Disconnecting Mitochondrial Content from Respiratory Chain Capacity in PGC-1-Deficient Skeletal Muscle

• Muscle deletion of PGC-1α/β dissociates mitochondrial content from ETC activity
• Dissociation of respiration and mitochondrial content is cell autonomous
• PGC-1 coactivators are dispensable for baseline locomotion and muscle function
• PGC-1α/β muscle double-knockout animals have normal fiber-type composition

SummaryThe transcriptional coactivators PGC-1α and PGC-1β are widely thought to be required for mitochondrial biogenesis and fiber typing in skeletal muscle. Here, we show that mice lacking both PGC-1s in myocytes do indeed have profoundly deficient mitochondrial respiration but, surprisingly, have preserved mitochondrial content, isolated muscle contraction capacity, fiber-type composition, in-cage ambulation, and voluntary running capacity. Most of these findings are recapitulated in cell culture and, thus, are cell autonomous. Functional electron microscopy reveals normal cristae density with decreased cytochrome oxidase activity. These data lead to the following surprising conclusions: (1) PGC-1s are in fact dispensable for baseline muscle function, mitochondrial content, and fiber typing, (2) endurance fatigue at low workloads is not limited by muscle mitochondrial capacity, and (3) mitochondrial content and cristae density can be dissociated from respiratory capacity.

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