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Pre-translational changes in myosin isoforms, myostatin and IGF1 in stimulated skeletal muscle

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Title: Pre-translational changes in myosin isoforms, myostatin and IGF1 in stimulated skeletal muscle


1
Pre-translational changes in myosin isoforms,
myostatin and IGF1 in stimulated skeletal muscle
Lauren Moore
Department of Human Anatomy and Cell biology
Skeletal muscle characteristics
qRT-PCR Results - MHCs
MHC I
MHC IIa
Differential mRNA expression in stimulated vs.
unstimulated muscle.
Contractile properties
  • Skeletal muscle is a highly plastic tissue which
    adapts readily to changes is load and activity.
  • Myosin, the principle contractile protein in
    skeletal muscle, consists of 2 myosin heavy
    chains (MHC) and 4 myosin light chains (MLCs).
  • The proportions of MHC isoforms are the main
    determinant of the contractile characteristics of
    the muscle.
  • 4 major MHCs in mammalian skeletal muscle MHCI,
    IIa, IIx and IIb.
  • Type I is slow contracting and fatigue resistant
    whereas type II is fast contracting and fatigues
    more rapidly.
  • Muscle can change its isoform expression in
    response to hormonal or mechanical stimuli, such
    as electrical stimulation.

MHC IIx
MHC IIb
Mouse 1 Mouse 2 Mouse 3 Mouse 4
Mouse 1 Mouse 2 Mouse 3 Mouse 4
Muscle Size
Muscle can increase (hypertrophy) or decrease
(atrophy) in size in response to biological
demands.
Stimulation Pattern 3
Stimulation Pattern 5
Stimulation Pattern 3
Stimulation Pattern 5
  • Myostatin
  • Inhibits muscle growth
  • Increased myostatin expression leads to atrophy
  • Mutation in myostatin gene leads to
    double-muscled phenotype in cattle
  • IGF1
  • Stimulates muscle growth
  • Increased IGF1 expression leads to hypertrophy

qRT-PCR Results Myostatin and IGF1
Differential mRNA expression in stimulated vs.
unstimulated muscle.
Myostatin
IGF1
Aims To assess pre-translational changes in the
expression of MHCs, myostatin and IGF1 in
response to various stimulation patterns in mouse
skeletal muscle
Methods
  • An implantable stimulator was used to stimulate
    the left Tibialis Anterior (TA) muscle of mouse
    subjects
  • The right TA muscle was used as an unstimulated
    control
  • Following stimulation muscles were excised and
    frozen at -80C, RNA was extracted and cDNA
    synthesised
  • Conclusion
  • Pre-translational changes in all genes of
    interest were detected using qRT-PCR
  • Both stimulation patterns show a decrease in the
    fastest MHC IIb isoform and a trend towards the
    intermediate (MHC IIa) and slower (MHC I)
    phenotypes, as shown in the graphs
  • Different stimulation patterns brought about
    different degrees of isoform transition
  • Both myostatin and IGF1 mRNA expression decrease
    following both types of stimulation this
    suggests a decrease in both protein synthesis and
    protein degradation following 1 week of both
    stimulation patterns

Stimulation patterns
Pattern 5 ON 100Hz, 250ms OFF 1000ms AVERAGE
20Hz
Pattern 3 ON 40Hz, 300ms OFF 700ms AVERAGE
12Hz
  • Where next?
  • We will assess changes in mRNA of genes of
    interest using a matrix of 3 different
    stimulation patterns, for 3 different time
    periods with 3 different loads ranging from
    unloaded to maximum loading.
  • We will look at the mRNA levels of all genes of
    interest in various muscles in mouse and rat such
    as TA and Extensor Digitorum Longus (EDL) which
    are predominantly fast muscles and Soleus and
    diaphragmatic muscle which are predominantly slow
    muscles to see how MHC isoform expression levels
    vary.

Mouse Samples
4
3
2
1
Acknowledgements Muscle Research Group, Dr. Judy
Coulson, Dr. Jonathan Jarvis
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