title: Hyperoxia-induced immature brain injury through the TLR4 signaling pathway in newborn mice.
abstract: Toll-like receptor 4 (TLR4), a pathogen-associated molecular pattern receptor, is known to initiate an inflammatory cascade in response to certain stimuli within the central nervous system (CNS). Although TLR4 activation is known to be a first-line response of the innate immune system, whether and how hyperoxia influences TLR4 signaling in an immature brain remains unclear. In this study, TLR4 wild-type (W) and TLR4 knock-out(M) mice were exposed to 100% oxygen (the WO2 and MO2 groups, respectively), and control groups were exposed to ambient air (the WA and MA groups, respectively) for 48 h after postnatal-day (PND) 3. Next, neuronal apoptosis was quantified, and Morris water maze assays were conducted. The WO2 mice showed increased TLR4 expression compared with the WA mice, additionally, the expression level of Tumor Necrosis Factor-α (TNF-α) in the WO2 mice was significantly increased compared with the levels in the WA, MA and MO2 mice. Electron microscopy and terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) assays showed a significant increase, compared to the WO2 mice, in neuronal apoptosis within the prefrontal cortex and hippocampal CA1 region in the WO2 mice. In contrast, there were no obvious differences in neuronal apoptosis between the MO2 and MA groups. The results of the Morris water maze tests demonstrated marked deficits in learning and memory in the WO2 mice but much milder deficits in the MO2 mice compared to the WA and MA groups, respectively. Moreover, cultured N9 (TLR4 wild-type, derived from ICR/CD1 mice) microglia exposed to hyperoxia showed an immediate increase in the expression of TLR4 mRNA, followed by an increase in the expression of both TNF-α and reactive oxygen species (ROS), but this increase was abrogated by the loss of TLR4 signaling in TLR4-knockout microglia (primary cells from a C3H/HeJ strain defective in TLR4). Taken together, these data suggest that 1) TLR4 signaling is involved in hyperoxia-induced immune responses in the immature brain and 2) the loss of TLR4 activation may abrogate the neuronal apoptosis and cognitive deficits following hyperoxia exposure in newborn mice.
authors: Department of Anesthesiology, Children׳s Hospital of Chongqing Medical University, Ministry of Education Key Laboratory of Child Development and Disorders, Key Laboratory of Pediatrics in Chongqing, Chongqing International Science and Technology Cooperation Center for Child Development and Disorders, Chongqing, China; Department of Anesthesiology, Sichuan Academy of Medical Sciences & Sichuan Provincial People׳s Hospital, Chengdu City, China. Electronic address: yang861104@163.com.
authors: Yang
authors: Y
authors: Liu
authors: Department of Forensic Medicine, College of Basic Medicine, Chongqing Medical University, Chongqing, China.
authors: Pu
authors: P
authors: Jiang
authors: Department of Anesthesiology, Children׳s Hospital of Chongqing Medical University, Ministry of Education Key Laboratory of Child Development and Disorders, Key Laboratory of Pediatrics in Chongqing, Chongqing International Science and Technology Cooperation Center for Child Development and Disorders, Chongqing, China.
authors: Min
authors: M
authors: Du
authors: Department of Forensic Medicine, College of Basic Medicine, Chongqing Medical University, Chongqing, China.
authors: Kun
authors: K
authors: Chen
authors: The Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030 United States.
authors: Amber
authors: A
authors: Chen
authors: School of Public Health, University of California, Berkeley, CA 94720 United States.
authors: Yang
authors: Y
authors: Wang
authors: Department of Anesthesiology and Pain Medicine, Tongji Hospital, Wuhan 430032, China.
authors: Fei
authors: F
authors: Cao
authors: Department of Forensic Medicine, College of Basic Medicine, Chongqing Medical University, Chongqing, China.
authors: Shixiong
authors: S
authors: Deng
authors: Department of Anesthesiology, Children׳s Hospital of Chongqing Medical University, Ministry of Education Key Laboratory of Child Development and Disorders, Key Laboratory of Pediatrics in Chongqing, Chongqing International Science and Technology Cooperation Center for Child Development and Disorders, Chongqing, China. Electronic address: xuyingxy3066@126.com.
authors: Ying
authors: Y
authors: Xu
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000502:physiology; D001921:Brain / Q000254:growth & development* / Q000473:pathology / Q000503:physiopathology*; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D004195:Disease Models, Animal; D018496:Hyperoxia / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D007859:Learning Disabilities / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D018782:Maze Learning / Q000502:physiology; D008569:Memory Disorders / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008813:Mice, Inbred ICR; D018345:Mice, Knockout; D017628:Microglia / Q000473:pathology / Q000502:physiology; D009474:Neurons / Q000473:pathology / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D011897:Random Allocation; D017382:Reactive Oxygen Species / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D016207:Cytokines; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha
keywords: Hyperoxia; Immature brain injury; Microglia; Newborn mice; Toll-like receptor 4 (TLR4)