Editorial [Hot Topic: Spinal Cord Injury and Repair - Part I (Executive Editor: Weihong Pan)]

Spinal cord injury (SCI) is followed by a series of dynamic changes in the injured spinal cord and the environment that influence the extent of structural and functional recovery. All therapeutic interventions work toward one goal: to restore balance in the spinal cord by promoting regenerative pathways and depressing the degenerative factors (Fig. 1). Caution comes from awareness that acute effects are not always sustained enough to lead to long-term restoration of spinal cord function, and that experimental results from animal models do not always translate into clinical success in injured people. Nonetheless, rapid progress has been seen in the past two decades in the research and pharmaceutical intervention required to repair the spinal cord. This Special Issue presents some of the major approaches. In the leading article, Tsai and Tator highlight the various paths toward a cure for SCI. The neuroprotective strategies include the use steroids and other anti-inflammatory agents as well as agents that are anti-ischemic, that antagonize glutamate excitoxicity, that are anti-apopototic, and that enhance axonal function [1]. The regenerative strategies are designed to overcome the inhibitory factors, create a regeneration-inducing environment with implants of synthetic or biological matrices, supplement neurotrophic factors, and transplant cells and tissue. The benefits and shortcomings of these approaches are discussed. This serves as an excellent introduction to the next group of reviews that addresses some of the specific areas. SCI is associated with primary and secondary pathology. The role of inflammation and immune reactions in tissue repair is no doubt crucial. Contrary to the conventional wisdom that inflammation is universally deleterious, accumulating evidence presented by Popovich and others indicates that inflammatory cells and mediators may facilitate endogenous repair processes when applied in adequate concentrations at the appropriate time. In this issue, Jones, McDaniel, and Popovich review the multiple faces and players involved in inflammatory-mediated injury and repair [2]. By contrast, cell elimination, as induced by radiation therapy, has been shown to significantly improve histological and electrophysiological parameters after contusion SCI in the rat [3]. In her review, Kalderon not only provides convincing results but also summarizes the window of opportunity, the principles of radiotherapy, and the involvement of the blood-brain and blood-spinal cord barrier (BBB) in the process. Also related to BBB function with specific emphasis on the transport systems for neurotrophic and inflammatory cytokines, Kastin and Pan stress potential strategies against myelin-associated growth inhibitory factors [4]. These approaches target the inhibitory molecules themselves, their NgR receptor, and intracellular pathways. In parallel, Phinney and Isakova discuss progress in the use of bone marrow - derived mesenchymal stem cells to promote regeneration. The history, derivatization, differentiation, technical expertise, as well as therapeutic effects of these mesenchymal stem cells are described in fine detail [5]. Further, Xiang, Pan, and Kastin [6] discuss some general mechanisms involved in spinal cord repair, serving to contrast and complement the strategies proposed by Tsai and Tator at the beginning of the Issue. This concludes the first half of the Special Issue.