| BackgroundTraumatic Brain Injury(TBI), which could reduce the life expectancy after injury, is the leading cause of death and disability under 45 years old throughout the world. The mortality rate of severe TBI is 35-70%, and the vast majority of survivors live with varying degrees of dysfunction. To date, there are still no effective treatment strategies to reduce mortality and disability rates after severe TBI. Traumatic brain edema caused by secondary brain injury has become an important prognostic factor, except for the primary brain injury such as age, severity, timely treatment et al. Therefore, how to effectively control traumatic brain edema to reduce mortality in severe TBI arising from secondary brain injury bears important clinical value and scientific significance.Angiogenesis after TBI is a protective mechanism of posttrauma, which could reduce secondary damage of brain tissue. Majority of studies mainly focus on protection of the brain and regeneration, while little attention pays to the blood vessels supplying the brain ischemic region. Studies have confirmed that endothelial progenitor cells(EPCs) originated from adult peripheral blood can differentiate into endothelial cells in vivo and have the ability to generate blood vessels. With the further understanding of EPCs, angiogenesis has become the focus on the field of regenerative medicine, which is previously thought to repair damaged blood vessels only by mature endothelial cells. EPCs can be mobilized from the bone marrow and other tissues into the circulation to repair lesions after a variety of stimulation. Recent studies illustrate that EPCs are the main cell sources to build vessels in physiological and pathological conditions. EPCs can differentiate into endothelial cells in vivo to participate in the repair of brain, heart, liver, kidney and other organ damage. Therefore, EPCs might play an important role and have important therapeutic effects and potential applications after TBI.During last decades, Researches have revealed that EPCs are involved in maintaining BBB homeostasis between the central nervous system and circulation. The secondary traumatic brain edema caused by BBB damage is the primary cause of death in patients with severe TBI. Recent studies suggest that the stability of BBB after TBI have been recommended as a promising therapeutic target, and in combination with neuroprotectant improving the effectiveness of treatment. BBB repair is one of the most important factors among causes impacting of neurological recovery and long-term prognosis after TBI. Furthermore, EPCs can be converted into endothelial cells involved in angiogenesis and repair of endothelial integrity to prevent BBB damage and accelerate neurological recovery. The study also shows that the level of circulating EPCs, which can be used as a potential prognostic markers, has correlation with severity and prognosis after TBI.There are lots of studies focusing on protection of brain tissue, to date, the influence of peripheral immune response is likely shortage of further research after severe TBI. Recent studies show that the peripheral immune system plays an important role in traumatic brain edema except for the local inflammation after TBI. Therefore, The spleen, which is the largest lymphoid organ and accounts for about 0.2% of body weight, greatly contributes to the traumatic brain edema afte TBI. The spleen also plays an important role in removing the aging red blood cells, producing antibodies and inducing immunity. The spleen monitors the status of circulation and removes the potential threats from blood to maintain a stable environment. Spleen has been considered as a direct reservoir for monocytes, and a lot of monocytes recruit into the spleen after injury. Researches have confirmed that the number of monocytes are significantly higher in spleen when suffering from inflammatory diseases and myocardial infarction. Studies have reported splenic atrophy and spleen-derived proinflammatory monocyte-macrophage cell mobilization into the circulation after stroke could induce the accumulation of proinflammatory factors around the ischemic brain tissue. the reducing size of spleen was negatively correlated with infarction area after stroke. Furthermore, splenectomy has neuroprotective effects in animals two weeks before the experiments.Our previous studies demonstrated that brain edema could effectively be mitigated in rats performed splenectomy immediately after severe TBI. Meanwhile, the mortality was significantly reduced and cognitive function was improved. But the underlying mechanism is still elusive. With these results, we speculate there are some corelation between the EPCs and splenectomy after severe TBI. At the same time, we also hold two questions:(1) Does splenectomy have any effect on the level of circulating EPCs and BBB permeability?(2) Does splenectomy mediate EPCs participating in BBB reconstruction? To verify the above questions, this study is designed to clarify the underlying mechanisms of the spleen in regulation of circulating EPCs and their effect on BBB repair after TBI.In addition to exploring the internal aspects of the underlying mechanisms of the spleen in regulation of circulating EPCs and their effect on BBB repair after TBI, we also explore the impact of environmental changes after severe TBI on traumatic brain edema from external aspects of the normal pressure, low pressure environment via penetrating brain injury to provide treatment guidance on high altitude.Contents: ① The effect of immediate splenectomy was investigated through evaluation of the blood routine, blood sugar, mortality and cerebral edema afte TBI in rats; ② The circulating mononuclear cells were isolated, cultured and investigated their basic biological characterization after 3 days with severe TBI in rats; The cytometry was used ③to detect the amount of circulating EPCs and the ELISA was performed to evaluate the expression of S100 B in peripheral blood at different time points to detect the corelation between them after splenectomy in rats; The changes in BBB permeability after TBI and ④its effect on BBB permeability after splenectomy were studied. The influence of EPCs transplantation and the underlying mechanisms were investigated using EPCs transfected with lentiviral vectors carrying the EGFP via the tail vein. The immunofluorescence was used to observe the homing of transplanted EPCs to damaged brain region, and Western blotting was used to detect the expression of GFP and VEGF protein; ⑤The characteristics of high altitude penetrating brain injury were investigated via mortality, pathological changes in brain water content, EB content, regional cerebral blood flow, cerebral oxygen partial pressure, brainstem auditory evoked potentials and other aspects of comparative influence of normal and low pressure environment of penetrating brain injury after the establishment of penetrating brain injury model.Results: ① The brain edema could be mitigated to improve survival rate after immediate splenectomy in rats with severe TBI, which was consistent with previouly reported. ②EPCs could be isolated from peripheral blood mononuclear cells obtained by density gradient centrifugation, and could differentiate into mature cells under conditioned medium. The cultured EPCs have phenotypic characteristics, could uptake Di I-Ac-LDL and bind to FITC-UEA-1 by flow cytometry. EPCs can form tubule-like structure on Matrigel. ③ The number of circulating EPCs is increased after TBI, especially more significant after splenectomy in rats. The S100 B protein expression in plasma is inceased after severe TBI, and its expression could be down-regulated after splenectomy in rats with severe TBI. EPCs and plasma S100 B protein were positively correlated. BBB permeability is incresed and ④splenectomy may improve BBB permeability after TBI in rats. Transplanted EPCs could mitigate traumatic brain edema and they are involved in the reconstruction of the BBB after TBI. VEGF may be molecular mechanism for EPCs to repair the BBB. ⑤The heavier status, higher velocity and longer duration are the characteristics of high altitude cerebral edema, and early and continued monitoring of r CBF and Pbt O2 plateau bears great value for the diagnosis and treatment of penetrating brain injury on high altitude.Conclusions: 1. BBB permeability is incresed and splenectomy may improve BBB permeability after severe TBI in rats. 2. The number of circulating EPCs is increased after TBI, especially more significant after splenectomy in rats, which implys that the spleen has a intercepted effect on bone marrow-derived EPCs. 3. Transplanted EPCs could mitigate traumatic brain edema and they are involved in the reconstruction of the BBB after TBI. 4. The heavier status, higher velocity and longer duration are the characteristics of high altitude cerebral edema, and early and continued monitoring of r CBF and Pbt O2 plateau bears great value for the diagnosis and treatment of penetrating brain injury on high altitude. |
PDF Full Text Request