Methylation age and inflammation in prodromal Alzheimer's disease.

Background: The most relevant risk factor in Alzheimer's disease (AD) is age. Aging is a complex process involving several biological changes which lead to chronic cellular stress and to a sterile tissue inflammation. During aging cells become senescent which is seen as morphological changes and secretion of immune signaling mediators associated with systemic low‐grade inflammation. Interestingly, during neurodegenerative processes such AD, microglia, astrocytes, and vascular unit cells become senescent. To explore the potential connection between immune signaling mediators, ageing, and biomarkers of AD, we have quantified in CSF several immune related molecules link to AD and analyzed their connection with known biological clocks. Method: Biological age was obtained by deriving the epigenetic clock in DNA derived from peripheral blood. To this end, DNA methylation data was generated using the EPIC array from Illumina in two cohorts including 348 individuals (cognitively normal, subjective cognitive decline and mild cognitive impairment) from DELCODE study and 267 individuals (mild cognitive impairment). Data was prepared and normalized using standard quality controls. Horvath's and Hannum epiClocks were computed for all individuals in both cohorts. AD biomarkers including Amyloid‐ß, phosphor‐tau and total tau along with a panel of inflammation markers were measured in CSF samples. Result: Both epiClocks showed a significant strong correlation with chronological age in both cohorts. Methylation age and chronological age showed both a significant association with classical AD biomarkers, as well as a subsets of inflammation markers. The meta‐analysis confirmed the association of the Epiclocks and the chronological age with all AD biomarkers as well as with YKL40, sTREM2, C‐1 and MIF. Based on the difference between the calculated epiClock and the chronological age, we derived an index reporting on increase in biological aging rate (age‐acceleration). This index, however, did not show significant association with any of the AD biomarkers and inflammation markers. Conclusion: Our study shows a link between inflammatory markers and methylation age in both healthy aging and pre‐dementia stages of AD. However, biological clocks derived from peripheral tissue seem to be independent of potential AD pathology and inflammation occurring in the aging brain. Thus, these biomarkers are not increasing the odds for methylation age‐acceleration. [ABSTRACT FROM AUTHOR]