Oncomodulin derived from regeneration-associated macrophages in dorsal root ganglia promotes axon regeneration in the spinal cord

Preconditioning peripheral nerve injury enhances axonal regeneration of dorsal root ganglia (DRG) neurons in part by driving pro-regenerative perineuronal macrophage activation. How these regeneration-associated macrophages influence the neuronal capacity of axon regeneration remains elusive. The present study reports that oncomodulin (ONCM) is an effector molecule derived from the regeneration-associated macrophages. ONCM was highly upregulated in DRG macrophages following preconditioning injury and necessary for the preconditioning-induced neurite outgrowth. ONCM-deficient macrophages failed to generate neurite outgrowth activity of the conditioned medium in the in vitro model of neuron-macrophage interaction. CCL2/CCR2 signaling is an upstream regulator of ONCM since the ONCM upregulation was dependent on CCR2 and CCL2 overexpression-mediated conditioning effects were attenuated in ONCM-deficient mice. Direct application of ONCM potently increased neurite outgrowth in cultured DRG neurons by activating a distinct gene set, particularly neuropeptide-related genes. AAV-mediated overexpression of ONCM construct with the signal sequence increased neuronal secretion of ONCM and enhanced neurite outgrowth in an autocrine manner. For a clinically relevant approach, we developed a nanogel-mediated system for localized delivery of recombinant ONCM to DRG tissue. Electrostatic encapsulation of ONCM by a reducible epsilon-poly(L-lysine)-nanogel (REPL-NG) resulted in a slow release of ONCM allowing sustained bioactivity. Intraganglionic injection of REPL-NG/ONCM complex achieved a remarkable long-range axonal regeneration beyond spinal cord lesion, surpassing the extent expected from the preconditioning effects. The NG-mediated ONCM delivery could be exploited as a therapeutic strategy for promoting sensory axon regeneration following spinal cord injury.

Effect of Botulinum Toxin Injection and Extracorporeal Shock Wave Therapy on Nerve Regeneration in Rats with Experimentally Induced Sciatic Nerve Injury

This study was designed to compare the roles of botulinum neurotoxin A (BoNT/A) and extracorporeal shock wave therapy (ESWT) in promoting the functional recovery and regeneration of injured peripheral nerves. A total of 45 six-week-old rats with sciatic nerve injury were randomly divided into two experimental groups and one control group. The experimental groups received a single session of intranerve BoNT/A or ESWT immediately after a nerve-crushing injury. The control group was not exposed to any treatment. Differentiation of Schwann cells and axonal sprouting were observed through immunofluorescence staining, ELISA, real-time PCR, and Western blot at 3, 6, and 10 weeks post-nerve injury. For clinical assessment, serial sciatic functional index analysis and electrophysiological studies were performed. A higher expression of GFAP and S100β was detected in injured nerves treated with BoNT/A or ESWT. The levels of GAP43, ATF3, and NF200 associated with axonal regeneration in the experimental groups were also significantly higher than in the control group. The motor functional improvement occurred after 7 weeks of clinical observation following BoNT/A and ESWT. Compared with the control group, the amplitude of the compound muscle action potential in the experimental groups was significantly higher from 6 to 10 weeks. Collectively, these findings indicate that BoNT/A and ESWT similarly induced the activation of Schwann cells with the axonal regeneration of and functional improvement in the injured nerve.

Integrin-driven Axon Regeneration in the Spinal Cord Activates a Distinctive CNS Regeneration Program

The peripheral branch of sensory dorsal root ganglion (DRG) neurons regenerates readily after injury unlike their central branch in the spinal cord. However extensive regeneration and reconnection of sensory axons in the spinal cord can be driven by the expression of α9 integrin and its activator kindlin-1(α9k1), which enable axons to interact with tenascin-C. To elucidate the mechanisms and downstream pathways affected by activated integrin expression and central regeneration, we conducted transcriptomic analyses of DRG sensory neurons transduced with α9k1, and controls, with and without axotomy of the central branch. Expression of α9k1 without the central axotomy led to upregulation of a known PNS regeneration program, including many genes associated with peripheral nerve regeneration. Coupling α9k1 treatment with dorsal root axotomy led to extensive central axonal regeneration and caused expression of a distinctive CNS regeneration program, including genes associated with ubiquitination, autophagy, endoplasmic reticulum, trafficking, and signalling. Pharmacological inhibition of these processes blocked the regeneration of axons from DRGs and human iPS-derived sensory neurons, validating their causal contributions. This CNS regeneration-associated program showed little correlation with either embryonic development or PNS regeneration programs. Potential transcriptional drivers of this CNS program coupled to regeneration include Mef2a, Runx3, E2f4, Tfeb, Yy1. Signalling from integrins primes sensory neurons for regeneration, but their axon growth in the CNS is associated with a distinctive program that differs from that involved in PNS regeneration.

The manipulation of spinal motor neuron axonal growth promotes spinal cord repair

The loss of motor function in patients with spinal cord injury (SCI) is primarily due to the severing of the corticospinal tract (CST). Spinal motor neurons are located in the anterior horn of the spinal cord, and as the lower neurons of the CST, they control voluntary movement. Furthermore, its intrinsic axonal growth ability is significantly stronger than that of cerebral cortex pyramid neurons, which are the upper CST neurons. Therefore, we established an axonal regeneration model of spinal motor neurons to investigate the feasibility of repairing SCI by promoting axonal regeneration of spinal motor neurons. We demonstrated that conditionally knocking out pten in mature spinal motor neurons drastically enhanced axonal regeneration in vivo, and the regenerating axons of the spinal motor neurons re-established synapses with other cells in the damaged spinal cord. Thus, this strategy may serve as a novel and effective treatment method for SCI.