Retinal endothelial cell apoptosis stimulates recruitment of endothelial progenitor cells.
OBJECTIVE
Bone marrow-derived endothelial progenitor cells (EPCs) contribute to vascular repair although it is uncertain how local endothelial cell apoptosis influences their reparative function. This study was conducted to determine how the presence of apoptotic bodies at sites of endothelial damage may influence participation of EPCs in retinal microvascular repair.


METHODS
Microlesions of apoptotic cell death were created in monolayers of retinal microvascular endothelial cells (RMECs) by using the photodynamic drug verteporfin. The adhesion of early-EPCs to these lesions was studied before detachment of the apoptotic cells or after their removal from the wound site. Apoptotic bodies were fed to normal RMECs and mRNA levels for adhesion molecules were analyzed.


RESULTS
Endothelial lesions where apoptotic bodies were left attached at the wound site showed a fivefold enhancement in EPC recruitment (P < 0.05) compared with lesions where the apoptotic cells had been removed. In intact RMEC monolayers exposed to apoptotic bodies, expression of ICAM, VCAM, and E-selectin was upregulated by 5- to 15-fold (P < 0.05-0.001). EPCs showed a characteristic chemotactic response (P < 0.05) to conditioned medium obtained from apoptotic bodies, whereas analysis of the medium showed significantly increased levels of VEGF, IL-8, IL-6, and TNF-alpha when compared to control medium; SDF-1 remained unchanged.


CONCLUSIONS
The data indicate that apoptotic bodies derived from retinal capillary endothelium mediate release of proangiogenic cytokines and chemokines and induce adhesion molecule expression in a manner that facilitates EPC recruitment.
Bhatwadekar
Ashay D
AD
Centre for Vision Science, Queen's University Belfast, Royal Victoria Hospital, Belfast, Northern Ireland, United Kingdom.
Glenn
Josephine V
JV
Curtis
Tim M
TM
Grant
Maria B
MB
Stitt
Alan W
AW
Gardiner
Tom A
TA
D000818:Animals; D017209:Apoptosis; D002196:Capillaries / Q000166:cytology; D002417:Cattle; D002448:Cell Adhesion / Q000502:physiology; D002465:Cell Movement / Q000502:physiology*; D002478:Cells, Cultured; D002633:Chemotaxis / Q000502:physiology; D016207:Cytokines / Q000378:metabolism; D019040:E-Selectin / Q000235:genetics / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology*; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D019084:Fluorescent Antibody Technique, Indirect; D018799:Intercellular Adhesion Molecule-1 / Q000235:genetics / Q000378:metabolism; D017319:Photosensitizing Agents / Q000633:toxicity; D011166:Porphyrins / Q000633:toxicity; D012333:RNA, Messenger / Q000378:metabolism; D012171:Retinal Vessels / Q000166:cytology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013234:Stem Cells / Q000502:physiology*; D015854:Up-Regulation; D019010:Vascular Cell Adhesion Molecule-1 / Q000235:genetics / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D000077362:Verteporfin; D014945:Wound Healing / Q000502:physiology
D016207:Cytokines; D019040:E-Selectin; D017319:Photosensitizing Agents; D011166:Porphyrins; D012333:RNA, Messenger; D019010:Vascular Cell Adhesion Molecule-1; D042461:Vascular Endothelial Growth Factor A; D000077362:Verteporfin; D018799:Intercellular Adhesion Molecule-1