Lack of VEGFR2 signaling causes maldevelopment of the intestinal microvasculature and facilitates necrotizing enterocolitis in neonatal mice.

The pathogenesis of necrotizing enterocolitis (NEC), a common gastrointestinal disease affecting premature infants, remains poorly understood. We previously found that intestinal VEGF-A expression is decreased in human NEC samples and in a neonatal mouse NEC model prior to detectable histological injury. Therefore, we hypothesized that lack of VEGF receptor 2 (VEGFR2) signaling facilitates neonatal intestinal injury by impairing intestinal microvasculature development. Here, we found that intestinal VEGF-A and its receptor, VEGFR2, were highly expressed at the end of fetal life and significantly decreased after birth in mice. Furthermore, selective inhibition of VEGFR2 kinase activity and exposure to a neonatal NEC protocol significantly decreased the density of the intestinal microvascular network, which was further reduced when both interventions were provided together. Furthermore, VEGFR2 inhibition resulted in greater mortality and incidence of severe injury in pups submitted to the NEC model. The percentage of lamina propria endothelial cells was decreased during NEC induction, and further decreased when VEGFR2 signaling was inhibited. This was associated with decreased endothelial cell proliferation rather than apoptosis. In conclusion, we found that VEGF-A and VEGFR2 proteins are highly expressed in the intestine before birth, and are significantly downregulated in the immediate neonatal period. Furthermore, VEGFR2 signaling is necessary to maintain the integrity of the intestinal mucosal microvasculature during the postnatal period and lack of VEGFR2 signaling predisposes to NEC in neonatal mice.

Characterization of a necrotizing enterocolitis model in newborn mice.

BACKGROUND: Necrotizingenterocolitis (NEC) is a major health concern for premature infants and its patho-genesis remains poorly understood. The current mouse NEC model has not well been characterized. OBJECTIVES: In this study, we develop a simple mouse model of NEC and determine the role of several factors modulating human NEC (i.e., breast milk, birth weight, cesarean section and bacteria) on intestinal injury. METHODS: In a first experiment, pups born naturally and dam fed for <12 hours were gavaged with adult commensal bacteria or E. Fecalis, and exposed to hypoxia-cold stress-formula feeding, and compared with controls without bacteria inoculation. 72-hour mortality was recorded, and small intestines were examined histologically. In a second experiment, we compared the incidence of NEC in mice dam fed for <12 hours to those dam fed for 12 to 24 hours or delivered by cesarean section prior to being submitted to the NEC protocol. RESULTS: In pups inoculated with 10(7) CFU of a standardized preparation of adult commensal bacteria or 10(5) CFU of E. Fecalis, the incidence of severe NEC (>grade 2) was 70% and 37% respectively vs 6% in the controls (no bacteria)(p<0.05). In pups dam fed for 12 to 24 hours, NEC incidence was 44(±12)% lower vs those dam fed less than 12 hours (p<0.05). We did not find any difference in the NEC incidence between naturally-born pups dam fed for less than 12 hours and these born by cesarean section. The incidence of severe NEC was higher in pups with low birth weight. CONCLUSIONS: we have simplified and characterized a neonatal mouse NEC model that shares several risk factors with human NEC. Now that transgenic mice are available, this model will be useful to study the role played by specific proteins in vivo in NEC development.