertation investigates the relationship between telomere length and metrics such as age, breed, environment, average breed lifespan, parity, and response to a mild social stressor in a population of dogs housed at commercial breeding facilities. FIDO scores (behavioral phenotypes) were collected for all dogs as a measurement of response to a social stressor. This study is not yet complete; many more dogs remain to be recruited in the near future. Telomere lengths were measured using qPCR and compared to a single-copy gene, <em>36B4</em>, for 309 dogs representing 37 breeds or breed crosses. Age was not significantly associated with telomere length after making appropriate corrections (p-value = 0.077). Breed and facility were significantly associated with telomere length after corrections (p-value = 0.010 and <2.2E-16, respectively). Neither parity nor average breed lifespan were associated with telomere length, however, response to a mild social stressor was, with dogs who responded positively having significantly longer telomeres than dogs who responded negatively across all analyses. This preliminary data indicates that, within this population, breed, environment, and response to stress have strong influences on telomere length, while parity and average breed lifespan did not. As this work continues, increased sample sizes will lead to increased power for detecting associations. Future work should examine these identified relationships in other populations of dogs.</p> <p>Taken together, these studies encompass phenotypes of various complexity, and each study encompassed different methodologies utilized in modern canine genetics. The overall goal for this work was to improve canine health, with the potential for translational implications to human health. The identification of genetic markers associated with or causative of disease, or indicative of health and welfare traits, is necessary for reducing the prevalence of disease and increasing the knowledge of welfare metrics in canines, respectively.</p>

Die Charcot-Marie-Tooth-Krankheit 1A (CMT1A) gehört zur Familie der erblichen Neuropathien des peripheren Nervensystems (PNS) und ist mit einer Prävalenz von 1 zu 2500 die häufigste Subform. Die Patienten leiden an einer distal ausgeprägten Muskelatrophie und sensorischen Beeinträchtigungen. Die Histopathologie zeigt sich im PNS durch Myelinisierungsdefekte, die Bildung von Zwiebelschalenformationen, eine langsam fortschreitende Demyelinisierung und einen axonalen Verlust in späteren Krankheitsstadien, die für die klinische Symptomatik verantwortlich sind. Bis heute gibt es keine Behandlungsmöglichkeiten. Die genetische Duplikation des Gens, das für das periphere Myelinprotein von 22kDa (PMP22) kodiert, ist Hauptursache der Erkrankung und betrifft speziell die myelinisierenden Gliazellen des PNS, die Schwannzellen. Erkrankte Schwannzellen induzieren eine de novo Expression des glialen Wachstumsfaktors Neuregulin 1-Typ I (NRG1-I). Die chronische NRG1-I Überexpression wurde als ein maßgeblicher Faktor der Krankheitspathogenese der CMT1A identifiziert. Aberrantes NRG1-I überstimuliert den ERBB2 Rezeptor, was zu einer Hyperaktivierung des MEK-ERK Signalwegs führt. Die genetische Ablation von NRG1 spezifisch in Schwannzellen verbesserte die klinische Präsentation und Histopathologie in CMT1A Mäusen. Damit einhergehend waren die ERBB2 und ERK Hyperaktivität in Schwannzellen normalisiert. Die Inhibition der NRG1-I-vermittelten pathologischen Signalkaskade stellt damit einen vielversprechenden therapeutischen Ansatz für die CMT1A dar. Die langfristige pharmakologische Inhibition entweder der ERBB2 oder der ERK Aktivierung verschlechterte jedoch die klinische Präsentation von adulten CMT1A Ratten. Die Verringerung der ERBB2 Aktivität verschlimmerte die axonale Funktion und bewirkte eine Zunahme von Zwiebelschalenformationen. Die Reduktion der ERK Hyperaktivität führte zu einem frühen behandlungsinduzierten Gewichtsverlust und einer Zunahme an demyelinisierten Axonen. Das Auftreten sekundär dysregulierter Signalkaskaden könnte zu dem Scheitern der Studien beigetragen haben. Das Scheitern beider Studien weist jedoch auch darauf hin, dass die Komplexität der CMT1A Pathobiologie besonders während der späten chronischen Phase noch immer unzureichend verstanden ist und weiterer Erforschung bedarf. Zusammenfassend ist die Interferenz mit der ERBB2-ERK Signalkaskade für die Behandlung der CMT1A ungeeignet. Dies weist auf die Notwendigkeit hin, ein tieferes Verständnis der Komplexität der späten chronischen CMT1A Pathobiologie und vor allem der NRG1-vermittelten Pathomechanismen zu erlangen. Beides schafft die Grundlage für die Identifizierung neuer therapeutischer Behandlungsansätze:Abbreviations 1. Introduction 1.1 The peripheral nervous system 1.1.1 Structure and functions of the nervous system 1.1.2 Neurons and glial cells 1.1.3 Signal transduction and myelination 1.1.4 Development and functions of Schwann cells 1.2 Peripheral neuropathies 1.2.1 Acquired and inherited peripheral neuropathies 1.2.2 Clinical presentation and classification of Charcot-Marie-Tooth diseases 1.2.3 The peripheral myelin protein of 22 kDa (PMP22) 1.2.4 Animal models of PMP22 – associated CMTs 1.2.5 Pathobiology and treatment options of CMT1A 1.2.6 Ablation of Schwann cell Neuregulin 1 ameliorates the phenotype of a CMT1A mouse model 1.3 The Neuregulin 1 – ERBB2 – ERK signaling axis in the Charcot-Marie-Tooth 1A disease 1.3.1 Functions of Neuregulin 1 in the peripheral nervous system 1.3.2 ERBB receptor tyrosine kinase signaling in Schwann cells 1.3.3 NRG1-I – ERBB mediated pathophysiological effects in CMT1A 1.3.4 Options for pharmacological interference with NRG1-I – mediated ERBB2 and ERK activation 1.4 Aim of the dissertation 2. Materials and Methods 2.1 Materials 2.1.1 Chemicals and Reagents 2.1.2 Consumable Supplies 2.1.3 Technical Equipment 2.1.4 Kits 2.1.5 Buffers and Solutions 2.1.6 Antibodies 2.1.7 Genotyping Primer 2.1.8 qPCR Primer 2.1.9 Enzymes 2.1.10 Software 2.2 Animal caretaking and treatment 2.2.1 Animal strains and breeding 2.2.2 Animal breeding and caretaking 2.2.3 Identification of animals 2.2.4 Herceptin® and Selumetinib treatment of CMT1A rats 2.2.5 Mechanical phenotyping 2.2.6 Electrophysiological examination 2.2.7 Euthanasia 2.2.8 Preparation and handling of peripheral nerve tissues 2.3 Histological methods 2.3.1 Embedding of isolated peripheral nerves in Agar 100 resin 2.3.2 Generation, imaging, and analysis of semi-thin sections 2.3.3 Coating of support copper grids for ultrastructure analysis 2.3.4 Generation, contrasting, imaging, and analysis of ultra-thin cross-sections 2.4 Protein Biochemistry 2.4.1 Isolation and quantification of (phospho-) proteins from frozen peripheral nerves 2.4.2 Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS PAGE) 2.4.3 Western blot and Fast Green staining 2.5 Molecular Biology Methods 2.5.1 Isolation of genomic DNA from tissues 2.5.2 Polymerase chain reaction of genomic DNA 2.5.3 Agarose gel electrophoresis of PCR products 2.5.4 RNA Isolation 2.5.5 Quality and quantity assessment of isolated RNA 2.5.6 cDNA Synthesis of total RNA 2.5.7 Quantitative real-time PCR analysis 2.6 Bioinformatics 2.6.1 Power analysis 2.6.2 Statistical methods 3. Results 3.1 NRG1 – ERBB2/ERBB3 – ERK signaling is increased in an adult CMT1A-resembling rat model 3.2 Late long-term blockage of ERBB2 signaling deteriorates the clinical and histopathological outcome of CMT1A rats 3.2.1 The clinical phenotype and histopathological hallmarks worsen after long-term Herceptin treatment of CMT1A rats 3.2.2 Herceptin application inhibits NRG1-I – mediated ERBB2/ERBB3 activation and concomitant downstream signaling 3.2.3 Inhibition of ERBB2 – mediated downstream signaling does not affect CMT1A Schwann cell dedifferentiation 3.3 Late long-term application of Selumetinib deteriorates the clinical presentation of CMT1A rats 3.3.1 Late short-term Selumetinib application ameliorates NRG1-I – ERBB2/3 – mediated downstream signaling 3.3.2 Long-term Selumetinib treatment deteriorates the clinical phenotype and promotes demyelination in CMT1A rats 3.3.3 Selumetinib treatment improved the dysbalance of the ERK and AKT pathways in CMT1A 4. Discussion 4.1 NRG1-I-mediated malsignaling may not have been sufficiently inhibited to impact the clinical outcome of CMT1A rats after ERBB2 suppression 4.2 Herceptin-binding of ERBB2 may interfere with the regeneration ability of Schwann cells in CMT1A 4.3 Dysregulation of ERK activity in late CMT1A promotes demyelination 5. Abstract 6. Zusammenfassung 7. References 8. Appendix 8.1 List of figures 8.2 List of tables 8.3 Eigenständigkeitserklärung 8.4 Curriculum vitae 8.5 Publikationen 8.6 Danksagungen / The Charcot-Marie-Tooth disease 1A (CMT1A) belongs to the family of inherited neuropathies of the peripheral nervous system (PNS) and is the most frequent subform with a prevalence of 1 in 2500. Patients present with a distally pronounced muscle atrophy and sensory impairments. Histologically, peripheral nerves display developmental myelination abnormalities, onion bulb formations, slowly progressive demyelination, and axonal loss during later disease stages, which account for clinical symptomatology. No treatment options are available upon today. Genetic testing revealed a genomic duplication of the gene encoding for the peripheral myelin protein of 22kDa (PMP22) as the primary cause of disease that affects specifically the myelinating glia of the PNS, the Schwann cells. Pmp22 overexpression has been shown to dysregulate physiological axon-glia interactions. Diseased Schwann cells respond with a de novo expression of the glial growth factor, Neuregulin 1-type I (NRG1-I). While not present under physiological conditions, chronic NRG1-I signaling was identified to be a major driver of disease pathogenesis in CMT1A. On the mechanistic level, aberrant NRG1-I has been demonstrated to overstimulate the ERBB2 receptor resulting in hyperactivation of the MEK-ERK pathway. Genetic disruption of NRG1 specifically in Schwann cells strongly improved the clinical presentation and histopathological manifestation of disease hallmarks in CMT1A-resembling rodents. This beneficial outcome was accompanied by a downregulation of ERBB2 and ERK hyperactivity in Schwann cells. Therefore, interfering with NRG1-I-mediated pathological signaling was proposed to constitute a promising therapeutic approach for CMT1A. However, long-term pharmacological obstruction of either ERBB2 or ERK activation deteriorated the clinical presentation of adult CMT1A rats. ERBB2 inhibition worsened axonal function and induced an increase in onion bulb formations. Reduction of ERK hyperactivity resulted in an early treatment-induced weight loss and an increase in demyelinated axons. The development maladaptive signaling mechanisms may have caused the observed outcome of the trials. However, failing of both trials instead also demonstrates that the complexity of late chronic CMT1A pathobiology is still poorly understood and has to be further investigated. In conclusion, interfering with ERBB2-ERK signaling, downstream of NRG1-I, turned out to be not a viable approach for CMT1A treatment. This points to the necessity to gain a deeper understanding of the late chronic CMT1A intricacy and especially of NRG1-mediated pathomechanisms in neuropathy. Both may build the foundation for the identification of novel therapeutic approaches and drug targets.:Abbreviations 1. Introduction 1.1 The peripheral nervous system 1.1.1 Structure and functions of the nervous system 1.1.2 Neurons and glial cells 1.1.3 Signal transduction and myelination 1.1.4 Development and functions of Schwann cells 1.2 Peripheral neuropathies 1.2.1 Acquired and inherited peripheral neuropathies 1.2.2 Clinical presentation and classification of Charcot-Marie-Tooth diseases 1.2.3 The peripheral myelin protein of 22 kDa (PMP22) 1.2.4 Animal models of PMP22 – associated CMTs 1.2.5 Pathobiology and treatment options of CMT1A 1.2.6 Ablation of Schwann cell Neuregulin 1 ameliorates the phenotype of a CMT1A mouse model 1.3 The Neuregulin 1 – ERBB2 – ERK signaling axis in the Charcot-Marie-Tooth 1A disease 1.3.1 Functions of Neuregulin 1 in the peripheral nervous system 1.3.2 ERBB receptor tyrosine kinase signaling in Schwann cells 1.3.3 NRG1-I – ERBB mediated pathophysiological effects in CMT1A 1.3.4 Options for pharmacological interference with NRG1-I – mediated ERBB2 and ERK activation 1.4 Aim of the dissertation 2. Materials and Methods 2.1 Materials 2.1.1 Chemicals and Reagents 2.1.2 Consumable Supplies 2.1.3 Technical Equipment 2.1.4 Kits 2.1.5 Buffers and Solutions 2.1.6 Antibodies 2.1.7 Genotyping Primer 2.1.8 qPCR Primer 2.1.9 Enzymes 2.1.10 Software 2.2 Animal caretaking and treatment 2.2.1 Animal strains and breeding 2.2.2 Animal breeding and caretaking 2.2.3 Identification of animals 2.2.4 Herceptin® and Selumetinib treatment of CMT1A rats 2.2.5 Mechanical phenotyping 2.2.6 Electrophysiological examination 2.2.7 Euthanasia 2.2.8 Preparation and handling of peripheral nerve tissues 2.3 Histological methods 2.3.1 Embedding of isolated peripheral nerves in Agar 100 resin 2.3.2 Generation, imaging, and analysis of semi-thin sections 2.3.3 Coating of support copper grids for ultrastructure analysis 2.3.4 Generation, contrasting, imaging, and analysis of ultra-thin cross-sections 2.4 Protein Biochemistry 2.4.1 Isolation and quantification of (phospho-) proteins from frozen peripheral nerves 2.4.2 Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS PAGE) 2.4.3 Western blot and Fast Green staining 2.5 Molecular Biology Methods 2.5.1 Isolation of genomic DNA from tissues 2.5.2 Polymerase chain reaction of genomic DNA 2.5.3 Agarose gel electrophoresis of PCR products 2.5.4 RNA Isolation 2.5.5 Quality and quantity assessment of isolated RNA 2.5.6 cDNA Synthesis of total RNA 2.5.7 Quantitative real-time PCR analysis 2.6 Bioinformatics 2.6.1 Power analysis 2.6.2 Statistical methods 3. Results 3.1 NRG1 – ERBB2/ERBB3 – ERK signaling is increased in an adult CMT1A-resembling rat model 3.2 Late long-term blockage of ERBB2 signaling deteriorates the clinical and histopathological outcome of CMT1A rats 3.2.1 The clinical phenotype and histopathological hallmarks worsen after long-term Herceptin treatment of CMT1A rats 3.2.2 Herceptin application inhibits NRG1-I – mediated ERBB2/ERBB3 activation and concomitant downstream signaling 3.2.3 Inhibition of ERBB2 – mediated downstream signaling does not affect CMT1A Schwann cell dedifferentiation 3.3 Late long-term application of Selumetinib deteriorates the clinical presentation of CMT1A rats 3.3.1 Late short-term Selumetinib application ameliorates NRG1-I – ERBB2/3 – mediated downstream signaling 3.3.2 Long-term Selumetinib treatment deteriorates the clinical phenotype and promotes demyelination in CMT1A rats 3.3.3 Selumetinib treatment improved the dysbalance of the ERK and AKT pathways in CMT1A 4. Discussion 4.1 NRG1-I-mediated malsignaling may not have been sufficiently inhibited to impact the clinical outcome of CMT1A rats after ERBB2 suppression 4.2 Herceptin-binding of ERBB2 may interfere with the regeneration ability of Schwann cells in CMT1A 4.3 Dysregulation of ERK activity in late CMT1A promotes demyelination 5. Abstract 6. Zusammenfassung 7. References 8. Appendix 8.1 List of figures 8.2 List of tables 8.3 Eigenständigkeitserklärung 8.4 Curriculum vitae 8.5 Publikationen 8.6 Danksagungen

The first dynein mutation found in humans that caused disease was a cytoplasmic dynein 1 heavy chain (DYNC1H1 in humans) p.His306Arg mutation, first described by Weedon et al. in 2011. This mutation caused Charcot-Marie-Tooth (CMT) subtype 2O. CMT has a prevalence of approximately 1 in 2500 people, making it the most common hereditary neuromuscular disorder. Cytoplasmic dynein 1 is used by eukaryotic cells for minus-end directed microtubule-based transport of cargo. One such cargo is Rab7, a late endosomal marker. The purpose of this study is to identify the effects of this mutation on the transport of GFP-tagged Rab7 cargo in neurons from wild type (HH), heterozygous mutant (HR), and homozygous mutant (RR) mice harboring a DYNC1HI His306Arg mutation. Mouse embryos were euthanized, dissected to collect the hippocampal and cortical brain tissues, and these tissues were digested to isolate neurons. Nucleofection was used to introduce the exogenous GFP-Rab7 gene construct. These neurons were plated and imaged at 10 days in vitro using wide-field epifluorescence microscopy to generate image stacks of fluorescent GFP-Rab7 vesicles. Kymograph analysis was performed on the image stacks using MetaMorph software to measure several characteristics of movement. Statistical analysis of the data from each of the three genotypes shows there is no significant difference in Rab-7 transport between the three genotypes.

Die Charcot-Marie-Tooth-Erkrankung (CMT) stellt die häufigste erbliche periphere Polyneuropathie des Menschen dar. Betroffene leiden unter einer symmetrischen distal ausgeprägten Muskelatrophie, die mit motorischen und sensorischen Defiziten einhergeht. Bis heute existieren keine kurativen Therapieoptionen. Das liegt unter anderem daran, dass die Pathomechanismen der CMT und vor allem die Reaktion der Schwannzellen in chronischen Neuropathien noch nicht ausreichend verstanden sind. In einem Mausmodell der CMT1A, der häufigsten Subform der CMT, konnte gezeigt werden, dass die Ablation des Myelindicke-regulierenden Wachstumsfaktors Neuregulin 1 (Nrg1) eine Verbesserung der typischen Krankheitsmerkmale hervorruft. Dies zeigt, dass es in der CMT1A einen Zusammenhang zwischen der übermäßigen Expression des gialen Nrg1 und der pathologischen Schwannzell-Reaktion gibt. Die CMT1B ist der dritthäufigste CMT-Subtyp, welcher durch Mutationen im MPZ (Myelin Protein Zero) - Gen verursacht wird. Um zu untersuchen, ob ein Knockout von glialem Nrg1 auch in der CMT1B Erkrankung zu einer Verbesserung der Symptomatik führt, wurden in dieser Arbeit der Phänotyp, die Histopathologie und die Genexpression auf mRNA-Ebene in einem CMT1B Mausmodell analysiert: Nach Ablation von glialem Nrg1 zeigten die Versuchstiere eine herabgesetzte motorische Leistung im Griffstärke- und Rotarod-Test. Passend dazu ergab sich eine Verlängerung der M- und F-Wellendauer in den elektrophysiologischen Untersuchungen sowie eine erhöhte Anzahl a- und demyelinisierter Axone in den histologischen Untersuchungen. Interessanterweise war die Zahl der Schwannzellen und Zwiebelschalenformationen nach Ablation von glialem Nrg1 trotz Verschlechterung des Phänotyps stark rückgängig. Dies lässt den Schluss zu, dass diese für die CMT typischen histopathologischen Merkmale in der CMT1B – im Gegensatz zur CMT1A – nur eine geringe Rolle für die Krankheitsausprägung und -progression spielen. Vielmehr scheinen in der CMT1B Erkrankung de- und remyelinsierende Prozesse im Vordergrund zu stehen. Die Beobachtung, dass die Ablation der glialen Neuregulin 1 Signalwirkung die Anzahl der a- und demyelinsierten Axone signifikant erhöht, lässt die Vermutung zu, dass gliales Neuregulin 1 für die Remyelinisierung von Axonen in der CMT1B Erkrankung essentiell ist. Die Ergebnisse legen zudem nahe, dass Remyelinisierungsprozesse in chronischen Neuropathien einen wesentlichen Einfluss auf die Krankheitsausprägung und den klinischen Phänotyp haben. Die vorliegende Arbeit zeigt, dass therapeutische Ansätze, die die Remyelinisierung fördern nicht nur im ZNS, sondern grundsätzlich auch im PNS erfolgreich sein könnten. Im Vergleich zu demyelinsierenden Erkrankungen des ZNS wird dem Prozess der Remyelinisierung in peripheren Neuropathien bis dato jedoch kaum Beachtung geschenkt. Des Weiteren wurden die Histopathologie und die Genexpression im longitudinalen Verlauf untersucht. Die proximal gelegenen Nerven, insbesondere die Vorderwurzeln, sind sowohl histopathologisch als auch auf Ebene der Schwannzell-Transdifferenzierungsfaktoren deutlich stärker betroffen als die distal gelegenen Nerven. Diesem Phänomen könnten unterschiedliche Ursachen zu Grunde liegen: Vorstellbar wäre eine Heterogenität in der Schwannzellpopulation entlang der peripheren Nerven, deren Folge verschiedene molekulare Charakteristika sowie eine divergierende Vulnerabilität für bestimmte pathologische und genetische Veränderungen sein könnte. Eine derartige Heterogenität könnte in der Entwicklung der Schwannzellen begründet sein. So entwickeln sich zwar alle Schwannzellvorläufer aus Zellen der Neuralleiste, die Schwannzellen der spinalen Nervenwurzeln entstammen jedoch speziellen Derivaten der Neuralleistenzellen, den sogenannten Boundary-Cap-Zellen. Neben unterschiedlichen Schwannzellpopulationen im proximalen und distalen Nerv - also primär intrinsischen Faktoren - könnte auch die Interaktion der Gliazellen mit anderen zellulären Komponenten im peripheren Nerv für den beobachteten Gradienten in der histologischen Krankheitsausprägung verantwortlich sein. Interessant erscheint hier insbesondere die Rolle der Axon-Glia-Interaktion und die Funktion axonaler Signale für die Integrität und Vulnerabilität der Schwannzelle. Zusammenfassend scheint es sehr vielversprechend die beobachteten Unterschiede im longitudinalen Verlauf weiter zu untersuchen, um die Pathogenese der CMT besser zu verstehen und somit die Grundlage für die Entwicklung suffizienter Therapieansätze zu schaffen.:Inhaltsverzeichnis Abkürzungsverzeichnis I 1. Einführung 1 1.1 Das Nervensystem 1 1.2 Schwannzell-Entwicklung und Myelinisierung 3 1.3 Neuregulin 1 6 1.4 Charcot-Marie-Tooth-Erkrankung 9 1.4.1 Charcot-Marie-Tooth-Erkrankung 1B 13 1.4.2 Verbesserung der klinischen und histopathologischen Erkrankungssymptomatik im CMT1A Tiermodell nach Ablation von Nrg1 in Schwannzellen 15 2. Aufgabenstellung 17 3. Material und Methoden 18 3.1 Material 18 3.1.1 Chemikalien und Reagenzien 18 3.1.2 Verbrauchsmaterialien 19 3.1.3 Enzyme, Nukleinsäuren und Reaktionssysteme (Kits) 20 3.1.4 Puffer und Lösungen 20 3.1.5 Oligonukleotide 22 3.1.6 Geräte 24 3.1.7 Software 25 3.2 Methoden 26 3.2.1 Versuchstiere 26 3.2.2 Rotarod- und Griffstärke-Test 28 3.2.3 Elektrophysiologische Untersuchung 28 3.2.4 Histologische Methoden 30 3.2.5 Molekularbiologische Methoden 33 3.2.6 Statistik 41 4. Ergebnisse 42 4.1 Verschlechterung des Phänotyps im CMT1B Mausmodell nach konditionaler Ablation von glialem Neuregulin 1 42 4.2 Zunahme der Demyelinisierung sowie Abnahme der Zellkerne und Zwiebelschalenformationen in peripheren Nerven nach Nrg1-Ablation in Schwannzellen 47 4.3 Die Schwannzell-Transdifferenzierung ist nach Deletion von glialem Neuregulin 1 in proximalen Nerven rückläufig 55 4.4 Proximale Anteile in der longitudinalen Analyse peripherer Nerven von CMT1B Mäusen deutlich stärker betroffen 58 5. Diskussion 62 5.1 Im Gegensatz zum CMT1A Modell führt die Ablation von glialem Neuregulin 1 im CMT1B Modell zu einer Verschlechterung des Phänotyps 62 5.2 Die Expression von Transdifferenzierungsmarkern wird durch Ablation von Schwannzell Nrg1 reduziert 64 5.3 Proximale Anteile peripherer Nerven sind in der CMT1B stärker betroffen als weiter distal gelegene Anteile 67 6. Zusammenfassung 69 Abbildungsverzeichnis 71 Literaturverzeichnis 72 Anlagen 79

This qualitative study focuses on the experiences of adults with Charcot-Marie-Tooth disease (CMT), a neuromuscular condition, and explores what living with this disease encompasses. The study is structured around two fundamental research questions that amount to people's experiences regarding how (in which areas) the disease affects them, and how they continuously deal with it. In order to address the research questions, data gathered from participants was qualitatively analysed, using grounded theory methodology. The study culminated in the formulation of a substantive grounded theory as to how affected people manage the disease's manifestations in order to optimise their continuous adaptation and well-being. A tripartite of concerns comprised the core concern, whereas the basic social psychological process of engaging with CMT emerged as the core strategy used by affected people to deal with the concerns. The core's three sub processes constituted three mostly sequential stages that CMT-affected people pass through in their adaptation to the disease. The identified theory and existing stage models of adaptation to chronic illnesses and disabilities were juxtaposed and discussed. The three stages were compared to and integrated with the relevant literature. These actions revealed that there are a number of new formulations and processes contained in all three stages, and that the first and last stages (orientating and optimising) are themselves unique. It emerged that there is no theoretical end-point to the adaptation process, but that a relative saturation point amounted to a variant of an outcome, called qualified wellness. For most, the core strategy was successful in resolving the main concern. A few, however, still experienced fear and agony about inheritance and dependency issues. This study contributes, via the route of knowledge and insight empowerment, to the well-being of people with CMT, including those who are struggling but do not know that they have this disease. Broadening of insight may also benefit medical help professionals and streamline service delivery. / Psychology / D. Litt. et Phil. (Psychology)