Tumor Necrosis Factor-α Decreases Insulin-Like Growth Factor-I Messenger Ribonucleic Acid Expression in C2C12 Myoblasts via a Jun N-Terminal Kinase Pathway

Endocrinology, May 2003

IGF-I is a major anabolic hormone for skeletal muscle in vivo. Yet the mechanisms by which GH and cytokines regulate IGF-I expression remain obscure. Lipopolysaccharide (LPS) dramatically alters the circulating concentration of both TNFα and IGF-I, and TNFα in part mediates the cachectic activity of LPS. Little is known about the local synthesis of IGF-I and TNFα in skeletal muscle per se. The purpose of the present study was to determine whether LPS alters the expression of TNFα and IGF-I in mouse skeletal muscle and whether TNFα directly inhibits IGF-I mRNA expression in C2C12 myoblasts. Intraperitoneal injection of LPS in C3H/SnJ mice increased the expression of TNFα protein in plasma (16-fold) and TNFα mRNA in skeletal muscle (8-fold). LPS also decreased the plasma concentration of IGF-I (30%) and IGF-I mRNA in skeletal muscle (50%, between 6 and 18 h after LPS administration). Addition of LPS or TNFα directly to C2C12 myoblasts decreased IGF-I mRNA by 50–80%. The TNFα-induced decrease in IGF-I mRNA was both dose and time dependent and occurred in both myoblasts and differentiated myotubes. TNFα selectively decreased IGF-I but not IGF-II mRNA levels, and the effect of TNFα was blocked by a specific TNF-binding protein. TNFα did not alter IGF-I mRNA levels in the presence of the protein synthesis inhibitor cycloheximide. TNFα did not change the half-life of IGF-I mRNA. TNFα completely prevented GH-inducible IGF-I mRNA expression, but this GH resistance was not attributable to impairment in signal transducer and activator of transcription-3 or -5 phosphorylation. TNFα increased both nitric oxide synthase-II mRNA and protein, and the nitric oxide donor sodium nitroprusside decreased IGF-I mRNA levels in C2C12 cells. Yet inhibitor studies indicate that nitric oxide did not mediate the effect of TNFα on IGF-I mRNA expression. TNFα stimulated the phosphorylation of c-Jun and specific inhibition of the Jun N-terminal kinase pathway, but not other MAPK pathways, completely prevented the TNFα-induced drop in IGF-I mRNA. These data suggest that LPS stimulates TNFα expression in mouse skeletal muscle and autocrine-derived cytokines may contribute to the reduced expression of IGF-I in this tissue.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://academic.oup.com/endo/article-pdf/144/5/1770/9018113/endo1770.pdf

Tumor Necrosis Factor-α Decreases Insulin-Like Growth Factor-I Messenger Ribonucleic Acid Expression in C2C12 Myoblasts via a Jun N-Terminal Kinase Pathway

Endocrinology Tumor Necrosis Factor- Decreases Insulin-Like Growth Factor-I Messenger Ribonucleic Acid Expression in C2C12 Myoblasts via a Jun N-Terminal Kinase Pathway ROBERT A. FROST 0 1 GERALD J. NYSTROM 0 1 CHARLES H. LANG 0 1 0 Abbreviations: 1400W, N-3-Aminomethyl benzylacetamidine; DRB , 5,6-dichloro- -d-ribofuranosyl-benzimidazole; GAPDH, glyceraldehyde- 3-phosphate dehydrogenase; IGFBP, IGF-binding protein; JNK, Jun N-terminal kinase; L-NMMA, N 1 Department of Cellular and Molecular Physiology, Pennsylvania State University, College of Medicine , Hershey, Pennsylvania 17033 , USA IGF-I is a major anabolic hormone for skeletal muscle in vivo. Yet the mechanisms by which GH and cytokines regulate IGF-I expression remain obscure. Lipopolysaccharide (LPS) dramatically alters the circulating concentration of both TNF and IGF-I, and TNF in part mediates the cachectic activity of LPS. Little is known about the local synthesis of IGF-I and TNF in skeletal muscle per se. The purpose of the present study was to determine whether LPS alters the expression of TNF and IGF-I in mouse skeletal muscle and whether TNF directly inhibits IGF-I mRNA expression in C2C12 myoblasts. Intraperitoneal injection of LPS in C3H/SnJ mice increased the expression of TNF protein in plasma (16fold) and TNF mRNA in skeletal muscle (8-fold). LPS also decreased the plasma concentration of IGF-I (30%) and IGF-I mRNA in skeletal muscle (50%, between 6 and 18 h after LPS administration). Addition of LPS or TNF directly to C2C12 myoblasts decreased IGF-I mRNA by 50 - 80%. The TNF - induced decrease in IGF-I mRNA was both dose and time dependent and occurred in both myoblasts and differentiated myotubes. TNF selectively decreased IGF-I but not IGF-II - I NFECTION, TRAUMA, cancer cachexia, AIDS, and chronic alcohol abuse are often associated with severe muscle wasting that cannot be solely explained by a reduction in caloric intake ( 1 ). Potential mediators of the wasting syndromes include inflammatory cytokines such as TNF , IL-1 , and IL-6 ( 2 ) as well as negative regulators of muscle mass such as myostatin ( 3, 4 ) and glucocorticoids (5). Administration of lipopolysaccharide (LPS) or proinflammatory cytokines to rats mimics the protein hypercatabolic aspects of cachexia. Conversely, prophylactic administration of TNF -binding protein (TNFBP) ( 6 ) and IL-1 receptor antagonist ( 7 ) partially reverses some of the effects of endogenous cytokines released in response to a bacterial infection. Cytokines such as TNF may have a direct effect on skeletal muscle protein metabolism and/or alter the expression and biological activity of anabolic hormones such as GH and IGF-I ( 8, 9 ). LPS and TNF stimulate the hepatic synthesis of suppressors of cytokine signaling, and this is thought to be mRNA levels, and the effect of TNF was blocked by a specific TNF-binding protein. TNF did not alter IGF-I mRNA levels in the presence of the protein synthesis inhibitor cycloheximide. TNF did not change the half-life of IGF-I mRNA. TNF completely prevented GH-inducible IGF-I mRNA expression, but this GH resistance was not attributable to impairment in signal transducer and activator of transcription-3 or -5 phosphorylation. TNF increased both nitric oxide synthase-II mRNA and protein, and the nitric oxide donor sodium nitroprusside decreased IGF-I mRNA levels in C2C12 cells. Yet inhibitor studies indicate that nitric oxide did not mediate the effect of TNF on IGF-I mRNA expression. TNF stimulated the phosphorylation of c-Jun and specific inhibition of the Jun N-terminal kinase pathway, but not other MAPK pathways, completely prevented the TNF -induced drop in IGF-I mRNA. These data suggest that LPS stimulates TNF expression in mouse skeletal muscle and autocrine-derived cytokines may contribute to the reduced expression of IGF-I in this tissue. (Endocrinology 144: 1770 –1779, 2003) important for the development of GH resistance at the level of the liver ( 10, 11 ). As a consequence, the ability of GH to stimulate hepatic IGF-I synthesis and increase blood-borne IGF-I is greatly attenuated ( 12 ). Infusion of TNF in rats lowers both the plasma concentration of IGF-I and expression of IGF-I mRNA in the gastrocnemius muscle ( 13 ). Because IGF-I is a major anabolic hormone for skeletal muscle, a local deficit in IGF-I may also be partially responsible for the muscle wasting that occurs in sepsis, trauma, and other catabolic conditions ( 14, 15 ). It is not known whether TNF generates GH resistance in skeletal muscle or acts directly on skeletal muscle to alter the local expression of IGF-I. TNF may alter the endocrine expression of other cytokines or signaling molecules that in turn suppress the expression of IGF-I in muscle. Investigators have had varied success in observing skeletal muscle responses to TNF in intact animals, epitrochlears incubated in vitro, and muscle cell lines. Yet a constant infusion of TNF decreases basal musc (...truncated)


This is a preview of a remote PDF: https://academic.oup.com/endo/article-pdf/144/5/1770/9018113/endo1770.pdf

Frost, Robert A., Nystrom, Gerald J., Lang, Charles H.. Tumor Necrosis Factor-α Decreases Insulin-Like Growth Factor-I Messenger Ribonucleic Acid Expression in C2C12 Myoblasts via a Jun N-Terminal Kinase Pathway, Endocrinology, 2003, pp. 1770-1779, Volume 144, Issue 5, DOI: 10.1210/en.2002-220808