Study On The Association Between Base Excision Repair Gene Variations,DNA Oxidative Damage, And Chronic Renal Failure

Part One:Association of Base Excision Repair Gene Variations with CRF Risk in a Chinese PopulationChronic renal failure (CRF) is a troublesome health problem worldwide. There is an upward trend in the incidence of kidney disease in China, and the latest research showed that overall prevalence of kidney disease is10.8%in China.The base excision repair (BER) pathway, containing OGG1, MTH1and MUTYH, is a major protector from oxidative DNA damage in humans, while8-hydroxy-2’-deoxyguanosine (8-OHdG), an index of DNA oxidation, is increased in maintenance hemodialysis (MHD) patients.Four variations of BER genes, OGG1c.977C>G (rs1052133), MTH1c.247G>A (rs4866), MUTYH c.972G>C (rs3219489), and AluYb8MUTYH (rs10527342), were examined in337HD patients and404healthy controls. The distribution of OGG1C.977C>G or MTH1c.247G>A did not differ between the two groups (P=0.394and0.444, respectively). The distribution of MUTYH C.972GG differed between the two groups (P=0.046) and was associated with a moderately increased risk for chronic renal failure (P=0.013). And compared to the A/A genotype, the AluYb8MUTYH insertion carriers (A/P or P/P) were significantly higher in CRF patients (P=0.034). Among267patients with anemia, the frequency of MUTYH c.972GG was markedly higher in patients than controls (P=0.006), whereas the AluYb8MUTYH insertion (A/P or P/P) significantly increased the risk for patients with anemia (P=0.003). A similar relationship was also detected among250patients with hypertension(P=0.019; P=0.042, respectively). Our study showed that MUTYH C.972GG, AluYb8MUTYH, and combination of OGG1C.977GG increased the risk for CRF development in China and suggested that DNA oxidative damage might be involved in such process.Part Two:DNA Oxidative Damage, Inflammation in Patients undergoing Maintenance HemodialysisThe kidney is highly vulnerable to ROS. Oxidative injury is thought to alter the structure and function of glomeruli and is suggested to be related to renal diseases risk and eventual CRF.The8-OHdG levels in leukocyte DNA were examined in116HD patients. The average8-OHdG/106dG value was significantly higher in patients with the OGG1C.977G, MUTYH C.972G or AluYb8MUTYH alleles (P<0.001via ANOVA). Further analysis showed that combination of MUTYH C.972GG with OGG1C.977GG or AluYb8MUTYH increased leukocyte DNA8-OHdG levels in patients undergoing maintenance hemodialysis.Chronic inflammation may increase the risk of mortality for patients undergoing hemodialysis, while enhanced oxidative stress and DNA oxidative damage are involved in the inflammatory response. Data were analyzed from167hemodialysis patients and66healthy controls. All subjects were evaluated for the expression of inflammatory cytokines IL-1β and IL-6. The results showed that the hemodialysis patients had significantly higher levels of IL-1β and IL-6than the healthy controls. In the healthy controls, no patterns of association were observed between the OGG1C.977C>G or MUTYH c.972G>C genotypes and IL-1β or IL-6levels; however, patients with the MUTYH c.972GG genotype presented higher levels of IL-1(3than those with the CC genotype. The AluYb8MUTYH genotype was strongly associated with increased IL-1β levels among controls and increased IL-1β and IL-6levels among hemodialysis patients. Additionally, the synergetic effect of these variations of the BER genes on the levels of IL-1β and IL-6was investigated. The combinations of the AluYb8MUTYH genotype with the OGG1c.977C>G or MUTYH c.972G>C genotypes were associated with the IL-1β and IL-6levels in hemodialysis patients.Part Three:AluYb8Insertion in MUTYH Gene Affects the Resistance Ability of Fibroblast-like Cells under Oxidative StressThe AluYb8insertion in MUTYH (AluYb8MUTYH) decreased the expression of the type1MUTYH protein which was located in the mitochondria, but it was not clear whether this mutation affects the resistance ability of cells under oxidative stress.Different AluYb8MUTYH genotype (A/A or P/P) fibroblast-like cells were treated with KBrO3(0mM,1mM,4mM) for24hours, and the mitochondrial potential, mtDNA content and apoptosis biomarkers (p53, p21, caspase-3and caspase-9) were analyzed between the two genotype cells.It was found out that the fibroblast-like cells with P/P genotype had significant decreased mitochondrial potential than the A/A genotype cells after treating with1mM or4mM KBrO3for24hours. The P/P genotype cells had increased p53and p21levels than the A/A genotype cells after treating with4mM KBrO3for24hours. These results revealed that the cells with P/P genotype had decreased resistance ability of oxidative stress than the A/A genotype cells.In summary, our study showed that the polymorphisms in BER system, including MUTYH C.972GG and AluYb8MUTYH, increased the risk for CRF development in China, especially their combined effect with OGG1C.977GG. As predictors of mortality, plasma IL-1β and IL-6levels were significantly higher in the hemodialysis patients than the healthy controls, and the increases were associated with the MUTYH c.972G>C and AluYb8MUTYH variations. These data suggested that oxidative DNA damage might be one common risk factor for related renal diseases, and the genes in BER pathway may be involved in the progress of renal function deterioration and complications, and the chronic inflammation of hemodialysis patients.