Role of the kynurenine pathway in neonatal intestinal microvascular maldevelopment and necrotizing enterocolitis

Necrotizing enterocolitis (NEC), characterized by acute onset intestinal tissue damage and ischemic necrosis, is a major cause of morbidity and mortality among premature infants. Intestinal VEGF/VEGFR2 proteins and intestinal endothelial cell (iEnC) proliferation are significantly decreased in our experimental NEC model prior to intestinal tissue injury and in resected human NEC tissue samples. We previously showed that neonatal iEnC are highly proliferative compared to adults. Growing evidence indicates that cell metabolism plays an important role in endothelial cell (EnC) proliferation and angiogenesis by providing energy for cell functions and generating biomass, such as nucleotides, for RNA/DNA synthesis. Currently, not much is known about the developmental regulation of iEnC metabolism and how it impacts iEnC proliferation. Furthermore, it is not known how neonatal iEnC metabolism is affected during stress and its impact on intestinal microvascular network development and NEC. Mechanistic studies that investigate the underlying molecular pathways may reveal new putative therapeutic targets for treating NEC and are strongly needed. Kynurenine (Kyn) is a tryptophan (Trp) metabolite and a key intermediate of the de novo Nicotinamide Adenine Dinucleotide (NAD) synthesis pathway, leading to formation of adenosine, a purine nucleoside. Abnormally high Kyn and nucleoside levels such as adenosine have been previously reported to inhibit cell proliferation. Our preliminary studies indicated that the levels of several metabolites of the Kyn pathway and purine related products (Kyn, adenosine and the purine waste product uric acid) were significantly lower in neonatal iEnCs compared to adult iEnCs. While the Kyn/Trp ratio and uric acid levels were low in normal neonatal serum, they were significantly increased in the serum of neonatal pups subjected to experimental NEC and at higher levels in adult animals, suggesting higher Indoleamine 2,3-Dioxygenase 1(IDO1) enzymatic activity and activation of the Kyn pathway. Therefore, we hypothesize that the activity of the Kyn pathway needs to be low to support the high proliferation rate of neonatal iEnC needed for postnatal gut angiogenesis at baseline, while high activity of the Kyn pathway contributes to impaired iEnC proliferation during NEC development. To test our hypothesis, we will conduct two specific aims: 1) To investigate whether and how iEnC metabolism is developmentally regulated and test the hypothesis that low activity of the Kyn pathway is required for the higher proliferation rate of neonatal iEnC. 2) To examine the role of the Kyn pathway during NEC development using our experimental mouse NEC model. This proposal will help characterize the role of the Kyn pathway in iEnC proliferation and during NEC development, so preventative and/or therapeutic interventions to preserve iEnC proliferation could be developed to mitigate neonatal morbidity and mortality due to NEC.