Direct cell reprogramming technology is

Direct cell-reprogramming technology is based on the dominant action of cell-lineage transcription factors (TFs) in converting adult somatic cells into different cell types (Graf and Enver, 2009). This technique represents a promising avenue in the field of regenerative medicine, with the potential to generate cellular sources suitable for cell-replacement therapies (Chambers and Studer, 2011). In fact, since the groundbreaking discovery of the induced pluripotent stem cells (iPSCs) (Takahashi and Yamanaka, 2006), increasing approaches of direct cell reprogramming have been established, culminating with the development of induced cellular types for neurons, cardiomyocytes, and hepatocytes (Vierbuchen et al., 2010; Ieda et al., 2010; Huang et al., 2011). In addition, we and others employed the forced expression of defined sets of TFs to generate specific induced neuronal sublineages for dopaminergic, cholinergic, and motor neurons (Caiazzo et al., 2011; Pfisterer et al., 2011; Kim et al., 2002; Son et al., 2011; Liu et al., 2013; Theka et al., 2013). More recently, two groups succeeded in the generation of induced oligodendrocyte precursors by direct conversion of fibroblasts (Najm et al., 2013; Yang et al., 2013). Surprisingly, to date, there is no report for the generation of astrocyte by means of direct cell reprogramming. Astrocytes are the most-abundant cell type in the CNS and a critical neural cell type responsible for the maintenance of c-kit inhibitor homeostasis. Indeed, they play irreplaceable roles in neurotransmitter trafficking and recycling, nutrient and ion metabolism, regulation of blood supply, release of transmitters and growth factors, and protection against oxidative stress (Molofsky et al., 2012). Consistent with such a variety of fundamental functions exerted by astrocytes in supporting neuronal survival and function, astrocyte dysfunctions have been found to contribute to several neurological diseases, such as epilepsy, amyotrophic lateral sclerosis (ALS), Alzheimer’s disease, lysosomal storage diseases (Di Malta et al., 2012), and Rett syndrome (Molofsky et al., 2012). Conversely, recent data showed that transplanted astrocyte progenitors display robust survival and differentiation in the host brain and are able to decelerate the disease course in ALS and Alzheimer’s disease models (Lepore et al., 2008; Pihlaja et al., 2008). However, current protocols rely on the isolation of astrocyte progenitors from neonatal brains with serious limitations for any therapeutic approach as the paucity of cell supply and unmatched immunoprofile with the host, leading to immune reaction and possible rejection after transplantation. Cell-reprogramming approaches, by generating astrocytes starting from adult skin fibroblasts from an immunomatched or autologous source, can represent a promising alternative system for overcoming those bottlenecks. Notably, procedures of direct iPSC differentiation into astrocytes have been established only very recently (Krencik et al., 2011; Emdad et al., 2012; Juopperi et al., 2012; Roybon et al., 2013; Serio et al., 2013; Shaltouki et al., 2013). However, these approaches rely on the previous generation of stable and mutation-free iPSC lines, and the cell differentiation protocols are considerably time-consuming, complex, and required extensive time up to 180 days. We therefore considered that a direct reprogramming approach could have interesting advantages, providing a more practical procedure to generate astrocyte-like cells. Indeed, after the identification of the reprogramming cocktail composed by the astroglial TFs NFIA, NFIB, and SOX9, we defined a straightforward and fast (∼2 weeks) protocol to generate induced astrocytes (iAstrocytes) derived from mouse embryonic and postnatal fibroblasts. Our experiments indicate that iAstrocyte molecular phenotype and biological functions closely recapitulate that of native astrocytes, thus validating the direct reprogramming technology as an alternative for the generation of astrocytes.