Investigating the cardiomyocyte rigidity sensing mechanism with micro patterned surfaces and nanopillars

Recent discoveries have shown that cells are guided by the stiffness of their environment in a process, called mechanosensing. This influences the fate of the cells in order to form a heart, a blood vessel or other tissue. The stiffness of the heart changes during development, in disease and also during ageing, thereby affecting how well the cells in the heart can beat. However, it is still unclear how the cells in the heart measure the stiffness, or if cells from healthy and diseased hearts can sense it in the same way.
In a previous study we found evidence that cells measure the stiffness at specific adhesive structures, known as costameres and focal adhesions through stretchable proteins. If the proteins are stretched, other proteins are activated to remodel certain cellular structures, called actin filaments.
The actin filaments come in different varieties. Some of them are specific for cardiomyocytes, while others are also found in other cell types, such as skin or immune cells and needed to anchor the cell, or for migration. On stiff surfaces we find an increased formation of the latter structures and we believe that this will reduce the formation of the former structures (which are needed for the heart to beat).
Moreover, based on others and our previous work we hypothesize that the composition of the adhesive structures changes during development and disease. Therefore, stretchable proteins with different characteristics could be located at adhesions at different times.
In order to understand how the cells in the heart sense the stiffness we need a clearer picture of what proteins are present at the adhesions and how this affects the formation of the different actin filaments.
Here, we want to answer these questions, by placing heart cells on synthetic substrates, which we can produce to have certain stiffnesses, or which we can use to measure the cellular forces. We can also print pattern onto these surfaces, on which the adhesive structures will form. This will allow us to monitor precisely, how much of which protein localizes to the adhesions.
Further, we will disturb different signalling pathways that are activated on stiffness comparable to a healthy or diseased heart and observe the changes in the way the cells behave in response to the treatment.
Together results from these experiments will lead to a deeper understanding how the heart senses the stiffness. This will allow the design of biomaterials to grow heart cells outside or inside the body to repair injuries from myocardial infarctions or other heart disease.

While chemical cues have well-established roles in guiding cellular processes from migration to differentiation or cell death, there is growing evidence of a role for mechanical stimuli. This has also been proposed for the cells in the heart, where changes to the extracellular matrix result in stiffening of the cellular microenvironment during development - and even further in heart disease.
Our previous results indicated cardiomyocytes simultaneously sense the contractions of muscle and non-muscle myosin. Depending on the activity of each class of myosin motors, this will lead to different dynamics of stretching of the mechanosensitive protein talin. Moreover, our results suggest that talin stretching feeds back into integrin activation and downstream actin assembly through the formin FHOD1.
Because there is competition between different actin assembly proteins this will impact the actin nucleation through other proteins and as a result the maturity of the contractile structures. However, the (inter-) regulation of the cardiomyocyte actin assembly in response to stiffness is still unclear. Moreover, based on the literature and our own results we hypothesise that not only the stiffness of the heart, but also the composition of the adhesions will change during development and disease, with important effects on how the mechanical sensing is regulated.
To answer these critical questions, we will use here a bottom up approach based on micropatterning to analyse adhesion composition and the cooperation - or competition between different actin nucleators in stem cell derived cardiomyocytes of different maturity, or genetic background. Moreover, we will use nanopillars and molecular tension sensors to analyse cardiomyocyte forces on different stiffness, extracellular matrix composition or after manipulation of key mechanosensor proteins. We expect this approach to result in a comprehensive understanding how cardiomyocytes sense the rigidity of their environment.

Ageing is a critical risk factor for heart disease. Because of the world's ageing population, with a doubling of the over 60 year olds from 2000 to 2050, this poses a major healthcare problem. Mechanobiology has the potential to open up new avenues for treating heart disease in general and, because ageing is associated with enhanced myocardial fibrosis and stiffening of the heart, especially ageing related cardiomyopathies. Detailed knowledge of how heart stiffness influences the behaviour of the cells will allow the development of new therapies based on novel biomaterials informed by our study or the identification of novel druggable targets - and this way contribute to the progress in the priority area 'Healthy ageing across the lifecourse'.
Further impact will be generated through collaborations, which we will establish during this project. We will especially look for collaborations with academics in complementary disciplines, such as materials science and drug development, or with the industry. With partners located within London, we will apply for PhD studentships as part of the BBSRC LIDo scheme (with academic partners) or the BBSRC CASE studentship scheme (with industry partners) to generate added value to the study. The School of Engineering and Materials Science at Queen Mary University of London is actively looking to enable collaborations with the industry through an annual Industrial Liaison Forum (ILF), which is an ideal opportunity to communicate the research to potential new industry partners. We will use these opportunities to seek new collaborations for a part industry sponsored studentship (BBSRC CASE or 50% QMUL funded PhDs). Finally, Queen Mary University of London will support this study with a fully funded PhD Studentship (UK/EU) to enhance the economic value to the BBSRC.

TI will work together with QM media relations to communicate the findings through news outlets or social media. The TI group has been previously involved in public engagement through the King's STARS (Science Training for Aspiring Research Scientists) program for talented school children from less privileged backgrounds, as well as involvement in Public Open Days at King's and will be similarly engaging with the general public at QM. Moreover, TI is currently collaborating with the British Heart Foundation Magazine 'Heart Matters' to make an animation movie to explain the use of nanotechnology in heart research to a broad non-scientific audience. In the future, we will be seeking similar collaborations to communicate the research outcomes to the public.