Deciphering Microglia-Synapse Interaction in Neuroligin-4 Knockout mouse model of Autism Spectrum Disorder

Abstract

As resident macrophages of the central nervous system (CNS), the role of microglia in synaptic refinement has recently been more appreciated. Accumulating evidence, mainly derived from genetic studies revealing Neuroligin mutations in autism spectrum disorders (ASD), suggests synaptopathy as an underlying reason of the disease; however, comprehensive studies characterizing microglia-synapse interaction in ASD models are lacking.Herein, we investigated interaction of microglia and synapses in a Neuroligin-4 knock-out (NL4-KO) mouse model of ASD along with the main pathways involved in their cross-talk. We analyzed engulfment of vGLUT1+ synapses by microglia in NL4-KO hippocampus and revealed deficits in synaptic engulfment in a sexually dimorphic manner using flow cytometry. We further analyzed expression of the most studied markers driving microglia-dependent synaptic engulfment such as TREM-2, CX3CR1, C3R, IL33R on freshly isolated hippocampal microglia along with their interaction partners (APOE, CX3CL1, C3, C1qb, C4A, IL33) in hippocampal lysates and observed significant dysregulations in the TREM-2 pathway. We detected lower surface expression of TREM-2 on NL4-KO microglia along with higher levels of soluble TREM-2, lower enzymatic activity of ADAM10 as well as lower levels of APOE in NL4KO hippocampus at adult stage (P90). We compared our findings at two different developmental points (P90 and P15) and showed that both vGLUT1-engulfment deficits and dysregulations in the TREM-2 pathway develop over time and create an aberrant state of microglia activation at the adult stage, which is also supported by single cell transcriptomics data. Our study suggest that dysregulation of TREM-2 pathway is a critical target in NL4-KO model and provides basis for future studies aiming to target this pathway to restore a functional microglia-synapse interaction.