The microRNAs let-7 and miR-9 down-regulate the axon-guidance genes Ntn1 and Dcc during peripheral nerve regeneration

• Published in: The Journal of biological chemistry 2019-03, Vol.294 (10), p.3489-3500
• Main Authors: Wang, Xinghui, Chen, Qianqian, Yi, Sheng, Liu, Qianyan, Zhang, Ruirui, Wang, Pan, Qian, Tianmei, Li, Shiying
• Format: Article
• Language: English
• Subjects: 3' Untranslated Regions - genetics; Animals; axon; Axon Guidance - genetics; Base Sequence; Cell Movement - genetics; DCC Receptor - genetics; deleted in colorectal carcinoma; Down-Regulation - genetics; Ganglia, Spinal - cytology; Humans; let-7; microRNA (miRNA); MicroRNAs - genetics; miR-9; Nerve Regeneration - genetics; Netrin-1; Netrin-1 - genetics; Netrin-1 - metabolism; Neurobiology; neuron; Neurons - cytology; Neurons - metabolism; peripheral nerve regeneration; Rats; regeneration; Schwann cells; Sciatic Nerve - cytology; Sciatic Nerve - injuries; Sciatic Nerve - metabolism; Sciatic Nerve - physiology; translation regulation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.RA119.007389

Axon guidance helps growing neural axons to follow precise paths to reach their target locations. It is a critical step for both the formation and regeneration of neuronal circuitry. Netrin-1 (Ntn1) and its receptor, deleted in colorectal carcinoma (Dcc) are essential factors for axon guidance, but their regulation in this process is incompletely understood. In this study, using quantitative real-time RT-PCR (qRT-PCR) and biochemical and reporter gene assays, we found that the Ntn1 and Dcc genes are both robustly up-regulated in the sciatic nerve stump after peripheral nerve injury. Moreover, we found that the microRNA (miR) let-7 directly targets the Ntn1 transcript by binding to its 3′-untranslated region (3′-UTR), represses Ntn1 expression, and reduces the secretion of Ntn1 protein in Schwann cells. We also identified miR-9 as the regulatory miRNA that directly targets Dcc and found that miR-9 down-regulates Dcc expression and suppresses the migration ability of Schwann cells by regulating Dcc abundance. Functional examination in dorsal root ganglion neurons disclosed that let-7 and miR-9 decrease the protein levels of Ntn1 and Dcc in these neurons, respectively, and reduce axon outgrowth. Moreover, we identified a potential regulatory network comprising let-7, miR-9, Ntn1, Dcc, and related molecules, including the RNA-binding protein Lin-28 homolog A (Lin28), SRC proto-oncogene nonreceptor tyrosine kinase (Src), and the transcription factor NF-κB. In summary, our findings reveal that the miRs let-7 and miR-9 are involved in regulating neuron pathfinding and extend our understanding of the regulatory pathways active during peripheral nerve regeneration.