MITOCHONDRIAL PLASTICITY IN SKELETAL MUSCLE CELLS

New evidence on mitochondria mtDNA

MITO TRACKER GREEN Mito Tracker Green is a mitochondrial-selective fluorescent label Morpho-functional changes

Mitochondria are dynamic organelles Mitochondria fuse and divide to form constantly changing tubular networks in most eukaryotic cells (A) Mitochondrial network (green) in a Saccharomyces cerevisiae cell. (B) Mammalian mitochondrial network in a fibroblast cells. Hales, K. G. (2010)

Confocal microscopy of myoblasts (A, B) and late myotubes (C,D,E) after Mito Tracker staining Bar=20μm Barbieri et al., 2011 Mitochondrial network in skeletal muscle cells D C

The mitochondrium is active when the mitochondrial membrane potential (MMP) is highly negative Δ Ψ ~ -180mV across the inner membrane of mitochondria

The electron transport system (ETS) pumps protons across the inner mitochondrial membrane (i.m) and thus generates mitochondrial membrane potential (MMP). The MMP is necessary for conversion of ADP to ATP (ATP synthesis).

When is a mitochondrium active? When the membrane potential (MMP) is highly negative When it produces ATP When it breathes

Mouli et al., Frequency and selectivity of mitochondrial fusion are key to its quality maintenance function, Biophysical Journal (2009) Mitchondria are in a constant state of fusion and division inside the cell

1 um BALANCE OF MITOCHONDRIAL FUSION AND FISSION

BALANCE OF MITOCHONDRIAL FUSION AND DIVISION Three central players belong to the dynamin superfamily : (1) mitofusins (outer mitochondrial membrane fusion), (2) OPA1/Mgm1 (inner mitochondrial membrane fusion), (3) Drp1/Dnm1 (division of outer and inner mitochondrial membranes).

A BC Representative confocal images of : (A) Cardiomyocites; (B) soleus fibers; (C) white gastrocnemius fibers. Vendelin et al., Am J Physiol Cell Physiol 288: C757–C767, 2005 MITOCHONDRIAL ARRANGEMENT IN MUSCLE CELLS

Birkedal, R. et al. Am J Physiol Cell Physiol 291: C1148-C MITOCHONDRIAL ARRANGEMENT IN MUSCLE CELLS

Recent studies have shown multiple functional interactions among mitochondria, sarcoplasmic reticulum and myofibrilles in skeletal muscle fiber sarcomere Sarcoplasmic membrane myofibrilles mitochondria sarcoplasmic reticulum MITOCHONDRIAL POPULATIONS IN MUSCLE CELLS

Transmission electron micrograph of SS subsarcolemmar and IMF intramyofibrillar mitochondria in muscle fiber IMF SS Kindly provided by Hood D, 2004

“The complete sequence of the 16,569- base pair human mitochondrial genome (mtDNA) is presented…” Anderson et al Nature 290,

Human mitochondrial genome (mtDNA) 16,569 base pairs mtDNA : 37 genes: 2 rRNA; 22 tRNA; 13 mRNA for oxidative enzimatic subunits MITOMAP (

Leber's hereditary optic neuropathy (LHON) visual loss, progressive degeneration of the optic nerves and retina Leigh syndrome, sclerosing encephalopathy Neuropathy, ataxia, retinitis pigmentosa, and ptosis (NARP) Myoclonic Epilepsy with Ragged Red Fibers (MERRF) progressive epilepsy, "Ragged Red Fibers" – clumps of diseased mitochondria accumulate in the subsarcolemmal region of the muscle fiber and appear as "Ragged Red Fibers”, short stature, hearing loss Mitochondrial myopathy, encephalomyopathy, acidosis, stroke-like symptoms (MELAS) MITOCHONDRIAL MYOPATHIES

Burger et al Nucleus Nucleus or mitochondria Mitochondria NUCLEAR AND MITOCHONDRIAL DNA COOPERATION Most mitochondrial components are encoded by the nuclear genome (blue); The components in pink are encoded by mtDNA in some eukaryotes but by the nuclear genome in other eukaryotes; while a small portion is specified by mtDNA (orange).

ComplexMitochondrial genesNuclear genes I NADH dehydrogenase7 > 25 II Succinate CoQ Reductase0 4 III Cytochrome b-c11 10 IV Cyctochrome c-oxidase3 10 V ATP synthase1 11 NUCLEAR AND MITOCHONDRIAL DNA COOPERATION

Maintenance of energy stores, ergogenics Thermogenesis Apoptosis Pathological processes associated with mtDNA mutations (MELAS MERRF NARP), MITOCHONDRIAL FUNCTIONS

The breakdown of chromatin in the nucleus Apoptosis, or programmed cell death, is a normal component of the development and health of multicellular organisms.health APOPTOSIS The end stages of apoptosis are characterised by membrane blebs. Small vesicles called apoptotic bodies are also sometimes observed (D, arrow).

APOPTOSIS

AdipoR1, adiponectin receptor 1; AMPK, AMP-activated protein kinase; AS160, Akt substrate of 160 kDa; GLUT4, glucose transporter 4; IMTG, intramyocellular triglyceride; IRS, insulin receptor substrate; LAT1, L-type amino acid transporter; mTOR, mammalian target of rapamycin; ROS, reactive oxygen species; SIRT1, sirtuin 1; PGC-1, peroxisome proliferator-activated receptor-γ coactivator-1; PPAR, peroxisome proliferator-activated receptor. (Hawley et al., 2010) FUNDAMENTALS OF MUSCLE MITOCHONDRIAL BIOGENESIS

 Six weeks of resistance training increases skeletal muscle mitochondrial content between ___% and ____% NYC Marathon