Paper of the Month - August 2016

Hughes MC, Ramos SV, Turnbull PC, Nejatbakhsh A, Baechler BL, Tahmasebi H, Laham R, Gurd BJ, Quadrilatero J, Kane DA, Perry CG. Mitochondrial Bioenergetics and Fiber Type Assessments in Microbiopsy vs. Bergstrom Percutaneous Sampling of Human Skeletal Muscle. Front Physiol. 2015 Dec 18;6:360. doi: 10.3389/fphys.2015.00360. eCollection 2015

RATIONALE: The most commonly adopted technique used for percutaneous sampling of human skeletal muscle is the Bergstrom biopsy technique. However, in recent years, the use of microbiopsy needles has become increasingly popular, particularly for the study of muscle metabolism. Anecdotally, microbiopsy sampling is often perceived as less invasive than the Bergstrom technique given they obtain smaller samples and do not require a preliminary incision on the skin and fascia. However, fibres from microbiopsies are smaller in length which may affect certain experimental assays. For example, lower rates of mitochondrial respiration in permeabilized muscle fibres (PmFB) has been reported in microbiopsy samples vs bergstrom biopsies but the mechanism was unknown. We have previously demonstrated that ADP-stimulated respiration also results in ADP-stimulated contraction of PmFB in vitro, leading to lower detectable mitochondrial respiration. We hypothesized that preventing this ADP-induced contraction with a blebbistatin – a myosin II ATPase inhibitor – would rescue mitochondrial respiration and H2O2 emission to levels that are similar to PmFB from Bergstrom biopsies. We also hypothesized that fibre type assessments by immunohistochemistry would be similar between microbiopsies and bergstrom biopsies.

METHODS AND RESULTS: 11 males and females each received a 2 mm diameter percutaneous microbiopsy and a 5 mm diameter Bergstrom percutaneous biopsy in opposite legs. Glutamate/malate (5 mM/2 mM) - supported respiration in microbiopsy PmFB was lower than Bergstrom at submaximal concentrations of ADP. 5 μM BLEB rescued this impairment in that there were no differences relative to Bergstrom +/- BLEB. Surprisingly, pyruvate (5 mM)-supported respiration was not different between either biopsy technique +/- BLEB, whereas BLEB increased succinate-supported respiration in Bergstrom only. H2O2 emission was lower in microbiopsy PmFB compared to Bergstrom PmFB in the presence of BLEB. Microbiopsies contained fewer type I fibres (37% vs 47%) and more type IIX fibres (20% vs 8%) compared to Bergstrom possibly due to sampling site depth and/or longitudinal location. These findings suggest that smaller diameter percutaneous biopsies yield lower glutamate-supported mitochondrial respiratory kinetics which is rescued by preventing ADP-induced rigor with myosin inhibition

CONCLUSION: Overall, our findings suggest that microbiopsies can be used for the assessment of mitochondrial bioenergetics when assay conditions are supplemented with BLEB but fibre type composition should be considered.

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