Sepsis is a host response to systemic inflammation and infection that may lead to multi-organ dysfunction and eventual death. While acute brain dysfunction is common among all sepsis patients, chronic neurological impairment is prevalent among sepsis survivors. The brain microvasculature has emerged as a major determinant of sepsis-associated brain dysfunction, yet the mechanisms that underlie its associated neuroimmune perturbations and behavioral deficits are not well understood. An emerging body of data suggests that inhibition of tissue-nonspecific alkaline phosphatase (TNAP) enzyme activity in cerebral microvessels may be associated with changes in endothelial cell barrier integrity. The objective of this study was to elucidate the connection between alterations in cerebrovascular TNAP enzyme activity and brain microvascular dysfunction in late sepsis. We hypothesized that the disruption of TNAP enzymatic activity in cerebral microvessels would be coupled to the sustained loss of brain microvascular integrity, elevated neuroinflammatory responses, and behavioral deficits. Male mice were subjected to cecal ligation and puncture (CLP), a model of experimental sepsis, and assessed up to seven days post-sepsis. All mice were observed daily for sickness behavior and underwent behavioral testing. Our results showed a significant decrease in brain microvascular TNAP enzyme activity in the somatosensory cortex and spinal cord of septic mice but not in the CA1 and CA3 hippocampal regions. Furthermore, we showed that loss of cerebrovascular TNAP enzyme activity was coupled to a loss of claudin-5 and increased perivascular IgG infiltration in the somatosensory cortex. Analyses of whole brain myeloid and T-lymphoid cell populations also revealed a persistent elevation of infiltrating leukocytes, which included both neutrophil and monocyte myeloid derived suppressor cells (MDSCs). Regional analyses of the somatosensory cortex, hippocampus, and spinal cord revealed significant astrogliosis and microgliosis in the cortex and spinal cord of septic mice that was accompanied by significant microgliosis in the CA1 and CA3 hippocampal regions. Assessment of behavioral deficits revealed no changes in learning and memory or evoked locomotion. However, the hot plate test uncovered a novel anti-nociceptive phenotype in our septic mice, and we speculate that this phenotype may be a consequence of sustained GFAP astrogliosis and loss of TNAP activity in the somatosensory cortex and spinal cord of septic mice. Taken together, these results demonstrate that the loss of TNAP enzyme activity in cerebral microvessels during late sepsis is coupled to sustained neuroimmune dysfunction which may underlie, in part, the chronic neurological impairments observed in sepsis survivors.

中文翻译：

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脑微血管中组织非特异性碱性磷酸酶 (TNAP) 酶活性的丧失与晚期脓毒症的持续神经炎症和行为缺陷有关

脓毒症是宿主对全身炎症和感染的反应，可能导致多器官功能障碍和最终死亡。虽然急性脑功能障碍在所有脓毒症患者中很常见，但慢性神经功能障碍在脓毒症幸存者中普遍存在。脑微血管系统已成为脓毒症相关脑功能障碍的主要决定因素，但其相关神经免疫扰动和行为缺陷的机制尚不清楚。一项新出现的数据表明，脑微血管中组织非特异性碱性磷酸酶 (TNAP) 酶活性的抑制可能与内皮细胞屏障完整性的变化有关。本研究的目的是阐明晚期脓毒症脑血管 TNAP 酶活性的改变与脑微血管功能障碍之间的联系。我们假设脑微血管中 TNAP 酶活性的破坏将与脑微血管完整性的持续丧失、神经炎症反应升高和行为缺陷相结合。对雄性小鼠进行盲肠结扎和穿刺 (CLP)，这是一种实验性败血症模型，并在败血症后长达 7 天进行评估。每天观察所有小鼠的疾病行为并进行行为测试。我们的结果表明，脓毒症小鼠的体感皮层和脊髓中的脑微血管 TNAP 酶活性显着降低，但在 CA1 和 CA3 海马区则没有。此外，我们发现脑血管 TNAP 酶活性的丧失与 claudin-5 的丧失和躯体感觉皮层血管周围 IgG 浸润的增加有关。对全脑髓样和 T 淋巴样细胞群的分析还显示浸润性白细胞持续升高，其中包括中性粒细胞和单核细胞髓源性抑制细胞 (MDSC)。对躯体感觉皮层、海马和脊髓的区域分析显示，脓毒症小鼠的皮层和脊髓中存在显着的星形胶质细胞增生和小胶质细胞增生，并伴有 CA1 和 CA3 海马区的显着小胶质细胞增生。行为缺陷的评估显示学习和记忆或诱发运动没有变化。然而，热板试验在我们的败血症小鼠中发现了一种新的抗伤害性表型，我们推测这种表型可能是脓毒症小鼠体感皮层和脊髓中持续的 GFAP 星形胶质细胞增生和 TNAP 活性丧失的结果。综上所述，这些结果表明，脓毒症晚期脑微血管中 TNAP 酶活性的丧失与持续的神经免疫功能障碍有关，这可能是在脓毒症幸存者中观察到的慢性神经功能障碍的部分原因。