Targeted Delivery of Neural Stem Cells to the Brain Using MRI-Guided Focused Ultrasound to Disrupt the Blood-Brain Barrier

Stem cell therapy is a promising strategy to treat neurodegenerative diseases, traumatic brain injury, and stroke. For stem cells to progress towards clinical use, the risks associated with invasive intracranial surgery used to deliver the cells to the brain, needs to be reduced. Here, we show that MRI-guided focused ultrasound (MRIgFUS) is a novel method for non-invasive delivery of stem cells from the blood to the brain by opening the blood brain barrier (BBB) in specific brain regions. We used MRI guidance to target the ultrasound beam thereby delivering the iron-labeled, green fluorescent protein (GFP)-expressing neural stem cells specifically to the striatum and the hippocampus of the rat brain. Detection of cellular iron using MRI established that the cells crossed the BBB to enter the brain. After sacrifice, 24 hours later, immunohistochemical analysis confirmed the presence of GFP-positive cells in the targeted brain regions. We determined that the neural stem cells expressed common stem cell markers (nestin and polysialic acid) suggesting they survived after transplantation with MRIgFUS. Furthermore, delivered stem cells expressed doublecortin in vivo indicating the stem cells were capable of differentiating into neurons. Together, we demonstrate that transient opening of the BBB with MRIgFUS is sufficient for transplantation of stem cells from the blood to targeted brain structures. These results suggest that MRIgFUS may be an effective alternative to invasive intracranial surgery for stem cell transplantation.

干细胞疗法（Stem cell therapy）是治疗神经退行性疾病、创伤性脑损伤及脑卒中的极具潜力的临床策略。推动干细胞走向临床应用的关键之一，是降低现有侵入式颅内细胞递送手术所伴随的风险。本研究证实，磁共振引导聚焦超声（MRI-guided focused ultrasound, MRIgFUS）是一种新型非侵入式递送方案：通过在特定脑区开放血脑屏障（blood brain barrier, BBB），可将血液来源的干细胞递送至脑部。我们借助磁共振引导定位超声波束，将经铁标记、表达绿色荧光蛋白（green fluorescent protein, GFP）的神经干细胞精准靶向递送至大鼠脑的纹状体与海马体。通过磁共振成像检测细胞内铁信号，证实移植细胞成功跨越血脑屏障进入脑组织。于移植后24小时处死实验动物，免疫组织化学分析进一步确认，靶向脑区内存在GFP阳性细胞。检测结果显示，留存的神经干细胞表达经典干细胞标志物巢蛋白（nestin）与多唾液酸（polysialic acid），表明其经MRIgFUS辅助移植后仍可存活。此外，体内实验证实移植的干细胞表达双皮质素（doublecortin），提示其具备向神经元分化的潜能。综上，本研究证明，利用MRIgFUS短暂开放血脑屏障即可实现血液来源干细胞向靶向脑结构的移植。上述结果表明，MRIgFUS有望成为替代侵入式颅内手术的有效干细胞移植方案。