Transcript MITOCHONDRIAL PLASTICITY IN SKELETAL MUSCLE CELLS

MITOCHONDRIAL PLASTICITY IN
SKELETAL MUSCLE CELLS
New evidence on mitochondria
mtDNA
Morpho-functional changes
MITO TRACKER GREEN
Mito Tracker Green is a mitochondrial-selective fluorescent label
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)
Mitochondrial network in skeletal muscle cells
C
D
Confocal microscopy of myoblasts (A, B) and late myotubes (C,D,E)
after Mito Tracker staining
Barbieri et al., 2011
Bar=20μm
The mitochondrium is active when
the mitochondrial membrane
potential (MMP) is highly negative
ΔΨ ~ -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
Mitchondria are in a constant state of fusion and division inside the cell
Mouli et al., Frequency and selectivity of mitochondrial fusion are key to its quality maintenance
function, Biophysical Journal (2009)
BALANCE OF MITOCHONDRIAL FUSION AND FISSION
1 um
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).
MITOCHONDRIAL ARRANGEMENT IN MUSCLE CELLS
A
B
C
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-C1158 2006
MITOCHONDRIAL POPULATIONS IN MUSCLE CELLS
Recent studies have shown multiple functional interactions among mitochondria,
sarcoplasmic reticulum and myofibrilles in skeletal muscle fiber
sarcomere
myofibrilles
Sarcoplasmic
membrane
sarcoplasmic
reticulum
mitochondria
SS
Transmission electron
micrograph of SS
subsarcolemmar and IMF
intramyofibrillar mitochondria
IMF
in muscle fiber
Kindly provided by Hood D, 2004
Anderson et al. 1981 Nature 290, 457 - 465
“The complete sequence of the 16,569base pair human mitochondrial genome
(mtDNA) is presented…”
Human mitochondrial genome (mtDNA)
mtDNA :
16,569
base pairs
MITOMAP
(http://www.mitomap.org/MITOMAP)
37 genes:
2 rRNA;
22 tRNA;
13 mRNA for oxidative
enzimatic subunits
MITOCHONDRIAL MYOPATHIES
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)
NUCLEAR AND MITOCHONDRIAL DNA COOPERATION
Nucleus or mitochondria
Mitochondria
Nucleus
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).
Burger et al. 2003
NUCLEAR AND MITOCHONDRIAL DNA COOPERATION
Complex
Mitochondrial genes
I NADH dehydrogenase
II Succinate CoQ Reductase
III Cytochrome b-c1
IV Cyctochrome c-oxidase
V ATP synthase
7
0
1
3
1
Nuclear genes
> 25
4
10
10
11
MITOCHONDRIAL FUNCTIONS


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
Maintenance of energy stores, ergogenics
Thermogenesis
Apoptosis
Pathological processes associated with mtDNA mutations (MELAS MERRF NARP),
APOPTOSIS
Apoptosis, or programmed cell death, is a normal component of the
development and health of multicellular organisms.
The breakdown of
chromatin in the nucleus
The end stages of apoptosis
are characterised by
membrane blebs.
Small vesicles called
apoptotic bodies are also
sometimes observed (D,
arrow).
APOPTOSIS
FUNDAMENTALS OF MUSCLE MITOCHONDRIAL BIOGENESIS
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