Sustained axon regeneration induced by a synergy of PTEN and SOCS3 deletion

A formidable challenge in neural repair in the adult central nervous system (CNS) is the long distances that regenerating axons often need to travel in order to reconnect with their targets. Thus, a sustained capacity for axon regeneration is critical for achieving functional restoration. Although deletion of either Phosphatase and tensin homolog (PTEN), a negative regulator of mammalian target of rapamycin (mTOR), or suppressor of cytokine signaling 3 (SOCS3), a negative regulator of Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway, in adult retinal ganglion cells (RGCs) individually promoted significant optic nerve regeneration, such regrowth tapered off around two weeks after the crush injury. Remarkably, we now find that simultaneous deletion of both PTEN and SOCS3 enable robust and sustained axon regeneration. We further show that PTEN and SOCS3 regulate two independent pathways that act synergistically to promote enhanced axon regeneration. Gene expression analyses suggest that double deletion not only result in the induction of many growth-related genes, but also allow RGCs to maintain the expression of a repertoire of genes at the physiological level after injury. Our results reveal concurrent activation of mTOR and STAT3 pathways as a key for sustaining long-distance axon regeneration in adult CNS, a crucial step toward functional recovery.