Traumatic brain injury (TBI) pathologies are caused by primary and secondary injuries. Primary injuries result from physical damage to the brain, and secondary injuries arise from cellular responses to primary injuries. A characteristic cellular response is sustained activation of inflammatory pathways commonly mediated by NF-κB transcription factors. Using a Drosophila melanogaster TBI model, we previously found that the main proximal transcriptional response to primary injuries is triggered by activation of Toll and Imd innate immune response pathways that engage NF-κB factors Dif and Relish (Rel), respectively. Here, we found by mass spectrometry that Rel protein level increased in fly heads at 4-8 h after TBI. To investigate the necessity of Rel for secondary injuries, we generated a null allele, Rel^del , by CRISPR/Cas9 editing. When heterozygous but not homozygous, the Rel^del mutation reduced mortality at 24 h after TBI and increased the lifespan of injured flies. Additionally, the effect of heterozygosity for Rel^del on mortality was modulated by genetic background and diet. To identify genes that facilitate effects of Rel^del on TBI outcomes, we compared genome-wide mRNA expression profiles of uninjured and injured +/+, +/Rel^del , and Rel^del /Rel^del flies at 4 h following TBI. Only a few genes changed expression more than two-fold in +/Rel^del flies relative to +/+ and Rel^del /Rel^del flies, and they were not canonical innate immune response genes. Therefore, Rel is necessary for TBI-induced secondary injuries but in complex ways involving Rel gene dose, genetic background, diet, and possibly small changes in expression of innate immune response genes.

中文翻译：

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NF-κB 先天免疫反应转录因子 Relish 突变的杂合性提高了果蝇脑外伤后的存活率。

创伤性脑损伤 (TBI) 病理由原发性和继发性损伤引起。原发性损伤是由大脑的物理损伤引起的，而继发性损伤是由细胞对原发性损伤的反应引起的。典型的细胞反应是通常由 NF-κB 转录因子介导的炎症途径的持续激活。使用果蝇TBI 模型，我们之前发现对原发性损伤的主要近端转录反应是由分别与 NF-κB 因子 Dif 和 Relish (Rel) 结合的 Toll 和 Imd 先天免疫反应途径的激活触发的。在这里，我们通过质谱分析发现，TBI 后 4-8 小时，果蝇头部的 Rel 蛋白水平增加。为了研究 Rel 对继发性损伤的必要性，我们通过 CRISPR/Cas9 编辑生成了一个无效等位基因Rel ^{del 。}当杂合而非纯合时，Rel ^del突变降低了 TBI 后 24 小时的死亡率，并延长了受伤果蝇的寿命。此外， Rel ^del杂合性对死亡率的影响受到遗传背景和饮食的调节。为了确定促进Rel ^del对 TBI 结果影响的基因，我们比较了TBI 后 4 小时未受伤和受伤的 +/+、+/ Rel ^del和Rel ^del / Rel ^del果蝇的全基因组 mRNA 表达谱。相对于 +/+ 和Rel ^del / Rel ^del果蝇，只有少数基因在 +/ Rel ^del果蝇中的表达变化超过两倍，并且它们不是典型的先天免疫应答基因。因此，Rel 对于 TBI 引起的继发性损伤是必要的，但其方式复杂，涉及Rel基因剂量、遗传背景、饮食以及先天免疫反应基因表达的可能微小变化。