Anxiety-depression-like Behavior And Altered Expression Of RNA Methyltransferase METTL3 In Different Brain Regions In Mice After Stress

The development of the modern society with the speeding up of life pace has brought increasingly strong pressure to various populations.While temporary mental pressure or stress will not cause physical damage,accumulated stress might bring spiritual abnormality and even depression.Depression is a common mental disorder characterized by a blue mood and abnormal behaviors.In recent years,epigenetic mechanisms like DNA methylation and histone modifications have been well documented in gene regulation during the pathogenesis of depression.Meanwhile,the latest studies have highlighted the critical involvement of a type of messenger RNA(mRNA)modification,N6-methyladenosine(m6A),in the development of clinical disorders including those occur in the nervous system.Nonetheless,it is largely unknown whether and how m6A modification plays a regulatory role in stress-evoked dysthymic disorders.In the present study,we explored the relationship between mode disorder and m6A modification in the context of chronic and acute stress in mice.Chronic unpredictable stress(CUMS)stimuli were first applied to male C57BL/6J mice for 21 days.Behavioral and molecular biological examinations were conducted on days 7,14 and 21.After the completion of each stage of stress,open field,elevated cross maze,sugar water preference,forced swimming,and tail suspension paradigms were used to evaluate the anxiety and depression-like behaviors of mice.Morris water maze test was used to evaluate spatial learning and memory.Bilateral hippocampi,amygdalae and prefrontal cortexes were dissected,and total protein samples were prepared for Western blotting analysis of the m6A methyltransferase METTL3.Brain slices of amygdala region were prepared by frozen section method,and the expression level of METTL3 on neurons was determined by immunofluorescence assay.Secondly,three methods of acute stress including foot shock,forced swimming and elevated stress were used to generate acutely stressed mouse model.After the stimuli,open-field and elevated plus maze tests were used to evaluate the anxiety-like behaviors of mice.We obtained the results in the aforementioned examinations as follows:1)7 days of short-term chronic stress did not affect the anxiety-like behavior of mice,while 14 days and 21 days of long-term chronic stress caused anxiety-like behavior of mice;2)21 days of long-term chronic stress impaired the memory extraction of mice in the water maze test;3)through Western blot experiments we found,chronic stress had no effect on the expression level of METTL3 protein in the hippocampus and prefrontal cortex of mice,but the expression of METTL3 protein decreased in the amygdala after 14 days of chronic stress;4)through the immunofluorescence double standard experiment we found,the expression of METTL3 protein in amygdala neurons was not affected by chronic stress;5)acute stress did not cause anxiety-like behavior of mice;6)acute stress had no effect on the expression level of METTL3 protein in the prefrontal cortex,but the acute stress of foot shock and forced swimming reduced the expression of METTL3 protein in the amygdala.In conclusion,the behavioral disorders induced by acute and chronic stress were frequently accompanied by the downregulation of METTL3 protein in the amygdala,suggesting that the impairment of m6A modification of mRNAs plays an essential role in stress-induced learning,memory and dysthymic disorders.