Characteristics of SIM-A9 Microglia Cells: New Data

SIM-A9 is a line of spontaneously immortalized mouse microglial cells obtained from the brain of newborn C57BL/6 mice. The purpose of this work is to characterize the microglia of the SIM-A9 mouse line on the basis of the ratio of cells with the phenotype of resting and activated microglia in culture and to analyze the expression of markers of CD133 stem (progenitor) cells and nestin, which are receptors for growth factors CSF-1R and EGFR, as well as to analyze the karyotype of this line. Light microscopy and immunocytochemistry combined with flow cytometry and RT–PCR were used to analyze the morphology, phenotype, and expression level of pro-inflammatory cytokine genes, and the mFISH method was used to analyze the karyotype. It has been shown for the first time that SIM-A9 cells express a high level of TSPO protein and CD68, CD11b, and CD45high markers on the surface membrane of cells, which corresponds to the phenotype of activated microglia. Despite this, the cells of the line respond with additional activation in response to lipopolysaccharide stimulation, which leads to an increase in the expression of pro-inflammatory cytokine genes IL-1β, TNFα, and IL-6 and the formation of a high level of active oxygen and nitrogen metabolites. SIM-A9 cells were shown to express markers of stem and progenitor cells CD133+ and nestin, which allows us to consider them as early poorly differentiated progenitor cells, despite their phenotype corresponding to activated microglia. It was also found that SIM-A9 cells express receptors of the two growth factors CSF-1 and EGF, CSF-1R and EGFR, which indicates the possibility of stimulation of SIM-A9 cell proliferation by two alternative mechanisms under the action of corresponding factors. SIM-A9 cells have a hypotetraploid karyotype with a large number of structural and quantitative chromosome anomalies.