The prevalence of chronic liver disease is rising worldwide with a clear unmet need for therapy: The only current treatment is liver transplant or elimination of the underlying cause. The hepatic stellate cell (HSC) has been identified as the fibrogenic cell type responsible for scarring. Following liver injury HSCs are activated, transforming into a proliferating, perpetuating population of myofibroblast-like cells, that secrete extracellular matrix. Evidence that serotonin (5-HT) influences HSC biology has been reported, with activation up-regulating the expression of 5-HT2A, 5-HT2B and 5HT1B receptors and therefore have potential as targets for therapy. In this thesis an 'in-depth' quantitative pharmacological characterisation of the 5-HT receptors present on mouse and human HSCs was undertaken to fully evaluate and extend the evidence for a role of 5-HT in driving the fibrogenic process. The 5-HT2A receptor was demonstrated pharmacologically to be responsible for both 5-HT-stimulated intracellular calcium signalling in mouse and human HSCs and for extracellular regulated kinase (ERK) phosphorylation signal in mouse HSCs. A second 5-HT receptor responsible for ERK phosphorylation was found to be present on mouse HSCs, with pharmacological properties suggesting the 5-HT1B receptor as the most likely candidate. The role of 5-HT in fibrotic phenotypic endpoints of proliferation and collagen production was also investigated with no evidence of a role for 5-HT identified. Although 5-HT was reported to enhance platelet derived growth factor (PDGF)-induced proliferation, 5-HT was found only to enhance the PDGF-induced ERK phosphorylation in mouse HSCs. These data, therefore, did not support a role for 5-HT in driving HSCs fibrogenesis in a mouse CCl4 liver injury model the consistent delivery of low pharmacologically selective doses of a selective 5-HT2A and 5-HT2B antagonist, volinanserin and GSK1606260A respectively, were evaluated. Volinanserin was found to have no anti-fibrotic effect whereas GSK1606260A was pro-fibrotic. These data highlights the challenge of reliance on in vitro single cell type assays and their translation into in vivo models. Taken together these data were not consistent with the functional 5-HT2A and 5-HT1B receptors present on HSCs playing a key role in driving fibrosis and suggest they do not present a viable anti-fibrotic therapy opportunity.
|Date of Award||25 May 2017|
- University Of Strathclyde
|Sponsors||University of Strathclyde|
|Supervisor||Nigel Pyne (Supervisor) & Luke Chamberlain (Supervisor)|