Generation and Characterization of Human Induced Pluripotent Stem Cell-derived Astrocytes Lacking Fragile X Messenger Ribonucleoprotein

Fragile X syndrome (FXS), a leading inherited cause of autism spectrum disorder and intellectual disability, has been studied extensively using rodent models. More recently, human stem cell-derived model systems have also been used to gain mechanistic insights into the pathophysiology of FXS. However, these studies have focused almost exclusively on neurons. Further, despite growing evidence for a key role of glia in neuronal function in health and disease, little is known about how human astrocytes are affected by FXS. Therefore, in this study, we successfully developed a protocol that captures key spatiotemporal milestones of brain development and aligns with the process of gliogenesis as well. Together this offers a useful framework for studying neurodevelopmental disorders. First, we patterned the human induced pluripotent stem cells into the neuroectodermal lineage with dual Suppressor of Mothers against Decapentaplegic (SMAD) inhibition and small molecules. Subsequently, we utilized specific growth factors and cytokines to generate control (CTRL) and FXS patient-derived astrocytic progenitor cells (APCs). Treatment of APCs with ciliary neurotrophic factor, a differentiating cytokine, regulated and drove the progenitor cells towards astrocytic maturation, yielding forebrain-specific glial fibrillary acidic protein-expressing astrocytes. We found that these astrocytes are functional, as evidenced by their calcium responses to ATP application, and they exhibit dysregulated glycolytic and mitochondrial metabolism in FXS. Taken together, these findings provide a useful experimental platform of human origin for the investigation of cell-autonomous and non-cell-autonomous consequences of alterations in astrocytic function caused by neurodevelopmental disorders.