Title: Pre-translational changes in myosin isoforms, myostatin and IGF1 in stimulated skeletal muscle
1Pre-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