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
- 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