Tyrosine hydroxylase deficiency: Studies in patient samples and in a cellular model
- Autores: Alba Tristán Noguero
- Directores de la Tesis: Angels García Cazorla (dir. tes.), Antonella Consiglio (codir. tes.), Soledad Alcántara Horrillo (tut. tes.)
- Lectura: En la Universitat de Barcelona ( España ) en 2019
- Idioma: inglés
- Tribunal Calificador de la Tesis: Rafael Artuch Iriberri (presid.), Daniel Grinberg Vaisman (secret.), Aurora Martínez Ruiz (voc.)
- Programa de doctorado: Programa de Doctorado en Biomedicina por la Universidad de Barcelona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TESEO
- Resumen
Monoamine Neurotransmitter diseases are a rare group of inherited disorders of metabolism that encompass 12 different genetic defects leading to abnormal dopamine and/or serotonin brain homeostasis. They correspond to enzymatic deficiencies involved in the biosynthesis, catabolism and transport of dopamine and serotonine. From a clinical point of view, they can appear at any age and manifest diverse clinical features. However, movement disorders ranging from dopa-responsive dystonia to severe parkinsonism, associated to variable degrees of cognitive impairment is the most common form of presentation. The pathophysiology underlying the wide spectrum of clinical phenotypes (from mild to severe) and response to neurotransmitter precursors (L-Dopa+carbidopa, BH4 and other dopaminergic enhancers) has not been studied in detail. Here we aim to address this important issue through different approaches: i) the study of a particular disease of neurotransmitters, Tyrosine Hydroxylase deficiency (THD), as a model of dopaminergic deficiency. Tyrosine hydroxylase (TH) enzyme catalyses the rate-limiting step in the biosynthesis of dopamine (DA). THD exhibits a wide spectrum of clinical manifestations that have been grouped according to the severity in two clinical phenotypes: “Type A” tends to present as L-Dopa responsive parkinsonism-dystonia whereas “Type B” produces a severe encephalopathy of early-onset with sub-optimal L-Dopa response. ii) The study of a large cohort of patients with neurotransmitter defects thanks to an international collaboration (I-NTD group). We have used both patients’ samples and an iPSc model to address these questions. A) Patients’ samples: A.1) We studied one THD B phenotype postmortem brain and we observed that the expression of key synaptic proteins and neurodevelopmental markers were altered: TH, VMAT 1 and 2 and dopamine receptors, especially D2DR were decreased. GABAergic and glutamatergic proteins such as GABAVT, NMDAR1 and calbindin were also altered. Finally, developmental markers for synapses, axons and dendrites were decreased, whereas markers of neuronal volume were preserved. A.2) 94 CSF samples of patients with neurotransmitter defects from 9 centres belonging to different countries/continents were collected in an international collaboration through the I-NTD working group. The proteomic study showed that the main category of overrepresented proteins was related to nervous system development. Moreover, different proteins were detected that could be useful biomarkers for severity prognosis and response to treatment that are specific of disorders. Four of them were correctly validated with an ELISA analysis: APOD, COL6A3, APOH and OMGP. These proteins are involved in diverse important biological functions such as myelination, phospholipid and other lipid related processes. B) iPSC model of THD: iPSC lines from Type A and B patients, controls and an isogenic corrected iPSC line were generated. Upon Dopaminergic differentiation, THD A and B neurons reproduced the disease-associated phenotype: decreased TH Protein, reduced enzyme activity and alteration on DA genes expression. A new neuronal phenotype was also described: less TH-immunoreactive cells and fiber density in both mutant TH+ neurons, Type A and B DAn presented altered morphology (reduced neuronal arborisation only in THD-Type B) and a reduced axonal TH localization was observed in THD-Type A. We were also able to test therapeutic approaches such as L-Dopa + carbidopa. To conclude, we have performed extensive and novel studies using different approaches and techniques to better characterize the pathophysiology underlying the spectrum of severity and response to the current pharmacological treatments of neurotransmitter defects. We have provided new information pointing towards a dysregulation of multiple neurodevelopmental functions in these diseases, and biomarkers of clinical severity that could be explored in the future as therapeutic targets. Additionally, an iPSC model for THD has been developed for the first time that introduces mechanistic and therapeutic insights in this early-parkinsonism model.
