Effects of CD11b agonist leukadherin-1 on dextran sulfate sodium-induced acute experimental colitis in mice and the underlying mechanism

Objective To investigate the role of CD11b agonist leukadherin-1 (LA1) in the development of intestinal inflammation and colitis disease in a mouse model of dextran sulfate sodium (DSS)-induced colitis. Methods The mouse model of experimental colitis was induced by DSS. Body weight changes and survival status were monitored every day. The length of colons was measured at day 7. Colon tissue sections were stained with hematoxylin and eosin (HE) and observed under an optical microscope for pathological analysis. The percentages of apoptotic cells in colon tissues were observed by TUNEL staining. Myeloperoxidase (MPO) activity was measured with MPO activity detection kit. IL-1β and TNF-α levels were detected by ELISA. Macrophages and TNF-α in colon tissues were observed using immunofluorescence staining and confocal microscopy. Flow cytometry was performed to detect the changes in TLR4 expression on macrophages after stimulating mice with LA1 for 0, 3, 6 and 12 h. Moreover, TLR4 expression was also measured by Western blot after treating bone marrow-derived macrophages (BMDMs) with LA1 for 0, 3, 6 and 12 h. Unpaired t-test was used for statistical analysis. Results Compared with the DSS group, the LA1+ DSS group presented lower mortality rate, greater body weight and longer colon and the differences between the two groups were statistically significant. Moreover, the LA1+ DSS group showed lighter pathological damages, decreased percentage of apoptotic cells and suppressed MPO activity as compared with those of the DSS group. The number of macrophages and the relative concentrations of IL-1β and TNF-α in colon tissues were lower in the LA1+ DSS group than in the DSS group, and the differences between the two groups were statistically significant. There was no significant difference in the total expression of TLR4 on macrophages before and after LA1 treatment. However, the mean flourscence indensity (MFI) of TLR4 was weaker on the LA1-treated macrophages than on the untreated macrophages. Conclusions LA1 could alleviate the DSS-induced experimental colitis in mice through suppressing the activation of TLR4 pathway on macrophages. This study provided a new insight and theoretical reference for understanding the pathogenesis of inflammatory bowel diseases. Key words: Inflammatory bowel disease; Macrophage; LA1; Toll-like receptor 4