脑缺血缺氧的病理生理及研究进展

脑缺血缺氧的病理生理及研究进展,脑的重量： 占全身体重的2%-3%脑的血流量： 占全身血流量15-20%脑的氧糖耗量：占全身的20-25， 且几乎无氧糖储备,概 述,脑血管的入颅路径,颈内动脉系统 internal carotid artery system,眼动脉 optic artery 大脑前动脉 anterior cerebral artery 前交通动脉 anterior communication artery 大脑中动脉 middle cerebral artery 后交通动脉 posterior communication artery 脉络膜前动脉 anterior choroidal artery,主要供应: 眼及以下组织 额叶 frontal lobe 顶叶 parietal lobe 颞叶 temporal lobe 基底节 basal ganglion,概念: 血液由脑血管内逸出，称为脑出血。 内出血血液进入器官、组织或体腔。 外出血血液流出体外。,概念： 颈动脉或椎动脉系统-过性供血不足，导致供血区的局灶性神经功能障碍，出现相应的症状及体征。 特点： 一般症状在5分钟内即达高峰，一次发作常持续5-20分钟，最长不超过24小时，但可反复发作。,transient ischemic attack ,TIA,短暂性脑缺血发作,在脑血管腔内，血液发生凝固或血液中某些成分凝集形成的固体质块称为脑血栓。,脑 血 栓 cerebral thrombosis,概念:,“半暗带”缺血区,梗死灶,梗死灶中心坏死区周围可恢复的部分血流灌注区。,脑梗,脑水肿,脑缺血性病变的病理分期,超早期（16小时）：病变脑组织变化不明显，可见部分血管内皮细胞、神经细胞及星形胶质细胞肿胀，线粒体肿胀空化；急性期（624小时）：缺血区脑组织苍白和轻度肿胀，神经细胞、胶质细胞及内皮细胞呈明显缺血改变；,坏死期（2448小时）：大量神经细胞消失，胶质细胞坏变，中性粒细胞、淋巴细胞及巨噬细胞浸润，脑组织明显水肿；软化期（3天3周）：病变区液化变软；恢复期（34周后）：液化坏死脑组织被格子细胞清除，脑组织萎缩，小病灶形成胶质瘢痕，大病灶形成中风囊，此期持续数月至2年。,脑缺血性病变的病理分期,脑缺血时间 脑组织对缺血缺氧非常敏感，阻断血流30秒钟脑代谢即发生改变，1分钟后神经元功能活动停止，脑动脉闭塞导致缺血超过5分钟可发生脑梗死。脑缺血程度 缺血后神经元损伤具有选择性，轻度缺血时仅有某些神经元丧失，完全持久缺血时缺血区各种神经元、胶质细胞及内皮细胞均坏死。,脑缺血/缺氧的病理生理,急性脑梗死病灶由中心坏死区及周围的缺血半暗带组成。坏死区由于完全性缺血导致脑细胞死亡，但缺血半暗带仍存在侧枝循环，可获得部分血液供应，尚有大量可存活的神经元，如果血流迅速恢复使脑代谢改善，损伤仍然可逆，神经细胞仍可存活并恢复功能。因此，保护这些可逆性损伤神经元是急性脑梗死治疗的关键。,脑缺血/缺氧的病理生理,脑梗死区血流再通后氧与葡萄糖供应及脑代谢恢复，脑组织损伤理应得到恢复。然而，实际上并非如此，这是因为存在有效时间即再灌注时间窗。如果脑血流再通超过此时间窗时限，脑损伤可继续加剧，产生再灌注损伤。研究证实，脑缺血超早期治疗时间窗为6小时之内。缺血半暗带和再灌注损伤概念的提出，更新了急性脑梗死的临床治疗观念，抢救缺血半暗带的关键是超早期溶栓治疗，减轻再灌注损伤核心是积极采取脑保护措施。,脑缺血/缺氧的病理生理,低氧诱导因子的作用,存在时间短； 高度化学活泼性； 氧化性强。,自由基的特性 （property of free radicals）,自由基分类 氧自由基 oxygen free radical 脂性自由基 lipid radicals 氮中心自由基 reactive nitrogen species,白细胞呼吸爆发产生大量氧自由基, 膜脂质过氧化增强 lipid peroxidation生物膜是自由基攻击主要部位脂肪酸、芳香环的不饱和键 OFR (ROS） 脂质过氧化 细胞膜结构损伤和破坏,a physiological balance between ROS production and elimination, 线粒体自噬 mitophagy,Molecular mechanisms regulating mitophagy. Increases in cellular ROS lead to loss of mitochondrial membrane potential (DCm) which, in turn, signals for mitochondrial fragmentation (fission) and delivery to autophagosomes (mitophagy). Two pathways have been proposed to mediate this process: PINK1 recruits the E3 ligase parkin to damaged mitochondria, which then mediates mitochondrial fragmentation and subsequent targeting to autophagosomes in a process that involves ubiquitination of VDAC and binding to p62. Then p62 targets this complex to autophagosomes by interacting with the autophagic protein LC3. Alternatively, NIX, localized to the mitochondrial outer membrane, interacts directly with GABARAP or LC3 upon decrease of DCm, and thereby mediates the recruitment of damaged mitochondria to autophagosomes. Trends in Biochemical Sciences January 2011, Vol. 36.,primary hepatocytes,28 JANUARY 2011 VOL 331 SCIENCE ,murine liver lysates,Red, mitochondria; blue, cytoplasm; green, nuclei,低氧诱导因子的作用,Ca 2+的稳态调节,低氧诱导因子的作用,Figure 1 Chronology of blood circulation and cerebral expression of cytokines, lymphocyte infiltrationand brain infarct growth after mild to moderate brain ischemia. Treg cells prevent delayed lesionexpansion in an IL-10dependent manner. They also temper the proinflammatory cytokine burststarting early time points after ischemia. Injection of IL-10 in the brain reduces infarct volume. TNF-, tumor necrosis factor-; IFN-, interferon-. Regulatory T cells protect the brain after strokeVOLUME 15 NUMBER 2 FEBRUARY 2009 NATURE MEDICINE,（二） 调节性T细胞的作用（role of regulatory T cells）,Treg cells reduce the early invasion of neutrophils into the brain and the activation of invading T cells(a,b) Topographic map of five accumulated brain sections and representative histological section 24 h after MCAO showing myeloperoxidase-positive (MPO+) neutrophilic granulocytes predominantlylocated in the necrotic area and the border of the ischemic zone.(c,d) Topographic map and representative histological section of CD3+ T lymphocytes invadingthe ischemic brain 5 d after MCAO.(e) Immunohistochemical sections showing Treg cells predominantly in the peri-infarct area.Arrows indicate Foxp3+ Treg cells.,Ipsilateral,Contralateral,Microglia are activated after ischemia, are the main source of cerebral TNF-a and are more abundant in brains of Treg celldepleted mice.Statistical analysis of counted IBA-1+ cells in ipsilateral and contralateral regions in control (PBS) and Treg celldepleted mice (anti-CD25) at 24 h and 5 d after MCAO induction. *P 0.01.,低氧诱导因子的作用,64,一系列生化改变,缺血/缺氧,细胞能量储备耗竭,Na+/K+泵衰竭,酸中毒,细胞膜去极化,电压控制钙通道开放,谷氨酸释放,细胞内Ca2+浓度升高,激活,脂酶,NMDA，AMPA及代谢性受体激活,NO合成酶,NO,自由基生成,蛋白酶,核酸内切酶,细胞死亡,再灌注,A,B,C,D,图例:A: 钙离子拮抗剂B: 谷氨酸释放抑制剂C :NMDA及非NMDA受体拮抗剂D: 自由基清除剂,低氧诱导因子的作用,低氧诱导因子的作用(role of hypoxia-inducibe factor),Before HIF-1 was found, HRE had been identified in the 3-enhancer region of the erythropoietin gene, whose transcription is up-regulated by more than 100-fold by severe hypoxia. Semenza and Wang defined a binding site critical for the hypoxia-inducible function, which involves a transcription factor induced by hypoxia.,DISCOVERY OF HIF-1,STRUCTURE OF HIF-1,Fig. 2. Structures of the Hif1 gene and HIF-1 protein. The Hif1 gene is composed of 15 exons and 14 introns. HIF-1 protein possesses a basic helix-loop-helix (bHLH) and a PER-ARNT-SIM (PAS) domain, which are involved in HRE-binding and dimerization with ARNT. Its C-terminal contains two transacting domains (TAD) and a nuclear localization signal (NLS). The oxygen-dependent degradation domain (ODDD) contains two proline residues (P402 and P564), targeted by prolyl hydroxylases, and a lysine residue (K532), targeted by ARD1 acetyl transferase.,Correlated background,HIF-1 (hypoxia-inducible factor-1) pVHL (von Hippel-Lindau) EGLN (Egl-nine: egg laying nine) Semenza and Wang (1992) identified originally HIF-1 by its binding to a hypoxia response element in the human (EPO) gene. Maxwell et al. (1999) were the first to show that ubiquitination and proteasomal degradation of HIF-1 requires the pVHL, the substrate recognition subunit for an E3 ubiquitin ligase. Ivan et al. and Jaakkola et al. ( 2001) two laboratories simultaneously reported that oxygen-dependent hydroxylation of a conserved proline residue in HIF-1 was critical for mediating its interaction with pVHL. Epstein et al.(2001) identified the HIF prolyl hydroxylase in C. elegans and provided evidence for a related family of enzymes in humans: EGLN1, EGLN2, EGLN3,Figure 1. Simplified schematic modelof oxygen sensing and HIF regulation.Under hypoxic conditions, HIF-1 isstabilized, undergoes modifications,translocates into the nucleus, recruitscofactors, and activates gene expression.Under normoxic conditions, theODD domain of HIF-1 is hydroxylatedby oxygen-dependent prolyl hydroxylases(targeting HIF-1 forpVHL-mediated proteolytic destruction)and the carboxyl-terminal TAdomain is hydroxylated by an oxygendependentasparaginyl hydroxylase(blocking the interaction with theCBP/p300 coactivator). For details.see text. bHLH, basic helix-loop-helix;HBS, HIF-1 binding site; HRE, hypoxiaresponse element; ODD, oxygen-dependentdegradation; OH, hydroxylation;P, phosphorylation; PAS, Per-AhR/ARNT-SIM; TA trans-activation;Ub, ubiquitin.CELLULAR ADAPTATION,治 疗,病因治疗药物治疗外科治疗,病因治疗控制血压；降低