Exploring the inter-relationship between vasculopathy, inflammation and fibrosis in Systemic Sclerosis

Abstract

Systemic sclerosis (SSc) is a rare but potentially devastating multisystem disease with unknown aetiology. The pathological hallmarks constitute a triad of autoimmunity, unique disease specific patterns of vasculopathy and tissue fibrosis. LeRoy’s vascular hypothesis links these features through early endothelial injury resulting in tissue hypoxia and subsequent aberrant tissue remodelling by over-active fibroblasts, most readily manifesting as Raynaud’s phenomenon and cutaneous fibrosis respectively. Existing evidence supports a vascular-fibrotic link, but current therapeutic options are few and strategies tend to target each one individually, in part due to a lack of comprehensive understanding of the complex and evolving pathogenesis. Vascular biomarkers such as vascular endothelial growth factor-A (VEGF-A) and associated angiopoietins are potential drivers of both vasculopathy and fibrosis and have been implicated in SSc pathogenesis. We hypothesize that differential VEGF-A isoform expression (through conventional and alternative VEGF-A splicing), may dictate the relevant burden of vasculopathy and fibrosis thus explaining disease heterogeneity and disease progression. Associated antiangiogenic angiopoietin-2 may also play role. Furthermore, VEGF-A isoform expression may be directed by hypoxia inducible factor-α (HIF1α/2α) paralog expression driven by the unique hypoxic stimulus that results from SSc vasculopathy. The advancement of medicinal products for SSc is limited on a second front, namely the shortcomings of current subjective outcome measures for both vasculopathy and cutaneous fibrosis used in clinical trials. This research therefore aimed to investigate the use of non-invasive imaging techniques as potential future outcome measures in SSc. Secondly, we aimed to use these objective measures to further explore the inter-relationship between vasculopathy, inflammation and fibrosis and the role of vascular biomarkers in driving disease. Herein, we report on the potential for laser speckle contrast imaging (LSCI) to demonstrate vascular dysfunction in SSc and for novel applications of high frequency ultrasound (HFUS) to document reduced vascularity in the fingers even at ambient temperatures. We have provided evidence that HFUS is a reproducible method of objectively assessing skin pathology through the combination of three HFUS applications and for the first time we provide histological validation for its use. We report on the over-expression of VEGF-A165b in plasma and skin and its negative relationships with finger perfusion and skin fibrosis demonstrating inhibitory associations with both features. We additionally report of the association between increased angiopoietin-2 expression and both vasculopathy and increased skin fibrosis. We report for the first time that HIF2α is over-expressed in SSc skin demonstrating the hypoxic stimuli in fibrotic skin and its associations with VEGF-A165b isoform expression. In summary, this thesis presents evidence for the translational potential of non-invasive imaging techniques in SSc as well as advancing the understanding of its pathogenesis through the inter-relationship of the pathogenic triad with vascular biomarkers and implicating such as potential future therapeutic targets.

Date of Award	16 Sept 2020
Original language	English
Awarding Institution	University of Bath
Supervisor	Stephen Ward (Supervisor), Amanda Mackenzie (Supervisor) & John Pauling (Supervisor)