The large surface area covered by the intestinal epithelium is particularly prone to inflammation-associated hypoxia as may occur during inflammatory bowel disease. Here, extracellular adenosine signaling events play a major role in attenuating acute inflammation, particularly during conditions of limited oxygen availability. However, extracellular adenosine has an extremely short half-life on the epithelial surface of the intestine. This is due to rapid transport by nucleoside transporters and enzymatic metabolism. Therefore, we hypothesized the existence of endogenous non-adenosine-like compounds with biological activity on adenosine receptors (ARs). To pursue this hypothesis, we screened fractions derived from supernatants of hypoxic epithelia for AR activity. These studies found a single fraction with biological activity. Using mass spectrometry, we found that this fraction contained a dominant peak consistent with the mass of the neuronal guidance molecule netrin-1. Such studies revealed a surprising role for neuronal guidance molecule netrin-1 in alternative adenosine receptor activation and attenuation of mucosal inflammation during hypoxia. Based on these preliminary studies, it is our hypothesis that endogenous netrin-1 is released from hypoxic epithelia, and attenuates inflammatory hypoxia through AR-dependent signaling pathways. In the present proposal, we will further characterize the role of netrin-1 in alternative AR activation and its biological role in endogenous attenuation of mucosal inflammation as occurs during experimental colitis.
The present studies are designed to identify endogenous anti-inflammatory signaling pathways and to test these pathways in a therapeutic setting. This work will lay the groundwork for novel and specific therapeutic approaches in the treatment of mucosal inflammation, which are urgently needed - for example in the treatment of patients suffering from inflammatory bowel disease.
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