Regulatory mechanism of mesalazine on TLR4/MyD88-dependent pathway in mouse ulcerative colitis model

The aim of this study was to investigate the regulatory mechanism of mesalazine (MSLZ) on microRNA-21, microRNA-31 and Toll-like receptor 4/myeloid differentiation primary response 88 (TLR4/MyD88)-dependent pathway in 2,4,6-trinitrobenzene sulfonic acid (TNBS)/ethanol-induced ulcerative colitis (UC) model in mice.

The UC model was constructed by coloclysis of TNBS/ethanol in mice. 60 male mice were randomly assigned into control group, model group, MSLZ group and Azathioprine (AZA) group, with 15 mice in each. Corresponding drug or saline was i.g. injected in mice for consecutive 14 days. Pathological lesions in colon tissues were observed by hematoxylin and eosin (HE) staining under the microscope. The expression levels of microRNA-21 and microRNA-31 in mouse colon tissues were determined by quantitative Real Time-Polymerase Chain Reaction (qRT-PCR). The mRNA and protein levels of relative genes in TLR4/MyD88-dependent pathway in mouse colon tissues were detected by qRT-PCR and Western blot, respectively.

A mouse UC model was successfully constructed based on scores of DAI, colonic damage and pathological lesions under the microscope. MSLZ markedly improved clinical symptoms and mucosal healing. Meanwhile, the protective effect of MSLZ was similar or even stronger than that of AZA. The expression levels of microRNA-21 and microRNA-31 in mouse colon tissues in the model group were significantly higher than those of the control group (p<0.01). Compared with the model group, both MSLZ and AZA treatment could remarkably inhibit the expressions of microRNA-21 and microRNA-31 (p<0.01). The mRNA and protein levels of relative genes in TLR4/MyD88-dependent pathway in mouse colon tissues were markedly upregulated in the model group when compared with those of the control group. The inhibitory effect of MSLZ on the expressions of upstream factors in TLR4/MyD88-dependent pathway (including TLR4, MyD88, TRAF-6 and NF-κB) was slightly stronger than AZA, which was weaker in inhibiting downstream factors (including TNF-α and IL-1β). However, no significant difference in the inhibition of TLR4/MyD88-dependent pathway was found between MSLZ and AZA (p>0.05).

In the TNBS/ethanol-induced UC mouse model, MSLZ could inhibit the expressions of microRNA-21 and microRNA-31 in colon tissues. Furthermore, MSLZ also inhibited the release of inflammatory factors by inhibiting the TLR4/MyD88-dependent pathway in UC mice.