Bdnf Gene Hydroxymethylation In Hippocampus Related To Neuroinflammation-induced Depression In Mice

Depression is a complex affective disorder and currently affects about 280 million people in the world,but its pathogenesis remains unclear.Clinical data showed that the levels of inflammatory factors in the brain of depressive patients were significantly higher than healthy people.Microglia mediate inflammatory processes as immune cells in the brain.Microglia activation is considered to related with the occurrence and development of depression.Neuroinflammation has been reported to reduce the expression of brain derived-neurotrophic factor(BDNF)in the hippocampus.However,the mechanism of how neuroinflammation affects the decreased BDNF expression remains unclear.Our study investigated the changes of BDNF expression in hippocampus of depressed mice induced by neuroinflammation and the regulation of DNA hydroxymethylation on BDNF expression.In this study,lipopolysaccharide(LPS)was used to induce neuroinflammatory depression in mice.The results showed that LPS treatment in mice could significantly induce depression-like behaviors as follows:(1)the body weight was decreased significantly in LPS treatment mice;(2)In sucrose preference test,the percentage of sucrose preference in LPS-treated mice decreased significantly.(3)In forced swimming and tail suspension test,the immobility time was significantly increased and the latency to first immobility was significantly shortened in LPS treatment mice.These results manifested the behavioral despair and anhedonia in LPS treatment mice.The neuroinflammation induced by LPS treatment was detected by q PCR and immunohistochemical staining.As a marker of neuroinflammation,the expressions of IBA-1 m RNA and protein were significantly increased in LPS group,compared with the saline group.These results suggest that LPS administration can induce neuroinflammation and subsequent behavioral changes in mice.Secondly,we detected whether the expression of Bdnf gene,an important molecule of neurogenesis and synaptic plasticity,was affected in the hippocampus of depressed mice induced by neuroinflammation.q PCR results showed that compared with the Saline group,The m RNA expression levels of Bdnf transcript variant1 and total Bdnf(Bdnf transcript all)in LPS-induced depressed mice were significantly down-regulated.Next,we examined whether there were changes in DNA hydroxymethylation in the hippocampus of neuroinflammation-induced depressve mice.The results of q PCR showed that the m RNA levels of Tet1,Tet2 and Tet3 in LPS-induced depression mice were significantly down-regulated,compared with the saline group.Further,we detected the global 5-hm C levels and the localization of 5-hm C immunofluorescence in the hippocampus by DNA Dot blot analysis and immunofluorescence staining.The results showed that the global 5-hm C levels in the hippocampus of LPS-treated mice were significantly decreased,compared with the saline group.The 5-hm C immunofluorescence in the hippocampus was located on excitatory neurons identified by Ca MKII(a marker for excitatory neurons)immunostaining.Therefore,we concluded that neuroinflammation-induced depression-like behaviors are strongly associated with a reduction of DNA hydroxymethylation in excitatory neurons of the hippocampus.Finally,we examined whether hydroxymethylation of the Bdnf exon Ⅰ promoter is involved in neuroinflammation-induced depression.The results of hydroxymethylated DNA Immunoprecipitation(h Me DIP)showed that the level of hydroxymethylation of Bdnf exon Ⅰ promoter in hippocampus of mice administered with LPS was significantly lower than that of Saline group.In conclusion,our study suggests that LPS-induced neuroinflammation reduces hippocampal DNA hydroxymethylation levels,decreases hippocampal neuronal Bdnf exon Ⅰ promoter hydroxymethylation,decreases Bdnf gene expression,and leads to depression-like behavior.We can draw the following conclusions:1.Neuroinflammation reduces hippocampal DNA hydroxymethylation levels.2.Neuroinflammation induces hydroxymethylation of the hippocampal Bdnf exon Ⅰ promoter and regulates depression-like behavior in animals.