Influence of stress and health-behaviour on miRNA expression.

Psychological stress is correlated with and may even cause DNA damage, which contributes to the etiology of various diseases. Recent studies point to the role of micro-RNA (miRNA), small molecules that regulate gene expression, in health and disease. This study investigated the relationship between transient stress and two cancer-related miRNAs, and determined whether health-behaviour moderated these relationships. Using a pre-post design, 37 German students completed measures on health-behaviour and perceived stress, the latter after a study break (low stress) and after an exam (high stress). On both occasions, students underwent blood tests to determine the expression of let-7b and miR-21, two miRNAs recently found to be related to cancer. The students reported significantly higher stress after the exam than in the study break period. The levels of let-7b and miR-21 expression significantly declined from low- to high-stress periods. Importantly, baseline health-behaviour interacted with time in relation to miR-21, such that the expression of this marker decreased only in students with inadequate health-behaviour, while it did not change in students with adequate health-behaviour. This is the first study showing that brief academic stress can alter the expression of two cancer-related miRNA molecules, and that health-behaviour may moderate these effects for miR-21.