Comparison of mechanisms of anemia in mice with sickle cell disease and beta-thalassemia: peripheral destruction, ineffective erythropoiesis, and phospholipid scramblase-mediated phosphatidylserine exposure.
OBJECTIVE
1). To study the mechanisms of anemia, erythroid hyperplasia, and red blood cell (RBC) clearance in murine models of sickle cell disease (Sickle) and beta-thalassemia (Th1/Th1); 2) To determine the contribution of the phospholipid scramblase enzyme to phosphatidylserine (PS) exposure and RBC death in Sickle and Th1/Th1 mice.


METHODS
We used a combination of flow-cytometric analysis and assays for phospholipid remodeling to determine the extent and sites of erythroid hyperplasia, PS exposure, and cell death.


RESULTS
1) Sickle RBCs have a much shorter half-life than Th1/Th1 RBCs (0.8 days vs. 11 days). A significant proportion of Th1/Th1 peripheral reticulocytes mature into erythrocytes, however, approximately fivefold fewer Sickle reticulocytes mature. While erythroid hyperplasia exists in both Sickle and Th1/Th1 mice, Th1/Th1 produce fourfold more RBCs than necessary to maintain steady state, while Sickle produce no excess RBCs. 2) 61% of Sickle and 34% of Th1/Th1 RBCs are scramblase(+) as measured by internalization assays of the fluorescent phospholipid NBD-PC. The majority of NBD-PC(+) RBCs are also annexin-V(+), supporting a mechanistic link between scramblase activity and PS exposure. A proportion of both reticulocytes and older RBCs in Sickle and Th1/Th1 mice have active scramblase, and the degree of scramblase activation in these strains correlates with the propensity for RBC death.


CONCLUSIONS
Sickle and Th1/Th1 mice are both anemic, with significant erythroid hyperplasia. Th1/Th1 mice display ineffective erythropoiesis while Sickle mice show rapid peripheral destruction of RBCs. PS exposure and phospholipid scramblase activity serve as markers of RBCs with altered phospholipid asymmetry and greater propensity for cell death.
Kean
Leslie S
LS
Division of Hematology, Oncology, Blood and Marrow Transplantation, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA 30303, USA.
Brown
Laura E
LE
Nichols
J Wylie
JW
Mohandas
Narla
N
Archer
David R
DR
Hsu
Lewis L
LL
D000755:Anemia, Sickle Cell / Q000097:blood* / Q000473:pathology; D000818:Animals; D019921:Biotinylation; D017301:Ca(2+) Mg(2+)-ATPase / Q000097:blood; D002352:Carrier Proteins / Q000097:blood*; D004195:Disease Models, Animal; D004912:Erythrocytes / Q000502:physiology*; D004920:Erythropoiesis; D006207:Half-Life; D008563:Membrane Lipids / Q000097:blood; D008565:Membrane Proteins / Q000097:blood*; D051379:Mice; D008810:Mice, Inbred C57BL; D010718:Phosphatidylserines / Q000097:blood*; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids / Q000097:blood*; D017086:beta-Thalassemia / Q000097:blood* / Q000473:pathology
D002352:Carrier Proteins; D008563:Membrane Lipids; D008565:Membrane Proteins; D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; D017301:Ca(2+) Mg(2+)-ATPase