Published papers

In ossification of the posterior longitudinal ligaments (OPLL), axonal disruption results in motor and sensory function impairment. Twy (tiptoe-walking Yoshimura) mice develop spontaneous calcification in the cervical ligaments, thereby causing chronic compression of the spinal cords. To determine whether in vivo diffusion tensor tractography (DTT) can evaluate the axonal disruption of the chronic compressive spinal cords in twy mice, 6-, 15-, and 20-week-old twy mice were chronologically subjected to DTT. MRI was performed using a 7.0-Tesla magnet with a surface coil (CryoProbe). Diffusion tensor images were analyzed using TrackVis (Massachusetts General Hospital, MA, USA). We succeeded in depicting in vivo high-resolution DTT of the twy mice. The progress of the ligamentous calcification was observed at C2-3 level in each twy mouse, and the number of RT-97 or SMI31 positive fibers was decreased depending on the severity of the compression of the spinal cord. Quantitative analysis of sequential DTT enabled to detect subtle damage of the compressed spinal cord prior to the deterioration of neurological function in twy mice. Thus, in a clinical setting, DTT could be a new effective imaging modality in patients with cervical OPLL.

In spinal cord injury (SCI), the evaluation of axonal fibers is important to assess the severity of injury and efficacy of any treatment protocol, but conventional methods such as tracer injection in the brain parenchyma are highly invasive and require histological evaluation, precluding clinical applications. Magnetic resonance imaging (MRI) is essential for predicting prognosis and planning treatment of patients with SCI noninvasively. However, the information provided by conventional T1- and T2-weighted MRI of the spinal cord is essentially limited to the differentiation of the white matter from the gray matter. By contrast, diffusion-weighted magnetic resonance imaging (DWI) provides much information about biological structures. In particular, diffusion tensor imaging (DTI) and diffusion tensor tractography (DTT) are powerful tools for evaluating white matter fibers in the central nervous system. We previously established a reproducible SCI model in adult common marmosets and demonstrated that DTT could be used to trace the neural tracts in the intact and injured spinal cord of these animals in vivo. Recently, many reports using DTT to analyze the spinal cord area have been published. Based on the findings from our experimental studies, we are now routinely performing DTT of the human spinal cord clinically. In this chapter, we outline the basic principles of DTT and describe the characteristics, limitations, and clinical application of DTT in the spinal cord.

Hepatocyte growth factor (HGF), which is a potent mitogen for mature hepatocytes and a mediator of the inflammatory responses to tissue injury, was recently highlighted as a potent neurotrophic factor in the central nervous system. We revealed that introducing exogenous HGF into the injured rat spinal cord using a herpes simplex virus-1 vector significantly reduces the area of damaged tissue and promotes functional recovery. However, this rat study did not examine the therapeutic effects of administering HGF after injury, which is the most critical issue for clinical application. To translate this strategy to human treatment, we induced a contusive cervical SCI in the common marmoset, a primate, and then administered recombinant human HGF (rhHGF) intrathecally. Motor function was assessed using an original open-field scoring system focusing on manual function, including reach-and-grasp performance and hand placement in walking. The intrathecal rhHGF preserved the corticospinal fibers and myelinated areas, thereby promoting functional recovery. This study demonstrates the therapeutic effects, safety, and clinical efficacy of intrathecal rhHGF treatment for SCI in adult nonhuman primates and the possibility that this novel therapy may be suitable for clinical application.

Reports of functional recovery from spinal cord injury (SCI) after the transplantation of rat-fetus-derived neural stem/precursor cells (NS/PCs) and murine embryonic stem cells (ES cells) have raised great expectations for the successful clinical trial of stem cell transplantation therapy. However, the ethical issues concerning about destroying human embryos or fertilized oocytes to obtain such stem cells have been a major impediment to developing clinically useful stem cell sources and to use them in clinical applications. Recently, induced pluripotent stem cells (iPS cells), which can serve as a source of autologous cell transplantation, have been attracting a lot of attention as a clinically practical alternative to stem cells obtained directly from tissues. In this chapter, we outline the neural induction of murine and human iPS cells, their therapeutic efficacy in mouse and primate SCI models, and their safety in vivo.

Because of its high oxygen demands, neural tissue is predisposed to oxidative stress. Here, our aim was to clarify the cellular localization of antioxidant enzymes in the trigeminal ganglion. We found that the transcriptional factor Sox10 is localized exclusively in satellite glial cells (SGCs) in the adult trigeminal ganglion. The use of transgenic mice that express the fluorescent protein Venus under the Sox10 promoter enabled us to distinguish between neurons and SGCs. Although both superoxide dismutases 1 and 2 were present in the neurons, only superoxide dismutase 1 was identified in SGCs. The enzymes relevant to hydrogen peroxide degradation displayed differential cellular localization, such that neurons were endowed with glutathione peroxidase 1 and thioredoxin 2, and catalase and thioredoxin 2 were present in SGCs. Our immunohistochemical finding showed that only SGCs were labeled by the oxidative damage marker 8-hydroxy-2'-deoxyguanosine, which indicates that the antioxidant systems of SGCs were less potent. The transient receptor potential vanilloid subfamily member 1 (TRPV1), the capsaicin receptor, is implicated in inflammatory hyperalgesia, and we demonstrated that topical capsaicin application causes short-lasting mechanical hyperalgesia in the face. Our cell-based assay revealed that TRPV1 agonist stimulation in the presence of TRPV1 overexpression caused reactive oxygen species-mediated caspase-3 activation. Moreover, capsaicin induced the cellular demise of primary TRPV1-positive trigeminal ganglion neurons in a dose-dependent manner, and this effect was inhibited by a free radical scavenger and a pancaspase inhibitor. This study delineates the localization of antioxidative stress-related enzymes in the trigeminal ganglion and reveals the importance of the pivotal role of reactive oxygen species in the TRPV1-mediated caspase-dependent cell death of trigeminal ganglion neurons. Therapeutic measures for antioxidative stress should be taken to prevent damage to trigeminal primary sensory neurons in inflammatory pain disorders. © 2013 IBRO.