Food reward induction of rhythmic clock gene expression in the prefrontal cortex of rats is accompanied by changes in miR-34a-5p expression

The disruption of circadian rhythmicity of gene expression in the hippocampus and associated structures in Gria2R/R mice; a comparison with C57BL/6J and Adar2-/- mice strains

Adar2-/- mice are a widely used model for studying the physiological consequences of reduced RNA editing. These mice are viable only when the Q/R editing site of the Gria2 subunit of the AMPA receptor is constitutively mutated to the codon for arginine, and Gria2R/R mice often serve as the sole control for Adar2-/- mice. Our study aimed to investigate whether ADAR2 inactivity and the Gria2R/R phenotype affect the rhythmicity of the circadian clock gene pattern and the expression of Gria1 and Gria2 subunits in the suprachiasmatic nucleus (SCN), hippocampus, parietal cortex and liver. Our data show that Gria2R/R mice completely lost circadian rhythmicity in the hippocampus compared to Adar2-/- mice. Compared to C57BL/6J mice, the expression profiles in the hippocampus and parietal cortex of Gria2R/R mice differ to the same extent as in Adar2-/-. No alterations were detected in the circadian profiles in the livers. These data suggest that the natural gradual postnatal increase in the editing of the Q/R site of the Gria2 subunit may be important for the development of circadian clockwork in some brain structures, and the use of Gria2R/R mice as the only control to Adar2-/- mice in the experiments dependent on the hippocampus and parietal cortex should therefore be considered.

Impact of Long-Lasting Environmental Factors on Regulation Mediated by the miR-34 Family

The present review focuses on the interactions of newly emerging environmental factors with miRNA-mediated regulation. In particular, we draw attention to the effects of phthalates, electromagnetic fields (EMFs) and a disrupted light/dark cycle. miRNAs are small non-coding RNA molecules with a tremendous regulatory impact, which is usually executed via gene expression inhibition. To address the capacity of environmental factors to influence miRNA-mediated regulation, the miR-34 family was selected for its well-described oncostatic and neuro-modulatory properties. The expression of miR-34 is in a tissue-dependent manner to some extent under the control of the circadian system. There is experimental evidence implicating that phthalates, EMFs and the circadian system interact with the miR-34 family, in both lines of its physiological functioning. The inhibition of miR-34 expression in response to phthalates, EMFs and light contamination has been described in cancer tissue and cell lines and was associated with a decline in oncostatic miR-34a signalling (decrease in p21 expression) and a promotion of tumorigenesis (increases in Noth1, cyclin D1 and cry1 expressions). The effects of miR-34 on neural functions have also been influenced by phthalates, EMFs and a disrupted light/dark cycle. Environmental factors shifted the effects of miR-34 from beneficial to the promotion of neurodegeneration and decreased cognition. Moreover, the apoptogenic capacity of miR-34 induced via phthalate administration in the testes has been shown to negatively influence germ cell proliferation. To conclude, as the oncostatic and positive neuromodulatory functions of the miR-34 family can be strongly influenced by environmental factors, their interactions should be taken into consideration in translational medicine.

2.4 GHz Electromagnetic Field Influences the Response of the Circadian Oscillator in the Colorectal Cancer Cell Line DLD1 to miR-34a-Mediated Regulation

Radiofrequency electromagnetic fields (RF-EMF) exert pleiotropic effects on biological processes including circadian rhythms. miR-34a is a small non-coding RNA whose expression is modulated by RF-EMF and has the capacity to regulate clock gene expression. However, interference between RF-EMF and miR-34a-mediated regulation of the circadian oscillator has not yet been elucidated. Therefore, the present study was designed to reveal if 24 h exposure to 2.4 GHz RF-EMF influences miR-34a-induced changes in clock gene expression, migration and proliferation in colorectal cancer cell line DLD1. The effect of up- or downregulation of miR-34a on DLD1 cells was evaluated using real-time PCR, the scratch assay test and the MTS test. Administration of miR-34a decreased the expression of per2, bmal1, sirtuin1 and survivin and inhibited proliferation and migration of DLD1 cells. When miR-34a-transfected DLD1 cells were exposed to 2.4 GHz RF-EMF, an increase in cry1 mRNA expression was observed. The inhibitory effect of miR-34a on per2 and survivin was weakened and abolished, respectively. The effect of miR-34a on proliferation and migration was eliminated by RF-EMF exposure. In conclusion, RF-EMF strongly influenced regulation mediated by the tumour suppressor miR-34a on the peripheral circadian oscillator in DLD1 cells.