The Cell Culture Environment Regulates the Transcription Factor MafB in BV-2 Microglia

Microglia experience dramatic molecular and functional changes when transferred from the central nervous system (CNS) to a cell culture environment. Investigators largely attribute these findings to the loss of CNS-specific microenvironmental cues that dictate the gene-regulatory networks specified by master regulator transcription factors such as V-maf musculoaponeurotic fibrosarcoma oncogene homolog B (MafB). MafB regulates macrophage differentiation and activation by activating or repressing target genes critical to these processes. Here, we show that basal MafB levels in the BV-2 microglial cell line depend on the availability of lipids in the cell culture environment. Depletion of lipids, either by serum deprivation or the use of lipid-depleted serum, reduced MafB protein levels in BV-2 cells. Using live imaging, we also observed the engulfment of apoptotic BV-2 cell debris by neighboring BV-2 cells, highlighting an additional potential source of lipids in the cell culture environment. This observation was supported by experiments showing reduced MafB protein levels in BV-2 cells cultured with various phagocytosis inhibitors (cytochalasin D, annexin V) and reduced BV-2 cell phagocytic activity with serum deprivation. In aggregate, our data suggest that serum exposure regulates the transcription factor MafB in BV-2 cells through direct and indirect mechanisms.