Systematic analysis of brain and skull ischemic injury expression profile reveals associations of tumor immune microenvironment and cell death with ischemic stroke

Background: Previous study showed that stroke may be a potential first sign of neoplasia. But the relationship between them remains unclear. Besides, ischemic stroke is a complex brain disease, which involves cell death or complex immune regulation. Thus, it is necessary to reveal the association of tumor immune microenvironment and cell death with ischemic stroke. Methods: Here, a photothrombosis-induced ischemic injury models of brain and skull was established. We compared and analyzed the pattern of gene expression profile between brain and skull after ischemic injury by transcriptome analysis. Further, we investigated the enrichment of relevant differential genes in cancer pathways and cell death pathways, and analyzed changes in the immune microenvironment after ischemic injury. Moreover, the pan-cancer genomic and prognosis analysis of ischemic injury related gene set were performed. Results: The results showed that the gene expression patterns were different in temporal and spatial locations after ischemic injury. We found that the effect on the transcriptome of the brain after skull ischemic injury was particularly large, but it could be recovered in a short period, while the effect on the skull after brain ischemic injury was long-lasting. The expression of genes related to ischemic injury is also associated with cell death and cancer hallmark pathways. In addition, changes in the abundance of immune cells indicate that brain ischemic injury may disrupt its immune microenvironment for a longer time, while skull can better balance the stability of immune microenvironment. Moreover, the brain ischemic injury-related gene sets are highly correlated with a variety of tumors, especially GBM, KIRC, LGG and UVM after stroke have a greater risk of death. Conclusion: This study gives us a new understanding of the role of the skull in brain ischemic injury, and reveals the association of tumor immune microenvironment and cell death with ischemic stroke. Transcriptome changes in brain and skull at representative time points after ischemic injury were analyzed. The mouse brain and skull tissue contains ischemic and peri-ischemic regions were harvested for RNA sequencing.

背景：既往研究显示，脑卒中（stroke）可能是肿瘤（neoplasia）潜在的首发表现，但二者之间的关联尚不明确。此外，缺血性脑卒中（ischemic stroke）是一类复杂的脑部疾病，其发生涉及细胞死亡（cell death）与复杂的免疫调控过程。因此，揭示肿瘤免疫微环境（tumor immune microenvironment）、细胞死亡与缺血性脑卒中之间的关联具有重要意义。
方法：本研究构建了光血栓诱导（photothrombosis）的脑部与颅骨缺血损伤模型。通过转录组分析（transcriptome analysis），比较并分析了缺血损伤后脑部与颅骨的基因表达谱特征。进一步探究了相关差异基因（differential genes）在癌症通路与细胞死亡通路中的富集情况，并分析了缺血损伤后免疫微环境的变化。此外，本研究还针对缺血损伤相关基因集（gene set）开展了泛癌（pan-cancer）基因组学与预后分析。
结果：研究结果显示，缺血损伤后基因表达模式在时空维度上存在显著差异。我们发现，颅骨缺血损伤对脑部转录组的影响尤为显著，但该影响可在短时间内恢复；而脑部缺血损伤对颅骨转录组的影响则更为持久。缺血损伤相关基因的表达与细胞死亡及癌症特征通路（cancer hallmark pathways）密切相关。此外，免疫细胞丰度的变化表明，脑部缺血损伤可较长时间破坏其自身免疫微环境，而颅骨则能更好地维持免疫微环境的稳定性。进一步分析显示，脑部缺血损伤相关基因集与多种肿瘤存在高度关联，其中脑卒中后胶质母细胞瘤（GBM）、肾透明细胞癌（KIRC）、低级别胶质瘤（LGG）及葡萄膜黑色素瘤（UVM）患者的死亡风险更高。
结论：本研究为理解颅骨在脑部缺血损伤中的作用提供了全新视角，并揭示了肿瘤免疫微环境、细胞死亡与缺血性脑卒中之间的关联。本研究分析了缺血损伤后代表性时间点下脑部与颅骨的转录组变化，采集了包含缺血区域及缺血周边区域（peri-ischemic regions）的小鼠脑组织与颅骨组织进行RNA测序（RNA sequencing）。