The role of ERK1/2 in colitis through regulation of NADPH oxidase and mitochondrial fission

Objective To investigate the role of extracellular signal regulated kinase 1/2 （ERK1/2） in colitis through the regulation of NADPH oxidase and mitochondrial fission. Methods Mice models of acute colitis were induced by 3% dextran sulfate sodium （DSS）. Thirty C57BL/6J mice were randomly divided into six groups by random number table method： control group， 3%DSS group，1% dimethyl sulfoxide （DMSO） group， ERK1/2 inhibitor（PD98059） group， 3%DSS+1%DMSO group and 3%DSS+PD98059 group， with five mice in each group. The changes of body weight， colonic length， disease activity index and colonic histopathological changes of mice in the control and 3%DSS groups were evaluated， and the expression levels of ERK1/2， p-ERK1/2， Nicotinamide adenine dinucleotide phosphate oxidase 1 （Nox1） and Nox2 in colonic mucosa of mice were detected. Mice in 1%DMSO and 3%DSS+1%DMSO groups were intraperitoneally injected with 1%DMSO. Mice in the PD98059 and 3%DSS+PD98059 groups were intraperitoneally injected with PD98059. The colonic histopathological changes were evaluated among four groups， and the expression levels of Nox1， Nox2， Dynamin related protein 1 （DRP1）， p-DRP1-S616 and p-DRP1-S637 mitochondrial fission related proteins were detected. Mitochondrial fission of colonic epithelial cells in the control and 3%DSS groups was observed by transmission electron microscopy. The co-localization of Nox2 and mitochondrial outer membrane translocator enzyme TOM complex （TOMM20） in colonic mucosa of mice in two groups was analyzed by double-immunofluorescence staining. The correlation between relative expression levels of DRP1 and Nox2 mRNA in mouse colonic mucosa was analyzed in two groups. Results Compared with the control group， mice in the 3%DSS group exhibited body weight loss， shortened colonic length， increased disease activity index and increased colonic histopathological score. The expression levels of p-ERK1/2， Nox1， Nox2 in colonic mucosa of mice were significantly up-regulated in the 3%DSS group （all P < 0.05）. In mice with colitis， mitochondrial fission in colonic epithelial cells was increased， and the colonic mucosa co-localization of DRP1 and Nox2 was elevated， and the relative mRNA expression levels of both target genes were positively correlated （r = 0.678， P < 0.05）. ERK1/2 inhibitor PD98059 improved colonic histopathological changes in mice with colitis， and down-regulated the expression levels of Nox1， Nox2， DRP1， p-DRP1-S616 in colonic mucosa. Conclusion Inhibition of ERK1/2 may ameliorate colitis by down-regulating NADPH oxidase expression and alleviating mitochondrial fission.