Neuronal and Astroglial contribution to intellectual disability – NACID

The clinical spectrum of cognitive disorders (CD) varies widely from Intellectual Disability (ID) to Autism Spectrum Disorder (ASD) and is estimated to affect 1-3% of the population. Genetic evidence indicates that one major functional group of CD-related proteins corresponds to proteins that are enriched at synaptic compartments, defining the concept of synaptopathies. While many studies have focused on the involvement of neurons in the pathology, the multi-partite synapse questions the contribution of the glia in CD, thus urging the study of the astrocyte-to-neuron bidirectional communication in cellular and animal models.
This project is based on the functional characterization of the interactions between astroglia and neurons in the context of synaptopathies. We will focus our studies on Oligophrenin1 gene, which mutations are associated with ID, ASD or schizophrenia. The Ophn1 gene encodes a RhoGAP protein that is expressed not only in neurons, but also in astrocytes during development and in adult. At the synapse, its neuronal functions have been largely reported, but its roles in astroglial cells are still unexplored. We have shown in a mouse model of the pathology that ophn1 loss is responsible for endocytosis defects in astrocytes together with hyperactivation of RhoA/ROCK and PKA pathways. Preliminary data suggest that loss of ophn1 function in glia also contributes to the dendritic spine phenotype observed in neurons. The cellular and molecular defects in astrocytes deserve a full characterization of the consequences of ophn1 inactivation in these cells.
In this context, we will address the two following scientific questions:
1. What are the cell autonomous and non-cell autonomous consequences of oligophrenin1 loss of function in astrocytes?
(i) To decipher its function in astrocytes, we will establish primary astroglial cultures from constitutive KO brain and monitor their morphology, adhesion capacities and vesicular trafficking. Given the well-known function of ophn1 on synapses, we will investigate the synaptic densities on co-culture systems of WT neurons on KO astrocytes and vice versa. Since we have access to iPS cells developed from cutaneous fibroblasts of OPHN1 mutated ID patients, we will differentiate them into glia or neurons to allow us to extend and confirm our results to humans.
(ii) Beside these in vitro studies, conditional floxed alleles of ophn1 will be crossed to neuronal or astroglial Cre driver lines. Double transgenic animals (Flox;Cre) will be assessed in behavioral tests and we will compare their phenotypes to previously reported constitutive models.
(iii) In parallel, we will perform stereotaxic injections of Cre expressing lentiviral vectors in floxed animals in order to study in only few cells the consequences of ophn1 inactivation. We will analyze astroglia cells at the molecular level (markers), cellular level (morphology) and functional level (electrophysiological recording and Ca2+ imaging).
2. Does restoring or improving astroglial functions can rescue some of the ID-linked phenotype observed in mice?
We will tackle this question using two different approaches either genetic or pharmacologic. Since Ophn1 has been shown to negatively regulate the RhoA/ROCK signaling pathway, we will test whether reducing RhoA levels can restore ophn1 function in astrocytes from the conditional mouse model. Alternatively, we will treat conditional KO mice with drugs previously identified as beneficial in in vitro or in vivo systems.
Our consortium aims to decipher the astroglial function of ophn1 a molecule involved in synaptopathy and to highlight the astrocyte contribution to the pathology. Our goal is ambitious because we have a comprehensive and multi-disciplinary strategy to explore Ophn1 mouse ID models. Through this comprehensive study from cell to the animal, we also hope to uncover new pharmacological approaches targeting the glial cells to improve the learning capacities of ID patients.