Effects of genetic background on cardiovascular anomalies in the Ts16 mouse

Regulator of G Protein Signaling 2 Facilitates Uterine Artery Adaptation During Pregnancy in Mice

Background Decreased uterine blood flow is known to contribute to pregnancy complications such as gestational hypertension and preeclampsia. Previously, we showed that the loss of regulator of G protein signaling 2 ( RGS 2), a GTP ase activating protein for G_q/11 and G_i/o class G proteins, decreases uterine blood flow in the nonpregnant state in mice. Here, we examined the effects of the absence of RGS 2 and 5 on uterine blood flow and uterine vascular structure and function at early, mid, and late gestation, as well as peripartum period in mice. Methods and Results Abdominal Doppler ultrasonography was performed on adult female wild-type, Rgs2^-/-, and Rgs5^-/- mice at pre-pregnancy, gestational days 10, 15, and 18, and postpartum day 3. Uterine artery structure and function were also assessed by vessel myograph studies. At mid-pregnancy, uterine blood flow decreased in both Rgs2^-/- and Rgs5^-/- mice, whereas resistive index increased only in Rgs2^-/- mice. In uterine arteries from wild-type mice, mRNA expression of RGS 2 and 4 increased, whereas RGS 5 expression remained elevated at mid-pregnancy. These changes in gene expression were unique to uterine arteries because they were absent in mesenteric arteries and the aorta of wild-type mice. In Rgs2^-/- mice, uterine artery medial cross-sectional area and G protein-coupled receptor-mediated vasoconstriction increased in mid-pregnancy, implicating a role for RGS 2 in structural and functional remodeling of uterine arteries during pregnancy. In contrast, RGS 5 absence increased vasoconstriction only in the peripartum period. Conclusions These data together indicate that RGS 2 plays a critical role in the structural and functional remodeling of uterine arteries to impact uterine blood flow during pregnancy. Targeting the signaling pathway regulated by RGS 2 may therefore be a therapeutic strategy for ameliorating utero-placental perfusion disorders during pregnancy.

Pharyngeal arch artery defects and lethal malformations of the aortic arch and its branches in mice deficient for the Hrt1/Hey1 transcription factor

The aortic arch and major branch arteries are formed from the three pairs of pharyngeal arch arteries (PAAs) during embryonic development. Their morphological defects are clinically observed as isolated diseases, as a part of complicated cardiovascular anomalies or as a manifestation of multi-organ syndromes such as 22q11.2 deletion syndrome. Although numerous genes have been implicated in PAA formation and remodeling, detailed mechanisms remain poorly understood. Here we report that the mice null for Hrt1/Hey1, a gene encoding a downstream transcription factor of Notch and ALK1 signaling pathways, show perinatal lethality on the C57BL/6N, C57BL/6N × C57BL/6J or C57BL/6N × 129X1/SvJ background. Hrt1/Hey1 null embryos display abnormal development of the fourth PAA (PAA4), which results in congenital vascular defects including right-sided aortic arch, interruption of the aortic arch and aberrant origin of the right subclavian artery. Impaired vessel formation occurs randomly in PAA4 of Hrt1/Hey1 null embryos, which likely causes the variability of congenital malformations. Endothelial cells in PAA4 of null embryos differentiate normally but are structurally disorganized at embryonic day 10.5 and 11.5. Vascular smooth muscle cells are nearly absent in the structurally-defective PAA4, despite the appropriate migration of cardiac neural crest cells into the fourth pharyngeal arches. Endothelial expression of Jag1 is down-regulated in the structurally-defective PAA4 of null embryos, which may be one of the mechanisms underlying the suppression of vascular smooth muscle cell differentiation. While the direct downstream phenomena of the Hrt1/Hey1 deficiency remain to be clarified, we suggest that Hrt1/Hey1-dependent transcriptional regulation has an important role in PAA formation during embryonic development.

Cardiac teratogenicity in mouse maternal phenylketonuria: defining phenotype parameters and genetic background influences

Maternal phenylketonuria (MPKU) is a syndrome including cardiovascular malformations (CVMs), microcephaly, intellectual impairment, and small size for gestational age, caused by in-utero exposure to elevated serum phenylalanine (Phe) due to PKU in the mother. It is becoming a public health concern as more women with PKU reach child bearing age. Although a mouse model of PKU, BTBR Pah(enu2), has been available for 20 years, it has not been well utilized for studying MPKU. We used this model to delineate critical parameters in Phe cardiovascular teratogenicity and study the effect of genetic background. Dosing and timing experiments were performed with the BTBR Pah(enu2) mouse. A dose response curve was noted, with CVM rates at maternal serum Phe levels <360 μM (control), 360-600 μM (low), 600-900 μM (mid), and >900 μM (high) of 11.86%, 16.67%, 30.86%, and 46.67% respectively. A variety of CVMs were noted on the BTBR background, including double outlet right ventricle (DORV), aortic arch artery (AAA) abnormalities, and ventricular septal defects (VSDs). Timed exposure experiments identified a teratogenic window from embryonic day 8.5-13.5, with higher rates of conotruncal and valve defects occurring in early exposure time and persistent truncus arteriosus (PTA) and aortic arch branching abnormalities occurring with late exposure. Compared to the BTBR strain, N10+ Pah(enu2) congenics on the C3H/HeJ background had higher rates of CVMs in general and propensity to left ventricular outflow tract (LVOT) malformations, while the C57B/L6 background had similar CVM rates but predominately AAA abnormalities. We have delineated key parameters of Phe cardiovascular teratogenicity, demonstrated the utility of this MPKU model on different mouse strains, and shown how genetic background profoundly affects the phenotype.

Cardiovascular development and survival during gestation in the Ts65Dn mouse model for Down syndrome

The Ts65Dn mouse model for Down syndrome (DS) exhibits many phenotypes seen in human DS. Previous research has revealed a reduced rate of transmission of the T65Dn marker chromosome in neonates. To analyze potential fetal loss, litters from trisomic females at 10.5dpc through 14.5dpc were genotyped. No significant differences from the expected Mendelian ratio were found in transmission of T65Dn at any stage. Cardiovascular defects found in trisomic neonates are associated with formation of pharyngeal arch arteries. Vessel tracing was used to identify anomalies in 10.5dpc, 11.5dpc, and 13.5dpc embryos. Comparison of trisomic versus euploid embryos injected with India ink revealed delay and abnormality in cardiovascular development in trisomic embryos at each stage. Through the analysis of transmission rate and cardiovascular development in embryonic mice, we learn more about prenatal mortality and the origins of cardiac abnormality in the Ts65Dn mice to assist in understanding cardiovascular malformation associated with DS.

The power of comparative and developmental studies for mouse models of Down syndrome

Since the genetic basis for Down syndrome (DS) was described, understanding the causative relationship between genes at dosage imbalance and phenotypes associated with DS has been a principal goal of researchers studying trisomy 21 (Ts21). Though inferences to the gene-phenotype relationship in humans have been made, evidence linking a specific gene or region to a particular congenital phenotype has been limited. To further understand the genetic basis for DS phenotypes, mouse models with three copies of human chromosome 21 (Hsa21) orthologs have been developed. Mouse models offer access to every tissue at each stage of development, opportunity to manipulate genetic content, and ability to precisely quantify phenotypes. Numerous approaches to recreate trisomic composition and analyze phenotypes similar to DS have resulted in diverse trisomic mouse models. A murine intraspecies comparative analysis of different genetic models of Ts21 and specific DS phenotypes reveals the complexity of trisomy and important considerations to understand the etiology of and strategies for amelioration or prevention of trisomic phenotypes. By analyzing individual phenotypes in different mouse models throughout development, such as neurologic, craniofacial, and cardiovascular abnormalities, greater insight into the gene-phenotype relationship has been demonstrated. In this review we discuss how phenotype-based comparisons between DS mouse models have been useful in analyzing the relationship of trisomy and DS phenotypes.