Background & Aims

Patients with inflammatory liver disease commonly develop debilitating symptoms, called sickness behaviors, which arise via changes in brain function. Monocytes that produce tumor necrosis factor interact with cerebral endothelial cells to activate microglial cells and promote sickness behavior. Platelets regulate inflammation, and aggregates of monocytes and platelets are increased in the circulation of patients with liver disease. We investigated the role of platelets in inducing inflammatory features of circulating monocytes and promoting sickness behaviors in mice with cholestatic liver injury.

Methods

We performed bile-duct ligations or sham surgeries on C57BL/6 or toll-like receptor 4 (TLR4)-knockout mice to induce liver inflammation. Liver inflammation was also induced in a separate group of mice by administration of concanavalin A. Circulating platelets, aggregates of monocytes and platelets, and activation of microglial cells were measured by flow cytometry. To deplete platelets, mice were given anti-thrombocyte serum or normal rabbit serum (control) 4 days after surgery. Interactions between monocytes and cerebral endothelial cells were analyzed by intravital microscopy. Sickness behaviors were quantified based on time spent by adult mice engaging in social behaviors toward a juvenile mouse, compared with time spent in nonsocial behavior or remaining immobile.

Results

Aggregates of monocytes and platelets in circulation of mice increased significantly following bile-duct ligation. Platelet-monocyte interactions were required for activation of inflammatory monocytes and production of tumor necrosis factor. Platelet depletion greatly reduced adhesive interactions between inflammatory monocytes and adhesive interactions with cerebral endothelial cells and activation of the microglia, as well as development of sickness behavior. Furthermore, TLR4 signaling was important for aggregation of monocytes and platelets, and development of sickness behavior following bile-duct ligation. These findings were confirmed in mice with concanavalin A–induced liver injury.

Conclusions

In mice with liver inflammation, we found TLR4 and aggregates of monocytes and platelets to regulate microglial activation and development of sickness behavior. These findings might lead to new therapeutic strategies for liver disease–associated symptoms.

中文翻译：

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血小板与炎性单核细胞之间的相互作用影响肝炎小鼠的疾病行为。

背景与目标

患有炎症性肝病的患者通常会出现虚弱的症状，称为疾病行为，这种疾病是由于脑功能的变化而引起的。产生肿瘤坏死因子的单核细胞与脑内皮细胞相互作用以激活小胶质细胞并促进疾病行为。血小板调节炎症，并且在肝病患者的血液循环中单核细胞和血小板的聚集增加。我们调查了血小板在诱导胆汁淤积性肝损伤小鼠中循环单核细胞的炎症特征和促进疾病行为中的作用。

方法

我们对C57BL / 6或toll样受体4（TLR4）敲除小鼠进行了胆管结扎或假手术，以诱导肝脏炎症。通过给予伴刀豆球蛋白A也可以在另一组小鼠中诱发肝炎症。通过流式细胞术测量循环血小板，单核细胞和血小板的聚集体以及小胶质细胞的活化。为了耗尽血小板，在手术后4天给小鼠抗血小板血清或正常兔血清（对照）。通过活体显微镜分析单核细胞和脑内皮细胞之间的相互作用。根据成年小鼠对未成年小鼠进行社交行为所花费的时间与在非社交行为或保持静止状态下所花费的时间进行比较，来量化疾病行为。

结果

胆管结扎后，小鼠循环中单核细胞和血小板的聚集显着增加。炎性单核细胞的激活和肿瘤坏死因子的产生需要血小板-单核细胞的相互作用。血小板耗竭极大地减少了炎性单核细胞之间的粘附相互作用以及与脑内皮细胞的粘附相互作用以及小胶质细胞的活化以及疾病行为的发展。此外，TLR4信号传导对于单核细胞和血小板的聚集以及胆管结扎后疾病行为的发展非常重要。这些发现在伴刀豆球蛋白A引起的肝损伤的小鼠中得到证实。

结论

在患有肝炎的小鼠中，我们发现TLR4以及单核细胞和血小板的聚集体可调节小胶质细胞的活化和疾病行为的发展。这些发现可能会导致针对肝脏疾病相关症状的新治疗策略。