The Telomerase Reverse Transcriptase (TERT) and p53 Regulate Mammalian PNS and CNS Axon Regeneration downstream of c-Myc

Abstract

36Although several genes have been identified to promote axon regeneration in the central nervous 37 system, our understanding of the molecular mechanisms by which mammalian axon regeneration 38 is regulated is still limited and fragmented. Here by using sensory axon and optic nerve 39 regeneration as model systems, we revealed an unexpected role of telomerase reverse 40 transcriptase (TERT) in regulation of axon regeneration. We also provided strong evidence that 41 TERT and p53 acted downstream of c-Myc to control sensory axon regeneration. More 42 importantly, overexpression of p53 in sensory neurons and retinal ganglion cells (RGCs) was 43 sufficient to promote sensory axon and optic never regeneration, respectively. The study revealed 44 a novel c-Myc-TERT-p53 signaling pathway, expanding horizons for novel approaches 45 promoting CNS axon regeneration.46 47 Keywords: c-Myc, telomerase reverse transcriptase, telomere, p53, axon regeneration, optic 48 nerve regeneration 49 50 51 94 (Di Giovanni and Rathore, 2012; Floriddia et al., 2012;Gaub et al., 2011;Gaub et al., 2010; 95 Joshi et al., 2015;Tedeschi et al., 2009). TERT is the catalytic subunit of the enzyme telomerase, 96 which is well known for its role in regulation of telomere extension, cellular aging, and cancer 97 (Maciejowski and de Lange, 2017). In post-mitotic neurons, TERT has been shown to protect 98 neurons from oxidative damages and degenerative changes during aging Miwa 99 and Saretzki, 2017;Spilsbury et al., 2015). Inhibition of TERT during iPSC induced neuronal 100 differentiation can produce aged neurons suitable for studying late onset neurodegenerative 101 diseases (Vera et al., 2016). Whether TERT plays any role in regulation of axon growth or 102 regeneration has not been investigated. 103In the present study, we demonstrated that c-Myc was both necessary and sufficient for 104 supporting sensory axon growth in vitro and in vivo. Importantly, we provided clear and strong 105 evidence that TERT level was markedly increased in sensory neurons upon peripheral nerve 106 injury. Functionally, inhibition or deletion of TERT in sensory neurons significantly impaired 107 sensory axon regeneration in vitro and in vivo. Moreover, TERT level was regulated by c-Myc in 108 sensory neurons and activation of TERT was able to rescue sensory axon regeneration impaired 109 by down regulation of c-Myc, suggesting that TERT acted downstream of c-Myc to regulate 110 sensory axon regeneration. Lastly, we found that p53 was also up regulated in sensory neurons 111 upon peripheral nerve injury and acted downstream of TERT to regulate sensory axon 112 regeneration. Importantly, overexpression of p53 in sensory neurons and RGCs was sufficient to 113 promote sensory axon regeneration in vivo optic nerve regeneration, respectively. Collectively, 114 our data not only revealed an unexpected function of TERT in regulation of axon regeneration, 115 but also suggested that c-Myc, TERT, p53 signaling might act coordinately to regulate both PNS 116 and CNS ...

A Brief Review of In Vitro Models for Injury and Regeneration in the Peripheral Nervous System

“…Other morphological features that are consistently observed in axonal injury, including the dissipation of chromatin [ 37 ], chromatolysis [ 38 ], endoplasmic blebbing [ 39 ], and loss of dendritic spines [ 40 ], have been widely demonstrated in various in vitro models [ 17 ]. In addition to mimicking injury-induced morphological changes, in vitro models have also been successfully utilized to study the injury-induced influx of Ca 2+ ions in axons [ 41 , 42 ] and associated downstream events [ 43 , 44 ]. Overall, it is quite apparent that in vitro models can significantly contribute to our understanding of various neuronal events, both during and after injury.…”