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. Methods: 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 ¹⁸F-labeled N,N-diethyl-2-(2-[4-(2-fluoroethoxy)phenyl]-5,7-dimethylpyrazolo[1,5-α]pyrimidine-3-yl)acetamide (¹⁸F-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. Results: Repopulation significantly increased ¹⁸F-DPA-714 uptake within the infarct on days 14 (P < 0.001) and 21 (P = 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 (csf-1r, aif1, and p2ry12) with repopulation, whereas peripheral cell recruitment–related gene expression decreased (cx3cr1 and ccr2), indicative of peripheral recruitment during CSF-1R inhibition. Similarly, uncorrected spleen uptake was significantly higher on day 7 after ischemia with treatment (P = 0.001) and decreased after drug withdrawal. PLX5622-treated mice walked a longer distance (P < 0.001) and more quickly (P = 0.009), and showed greater forelimb strength (P < 0.001), than control mice on day 14. Conclusion: This study highlighted the potential of ¹⁸F-DPA-714 PET/CT imaging to track microglia and macrophage repopulation after short-term CSF-1R inhibition in stroke.

对集落刺激因子 1 受体 (CSF-1R) 抑制诱导的小胶质细胞耗竭的研究表明，抑制剂撤除允许通过再增殖更新小胶质细胞隔室并解决炎症失衡。因此，我们首次（据我们所知）使用易位蛋白 (TSPO)-PET/CT 和 MR 成像、离体表征和行为测试研究了小胶质细胞再增殖对缺血小鼠模型炎症和功能结果的影响。方法：每组 8 只 C57BL/6 小鼠经历了 30 分钟的大脑中动脉短暂闭塞。治疗组从第 3 天到第 7 天在 1,200 ppm PLX5622 食物（Plexxikon Inc.）中接受 CSF-1R 抑制剂以诱导小胶质细胞/巨噬细胞耗竭，然后返回对照饮食以允许重新繁殖。^{在缺血和18} F-标记的N,N -diethyl-2-(2-[4-(2-fluoroethoxy)phenyl]-5,7-dimethylpyrazolo[1,5-α]后第 1 天，小鼠接受了 T2 加权 MRI ]嘧啶-3-基)乙酰胺( ¹⁸F-DPA-714) (TSPO) 第 7、14、21 和 30 天的 PET/CT。评估了梗塞、对侧纹状体和脾脏内每毫升注射示踪剂剂量的百分比。进行行为测试以评估运动功能恢复。在缺血后第 14 天和第 35 天收获大脑，用于小胶质细胞和巨噬细胞相关标记物的离体分析（免疫反应性和实时定量聚合酶链反应）。结果：在第 14 天（^P < 0.001）和第 21 天（P= 0.002) 缺血后。第 14 天，电离钙结合衔接分子 1 (Iba-1) 阳性细胞群显示出显着更高的 TSPO、CSF-1R 和 CD68 表达，这与小胶质细胞重新增殖一致。第 14 天的基因表达分析表明，小胶质细胞相关标记物（ csf-1r、aif1和p2ry12 ）随再增殖显着增加，而外周细胞募集相关基因表达下降（cx3cr1和ccr2），表明在 CSF- 1R抑制。同样，未校正的脾脏摄取在治疗缺血后第 7 天显着更高 ( P = 0.001)，并在停药后减少。PLX5622 处理的小鼠走的距离更长（P < 0.001) 和更快 ( P = 0.009)，并且在第 14 天表现出比对照小鼠更大的前肢力量 ( P < 0.001) 。结论：本研究强调了¹⁸ F-DPA-714 PET/CT 成像的潜力跟踪中风短期 CSF-1R 抑制后的小胶质细胞和巨噬细胞再增殖。