Modulation of Microglial Activity by GDNF

• Autor(a) principal: Tomé, Diogo Alexandre da Silva
• Data de Publicação: 2015
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.6/5963
• topic: Doença de Parkinson; Gdnf; Gfra1; Microglia; Ncam; Neuroinflamação; Ret; Stress Oxidativo; Domínio/Área Científica::Ciências Médicas::Ciências Biomédicas

Parkinson’s disease (PD) is an age-related disease characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Increasing evidence suggests that inflammation and oxidative stress mediated by activated microglia, the resident immune cells of the central nervous system (CNS), play a critical role in dopaminergic neuronal loss and in the pathophysiology of PD. For this reason, it is crucial to understand the mechanisms capable of controlling microglial reactivity. Glial cell line-derived neurotrophic factor (GDNF), a potent neuroprotective factor for dopaminergic neurons, is able to inhibit the increase in the production of reactive oxygen species (ROS) and in the phagocytosis triggered by an inflammatory agent in midbrain microglial cells, but the mechanisms by which GDNF exerts its effects on microglia are still not completely understood. The control of microglia activation exerted by GDNF depends on GFRa1. However, the signalling mechanism mediated by this co-receptor can be coupled to the transmembrane RET tyrosine kinase or to the cell adhesion molecule NCAM. To elucidate which are the signalling pathways involved in the modulation of microglial activity by GDNF, the effect of GDNF on the activity of RET and of the NCAM target, the focal adhesion kinase (FAK), and the effect of FAK inhibition in GDNF action were evaluated. For these experiments, LPS-stimulated midbrain microglia cultures were used. GDNF was able to inhibit the increase in the number of phagocytic cells triggered by LPS in midbrain microglia cultures when FAK was inhibited. Furthermore, GDNF had no effect on FAK phosphorylation levels but it seems to prevent the decrease in RET phosphorylation levels induced by LPS. In order to determine possible changes in GDNF levels, or in the proteins associated with GDNF signal transduction in PD, an animal model of PD based on the intranigral injection of LPS was used. The results showed that exposure to LPS induces a significant reduction in the GFRa-1 levels in the injected SN. Taken together, these results suggest that the modulation of microglial activity by GDNF involves the receptor RET and not the cell adhesion molecule NCAM. Furthermore, the GDNF signalling may be impaired in PD due to low levels of GDNF co-receptor GFRa-1 in the SN of LPS-exposed animals.