Abstract
The role of mitofusin-2 (MFN-2) in regulating mitochondrial dynamics has been well-characterized in lower order eukaryotic cell lines through the complete ablation of MFN-2 protein. However, to support the contractile function of mature skeletal muscle, the subcellular architecture and constituent proteins of this tissue differ substantially from simpler cellular organisms. Such differences may also impact the role of MFN-2 in mature mammalian muscle, and it is unclear if minor fluctuations in MFN-2, as observed in response to physiological perturbations, has a functional consequence. Therefore, we have transiently transfected MFN-2 cDNA into rat tibialis anterior muscle to determine the effect of physiolgically relevant increases in MFN-2 protein on mitochondrial bioenergetics. Permeabilized muscle fibres generated from muscle following MFN-2-transfection were used for functional assessments of mitochondrial bioenergetics. In addition, we have further established a novel method for selecting fibre bundles that are positively transfected, and using this approach transient transfection increased MFN-2 protein ∼2.3 fold in selected muscle fibres. However, this did not alter maximal rates of oxygen consumption or the sensitivity for ADP-stimulated respiration. In addition, MFN-2 over-expression did not alter rates of H2O2 emission. Altogether, and contrary to evidence from lower order cell lines, our results indicate that over-expressing MFN-2 in healthy muscle does not influence mitochondrial bioenergetics in mature mammalian skeletal muscle.
Highlights
Over the past decade the physiological role of mitochondria has been expanded
Work in lower eukaryotic cells has shown that mitochondria can migrate within these models [19], and the subsequent fusion events allows for the sharing of matrix constituents and signal transduction between organelles [20], which may be advantageous for mitochondrial bioenergetics [19]
Perspectives and conclusions In the current study we have assessed the direct effects of overexpressing MFN-2 in mature mammalian muscle, and find that increasing MFN-2 protein in isolation does not alter mitochondrial bioenergetics in healthy mature mammalian muscle
Summary
Over the past decade the physiological role of mitochondria has been expanded They are most well known for providing ATP for cellular processes, it appears that mitochondria are dynamic organelles, both with respect to their structure and function [1,2]. While mammalian cells contain homologous proteins, suggesting the regulation of the mitochondrial reticular morphology is evolutionarily conserved, the functional role of these proteins in mature mammalian skeletal muscle is not yet known. This tissue differs markedly from lower eukaryotic cells with respect to its architecture, which supports its physiologic contractile function. These tubular filaments may optimize conductance of membrane potential from subsarcolemmal mitochondria, where oxygen and oxidizable substrates are most available, to intermyofibrillar mitochondrial regions where the delivery of these compounds may be compromised, but where ATP requirement is substantial during muscle contraction [7,21]
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