脑室下区神经发生与恶性胶质瘤相互作用关系的在体MRI研究

Malignant glioma is the most common primary brain tumor in adults. Despite advances in surgical treatment, radiotherapy, chemotherapy and immunotherapy to glioma, the median survival for malignant glioma remain less than 2 years. Recent studies demonstrate that stem cells especially such as neural stem cells(NSCs)/neural progenitor cells(NPCs), may be critical for inhibiting tumor growth and relapse. Subventricular zone (SVZ) harbors abundant of NSCs/NPCs in mammalian brain. However, the relationship between NSCs/NPCs from SVZ response to malignant glioma remains controversial. Our latest magnetic resonance imaging (MRI) study demonstrated that the cells from SVZ labeled with iron oxide particles surrounded C6 glioma tumor in rat brain after 3 weeks following the injection of iron oxide particles into ventricle, producing a low signal ring in T2 weighted images. This result implied that the SVZ cells,such as NSCs/NPCs, maybe contribute some impacts to glioma. Therefore, the aim of the present project is to explore mechanism of the NSCs/NPCs migration from SVZ at the time of tumorigenesis in rat brain by using cells tracer technology with MRI..In current study, we plan to inject a mixture composed of micron-sized iron oxide particles(MPIOs) and protamine sulfate to label endogenous NSCs/NPCs residing in SVZ strategically, follow by a serial high-resolution MRI study at 7.0 tesla MR for 3 weeks. The cells with glioma tropism will be isolated by magnetically activated cell sorting and the phenotype and proportion determined by fluorescence activated cell sorting analysis. Furthermore, epidermal growth factor introventricular infusion and MR guided high intensity focused ultrosound(HIFU) heating are designed to promote and damage neurogenesis ability of SVZ respectively. Then the migration of NSCs/NPCs from SVZ and the growth of C6 glioma will be observed under MRI study comparing with histology to assess the impact of SVZ neurogenesis on glioma growth..In summary, this study provides in vivo MRI evidences of an animal model to discuss the relationship between malignant gliomas and NSCs/NPCs from SVZ, which may be a potential stem cells for malignant glioma therapy in the future.

恶性胶质瘤是中枢神经系统发病第一位的肿瘤，至今尚无有效的治疗手段。研究发现移植的外源性神经干/祖细胞可作为细胞载体，定向地携带治疗基因至恶性胶质瘤,达到抑制肿瘤生长的作用。但是内源性神经干细胞与恶性胶质瘤生长之间的关系尚不明晰。我们前期发现氧化铁颗粒标记的脑室下区（SVZ）神经干/祖细胞三周后聚集于大鼠脑C6胶质瘤周围，产生T2WI低信号环。由此推测SVZ细胞与恶性胶质瘤存在密切的相互作用关系。本课题拟复制大鼠C6恶性胶质瘤模型，采用微米量级氧化铁颗粒标记SVZ细胞，利用高空间分辨率的MRI动态观察SVZ细胞向胶质瘤迁移的时空变化规律，定性、定量分析磁标记细胞的生物学属性，揭示其在恶性胶质瘤微环境下的转归；通过表皮生长因子（EGF）和高强度聚焦超声分别促进和破坏SVZ细胞的增殖和迁移，探讨SVZ细胞对恶性胶质瘤作用的确切机制，为恶性胶质瘤的靶向治疗提供理论基础和方法学依据。

恶性胶质瘤是中枢神经系统发病第一位的原发性肿瘤，预后差，至今尚无有效的治疗手段。研究表明移植的外源性神经干/祖细胞、巨噬细胞等可作为细胞载体，定向地携带治疗基因至恶性胶质瘤,达到抑制肿瘤生长的作用。但是内源性神经干/祖细胞、巨噬细胞与恶性胶质瘤生长之间的关系尚不明晰。磁性氧化铁颗粒作为T2造影剂，具有对比增强显著的特点，是分子影像首选的MRI造影剂。本研究小组通过实验发现微米量级的氧化铁颗粒（micron-sized iron oxide particles，MPIO）标记的脑室下区（subventricular zone,SVZ）神经干/祖细胞四周后聚集于大鼠脑C6 胶质瘤周围，产生T2WI 低信号。通过免疫荧光分析发现，肿瘤组大鼠SVZ及肿瘤区可见绿色荧光MPIO分布,并且观察到MPIO标记的神经干细胞由SVZ区向肿瘤区迁移的现象。肿瘤区域及同侧SVZ神经干/祖细胞明显多于对侧，说明大脑恶性胶质瘤可引起同侧SVZ内源性神经干/祖细胞的增殖并且向胶质瘤迁移。同时，本课题组通过回顾性研究发现人单发性大脑恶性星形细胞瘤（胶质瘤中最常见的类型）与SVZ的接触率远高于单发性大脑转移瘤，证明恶性胶质瘤起源与SVZ存在密切关联，此结果可作为鉴别两者的可靠依据。此外，本课题组还发现经大鼠静脉注射超顺磁性氧化铁颗粒（superparamagnetic iron oxide,SPIO）后，可通过磁共振活体观察到外周血巨噬细胞向胶质瘤的聚集的时空变化规律。通过本项目的实施，我们发现磁性氧化铁颗粒是良好的MRI细胞示踪剂，用于活体观察特异性细胞的时空变化。恶性胶质瘤的起源、生长、侵袭等生物学行为与内源性神经干/祖细胞、单核/巨噬细胞都存在密切关联，是多细胞共同作用的结果，具有复杂的细胞微环境。单独针对某一种细胞进行干预，可能都无法获得满意的治疗效果。