STALLED CAPILLARY FLOW: A NOVEL MECHANISM FOR HYPOPERFUSION IN ALZHEIMER DISEASE

 描述(申请人提供)：阿尔茨海默病(AD)的特征是由于大脑中神经元和其他细胞的功能障碍和死亡而导致的认知功能丧失。这种细胞损伤在很大程度上是由于淀粉样β蛋白聚集体(A？)的毒性作用，它在大脑中积聚成致密的斑块。此外，脑部炎症也会增加，这是由A？聚集体应激产生的细胞产生的活性氧(ROS)介导的，这表明A？聚集体创造了一个有毒的微环境，可能会影响许多功能。在人类和动物身上的研究表明，阿尔茨海默病患者的脑血流量减少了约30%。尽管它可能导致认知障碍和疾病进展，但目前还没有出现对这种低灌注率的生理学解释。采用慢性活体双光子激发荧光显微镜观察AD模型小鼠的脑血管血流。虽然没有观察到皮质小动脉或小静脉的血流中断，但在AD小鼠模型中，平均有1.8%的皮质毛细血管血流停滞，而野生型对照组的这一比例为0.25%(p&lt；0.005)。这些毛细血管停滞出现在疾病进展的早期，在淀粉样蛋白沉积之前。由于一个停滞的毛细血管减少了几个下游血管的流量，即使是~2%的毛细血管停滞也可能对脑血流产生很大影响。事实上，当AD小鼠的白细胞被耗尽，毛细血管停顿的比例降至接近零时，脑血流量改善了约30%，这表明毛细血管停滞可能导致AD患者的脑低灌流。大约80%的毛细血管停滞是由白细胞堵塞毛细血管段引起的，这表明AD大脑中血管炎症的增加是导致毛细血管停滞的机制。这些数据提出了一个解释AD低灌注率来源的工作模型：Aü积聚导致ROS产生增加，从而给内皮细胞带来压力，并导致血管管腔上炎性受体的增加。这种血管炎症导致白细胞黏附并堵塞毛细血管，导致灌注量减少。这种血流不足可能会导致痴呆症，而不受A？的直接影响，还可能通过减少A？单体的清除而加速A？聚集。在这个方案中，我们仔细地描述了小鼠AD模型中白细胞对毛细血管的堵塞，然后检验了三个重要的假设：第一，白细胞黏附发生在血管炎症部位，这是ROS激活血管内皮细胞的结果。第二，毛细管的集体效应 Plugs的作用是大幅减少全球脑血流量，阻断白细胞黏附可以改善血流。第三，消除毛细血管堵塞和改善血流将导致认知能力的急剧改善，随着时间的推移，长期阻断毛细血管堵塞将导致淀粉样蛋白负担的减少和认知能力的长期改善。阿尔茨海默病的脑低灌流是由于毛细血管中的白细胞堵塞所致，这一假设是新颖的，并得到了初步数据的支持，并直接提出了与抗淀粉样蛋白治疗方法互补的治疗靶点。

 DESCRIPTION (provided by applicant): Alzheimer's disease (AD) is characterized by a loss of cognitive function caused by the dysfunction and death of neurons and other cells in the brain. This cell injury is largely due to the toxic effects of aggregates of amyloid-beta (Aß), whch accumulates into dense plaques in the brain. There is also increased brain inflammation, mediated by reactive oxygen species (ROS) produced by cells stressed by Aß aggregates, suggesting that Aß aggregates create a toxic microenvironment that could affect many functions. Research in humans and in animals suggests that brain blood flow is reduced in AD by ~30%. Although it likely contributes to cognitive impairment and disease progression, no physiological explanation for this hypoperfusion has emerged. Chronic in vivo two-photon excited fluorescence microscopy was used to study cerebrovascular blood flow in mouse models of AD. While no blood flow disruption in cortical arterioles or venules were observed, blood flow was found to be stalled in an average of 1.8% of cortical capillaries in mouse models of AD, as compared to 0.25% in wild type controls (p<0.005). These capillary stalls appeared early in disease progression, before any amyloid deposition. Because one stalled capillary reduces flow in several downstream vessels, even ~2% of capillaries stalled could have a large impact on brain blood flow. Indeed, when leukocytes were depleted in AD mice and the fraction of capillary stalls dropped to near zero, brain blood flow improved by ~30%, suggesting that capillary stalling may cause brain hypoperfusion in AD. About 80% of the capillary stalls were caused by leukocytes that plugged a capillary segment, suggesting increased vascular inflammation in the AD brain as the mechanism that leads to capillary stalling. These data suggest a working model to explain the origin of hypoperfusion in AD: Aß accumulation leads to increased production of ROS that stresses endothelial cells and leads to increases in inflammatory receptors on the vessel lumen. This vascular inflammation causes leukocytes to adhere and plug capillaries, resulting in decreases in perfusion. This blood flow deficit could contribute to dementia independently of the direct effects of Aß and could also accelerate Aß aggregation by decreasing clearance of Aß monomers. In this proposal, this leukocyte plugging of capillaries in mouse models of AD is carefully characterized and then three important hypotheses are tested: First, that leukocyte adhesion occurs at sites of vascular inflammation that result from endothelial activation by ROS. Second, that the collective effect of the capillary plugs is to substantially reduce global cerebral blood flow and that blocking leukocyte adhesion can improve flow. Third, that eliminating capillary plugs and improving blood flow will lead to an acute improvement in cognitive performance and that chronically blocking capillary plugging over time will lead to decreased amyloid burden and chronically improved cognitive performance. The hypothesis that brain hypoperfusion in AD is due to leukocyte plugging in capillaries is both novel and supported by preliminary data, and directly suggests therapeutic targets that are complementary to anti-amyloid approaches.