Inhibition of myoblast differentiation by tumor necrosis factor αis mediated by c-Jun N-terminal kinase 1 and leukemia inhibitory factor

Abstract

The proinflammatory cytokine, TNFα plays a major role in muscle wasting occurring in chronic diseases and muscular dystrophies. Among its other functions, TNFα perturbs muscle regeneration by preventing satellite cell differentiation. In the present study, the role of c-Jun N-terminal kinase (JNK), a mediator of TNFα, was investigated in differentiating myoblast cell lines. Addition of TNFα to C2 myoblasts induced immediate and delayed phases of JNK activity. The delayed phase is associated with myoblast proliferation. Inhibition of JNK activity prevented proliferation and restored differentiation to TNFα-treated myoblasts. Studies with cell lines expressing MyoD:ER chimera and lacking JNK1 or JNK2 genes indicate that JNK1 activity mediates the effects of TNFα on myoblast proliferation and differentiation. TNFα does not induce proliferation or inhibit differentiation of JNK1-null myoblasts. However, differentiation of JNK1-null myoblasts is inhibited when they are grown in conditioned medium derived from cell lines affected by TNFα. We investigated the induced synthesis of several candidate growth factors and cytokines following treatment with TNFα. Expression of IL-6 and leukemia inhibitory factor (LIF) was induced by TNFα in wildtype and JNK2-null myoblasts. However, LIF expression was not induced by TNFα in JNK1-null myoblasts. Addition of LIF to the growth medium of JNK1-null myoblasts prevented their differentiation. Moreover, LIF-neutralizing antibodies added to the medium of C2 myoblasts prevented inhibition of differentiation mediated by TNFα. Hence, TNFα promotes myoblast proliferation through JNK1 and prevents myoblast differentiation through JNK1-mediated secretion of LIF. © 2008 by The American Society for Biochemistry and Molecular Biology, Inc.