International Immunology Advance Access originally published online on December 20, 2004
International Immunology 2005 17(2):155-165; doi:10.1093/intimm/dxh196
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© 2004 The Japanese Society for Immunology
Heme-induced heme oxygenase-1 (HO-1) in human monocytes inhibits apoptosis despite caspase-3 up-regulation
1 Department of Medicine D and 2 Institute of Pathology, University of Muenster, Muenster, Germany
Correspondence to: D. Lang; E-mail: langd{at}uni-muenster.de
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.
Keywords: apoptosis, caspase-3, heme oxygenase-1, monocytes
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