Immediate splenectomy down-regulates the MAPK–NF-κB signaling pathway in rat brain after severe traumatic brain injury

Abstract

BACKGROUND 

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.

METHODS 

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.

RESULTS 

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.

CONCLUSION 

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.