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

Abstract

Maternal phenylketonuria (MPKU) is a syndrome including cardiovascular malformations (CVMs), microcephaly, intellectual impairment, and small 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 Pahenu2, 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 Pahenu2 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 >900μM (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+ Pahenu2 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.

Congenital heart disease in maternal PKU

“…In this issue of Molecular Genetics and Metabolism Seagraves and McBride describe studies of cardiac teratogenicity in fetuses from female Pah enu2 mice, the mouse model for PKU [3]. The defects observed bore similarities to those noted in the affected fetuses from human maternal PKU [4] as well as to those previously reported by McDonald et al in the same mouse model for maternal PKU employed in the current study [5].…”

“…One indication of the importance of background genetic factors would be repetitive congenital heart disease from maternal PKU in siblings. In the Maternal PKU Collaborative Study there was repetitive offspring congenital heart disease but in only one family [3]. However, only three of the 33 mothers who bore children with congenital heart disease had another child.…”

Methylome repatterning in a mouse model of Maternal PKU Syndrome

“…The PAH enu2 mouse models classical PKU while the offspring of PHE unrestricted PAH enu2 dams model MPKU [27,28]. The MPKU mouse model was employed to investigate DNA methylation in brain tissue from offspring of hyperphenylalaninemic dams, offspring of dietary PHE restricted dams, and serving as experimental controls the offspring of heterozygotes (enu2/WT) where in utero PHE exposure is normal.…”

“…Methylation was assayed using methylated DNA immunoprecipitation (Me-DIP) and paired-end sequencing. Extensive differential methylation was observed in offspring of [28]. Dietary PHE restriction used PHE-free chow (Harlan Laboratories) and water supplemented with PHE at 0.5 g/l.…”

The role of teratogens in neural crest development

“…The Maternal Phenylketonuria (PKU) syndrome refers to the teratogenic effects of PKU during pregnancy, caused by in‐utero exposure to elevated serum phenylalanine due to PKU in the mother. These effects include mental retardation, microcephaly, congenital heart disease, and intrauterine growth retardation (Fiori et al, ; Seagraves & McBride, ). MPKU symptoms comprise abnormalities of the outflow tract and aortic arch.…”