Changes in microglia, the immune cells of the brain, have been recognized in brain tissue of individuals with autism spectrum disorders (ASD) for over 15 years, but it is not clear whether these microglia changes contribute to the primary cause of ASD or whether these are the secondary consequence of the disorder. As immunomodulatory therapies are seen as one of the promising avenues to explore for the treatment of ASD, it is essential to better understand the role of microglia in ASD. Understanding the neurobiological function of high-confidence ASD risk genes is one of the key avenues to increase the understanding of the pathogenesis of ASD. Thus far, these translational studies have primarily focused on the role of these genes in neurons. Cell-type specific transcriptomic data shows that expression of a considerable portion of these genes is much higher in microglia than in neurons. The open question is how these microglia-enriched ASD risk genes affect microglia function and whether dysfunction contributes to the primary cause of ASD.

For this project, Lotte de Witte and her colleagues will use a human induced pluripotent stem cell (hiPSC)-derived microglia-neuron-astrocyte co-culture system that can be used to screen for cell-type specific contributions under basal and inflammatory conditions. De Witte’s preliminary analyses showed that microglia integrate in these neuronal networks, facilitate network maturation, render the networks more dependent on NMDA receptors, and facilitate network recovery after seizurogenic triggers. Based on their preliminary results, they hypothesize that microglia can have a protective function in ASD by facilitating neuronal network maturation and reducing network hyperactivation. De Witte further hypothesizes that this protective function is lost and might even convert to a detrimental phenotype when the systems are challenged by inflammatory triggers, in response to ASD networks, or when the cell harbors ASD risk genes mutation. To test these hypotheses, they have selected six ASD-high-confidence genes, with enriched expression in microglia: ARID1B, CHD2, EHMT1, KANSL1, KMT2C, and SETD1A. Using a mix-and-match approach the team will investigate how loss-of-function of these genes in microglia affects neurons, and vice versa. To study neuroimmune interactions in an inflammatory context, they will expose the cultures to TNF-α, IFN-ƴ and lipopolysaccharide. To study the protective role of microglia on induced hyperexcitation, they will expose the networks to increased temperature or kainic acid. De Witte’s team will analyze development, organization and function of neuronal networks using multi-electrode arrays. They will assess synapse number and perform somatodendritic reconstructions using immunostainings. de Witte’s team’s goal is to goal disentangle neuroimmune interactions in ASD, revealing specific effects of microglia and neurons on neuronal network formation and to compare ASD-risk genes and their functional consequences. The identification of points of convergence could lead to