Assessment of UVR-Induced DNA Damage and Repair in Nuclear Genome versus Mitochondrial Genome

DNA is a key molecular-target for the deleterious effects of ultraviolet radiation (UVR). Cells contain two types of DNA: nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) and UVR induces various types of damage in the both DNAs, notably CPDs and 8-oxodG. The aim of this thesis is to examine UVR induced DNA damage formation and repair in nDNA and mtDNA and to determine which is the most important genomic target with respect to cell killing in vitro using HaCaT calls as models of human skin. The cell viability data showed that UVB induces significant cell death, which increased over 48 h. SSR-exposure also showed significant levels of cell death after 24 h but with evidence of significant survival after 48 h. Alkaline modified comet assay data showed that CPDs and 8-oxodG were significantly produced in HaCaT cells exposed to UVB and SSR, with CPDs being formed in a greater yields and there being no significant repair of CPDs over 48 h post-exposure to UVB. However, HaCaT cells irradiated with SSR showed significant repair of both CPD and 8-oxodG over 48 h. QPCR data showed that UVB and SSR induced similar profiles of damage in both nDNA and mtDNA; despite the induced damage levels being higher with UVB. The data also showed that nDNA is the main target for UVR in HaCaT cells exposed to UVB and SSR. The UVB-induced QPCR-detectable DNA damage in nDNA and mtDNA was not fully repaired, with a significant level of DNA damage remaining at 48 h, however, there was significant repair of the induced-damage in nDNA post-exposure to SSR (correlating with survival/re-growth), whereas the damage to mtDNA was not fully repaired. The greater lethality of UVB is probably due to more the damage induced and poorer repair (notably of CPD) in nuclear DNA following UVB exposure. Whereas the proficient repair of SSR-induced CPD in nDNA probably dictates survival following SSR exposure – as there was still a notable level of residual damage in mtDNA post-SSR exposure. However, nDNA is the main target for UVR causing DNA damage and may lead to mutations, which increase the risk of skin cancer development.