Effects of Obesity on Cardiotoxin Induced Damage and Regeneration of Lean and Obese Human Myotubes

Obesity increases the susceptibility of skeletal muscle to damage and impairs the regenerative response following muscle damage. Obesity is associated with an increase in ectopic lipid accumulation and inflammatory cell infiltration in skeletal muscle. It is unclear if the impairments in skeletal muscle regeneration and increased susceptibility to damage is due to these factors or if defects in integrity and repair are inherent to muscle of obese subjects. PURPOSE: To investigate if myotubes isolated from obese donors are (1) more susceptible to damage and (2) have a blunted regeneration response. METHODS: Differentiated myotubes from lean (LN) and obese (OB) donors were treated with 0.5 μM of cardiotoxin (CTX) for 1 hr. Cells were allowed to recover in skeletal muscle growth media for 3 days and then differentiation media for 2 days. Cells were isolated immediately (ImPost), 3 and 5 days following CTX treatment. RESULTS: CTX significantly reduced the fusion index of differentiated cells, but there were no differences between LN and OB at ImPost (no-CTX: LN 28% vs. OB 28%; CTX: LN 15% vs. OB 12%), 3 Days (no-CTX: LN 38% vs. OB 38.0%; CTX: LN 30% vs. OB 29%), or 5 Days (no-CTX: LN 41% vs. OB 39%; CTX: LN 37% vs. OB 34%). CTX significantly reduced cell viability assessed via MTT but no differences were observed between LN and OB at ImPost (no-CTX: LN 0.20 au vs. OB 0.21 au; CTX LN 0.11 au vs. OB 0.14 au), 3 days (no-CTX: LN 0.37 au vs. OB 0.37 au; CTX LN 0.08 au vs. OB 0.12 au), or 5 days (no-CTX: LN 0.34 au vs. OB 0.34 au; CTX LN 0.19 au vs. OB 0.22 au). No differences were observed in the expression of key metabolic proteins PFK-1, Citrate Synthase, or β-Had following CTX administration in LN or OB. CONCLUSION: When cultured under identical conditions, myotubes isolated from young, healthy obese donors demonstrate similar damage following CTX treatment and similar regenerative responses compared to myotubes from lean donors.