Heterogeneity of Notch signaling in astrocytes and the effects of GFAP and vimentin deficiency

Abstract Astrocytes have multiple roles in the CNS including control of adult neurogenesis. We recently showed that astrocyte inhibition of neurogenesis through Notch signaling depends on the intermediate filament proteins glial fibrillary acidic protein ( GFAP ) and vimentin. Here, we used real‐time quantitative PCR to analyze gene expression in individual mouse astrocytes in primary cultures and in GFAP POS or Aldh1L1 POS astrocytes freshly isolated from uninjured, contralesional and lesioned hippocampus 4 days after entorhinal cortex lesion. To determine the Notch signaling competence of individual astrocytes, we measured the mRNA levels of Notch ligands and Notch1 receptor. We found that whereas most cultured and freshly isolated astrocytes were competent to receive Notch signals, only a minority of astrocytes were competent to send Notch signals. Injury increased the fraction of astrocyte subpopulation unable to send and receive Notch signals, thus resembling primary astrocytes in vitro . Astrocytes deficient of GFAP and vimentin showed decreased Notch signal sending competence and altered expression of Notch signaling pathway‐related genes Dlk2, Notch1, and Sox2 . Furthermore, we identified astrocyte subpopulations based on their mRNA and protein expression of nestin and HB ‐ EGF . This study improves our understanding of astrocyte heterogeneity, and points to astrocyte cytoplasmic intermediate filaments as targets for neural cell replacement strategies. image We previously demonstrated that Notch signaling from astrocytes to neural stem cells, that inhibits neurogenesis, depends on the intermediate filament (nanofilament) system of astrocytes. Here we report the existence of four subpopulations of astrocytes with respect to their Notch signaling competence. We show that the fraction of astrocytes that are Notch signaling incompetent increases after brain injury and corresponds to the fraction of Notch signaling incompetent astrocytes in primary astrocyte cultures. We also demonstrate that the subpopulation of Notch signal sending competent astrocytes decreases when their intermediate filament system is genetically ablated.