Traumatic brain injury (TBI) causes acute and subacute tissue damage, but is also associated with chronic inflammation and progressive loss of brain tissue months and years after the initial event. The trigger and the subsequent molecular mechanisms causing chronic brain injury after TBI are not well understood. The aim of the current study was therefore to investigate the hypothesis that necroptosis, a form a programmed cell death mediated by the interaction of Receptor Interacting Protein Kinases (RIPK) 1 and 3, is involved in this process. Neuron-specific RIPK1- or RIPK3-deficient mice and their wild-type littermates were subjected to experimental TBI by controlled cortical impact. Posttraumatic brain damage and functional outcome were assessed longitudinally by repetitive magnetic resonance imaging (MRI) and behavioral tests (beam walk, Barnes maze, and tail suspension), respectively, for up to three months after injury. Thereafter, brains were investigated by immunohistochemistry for the necroptotic marker phosphorylated mixed lineage kinase like protein(pMLKL) and activation of astrocytes and microglia. WT mice showed progressive chronic brain damage in cortex and hippocampus and increased levels of pMLKL after TBI. Chronic brain damage occurred almost exclusively in areas with iron deposits and was significantly reduced in RIPK1- or RIPK3-deficient mice by up to 80%. Neuroprotection was accompanied by a reduction of astrocyte and microglia activation and improved memory function. The data of the current study suggest that progressive chronic brain damage and cognitive decline after TBI depend on the expression of RIPK1/3 in neurons. Hence, inhibition of necroptosis signaling may represent a novel therapeutic target for the prevention of chronic post-traumatic brain damage.

中文翻译：

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RIPK1 或 RIPK3 缺失可防止进行性神经元细胞死亡并改善创伤性脑损伤后的记忆功能

创伤性脑损伤 (TBI) 会导致急性和亚急性组织损伤，但也与慢性炎症和初始事件后数月和数年的脑组织进行性丢失有关。TBI 后导致慢性脑损伤的触发因素和随后的分子机制尚不清楚。因此，本研究的目的是研究坏死性凋亡（一种由受体相互作用蛋白激酶 (RIPK) 1 和 3 的相互作用介导的程序性细胞死亡）参与这一过程的假设。神经元特异性 RIPK1 或 RIPK3 缺陷小鼠及其野生型同窝小鼠通过受控的皮质冲击进行实验性 TBI。通过重复磁共振成像 (MRI) 和行为测试 (beam walk, 巴恩斯迷宫和尾巴悬吊），分别在受伤后长达三个月。此后，通过免疫组织化学研究大脑的坏死标志物磷酸化混合谱系激酶样蛋白 (pMLKL) 以及星形胶质细胞和小胶质细胞的激活。WT 小鼠在 TBI 后表现出皮质和海马的进行性慢性脑损伤和 pMLKL 水平升高。慢性脑损伤几乎只发生在有铁沉积的区域，并且在 RIPK1 或 RIPK3 缺陷小鼠中显着减少高达 80%。神经保护伴随着星形胶质细胞和小胶质细胞活化的减少和记忆功能的改善。目前研究的数据表明，TBI 后进行性慢性脑损伤和认知能力下降取决于神经元中 RIPK1/3 的表达。因此，