Uterine Artery Remodeling and Reproductive Performance Are Impaired in Endothelial Nitric Oxide Synthase-Deficient Mice1

Abstract

The progressive rise in uterine blood flow during pregnancy is accompanied by outward hypertrophic remodeling of the uterine artery (UA). This process involves changes of the arterial smooth muscle cells and extracellular matrix. Acute increases in blood flow stimulate endothelial production of nitric oxide (NO). It remains to be established whether endothelial NO synthase (eNOS) is involved in pregnancy-related arterial remodeling. We tested the hypothesis that absence of eNOS results in a reduced remodeling capacity of the UA during pregnancy leading to a decline in neonatal outcome. UA of nonpregnant and pregnant wild-type (Nos3+/+) and eNOS-deficient (Nos3-/-) mice were collected and processed for standard morphometrical analyses. In addition, cross sections of UA were processed for cytological (smoothelin, smooth muscle alpha-actin) and proliferation (Ki-67) immunostaining. We compared the pregnancy-related changes longitudinally and, together with the data on pregnancy outcome, transversally by analysis of variance with Bonferroni correction. During pregnancy, the increases in radius and medial cross sectional area of Nos3-/- UA was significantly less than those of Nos3+/+ UA. Smooth muscle cell dedifferentiation and proliferation were impaired in gravid Nos3-/- mice as deduced from the lack of change in the expression of smoothelin and smooth muscle alpha-actin, and the reduced Ki-67 expression. Until 17 days of gestation, litter size did not differ between both genotypes, but at birth the number of viable newborn pups and their weights were smaller in Nos3-/- than in Nos3+/+ mice. We conclude that absence of eNOS adversely affects UA remodeling in pregnancy, which may explain the impaired pregnancy outcome observed in these mice.

Maternal Endothelial Nitric Oxide Synthase Genotype Influences Offspring Blood Pressure and Activity in Mice

“…Our data revealed a significant elevation of the nocturnal diastolic arterial pressure level of the eNOS ϩ/ϪMAT group relative to the eNOS ϩ/ϪPAT group. Because the pressor response to L-NAME did not differ between the eNOS ϩ/ϪMAT and eNOS ϩ/ϪPAT groups, our results are consistent with the differences in their blood pressures being secondary to the IUGR that has been described in the offspring of eNOS Ϫ/Ϫ mothers 8,10 and not a reduced activity of eNOS within the vascular system of eNOS ϩ/ϪMAT mice as a consequence of genetic imprinting or other factors ( Figure 5). These results provide a novel illustration of the influence that maternal genotype can have on offspring blood pressure independent of the offspring's genotype.…”

“…eNOS Ϫ/Ϫ mice and has been described by others. 8,17,18 The litter size data reported in the Table actually overestimate the productivity of eNOS Ϫ/Ϫ mothers, because only successful pregnancies producing the pups used in the present study are included. In our broader experience breeding these animals, eNOS Ϫ/Ϫ mothers frequently had pregnancies in which all of the pups were lost or destroyed (46% of litters [23 of 50] of eNOS Ϫ/Ϫ pups and 44% of litters [14 of 32] of eNOS ϩ/ϪMAT compared with 26% [6 of 23] in eNOS ϩ/ϪPAT and 15% [5 of 34] in eNOS ϩ/ϩ ).…”

“…Maternal endothelial NO synthase (eNOS) is a potential candidate in this regard, because eNOS has been shown to play an important role in the regulation of uterine blood flow, 8,9 and IUGR has been observed in rats treated with inhibitors of NO synthase 6,7 and in mice with targeted deletion of the eNOS gene (eNOS Ϫ/Ϫ ) 8,10 . In humans, polymorphisms of the eNOS gene are common and are associated with endothelial dysfunction, 11-13 increased uterine artery resistance, 14 and poor pregnancy outcomes.…”

Transcriptional regulation of endothelial nitric oxide synthase expression in uterine artery endothelial cells by c-Jun/AP-1

“…The importance of the NOS3-NO system during pregnancy has recently been reinforced by the findings that uterine artery remodeling is impaired and litter size is reduced in NOS3-null compared to wild-type mice (van der Heijden et al, 2005). In vivo, there is solid evidence showing that uterine artery endothelial NOS3 protein is increased during pregnancy Magness et al, 2001) and in the follicular phase of the estrous cycle or by estrogen replacement therapy in association with elevated circulating estrogen levels (Chen et al, 2006;Rosenfeld et al, 2003;Rupnow et al, 2001;.…”

“…The primary NOS responsible for NO/endothelium-dependent mechanism for uterine vasodilatation is endothelial NOS3 (Byers et al, 2005;Rupnow et al, 2001), although iNOS and nNOS may play a minor role, but none of them are expressed in the uterine artery endothelium in vivo (Mershon et al, 2002;Rosenfeld et al, 2003). The importance of the NOS3-NO system has been recently further emphasized to be critical for pregnancy outcomes in the NOS3-deficient mice (van der Heijden et al, 2005).…”