Neurovascular frataxin and cognitive dysfunction in sickle cell disease

脑血管损伤，包括显性中风、伴有弥漫性白质神经轴突病变的无症状脑梗死，被认为是血管性认知障碍和痴呆（VCID）的发病机制之一。镰状细胞病（SCD）的一个重要疾病负担包括影响bbb50 %的成年患者影响记忆和执行功能，主要与白质高信号有关。镰状血红蛋白聚合引起的脑微血管闭塞导致缺氧和随后的再氧合（H/R），导致缺血性组织损伤。本提案旨在确定SCD背景下脑血管空间H/R与诱发VCID的白质高信号之间的机制联系，从而为填补VCID发病机制的知识空白创造一个原型。通过临床前小鼠SCD模型，我们发现镰状（SS）小鼠与正常（AA）小鼠相比，通过基于磁共振成像的弥散张量成像和组织病理学鉴定的微结构白质高信号明显丰富。SS小鼠的白质高强度与认知能力下降和星形胶质细胞的激活有关，星形胶质细胞是连接大脑微血管和神经元的修饰胶质细胞。Frataxin （FXN）是一种线粒体蛋白，负责铁硫聚集，调节星形胶质细胞功能，并与弗里德赖希共济失调的神经变性有关。我们的初步数据显示，在星形胶质细胞中，FXN的表达减少伴随着缺氧诱导因子-1a （HIF-1a）的增加，HIF-1a是一种在H/R事件中升高的稳态调节转录因子。最重要的科学假设是HIF-1a的升高抑制星形细胞卵黄蛋白，促进SCD中的白质损伤和VCID。在Aim 1中，我们将进行扩散张量成像和免疫荧光实验，以评估H/ r挑战的SS和AA小鼠的微结构损伤、神经元钙积累和星形胶质细胞活化。利用骨髓移植（BMT），我们将评估FXN在缺乏星形细胞FXN表达的镰状嵌合体小鼠H/R损伤后白质损伤和认知功能障碍的发展中的作用。在Aim 2中，将使用BMT生成星形胶质细胞中HIF-1a靶向缺失的镰状嵌合体小鼠。新的镰状嵌合体小鼠将用于确定HIF-1a是否对抑制FXN促进白质损伤和认知能力下降至关重要。该研究的成功完成将确定FXN作为白质保护的有希望的治疗靶点，可能有助于提供抗VCID的弹性。由于SCD中潜在的炎症和缺血往往会加速年龄相关的病理生理，本研究将为确定渐进性VCID发病机制中缺血和星形细胞功能之间的因果关系奠定基础，也有可能推广到SCD中VCID以外的常见混合性痴呆，如临床阿尔茨海默病。

Cerebrovascular injuries, including overt stroke, silent cerebral infarction involving diffused white matter neuroaxonal lesions are integrated within the pathogenesis of vascular contributions to cognitive impairment and dementia (VCID). A significant disease burden in sickle cell disease (SCD) includes cognitive decline affecting >50% of the adult patients impacting memory and executive functioning primarily associated with white matter hyperintensities. Occlusions of the cerebral microvessels due to sickle hemoglobin polymerization results in hypoxia and subsequent reoxygenation (H/R) leading to ischemic tissue damage. The present proposal, set to determine the mechanistic link between H/R within the cerebrovascular space and the white matter hyperintensities instigating VCID in SCD setting, thus create a prototype to fill the knowledge gap in the pathogenesis of VCID. Using a preclinical mouse model of SCD, we found that microstructural white matter hyperintensities, identified by magnetic resonance imaging-based diffusion tensor imaging and histopathology are substantially abundant in sickle (SS) mice compared to normal (AA) mice. The white matter hyperintensities in the SS mice were associated with cognitive decline and activation of astrocytes, the modified glial cells connecting cerebral microvasculature and the neurons. Frataxin (FXN), a mitochondrial protein responsible for iron-sulfer clustering, regulates astrocyte function and is associated with neurodegeneration in Friedreich’s ataxia. Our pilot data showed that expression of FXN is reduced in the astrocytes concomitant with an increase in hypoxia inducible factor-1a (HIF-1a), a homeostatic regulatory transcription factor that is elevated during H/R events. The overarching scientific hypothesis is that elevated HIF-1a inhibits astrocytic frataxin and promotes white matter injury and VCID in SCD. In Aim 1, we will be performing diffusion tensor imaging and immunofluorescence experiments to assess microstructural damage, neuronal calcium accumulation and astrocyte activation in H/R-challenged SS and AA mice. Using bone marrow trasplantation (BMT), we will be assessing the role of FXN in the development of white matter injury and cognitive impairment following H/R injury in the sickle chimera mice lacking expression of astrocytic FXN. In Aim 2, a sickle chimera mice with targeted deletion of HIF-1a in the astrocytes will be generated using BMT. The new sickle chimera mice will be used to determine whether HIF-1a is critical for inhibition of FXN promoting white matter injury and cognitive decline. Successful completion of the study will identify FXN as a promising therapeutic target for white matter protection that may help provide resilience against VCID. Since underlying inflammation and ischemia often accelerate age-related pathophysiology in SCD, this study will lay the foundation to identify the causal link between ischemia and astrocyte function in the pathogenesis of progressive VCID, which also has the potential to generalize beyond VCID in SCD to common mixed dementias such as clinical Alzheimer’s disease.