Epigenetic modification related to cognitive changes during a cognitive training intervention in depression

Background: DNA methylation as a biomarker is well suited to investigate dynamic processes, such as symptom improvement. For this study we focus on epigenomic state or trait markers as early signatures of cognitive improvement in individuals receiving a cognitive intervention. We performed a first epigenome-wide association study (EWAS) on patients with cognitive dysfunction in depression comparing those with vs without cognitive dysfunction and those cognitively improving vs non-improving following a cognitive intervention.Method: Data from a randomized controlled trial (RCT) were used for this analysis, where cognitive function of 112 patients randomly assigned to a personalized cognitive intervention was compared to standard cognitive treatment. Cognition was measured for this study using the four cognitive tasks from the THINC-it battery. We compared individuals with cognitive impairment with individuals without cognitive impairment at baseline and after a cognitive intervention of 8 weeks. Blood for DNA methylation analysis (Illumina Infinium MethylationEPIC 850 k BeadChip) was collected at baseline and 8 weeks into the treatment. For the baseline analysis, after quality control, the final sample comprised 90 individuals, and analyses at week 8 were performed on 84 individuals. Data cleaning, quality control, and differential methylation analysis of DNA methylation data was performed using the RnBeads package (R). Analyses were corrected for gender, age, depression score (MADRS), reported years of education, height and weight, as well as surrogate variables estimated by the pipeline used. The within-individual paired longitudinal analysis was performed using Welch's t-test. Results: Analyses at baseline and at week 8 did not show any genome-wide significant CpGs (p < 5 x 10(-8)) comparing patients with and without cognitive impairment. The most significant result in the baseline analysis comparing the groups with and without cognitive impairment at baseline is located in an open Sea region with predominantly regulatory qualities (cg10962945; 6.61 x 10(-7)). The most significant CpG at 8 weeks was also located in open sea, though in exon 13 of the NTRK2-gene, linked to the BDNF pathway (cg13620631, 5.56 x 10(-7)). Finally, a within-individual paired longitudinal analysis with only patients that show improved cognitive function over time was performed, showing 65 CpGs that overlapped between the 1% most significant of this analysis and the 1% most significant CpGs from the cross-sectional analysis at 8 weeks.Conclusion: Our result suggest that DNA methylation can be suitable to capture early signs of treatment response of a cognitive intervention in depression. In our layered approach we could capture dynamics that can help differentiate between biological trait and state markers of cognitive function in depression. Despite not being genome-wide significant, the CpG locations returned by our analysis comparing patients with and without cognitive impairment, are in line with prior knowledge on pathways and genes relevant for depression treatment and cognition.