Figure 1.

Analyses of ApoE mRNA and protein levels in various cell types reveal that ApoE expression is low in neurons but high in astrocytes and microglia. A, ApoE mRNA levels are high in mouse glia and human H1 ES cells, but barely detectable in human neurons (iNs) and mouse embryonic fibroblasts (MEFs) as determined by qRT-PCR using species-specific primers. Levels were normalized to GAPDH as an internal standard. Human neurons were examined at day 10 after induction (D10) with neurons cultured on Matrigel in the absence of glia, MEFs, or serum. B, Immunoblotting detects robust levels of ApoE protein in cultured mouse glia and human H1 ES cells, but not in human neurons (iNs) or MEFs. β-actin was analyzed as an internal standard, and synapsin-1 (Syn1) and synaptobrevin-1 (Syb1) as neuron-specific synaptic proteins. C, D, Single-cell RNAseq data obtained by Saunders et al. (2018) (C) and Zeisel et al. (2018) (D) were analyzed for relative expression levels of the indicated genes. Using the clusters as defined by each of these studies, cell types were grouped into the following populations: neurons, microglia/macrophages, astrocytes, and oligodendrocytes. Gene expression levels were compiled from each dataset with no further processing, using the units as displayed from each database.