RSK1 promotes mammalian axon regeneration by inducing the synthesis of regeneration-related proteins.

In contrast to the adult mammalian central nervous system (CNS), the neurons in the peripheral nervous system (PNS) can regenerate their axons. However, the underlying mechanism dictating the regeneration program after PNS injuries remains poorly understood. Combining chemical inhibitor screening with gain- and loss-of-function analyses, we identified p90 ribosomal S6 kinase 1 (RSK1) as a crucial regulator of axon regeneration in dorsal root ganglion (DRG) neurons after sciatic nerve injury (SNI). Mechanistically, RSK1 was found to preferentially regulate the synthesis of regeneration-related proteins using ribosomal profiling. Interestingly, RSK1 expression was up-regulated in injured DRG neurons, but not retinal ganglion cells (RGCs). Additionally, RSK1 overexpression enhanced phosphatase and tensin homolog (PTEN) deletion-induced axon regeneration in RGCs in the adult CNS. Our findings reveal a critical mechanism in inducing protein synthesis that promotes axon regeneration and further suggest RSK1 as a possible therapeutic target for neuronal injury repair.

The metabolomic profiling identifies N, N-dimethylglycine as a facilitator of dorsal root ganglia neuron axon regeneration after injury.

Identifying novel molecules involved in axon regeneration of neurons in the peripheral nervous system (PNS) will be of benefit in obtaining a therapeutic strategy for repairing axon damage both in the PNS and the central nervous system (CNS). Metabolism and axon regeneration are tightly connected. However, the overall metabolic processes and the landscape of the metabolites in axon regeneration of PNS neurons are uncovered. Here, we used an ultra high performance liquid tandem chromatography quadrupole time of flight mass spectrometry (UHPLC-QTOFMS)-based untargeted metabolomics to analyze dorsal root ganglia (DRG) metabolic characteristics at different time points post sciatic nerve injury and acquired hundreds of differentially changed metabolites. In addition, the results reveal that several metabolic pathways were significantly altered, such as 'Histidine metabolism', 'Glycine serine and threonine metabolism', 'Arginine and proline metabolism', 'taurine and hypotaurine metabolism' and so on. Given metabolite could alter a cell's or an organism's phenotype, further investigation demonstrated that N, N-dimethylglycine (DMG) has a promoting effect on the regenerative ability post injury. Overall, our data may serve as a resource useful for further understanding how metabolites contribute to axon regeneration in DRG during sciatic nerve regeneration and suggest DMG may be a candidate drug to repair nerve injury.

The long noncoding RNA Arrl1 inhibits neurite outgrowth by functioning as a competing endogenous RNA during neuronal regeneration in rats.

The intrinsic regeneration ability of neurons is a pivotal factor in the repair of peripheral nerve injury. Therefore, identifying the key modulators of nerve regeneration may help improve axon regeneration and functional recovery after injury. Unlike for classical transcription factors and regeneration-associated genes, the function of long noncoding RNAs (lncRNAs) in the regulation of neuronal regeneration remains mostly unknown. In this study, we used RNA-Seq-based transcriptome profiling to analyze the expression patterns of lncRNAs and mRNAs in rat dorsal root ganglion (DRG) following sciatic nerve injury. Analyses using the lncRNA-mRNA co-expression network, gene ontology enrichment, and Kyoto Encyclopedia of Genes and Genomes pathway databases indicated that the lncRNA Arrl1 decreases neurite outgrowth after neuronal injury. shRNA-mediated Arrl1 silencing increased axon regeneration both in vitro and in vivo and improved functional recovery of the sciatic nerve. Moreover, inhibiting an identified target gene of Arrl1, cyclin-dependent kinase inhibitor 2B (Cdkn2b), markedly promoted neurite outgrowth of DRG neurons. We also found that Arrl1 acts as a competing endogenous RNA that sponges a Cdkn2b repressor, microRNA-761 (miR-761), and thereby up-regulates Cdkn2b expression during neuron regeneration. We conclude that the lncRNA Arrl1 affects the intrinsic regeneration of DRG neurons by derepressing Cdkn2b expression. Our findings indicate a role for an lncRNA-microRNA-kinase pathway in the regulation of axon regeneration and functional recovery following peripheral nerve injury in rats.

LncRNA BC088259 promotes Schwann cell migration through Vimentin following peripheral nerve injury.

Schwann cell, the major glial cell in the peripheral nervous system, plays an essential role in peripheral nerve regeneration. However, the regulation of Schwann cell behavior following nerve injury is insufficiently explored. According to the development of high-throughput techniques, long noncoding RNAs (lncRNAs) have been recognized. Accumulating evidence shows that lncRNAs take part in diverse biological processes and diseases. Here, by microarray analysis, we identified an upregulated lncRNA profile following sciatic nerve injury and focused on BC088259 for further investigation. Silencing or overexpression of BC088259 could affect Schwann cell migration. Mechanistically, BC088259 might exert this regulatory role by directly binding with Vimentin. Collectively, our study not only revealed a set of upregulated lncRNAs following nerve injury but also identified a new functional lncRNA, BC088259, which was important for Schwann cell migration, providing a therapeutic avenue toward peripheral nerve injury.

A Schwann cell-enriched circular RNA circ-Ankib1 regulates Schwann cell proliferation following peripheral nerve injury.

Schwann cells (SCs) play an essential role in nerve injury repair. A striking feature of the cellular response to peripheral nerve injury is the proliferation of SCs. Circular (circ)RNAs are enriched in the nervous system and are involved in physiologic and pathologic processes. However, the potential role of circRNAs in SC proliferation post nerve injury remains largely unknown. Using a sciatic nerve crush model, we obtained an expression profiling of circRNAs in injured sciatic nerves in rats by RNA sequencing and bioinformatics analysis, and we further identified a circRNA [circ-ankyrin repeat and in-between Ring finger (IBR) domain containing 1 (Ankib1)] involved in SC proliferation by the transfection of specific small interfering RNAs. Overexpression of circ-Ankib1, which was specifically and highly enriched in SCs, impaired SC proliferation and axon regeneration following sciatic nerve injury. Mechanistically, increased expression of DEx/H-box helicase 9 (DHX9) postinjury might contribute to the down-regulation of circ-Ankib1, which further suppressed cytochrome P450, family 26, subfamily B, polypeptide 1 expression by sponging miR-423-5p, miR-485-5p, and miR-666-3p, leading to the induction of SC proliferation and nerve regeneration. Taken together, our results reveal a crucial role for circRNAs in regulating proliferation of SCs involved in sciatic nerve regeneration; as such, circRNAs may serve as a potential therapeutic avenue for nerve injury repair.-Mao, S., Zhang, S., Zhou, S., Huang, T., Feng, W., Gu, X., Yu, B. A Schwann cell-enriched circular RNA circ-Ankib1 regulates Schwann cell proliferation following peripheral nerve injury.

lncRNA TNXA-PS1 Modulates Schwann Cells by Functioning As a Competing Endogenous RNA Following Nerve Injury.

As the major glia in PNS, Schwann cells play a critical role in peripheral nerve injury repair. Finding an efficient approach to promote Schwann cell activation might facilitate peripheral nerve repair. Long noncoding RNAs (lncRNAs) have been shown to regulate gene expression and take part in many biological processes. However, the role of lncRNAs in peripheral nerve regeneration is not fully understood. In this study, we obtained a global lncRNA portrayal following sciatic nerve injury in male rats using microarray and further investigated one of these dys-regulated lncRNAs, TNXA-PS1, confirming its vital role in regulating Schwann cells. Silencing TNAX-PS1 could promote Schwann cell migration and mechanism analyses showed that TNXA-PS1 might exert its regulatory role by sponging miR-24-3p/miR-152-3p and affecting dual specificity phosphatase 1 (Dusp1) expression. Systematic lncRNA expression profiling of sciatic nerve segments following nerve injury in rats suggested lncRNA TNXA-PS1 as a key regulator of Schwann cell migration, providing a potential therapeutic target for nerve injury repair.SIGNIFICANCE STATEMENT The PNS has an intrinsic regeneration capacity after injury in which Schwann cells play a crucial role. Therefore, further exploration of functional molecules in the Schwann cell phenotype modulation is of great importance. We have identified a set of dys-regulated long noncoding RNAs (lncRNAs) in rats following sciatic nerve injury and found that the expression of TNXA-PS1 was significantly downregulated. Mechanically analyses showed that TNXA-PS1 might act as a competing endogenous RNA to affect dual specificity phosphatase 1 (Dusp1) expression, regulating migration of Schwann cells. This study provides for the first time a global landscape of lncRNAs following sciatic nerve injury in rats and broadens the known functions of lncRNA during nerve injury. The investigation of TNXA-PS1 might facilitate the development of novel targets for nerve injury therapy.

miR-17-92 facilitates neuronal differentiation of transplanted neural stem/precursor cells under neuroinflammatory conditions.

BACKGROUND: Neural stem/precursor cells (NSCs) are of particular interest because of their potential application in cell therapy for brain damage. However, most brain injury cases are followed with neuroinflammatory stress, which affects the lineage selection of grafted NSCs by promoting astrocytogenesis, thus hampering the potential for neural replacement. The present study investigated the role of miR-17-92 in protecting against detrimental effects of neuroinflammation on NSC differentiation in cell therapy. METHODS: NSCs were treated with conditioned medium from lesioned astrocytes with/without neutralizing antibodies of leukemia inhibitory factor (LIF) or/and ciliary neurotrophic factor (CNTF), respectively. Afterward, the levels of p-STAT3 and p-JAK2 were determined by western blotting while expression of glial fibrillary acidic protein (GFAP) and ß-tubulin III was assessed by immunostaining. The activation of JAK-STAT pathway and cell differentiation were also evaluated after we overexpressed miR-17-92 in NSCs under different neuroinflammatory conditions. After the transplantation of miR-17-92-overexpressing NSCs into injured mouse cortex, PH3, nestin, GFAP, and NeuN were analyzed by immunostaining. In addition, motor coordination of mice was evaluated by rotarod test. RESULTS: Conditioned medium from lesioned astrocytes activated JAK-STAT pathway and facilitated astrocytic differentiation in NSCs while neutralizing antibodies of LIF and CNTF remarkably attenuated such effects. miR-17-92 cluster repressed the expression of multiple proteins including GP130, CNTFR, JAK2, and STAT3 in JAK-STAT pathway. Overexpression of miR-17-92 in NSCs systematically blocked the activation of JAK-STAT pathway mediated by LIF and CNTF, which facilitated neuronal differentiation in vitro. Furthermore, miR-17-92 increased neuronal generation of grafted NSCs and reduced astrogliosis, which resulted in the improvement of motor coordination of brain-injured mice. CONCLUSIONS: Our results suggest that miR-17-92 promotes neuronal differentiation of grafted NSCs under neuroinflammatory condition via inhibition of multiple proteins in JAK-STAT pathway.

The roles of circular RNAs in nerve injury and repair.

Nerve injuries significantly impact the quality of life for patients, with severe cases posing life-threatening risks. A comprehensive understanding of the pathophysiological mechanisms underlying nerve injury is crucial to the development of effective strategies to promote nerve regeneration. Circular RNAs (circRNAs), a recently characterized class of RNAs distinguished by their covalently closed-loop structures, have been shown to play an important role in various biological processes. Numerous studies have highlighted the pivotal role of circRNAs in nerve regeneration, identifying them as potential therapeutic targets. This review aims to succinctly outline the latest advances in the role of circRNAs related to nerve injury repair and the underlying mechanisms, including peripheral nerve injury, traumatic brain injury, spinal cord injury, and neuropathic pain. Finally, we discuss the potential applications of circRNAs in drug development and consider the potential directions for future research in this field to provide insights into circRNAs in nerve injury repair.

LINC MIR503HG Controls SC-ß Cell Differentiation and Insulin Production by Targeting CDH1 and HES1.

Stem cell-derived pancreatic progenitors (SC-PPs), as an unlimited source of SC-derived ß (SC-ß) cells, offers a robust tool for diabetes treatment in stem cell-based transplantation, disease modeling, and drug screening. Whereas, PDX1+/NKX6.1+ PPs enhances the subsequent endocrine lineage specification and gives rise to glucose-responsive SC-ß cells in vivo and in vitro. To identify the regulators that promote induction efficiency and cellular function maturation, single-cell RNA-sequencing is performed to decipher the transcriptional landscape during PPs differentiation. The comprehensive evaluation of functionality demonstrated that manipulating LINC MIR503HG using CRISPR in PP cell fate decision can improve insulin synthesis and secretion in mature SC-ß cells, without effects on liver lineage specification. Importantly, transplantation of MIR503HG-/- SC-ß cells in recipients significantly restored blood glucose homeostasis, accompanied by serum C-peptide release and an increase in body weight. Mechanistically, by releasing CtBP1 occupying the CDH1 and HES1 promoters, the decrease in MIR503HG expression levels provided an excellent extracellular niche and appropriate Notch signaling activation for PPs following differentiation. Furthermore, this exhibited higher crucial transcription factors and mature epithelial markers in CDH1High expressed clusters. Altogether, these findings highlighted MIR503HG as an essential and exclusive PP cell fate specification regulator with promising therapeutic potential for patients with diabetes.

Insight into protein synthesis in axon regeneration.

Successful axon regeneration is crucial for the treatment of numerous nerve injuries and neurodegenerative diseases, which requires adequate and accurate protein synthesis, including mRNA translation, both in the neuron somas and locally in the axons. Recent studies have shed light on novel functions and mechanisms of protein synthesis that are relevant for axon regeneration, with a particular focus on local translation. Here, we review the new developed technologies and approaches for investigating local translation, discuss the roles of local translation in axon regeneration, and summarize the key signaling molecules and pathways that regulate local translation during axon regeneration. Additionally, we give an overview of local translation in the peripheral and central nervous systems neurons and the latest progress in protein synthesis in neuron somas respectively. Finally, we consider the potential directions for future research in this field to provide insights into protein synthesis in axon regeneration.