Investigating biomechanical responses in healthy and diseases ageing cartilage - a tissue engineering approach

Why did we fund this project?

This award aims to grow cartilage cells in an in vitro stratified mechanoresponsive model replacing mice used in studies of disease progression in musculoskeletal disease and ageing, such as osteoarthritis. 

Chondrocytes are the only cell type present in healthy cartilage, which produce structural components maintaining the functionality of the tissue. Cartilage is an avascular tissue with limited regenerative capacity, which can lead to degenerative conditions such as osteoarthritis. The most common study for osteoarthritis is a surgical procedure, performed under general anaesthetic, to transect the knee meniscus in mice. Due to the level of suffering caused, this procedure is classified as moderate under the UK’s Animals (Scientific Procedures) Act 1986. Transgenic animals are also often generated to better understand the role of specific genes and pathways in musculoskeletal disease and ageing. Chondrocytes are difficult to maintain in vitro as the cells lose function outside their specific niche and without the mechanical stimulation usually present in the cartilage. This limits their use as a replacement model.

Building on preliminary data, the student will use synthetic hydrogels and bioprinting to replicate the structure of cartilage in vitro. Growth factor gradients will be used to sustain human chondrocytes in the microtissues, which will then be mechanically stimulated using a commercially available compression system. The student will characterise the system by comparing transcriptomic data from the in vitro model to historic data from animal models. The student will develop skills in RNA sequencing, mass spectrometry and histological techniques.

Musculoskeletal conditions are a severe burden on the modern ageing society, with an estimated 8.5 million people affected by osteoarthritis (OA) in the UK alone, and an economic impact of 1-2.5% of GDP in most developed countries. There is currently no effective OA treatment available other than pain alleviation and a full joint replacement therapy. As the life expectancy of modern populations increases, there is an urgent clinical need for understanding the molecular pathways involved in healthy cartilage ageing and for developing cost - effective therapies to enhance the quality of life of patients with age-related conditions. However, studies of disease progression and of efficacy of proposed treatments are largely hindered by the low regenerative potential of musculoskeletal tissues that leads to limited amount of study material. Moreover, the mechanoresponsive nature of these tissues and the timescale of development of age-related changes means that many studies require the use of mammals (mice, guinea pigs, rats) as disease models.

The challenge for reducing animal use in research lies in the maintenance of human primary cells that often de-differentiate in the laboratory setting due to their dependence on three dimensional microniches and mechanical stimulation. Up to 70% of all animal ageing experiments are performed in mice, with 17,449 out of 24,477 musculoskeletal basic studies and 3,651 out of 5,958 musculoskeletal disease studies reported in mice in the 2017 Annual Return of Procedures in the UK. A commonly used OA study is a moderate severity surgical protocol under general anaesthesia that requires transection of the medial meniscus and utilises 10-30 mice, and on average 100 animals are required to maintain a genetically modified line. Moreover, studies of mechanosignalling often require restraint, anaesthesia and impact of moderate severity. The majority of tissue engineering efforts at present centre on developing transplantable grafts or vehicles for delivery of cell therapy to the injured site.

In contrast, we propose to develop a zonally stratified mechanoresponsive model of cartilage that is specifically designed to enable studies of disease progression and therapeutic intervention in musculoskeletal disease and ageing. This model will lead to consistency and reproducibility of laboratory experiments and dramatically reduce the need for animal models of cartilage disease. Recent advances in tissue engineering, such as the use of hydrogels and bioprinting, coupled with relevant biomechanical cues, present new exciting avenues for tissue modelling and disease mechanism discovery.

This project builds on a recently established collaboration in which tissue engineered models of cartilage have been developed at Newcastle University. It combines the expertise of a cartilage biologist and a tissue engineer in order to build a biomechanically responsive in vitro model of cartilage that will reduce the need for animal models to study cartilage homeostasis. During the project, novel bioprinting approaches will be employed to re-create the hierarchical organisation of cartilage with correct growth factor supplementation. Cartilage micro-tissues will be fabricated using commercially available foetal, adult and OA chondrocytes embedded in hydrogel matrix reminiscent of native tissue micro-environment, and mechanically stimulated during 28 day chondrogenesis protocol using state-of-the-art Flexcell FX500TM dynamic compression system. Cellular differentiation and senescence will be analysed using histology, extracellular matrix proteome will be assessed by mass spectrometry, and RNA sequencing will be used to assess gene expression changes in the engineered tissues. The data will uncover age and disease specific molecular pathways and will be compared to transcriptomic data previously obtained from animal models of musculoskeletal disease to further uncover potential therapeutic targets for healthy cartilage ageing.