Impaired Mitochondrial Dynamics and Bioenergetics in Diabetic Skeletal Muscle

Abstract

In most cells, mitochondria are highly dynamic organelles that constantly fuse, divide and move. These processes allow mitochondria to redistribute in a cell and exchange contents among the mitochondrial population, and subsequently repair damaged mitochondria. However, most studies on mitochondrial dynamics have been performed on cultured cell lines and neurons, and little is known about whether mitochondria are dynamic organelles in vivo, especially in the highly specialized and differentiated adult skeletal muscle cells. Using mitochondrial matrix-targeted photoactivatable green fluorescent protein (mtPAGFP) and electroporation methods combined with confocal microscopy, we found that mitochondria are dynamic in skeletal muscle in vivo, which enables mitochondria exchange contents within the whole mitochondrial population through nanotunneling-mediated mitochondrial fusion. Mitochondrial network promotes rapid transfer of mtPAGFP within the cell. More importantly, the dynamic behavior was impaired in high-fat diet (HFD)-induced obese mice, accompanying with disturbed mitochondrial respiratory function and decreased ATP content in skeletal muscle. We further found that proteins controlling mitochondrial fusion MFN1 and MFN2 but not Opa1 were decreased and proteins governing mitochondrial fission Fis1 and Drp1 were increased in skeletal muscle of HFD-induced mice when compared to normal diet-fed mice. Altogether, we conclude that mitochondria are dynamic organelles in vivo in skeletal muscle, and it is essential in maintaining mitochondrial respiration and bioenergetics.

Mitochondrial dynamics, quality control and miRNA regulation in skeletal muscle: implications for obesity and related metabolic disease

“…These high-fat diet-induced changes were paralleled by a 25 % reduction in ADP-stimulated oxygen consumption rate, a lower respiratory control ratio, a reduced ATP production and a reduced mitochondrial content exchange (i.e. the dynamic propagation of a GFP-tagged mitochondrial protein through the mitochondrial network), as observed using confocal microscopy to study mitochondrial dynamics in living animals [16]. Although focused on the liver, another study compared high-fat diets with different fat composition (lard compared with fish-oil) and found that rats fed a high-lard diet, showed an increased number of small and fragmented liver mitochondria as well as reduced Mfn-1, Mfn-2 and Opa1 and increased Drp-1 and Fis1 levels, as compared with both the high fish-oil and chow diet [17].…”

“…Furthermore, in vivo animal studies revealed that 40 weeks of high-fat feeding decreased both protein levels of Mfn-1 and Mfn-2 in skeletal muscle by 20 %, which was associated with a 50 % increase in Fis1 and Drp-1 protein levels [16]. These high-fat diet-induced changes were paralleled by a 25 % reduction in ADP-stimulated oxygen consumption rate, a lower respiratory control ratio, a reduced ATP production and a reduced mitochondrial content exchange (i.e.…”

Chronology of mitochondrial and cellular events during skeletal muscle ischemia-reperfusion

“…This location allows mitochondria to communicate with one another via a complex network (100) and to participate in physiological functions by regulated fission and fusion mechanisms, termed "mitochondrial dynamics." Although little is known about mitochondrial dynamics in skeletal muscle, mitochondrial dynamics have been implicated in mitochondrial DNA renewal, cell differentiation and development, mitochondrial respiration, and bioenergetics (46,100,120,129,142).…”

Photoactivatable Green Fluorescent Protein-Based Visualization and Quantification of Mitochondrial Fusion and Mitochondrial Network Complexity in Living Cells

“…Since the original publication (Karbowski et al, 2004), the mito-PAGFP-based mitochondrial fusion imaging method has been applied to various cell types, including skeletal muscle (Liu et al, 2014), control and LPS+IFNγ-treated astrocytes (Motori et al, 2013), cortical (Berman et al, 2009) and hippocampal neurons (Karbowski et al, 2004), C. elegans (Rolland et al, 2013) and many others. This assay was instrumental in several important discoveries within the field of mitochondrial biology, including the role of mitochondrial fusion in activation of mitochondrial steps in apoptosis (Karbowski et al, 2004; Lee et al, 2004), participation of Bcl-2 family proteins in mitochondrial morphogenesis (Berman et al, 2009; Karbowski et al, 2006; Perciavalle et al, 2012), stress induced mitochondrial hyperfusion (Tondera et al, 2009), and the recently discovered, novel role of the mitochondrial fusion protein Opa1 in the control of mitochondrial division (Anand et al, 2014).…”