The intrinsic axon regenerative properties of mature neurons after injury

Revisiting the immune landscape post spinal cord injury: More than black and white

Spinal cord injury (SCI) induced catastrophic neurological disability is currently incurable, especially in elderly patients. Due to the limited axon regeneration capacity and hostile microenvironment in the lesion site, essential neural network reconstruction remains challenging. Owing to the blood-spinal cord barrier (BSCB) created immune cells and cytokines isolation, the immune elements were incorrectly recognized as innocent bystanders during the SCI pathological process traditionally. Emerging evidence demonstrated that the central nervous system (CNS) is an "immunological quiescent" rather than "immune privileged" area, and the CNS-associated immune response played mixed roles which dedicate beneficial and detrimental contributions throughout the SCI process. Consequently, coordinating double-edged immunomodulation is vital to promote tissue repair and neurological recovery post-SCI. The comprehensive exploration and understanding of the immune landscape post-SCI are essential in establishing new avenues for further basic and clinical studies. In this context, this review summarizes the recent significant breakthroughs in key aspects of SCI-related immunomodulation, including innate and adaptive immune response, immune organ changes, and holistic immune status modification. Moreover, the currently existing immune-oriented therapies for SCI will be outlined.

A bionic multichannel nanofiber conduit carrying Tubastatin A for repairing injured spinal cord

Spinal cord injury is a kind of nerve injury disease with high disability rate. The bioscaffold, which presents a biomimetic structure, can be used as “bridge” to fill the cavity formed by the liquefaction and necrosis of spinal nerve cells, and connects the two ends of the fracture to promote the effective recovery of nerve function. Tubasatin A (TUBA) is a potent selective histone deacetylase 6 (HDAC6) inhibitor, which can inhibit the overexpression of HDAC6 after spinal cord injury. However, TUBA is limited by high efflux ratios, low brain penetration and uptake in the treatment of spinal cord injury. Therefore, an effective carrier with efficient load rate, sustained drug release profile, and prominent repair effect is urgent to be developed. In this study, we have prepared a bionic multichannel Tubasatin A loaded nanofiber conduit (SC-TUBA(+)) through random electrospinning and post-triple network bond crosslinking for inhibiting HDAC6 as well as promoting axonal regeneration during spinal cord injury treatment. The Tubasatin A-loaded nanofibers were shown to be successfully contained in poly(glycolide-co-ε-caprolactone) (PGCL)/silk fibroin (SF) matrix, and the formed PGCL/SF-TUBA nanofibers exhibited an uniform and smooth morphology and appropriate surface wettability. Importantly, the TUBA loaded nanofibers showed a sustained-release profile, and still maintains activity and promoted the extension of axonal. In addition, the total transection large span model of rat back and immunofluorescent labeling, histological, and neurobehavioral analysis were performed for inducing spinal cord injury at T9-10, evaluating therapeutic efficiency of SC-TUBA(+), and elucidating the mechanism of TUBA release system in vivo. All the results demonstrated the significantly reduced glial scar formation, increased nerve fiber number, inhibited inflammation, reduced demyelination and protected bladder tissue of TUBA-loaded nanofibers for spinal cord injury compared to SC-TUBA, SC and Control groups, indicating their great potential for injured spinal cord healing clinically.

Gas5 inhibition promotes the axon regeneration in the adult mammalian nervous system

Neurons in the peripheral nervous system (PNS) have robust regenerative capacity after axon injury, but the regenerative capacity is generally absent in the neurons of the central nervous system (CNS) in mammals. Increasing evidence highlighted the pivotal roles of long-noncoding RNAs (lncRNAs) in development and disease, but the role of LncRNA in triggering the regenerative capacity in CNS and PNS is not well studied. Here, we reported that lncRNA Gas5 is a suppressor for axon regeneration. Bioinformatics analysis shows that Gas5 is age-dependent up-regulated during DRG neurons development and down-regulated after sciatic nerve injury. In vitro, inhibiting the expression of Gas5 promotes the neurite growth of DRG neurons both in mice and rats. Consistently, Gas5 overexpression inhibits axon growth of mice DRG neurons. In vivo, Gas5 knockout(Gas5-/-) mice display enhanced nerve regeneration ability after sciatic nerve injury. RNA pull-down analysis indicates that Gas5 can interacts with soluble Vimentin, which is essential for peripheral nerve development and regeneration. Vimentin knockdown reverses the Gas5 silence-regulated axon pro-regeneration demonstrating that the function of Gas5 depending on Vimentin. Besides, inhibition of Gas5 expression can also enhance optic nerve regeneration indicating a potential pro-regenerative ability of Gas5 silence in CNS. Our study for the first time provides direct evidence in vivo that lncRNA plays a role in regulating central axon regrowth and Gas5 might be a novel therapeutic target for axon regeneration in both PNS and CNS.

Protein post-translational modifications after spinal cord injury

Deficits in intrinsic neuronal capacities in the spinal cord, a lack of growth support, and suppression of axonal outgrowth by inhibitory molecules mean that spinal cord injury almost always has devastating consequences. As such, one of the primary targets for the treatment of spinal cord injury is to develop strategies to antagonize extrinsic or intrinsic axonal growth-inhibitory factors or enhance the factors that support axonal growth. Among these factors, a series of individual protein level disorders have been identified during the generation of axons following spinal cord injury. Moreover, an increasing number of studies have indicated that post-translational modifications of these proteins have important implications for axonal growth. Some researchers have discovered a variety of post-translational modifications after spinal cord injury, such as tyrosination, acetylation, and phosphorylation. In this review, we reviewed the post-translational modifications for axonal growth, functional recovery, and neuropathic pain after spinal cord injury, a better understanding of which may elucidate the dynamic change of spinal cord injury-related molecules and facilitate the development of a new therapeutic strategy for spinal cord injury.