Mitochondrial and autophagic alterations in human-derived cell models of Parkinson's disease related to LRRK2 (G2019S) and GBA (N370S) mutations

Abstract

Parkinson's disease (PD) is the second most common neurodegenerative disease, and the most common movement disorder in the world population. In most cases its aetiology is still unknown, however, mitochondrial alterations and autophagy deregulations are some of the molecular mechanisms that are altered in this disease.

These molecular alterations of PD are not limited only to the destruction of dopaminergic neurons in the substantia nigra pars compacta, but they have also been described in the peripheral nervous system and the organs that it innervates. There is also evidence of the presence of other molecular alterations in diverse tissues, such as dysfunction of Complex I of the mitochondrial respiratory chain and accumulation of alpha synuclein in fibroblasts of patients with PD.

One of the great difficulties the research and understanding of the mechanisms that lead to PD is the inaccessibility of the target tissue of the disease. In the best of cases, autopsy tissue from patients with advanced PD is available, leaving a question mark about the molecular processes of prodromal and early stages of the disease. Animal models have helped to unravel some questions, but the development of accessible and replicable cell models, preferably at low cost, is much needed. It is in this context that the cellular models obtained from PD patients and from asymptomatic carriers of genes associated with the disease are of great importance and require validation.

The present thesis consists of the study of two cell models obtained from patients with PD associated with the LRRK2 mutation (G2019S), asymptomatic carriers of LRRK2 (G2019S) and homozygous and heterozygous carriers of GBA (N370S); which are the genes most frequently associated with familial PD and the most important genetic risk factor for PD, respectively.

First, the mitochondrial and autophagic profile of fibroblasts derived from the skin of asymptomatic carriers of the LRRK2 (G2019S) mutation and with PD were analysed. The analysis was carried out under two conditions, keeping the fibroblasts in a standard culture medium (DMEM with 25mM glucose) and after subjecting them to a mitochondrial challenge for 24 hours (DMEM with 10mM galactose), in order to simulate the oxidative environment of neurons. dopaminergic. In this study, a genotype-phenotype correlation was confirmed in fibroblasts obtained from asymptomatic carriers of the LRRK2 (G2029S) mutation and patients with PD linked to this same mutation, and it was demonstrated that a mitochondrial and autophagic function profile allows to differentiate between groups.

The second study explored the genotype-phenotype correlation in a cellular model characterized by neurospheres, a conglomerate of cells obtained from the dedifferentiation of human adipocytes into neuronal stem cells, and its relationship with the onset of macroautophagy in subjects carrying the mutation GBA (N370S). The main finding of this study is that mitochondrial dysfunction preceded alterations of macroautogphagic flux in subjects carrying the GBA (N370S) mutation.

In conclusion, the study of asymptomatic subjects carrying mutations associated with PD represents a relevant study method that shows initial molecular alterations and the presence of compensatory mechanisms that can be studied for the development of preventive strategies and treatments in early stages of the disease.

La enfermedad de Parkinson (EP) es el trastorno de movimiento más frecuente en la población mundial. Considerada mayoritariamente idiopática y multifactorial, alteraciones mitocondriales y en la regulación autofagica son algunos de los mecanismos moleculares que se han encontrado alterados en la etiopatología de la enfermedad.

El descubrimiento de genes relacionados a formas familiares de EP, del cual LRRK2 es el más frecuente, y los genes que aumentan el riesgo de padecer la enfermedad, como GBA, han abierto un campo de estudio en el cual se pueden analizar los mecanismos moleculares que llevan a la neurodegeneración en formas genéticas de la EP.

La presente tesis consiste en el estudio de dos modelos celulares obtenidos a partir de portadores asintomáticos de LRRK2(G2019S) (NMLRRK2(G2019S)), pacientes con EP asociada a la mutación LRRK2(G2019S) (PDLRRK2(G2019S)), así como de portadores homozigotos y heterozigotos de GBA(N370S).

El primer estudio analizó el perfil mitocondrial y autofágico de fibroblastos NMLRRK2(G2019S) y PDLRRK2(G2019S). El análisis se realizó en dos condiciones, en un medio de cultivo estándar (DMEM, glucosa 25mM) y tras someterlos 24 horas a un reto mitocondrial (DMEM, galactosa 10mM), simulando el ambiente oxidativo de las neuronas dopaminérgicas. En este estudio se confirmó una correlación genotipo-fenotipo en fibroblastos obtenidos de ambos grupos y una función mitocondrial y autofágica que permite diferenciarlos entre ellos.

El segundo estudio exploró la correlación genotipo-fenotipo en un modelo celular caracterizado por neuroesferas, un conglomerado de células obtenido a partir de la desdiferenciación de adipocitos humanos en células madres neuronales, y su relación con el inicio de la macroautofagia en sujetos portadores de la mutación GBA(N370S). El hallazgo principal de este segundo estudio es que la disfunción mitocondrial precede a las alteraciones del flujo macroautofágico en sujetos portadores de la mutación GBA(N370S).

El estudio de sujetos asintomáticos portadores de mutaciones asociadas a PD representa un relevante método de estudio que evidencia alteraciones moleculares iniciales y la presencia de mecanismos compensatorios que pueden ser estudiados para el desarrollo de estrategias preventivas y tratamientos en lateabas tempranas de la enfermedad.