Transcript Ca2+- independent Positive Inotropy for Failing Cardiac Muscle by α

Presentation by Les Sprague
HF is a syndrome that is the end product of many diseases in
developed countries. It is caused by cardiac dysfunction due
to myocardial muscle loss or dysfunction. HF leads to
abnormalities in circulation which can result in fluid retention,
shortness of breath, and fatigue. Without treatment, it is
normally a progressive disease and often times fatal.
HF is very common, and
is also extremely
expensive to treat. HF
is estimated to cause
the suffering of about
2% of the adult
population in
developing countries.
Also, it is estimated
that its treatment in
the US alone costs
about $35 billion/year!
That is enough money
to buy every person in
America about 114
McChickens…
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Inotrope – An agent that mediates an
alteration in the force of muscular
contraction. Negative agents weaken force,
while positive inotropic agents increase force
of contraction.
Ischemia – a lack of blood supply which
causes the death or dysfunction of tissue
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The functional heart provides the body with
essential oxygen and waste removal from
tissues throughout the body.
Intercalated disks in cardiac muscle
propagate a rapid depolarization to adjacent
cells which stimulates the heart muscle to
contract.
“functional syncytium” – the myocardium acts
as one contractile unit
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Myocardial cells have a negative membrane
potential at rest.
Stimulation induces voltage gated channels to
open, causing cations to move into the cell. The
cations entering the cell cause an action potential.
Depolarization causes voltage gated calcium
channels to open, releasing Ca2+from the ttubules.
Calcium influx causes calcium to be released from
the sarcoplasmic reticulum.
Extracellular calcium is required for contraction to
occur in myocardium
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Many of the traditional methods for the
treatment of HF focus on up-regulating the
amount of calcium available in cardiac
muscle
This increase in calcium induces positive
inotropy of the heart muscle, thus
increasing cardiac muscle contraction
strength
Calcium modification has been shown to
increase the likelihood of fatal arrhythmias
over long term use
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The method to increase cardiac output in
ischemic failing hearts without modification
of calcium could prove extremely beneficial
to the treatment of HF patients.
Myosin is a key motor protein in cardiac
muscle
α-myosin motor gene transfer could prove
to be a method for calcium free positive
inotropy
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The gene that encodes the heart’s fast
motor protein (α-MyHC) is MYH6
The cDNA for α-MyHC is ~5820 bp and was
cloned using PCR and isolated from a
human heart cDNA library
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Healthy hearts normally have ~10% α-MyHC
comprising the total cardiac myosin, with
the remaining 90% being β-MyHC.
HF cases with ischemic failing hearts have
shown a reduction of α-MyHC to
undetectable levels in cardiac myosin
This supports a link between cardiac
myosin isoform expression and heart
performance and is the target of this study
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New Zealand White rabbit myocytes were
isolated for study
Human myocytes were also isolated from the
explanted heart of a HF patient
To deliver the gene to cardiac myocytes, a
recombinant adenoviral vector (AdMYH6) was
made for gene transfer of the full MYH6 gene
in vitro
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Double stranded DNA viruses
Are NOT incorporated into host DNA
Adeno DNA is free in the nucleus, where it is
transcribed
Are not replicated during cell division
Often require repeated administration
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There is evidence that the transduction of αMyHC into a failing heart can increase the
cardiac output of the heart muscle while not
affecting the calcium concentrations in the
myocytes
It is also clear that the AdMYH6 is an effective
and efficient method for gene delivery in vitro
"Cardiac action potential." Wikipedia. Web.
<http://en.wikipedia.org/wiki/Cardiac_action_potential>.
Freeman, Scott. Biological Sciences. 2. Upper Saddle River:
Pearson Prentice Hall, 2005. 1018-1021.
Herron, Todd. "Ca2+ - independent positive molecular inotropy
for failing rabbit and human cardiac muscle by a-muosin
motor gene transfer." FASEB Journal. 24. (2009): 1-10.
"Heart failure." Wikipedia. Web.
<http://en.wikipedia.org/wiki/Heart_failure>.
"Inotrope." Wikipedia. Web.
<http://en.wikipedia.org/wiki/Inotropy>.
"Ischemia." Wikipedia. Web.
<http://en.wikipedia.org/wiki/Ischemia>.