Inflammatory mediators are perpetuated in macrophages resistant to apoptosis induced by hypoxia.
A hypoxic/anoxic microenvironment has been proposed to exist within a vascular lesion due to intimal or medial cell proliferation in vascular diseases. Here, we examined whether hypoxia alters macrophage function by exposing murine macrophage-like RAW 264.7 (RAW) cells to hypoxia (2% O2). When cells were exposed to hypoxia, a significant number of RAW cells underwent apoptosis. Additionally, small subpopulations of RAW cells were resistant to hypoxia-induced apoptosis. Through repeated cycles of hypoxia exposure, hypoxia-induced apoptosis-resistant macrophages (HARMs) were selected; HARM cells demonstrate >70% resistance to hypoxia-induced apoptosis, as compared with the parental RAW cells. When heat shock protein (HSP) expression was examined after hypoxia, we observed a significant decrease in constitutive heat shock protein 70 (HSC 70) in RAW cells, but not in HARMs, as compared with the control normoxic condition (21% O2). In contrast, the expression level of glucose-regulated protein 78 (GRP 78) in RAW and HARM cells after hypoxia treatment was not altered, suggesting that HSC 70 and not GRP 78 may play a role in protection against hypoxia-induced apoptosis. When tumor necrosis factor alpha (TNF-alpha) production was examined after hypoxic treatment, a significant increase in TNF-alpha production in HARM but decrease in RAW was observed, as compared with cells cultured in normoxic conditions. HARM cells also exhibit a much lower level of modified-LDL uptake than do RAW cells, suggesting that HARMs may not transform into foam cells. These results suggest that a selective population of macrophages may adapt to potentially pathological hypoxic conditions by overcoming the apoptotic signal.
Yun
J K
JK
Molecular Cardiovascular Research Center, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, OH 44106-4958, USA.
McCormick
T S
TS
Villabona
C
C
Judware
R R
RR
Espinosa
M B
MB
Lapetina
E G
EG
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D015687:Cell Hypoxia / Q000502:physiology*; D002460:Cell Line; D000091342:Endoplasmic Reticulum Chaperone BiP; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins; D018836:Inflammation Mediators / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism; D008264:Macrophages / Q000166:cytology* / Q000378:metabolism*; D051379:Mice; D018613:Microscopy, Confocal; D018832:Molecular Chaperones / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C494372:Hspa8 protein, mouse; D018836:Inflammation Mediators; D008077:Lipoproteins, LDL; D018832:Molecular Chaperones; D014409:Tumor Necrosis Factor-alpha