Psychostimulant-induced aberrant DNA methylation in an in vitro model of human peripheral blood mononuclear cells.

BACKGROUND: Several reports have provided crucial evidence in animal models that epigenetic modifications, such as DNA methylation, may be involved in psychostimulant-induced stable changes at the cellular level in the brain. Epigenetic editors DNA methyltransferases (DNMTs) and ten-eleven translocation enzymes (TETs) coordinate expression of gene networks, which then manifest as long-term behavioural changes. However, the extent to which aberrant DNA methylation is involved in the mechanisms of substance use disorder in humans is unclear. We previously demonstrated that cocaine modifies gene transcription, via DNA methylation, throughout the brain and in peripheral blood cells in mice. RESULTS: We treated human peripheral blood mononuclear cells (PBMCs) from healthy male donors (n = 18) in vitro with psychostimulants (amphetamine, cocaine). After treatment, we assessed mRNA levels and enzymatic activities of TETs and DNMTs, conducted genome-wide DNA methylation assays and next-generation sequencing. We found that repeated exposure to psychostimulants decreased mRNA levels and enzymatic activity of TETs and 5-hydroxymethylation levels in PBMCs. These data were in line with observed hyper- and hypomethylation and mRNA expression of marker genes (IL-10, ATP2B4). Additionally, we evaluated whether the effects of cocaine on epigenetic editors (DNMTs and TETs) and cytokines interleukin-6 (IL-6) and IL-10 could be reversed by the DNMT inhibitor decitabine. Indeed, decitabine eliminated cocaine's effect on the activity of TETs and DNMTs and decreased cytokine levels, whereas cocaine increased IL-6 and decreased IL-10. CONCLUSIONS: Our data suggest that repeated psychostimulant exposure decreases TETs' enzymatic activity in PBMCs. Co-treatment with decitabine reversed TETs' levels and modulated immune response after repeated cocaine exposure. Further investigation is needed to clarify if TET could represent a putative biomarker of psychostimulant use and if DNMT inhibition could have therapeutic potential.

Enhanced Cognition and Neurogenesis in miR-146b Deficient Mice.

The miR-146 family consists of two microRNAs (miRNAs), miR-146a and miR-146b, which are both known to suppress a variety of immune responses. Here in this study, we show that miR-146b is abundantly expressed in neuronal cells, while miR-146a is mainly expressed in microglia and astroglia of adult mice. Accordingly, miR-146b deficient (Mir146b-/-) mice exhibited anxiety-like behaviors and enhanced cognition. Characterization of cellular composition of Mir146b-/- mice using flow cytometry revealed an increased number of neurons and a decreased abundancy of astroglia in the hippocampus and frontal cortex, whereas microglia abundancy remained unchanged. Immunohistochemistry showed a higher density of neurons in the frontal cortex of Mir146b-/- mice, enhanced hippocampal neurogenesis as evidenced by an increased proliferation, and survival of newly generated cells with enhanced maturation into neuronal phenotype. No microglial activation or signs of neuroinflammation were observed in Mir146b-/- mice. Further analysis demonstrated that miR-146b deficiency is associated with elevated expression of glial cell line-derived neurotrophic factor (Gdnf) mRNA in the hippocampus, which might be at least in part responsible for the observed neuronal expansion and the behavioral phenotype. This hypothesis is partially supported by the positive correlation between performance of mice in the object recognition test and Gdnf mRNA expression in Mir146b-/- mice. Together, these results show the distinct function of miR-146b in controlling behaviors and provide new insights in understanding cell-specific function of miR-146b in the neuronal and astroglial organization of the mouse brain.

Development of depression-like behavior and altered hippocampal neurogenesis in a mouse model of chronic neuropathic pain.

Chronic-pain patients often suffer from depression. In rodent models of neuropathic pain, animals develop depression-like and anxiety behaviors, indicating a relationship between chronic pain and affective disorders. However, the underlying neurobiological mechanisms linking chronic pain and depression are not yet fully understood. Neurogenesis in the hippocampus is a fundamental process related to brain plasticity. Reduced neurogenesis has been associated with the development of mood disorders and cognitive impairments. The current study aims to elucidate the underlying long-term changes in brain plasticity induced by neuropathic pain in mice at a time point when depression-like behavior has already developed. Furthermore, our focus is set on alterations in neurogenesis in the hippocampus. We found that manifestation of anxiety- and depressive-like behavior as well as cognitive impairment co-occur with decreased survival of newly generated cells but not with impaired proliferative activity or reduced number of immature neurons in the dentate gyrus area of the hippocampus. Moreover, we detected an impairment of differentiation of newly generated cells into mature calbindin-positive neurons, accompanied with a shift towards increased differentiation into astroglial cells. These findings indicate that a reduction in mature functional neurons, rather than reduced proliferation or neuronal progenitor cells, are the long-term changes in hippocampal plasticity that manifest in neuropathic pain conditions after depression-like behavior has developed.