Identification of novel therapeutic targets and evaluation of pharmacological treatments in epigenetic and chromatin diseases- the case of Rett syndrome

INTRODUCTION: In 1966, Rett syndrome (RTT, OMIM#312750) was for the first time described as a clinical issue by Dr. Andreas Rett, an Austrian pediatrician. He has observed in 22 patients similar unique symptoms. A few years later Hagberg and colleagues described further the syndrome in 35 girls. Rett syndrome is the cause of mental retardation that affects 1 in 10.000 female births, which makes it the second cause of mental retardation in girls. In 1999 Zoghbi lab found out the genetic basis of Rett disease. Mutation in MeCP2 is in 95% cases the reason of classical Rett. MeCP2 is a nuclear protein, expressed widely in different tissues, but is most abundant in neurons of the mature nervous system. A few years earlier Bird and coworkers indentified MeCP2 as a new protein that binds to the methylated CpG dinucleotides. Although the function of the MeCP2 is still unknown, it is considered likely to regulate gene expression, either through the silencing or activation of the specific genes or by more global regulation of transcriptional processes. RTT was the first neurodevelopmental disorder related to epigenetics. AIM OF THE STUDY Hypotesis: The main aim of this thesis is to perform preclinical evaluation of drugs that are known to target pathways which are altered in Rett syndrome. It is also necessary to investigate new mechanisms associated with the development of Rett syndrome, aiming to find new pathways related to Rett phenotype that can be manipulated through the pharmacological approach. Aims: 1. Determine tests that can reflect the difference at the behavioral and molecular levels between the Mecp2 KO and WT littermate mice. 2. Optimize study design protocol for evaluation of in vivo drug treatments. 3. Identify candidate drugs against selected targets in order to improve Rett disease, with the goal to reverse the symptoms, prolong the life span or ameliorate dysfunctions based on inflammation and neural mechanisms. 4. Determine the potential effects of novel therapeutic approaches for newly discovered pathways dysregulated in Rett syndrome. Methods: Animals knockout (KO) to the MeCP2 gene are a well-established murine model that mimics RTT human disease. This model is an excellent tool for the study of the consequences of the loss of MeCP2 in neuronal function. Once we know the dose administered, use two experimental groups of treated and untreated animals. Treatment is initiated when the animals are 4 weeks old and start showing symptoms characteristic of this model: reduced mobility, retraction of the hind legs, tremors, hair frizzing and respiratory abnormalities, difficulty walking, retraction of the rear legs. During the test, the mice will be evaluated according to a set of symptoms resulting from MeCP2 deficiency. Results: Part 1 • We performed a comprehensive panel of experiments investigating the differences between Mecp2 KO and wt littermate mice at the behavioral and molecular levels. This was further extended to evaluate the specific drug treatments efficacy. Part 2 • Combined administration of Levodopa and a Dopa decarboxylase inhibitor in Rett syndrome mouse models was well tolerated, diminished Rett syndrome-associated symptoms and increased lifespan. • The use of L-Dopa + Ddci in the Mecp2 KO mice induced dendritic growth mediated by dopaminergic neurons. • L-Dopa + Ddci-treated group exhibited higher Th and pTh expression and dopamine levels in comparison to the vehicle treated group. Part 3 • The results presented here reveal an important role for the relationship between Mecp2 and GSK3 signaling in Rett syndrome disease • Inhibitor of GSK3, SB216763, improved life span and reduced single and total symptoms scores, as well as motor deficiency in Mecp2 KO mice • Inhibition of GSK3 is a possible line of stimulation of neuronal dendritic growth, supported by elevated levels of D2- receptor after drug administration. • Treatment with SB216763 decreased inflammation and strengthened antioxidant defense in the brain of Mecp2KO mice Part 4 • Treatment with copaxone, a BDNF analogue reflect rather low improvement in Mecp2 KO studied mice, displaying also very variable results between studied animals. • Treatment with dexamethasone, an example of glucocorticoids intervention display rather low improvement – approximately 20% when compared to untreated mice. • Ropirinol treatment confirmed that dopminergic pathway is dysregulated in Rett. Both life span and the phenotype were improved. However, the efficiency was lower compared to L-dopa + Ddci treatment. • Injections of bromperidol, a serotonin modulator, were toxic for Mecp2 KO mice. Even though the selected doses were very low, they caused significant reduction of body weight in the KO treated group. • Previously described positive effect of cysteamine was not reproduced in our laboratory (Roux et al., 2012). • Gabapentin, one of GABA modulators, improved the phenotype, but not life span of Mecp2 KO animals, being more efficient with the low dose. • TDZD8 treatment confirmed previously a described role of GSK3 inhibition in Rett. Both life span and phenotype were improved. However, the efficacy was lower than after SB216763 treatment. • Antioxidants studied in this thesis displayed improvement of 30% in Rett syndrome phenotype and some of them prolonged the life span by 25% when compared to the vehicle group. • Epigenetics drugs evaluated in this thesis, even though some of them were suggested to be relevant for Rett syndrome, did not show any specific improvement. Conclusions: The treatment with L-Dopa + Ddci is promising to overcome the dopaminergic defects observed in the preclinical model of Rett syndrome (Szczesna et al., 2014) The new data indicate selected inhibitor, SB216763, as a being potential drug treatment for Rett disease. The drug can be adressed to have neuroprotection properties via the improvement of synaptic plasticity, reduced oxidant and inflammation damage or partial rescue of mobility dysfunctions (Szczesna et al in preparation).