Functional changes of AMPA responses in human induced pluripotent stem cell-derived neural progenitors in fragile X syndrome.

Altered neuronal network formation and function involving dysregulated excitatory and inhibitory circuits are associated with fragile X syndrome (FXS). We examined functional maturation of the excitatory transmission system in FXS by investigating the response of FXS patient-derived neural progenitor cells to the glutamate analog (AMPA). Neural progenitors derived from induced pluripotent stem cell (iPSC) lines generated from boys with FXS had augmented intracellular Ca responses to AMPA and kainate that were mediated by Ca-permeable AMPA receptors (CP-AMPARs) lacking the GluA2 subunit. Together with the enhanced differentiation of glutamate-responsive cells, the proportion of CP-AMPAR and -methyl-d-aspartate (NMDA) receptor-coexpressing cells was increased in human FXS progenitors. Differentiation of cells lacking GluA2 was also increased and paralleled the increased inward rectification in neural progenitors derived from -knockout mice (the FXS mouse model). Human FXS progenitors had increased the expression of the precursor and mature forms of miR-181a, a microRNA that represses translation of the transcript encoding GluA2. Blocking GluA2-lacking, CP-AMPARs reduced the neurite length of human iPSC-derived control progenitors and further reduced the shortened length of neurites in human FXS progenitors, supporting the contribution of CP-AMPARs to the regulation of progenitor differentiation. Furthermore, we observed reduced expression of (the GluA2-encoding gene) in the frontal lobe of FXS mice, consistent with functional changes of AMPARs in FXS. Increased Ca influx through CP-AMPARs may increase the vulnerability and affect the differentiation and migration of distinct cell populations, which may interfere with normal circuit formation in FXS.