MicroRNA signature of leukocytes in the context of chronic systemic inflammation in vascular dementia

Chronic low-level inflammation during the aging process is a key risk factor for the activation of resident cells of the brain innate immune system of the (microglia and astrocytes). Such activation leads to the development of neuroinflammation and cognitive impairment which are typical to neurodegenerative diseases such as Alzheimer’s disease, vascular dementia, Parkinson disease etc. Currently, there is a lack of minimally invasive, affordable methods for diagnosing age-related neurodegenerative diseases and drugs that could slow down or prevent their progression. Hence, a search for new peripheral biomarkers is required, both for diagnostics and monitoring the efficiency of drug therapy. The option of using microRNAs as such biomarkers is under discussion. Our goal was to identify a leukocyte microRNA signature in vascular dementia as compared with healthy aging and reproductive age, in view of inflammation and cognitive deficits. We have examined 54 persons from young to senile age who were classified into the following groups: “Vascular dementia”, “Healthy aging” and “Reproductive age”. Expression of miRNAs known as regulators of communications between the immune and nervous systems (let-7d, let-7g, miR-21, miR-124, miR-146a, miR-155, miR-342-3p) was measured in peripheral blood leukocytes. The decision to study leukocytes was made, since these blood cells are responsible for immune functions, and, especially, cytokine production during aging. Total RNA was isolated by phenol-chloroform technique. The microRNA expression was determined by quantitative polymerase chain reaction with SYBRGreen. The U6 gene of small nuclear DNA was used as a reference “housekeeping” gene. The differences between groups were determined using the Kruskal–Wallis test with post hoc pairwise comparisons according to Conover–Inman. As a result of the study, it was found that the expression of microRNA-21 and microRNA-342 in leukocytes of elderly/senile people, both in healthy aging and in vascular dementia, was increased when compared to the persons in their reproductive age. In the persons with vascular dementia, the expression level of miRNA-124 and miRNA-342 in peripheral blood leukocytes was higher than in healthy aging group. Hence,, microRNA-124 and microRNA-342 may be informative biomarkers for the diagnostics of vascular dementia. However, large-scale studies of their biomarker potential are warranted.