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.