Activation of Sickle Red Cell Adhesion

描述（由申请人提供）： 镰状细胞病（SCD）患者的血管闭塞过程是复杂的，涉及血红蛋白S红细胞（SS RBC）和血管内皮之间的相互作用，以及SS RBC和粘附于内皮的白细胞之间的相互作用。血管闭塞事件导致儿童和成人的复发性疼痛和脑血管意外，以及其他类型的终末器官损伤，包括肺动脉高压和肾衰竭。然而，诱导SS RBC粘附和血管闭塞的生理触发因素知之甚少，在分子水平上阐明这些机制将允许开发新的预防和治疗策略以消除血管闭塞事件。我们已经开始探索SS RBC cAMP信号转导通路在上调SS RBC与内皮细胞（EC）粘附中的作用。我们已经发现，用诸如肾上腺素的药剂处理SS RBC，导致细胞内cAMP升高，诱导增强的SS RBC粘附于EC，并且该信号传导途径也依赖于酪氨酸磷酸化。我们还表明SS RBC和EC之间的相互作用至少主要由SS RBC上的粘附受体LW（ICAM-4）介导，其结合EC上的α v-β 3整联蛋白。LW还结合白细胞整联蛋白。因此，我们推测，异常循环SS RBC粘附内皮细胞和粘附的白细胞可能至少部分是由于SS RBC粘附受体在体内激活的过程中，涉及内源性cAMP的上调，导致激活的LW粘附受体SS RBC。因此，我们建议探讨SS红细胞粘附内皮细胞和白细胞的分子基础。我们的具体目标是：1）表征已知导致cAMP增加的生理性肾上腺素能激动剂对体外和离体LW介导的SS RBC与内皮细胞粘附的影响; 2）表征LW受体活化的机制; 3）研究LW在SS RBC与白细胞相互作用中的可能作用。总的来说，这些实验将阐明LW介导的SS RBC粘附到内皮细胞和白细胞的分子机制，以及生理应激和应激激素如何导致血管闭塞。

DESCRIPTION (provided by applicant): The vaso-occlusive process in patients with sickle cell disease (SCD) is complex and involves interactions both between hemoglobin S red blood cells (SS RBC) and vascular endothelium, and between SS RBC and leukocytes adherent to endothelium. Vaso-occlusive events lead to recurrent pain and cerebrovascular accidents in both children and adults, as well as other types of end-organ damage, including pulmonary hypertension and renal failure. However, the physiologic triggers inducing SS RBC adhesion and vaso-occlusion are poorly understood, and elucidation of these mechanisms at the molecular level would allow development of new preventive and treatment strategies to abrogate vaso-occlusive events. We have begun to explore the role of SS RBC cAMP signal transduction pathways in upregulating SS RBC adhesion to endothelial cells (EC). We have found that treatment of SS RBC with agents such as epinephrine, that lead to elevation of intracellular cAMP, induced enhanced SS RBC adhesion to EC and that this signaling pathway is also dependent on tyrosine phosphorylation. We have also shown that interaction between SS RBC and EC is mediated at least primarily by the adhesion receptor LW (ICAM-4) on SS RBC, which binds to alphav-beta3 integrin on EC. LW also binds to leukocyte integrins. We therefore hypothesize that abnormal circulating SS RBC adhesion to endothelium and to adherent leukocytes may at least in part be due to SS RBC adhesion receptor activation in vivo by processes involving upregulation of endogenous cAMP, leading to activation of LW adhesion receptor on SS RBC. We propose therefore to explore the molecular basis of SS RBC adhesion to both endothelium and leukocytes. Our specific aims are 1) to characterize the effects of physiologic adrenergic agonists known to lead to increased cAMP on LW-mediated SS RBC adhesion to endothelial cells both in vitro and ex vivo; 2) to characterize the mechanism of activation of the LW receptor; and 3) to investigate the possible role of LW in the interaction of SS RBC with leukocytes. Overall, these experiments will elucidate the molecular mechanisms of LW-mediated SS RBC adhesion to endothelium and leukocytes, and thus how physiologic stress and stress hormones may contribute to vaso-occlusion.