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Matters of the heart
Although mechanosensation is a fundamental
process it remains difficult to study because
it involves a vast array of very different
intracellular systems such as ion channels,
the cytoskeleton, kinases and phosphatases,
and changes in gene expression, which can
only be studied using different techniques
such as electrophysiology, biochemistry and
molecular biology.
Have you made any novel or interesting
discoveries towards the detection and
analysis of genes which could be involved
with cardiac mechanosensation?
To begin, what is the main focal point of your
research project?
Our objective is to understand how a single
mutation can cause a complex phenotype
or disease, particularly in the cardiovascular
system and the heart. We hope that by using
various assays, including generation and
analysis of genetically altered animals as well
as stem cell-derived cardiomyocytes, we can
identify the underlying molecular mechanism.
Could you explain the concept of cardiac
mechanosensation and outline the
importance of analysing this process?
Mechanosensation is the process whereby cells
perceive mechanical stimuli and translate them
into biochemical signals. It is a fundamental
process that can be found in every living cell
and is particularly important in the heart,
because it contracts and relaxes 2-3 billion
times during our lifespan.
How has your group’s previous work
led to improved understanding of the
macromolecular complex involved in
mechanosensensation in cardiomyocytes?
Mechanosensation had been analysed in
cardiomyocytes before, but our group was
the first to demonstrate that mutations in
structural proteins involved in the process of
mechanosensation lead to heart failure.
What are some of the major challenges
associated with a project of this type?
Recently we discovered that
mechanosensation is more directly linked to
cell survival pathways than initially thought.
In addition, mechanosensation seems to
be more directly linked to changes in gene
expression and factors that initiate these
processes, ie. transcription factors. My group
is currently focusing on trying to understand
the mechanisms that link mechanosensation
to changes in gene expression, an effect
that could be described as mechanotranscriptional coupling.
What are the characteristics of dilated
cardiomyopathy, and what role do Z-discs
play in this syndrome?
Dilated cardiomyopathy is a very common
disease, occurring in one out of every 2,000
individuals, and is a major cause of heart
transplantation. A significant proportion of
dilated cardiomyopathy cases are due to
mutations in the Z-discs, a structure now
called a ‘hot spot’ for mutations.
Z-discs constitute the lateral borders of
sarcomeres, the smallest functional units of
striated muscle cells, which can be found in the
heart or skeletal muscles. When proteins that
are part of these Z-discs become mutated, this
event can give rise to a wide variety of diseases
including dilated cardiomyopathy and heart
failure. Our group has reported on the first
Z-disc mutations that cause heart failure and
has termed all diseases linked to these novel
mutation ‘Z-discopathies’.
Why do you think hypertrophic
cardiomyopathy is particularly common
in competitive athletes?
This is a very interesting question but
not easy to answer. Hypertrophic
cardiomyopathy, in contrast to dilated
cardiomyopathy, is characterised by heart
wall thickening and increased myocardial
function. This condition, among others, is
also associated with life-threatening
arrhythmias and sudden cardiac death.
However, this disease manifests during our
midlife (ie. third, fourth or fifth decade of
our lifespan).
Professor Ralph Knöll
Professor Ralph Knöll studies the underlying molecular mechanisms that cause a genetic
mutation to lead to heart failure. Here, he discusses his group’s efforts in uncovering mechanisms
that could lead to the development of novel therapeutics to prevent heart failure in the future
It could very well be that evolution supported
the distribution of these genes simply
because for thousands of years we did not live
long enough to develop this disease and had
the advantage of being able to become more
successful hunters and gatherers (because of
the increase in myocardial function).
Could you highlight some of the
therapeutic methods or strategies that
have been employed in order to effectively
examine treatments for cardiomyopathy
and heart failure?
Due to our limited knowledge with regard
to the underlying molecular mechanisms
that link a single mutation to the disease,
it is very difficult to treat cardiomyopathy
and the associated heart failure. However,
recent genome-wide association studies and
experimental evidence suggest a link between
heart failure and loss of cardiomyocytes
via different forms of programmed cell
death (and hence cell survival pathways),
which offers the opportunity to interfere.
Another equally important strategy employs
regenerative medicine to replace the loss of
cardiomyocytes.
Where are you planning to concentrate your
research efforts in the near future?
Our group is focusing on understanding
mechanosensation, particularly how
mechanical stimuli are translated into various
adaptive responses. One poorly understood
aspect that needs to be investigated further
is epigenetics, which are inheritable traits not
based on DNA base pair changes. Ultimately,
we hope to translate the findings and
understanding of the underlying molecular
mechanisms into therapeutic solutions to
cardiomyopathies.
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Professor Ralph Knöll
Understanding cardiomyopathy
The heart translates billions of mechanical changes into biochemical signals during a lifetime. To truly understand how our hearts keep us alive and thus treat myriad heart disorders, we must understand the underlying molecular mechanisms and the proteins that bind various processes together
The heart is our most vital and precious
organ and diseases impacting its function,
known as cardiomyopathies, represent a major
cause of death worldwide. Cardiomyopathy is an
inherited disorder and affects people of all ages.
There are three main types of cardiomyopathy
– hypertrophic, dilated and arrhythmogenic
right ventricular. The former affects one in
500 people and is the most common inherited
cardiovascular disease, accounting for around
36 per cent of all sudden deaths in competitive
athletes in the US. Because of this high mortality
rate, it is of the utmost importance that our
understanding of this affliction improves. In
order to do so, the workings of the heart need to
be deciphered to the smallest detail.
Professor Ralph Knöll, Head of the Myocardial
Genetics group at Imperial College London, has
been researching cardiac mechanosensation,
a process where any mechanical change such
as contraction or reshaping of a heart cell
or cardiomyocyte is developed into a final
biochemical signal. By meticulously studying this
process, his group hopes to unravel the underlying
mechanisms involved in cardiomyopathies which
they then wish to translate into novel therapeutics.
Knöll’s team has focused on various structural
proteins found in the heart muscle which
are thought to play a role in this process of
mechanosensation. More importantly, they
have been studying how certain mutations
in these proteins are associated with various
cardiomyopathies and heart failure in vivo.
Over the past decade, they have identified
several proteins that play an important role in
mechanosensation in the heart.
Z-discs and dilated cardiomyopathy
To answer their many research questions, the
Myocardial Genetics group employs a vast array
of sophisticated methods and techniques such as
zebrafish analysis for in vivo function, yeast twohybrid screens to structurally analyse any new
players in mechanosensation, electron microscopy
of freshly isolated hearts and mouse models.
In trying to understand the molecular components
that play a role in mechanosensation, the
group studied a muscle LIM protein (MLP) in
the heart. This protein is part of the Z-disc
which is the lateral border of the sarcomere,
the smallest functional unit of striated muscle
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in the heart. The Z-disc plays a pivotal role in a
range of aspects of heart muscle structure and
function, including sarcomeric assembly and
organisation, sarcolemmal membrane integrity
and muscle force generation and transmission.
What they discovered through this investigation
of the MLP in the Z-disc was that this protein
has a selective role in mechanosensation and
interacts with telethonin protein, which is also
part of the Z-disc. Furthermore, they revealed
a mutation (W4R) in the human MLP protein
and linked it to dilated cardiomyopathy. The
mutation resulted in a significant alteration
of telethonin localisation and function. They
also discovered a mutation in telethonin. Thus,
in their studies they were the first to describe
human Z-disc protein mutations and link
Z-disks to the process of mechanosensation.
Telethonin and a
novel form of apoptosis
Part of the cardiac mechanosensory system
involves a signalosome – a compex of proteins
– that consists of telethonin and titin proteins.
Because of its role in this signalosome, as well
as the fact that several mutations have been
associated with cardiomyopathies, Knöll’s group
also decided to study the underlying molecular
mechanisms of telethonin in the human heart.
They discovered that, in contrast to what was
previously assumed, the telethonin protein was
in fact not vital for mechanical stability. However,
the group did find that the protein had a novel
function that links it to cell death (otherwise known
as apoptosis). It was shown that telethonin was
able to alter the turnover rate of the p53 tumour
suppressor following a spike of biomechanical
stress. The direct link of a mechanical event to
cell death was termed ‘mechanoptosis’, and this
finding was the first description of mechanoptosis
that was cell-type specific.
MLP and cardiomyopathy
One of Knöll’s main research agendas is searching
for novel mutations in structural proteins of
the Z-disc and linking these to various heart
disease pathologies. Also, his group is interested
in unravelling the underlying molecular
mechanisms. They had previously discovered a
missense mutation in the MLP protein gene, and
they wished to further investigate the effects of
this mutation in an in vivo setting.
Based on this previous research, where a
Tryptophan was replaced by an Arginine residue
at position 4, hence termed the W4R mutation,
they created a knock-in mouse model in which
they introduced this mutation into the MLP
gene. These mice developed cardiomyopathy
and heart failure, which was accompanied by
a devastating loss of contractile function under
stress. They also found that MLP mRNA and
protein levels were both greatly lowered in the
hearts of the W4R knock-in mice.
To tie in with their work on the telethonin
protein, the researchers found that there was
a lesser interaction between the W4R-MLP
protein and telethonin. This might explain why
there is increased localisation in the nucleus of
the mutated MLP protein. The finding of this
novel mutation was an important one, as Knöll
highlights: “This mutation is an important
human disease gene due to its high frequency
in the human population”.
Genetic research
In addition to being interested in the structural
role of Z-disc proteins in heart failure, the
Myocardial Genetics group also has a major
interest in the genetics of cardiomyopathy.
Their main genetics research foci centre
around several core themes: the relevance of
human mutations in genes involved in cardiac
mechanosensation; detection and analysis of
novel human disease genes; new therapeutic
approaches to treat cardiomyopathy and heart
failure, including kinase inhibitors, calcineurin
or
phosphatase
inhibitors;
structural
analysis of new components involved in
mechanosensation; zebrafish analysis to
explore in vivo function; generation and
analysis of novel genetically altered mouse
models; epigenetics of mechanosensation;
the relationship between mechanosensation
and
diastolic
dysfunction;
and
the
interactome, proteome and proteomics of
mechanosensation. By building up a full picture
of the genes and proteins involved in cardiac
mechanosensation, the researchers should
begin to unlock the secrets of heart disease,
which would constitute a major breakthrough
for cardiovascular science. It is the group’s goal
to keep moving forward with their research,
and they hope that their contributions will lead
to the development of novel therapies to treat
or prevent heart disease in the future.
Intelligence
British Heart Foundation –
Centre for Research Excellence
OBJECTIVES
• To analyse cardiac mechanosensation,
specifically the role of novel MLP
interacting proteins
• To understand the genetic basis of human
heart failure and cardiomyopathy
KEY GROUP MEMBERS
Dr Byambajav Buyadelger • Dr Catherine
Mansfield • Dr Onjee Choi • Sara Abou AlSaud • Peravin Mariathasan • Gudrun Knöll
KEY COLLABORATORS
Dr Paul J Barton • Professor Michael
A Ferenczi • Professor Steve Marston
• Professor Sian E Harding • Professor
Michael D Schneider
FUNDING
British Heart Foundation • German
National Genome Research Network
(Nationales Genomforschungsnetzes,
NGFN) • German Research Foundation
(Deutsche Forschungsgemeinschaft, DFG)
• Fritz Thyssen Foundation • EU Seventh
Framework Programme (FP7)
CONTACT
Professor Ralph Knöll, MD, PhD
Chair of Myocardial Genetics
Imperial College
British Heart Foundation –
Centre for Research Excellence
National Heart and Lung Institute Imperial
Centre for Translational and Experimental
Medicine
3rd floor, Hammersmith Campus
Du Cane Road
London
W12 0NN, UK
T +44 20 7594 3410
E [email protected]
www1.imperial.ac.uk/nhli/cardio/
heart/myogen/
Knöll’s team has focused on various structural proteins
found in the heart muscle that are thought to play a
role in this process of mechanosensation
PROFESSOR RALPH KNÖLL’s professional
training was conducted at the Max-PlanckInstitute of Physiological and Clinical
Research, Department of Experimental
Cardiology. He completed his clinical
training at the Free University of Berlin,
Universityhospital Benjamin Franklin (UKBF,
Charité) and was a postgraduate researcher
and then Group Leader at the Institute of
Molecular Medicine, University of California,
San Diego in 1999-2004, before joining the
Georg August University, Göttingen, Germany,
where he was Professor as well as Head of the
Working Group in Cardiovascular Molecular
Genetics. Knöll was recruited to Imperial
College as Professor and Chair of Myocardial
Genetics in October 2009.
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