Recombinant adeno-associated virus-mediated miR34a overexpression increases progenitor cell proliferation and modifies dendrite morphology of newborn neurons in vitro and in vivo

miR function is essential for the regulation of several differentiation pathways of progenitor populations. In particular, miR- 34a has been implicated in the regulation of the fate of different cell types. However, its role in the control of the differentiation program of neural cell types remains largely unknown. In this study, we examined the effects of miR-34a overexpression in developing rat neuronal cells both in vitro and in vivo. Using a recombinant adeno-associated virus (rAAV), we could efficiently and stably deliver a foreign miR-34a gene into cultured neuronal precursors which retained their capability to properly differentiate into neurons. We found that the overexpression of miR-34a significantly increased precursor proliferation in vitro and influenced the development of neuronal cell morphology and function. Indeed, overexpression of miR-34a in cultured cortical developing neurons provided evidence for a role of miR-34a in reducing dendritic arborization, associated with a decline of several synaptic proteins including synaptophysin, PSD95 and glutamate receptor subunits. Moreover, electrophysiological studies showed a decrease in NMDA current density which could reflect the observed reduced morphology complexity. In vivo, the rAAV-mediated overexpression of miR-34a influenced adult neurogenesis by increasing proliferation of cell precursors in the subventricular zone (SVZ) and dentate gyrus (DG). We found that miR-34a overexpression reduced Doublecortin (DCX) levels in migratory neuroblasts of the SVZ which showed a limited migratory capacity. Similarly, we found DCX decreased expression in maturing granule cells in the DG which affected their dendritic patterning. Our results provide new insight into the molecular mechanism by which miR-34a controls neuronal differentiation and thus, extends our understanding of miR-34a-mediated regulation of cell proliferation and differentiation in mammalian nervous system development.