BDNF delivery strategies in an experimental model of temporal lobe epilepsy.

Neurotrophic factors (NTFs) have been reported to play opposite, pro- and/or anti-epileptic effects in experimental models. Some NTFs favor epileptogenesis or progression of epilepsy whereas others oppose these processes. Still other NTFs, including Brain-Derived Neurotrophic Factor (BDNF), can exert both positive and negative effects. Moreover, BDNF has been clearly shown to be involved in all the cellular and tissue changes that occur during epileptogenesis. To get further insight in the involvement of BDNF in epilepsy and, on this basis, to develop new therapeutic strategies, there is a need to develop new, advanced tools for the modulation of the BDNF signal within defined brain regions. Therefore, the aim of this thesis was to develop new delivery systems to block or to enhance the BDNF signal. Specifically, the thesis deals the investigation of the validity of BDNF as a therapeutic target, using advanced tools to down regulate BDNF expression (Herpes simplex virus-1 based amplicon vectors) and to continuously secrete it [encapsulated cell biodelivery (ECB) devices]. Two amplicon-based silencing strategies have been developed. The first, antisense (AS), targets and degrades the cytoplasmic mRNA pool of BDNF, whereas the second, based on the convergent transcription (CT) technology, directly represses the BDNF gene. In vitro (cell lines) and in vivo (stereotaxic injection in the epileptic hippocampus) experiments demonstrated a reliable effect of amplicon vectors in knocking down gene expression. However, whereas the CT-BDNF strategy proved effective only in vitro, the AS-BDNF amplicon vector proved effective both in vitro and in vivo, knocking down efficiently BDNF protein levels in the injected hippocampus at different time points. The antisense strategy seems therefore a better choice for silencing BDNF expression in vivo. For a prolonged administration of BDNF, BDNF-producing cells encapsulated in ECB devices have been tested in a rat model of Temporal Lobe Epilepsy. These devices, implanted bilaterally in the hippocampus of chronically epileptic animals, proved capable to significantly decrease the frequency of spontaneous generalized seizures. These new tools and experiments help to further elucidate the role of BDNF in epilepsy and provide an initial proof-of-concept for a new, promising therapeutic approach.