Anxiety Induced BDNF-CRF Brain-gut Interaction In The Pathogenesis Of IBS

BackgroundA large proportion of IBS patients are accompanied by varying degrees of mental and emotional disorders,among which anxiety is the most common.studies have found that nxiety can aggravateabdominal pain or discomfort in IBS patients.but,the pathophysiological mechanism of anxiety-induced IBS symptoms has not been clarified.Studies on the pathogenesis of visceral hypersensitivity must be pay a lot of attention to the role of the brain-gut axis.brain-gut axis is a neuro-endocrine network that connects the gastrointestinal tract with the central nervous system at different levels.The regulation of gastrointestinal function through the interaction of each link of the neuro-endocrine pathway at the brain-gut axis is called brain-gut interaction.Mental mood disorders induced the activation of brain regions,and then cause the changes of neural pathways,endocrine pathways,or neuro-endocrine pathways,sensitizing the enteric nervous system(ENS).Then these signals are uploaded to the corresponding brain regions to aggravate the symptoms of pain.It is of great significance to solve the problem of how the anxiety-induced brain-gut axis dysfunction is involved in the occurrence of visceral hypersensitivity in IBS.It is of important meaning for further understanding the pathogenesis of mental mood disorder induced-visceral hypersensitivity in IBS and seeking new therapeutic targets.In brain-gut interaction,brain-gut peptides play an important role in bridging and regulating functions.Brain-derived neurotrophic factor(BDNF)is an important neurotrophic factor,which is distributed in the brain and intestine.Studies have found that BDNF expression in the amygdala,hippocampus,and other central nervous systems is closely related to the occurrence of anxiety.The BDNF in the intestine was involved in the occurrence of visceral hypersensitivity in IBS,which significantly correlated with the degree and frequency of abdominal pain in patients with IBS.Based on the above researches,we speculated that BDNF could be used as a brain-gut peptide to regulate the anxiety-induced visceral hypersensitivity in IBS.It plays an indispensable role in regulating brain-gut interaction in IBS.However,the molecular mechanism of BDNF transmitting anxiety information from brain to intestine and causing visceral hypersensitivity remains unclear.Corticotropin-releasing factor(CRF)is a key regulator of emotional and psychological stress responses,which is widely distributed in central and peripheral tissue and freely passes the blood-brain barrier.Studies have found that CRF is closely related to psychological stress and hypersensitivity in IBS patients.In the central,BDNF induces the synthesis and release of CRF by activating the protein tyrosine kinase receptor B(TrkB)receptor on CRF neurons.However,whether it is involved in regulating visceral hypersensitivity is not clear.Meanwhile,CRF activates the BDNF promoter through the activation of CRF1 receptors on central neurons,thereby contributing to the transcription,translation,and expression of BDNF.In the gut,CRF mainly acts on the CRF1 receptor.Blocking CRF1 receptors can reduce visceral hypersensitivity caused by the increased CRF in the central or peripheral regions.It is indicating that the CRF1 signaling pathway is involved in regulating the occurrence of visceral hypersensitivity in IBS,but the mechanism remains unclear.We hypothesis whether CRF acts on the CRF1 receptor through a resemble mechanism in the central region and causes the BDNF's expression,inducing visceral hypersensitivity.In this study,we explored the central and peripheral mechanisms of anxiety-induced BDNF-CRF brain-gut interaction from the level of the brain-gut axis by constructing a maternally separated(MS)rat model and combining it with the IBS patients with anxiety.Part 1:Anxiety-induced BDNF-CRF interaction in brain aggravates visceral hypersensitivity of IBSObjectiveTo explore the mechanism of BDNF-CRF interaction in anxiety-induced visceral hypersensitivity at the central level of the brain-gut axis.Methods1.MS rat model with brain-gut axis dysfunction,which represents anxiety with visceral hypersensitivity was established.An open-field test(OFT)was used to detect the Anxiety.CRD andAWR were used to evaluate the level of visceral hypersensitivity.Spearman's rank correlation analysis was used to verify the correlation between anxiety and visceral hypersensitivity.2.The expression,mRNA level,and concentration of BDNF in the limbic system(hippocampus,cingulate gyrus,and amygdala)and serum were detected by immunohistochemistry,ELISA,and PCR.Spearman's rank correlation analysis was used to assess the correlation between BDNF levels,anxiety,and visceral hypersensitivity.3.Combined with the intracerebroventricular injection(ICV)of TrkB receptor antagonists K252a,the visceral hypersensitivity in control,MS,and MS+k252a group were evaluated by AWR scores.Meanwhile,the expression and concentration of CRF in the brain(hippocampus)and serum were detected by immunohistochemistry and ELISA.Results1.MS rats displayed heightened anxiety-like behaviors and visceral hypersensitivity.Rats in the MS group showed a decreased percentage of time spent in the center,number of crossings past the center,and rearing compared to those in the control group(P<0.05),an increased number of grooming(P<0.05).Compared to control rats,MS rats showed higher AWR scores(P<0.05).Spearman's rank correlation analysis showed that there was a negative correlation between AWR scores and the percentage of time spent in the center in the MS group(r=-0.79,P<0.05).2.The expression,mRNA level,and protein concentration of BDNF in the hippocampus were significantly higher in MS rats than in control rats(P<0.05).However,there was no difference in BDNF concentration in the cingulate gyrus,amygdala,and serum between MS rats and control rats(P>0.05).Correlation analysis showed that BDNF concentration in the hippocampus was positively correlated with the AWR score(r=0.93,P<0.05)and negatively correlated with the percentage of time spent in the center(r=0.78,P<0.05).3.The expression and protein concentration of CRF in the hippocampus was significantly increased in MS rats compared to that in control rats(P<0.05).After the ICV of K252a in MS rats,the concentration of CRF in the hippocampus decreased(P<0.05).Meanwhile,the AWR scores decreased in the MS+K252a group compared with the MS group(P<0.05).However,there was no significant difference noted in the CRF concentration in the serum of control rats,MS rats,and MS+K252a rats(P>0.05).Conclusions1.MS rats showed significant anxiety with visceral hypersensitivity in abnormal brain-gut axis interaction.And anxiety was positively correlated with visceral hypersensitivity.2.The expression of BDNF in the hippocampus of MS rats was increased,which was positively correlated with anxiety and visceral hypersensitivity.It suggested that BDNF was involved in regulating brain-gut interaction.3.The expression of CRF in the hippocampus of MS rats increased,which was regulated by BDNF.This indicated that the central "BDNF-TRKB-CRF" pathway was involved in the abnormal interaction of the brain-gut axis in IBS.Part 2:Anxiety-induced BDNF-CRF interaction in gut participates in visceral hypersensitivity of IBSObjectiveTo explore the mechanism of BDNF-CRF interaction in anxiety-induced visceral hypersensitivity at the peripheral intestinal level of the brain-gut axis.Methods1.According to the inclusion and exclusion criteria of this study,health controls and IBS patients diagnosed by Rome ? criteria were recruited.IBS patients were divided into anxiety groups and non-anxiety groups according to the Hospital Anxiety and Depression Scale(HADS).The symptoms(severity and frequency)of abdominal pain were scored.2.The expression and concentration of colonic BDNF in control,IBS with anxiety,and IBS without anxiety group were detected by immunohistochemistry and ELISA.Spearman's rank correlation analysis was used to assess the correlation between BDNF levels,anxiety,severity,and frequency of abdominal pain.3.Combined with ICV of TrkB receptor antagonists K252a,the visceral hypersensitivity in the control,MS,and MS+k252a group were evaluated by AWR scores.Meanwhile,the expression and concentration of BDNF in the colon were detected by immunohistochemistry and ELISA.4.The concentration of CRF in the colon and serum were detected after CRD by ELISA in the control and MS group.The expression of the colonic CRF1 receptor was detected by Western blot.5.Combined with the intraperitoneal injection of CRF1 receptor antagonists assassin,the visceral hypersensitivity in MS+vehicle and MS+astressin group was evaluated by AWR scores.Meanwhile,the expression and concentration of BDNF in the colon were detected by immunohistochemistry and ELISA.Results1.IBS patients displayed heightened anxiety-like behaviors and visceral hypersensitivity.IBS patients showed a higher anxiety score,abdominal pain degree score,and abdominal pain frequency score compared to the control group(P<0.05),especially in IBS with anxiety(P<0.05).2.The expression and protein concentration of BDNF in the colon was significantly higher in IBS patients than in control(P<0.05),especially in IBS with anxiety(P<0.05).Correlation analysis showed that BDNF concentration in the colon was positively correlated with the anxiety score(r=0.89,P<0.05),abdominal pain degree score(r=0.89,P<0.05),and abdominal pain frequency score(r=0.77,P<0.05).3.The expression and protein concentration of BDNF in the colon was significantly increased in MS rats compared to that in control rats(P<0.05).After the ICV of K252a in MS rats,the concentration of BDNF in the colon decreased(P<0.05).Meanwhile,the AWR scores decreased in the MS+K252a group compared to the MS group(P<0.05).4.The protein concentration of CRF in the colon and serum were increased in MS rats after CRD(P<0.05).The expression of CRF1 receptor in the colon was increased in MS rats compared to that in control rats(P<0.05).5.After intraperitoneal injection of CRF1 receptor antagonist stress,the expression and protein concentration of BDNF were decreased in the MS+astressin group compared to the MS+vehicle group(P<0.05).Meanwhile,the AWR scores decreased in the MS+astressin group compared to the MS+vehicle group(P<0.05).Conclusions1.The level of colonic BDNF was increased in IBS patients with anxiety,which was positively correlated with anxiety,severity,and frequency of abdominal pain.It suggested that colonic BDNF participated in brain-gut interaction in IBS patients.2.The expression of colonic BDNF increased in MS rats and could be regulated by ICV of K252a.This demonstrated that colonic BDNF played an important role in braingut interaction.3.The CRF and CRF1 receptors were increased in the gut of MS rats,and the expression of BDNF was regulated by the CRFR1 receptor.It confirmed that the peripheral intestinal "CRF-CRFR1-BDNF" pathway was involved in the brain-gut interaction of IBS.SignificanceIn conclusion,this study demonstrated that the expression of BDNF in the hippocampus is involved in regulating anxiety and visceral hypersensitivity by activating TrkB to synthesis and release of CRF in the central.In the peripheral intestine,CRF causes synthesis and release of BDNF through activating the CRF1 receptor,which results in visceral hypersensitivity.This study confirmed for the first time that anxiety-induced BDNF-CRF brain-gut interaction is involved in the pathogenesis of visceral hypersensitivity in IBS from the brain-gut axis level.Moreover,it confirmed that BDNF can be used as a brain-gut peptide to regulate brain-gut interaction.Our study provides a theoretical basis for the study of the pathogenesis of anxiety-induced IBS-like visceral hypersensitivity as well as new insights into the therapeutic targets for IBS.