Department of Neurosurgery, Southwest Hospital, Third Military Medical University, Chongqing, 400038, China.
J Trauma Acute Care Surg. 2013 Jun;74(6):1446-53. doi: 10.1097/TA.0b013e31829246ad.
The treatment of severe traumatic brain injury (TBI) remains a difficult process. One key to improving treatment efficacy is to reduce secondary brain injury. Local and systemic inflammatory responses play an important role in secondary injury after TBI, which if unchecked can lead to fatal cerebral edema. Previous studies focused mainly on local brain tissue, whereas little is known about the contribution of peripheral organs in the pathogenesis of TBI. We previously showed that immediate splenectomy decreases mortality and improves cognitive function in rats after severe TBI by inhibiting the release of proinflammatory cytokines both systematically and locally in the injured brain. In this study, we further investigated the molecular mechanisms responsible for the effect of the spleen on local brain inflammation after TBI.
We established a severe TBI model with rats and performed splenectomy to study the effect of the spleen on mitogen-activated protein kinase (MAPK)-NF-κB activation in the brain tissue. The expression of p38 MAPK, extracellular regulated protein kinases (ERK), and NF-κB protein in the trauma region was examined by Western blotting. The neuron-like PC-12 cell line and microglia-like BV-2 cell line were used for in vitro experiments to test the effects of spleen supernatant after TBI. Cell apoptosis (annexin V/propidium iodide staining), NF-κB nuclear translocation (immunofluorescence microscopy), and MAPK signaling (phosphorylation of p-p38 and p-ERK) were examined.
We found that TBI significantly up-regulated MAPK signaling in the injured brain region, whereas immediate splenectomy suppressed MAPK activation. In vitro, the spleen supernatant from rats after TBI also resulted in increased MAPK activation and NF-κB nuclear translocation in microglia-like BV-2 cells, whereas the application of interleukin (IL)-1R antagonist (IL-1Ra) significantly reduced the expression of p-p38 and p-ERK as well as NF-κB nuclear translocation. In addition, spleen supernatant after TBI induced apoptosis in neuron-like PC-12 cells, and IL-1Ra could effectively reduce apoptosis.
Our study demonstrates that immediate splenectomy down-regulates the MAPK-NF-κB signaling pathway in rat brain after severe TBI. We also provide experimental evidence for the potential use of IL-1Ra to alleviate brain inflammation after TBI.
严重创伤性脑损伤（TBI）的治疗仍然是一个困难的过程。提高治疗效果的一个关键是减少继发性脑损伤。局部和全身炎症反应在 TBI 后的继发性损伤中起重要作用，如果不加以控制，可能导致致命性脑水肿。以前的研究主要集中在局部脑组织，而对于外周器官在 TBI 发病机制中的作用知之甚少。我们之前的研究表明，严重 TBI 后立即行脾切除术可通过系统性和局部抑制促炎细胞因子的释放，降低大鼠死亡率并改善认知功能。在这项研究中，我们进一步研究了脾对 TBI 后局部脑炎症的分子机制。
我们用大鼠建立了严重 TBI 模型，并进行脾切除术，以研究脾对脑组织中丝裂原活化蛋白激酶（MAPK）-核因子-κB（NF-κB）激活的影响。通过 Western blot 检测创伤区 p38 MAPK、细胞外调节蛋白激酶（ERK）和 NF-κB 蛋白的表达。使用神经元样 PC-12 细胞系和小胶质细胞样 BV-2 细胞系进行体外实验，检测 TBI 后脾上清液的作用。通过 Annexin V/碘化丙啶染色检测细胞凋亡、免疫荧光显微镜检测 NF-κB 核转位以及 MAPK 信号（p-p38 和 p-ERK 的磷酸化）。
我们发现 TBI 显著上调了损伤脑区的 MAPK 信号，而立即脾切除术则抑制了 MAPK 的激活。体外，TBI 后大鼠脾上清液也导致小胶质细胞样 BV-2 细胞中 MAPK 激活和 NF-κB 核转位增加，而白细胞介素（IL）-1R 拮抗剂（IL-1Ra）的应用则显著降低了 p-p38 和 p-ERK 的表达以及 NF-κB 核转位。此外，TBI 后的脾上清液诱导神经元样 PC-12 细胞凋亡，而 IL-1Ra 可有效减少凋亡。
本研究表明，严重 TBI 后立即脾切除术可下调大鼠脑内 MAPK-NF-κB 信号通路。我们还为使用 IL-1Ra 减轻 TBI 后脑炎症提供了实验依据。
