NoxO1 contributes to the differentiation of intestinal stem cells

The intestinal epithelium is one of the most rapidly renewing tissues in the body. Low constitutive ROS formation is needed for cellular differentiation in different tissues. In the intestine, Nox1 is the predominant Nox and the cytosolic scaffolding protein NoxO1 enables its constitutive activity. We hypothesize that NoxO1 by enabling a constitutive low Reactive Oxygen Species (ROS) formation impacts on proliferation of intestinal stem cells. In the mouse colon Nox1 mRNA was expressed at the bottom of the crypts where NoxO1 mRNA was expressed throughout the whole epithelium with reduced abundance toward the top of the crypt. Interestingly NoxO1 protein expression was restricted to the bottom of the crypts, indicating that Nox1 may impact on the protein stability of NoxO1. In Noxo1 knockout mice, Nox1 expression was increased in the crypts whereas the expression of a potential substitute for NoxO1, namely p47phox, was not changed. Accordingly superoxide anion production in intestinal crypts isolated from NoxO1 knockout mice as measured by LO12 chemiluminescence was reduced. In cells isolated from the crypt bottom of NoxO1-/- mice PCNA was decreased, indicating a decreased cell proliferation. Interestingly, Hes-1 was significantly reduced in colons of NoxO1-/- mice. We conclude that loss of NoxO1 may impact on the proliferation of epithelial cells in the gut, mediated by the formation of superoxide anions.