Efecto de diferentes pautas de administración de gdnf en las rutas mapk/erk y pi3k/akt y su potencial neuroprotector en neuronas dopaminérgicas mesencefálicas

Abstract

Parkinson's disease (PD) is a neurodegenerative disorder characterised by the loss of mesencephalic dopaminergic neurons and the decline of dopamine levels in the striatum. There is currently no treatment that alters the course of the disease. Experimental studies indicate that glial cell line-derived trophic factor (GDNF) may have protective effects on dopaminergic neurons. However, clinical trials have not shown the expected results, and relevant aspects of GDNF pharmacological actions, particularly those related to trophic and protective effects under different treatment schedules, remain unclear. The aim of this thesis was to study: 1. the trophic (levels of dopaminergic markers) and neuroprotective (response to neurotoxins) effects, and 2. the differences in Ret signalling pathways after different GDNF administration patterns (acute, prolonged and intermittent) in primary cultures of mesencephalic neurons and in the rat mesostriatal system. The results of in vitro experiments showed that acute GDNF treatment (24 hours) induces an increase in TH expression and protects dopaminergic neurons against 6-hidroxidopamine (6-OHDA) and rotenone. However, the opposite effects were found when cell cultures were treated with GDNF for 7 days, showing a decrease in TH expression and a higher vulnerability to neurotoxins than untreated cells. Consistent with these results, striatal injection of AAV1/2-V16-TetbidiON-GDNF and acute (doxycycline, 5 days) and intermittent (doxycycline, 3x72 hours/15 days) induction of GDNF delivery promote an increase in nigral and striatal TH expression and the mesostriatal pathway was protected against 6-OHDA. However, when GDNF delivery was sustained for 45 days, TH levels decrease below basal levels and mesostriatal dopaminergic neurons became more vulnerable to 6-OHDA than in untreated rats. Differences in Ret signalling were also found depending on the treatment schedule. Short-term and intermittent GDNF treatments led to an increased phosphorylation of Ret and its downstream effector kinases AKT, GSK3-β, ERK1/2 and S6, whereas prolonged GDNF treatment induced a decline in Ret signalling. Considering the chronic nature of Parkinson's disease and the regulatory mechanisms in response to prolonged GDNF treatment, inducible viral vectors may be an interesting alternative to control GDNF delivery and the design of therapeutic strategies according to the needs of each patient.