Activation of corticotropin-releasing hormone system in the locus ceruleus induces the visceral sensitivity of irritable bowel syndrome rats

Objective To study the role of corticotropin-releasing hormone (CRH) system in locus ceruleus (LC) in irritable bowel syndrome (IBS) and to explore its molecular mechanism. Methods The IBS rat was established by maternal separation following with postnatal stress. The tissues sample of LC was obtained by micropunched nuclei. The expression of c-Fos, CRH and its receptors including corticotropin-releasing hormone receptor (CRHR) 1 and CRHR2 of rats’ LC tissues of control group and IBS group was detected by quantitative polymerase chain reaction(PCR). The expression of DNA methyltransferase (DNTM) 1, DNMT3a and DNMT3b at the mRNA level were also measured. In addition, the expression of histone methyltransferase ASH2-like protein (ASH2L) and SET and MYND domain containing 2 (SMYD2) was determined by Western blotting. T test was used for statistical analysis. Results The rectal pneumatic pressure of IBS group was lower than that of control group ((69.82±5.47) mmHg vs. (86.86±5.98) mmHg; 1 mmHg=0.133 kPa), however compared with that of control group, the expression of c-Fos at the mRNA level increased (2.11±0.44 vs.1.00±0.19), and the differences were statistically significant (t=6.215 and 2.321, P 0.05). Conclusions Maternal separation combined with postnatal stress affect the transcription of Crh gene in LC and cause the activation of the stress regulation network CRH and norepinephrine system, resulting in the increase of the visceral sensitivity of rats. The abnormal transcription of Crh gene may be related with SMYD2-mediated histone H3K36 methylation, but not related with the modification of DNA methylation. Key words: Irritable bowel syndrome; Locus ceruleus; Maternal separation stress; Corticotropin-releasing hormone system; Epigenetics