Activation of Sickle Red Cell Adhesion

描述(由申请人提供)： 镰状细胞病患者的血管闭塞过程复杂，既涉及到血红蛋白S红细胞与血管内皮细胞的相互作用，也涉及到其与内皮细胞黏附的白细胞之间的相互作用。血管闭塞事件会导致儿童和成人反复出现疼痛和脑血管意外，以及其他类型的终末器官损害，包括肺动脉高压和肾功能衰竭。然而，引起SS-RBC黏附和血管闭塞的生理触发机制还知之甚少，在分子水平上阐明这些机制将有助于开发新的预防和治疗策略来消除血管闭塞事件。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)黏附中的作用。我们发现用肾上腺素等药物处理SS RBC，导致细胞内cAMP升高，诱导SS RBC与EC的黏附增加，并且这一信号通路也依赖于酪氨酸磷酸化。我们还发现SS RBC和EC之间的相互作用至少主要是由SS RBC上的黏附受体LW(ICAM-4)介导的，它与EC上的α-β3整合素结合。LW还与白细胞整合素结合。因此，我们推测，循环中SS RBC与内皮细胞和贴壁白细胞的异常黏附可能至少部分是由于体内SS RBC黏附受体的激活引起内源性cAMP上调，导致SS RBC上LW黏附受体的激活。因此，我们建议探索SS RBC与内皮细胞和白细胞黏附的分子基础。我们的具体目标是：1)研究生理性肾上腺素能激动剂在体外和体外对LW介导的SS RBC与内皮细胞黏附的影响；2)研究LW受体的激活机制；3)研究LW在SS RBC与白细胞相互作用中的可能作用。总之，这些实验将阐明LW介导的SS RBC与内皮细胞和白细胞黏附的分子机制，从而阐明生理应激和应激激素如何促进血管闭塞。

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.