title: Differential effects of membrane and soluble Fas ligand on cardiomyocytes: role in ischemia/reperfusion injury.
abstract: Cardiomyocyte apoptosis by Fas ligand (FasL)/Fas signaling is associated with various pathophysiological conditions, such as ischemia/reperfusion injury and congestive heart failure. In this study, we tested the hypothesis that shedding of membrane FasL is a mechanism for downregulating FasL/Fas signaling and both membrane and soluble FasL are involved in cardiomyocyte hypoxia/reoxygenation (H/R) injury. We also examined the relative importance of mitochondrial damage and direct cleavage of the executioner caspases by activated initiator caspase 8 in the propagation of FasL/Fas signaling activated by either recombinant membrane FasL or H/R. We demonstrated that in neonatal rat cardiomyocytes maintained under normal culture conditions, recombinant human soluble FasL increased caspase 3 activation by twofold but did not reduce cell viability. In contrast, infection with a recombinant adenoviral vector expressing the non-cleavable human FasL (Ad2/nchFasL) resulted in cardiomyocyte death that was attenuated by soluble FasL. H/R increased the mRNA levels of both FasL and Fas and activated caspases 8, 9 and 3, indicating the activation of FasL/Fas signaling. Z-IETD.fmk and Z-LEHD.fmk, selective inhibitors for caspases 8 and 9, respectively, abolished caspase 3 activation induced by Ad2/nchFasL or H/R. Z-IETD.fmk also significantly reduced Ad2/nchFasL- or H/R-induced cardiomyocyte death. H/R potentiated membrane FasL-induced cell death. These results suggest that shedding of membrane FasL downregulates FasL/Fas signaling in cardiomyocytes and both membrane and soluble FasL contribute to H/R injury. Activation of FasL/Fas signaling by either recombinant membrane FasL under normal culture conditions or H/R causes cardiomyocyte death mainly through the mitochondrial damage/caspase 9 activation pathway.
authors.affiliation: Genzyme Corporation, 31 New York Avenue, Framingham, MA 01701-9322, USA.
authors.forename: Taro
authors.initials: T
authors.lastname: Date
authors.forename: Seibu
authors.initials: S
authors.lastname: Mochizuki
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Belanger
authors.forename: Midori
authors.initials: M
authors.lastname: Yamakawa
authors.forename: Zhengyu
authors.initials: Z
authors.lastname: Luo
authors.forename: Karen A
authors.initials: KA
authors.lastname: Vincent
authors.forename: Seng H
authors.initials: SH
authors.lastname: Cheng
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Gregory
authors.forename: Canwen
authors.initials: C
authors.lastname: Jiang
mesh_terms: D000818:Animals; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D053222:Fas Ligand Protein; D006801:Humans; D000860:Hypoxia / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000378:metabolism*; D051381:Rats; D015427:Reperfusion Injury / Q000378:metabolism*
chemical_list: C505661:FASLG protein, human; D053222:Fas Ligand Protein; C505662:Faslg protein, rat; D008562:Membrane Glycoproteins; C506433:CASP9 protein, human; C506435:Casp9 protein, rat; D053453:Caspase 9; D020169:Caspases