Mitochondrial functional impairment with aging is exaggerated in isolated mitochondria compared to permeabilized myofibers

Abstract

SummaryMitochondria regulate cellular bioenergetics and apoptosis and have been implicated in aging. However, it remains unclear whether age-related loss of muscle mass, known as sarcopenia, is associated with abnormal mitochondrial function. Two technically different approaches have mainly been used to measure mitochondrial function: isolated mitochondria and permeabilized myofiber bundles, but the reliability of these measures in the context of sarcopenia has not been systematically assessed before. A key difference between these approaches is that contrary to isolated mitochondria, permeabilized bundles contain the totality of fiber mitochondria where normal mitochondrial morphology and intracellular interactions are preserved. Using the gastrocnemius muscle from young adult and senescent rats, we show marked effects of aging on three primary indices of mitochondrial function (respiration, H 2 O 2 emission, sensitivity of permeability transition pore to Ca 2+ ) when measured in isolated mitochondria, but to a much lesser degree when measured in permeabilized bundles. Our results clearly demonstrate that mitochondrial isolation procedures typically employed to study aged muscles expose functional impairments not seen in situ. We conclude that aging is associated with more modest changes in mitochondrial function in sarcopenic muscle than suggested previously from isolated organelle studies.

Quantification of in vivo oxidative damage in Caenorhabditis elegans during aging by endogenous F3‐isoprostane measurement

“…These systems furthermore rely on optically accessible systems, which restrict their usage. Oxidative damage assessment in isolated mitochondria can also suffer from artifact introduction in the isolation process (Picard et al, 2010). Finally, protein carbonylation is described as a marker for oxidative damage to proteins.…”

Mitochondria and aging: A role for the mitochondrial transition pore?

“…Sensitization of mPTP opening was also involved in the bone loss occurring in aging mice (Shum et al., 2016). However, it should be kept in mind that most of these data were obtained in isolated mitochondria, which may amplify mitochondrial functional impairment (Picard et al., 2010). …”

Redox homeostasis and age‐related deficits in neuromuscular integrity and function

“…Reactive oxygen and nitrogen species generation by myofibres has been detected and quantified by a variety of methods including high‐performance liquid chromatography techniques,30, 51 electron‐spin resonance spectroscopy (also known as electron paramagnetic resonance),52, 53 fluorescence‐based microscopic assays,54, 55 spectrophotometry,56, 57 chemiluminescence58, 59 and transfection methods including in vivo 60, 61 and in vitro. 62 It is widely accepted that superoxide and nitric oxide (NO) are the primary radical species generated by skeletal muscle 46, 63.…”

“…Considerable evidence has shown that age‐related mitochondrial oxidative damage can alter mitochondrial integrity and function in ageing skeletal muscle. Several key features have been observed in ageing skeletal muscle, including a reduction in mitochondrial abundance237 and oxidative‐phosphorylation,19 accumulation of mutated mtDNA238 associated with impaired mitophagy,21, 38 increased mitochondrial permeability transition pore sensitivity54 and increased mitochondrial‐mediated apoptosis,239 which collectively may contribute to age‐related loss of neuromuscular integrity and function. Together, these findings may support the conclusion that age‐related muscle atrophy and functional deficits are associated with increased oxidative damage and defective redox signalling.…”