Targeting alarmins to accelerate healing

Thesis

Promoting tissue repair in adults represents a major unmet medical need. Tissue regeneration relies on the activation of quiescent endogenous stem cells and whilst considerable progress has been made, novel therapies based on stem cells have thus far failed to translate to routine clinical practice. Much attention has focussed on administrating exogenous stem cells expanded or altered in vitro. However, this approach faces several major limitations, including poor engraftment, high cost and importantly, the necessity for immunosuppression for allogenic cells. An alternative strategy that overcomes these shortcomings is to promote repair by harnessing the regenerative potential of endogenous stem cells. This thesis focussed on the role of alarmins, the upstream group of mediators released immediately following injury, in promoting tissue regeneration. I show that the alarmin HMGB1 accelerates tissue regeneration in various systems by transitioning multiple stem cell types from the quiescent G₀ to the G_Alert state. Firstly, in vitro screening of candidate alarmins with human bone marrow-derived mesenchymal stromal cells showed that only pre-treatment with HMGB1 improved osteogenic differentiation. Using an optimised murine fracture model, I found that local administration of HMGB1 accelerated bone regeneration via the CXCL12-CXCR4 axis, whilst healing was impaired in inducible Hmgb1^-/- animals. Cell cycle analyses revealed that HMGB1 transitioned the skeletal stem cell from G₀ to G_Alert. In this intermediate phase, the cell is more metabolically active and efficiently enters the cell cycle when exposed to activating factors. This effect also extended to other types of stem cells, including murine haematopoietic and muscle stem cells, as well as human haematopoietic stem and progenitor cells, and MSCs. Using murine models, HMGB1 accelerated recovery from injury to these tissues. Finally, treatment with a single systemic dose of HMGB1 two weeks before injury also accelerated bone, haematopoietic, and muscle regeneration, which was indicative of an acquired pro-regenerative signature. These findings document that the HMGB1-G_Alert pathway results in a dynamic and adaptive multi-tissue regenerative response, and suggest that exogenous HMGB1 may be of therapeutic benefit in diverse clinical contexts, including trauma, chemotherapy, and elective surgery.

Authors: Lee, G

• DOI: 10.5287/ora-7rqj4dazy
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Cell cycle; Immunology; Stem cells; Fracture; Tissue regeneration
• Subjects: Cell cycle; Immunology; Stem cells; Tissue regeneration