Impact of Microglial CYFIP1 Deletion on Astrocytes, Oligodendrocytes, and Myelination in a conditional mouse model

Abstract

CYFIP1 is one of the five subunits of the WAVE regulatory complex, which is involved in controlling actin cytoskeleton remodeling, impacting many cell processes including cell motility (Eden et al., 2002; Rottner et al., 2021). A CYFIP1 dysregulation is associated with multiple neurological and psychiatric disorders. For example, a reduction of CYFIP1 is prevalent in patients with schizophrenia (Sayad et al., 2018; Stefansson et al., 2008). <br/> In this project, I used a conditional mouse model, in which CYFIP1 is deleted in myeloid cells including microglia, to study the effect of microglial CYFIP1 on astrocytes and oligodendrocytes in the murine CNS. I found a significant upregulation of GFAP in astrocytes, using immunofluorescence analysis of cerebral sections from young adult CYFIP1 KO mice, along with a decrease in astrocytic cell number, as quantified by the number of SOX-9-positive cells. <br/> In addition, I examined oligodendrocyte cell number, and myelination by immunofluorescence labeling of MBP, OLIG2, and APC in cerebral sections of the same mouse line. Here, I found a decrease in myelination in the corpus callosum, and a decrease in oligodendrocytes in the somatosensory cortex, as well as the corpus callosum. <br/> To better understand the mechanisms and to test whether soluble factors from CYFIP1 depleted microglia induce the altered astrocytic phenotype, I performed a set of experiments using astrocyte cultures, which were incubated with microglia-conditioned medium from cultured control vs. CYFIP1 KO microglia. To this end, I analyzed astrocytic phagocytosis with a functional assay, and a defined set of genes including synaptogenic genes, phagocytic genes, and interferon-stimulated genes by qPCR. There were no obvious results from these cell culture experiments that would explain the upregulation of GFAP or reduced astrocyte number that I detected in the conditional CYFIP1 mouse model, as I detected no decrease in cell number or proliferation of cultured astrocytes. However, there was a significant decrease of <em>Mtor</em>, the gene encoding mTOR, which has been shown to upregulate cell proliferation, and which may cause a decreased proliferation of astrocytes. Further experiments using astrocyte-microglia co-cultures and additional analyses in conditional CYFIP1 KO mice will be needed to elucidate potential pathways that underlie the changes in astrocytes and oligodendrocytes associated with conditional myeloid cell-specific CYFIP1 deletion.