Tumor necrosis factor-?-induced apoptosis is associated with suppression of insulin-like growth factor binding protein-5 secretion in differentiating murine skeletal myoblasts

Abstract

Wasting of muscle and fat during cachexia exceeds that explained by reduced food intake alone. This wasting may result from an imbalanced cytokine environment, which could lead to increased protein catabolism. Supporting this, tumor necrosis factor-alpha (TNF-alpha) is raised in several animal models of cachectic muscle wasting. Therefore, we assessed the effects of TNF-alpha and its second messenger, ceramide, on the proliferation, differentiation, and survival of murine C2 skeletal myoblasts. Because insulin-like growth factor binding protein-5 (IGFBP-5) and insulin-like growth factor-II (IGF-II) are potent regulators of myoblast proliferation and differentiation, we monitored the ability of exogenous TNF-alpha to manipulate this system. Fibroblast growth factor (FGF) ceramide, or TNF-alpha suppressed differentiation of C2 cells compared with controls. All treatments suppressed IGF-II production but only TNF-alpha blocked IGFBP-5 secretion. TNF-alpha increased apoptotic cell death, which otherwise remained basal (low serum differentiation medium (LSM), FGF) or low (ceramide). Suppression of both IGFBP-5 and IGF-II secretion may explain why of all triggers tested, only TNF-alpha not only blocked differentiation, but also promoted cell death. This suggests a fundamental role of IGFBP-5 for maintaining muscle survival. Supporting this hypothesis, no increase in apoptosis was seen in IGFBP-5 cDNA tranfected C2 cells after TNF-alpha treatment. In summary, the IGF system is essential for maintaining skeletal muscle cell survival and differentiation, and its suppression by TNF-alpha is fundamental regarding muscle wasting, and may be associated in vivo with cancer cachexia.

Ceramide inhibition of chondrocyte proliferation and bone growth is IGF-I independent

“…Strle et al (2004) demonstrated that ceramide inhibits IGF-I-induced protein synthesis and differentiation in myoblasts. However, it has also been reported that ceramide can inhibit myoblast growth and differentiation in the absence of exogenous IGF-I (Meadows et al 2000, Strle et al 2004. This apparent discrepancy is likely to be a consequence of experimental design, and in particular the presence or absence of serum and the concentration of ceramide used (Strle et al 2004).…”

“…Furthermore, in the presence of AG1024, an IGF-I and insulin receptor blocker, ceramide was still able to inhibit proliferation. These data suggest that C2-ceramide is able to inhibit bone proliferation by mechanisms that are independent of IGF-I signalling, which are in agreement with the previous studies (Meadows et al 2000, Strle et al 2004.…”

Death receptor-associated pro-apoptotic signaling in aged skeletal muscle

“…Furthermore, intravenous injection of recombinant TNF-α increases protein degradation in rat skeletal muscles and this is associated with the increased activity of the ubiquitin-dependent proteolytic pathway [33,34,36,38]. In addition, elevated TNF-α concentrations in cell culture for 24-48 h increases apoptosis in skeletal myoblasts as determined by DNA fragmentation [39,40]. A reduction of procaspase-8 occurs within 6 h of incubating myoblasts in vitro with recombinant TNF-α, suggesting a TNF-α mediated cleavage and activation of this initiator caspase in myoblast cultures [41].…”

Genome‐wide examination of myoblast cell cycle withdrawal during differentiation

“…IGFBP5 exhibits both inhibitory and stimulatory action in cultured muscle cells, presumably by binding IGFs and blocking or enhancing binding to IGF receptors (Kelley et al, 1996). Other IGF-independent functions of IGFBPs also have been proposed, including cell adhesion, migration, and anti-apoptosis (Meadows et al, 2000;Foulstone et al, 2001). Although our data suggest specific roles for IGFBP2 and IGFBP5 in early myoblast differentiation, their essential functions remain to be demonstrated.…”