Cellular FLIP is expressed in cardiomyocytes and down-regulated in TUNEL-positive grafted cardiac tissues

Objective: c-FLIP is a natural homologue of caspase 8, and may antagonize a ctivation of death pathways mediated by FADD. c-FLIP is highly expressed in the heart, and a recent report suggests that c-FLIP may protect against ce rtain types of myocyte death. The present study was designed to define the expression patterns of c-FLIP in the heart. Methods: The expression pattern of c-FLlP in end-stage human hearts, and rat cardiomyocyte grafting models was analyzed by in situ hybridization, immunohistochemistry and TUNEL assa y. In addition, to determine whether Fas-dependent pathway is active in car diomyocytes in vitro, we examined whether activated monocytes can kill neon atal cardiomyocytes in a co-culture system. Results: c-FLIP mRNA and protei n were abundantly expressed in normal cardiomyocytes from failing human hea rt. In animal models, c-FLIP protein was absent in TUNEL-positive grafted c ardiomyocytes. Double staining demonstrated that c-FLIP-positive cells rare ly had fragmented DNA, while TUNEL-positive cells rarely contained c-FLIP. Finally, activated monocytes induced death of neonatal rat cardiomyocytes v ia the Fas/FasL system. Conclusions: Loss of c-FLIP expression correlates w ith cardiomyocyte cell death. We hypothesize that diminished c-FLIP express ion may predispose cardiomyocytes to apoptotic death. (C) 2000 Elsevier Sci ence B.V. All rights reserved.