Understanding the activities of connective tissue fibroblasts during muscle formation towards understanding disease and engineering muscle tissue

Diseases that effect proper functioning of the musculoskeletal (MSK) system are common and can arise from birth defects, sports injuries, trauma, disease, normal wear-and-tear and age-related diseases. Together, MSK diseases contribute a significant burden on health care systems, carers and lead to lost productivity. The expanding ageing population means the number of cases of MSK disease, and the burden this imposes, will expand dramatically in the future. We aim to address the challenges of MSK disease and contribute to health benefits that will enhance quality of life, health and productivity.

The proposed work packages are unified in tackling the fundamental question of how are muscle tissues built and how this can become disrupted in disease. Understanding how tissues are built is essential to develop tissue engineering strategies and regenerative therapies that can replace tissue lost through trauma, wear-and-tear or disease. Disruption of tissue formation produces limb birth defects and understanding what and when events have gone wrong is critical for diagnosis, management and treatment regimes.

Our aim is by studying and understanding the molecular and cellular mechanisms that underpin how tissues are built, we can develop ways to replicate and harness these processes for tissue engineering and regenerative therapies.

We have chosen to focus on limb muscles as an experimentally tractable system and one that has clear clinical applicability. Tools are already available to make muscle fibres in a dish and we have a good understanding and control over how the progression of terminal differentiation of muscle precursors to myofibres is regulated. We have very poor understanding, however, of how myofibres are organised into blocks of tissue and as a result we are still a long way from being able to engineer functional muscle tissue.

Muscle tissue is not simply a collection of muscle fibres. A muscle bundle is a composite of muscle fibres and irregular connective tissue (ICT) fibroblasts, which are critical constituents of the highly organised architecture of a functional muscle bundle. Although the importance of ICT is well established, very little is known about what these cells do and how they act during muscle formation and repair. ICT and its derivatives, e.g. muscle fascia) is an essential component of muscle tissue. Learning and how to replicate or mimic the activities of ICT is an essential in any strategy to engineer muscle.

We are focussing on filling the current gap in understanding of the functions of ICT, in developing novel approaches to study ICT function and in developing novel approaches to engineer muscle tissue.

We are taking novel, mullti-disciplinary approaches to identify the mechanisms controlling muscle formation and repair and in developing tools to study these process and translate our findings into new treatments for MSK diseases.

We will also produce a freely accessible, reference database of human embryonic limb development that will create a permanent resource for educators, researchers and clinicians. This resource will help explain the precise origins of congenital limb abnormalities and reveal the sensitivity window when nascent tissues have been disrupted during human embryonic development.

My core objectives are to understand how tissues are constructed and how formation and maintenance of tissue integrity can go wrong in disease. Our focus is muscle tissue and specifically the action of a poorly understood population of cells called irregular connective tissue (ICT) fibroblasts. These ICT fibroblasts surround and are embedded within forming and mature muscles and have been implicated in muscle formation, repair and disease. While there is good evidence that ICT fibroblast are critical for muscle formation and disease, we do not understand how they are normally acting to control muscle formation and as a consequence, we do not know what process have been disrupted in diseases caused by malfunctioning ICT fibroblasts.

We are exploiting genetic tools in the mouse to carry out screens to identify the factors produced by ICT fibroblasts that orchestrate the formation of functional muscle bundles from a cohort of nascent muscle fibres. One approach we are taking is to examine the 'scaffolding' that surrounds all cells of the body, called the extracellular matrix (ECM). This 'scaffolding' can physically support and guide cells during tissue formation and influence the way cells respond to secreted signalling molecules. We have evidence that suggests that ICT fibroblasts control the behaviours of forming muscle fibres though their action on the ECM. We will carry out studies to test this hypothesis.
In parallel, using the knowledge we obtain from study of ICT fibroblasts, we will initiate efforts to engineer muscle tissue using co-culture of muscle cell and ICT precursors and study the abilities of artificial matrices to support tissue formation.

Diseases that affect proper functioning of the musculoskeletal (MSK) system are common and diverse. MSK disease can arise from birth defects, sports injuries, trauma, disease, normal wear-and-tear and age-related diseases. There are approximately 200 different musculoskeletal conditions that together account for 1 in 5 visits to the GP in the UK. This represents an annual cost of a £5 billion to the NHS and results in 30.6 million working days lost a year, adding a further cost to the UK of £7.4 billion annually (Health and Safety Executive, Health and Safety statistics 2009/10, 2009-10, Arthritis Research UK National Primary Care Centre, Keele University (2009), Musculoskeletal Matters.)

The effects of MSK disease are profound and wide reaching. Although MSK diseases are usually not life threatening, they are often chronic and in the case of birth defects they are life-long. MSK diseases therefore have significant impact on affected individuals, their carers and societal impacts in terms of health care costs and loss of productivity. Since many MSK diseases are associated with old age, the expanding ageing population means that the number of cases of MSK disease and the burden this imposes economically and societally, will expand dramatically in the future.

By understanding more about the underlying biology of how limb tissues are formed and how they repair and degenerate in old age or through disease, we aim to address the challenges of MSK disease and contribute to health benefits that will enhance quality of life, health and productivity.

This proposal will develop reagents and expertise and train researchers and clinician scientists in MSK research. It will expand our work into cross-disciplinary areas of biology, physics and chemistry impact into translational and clinical research.

A key objective is to develop muscle tissue engineering strategies for regenerative therapies and/or assay tools for drug discovery. If successful, these would lead to strategies in which tissue engineered muscle, grown from the patient's own cells, is used to reconstruct soft tissue defects following congenital anomalies, disease (e.g. cancer) or trauma. We also expect to identify biomarkers of muscle injury, repair and fibrosis that could provide diagnostic markers for disease progression or treatment outcomes improving early diagnostic and improved, targeted treatments. Commercialisation of tissue engineered muscle, other regenerative therapies and diagnostic tools will contribute to the UK biotech sector.