Diphtheria toxin induced but not CSF1R inhibitor mediated microglia ablation model leads to the loss of CSF/ventricular spaces in vivo that is independent of cytokine upregulation.
Diphtheria toxin induced but not CSF1R inhibitor mediated microglia ablation model leads to the loss of CSF/ventricular spaces in vivo that is independent of cytokine upregulation.
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DOI：
10.1186/s12974-021-02367-w
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发表时间：
2022-01-04
影响因子：
9.3
通讯作者：
Luo Y
中科院分区：
文献类型：
--
作者：
Bedolla A;Taranov A;Luo F;Wang J;Turcato F;Fugate EM;Greig NH;Lindquist DM;Crone SA;Goto J;Luo Y
据报道，最近开发的两种新型啮齿动物模型可以通过基因靶向小胶质细胞（通过Cx 3cr 1-creER：iDTR + Dtx）或通过用其抑制剂（PLX 5622）靶向CSF 1 R受体来消融小胶质细胞。近年来，这两种模型都被广泛用于定义小胶质细胞的基本功能，并导致了高影响力的研究，推动了该领域的发展。使用Cx 3cr 1-iDTR小鼠与Dtx组合或通过PLX 5622饮食来切除小胶质细胞，我们通过MRI和组织学比较了两种模型，以研究大脑和CSF/脑室系统的一般解剖结构。此外，我们分析了两种小胶质细胞消融模型中的细胞因子谱。我们发现，基因消融（Cx 3cr 1-iDTR + Dtx），而不是药理学小胶质细胞消融（PLX 5622），在脑中显示出令人惊讶的快速病理状况，表现为CSF/脑室的损失，而没有脑实质肿胀。在MRI和组织学分析中都观察到这种表型。令我们惊讶的是，我们发现单独iDTR等位基因会导致白喉毒素（Dtx）治疗后CSF/心室表型的丧失，而与cre表达无关。为了检查Cx 3cr 1-iDTR消融和iDTR模型中CSF损失的潜在机制，我们还研究了Cx 3cr 1-iDTR + Dtx、iDTR + Dtx和PLX模型中的细胞因子谱。我们发现Cx 3cr 1-iDTR + Dtx中多种细胞因子增加，但在CSF损失时（首次Dtx注射后3天），药物消融模型和iDTR + Dtx小鼠脑中均未发现。该结果表明，细胞因子的上调不是CSF损失的原因，这得到了我们的数据的支持，该数据表明在Cx 3cr 1-iDTR + Dtx小胶质细胞消融模型中未观察到脑实质肿胀或水肿。此外，KC/CXCR 2通路（Cx 3cr 1-iDTR + Dtx模型中上调最多的细胞因子）的药理学抑制并未解决遗传性小胶质细胞消融模型中的CSF/心室丢失表型。相反，Cx 3cr 1-iDTR + Dtx消融和iDTR + Dtx模型均显示脉络丛（CP）中激活的IBA 1+细胞增加，表明CP相关病理学可能是观察到的CSF/心室收缩表型的促成因素。我们的数据首次揭示了在Cx 3cr 1-iDTR基因消融模型中由iDTR等位基因引起的强大和全局CSF/脑室空间收缩病理学，但在PLX 5622消融模型中没有，并表明该病理学不是由于脑水肿形成，而是由于CP相关病理学。鉴于iDTR等位基因和Cx 3cr 1-iDTR模型的广泛应用，充分表征这种病理以了解潜在的因果机制至关重要。具体而言，在利用该模型解释被认为是由小胶质细胞介导的细微神经功能变化时需要谨慎，但在遗传消融模型中可能是由于CSF/心室丢失。
Two recently developed novel rodent models have been reported to ablate microglia, either by genetically targeting microglia (via Cx3cr1-creER: iDTR + Dtx) or through pharmacologically targeting the CSF1R receptor with its inhibitor (PLX5622). Both models have been widely used in recent years to define essential functions of microglia and have led to high impact studies that have moved the field forward. Using either Cx3cr1-iDTR mice in combination with Dtx or via the PLX5622 diet to pharmacologically ablate microglia, we compared the two models via MRI and histology to study the general anatomy of the brain and the CSF/ventricular systems. Additionally, we analyzed the cytokine profile in both microglia ablation models. We discovered that the genetic ablation (Cx3cr1-iDTR + Dtx), but not the pharmacological microglia ablation (PLX5622), displays a surprisingly rapid pathological condition in the brain represented by loss of CSF/ventricles without brain parenchymal swelling. This phenotype was observed both in MRI and histological analysis. To our surprise, we discovered that the iDTR allele alone leads to the loss of CSF/ventricles phenotype following diphtheria toxin (Dtx) treatment independent of cre expression. To examine the underlying mechanism for the loss of CSF in the Cx3cr1-iDTR ablation and iDTR models, we additionally investigated the cytokine profile in the Cx3cr1-iDTR + Dtx, iDTR + Dtx and the PLX models. We found increases of multiple cytokines in the Cx3cr1-iDTR + Dtx but not in the pharmacological ablation model nor the iDTR + Dtx mouse brains at the time of CSF loss (3 days after the first Dtx injection). This result suggests that the upregulation of cytokines is not the cause of the loss of CSF, which is supported by our data indicating that brain parenchyma swelling, or edema are not observed in the Cx3cr1-iDTR + Dtx microglia ablation model. Additionally, pharmacological inhibition of the KC/CXCR2 pathway (the most upregulated cytokine in the Cx3cr1-iDTR + Dtx model) did not resolve the CSF/ventricular loss phenotype in the genetic microglia ablation model. Instead, both the Cx3cr1-iDTR + Dtx ablation and iDTR + Dtx models showed increased activated IBA1 + cells in the choroid plexus (CP), suggesting that CP-related pathology might be the contributing factor for the observed CSF/ventricular shrinkage phenotype. Our data, for the first time, reveal a robust and global CSF/ventricular space shrinkage pathology in the Cx3cr1-iDTR genetic ablation model caused by iDTR allele, but not in the PLX5622 ablation model, and suggest that this pathology is not due to brain edema formation but to CP related pathology. Given the wide utilization of the iDTR allele and the Cx3cr1-iDTR model, it is crucial to fully characterize this pathology to understand the underlying causal mechanisms. Specifically, caution is needed when utilizing this model to interpret subtle neurologic functional changes that are thought to be mediated by microglia but could, instead, be due to CSF/ventricular loss in the genetic ablation model.
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