Epigenetic Clocks and Accelerated Aging in Sickle Cell Disease

Introduction: Sickle cell disease (SCD) is a hereditary hemoglobinopathy caused by a single point mutation in the β-globin gene. HbS polymerizes under deoxygenated conditions, causing red blood cells to assume a sickle shape, leading to hemolysis and vaso-occlusion. Recurrent vaso-occlusive episodes in SCD result in substantial organ damage over the lifespan of affected individuals and is considered a multi-organ disease, with significant complications impacting the brain, immune system, and neurons. Current treatments include Hydroxyurea, L-glutamine, Crizanlizumab, Voxelotor and blood transfusions, which reduce complications and improve quality of life. Aging in the context of SCD presents a unique and accelerated trajectory compared to the general population. Patients with SCD exhibit signs of premature aging typically seen in the elderly, such as neurodegeneration, mitochondrial dysfunction, and increased frailty, at a much younger age. DNA methylation (DNAm) changes play a critical role in the pathophysiology of SCD, influencing gene expression and contributing to the disease's clinical heterogeneity. The aim of this study is to explore the relationship between epigenetic aging and sickle cell disease, with a focus on understanding how epigenetic modifications contribute to the premature aging in this population.

Methods: In this cross-sectional study, we collected blood samples from participants diagnosed with SCD (N=47, mean age = 39.5 years [32-45years], 62% female). Genome-wide DNAm was profiled on the Illumina Infinium MethylationEPIC v2 for 46 participants. Following initial data processing and data quality checks on the R platform, two samples were excluded (n=44). Global variance patterns were estimated using principal component analysis (PCA), and different DNAm-based biomarkers of aging were computed using the dnaMethyAge R package. Participant characteristics (e.g., age, sex), and treatment variables were then tested for association with the DNAm readouts, and statistical tests were based on t-test or linear regression.

Results: Overall, the cohort had higher pace of aging with a DunedinPACE score of 1.19±0.13 (interpreted as 19% faster rate of aging relative to a DunedinPACE=1). There was no difference by gender. Treatment with hydroxyurea and blood transfusion had contrasting and strong influence on the global methylation patterns and were significantly related to the top PC. Participants who received hydroxyurea had higher pace of aging (DunedinPACE of 1.25±0.12 vs. 1.15±0.13 in 19 hydroxyurea=Yes and 25 hydroxyurea=No; p=0.02). In contrast, blood transfusion was modestly related to a lower pace of aging (1.10±0.16 for 6 blood transfusion=Yes, 1.21±0.12 for 38 blood transfusion=No; p=0.09). The two treatments also had significant contrasting effects on inferred telomere length. Mean telomere length based on Lu 2019 estimate was 6.92±0.26 for hydroxyurea=Yes and 7.21±0.21 for No (p=0.0006); and 7.30±0.21 for blood transfusion=Yes, and 7.07±0.26 for blood transfusion=No.

Conclusion: The current study is the first to our knowledge to examine the effects of hydroxyurea and blood transfusion on accelerated aging in SCD. Participants showed a 19% faster aging rate, with hydroxyurea increasing and blood transfusion modestly reducing the pace of aging. Hydroxyurea treatment is associated with a higher pace of aging and shorter telomere length, whereas blood transfusions show a modest reduction in the pace of aging and longer telomeres. These findings highlight the differential impacts of SCD treatments on epigenetic aging markers. Understanding these relationships can guide personalized therapeutic strategies to mitigate premature aging and improve the quality of life in SCD patients.