RA–RAR-β counteracts myelin-dependent inhibition of neurite outgrowth via Lingo-1 repression

After an acute central nervous system injury, axonal regeneration is limited as the result of a lack of neuronal intrinsic competence and the presence of extrinsic inhibitory signals. The injury fragments the myelin neuronal insulating layer, releasing extrinsic inhibitory molecules to signal through the neuronal membrane-bound Nogo receptor (NgR) complex. In this paper, we show that a neuronal transcriptional pathway can interfere with extrinsic inhibitory myelin-dependent signaling, thereby promoting neurite outgrowth. Specifically, retinoic acid (RA), acting through the RA receptor β (RAR-β), inhibited myelin-activated NgR signaling through the transcriptional repression of the NgR complex member Lingo-1. We show that suppression of Lingo-1 was required for RA-RAR-β to counteract extrinsic inhibition of neurite outgrowth. Furthermore, we confirm in vivo that RA treatment after a dorsal column overhemisection injury inhibited Lingo-1 expression, specifically through RAR-β. Our findings identify a novel link between RA-RAR-β-dependent proaxonal outgrowth and inhibitory NgR complex-dependent signaling, potentially allowing for the development of molecular strategies to enhance axonal regeneration after a central nervous system injury.