Interleukin-1 stimulates catabolism in C2C12 myotubes

Abstract

Interleukin-1 (IL-1) is an inflammatory cytokine that has been linked to muscle catabolism, a process regulated by muscle-specific E3 proteins of the ubiquitin-proteasome pathway. To address cellular mechanism, we tested the hypothesis that IL-1 induces myofibrillar protein loss by acting directly on muscle to increase expression of two critical E3 proteins, atrogin1/muscle atrophy F-box (MAFbx) and muscle RING-finger 1 (MuRF1). Experiments were conducted using mature C2C12 myotubes to eliminate systemic cytokine effects and avoid paracrine signaling by nonmuscle cell types. Time-course protocols were used to define the sequence of cellular responses. We found that atrogin1/MAFbx mRNA and MuRF1 mRNA are elevated 60-120 min after myotube exposure to either IL-1alpha or IL-1beta. These responses are preceded by signaling events that promote E3 expression. Both IL-1 isoforms stimulate phosphorylation of p38 mitogen-activated protein kinase and stimulate nuclear factor-kappaB (NF-kappaB) signaling; I-kappaB levels fall and NF-kappaB DNA binding activity increases. Other regulators of E3 expression are unaffected by IL-1 [cytosolic oxidant activity, Forkhead-O (Foxo) activity] or respond paradoxically (AKT). Chronic exposure of C2C12 myotubes over 48 h resulted in reduced myotube width and loss of sarcomeric actin. We conclude that IL-1alpha and IL-1beta act via an oxidant- and AKT/Foxo-independent mechanism to activate p38 MAPK, stimulate NF-kappaB signaling, increase expression of atrogin1/MAFbx and MuRF1, and reduce myofibrillar protein in differentiated myotubes.

Interleukin-1β stimulates early myogenesis of mouse C2C12 myoblasts: the impact on myogenic regulatory factors, extracellular matrix components, IGF binding proteins and protein kinases

“…Recent studies have shown that chronic exposure to IL-1β reduced myofibrillar proteins and myotube diameter in C2C12 culture (Li et al 2009), which is in apparent contrast to our observation indicating the promotion of myoblast growth and differentiation under IL-1β treatment. In potential explanation of this discrepancy the differences in experimental protocols should be taken into consideration, as Li et al (2009) used mature myotubes subjected to cytokine treatment, whereas in our study the effects of IL-1β on cell cycle regulatory mechanisms and the onset of myogenesis were investigated, and appeared to be limited in time to the period preceding myoblast fusion.…”

“…Both plasma IL-1β and hindlimb muscle ubiquitin-proteasome pathway were elevated in tumor-bearing and cachectic mice (Cannon et al 2008). According to in vivo (Cai et al 2004) and in vitro studies (Luo et al 2003, Chevrel et al 2005 IL-1β activated p38 MAPK and NF-kB: the signaling elements that promote the proteolysis in muscle and the reduction of myofibrillar proteins (Li et al 2009). …”

Small‐molecule inhibition of MuRF1 attenuates skeletal muscle atrophy and dysfunction in cardiac cachexia

“…Consistent with the view that MuRF1 acts as an atrogin, its expression is intimately associated with muscle wasting in numerous clinical conditions (as reviewed in Bodine and Baehr2) or following exposure to pharmacological treatments (e.g. glucocorticoids, inflammatory cytokines, reactive oxygen species7, 8, 9, 10), while its gene inactivation confers partial resistance to muscle wasting conditions 7, 8, 11, 12. Therefore, several approaches have attempted to down‐regulate MuRF1 activity therapeutically, either directly in vitro via targeted inhibition of MuRF1 by a muscle‐specific small molecule13 and adenoviral knockdowns14, 15 or indirectly in vivo via exercise training16 or antioxidant administration17, which resulted in a significant reduction in muscle wasting.…”

Adrenocortical Scavenger Receptor Class B Type I Deficiency Exacerbates Endotoxic Shock and Precipitates Sepsis-Induced Mortality in Mice

“…This catabolic response to endotoxic/septic shock in skeletal muscle involves increased protein breakdown, but also reduced protein synthesis and inhibition of amino acid uptake. Numerous reports have documented the potential contribution of GC (32), proinflammatory cytokines (33,34), and LPS (35) to this effect. However, recent studies have substantially evidenced that GC were indeed requisite to this process, because activation of the genes involved in muscle atrophy after LPS-induced peripheral inflammation was essentially blocked by adrenalectomy (36).…”