DiMeN Doctoral Training Partnership: Studying energy metabolism in tissue engineered cartilage – are mitochondria crucial regulators of joint rejuvenation?

In this project we will investigate how exercise helps to maintain healthy joints by using a novel combination of tissue engineered cartilage, bioreactors, nanoparticle-based environmental reporters and mitochondrial analysis.

Cartilage is a very unusual environment which restricts the availability of both glucose and oxygen to cells. We are interested to see therefore how cartilage cells (chondrocytes) balance their energy requirements with the need for tissue regeneration. In particular, we want to discover how they sense and respond to healthy levels of exercise by forming more resilient cartilage, and investigate the role of mitochondria as regulators of this process which might be novel targets for treating osteoarthritis.

Since cartilage contains no blood vessels, chondrocytes at the articulating surface of the joint obtain all of their nutrients and oxygen from the synovial fluid, and exercise helps to physically perfuse these cells with dissolved metabolites and nutrients much like squeezing a sponge. At other times, stagnation of this fluid (during prolonged bed rest or sedentary old age) means that chondrocytes have less access to nutrients and oxygen, and damaging waste products including reactive oxygen species can accumulate.

Cartilage biology is therefore very clearly reliant on both dynamic mechanical loading and energy metabolism, but studying this in live humans not possible, and small rodent models have a very thin layer of cartilage which is completely unrepresentative of nutrient transfer in thicker human cartilage. We will instead adopt the novel approach of using ‘tissue engineered’ human cartilage in which we recreate a replica of human joint tissue in the lab from a combination of hydrogel and primary human stem cells/chondrocytes. This tissue engineered cartilage is being developed as a source of replacement joint tissue for osteoarthritis, but in our project we will use it as an advanced 3D platform for studying cell biology which would be impossible using any other means.

The core research in this project is to investigate metabolism in tissue engineered cartilage using advanced nanoparticle-based reporters, provided by a senior collaborator at the National Tsing Hua University, Taiwan. These nanoparticles uniquely integrate fluorescence reporters for glucose, oxygen and pH into a combined nanoparticle that identifies highly localised chemical changes in the environment. Furthermore, they can be located to either the extracellular environment or functionalised for internalisation within cells and organelles (in this case, mitochondria).

We will then put the tissue engineered cartilage into bioreactors – machines which dynamically compress the TE cartilage and simulate the type of exercise that would normally be experienced by cells in an active joint. After set periods of this simulated exercise we will identify changes in the intracellular and pericellular physical/chemical environment via the nanoparticles and analyse the mitochondria using fluorescent imaging to look at their morphological changes in response to compressive loading, measure their ROS production, mitochondrial membrane potential, and perform qPCR/western blotting for changes in gene expression/proteins. A co-supervisor at the University of Leeds will lead the mitochondrial analysis training, and you will have the opportunity to regularly visit and work in this laboratory as part of the PhD.

You will learn cell culture, tissue engineering, bioreactor physics and materials science as well as live cell imaging, confocal laser scanning microscopy and the cutting-edge technique of Lightsheet microscopy, then further even more specialist expertise in advanced mitochondrial analysis at the partner lab. We also intend that you will have opportunity to visit and work in the labs in Taiwan for a short period to learn the nanoparticle fabrication techniques and design new reporter coatings. We strongly support opportunities for international travel, conference presentations and all types of networking to increase our core strengths and presence in the global research community.

This project has excellent opportunities for extremely interdisciplinary doctoral training in tissue engineering, nanotechnology, functional materials science and mitochondrial biology. Treating degenerative diseases of cartilage (osteoarthritis) is a primary focus in ongoing healthcare research and therefore has substantial opportunities for subsequent postdoctoral or clinical research. You will therefore obtain an extremely adaptable and translational interdisciplinary PhD which will act as a springboard into an academic, clinical or industrial career.