Abstract
We identify calcium-permeable alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors on human neural progenitor cells (NPCs) and present a physiological role in neurogenesis. RNA editing of the GluR2 subunit at the Q/R site is responsible for making most AMPA receptors impermeable to calcium. Because a single-point mutation could eliminate the need for editing at the Q/R site and Q/R-unedited GluR2 exists during embryogenesis, the Q/R-unedited GluR2 subunit presumably has some important actions early in development. Using calcium imaging, we found that NPCs contain calcium-permeable AMPA receptors, whereas NPCs differentiated to neurons and astrocytes express calcium-impermeable AMPA receptors. We utilized reverse-transcription polymerase chain reaction and BbvI digestion to demonstrate that NPCs contain Q/R-unedited GluR2, and differentiated cells contain Q/R-edited GluR2 subunits. This is consistent with the observation that the nuclear enzyme responsible for Q/R-editing, adenosine deaminase (ADAR2), is increased during differentiation. Activation of calcium-permeable AMPA receptors induces NPCs to differentiate to the neuronal lineage and increases dendritic arbor formation in NPCs differentiated to neurons. AMPA-induced differentiation of NPCs to neurons is abrogated by overexpression of ADAR2 in NPCs. This elucidates the role of AMPA receptors as inductors of neurogenesis and provides a possible explanation for why the Q/R editing process exists.