Abstract
miR-124 plays a major regulatory role in neurogenesis and neuronal differentiation during brain development through control of its multiple non-neuronal targets and has therefore been employed in direct reprogramming protocols supplementary to neurogenic TFs, and other miRNAs to enhance neurogenic conversion. However, its capacity to instruct neurogenic conversion of astrocytes and its independent mechanism of direct reprogramming action have been poorly investigated. Aim of the study was to investigate whether miR-124 is a master-regulatory reprogramming agent, potent to drive direct reprogramming of astrocytes to induced-neurons (iNs) on its own and to elucidate its mechanism of reprogramming action. To this end we overexpressed miR-124 either alone or in combination with the small neurogenic compound ISX9 both in vitro and in in vivo in a mouse mechanical cortical trauma model and analyzed their mechanism of reprogramming action. Our data indicate that miR-124 and ISX9 exhibit both unique and convergent molecular contributions in the reprogramming process to iNs. miR-124 is a potent driver of the astrocytic reprogramming switch of astrocytes towards an immature neuronal fate by repressing genes regulating astrocytic function, among which we identified the RNA-binding protein Zfp36l1 as a novel miR-124 direct target. We also provide evidence that ISX9 greatly improves both miR-124-induced reprogramming efficiency and functional maturation of iNs. Importantly, miR-124 either alone or along with ISX9 is potent to guide direct neuronal reprogramming of reactive astrocytes to iNs of cortical identity in vivo, a novel finding confirming the robust direct reprogramming action of the two molecules in activated astrocytes in vivo.
Competing Interest Statement
The authors have declared no competing interest.