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 activation 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 certain 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-FLIP in end-stage human hearts, and rat cardiomyocyte grafting models was analyzed by in situ hybridization, immunohistochemistry and TUNEL assay. In addition, to determine whether Fas-dependent pathway is active in cardiomyocytes in vitro, we examined whether activated monocytes can kill neonatal cardiomyocytes in a co-culture system.


RESULTS
c-FLIP mRNA and protein were abundantly expressed in normal cardiomyocytes from failing human heart. In animal models, c-FLIP protein was absent in TUNEL-positive grafted cardiomyocytes. Double staining demonstrated that c-FLIP-positive cells rarely had fragmented DNA, while TUNEL-positive cells rarely contained c-FLIP. Finally, activated monocytes induced death of neonatal rat cardiomyocytes via the Fas/FasL system.


CONCLUSIONS
Loss of c-FLIP expression correlates with cardiomyocyte cell death. We hypothesize that diminished c-FLIP expression may predispose cardiomyocytes to apoptotic death.
Imanishi
T
T
Division of Cardiology, Department of Medicine, Wakayama Medical College, 811-1, Kimiidera, Wakayama 641-8510, Wakayama City, Japan. imanishi@wakayama.hosp.go.jp
Murry
C E
CE
Reinecke
H
H
Hano
T
T
Nishio
I
I
Liles
W C
WC
Hofsta
L
L
Kim
K
K
O'Brien
K D
KD
Schwartz
S M
SM
Han
D K
DK
D000328:Adult; D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism*; D017690:Cell Transplantation; D018920:Coculture Techniques; D053938:DNA Fragmentation; D004285:Dogs; D004791:Enzyme Inhibitors / Q000378:metabolism; D053222:Fas Ligand Protein; D005260:Female; D015870:Gene Expression; D006333:Heart Failure / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D020287:In Situ Nick-End Labeling; D007963:Leukocytes, Mononuclear; D008213:Lymphocyte Activation; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism; D008875:Middle Aged; D023421:Models, Animal; D009206:Myocardium / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D011916:Rats, Inbred F344; D019014:fas Receptor / Q000378:metabolism
D004791:Enzyme Inhibitors; C505661:FASLG protein, human; D053222:Fas Ligand Protein; C505662:Faslg protein, rat; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D019014:fas Receptor; D020169:Caspases