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Interleukin-4 induces human hepatocyte apoptosis through a Fas-independent pathway

Lynda Aoudjehane^*, Philippe Podevin^*, Olivier Scatton, Patrick Jaffray, Isabelle Dusanter-Fourt, Gérard Feldmann^||, Pierre-Philippe Massault, Lilia Grira, Annie Bringuier^||, Bertrand Dousset, Sandrine Chouzenoux^*, Olivier Soubrane, Yvon Calmus^* and Filomena Conti^*

^* Laboratoire de Biologie Cellulaire, UPRES 1833, Université Paris5;

Service de Chirurgie, Hôpital Cochin, APHP;

Laboratoire de Biochimie, Hôpital Cochin, APHP;

Département d’Hématologie, Institut Cochin, INSERM U567, Paris, France; and

^|| Laboratoire de Biologie Cellulaire, INSERM U327, Faculté Xavier Bichat, Paris, France

¹Correspondence: Service de Chirurgie, Hôpital Cochin, 75674 Paris Cedex 14, France. E-mail: filomena.conti{at}cch.aphp.fr

IL-4 is overexpressed in liver grafts during severe recurrent hepatitis C and rejection. Hepatocyte apoptosis is involved in both these phenomena. We therefore examined the proapoptotic effect of IL-4 on HepG2 cells and human hepatocytes in vitro, together with the underlying mechanisms. We first measured IL-4 receptor expression, STAT6 activation by IL-4, and STAT6 inhibition by an anti-IL-4 antibody or by STAT6 siRNA transfection. We then focused on the pathways involved in IL-4-mediated apoptosis and the role of STAT6 activation in apoptosis initiation. The IL-4 receptor was expressed on both cell types, and STAT6 was activated by IL-4. Both anti-IL-4 and STAT-6 siRNA inhibited this activation. IL-4 induced apoptosis of both HepG2 cells (P=0.008 vs. untreated control) and human hepatocytes (P<0.001 vs. untreated control). IL-4 reduced the mitochondrial membrane potential, activated Bid and Bax, and augmented caspase 3, 8, and 9 activity. STAT6 blockade inhibited IL-4-induced apoptosis. Expression of Fas and Fas ligand was unaffected when HepG2 cells and hepatocytes were cultured with IL-4, and Fas/FasL pathway blockade failed to inhibit IL-4-induced apoptosis. These results show that IL-4 induces apoptosis of human hepatocytes through IL-4 receptor binding, STAT6 activation, decreased mitochondrial membrane potential, and increased caspase activation, independently of the Fas pathway. IL-4 might thus contribute to the progression of severe liver graft damage.—Aoudjehane, L., Podevin, P., Scatton, O., Jaffray, P., Dusanter-Fourt, I., Feldmann, G., Massault, P. P., Grira, L., Bringuier, A., Dousset, B., Chouzenoux, S., Soubrane, O., Calmus, Y., Conti, F. Interleukin-4 induces human hepatocyte apoptosis through a Fas-independent pathway.

Key Words: liver transplantation • IL-4