Erythrophagocytosis by angiogenic endothelial cells is enhanced by loss of erythrocyte deformability.
OBJECTIVE
Angiogenic endothelial cells can function as phagocytes, and phagocytosis is initiated via the opsonin lactadherin. In this study, we examined the interaction between lactadherin-opsonized erythrocytes with reduced deformability and angiogenic endothelium, as loss of deformability is characteristic for suicidal and aged erythrocytes.


METHODS
We used the Arg-Gly-Asp (RGD)-modified erythrocyte model and investigated the deformability parameter by cross-linking erythrocyte membranes through treatment with glutaraldehyde. Association in vitro with primary endothelial cells was detected by flow cytometry and visualized by light, fluorescent, and electron microscopy. Involvement of two crucial factors in phagocytosis, alpha(v)-integrins and Rho guanosine triphosphatase family member Rac1, was studied using small interfering RNA technology. Modified erythrocytes were administered in vivo into tumor-bearing mice to detect phagocytosis by endothelial cells.


RESULTS
Glutaraldehyde-treated (rigid) RGD-modified erythrocytes showed a strongly enhanced endothelial cell association compared to flexible RGD-modified erythrocytes. Knockdown by small interfering RNA lipoplexes of alpha(v)-integrins and Rac1 confirmed classical tethering and internalization of rigid RGD-erythrocytes. Upon in vivo administration, tumor endothelium showed pronounced erythrophagocytosis.


CONCLUSIONS
The pronounced phagocytosis of opsonized erythrocytes with reduced deformability by angiogenic growth factor-activated endothelial cells evokes new insights in endothelial cell function and suggests a role for these endothelial cells in (hematological) disorders because of their capacity to clear disordered erythrocytes.
Department of Pharmaceutics, Utrecht Institute for Pharmaceutical Sciences (UIPS), Utrecht University, Utrecht, The Netherlands.
Marcel H A M
MH
Fens
Gert
G
Storm
Ralf C M
RC
Pelgrim
Anton
A
Ultee
Annette T
AT
Byrne
Carlo A
CA
Gaillard
Wouter W
WW
van Solinge
Raymond M
RM
Schiffelers
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000502:physiology*; D004730:Endothelium, Vascular / Q000502:physiology*; D004907:Erythrocyte Deformability; D004912:Erythrocytes / Q000187:drug effects / Q000502:physiology*; D005434:Flow Cytometry; D005976:Glutaral / Q000494:pharmacology; D006801:Humans; D039001:Integrin alpha Chains / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008855:Microscopy, Electron, Scanning; D009389:Neovascularization, Pathologic; D009842:Oligopeptides / Q000494:pharmacology; D010587:Phagocytosis; D013499:Surface Properties; D020830:rac1 GTP-Binding Protein / Q000378:metabolism
D000970:Antineoplastic Agents; D039001:Integrin alpha Chains; D009842:Oligopeptides; C047981:arginyl-glycyl-aspartic acid; D020830:rac1 GTP-Binding Protein; D005976:Glutaral