PhD ThesisIt has been hypothesised that patients with long-term treated HIV infection may exhibit
features of accelerated physiological ageing. Given previously established links
between, a) anti-retroviral therapy and mitochondrial DNA (mtDNA), and b) mtDNA
and ageing, I hypothesised that anti-retroviral therapy may lead to the accumulation of
mtDNA mutations, in an acceleration of the molecular process seen in normal human
ageing.
Using a combination of single cell molecular analyses and ultra-deep sequencing
(UDS), I demonstrated that HIV-infected patients with prior exposure to polymerase
(pol) γ inhibiting NRTI (nucleoside analogue reverse transcriptase inhibitor) therapy
show increased accumulation of somatic mtDNA mutations within cells, in a pattern
similar to that seen much later in life due to normal ageing. Empirical data and in silico
modelling suggested this is likely to be mediated by the accelerated clonal expansion of
pre-existing (age-associated) mtDNA mutations, rather than by increased mutagenesis.
I went on to further develop the UDS methodology, to explore more fundamental
questions about the characteristics of mtDNA mutations in ageing, health and disease.
In so doing, I showed that low-level mtDNA heteroplasmic mutation appears to be
universal, and that many ostensibly somatic mutations may in fact have been maternally
transmitted at very low levels.
I explored the utility of serum FGF-21 (fibroblast growth factor 21) and phosphorus
magnetic resonance spectroscopy (31P-MRS) as non-invasive measures of muscle
mitochondrial dysfunction in anti-retroviral treated patients. Both showed significant
abnormalities, although neither proved sensitive or specific in my patient group.
Finally I explored the frequency and severity of fatigue in contemporary HIV-infected
patients, showing that half of all patients have excessive fatigue despite good immune
function and suppressed HIV viraemia. Patients with prior exposure to pol γ inhibiting
NRTIs were almost universally fatigued, suggesting that persistent mitochondrial
dysfunction due to accumulated mtDNA mutations may be important in driving fatigue
in this patient group.Medical Research Council (MRC) UK (Clinical
Research Training Fellowship), British Infection Association (BIA) (Clinical Research
Fellowship), National Institute for Health Research (NIHR) Biomedical Research
Centre for Ageing and Age-Related Disease (awarded to Newcastle-upon-Tyne
Hospitals NHS Foundation Trust and Newcastle University), Newcastle Healthcare
Charity
