REGULATION OF NERVE GROWTH FACTOR TROPHIC FUNCTIONS BY AN AXONAL RNA, TP53INP2

[摘要] The subcellular localization of RNA is a mechanism used across species and cell types to spatially control gene expression. This phenomenon is particularly relevant in highly polarized cells such as neurons that benefit from having a resident cache of RNA that affords quick independent responses to environmental cues.Nerve Growth Factor (NGF) is a neurotrophic factor essential for the survival and growth of sympathetic and sensory neurons. Localization of mRNA in axons of NGF-dependent neurons supports growth and maintains axon integrity; however whether axonal transcripts mediate trophic factor responses is unknown. Tp53inp2 is a transcript that is enriched in developing peripheral axons. By means of in situ hybridization I revealed that Tp53inp2 mRNA has robust expression in sympathetic neurons during a developmental period of target innervation and neuronal competition for target-derived NGF. I then employed a conditional Tp53inp2 knockout mouse model to investigate the role of Tp53inp2 in the developing mouse sympathetic nervous system. I found that conditional deletion of Tp53inp2 in mice resulted in decreased sympathetic innervation of peripheral target organs in vivo, and impaired axon growth in response to NGF in vitro. Interestingly, there was no direct effect on neuronal cell survival in the neurons lacking Tp53inp2, indicating a local role for Tp53inp2 in axon growth separate from cell survival.Intriguingly, Tp53inp2 is among the most highly enriched axonal transcripts, yet it is not efficiently translated into a protein.Despite coding for a protein and having a known function in autophagy in muscle cells, polysome fractionation revealed that Tp53inp2 mRNA is predominantly associated with monosomes or lighter polysosmes in sympathetic neurons. Furthermore, the Tp53inp2 protein was undetectable in axons and barely detectable in neuronal cell bodies of sympathetic neurons, indicating that despite its abundance, Tp53inp2 is not translated into a protein within these axons. Notably, a non-translatable form of Tp53inp2 rescued the axon growth phenotype in Tp53inp2-deficient sympathetic neurons. RNA immunoprecipitation showed that Tp53inp2 RNA associates with the NGF receptor, TrkA. Moreover, Tp53inp2 deletion attenuated TrkA activation and signaling in axons. Thus, Tp53inp2 mRNA regulates sympathetic axon growth in a coding-independent manner by interacting with TrkA receptor and enhancing axonal NGF-dependent signaling. Altogether, this study reveals that an axonally enriched transcript, Tp53inp2, functions in a coding-independent manner to mediate NGF signaling and growth during neuronal development. This is the first evidence for an axonal RNA mediating NGF trophic function. It is also one of the first to show role of a dual function of coding and non-coding RNA in cell type specific manner in the sympathetic nervous system.

[发布机构] Johns Hopkins University

[效力级别] axonal RNA mediating NGF trophic function

[关键词] subcellular localization of RNA;axonal RNA mediating NGF trophic function;Tp53inp2;dual function of coding and non-coding RNA in cell type specific manner;Neuroscience