Investigations into telomere biology in systemic sclerosis

Chee, Meng May (2012) Investigations into telomere biology in systemic sclerosis. MD thesis, University of Glasgow.

Abstract

Systemic sclerosis (SSc) is a complex multisystem autoimmune connective tissue disease of yet unknown aetiology. It is characterised by vascular damage, autoimmunity and progressive fibrosis in the skin and internal organs, with 2 main subsets of disease: diffuse cutaneous SSc (dcSSc) and limited cutaneous SSc (lcSSc), classified mainly according to skin involvement.

Although there has been tremendous progress in the understanding and treatment of autoimmune diseases in the last 20 years, SSc remains a disease with high morbidity and mortality, with no proven treatments that improve long-term outcome. There is therefore a need to improve the understanding of such a devastating disease to facilitate the development of future treatments and improve the prognosis for patients with SSc.

Telomeres are nucleo-protein complexes, comprising tandem TTAGGG repeats at the ends of eukaryotic chromosomes, which protect the chromosomes from end-to-end fusion, recombination and degradation. There are a variety of telomere binding proteins which maintain telomere stability and function in sensing, signalling and repairing DNA damage. Telomere lengths have been used as a marker of biological aging for over a decade, and the technologies for measuring telomere lengths have also advanced in recent years. Quantitative real time PCR (QPCR) has now superseded Southern Blotting (SB) for telomere length measurements.

Telomere erosion has been implicated in a wide range of diseases and its impact on autoimmune diseases remains unclear. As SSc is associated with particular autoantibodies which have been linked to telomeres, this thesis sought to explore telomere biology in SSc. Initial work measuring telomere lengths in SSc patients using the SB method revealed surprising results, with a lack of age-related telomere erosion in patients with lcSSc, which was in contrast to published literature at the time.

The aim of this research was to measure telomere lengths of peripheral blood mononuclear cells (PBMC) in patients with SSc and related connective tissue diseases using QPCR, with the hypothesis that telomere lengths would be shorter in disease, and to explore telomere binding protein genes, with a view to gaining insight into any mechanistic differences in telomere biology in the different subsets of disease.

Measurement of telomere lengths of PBMC from healthy controls and patients using QPCR showed that telomere lengths were significantly shorter in disease compared to controls, but when adjusted for age, there was no statistically significant difference in telomere lengths of patients with lcSSc compared to controls.
Taking into account the complexity of telomere biology, it is possible that mediators of the inflammatory reaction at the systemic level or autoantibodies against nucleoprotein complexes directly or indirectly interfere with the homeostasis of telomere length in blood. This could occur through disrupting the proteins of the shelterin complex or associated factors relating to DNA repair. Hence, the gene expression of telomere binding proteins and other genes associated with inflammation and DNA repair were explored in patients with SSc using Taqman Low Density Arrays.

The majority of these genes were under expressed in disease compared to controls, but when samples were age-matched, only 4 genes were under-expressed in patients with dcSSc: BCL2, POT1, SIRT6 and WRN, and 4 genes were under-expressed in lcSSc: ATM, BCL2, STAU1 and WRN. There was no correlation between telomere lengths and gene expression. These observations are intriguing, and the role of BCL2 and WRN merit further investigation in patients with SSc.

This work has confirmed that telomeres shorten with age and disease, in keeping with the original hypothesis and published literature. However, there was no significant difference in age-related telomere erosion in patients with lcSSc. Gene expression analysis of telomere associated genes in SSc revealed lower expression in disease compared with controls. Whether this observation is a cause or effect of disease remains to be proven, but suggests that telomeres may be implicated in the pathophysiology of SSc and there are mechanistic differences between the subsets of disease.

• Item Type: Thesis (MD)
• Qualification Level: Doctoral
• Additional Information: Due to copyright restrictions the full text of this thesis cannot be made available online. Access to the printed version is available.
• Keywords: systemic sclerosis, telomeres, telomere binding protein genes,
• Subjects: R Medicine > R Medicine (General)
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Cancer Sciences
• Supervisor's Name: Shiels, Dr. Paul
• Date of Award: 2012
• Depositing User: Dr Meng May Chee
• Unique ID: glathesis:2012-3615
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 12 Oct 2012
• Last Modified: 10 Dec 2012 14:09
• URI: https://theses.gla.ac.uk/id/eprint/3615