Pluripotent and embryonic stem cells
Overview of the work of the Pluripotent and Embryonic Stem Cells Group
Induced pluripotent stem cells. Like embryonic stem cells these cell stain for pluripotency markers, OCT4 and NANOG (Red). Cell nuclei are stained blue using DNA stain (DAPI).
The group is directed by Dr Wael Kafienah, Lecturer in Stem Cell Biology. The team is currently investigating the molecular regulation of human embryonic stem cells and induced pluripotent stem (iPS) cells. The iPS cell technology promises an unlimited source of autologus, pluripotent stem cells for regenerative medicine applications. Our research programme in this area is mainly focused on understanding the mechanisms for driving the differentiation of human embryonic stem cells and iPS cells into skeletal cells using novel biomaterials as well as the pharmacological regulation of differentiating embryonic and iPS cells. This technology is a new area in regenerative medicine that promises precise control of stem cell fate in vitro and in vivo and paves the way for animal free, clinical grade stem cells.
Pluripotent stem cells
There are several types of stem cell and these can be divided into those derived from embryos (Embryonic stem cells), those derived from adult tissue (adult stem cells) and those derived from the reprogramming of adult cells so that they behave as if they were embryonic stem cells (induced pluripotent stem cells). Our work focuses on pluripotent stem cells including embryonic stem cells and induced pluripotent stem cells. We also collaborate with Prof. Hollander's team on their adult stem cell research. Unlike multipotent adult stem cells, pluripotent stem cells have the capacity to multiply indefinitely hence, providing unlimited supply of cells for therapeutic purposes and research. Pluripotent stem cells can differentiate into all cell types of the body compared to adult stem cells that differentiate into a small, tissue specific cell types. These advantages give them greatest versatility but also necessitate in-depth understanding of signalling pathways that control their fate.
Cartilage repair using pluripotent stem cells
Cartilage tissue engineering using embryonic stem cells. Top panel shows cells incubated on scaffolds coated with fibronectin, a sticky protein. When protein is not included in engineering process, tissue fails to mature (lower panel).
Several groups including the Bristol team have demonstrated the capacity of adult stem cells to engineer cartilage to treat defect that results from trauma or osteoarthritis. However in order to move forward with an of-the-shelf cell therapy for cartilage tissue engineering, allogeneic (i.e. immunologically compatible) stem cell sources that are unlimited in number need to be explored. Pluripotent stem cells derived from embryonic stem cells or reprogrammed can provide such a source. Even better, pluripotent stem cells derived from reprogrammed adult cells can be obtained from the same patient therefore providing an unlimited source of autologous pluripotent stem cells for that patient. Through funding from the University of Bristol Centenary Campaign, our team is investigating the factors that drive the process of generating chondrocytes from pluripotent stem cells. This is done through learning from signaling pathways taking place during body development and adapting these signals for optimal tissue engineering using pluripotent stem cells.
Novel biomaterials for cartilage tissue engineering
Scanning electron microscopy photographs of the surface of macroporous (left) and microporous (right) elastomers.
Stem cells seeded onto a film of cellulose (left) showing changed phenotype compared stem cells grown on plastic as a standard (right).
Engineering cartilage tissue is a sophisticated process that requires stem cells, signals that can drive their differentiation into chondrocytes and a scaffold that holds the cells in a 3D structure to form the new tissue. Successful cartilage tissue engineering requires the scaffold to fill the defect space and signal to the cells to sustain their function. Through funding from Qatar Foundation our team is collaborating with Dr Husam Younes in Qatar University to explore a novel class of scaffolds that can polymerise at the defect site once exposed to light. These photopolymers can take the shape of the defect, that is usually irregular, and ensure complete fit with surrounding cartilage.
The use of soluble factor to drive the differentiation of stem cells is commonplace. Progress towards clinical grade tissue engineering favours reducing the need to rely on soluble factors, which are normally from potentially contaminated animal sources. One method to do that would be to facilitate the differentiation of stem cells by the scaffold itself. This can be achieved by manipulating the stiffness the scaffolds on which the cells are seeded. Indeed the stiffness of the extracellular matrix (ECM) of proteins was shown to significantly affect cell function: cells can detect and respond distinctly to soft versus stiff ECM. For example a soft matrix favours differentiation of stem cells into neuronal-like cells and a high stiffness substrates stimulated osteogenic (bone like cells) differentiation. Through pilot funding from the UK Engineering and Physical Sciences Research Council (EPSRC) and in collaboration with Dr Sameer Rahatekar in Aerospace Engineering, we aim to fabricate blends of naturally occurring fibres with varying degrees of stiffness as a substrate for driving stem cell to become chondrocytes.
Stem cells and disease: Bacterial-stem cell interaction in osteomyelitis
Photographs showing adhesion of S. aureus strain to bone marrow stromal stem cells at low infection multiplicity (left) and high infection multiplicity (right).
Osteomyelitis (OM), an infection of the bone, is most commonly caused by the bacterium Staphylococcus aureus (80%). OM is a potential complication of bacteraemia (infection of the blood) and traumatic injuries that allow bacteria access to the bone. Up to 40% of people with diabetes, who experience a puncture injury to the foot, will develop OM and one in every 200 people with sickle cell anaemia will develop OM in any given year in the UK. Antibiotics remain the treatment of choice for acute OM if diagnosed early. In chronic OM antibiotic therapy often fails making bone debridement and amputation common options. S. aureus has been shown to invade the osteoblasts, the cells responsible for bone formation, via fibronectin and integrin α5β1. However, the mechanism(s) by which this microbe persists in the bone and evades the immune system in chronic OM remains unknown. In collaboration with Dr Darryl Hill in the School of Cellular and Molecular Medicine, we have been investigating how bacteria can bind to and influence the function of stem cells in the bone marrow. Dysfunctional stem cells lead to limited capacity to beat the infection and repair the damaged bone tissue. By understanding this interaction more targeted therapies can be designed and tested.