Exploiting the helminth-derived immunomodulator, ES-62 and its small molecule analogues to dissect the mechanisms underpinning the development of the pathogenic phenotype of synovial fibroblasts in autoimmune arthritis.

Corbet, Marlene (2017) Exploiting the helminth-derived immunomodulator, ES-62 and its small molecule analogues to dissect the mechanisms underpinning the development of the pathogenic phenotype of synovial fibroblasts in autoimmune arthritis. PhD thesis, University of Glasgow.

Abstract

Parasitic helminths are able to survive within their hosts due to their ability to dampen immune responses by secreting molecules with anti-inflammatory and tissue repair properties. Reflecting this, there is increasing evidence of an inverse correlation between parasitic worm infection and the incidence of allergic and autoimmune disorders on a global scale. Such epidemiological evidence has led to the “hygiene hypothesis” which postulates that the recent rapid eradication of parasitic worms in developed countries has resulted in unbalanced hyper-reactive immune systems and consequently, inflammatory disease. As “worm therapy” per se is not ideal, this in turn triggered the idea that exploiting the ability of helminth-derived “immunomodulators” to dampen pathological host inflammation would potentially allow identification of the key pathogenic events in models of human inflammatory disease and hence provide a starting point for development of new and safer therapeutics. Consistent with this, as a serendipitous side-effect of its anti-inflammatory actions, ES-62, a phosphorylcholine (PC)-containing glycoprotein secreted by the filarial nematode, Acanthocheilonema viteae exhibits therapeutic potential in mouse models of inflammatory disorders such as asthma, lupus and rheumatoid arthritis (RA).
RA is a chronic autoimmune inflammatory disorder that affects 1 % of the population in industrialized countries, with no known cure. This disorder causes joint destruction and leads to reduced mobility and disability. Deregulation of T cell activation has long been considered to be a major force driving inflammation and thus to date, therapies have focused on systemic anti-inflammatory treatments, which generally leave individuals immunosuppressed and open to infection. Thus, interest has begun to focus on the role(s) that synovial fibroblasts (SF) in the joint play in the early onset of the disease, the maintenance of established inflammation and even in the spread of disease to unaffected joints. This reflects that despite not being part of the immune system, SF produce pro-inflammatory cytokines during the pathogenesis of RA and also directly mediate joint destruction by secreting matrix metalloproteinases (MMPs) that damage cartilage and bone. Indeed, there is increasing evidence that the local pro-inflammatory environment pertaining in the joints drives SF to become
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imprinted pathogenic aggressors that initiate, drive and spread joint inflammation and bone resorption during development of collagen-induced arthritis (CIA), a mouse model of RA. Intriguingly, therefore, whilst it is established that protection afforded by ES-62 against joint inflammation and bone destruction in CIA is associated with reduced production of the pathogenic cytokine, IL-17 by  and CD4+ T cells, recent evidence suggested that ES-62 could also act directly to suppress the aggressive hyper-inflammatory phenotype of SF in the joint. The molecular mechanisms involved were not defined but interestingly, given that SF express the ES-62 target TLR4 and are the only cells in the joint to express the IL-22 receptor, the parasite product appeared to harness the inflammation-resolving and/or tissue repair actions of IL-22 to suppress SF responses during the established phase of disease.
Thus the core goal of this thesis was to advance our fundamental understanding of how SF become imprinted pathogenic aggressors that initiate, drive and spread joint inflammation and bone resorption in the CIA mouse model, as a surrogate for the pathogenic events in the joints in RA. In particular, the primary major aim was to investigate the impact of the local pro-inflammatory environment pertaining during disease, specifically focusing on the signalling and epigenetic mechanisms by which IL-17 and IL-22 potentially (counter)regulate the pathogenic phenotype of SF. Complementing this, another major aim was to establish whether ES-62 acted directly to modulate the phenotype of SF and thus, to identify the key mechanisms by which ES-62 could prevent SF from promoting inflammation and bone destruction and in this way render them insensitive to pro-inflammatory signals. From a therapeutic point of view, being a large immunogenic molecule, ES-62 is not suitable for use in the clinic and thus candidate small molecule analogues (SMAs) of ES-62, based around its active PC moiety have been designed, some which mimic its therapeutic potential in a variety of inflammatory disorders. Thus, it was also important to address whether ES-62 and its SMAs were similarly able to affect SF and prevent their pathogenicity.
These studies revealed that the microenvironment of the joint during induction and progression of CIA did indeed result in remodelling of the epigenetic landscape of SF and that such cell reprogramming was associated with the acquisition of a hyperinflammatory, tissue destructive phenotype. Such
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reprogramming could be recapitulated in vitro, at least in part, by chronic exposure of normal SF to pro-inflammatory cytokines such as IL-17 and IL-1 pathogenic mediators that are found at high levels in the arthritic joint. Such reprogramming was dependent on ERK and STAT3 signalling converging on miR-155-mediated regulation of inflammatory networks via global DNA hypomethylation. ES-62 was able to counteract this by suppressing the levels of ERK, STAT3 and miR-155 signalling but rather surprisingly, this did not result in abrogation of this hypomethylated epigenetic landscape. Rather, whereas the SMA 12b appeared to act simply by preventing/reversing global DNA demethylation to suppress the induction of genes that drive pathogenesis in CIA, ES-62 induced further global DNA hypomethylation and modulation of the epigenetic landscape by inducing HDAC1: collectively these findings suggested that ES-62 might additionally induce (homeostatic) inflammation-resolving and tissue repair genes that would have translational impact in established disease. In any case, these studies suggest that the proposal to use the global DNA methylation status of RA patients as a biomarker of disease should be treated with caution.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Rheumatoid arthritis, synovial fibroblasts, ES-62, DNA methylation, miR-155, ERK, STAT3.
• Subjects: Q Science > QH Natural history > QH301 Biology; Q Science > QH Natural history > QH426 Genetics; Q Science > QR Microbiology > QR180 Immunology
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Life Sciences > Life Sciences Infection Biology
• Supervisor's Name: Harnett, Prof. M.
• Date of Award: 2017
• Depositing User: Miss Marlene CORBET
• Unique ID: glathesis:2017-8007
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 13 Mar 2017 08:34
• Last Modified: 06 Apr 2018 08:45
• URI: https://theses.gla.ac.uk/id/eprint/8007