Effect of PGC1‐α Overexpression on Cardiotoxin‐Induced Damage and Repair of Human Myotubes

Abstract

Introduction Metabolic disease alters many biochemical and morphological characteristics of skeletal muscle, including reductions in fiber integrity and the regenerative response following muscle damage. In obesity and diabetes, skeletal muscle peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α) is reduced and may contribute to impairments in inflammatory and metabolic signaling. PGC-1α is important in regulating skeletal muscle cellular energy metabolism, mitochondrial biogenesis, and myofiber integrity. The purpose of the present study was to examine if PGC-1α overexpression (OE) reduces cardiotoxin (CTX)-induced skeletal muscle damage and improves regeneration after CTX treatment in human myotubes. Methods Differentiated primary, human myotubes were transfected with adenovirus containing PGC-1α (PGC-AV) or green fluorescent protein (GFP). At 48 h following transfection, myotubes were treated with 1.0 μM CTX or vehicle control (CTL) for 1 h. Cells were allowed to recover in skeletal muscle growth media for 3 days. Cells were isolated for analysis immediately (0D) and 3 days (3D) following CTX or CTL administration. Significance was established at P ≤ 0.05. Results Under control conditions, PGC-AV increased myotube metabolic activity compared to GFP and CTX administration lowered metabolic activity assessed by MTT (GFP-CTL = 1.00 au; GFP-CTX= 0.51 au; PGC-CTL = 1.65 au; PGC-CTX= 1.13 au). CTX administration reduced the fusion index (FI) similarly in PGC-AV and GFP groups (GFP-CTL = 27.8%; GFP-CTX= 21.9%; PGC-CTL = 26.9%; PGC-CTX= 20.5%). At time 0D, both PGC-AV and CTX lowered myotube numbers (GFP-CTL = 13.5 tubes; GFP-CTX= 9.5 tubes; PGC-CTL = 7.3 tubes; PGC-CTX = 6.8 tubes). PGC-AV tended (P < 0.10) to reduce CTX-induced myotube damage as measured by media content of lactate dehydrogenase (LDH) (GFP-CTL = 1.0 au; GFP-CTX= 1.5 au; PGC-CTL control = 1.0 au; PGC-CTX= 1.2 au). At 3D, PGC-AV treatment lowered %Edu+ nuclei (GFP-CTL = 31.3%; GFP-CTX= 34.4%; PGC-CTL =25.5%; PGC-CTX= 20.3%) and MyoD mRNA expression (GFP-CTL = 1.0 au; GFP-CTX= 1.0 au; PGC-CTL control = 0.2 au; PGC-CTX= 0.3 au) indicating a reduction in proliferation and an increase in quiescent myoblasts. Conclusion Overexpression of PGC-1α may limit CTX induced damage, but may also blunt the proliferation of myoblasts following CTX treatment.