Molecular mechanisms underlying the role of syngap in cognition and synaptopathies
- Autores: Gemma Gou Alsina
- Directores de la Tesis: Alex Bayés (dir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Angels García Cazorla (presid.), Albert Quintana Romero (secret.), René A. W. Frank (voc.)
- Programa de doctorado: Programa de Doctorado en Neurociencias por la Universidad Autónoma de Barcelona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TESEO
- Resumen
Forebrain postsynaptic densities (PSDs), found in dendritic spines, express more than 2,000 different proteins, endowing neurons with the synaptic plasticity mechanisms required for cognition and behaviour. Some of the most abundant PSD proteins are SynGAP and Shanks. In rodents, like in other mammals, the Syngap1 gene encodes for different isoforms that vary in their N- and C-termini. Mutations in the SYNGAP1 gene cause autosomal mental retardation type five (MRD5), which is characterized by intellectual disability (ID) and epilepsy, as well as autistic traits in approximately half of the affected individuals, among other impairments.
The first part of the present thesis focused on the study of SynGAP isoforms during mouse neurodevelopment. Their differential abundance in five different brain regions and four developmental stages were systematically investigated using a variety of molecular approaches that allowed for their relative and absolute quantification. Furthermore, their sub-cellular distribution in similar neurodevelopmental stages and expression in human cortices were studied. This work indicated that out of the six previously unreported SynGAP variants identified in-silico, three and one were found expressed at the transcript or protein level, respectively. The expression of SynGAP isoforms carrying three out of the four C-terminal variants was also demonstrated in human cortex. Importantly, this work identified differential spatio-temporal regulation and subcellular distribution of SynGAP isoforms containing α1, α2 and β C-term variants. Specifically, the expression of SynGAP-α1 isoforms was found highly restricted to the PSD, while β isoforms predominated in the cytosolic fraction, even at PND56. Isoforms bearing the α2 C-term showed an intermediate pattern, having a primarily cytosolic location until PND21 but being mainly at the PSD afterwards. Interestingly, SynGAP-β and -γ isoforms could have a leading role in early stages of cortical development, as they were found particularly abundant compared to the other ones.
The second part of this thesis addressed the study of the proteomic alterations derived from Syngap1 haploinsufficiency in the hippocampal PSD. The rescue of these alterations, as well as the effect of SynGAP ablation, both at PND21, was also investigated in two conditional Syngap1+/- mouse lines. These analyses revealed that proteins related to small GTPases, translation and energy production among others, were significantly altered in Syngap1+/- mice. In addition, ~83% of the alterations observed could be recovered if normal SynGAP levels were restored at PND21. Yet, some alterations persisted or newly arose in Syngap1+/- rescued mice. These alterations were mainly associated to protein processing at endoplasmic reticulum, transport of small molecules and proteasomal degradation. Based on gene set enrichment analyses, the molecular alterations observed after SynGAP rescue would be compatible with a less clinically severe scenario. Lastly, the induction of SynGAP deficit at PND21 resulted in a similar number of altered proteins as in embryonic Syngap1 haploinsufficiency, yet these two scenarios shared few affected proteins, suggesting a developmental role in the molecular alterations observed in the embryonic deficit of SynGAP.
Finally, the present thesis also includes a series of experiments aimed at developing a Shank2+/- mouse model for genetic rescue experiments, as mutations in SHANK genes are a potential monogenic cause for ASD and other neurodevelopmental disorders, including ID.
