Cell-free mitochondrial DNA as a biomarker for cardiac function: role of genetic and epigenetic factors

PhD project (3/4 yr research project leading to independent research at the doctorate level)

Dr Santi Rodriguez, Professor Raimondo Ascione, Professor Caroline Relton, Dr Kimberley Burrows


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Rationale

Mitochondrial DNA (mtDNA) is mainly located within the mitochondria1. It is present in variable number of copies within the cell. There is also tissue and inter-individual variation of mtDNA copy number (CN)2. mtDNA is directly related to the creation of energy in the cell3. There is also cell-free mtDNA1 arising mainly in plasma as a result of biological processes including apoptosis and cellular stress.
Cardiac conditions are also associated with both apoptosis and cellular stress. We aim to explore whether mtDNA copy number in plasma could be used as a biomarker for adverse cardiac outcomes.
A potential mechanism relating mtDNA CN variation with disease risk is via alterations to DNA methylation of the nuclear genome. Changes in mtDNA CN have been linked to hypo- and hypermethylation of several nuclear genes4. A plausible hypothesis that we will explore is that cell-free mtDNA copy number in plasma may mediate its downstream effects by altering DNA methylation of the nuclear genome

Aims & objectives

1.To measure cell-free mtDNA CN in plasma from humans and a porcine model of cardiac disease
2.To study the association between cell-free mtDNA CN and biomarkers of oxidative stress
3.To relate mtDNA CN and methylation of the nuclear genome
4.To compare the predictive utility of cell-free mtDNA CN in plasma
5.To compare the predictive utility of DNA methylation
4 and 5 will be done:
-in a pilot study of patients before and after cardiac surgery
-in cardiac conditions in a porcine model of CVD

Methods

•To measure plasma mtDNA CN on ARIES samples to run an epigenome-wide association study (EWAS) of methylation (existing data) and mtDNA CN
•To extract DNA from 50 human plasma samples (pre- and post-surgery) and from 100 pigs
•To quantify CN of cell-free mtDNA/ml of plasma by qPCR in each patient and in each pig
•To optimise a lab assay to know the methylation status of candidate loci in humans (informed by our EWAS)
•To assess the association between methylation and both cell-free mtDNA CN and major cardiac events including myocardial infarction
•To quantify potential differences in cell-free mtDNA CN between pre- and post-surgery
•To correlate both cell-free mtDNA and levels of nuclear DNA methylation with biomarkers of oxidative stress and inflammation.
•To explore plasma mtDNA CN and methylation levels as predictors of phenotype in both human and porcine samples.
•To explore in cardiomyocytes cultures the correlation between cell-free mtDNA and hypoxia, apoptosis and necrosis.

References

1. Yu, M. (2012). Mitochondrial DNA 23, 329-332.
2. Guyatt AL, Burrows K, Guthrie PAI, Lawlor DA, Ring S, Gaunt TR, Ascione R, Day INM, Rodriguez S. (in prep.).
3. Schon, E.A. et al (2012). Nat Rev Genet 13, 878-890.
4. Smiraglia, D.J. et al. (2008). Cancer biology & therapy 7, 1182-1190.


Created on Oct. 1, 2015, 9 a.m.

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