To determine whether the obesity-related decrement in fatty acid oxidation (FAO) in primary human skeletal muscle cells (HSkMC) is linked with lower mitochondrial content and whether this deficit could be corrected via overexpression of peroxisome proliferator–activated receptor-γ coactivator-1α (PGC-1α).

FAO was studied in HSkMC from lean (BMI 22.4 ± 0.9 kg/m²; N = 12) and extremely obese (45.3 ± 1.4 kg/m²; N = 9) subjects. Recombinant adenovirus was used to increase HSkMC PGC-1α expression (3.5- and 8.0-fold), followed by assessment of mitochondrial content (mtDNA and cytochrome C oxidase IV [COXIV]), complete (¹⁴CO₂ production from labeled oleate), and incomplete (acid soluble metabolites [ASM]) FAO, and glycerolipid synthesis.

Obesity was associated with a 30% decrease (P < 0.05) in complete FAO, which was accompanied by higher relative rates of incomplete FAO ([¹⁴C]ASM production/¹⁴CO₂), increased partitioning of fatty acid toward storage, and lower (P < 0.05) mtDNA (−27%), COXIV (−35%), and mitochondrial transcription factor (mtTFA) (−43%) protein levels. PGC-1α overexpression increased (P < 0.05) FAO, mtDNA, COXIV, mtTFA, and fatty acid incorporation into triacylglycerol in both lean and obese groups. Perturbations in FAO, triacylglycerol synthesis, mtDNA, COXIV, and mtTFA in obese compared with lean HSkMC persisted despite PGC-1α overexpression. When adjusted for mtDNA and COXIV content, FAO was equivalent between lean and obese groups.

Reduced mitochondrial content is related to impaired FAO in HSkMC derived from obese individuals. Increasing PGC-1α protein levels did not correct the obesity-related absolute reduction in FAO or mtDNA content, implicating mechanisms other than PGC-1α abundance.