Erythrocyte NADPH oxidase activity modulated by Rac GTPases, PKC, and plasma cytokines contributes to oxidative stress in sickle cell disease.
Chronic inflammation has emerged as an important pathogenic mechanism in sickle cell disease (SCD). One component of this inflammatory response is oxidant stress mediated by reactive oxygen species (ROS) generated by leukocytes, endothelial cells, plasma enzymes, and sickle red blood cells (RBC). Sickle RBC ROS generation has been attributed to sickle hemoglobin auto-oxidation and Fenton chemistry reactions catalyzed by denatured heme moieties bound to the RBC membrane. In this study, we demonstrate that a significant part of ROS production in sickle cells is mediated enzymatically by NADPH oxidase, which is regulated by protein kinase C, Rac GTPase, and intracellular Ca(2+) signaling within the sickle RBC. Moreover, plasma from patients with SCD and isolated cytokines, such as transforming growth factor β1 and endothelin-1, enhance RBC NADPH oxidase activity and increase ROS generation. ROS-mediated damage to RBC membrane components is known to contribute to erythrocyte rigidity and fragility in SCD. Erythrocyte ROS generation, hemolysis, vaso-occlusion, and the inflammatory response to tissue damage may therefore act in a positive-feedback loop to drive the pathophysiology of sickle cell disease. These findings suggest a novel pathogenic mechanism in SCD and may offer new therapeutic targets to counteract inflammation and RBC rigidity and fragility in SCD.
Texas Children's Hematology Center, Texas Children's Hospital, Houston, TX 77030, USA. axgeorge@txch.org
Alex
A
George
Suvarnamala
S
Pushkaran
Diamantis G
DG
Konstantinidis
Sebastian
S
Koochaki
Punam
P
Malik
Narla
N
Mohandas
Yi
Y
Zheng
Clinton H
CH
Joiner
Theodosia A
TA
Kalfa
D000755:Anemia, Sickle Cell / Q000097:blood / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000494:pharmacology; D016922:Cellular Senescence / Q000187:drug effects / Q000502:physiology; D002648:Child; D016207:Cytokines / Q000097:blood / Q000378:metabolism / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D004912:Erythrocytes / Q000201:enzymology* / Q000473:pathology / Q000502:physiology; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D008954:Models, Biological; D019255:NADPH Oxidases / Q000378:metabolism / Q000502:physiology*; D018384:Oxidative Stress / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism / Q000494:pharmacology; D020744:rac GTP-Binding Proteins / Q000378:metabolism*
D016207:Cytokines; D007527:Isoenzymes; D017382:Reactive Oxygen Species; D019255:NADPH Oxidases; D011493:Protein Kinase C; D020744:rac GTP-Binding Proteins; D002118:Calcium