European Institute for Molecular Imaging, University of Münster, Münster, Germany;
Department of Medical Imaging/Anatomy, Radboud University Medical Center, Radboud, The Netherlands.
J Nucl Med. 2022 Sep;63(9):1408-1414. doi: 10.2967/jnumed.121.263004. Epub 2022 Feb 3.
Studies on colony-stimulating factor 1 receptor (CSF-1R) inhibition-induced microglia depletion indicated that inhibitor withdrawal allowed the renewal of the microglia compartment via repopulation and resolved the inflammatory imbalance. Therefore, we investigated for the first time (to our knowledge) the effects of microglia repopulation on inflammation and functional outcomes in an ischemic mouse model using translocator protein (TSPO)-PET/CT and MR imaging, ex vivo characterization, and behavioral tests. Eight C57BL/6 mice per group underwent a 30-min transient occlusion of the middle cerebral artery. The treatment group received CSF-1R inhibitor in 1,200 ppm PLX5622 chow (Plexxikon Inc.) from days 3 to 7 to induce microglia/macrophage depletion and then went back to a control diet to allow repopulation. The mice underwent T2-weighted MRI on day 1 after ischemia and F-labeled -diethyl-2-(2-[4-(2-fluoroethoxy)phenyl]-5,7-dimethylpyrazolo[1,5-α]pyrimidine-3-yl)acetamide (F-DPA-714) (TSPO) PET/CT on days 7, 14, 21, and 30. The percentage injected tracer dose per milliliter within the infarct, contralateral striatum, and spleen was assessed. Behavioral tests were performed to assess motor function recovery. Brains were harvested on days 14 and 35 after ischemia for ex vivo analyses (immunoreactivity and real-time quantitative polymerase chain reaction) of microglia- and macrophage-related markers. Repopulation significantly increased F-DPA-714 uptake within the infarct on days 14 ( < 0.001) and 21 ( = 0.002) after ischemia. On day 14, the ionized calcium binding adaptor molecule 1 (Iba-1)-positive cell population showed significantly higher expression of TSPO, CSF-1R, and CD68, in line with microglia repopulation. Gene expression analyses on day 14 indicated a significant increase in microglia-related markers ( and ) with repopulation, whereas peripheral cell recruitment-related gene expression decreased ( and ), indicative of peripheral recruitment during CSF-1R inhibition. Similarly, uncorrected spleen uptake was significantly higher on day 7 after ischemia with treatment ( = 0.001) and decreased after drug withdrawal. PLX5622-treated mice walked a longer distance ( < 0.001) and more quickly ( = 0.009), and showed greater forelimb strength ( < 0.001), than control mice on day 14. This study highlighted the potential of F-DPA-714 PET/CT imaging to track microglia and macrophage repopulation after short-term CSF-1R inhibition in stroke.
这项研究旨在探讨集落刺激因子 1 受体（CSF-1R）抑制剂诱导小胶质细胞耗竭后，抑制剂撤药是否能通过小胶质细胞再殖恢复小胶质细胞区室，并解决炎症失衡的问题。因此，我们首次（据我们所知）通过使用 18F 标记的二乙-2-（2-（4-（2-氟乙氧基）苯基）-5,7-二甲基吡唑并[1,5-α]嘧啶-3-基）乙酰胺（F-DPA-714）（TSPO）正电子发射断层扫描（PET）/CT 和磁共振成像（MRI）、离体特征分析和行为测试，研究了小胶质细胞再殖对缺血性小鼠模型中炎症和功能结果的影响。每组 8 只 C57BL/6 小鼠接受 30 分钟短暂性大脑中动脉闭塞。治疗组在第 3 至 7 天接受 CSF-1R 抑制剂 1,200 ppm PLX5622 饲料（Plexxikon Inc.）喂养以诱导小胶质细胞/巨噬细胞耗竭，然后恢复正常饮食以允许再殖。缺血后第 1 天进行 T2 加权 MRI，第 7、14、21 和 30 天进行 F-DPA-714（TSPO）PET/CT。评估梗塞、对侧纹状体和脾脏内注射示踪剂剂量的毫升百分比。进行行为测试以评估运动功能恢复情况。缺血后第 14 和 35 天收获大脑，进行小胶质细胞和巨噬细胞相关标志物的离体分析（免疫反应性和实时定量聚合酶链反应）。再殖可显著增加缺血后第 14 天（ < 0.001）和第 21 天（ = 0.002）梗塞内的 F-DPA-714 摄取。在第 14 天，离子钙结合衔接蛋白 1（Iba-1）阳性细胞群表现出 TSPO、CSF-1R 和 CD68 的表达显著增加，与小胶质细胞再殖一致。第 14 天的基因表达分析表明，再殖后与小胶质细胞相关的标志物（和）显著增加，而与外周细胞募集相关的基因表达减少（和），表明 CSF-1R 抑制期间存在外周细胞募集。同样，治疗后第 7 天未经校正的脾脏摄取率明显升高（ = 0.001），撤药后降低。与对照组相比，PLX5622 治疗组的小鼠在第 14 天行走距离更长（ < 0.001），速度更快（ = 0.009），且前肢力量更强（ < 0.001）。本研究强调了 F-DPA-714 PET/CT 成像在短暂 CSF-1R 抑制后追踪中风中小胶质细胞和巨噬细胞再殖的潜力。
