Aging and microRNA messaging : associations with systemic estrogen levels and physical performance

Abstract

This thesis took an innovative approach, which involved methodological development, to investigate microRNAs as candidate molecules and as genome-wide regulators of age, menopausal status and physical condition in both sexes. The focus was on potential serum microRNAs indicative of age, pre- or postmenopausal status, with or without estrogen- based hormone replacement therapy (HRT), and long-term physical training. MicroRNA associations with adiposity and inflammatory markers were also analyzed. Three different study designs were used: 1) the SAWEs study comprised healthy postmenopausal monozygotic twin sisters (n=11, 54-62 years) with discordance for HRT and premenopausal women (n=30, 20-40 years) without hormonal contraceptives; 2) the miRBody study comprised non-related postmenopausal women (54-62 years) either on (n=16) or not on HRT (n=17); and 3) the ATHLAS study comprised male masters sprinters in a 10-year follow-up design (n=49, baseline age 40-80 years) and in a cross-sectional design (n=67, 18-90 years). For the explorative microRNA discovery, we set up next generation sequencing method for serum exosome microRNAs, exomiRs, and utilized arrays for freely circulating serum and adipose tissue microRNAs. Selected microRNAs were further validated. MiR-21-5p and -146a-5p were analyzed in both sexes, owing to their hypothesized role in aging, inflammation and exercise response. Sex steroids, inflammatory markers and fat/glucose metabolites were measured. Profiled microRNA patterns in serum and adipose tissue differed by age and HRT use vs. non-use. Validations revealed age associations for five, and HRT associations for three microRNAs in serum. In addition, seven adipose tissue microRNAs were higher with higher ages. MiR-146a-5p was negatively associated with HRT use in both serum and muscle. In the sprinters, a negative association with age was detected for serum miR-146a- 5p and non-linear associations with specific power and speed capacity measures in 10 years for miR-146a-5p and -21-5p. The depth of the methodologies and human designs used, enabled novel discoveries regarding aging, 17ǃ-estradiol (E2), and physiological (health) status-associated microRNAs. Of them, exomiR-27b-3p and -148a-5p, indicative of higher age, lower serum E2 and poorer adiposity and inflammatory status in women, were the most promising candidates for early markers of worsening metabolism with declining systemic E2. Moreover, serum miR-21-5p was indicative of more inflamed and fatty phenotype in women, whereas miR-146a-5p appeared indicative of a healthier phenotype in both sexes. Overall, this research underlines the potential for using serum microRNAs, together with other traditional markers, as tools in evaluating the physiological status of an individual, thus contributing new information to the health and aging field.