DNA methylation of BAX and PLAU in peripheral blood is associated with Alzheimer’s disease in a Han Chinese population

<title>Abstract</title> <p> Background Alzheimer’s disease (AD), the most common form of dementia accounting for approximately 60% of cases, currently lacks effective preventive or curative treatments. DNA methylation analysis offers new avenues for understanding AD pathogenesis. Purpose This study aimed to explore the association between methylation levels of five potential risk genes ( <italic>APOE</italic> , <italic>BAX</italic> , <italic>OGG1</italic> , <italic>PLAU</italic> , and <italic>A2M</italic> ) in peripheral blood of AD and health control in a Han Chinese population, and to evaluate the diagnostic value of positively associated genes ( <italic>BAX</italic> and <italic>PLAU</italic> ) as biomarkers for AD. Additionally, we compared methylation levels between Zhejiang and Xinjiang Han populations to investigate whether environmental factors contribute to regional differences in DNA methylation. Patients and methods: A total of 53 AD patients and 54 age-matched healthy controls without a family history of dementia were recruited from the Affiliated Hospital in Ningbo. Genomic DNA was extracted using a magnetic bead-based method and subjected to bisulfite conversion. Methylation levels of CpG islands in the promoter regions of <italic>APOE</italic> , <italic>BAX</italic> , <italic>OGG1, PLAU</italic> , and <italic>A2M</italic> were measured using real-time quantitative methylation-specific PCR (qMSP). Statistical analyses were performed to assess the association between gene methylation and AD. Furthermore, methylation data from Zhejiang participants were compared with those from a previously studied Xinjiang cohort (17 AD cases and 34 controls) to evaluate the influence of environmental factors on methylation patterns. Results The AD group showed a significantly higher frequency of <italic>APOE ε4</italic> carriers compared to controls ( <italic>p</italic>  = 3.75 × 10 ^− 4 ). Hypomethylation of <italic>BAX</italic> and <italic>PLAU</italic> was significantly associated with AD ( <italic>BAX</italic> : <italic>p</italic>  = 3.49 × 10 ^− 7 ; <italic>PLAU</italic> : <italic>p</italic>  = 0.018). Gender-stratified analysis revealed that BAX hypomethylation was present in both male and female AD patients (males: <italic>p</italic>  = 2.88 × 10 ^− 5 ; females: <italic>p</italic>  = 0.001), whereas <italic>PLAU</italic> and <italic>OGG1</italic> hypomethylation was specific to male AD patients ( <italic>PLAU</italic> : <italic>p</italic>  = 0.0496; <italic>OGG1</italic> : <italic>p</italic>  = 4.025 × 10 ^− 4 ). Receiver operating characteristic (ROC) analysis indicated that both <italic>BAX</italic> and <italic>PLAU</italic> methylation had diagnostic value for AD, with <italic>BAX</italic> demonstrating superior performance ( <italic>BAX</italic> : AUC = 0.786, sensitivity = 0.66, specificity = 0.83, <italic>p</italic>  = 5.88 × 10 ^− 7 ; <italic>PLAU</italic> : AUC = 0.615, sensitivity = 0.42, specificity = 0.906, <italic>p</italic>  = 0.044). Comparative analysis between Zhejiang and Xinjiang Han populations revealed significantly lower methylation levels of <italic>APOE</italic> and <italic>BAX</italic> in the Xinjiang cohort, even after adjustment for age, gender, and <italic>APOE</italic> ε4 carrier status ( <italic>APOE</italic> : AD group <italic>p</italic>  = 0.006, adjusted <italic>p</italic>  = 0.003; control group <italic>p</italic>  = 2.44 × 10 ^− 14 , adjusted <italic>p</italic>  = 0.002; <italic>BAX</italic> : AD group <italic>p</italic>  = 1.58 × 10 ^− 8 , adjusted <italic>p</italic>  = 0.015; control group <italic>p</italic>  = 2.70 × 10 ^− 14 , adjusted <italic>p</italic>  = 0.001). For <italic>OGG1</italic> , methylation was lower in Xinjiang AD patients compared to Zhejiang AD patients ( <italic>p</italic>  = 5.97 × 10 ^− 5 ), whereas in controls, methylation was higher in Xinjiang after adjustment ( <italic>p</italic>  = 4.59 × 10 ^− 15 , adjusted <italic>p</italic>  = 0.002). Conclusion Hypomethylation of <italic>BAX</italic> and <italic>PLAU</italic> constitutes a risk factor for AD. Methylation levels of these genes in peripheral blood may serve as potential diagnostic biomarkers for AD, with <italic>BAX</italic> demonstrating superior diagnostic value compared to <italic>PLAU</italic> . Regional differences in the methylation of <italic>APOE, BAX</italic> , and <italic>OGG1</italic> suggest that environmental factors influence epigenetic modifications. Further research is warranted to elucidate the epigenetic mechanisms of <italic>BAX</italic> and <italic>PLAU</italic> in AD progression. </p>