Tuszynski M H, Weidner N, McCormack M, Miller I, Powell H, Conner J
Department of Neurosciences, University of California-San Diego, La Jolla 92093-0608, USA.
Cell Transplant. 1998 Mar-Apr;7(2):187-96. doi: 10.1177/096368979800700213.
Schwann cells naturally support axonal regeneration after injury in the peripheral nervous system, and have also shown a significant, albeit limited, ability to support axonal growth and remyelination after grafting to the central nervous system (CNS). It is possible that Schwann cell-induced axonal growth in the CNS could be substantially increased by genetic manipulation to secrete augmented amounts of neurotrophic factors. To test this hypothesis, cultured primary adult rat Schwann cells were genetically modified using retroviral vectors to produce and secrete high levels of human nerve growth factor (NGF). These cells were then grafted to the midthoracic spinal cords of adult rats. Findings were compared to animals that received grafts of nontransduced Schwann cells. Spinal cord lesions were not placed prior to grafting because the primary aim of this study was to examine features of grafted Schwann cell survival, growth, and effects on host axons. In vitro prior to grafting, Schwann cells secreted 1.5+/-0.1 ng human NGF/ml/10(6) cells/day. Schwann cell transplants readily survived for 2 wk to 1 yr after in vivo placement. Some NGF-transduced grafts slowly increased in size over time compared to nontransduced grafts; the latter remained stable in size. NGF-transduced transplants were densely penetrated by primary sensory nociceptive axons originating from the dorsolateral fasciculus of the spinal cord, whereas control grafts showed significantly fewer penetrating sensory axons. Over time, Schwann cell grafts also became penetrated by TH- and DBH-labeled axons of putative coerulospinal origin, unlike control cell grafts. Ultrastructurally, axons in both graft types were extensively myelinated by Schwann cells. Grafted animals showed no changes in gross locomotor function. In vivo expression of the human NGF transgene was demonstrated for periods of at least 6 m. These findings demonstrate that primary adult Schwann cells 1) can be transduced to secrete augmented levels of neurotrophic factors, 2) survive grafting to the CNS for prolonged time periods, 3) elicit robust growth of host neurotrophin-responsive axons, 4) myelinate CNS axons, and 5) express the transgene for prolonged time periods in vivo. Some grafts slowly enlarge over time, a feature that may be attributable to the propensity of Schwann cells to immortalize after multiple passages. Transduced Schwann cells merit further study as tools for promoting CNS regeneration.
施万细胞在周围神经系统损伤后能自然支持轴突再生，并且在移植到中枢神经系统（CNS）后，也显示出显著的（尽管有限）支持轴突生长和重新髓鞘化的能力。通过基因操作使施万细胞分泌增加量的神经营养因子，有可能显著增强其在中枢神经系统中诱导的轴突生长。为了验证这一假设，使用逆转录病毒载体对培养的成年大鼠原代施万细胞进行基因改造，使其产生并分泌高水平的人神经生长因子（NGF）。然后将这些细胞移植到成年大鼠的胸段脊髓中部。将结果与接受未转导施万细胞移植的动物进行比较。移植前未进行脊髓损伤，因为本研究的主要目的是检查移植的施万细胞存活、生长以及对宿主轴突的影响特征。移植前在体外，施万细胞分泌1.5±0.1 ng人NGF/ml/10⁶细胞/天。施万细胞移植在体内植入后能轻松存活2周至1年。与未转导的移植相比，一些NGF转导的移植随着时间推移大小缓慢增加；后者大小保持稳定。源自脊髓背外侧束的初级感觉伤害性轴突密集穿透NGF转导的移植，而对照移植显示穿透的感觉轴突明显较少。随着时间推移，与对照细胞移植不同，施万细胞移植也被假定为蓝斑脊髓起源的TH和DBH标记的轴突穿透。超微结构上，两种移植类型中的轴突都被施万细胞广泛髓鞘化。移植动物的总体运动功能没有变化。人NGF转基因在体内至少表达6个月。这些发现表明成年大鼠原代施万细胞1）可以被转导以分泌增加水平的神经营养因子，2）移植到中枢神经系统后能长时间存活，3）引发宿主神经营养因子反应性轴突的强劲生长，4）使中枢神经系统轴突髓鞘化，5）在体内长时间表达转基因。一些移植随着时间推移会缓慢增大，这一特征可能归因于施万细胞在多次传代后具有永生化的倾向。转导的施万细胞作为促进中枢神经系统再生的工具值得进一步研究。
