TNF-alpha in vivo stimulates apoptosis in fibroblasts through caspase-8 activation and modulates the expression of pro-apoptotic genes.
Apoptosis of matrix producing cells is common among many inflammatory diseases. The goal of the present study was to examine the apoptotic effects of tumor necrosis factor-alpha (TNF-alpha) on fibroblastic cells in vivo and to investigate the role of different caspases in this process. This was accomplished in vivo by subcutaneous injection of TNF-alpha in mice. The direct effects of TNF-alpha on fibroblast apoptosis were studied in vitro with normal diploid human fibroblasts. The results indicate that TNF-alpha in vivo induces apoptosis of fibroblasts. By RNase protection assay, we demonstrated that TNF-alpha stimulates expression of 12 apoptotic genes. Fluorometric studies demonstrated that TNF-alpha in vivo predominantly increased caspase-8 and -3 activity and by use of specific inhibitors, the activation of caspase-3 was shown to be initiated by caspase-8 with only a minor contribution from caspase-9. Thus, TNF-alpha acts to modulate the expression of many genes that favors apoptosis of fibroblastic cells, which is dependent mostly upon signaling through caspase-8.
Alikhani
Mani
M
Department of Periodontology and Oral Biology, Boston University School of Dental Medicine, Boston, Massachusetts 02118, USA.
Alikhani
Zoubin
Z
Raptis
Markos
M
Graves
Dana T
DT
D000375:Aging / Q000502:physiology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics*; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D014409:Tumor Necrosis Factor-alpha; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; C505409:Casp3 protein, mouse; C505526:Casp8 protein, mouse; C506434:Casp9 protein, mouse; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases