Heme-induced heme oxygenase-1 (HO-1) in human monocytes inhibits apoptosis despite caspase-3 up-regulation.
Monocyte activation, apoptosis and differentiation are hallmarks of most inflammatory vascular disorders. We studied the effects of heme oxygenase-1 (HO-1) induced by its substrate hemin on apoptosis, caspase-3 expression and the differentiation of freshly isolated human monocytes. Hemin induced HO-1 in a dose- and time-dependent fashion as measured by semi-quantitative RT-PCR and flow cytometry. Apoptosis was markedly suppressed by hemin in cells rendered apoptotic by serum deprivation or dexamethasone as determined by flow cytometric detection of annexin V binding or transmission electron microscopy (TEM). The specific HO-1 inhibitor zinc protoporphyrin (ZnPP) reversed the effects of hemin on monocyte apoptosis and diminished cell lifespan. Surprisingly, the cytoprotective effects of hemin were positively correlated with caspase-3 up-regulation. Hemin-induced apoptosis suppression was enhanced by the caspase-3 inhibitor DEVD-CHO, indicating that caspase-3 was active in a pro-apoptotic fashion. Hemin inhibited CD95 as a putative cytoprotective mechanism. Morphological studies and detection of CD86 showed that monocytes differentiated into macrophages in response to hemin after relatively long incubation times, a phenomenon that might be provoked by caspase-3-regulated pathways. Our results confirm a similar cytoprotective effect of hemin/HO-1 for monocytes as has been shown for other cells, despite caspase-3 up-regulation. The fact that HO-1 may adversely affect monocyte survival and differentiation could be of particular significance in future therapies for occlusive vascular diseases or transplant rejection.
Lang
Detlef
D
Department of Medicine D, University of Muenster, Germany. langd@uni-muenster.de
Reuter
Stefan
S
Buzescu
Tania
T
August
Christian
C
Heidenreich
Stefan
S
D015703:Antigens, CD / Q000032:analysis / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051940:B7-2 Antigen; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002478:Cells, Cultured; D006419:Heme Oxygenase (Decyclizing) / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D051547:Heme Oxygenase-1; D006427:Hemin / Q000494:pharmacology / Q000502:physiology*; D006801:Humans; D008562:Membrane Glycoproteins / Q000032:analysis / Q000378:metabolism; D008565:Membrane Proteins; D009000:Monocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis / Q000378:metabolism; D015854:Up-Regulation; D019014:fas Receptor / Q000032:analysis / Q000378:metabolism
D015703:Antigens, CD; D051940:B7-2 Antigen; C497964:CD86 protein, human; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D019014:fas Receptor; D006427:Hemin; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases