Microglial responses to CSF1 overexpression do not promote expansion of other glial lineages
CSF1 expression in the central nervous system (CNS) increases in response to a variety of stimuli, and CSF1 is overexpressed in many CNS diseases. In young adult mice we previously showed that CSF1 overexpression in the CNS caused proliferation of IBA1+ microglia without promoting expression of M2 polarization markers. Here we further examine the impacts of increased CSF1 levels in the brain. As CSF1 over-expressing mice age, IBA1+ cell numbers are constrained by a decline in proliferation rate. Compared to controls, there were no differences in expression of the M2 markers ARG1 and MRC1 (CD206) in CSF1 overexpressing mice of any age, indicating that even prolonged exposure to increased CSF1 is not sufficient to promote M2 polarization in vivo. Moreover, RNA-sequencing (RNA-seq) confirmed the lack of increased expression of markers of M2 polarization in microglia exposed to CSF1 over-expression, but did reveal changes in expression of other immune related genes. Although treatment with inhibitors of the CSF1 receptor, CSF1R, has been shown to impact other glia, no increased expression of astrocyte or oligodendrocyte lineage markers was observed in CSF1 OE mice. Our data indicate that CSF1 overexpression as an isolated stimulus has limited impacts in the CNS, and that microglia ultimately adapt to the presence of the CSF1 mitogenic signal. Overall design: Compared mRNA profiles of 4 samples from CSF1 over-expression mice with 4 control mice samples.