Dr Mark Bass
Room: B2 05 Florey building
Brief career history
Fibroblast migration during wound healing: signalling from extracellular matrix receptors to Rho-family GTPases.
Fibroblast migration during wound healing: signalling from extracellular matrix receptors to Rho-family GTPases
However, these processes become less efficient with age and risk factors such as diabetes, obesity or smoking, eventually leading to the formation of chronic wounds that include pressure ulcers, venous leg ulcers and diabetic foot ulcers.
The two hallmarks of a chronic wound are a chronic inflammatory response as the skin tries unsuccessfully to deal with infection and failure by fibroblasts to proliferate and migrate. The fact that scars are usually a fraction of the size of the original wound demonstrates very simply the importance of fibroblast migration and wound contraction, and improving this process is the core objective of our work.
Our laboratory investigates the activation of fibroblasts upon wounding, and the mechanisms by which migration is directed by regulation of the Rho family GTPases, especially the protrusion regulator, Rac1. Our work ranges from the investigation of signalling networks in single cells, through the analysis of in vivo wound healing models, to the development of therapies for treatment of patients.
The work can be divided into three main areas:
1) Regulation of membrane protrusion by Rho-family GTPases
Cell migration requires cycles of protrusion at the leading edge and contraction within the cell body, driven by the activation of Rac1 and RhoA respectively. The appearance of fibronectin in wounded tissue triggers cycles of Rac1 and RhoA activity in fibroblasts by engagement of the fibronectin sensor, syndecan-4.
We are examining how syndecan-4 regulates and coordinates Rac1 and RhoA signals by combining traditional biochemistry (A) with live cell imaging and FRET-based analysis (B). Perturbation of components of the syndecan-4 signalling chain by RNAi is revealing that syndecan-4 synchronises the activation/inhibition of Rac1 and RhoA signals and more importantly localises protrusion. By examining the migration of cells through complex fibrillar matrices, which are structurally similar to skin (C), we find that sydecan-4-directed GTPase regulation is necessary for persistent migration along matrix fibers.
A) Activation of Rac1 upon engagement of syndecan-4 by fibronectin, detected by pull-down assay.
2) Cooperation between extracellular matrix receptors regulates focal adhesion dynamics
Membrane protrusion must be coordinated with formation and dissolution of focal adhesions for migration to occur. We are investigating the regulation of integrin trafficking by syndecan-4 using atomic force microscopy to measure adhesive strength (D+E) and TIRF to follow removal of β1-integrin from the adhesion plane upon engagement of syndecan-4 (F). We are also using mass spectrometry to identify key trafficking regulators, and through this approach uncovering key roles for sorting nexins in integrin trafficking (G).
D) Single cells captured on the cantilever of an atomic force microscope can be brought into contact with an extracellular matrix before withdrawal of the cell to measure strength of adhesion.
3) Regulation of Rac1 by matrix receptors regulates cell migration in vivo and allows the development of healing therapies
The translation of our findings to in vivo healing models, and subsequently patient therapies is a crucial aspect of our work. The consequences of disrupting Rac1 signalling are that migration becomes less efficient, leading to delays in developmental and healing processes, and can be demonstrated in both fish (H) and mammalian (I) models.
We are investigating techniques to reverse healing defects by activating Rac1. Our most notable advances have come from the use of low-intensity pulsed ultrasound to stimulate fibroblast migration (Video protocol). (J) We find that skin wounds heal more slowly in diabetics (green curve) than healthy individuals (orange curve).
However, normal healing can be restored by daily treatments with ultrasound (pink line). The effect of ultrasound can be seen at the cellular level in biopsies as the number of brown fibroblasts recruited to an ultrasound-treated diabetic wound far exceeds that recruited to an untreated wound (K).
H) Knockdown of the Rac1 trafficking molecule, coronin 1C causes misalignment of pharyngeal arches in the developing zebrafish, due to compromised neural crest migration.
By combining this range of approaches to address the mechanism of fibroblast migration during wound healing, we move closer to developing some promising therapies, and bringing them into mainstream clinical use.
Undergraduate and postgraduate taught modules
Postgraduate PhD Opportunities
Title: Developing tumour treatments by modulating the senescent and secretory phenotypes of cancer-associated fibroblasts using ultrasound
Supervisor 1: Dr Mark Bass
Supervisor 2: Dr Daniel Lambert
Funding status: Competition funded project European/UK students only
This project is eligible for a department scholarship. These scholarships are awarded on a competitive basis – find out more on our funding webpage.
Tumours are commonly described as wounds that do not heal. Tumours and chronic wounds comprise dysregulated epithelial cells, senescent fibroblasts, and share similar gene expression profiles. Fibroblast senescence is the major hallmark of chronic wounds, as proliferation defects prevent wound contraction and alters secretion that in turn directs epithelial cell behaviour. Cancer-associated fibroblasts (CAFs) play a similar role in tumour formation. Senescent CAFs promote the growth and metastasis of cancer cells.
Over time, fibroblasts naturally tend towards senescence, which results in a decrease in healing rates and predisposition towards cancer as we age. We recently discovered that low-intensity ultrasound can promote healing in mice with pathological healing defects caused by diabetes or old age, by reversing and protecting fibroblasts from senescence. This PhD will investigate the effect of ultrasound on CAF senescence, leading to the development of new cancer therapies.
Such an application could have two possible impact points:
1) If ultrasound can reduce the senescence of established CAFs, it could be used to abolish the senescence-associated secretory phenotype that supports tumour growth, thereby directly acting as a cancer therapy.
2) One of the greatest limitations of conventional chemotherapy is the collateral damage to surrounding tissue. Therefore, if fibroblasts in proximity to tumours could be protected from stress-induced senescence by ultrasound, conventional chemotherapy could be improved.
Therefore the aims of this project are:
1) To determine whether ultrasound can restore proliferation, metabolism and regulated apoptosis to skin fibroblasts and squamous cell carcinoma-derived CAFs that have already reached either replicative or stress-activated senescence. Such an application would allow treatment of existing cancers.
2) To determine whether application of ultrasound during induction of stress-activated senescence can protect skin fibroblasts and CAFs from senescence, thus allowing the development of future combination therapies.
3) To resolve the effect of ultrasound on the secretory phenotype of senescent fibroblasts. Ultimately, the influence of CAFs over associated tumour cells is more important than the health of the fibroblasts themselves as it will regulate the proliferation and invasion of the tumour itself. This section of the project will assess the effects of senescence and ultrasound on levels of secreted factors, such as IL-6, as well as the effects of fibroblast-conditioned media on tumour cell migration and proliferation.
Therefore this project will involve the investigation of cell proliferation and migration, including both cancer cell migration and invasion analysis in vitro. The project will involve fluorescent techniques including time-lapse microscopy and flow cytometry, as well as ELISA approaches and mass spectrometry to analyse the secretome of treated fibroblasts. The project will place great emphasis on the development of protocols to stimulate live samples with ultrasound, providing great opportunity for innovation under the tutelage of experienced cell biologists and ultrasound experts. Importantly, by running this project in parallel with our ongoing healing studies, there will be many opportunities to meet with clinicians, engineers, and industrial partners thus providing a broad education in research with direct insight into the development of products for clinical application.
Keywords: Biochemistry, Biomedical Engineering, Biotechnology, Cancer / Oncology, Cell Biology / Development, Medical/Biomedical Physics, Medical/Clinical Science, Molecular Biology
Roper, Williamson, Bally, Cowell, Brooks, Stephens, Harrison, Bass. (2015)
Bass, Williamson, Nunan, Humphries, Byron, Morgan, Martin, Humphries. (2011)
Kabir, Leigh, Tasena, Mellone, Coletta, Parkinson, Lambert (2016). A miR-335/COX-2/PTEN axis regulates the secretory phenotype of senescent cancer-associated fibroblasts.
For informal enquiries about the project or application process, please feel free to contact
For further information about these projects and how to apply, see our PhD Opportunities page:
- Williamson RC, Cowell CAM, Reville T, Roper JA, Rendall TCS & Bass MD (2015) Coronin-1C Protein and Caveolin Protein Provide Constitutive and Inducible Mechanisms of Rac1 Protein Trafficking. Journal of Biological Chemistry, 290(25), 15437-15449. View this article in WRRO
- Roper JA, Williamson RC, Bally B, Cowell CAM, Brooks R, Stephens P, Harrison AJ & Bass MD (2015) Ultrasonic Stimulation of Mouse Skin Reverses the Healing Delays in Diabetes and Aging by Activation of Rac1. Journal of Investigative Dermatology, 135(11), 2842-2851. View this article in WRRO
- Williamson RC, Cowell CAM, Hammond CL, Bergen DJM, Roper JA, Feng Y, Rendall TCS, Race PR & Bass MD (2014) Coronin-1C and RCC2 guide mesenchymal migration by trafficking Rac1 and controlling GEF exposure. Journal of Cell Science, 127(19), 4292-4307. View this article in WRRO
- Bass MD, Williamson RC, Nunan RD, Humphries JD, Byron A, Morgan MR, Martin P & Humphries MJ (2012) A Syndecan-4 Hair Trigger Initiates Wound Healing through Caveolin- and RhoG-Regulated Integrin Endocytosis. Developmental Cell, 23(5), 1081-1082.
- Bass MD, Roach KA, Morgan MR, Mostafavi-Pour Z, Schoen T, Muramatsu T, Mayer U, Ballestrem C, Spatz JP & Humphries MJ (2007) Syndecan-4–dependent Rac1 regulation determines directional migration in response to the extracellular matrix. The Journal of Cell Biology, 177(3), 527-538. View this article in WRRO