The do not eat me signal CD47 contributes to microglial phagocytosis defects and autism-like behaviors in 16p11.2 deletion mice

Abstract

Various pathological characteristics of autism spectrum disorder (ASD) stem from abnormalities in brain resident immune cells, specifically microglia, to prune unnecessary synapses or neural connections during early development. Animal models of ASD exhibit an abundance of synapses in different brain regions, which is strongly linked to the appearance of ASD behaviors. Overexpression of CD47 on neurons acts as a "dont eat me" signal, safeguarding synapses from inappropriate pruning by microglia. Indeed, CD47 overexpression occurs in 16p11.2 deletion carriers, causing decreased synaptic phagocytosis and the manifestation of ASD characteristics. However, the role of CD47 in synaptic pruning impairment leading to ASD phenotypes in the 16p11.2 deletion mouse model is unclear. Moreover, whether blocking CD47 can alleviate ASD mices behavioral deficits remains unknown. Here, we demonstrate a strong link between increased CD47 expression, decreased microglia phagocytosis capacity, and increased impairment in social novelty preference in the 16p11.2 deletion mice. The reduction in microglia phagocytosis caused a rise in excitatory synapses and transmission in the prefrontal cortex of 16p11.2 deletion mice. Importantly, blocking CD47 using a specific CD47 antibody or reducing CD47 expression using a specific shRNA enhanced the microglia phagocytosis and reduced excitatory transmission. Reduction in CD47 expression improved social novelty preference deficits in 16p11.2 mice. These findings demonstrate that CD47 contributes to the ASD phenotypes in the 16p11.2 deletion mice and could be a promising target for the development of treatment for ASD. Significance StatementAutism spectrum disorder (ASD) is a neurological developmental condition characterized by stereotyped behaviors and cognitive deficits. However, therapeutic options for ASD remain limited. Activation of the classical complement system, an innate immune signaling pathway component, supports microglia-mediated synaptic pruning during development and disease. In particular, CD47, a "dont eat me" signal, protects synapses from inappropriate clearance. Here, we investigated the role of CD47 in microglial phagocytosis using the 16p11.2 deletion mouse model, demonstrating that reducing CD47 signaling enhances microglial phagocytose synapses in the prefrontal cortex. This enhancement leads to improved synaptic function and reduced social behavioral deficits. These findings provide mechanistic insights into the role of CD47, laying the groundwork for developing more effective treatments for ASD.