Astrocytes are the most abundant cell type in the CNS, rivaling the diversity of neurons in cellular morphologies, gene expression profiles, developmental origins, physiological properties, functions, and responses to injury and disease (Zhang and Barres, 2010). Within the human brain, astrocytes have a variety of essential functions including glutamate biology, axonal guidance, trophic support, inflammatory response and wound healing, formation of the blood-brain barrier, and neuronal synapse formation, and plasticity (Barres, 2008, Eroglu and Barres, 2010, Freeman and Rowitch, 2013). Although the full contribution of astrocytes to neurological disease remains unresolved, astrocyte cell-autonomous deficits have been implicated in a variety of neurological disorders (Seifert et al., 2006, Tong et al., 2014). The most significant genetic risk factor for Alzheimer's disease (AD), apolipoprotein E4 (APOE4), is predominantly synthesized and secreted by astrocytes (Xu et al., 2006). Furthermore, astrocytes derived from human induced pluripotent stem cell (hiPSC)- or mouse-based models of amyotrophic lateral sclerosis (Di Giorgio et al., 2008, Marchetto et al., 2008, Papadeas et al., 2011), Rett syndrome (Ballas et al., 2009), and Huntington disease (Bradford et al., 2009) damage neurons in co-culture or after transplantation.
