Caspase activation is not required for villous cytotrophoblast fusion into syncytiotrophoblasts.
The villous trophoblast renews itself by fusion of individual stem cells (cytotrophoblasts, CT) with a functional syncytium (syncytiotrophoblast, ST). The literature indicates that fusion occurs with limited activation (proteolytic cleavage) of caspase-8 in CT and is inhibited either by blocking caspase-8 synthesis or inhibiting activation with a caspase-8-specific inhibitor, zIETD. We challenge part of this evidence: inhibition of differentiation with caspase-8 inhibitors. Br-cAMP-stimulated differentiation of isolated CT into multinucleated syncytia in culture is not blocked with three different low molecular weight inhibitors of caspase-8: broad caspase inhibitors zVAD-fmk and qVD-OPh and the caspase-8-specific inhibitor zIETD-fmk. Syncytialization was determined by desmoplakin staining of intracellular boundaries surrounding >2 nuclei and by diffusion within fused cells of long-lived cytoplasmic staining from half of original CT to the unstained half. Differentiation of isolated CT into hCGβ-secreting syncytiotrophoblast was also not blocked by the inhibitors nor was upregulation of hCGβ secretion blocked in ST-stripped and regenerated 5 day explant cultures. The ratio of CT to ST nuclei present was also not changed in explant cultures by caspase inhibitors. The effectiveness of caspase inhibitors was demonstrated by their ability to completely block TNFα-induced apoptosis. We conclude that activation of caspases in general, and caspase-8 in particular, is not required for villous CT differentiation into ST. However, another role of intact caspase-8 (proform) in CT differentiation remains possible.
Guilbert
L J
LJ
Department of Medical Microbiology, University of Alberta, Edmonton, Canada T6G 2H7. larry.guilbert@ualberta.ca
Riddell
M
M
Winkler-Lowen
B
B
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D053181:Caspase 8 / Q000378:metabolism*; D061945:Caspase Inhibitors; D002454:Cell Differentiation / Q000187:drug effects*; D002459:Cell Fusion; D002478:Cells, Cultured; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D015726:Giant Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D009842:Oligopeptides / Q000494:pharmacology; D009924:Organ Culture Techniques; D010920:Placenta / Q000166:cytology; D011247:Pregnancy; D011804:Quinolines / Q000494:pharmacology; D013997:Time Factors; D014327:Trophoblasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism
D000590:Amino Acid Chloromethyl Ketones; D061945:Caspase Inhibitors; D018997:Chorionic Gonadotropin, beta Subunit, Human; D015853:Cysteine Proteinase Inhibitors; D009842:Oligopeptides; D011804:Quinolines; C403753:benzyloxycarbonyl-isoleucyl-glutamyl-threonyl-aspartic acid fluoromethyl ketone; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; C468548:quinoline-val-asp(OMe)-CH2-OPH; D015124:8-Bromo Cyclic Adenosine Monophosphate; C505530:CASP8 protein, human; D053181:Caspase 8