Novel insights from fetal and placental phenotyping in 3 mouse models of Down syndrome

Abstract

Background: In human fetuses with Down syndrome, placental pathology, structural anomalies and growth restriction are present. There is currently a significant lack of information regarding the early life span in mouse models of Down syndrome.

Objective: The objective of this study was to examine embryonic day 18.5 and placental phenotype in the 3 most common mouse models of Down syndrome (Ts65Dn, Dp(16)1/Yey, Ts1Cje). Based on prenatal and placental phenotyping in 3 mouse models of Down syndrome, we hypothesized that one or more of them would have a similar phenotype to human fetuses with trisomy 21, which would make it the most suitable for in utero treatment studies.

Study design: Here, C57BL6J/6 female mice were mated to Dp(16)1/Yey and Ts1Cje male mice and Ts65Dn female mice to C57BL/B6Eic3Sn.BLiAF1/J male mice. At embryonic day 18.5, dams were euthanized. Embryos and placentas were examined blindly for weight and size. Embryos were characterized as euploid or trisomic, male or female by polymerase chain reaction. A subset of embryos (34 euploid and 34 trisomic) were examined for malformations.

Results: The Ts65Dn mouse model showed the largest differences in fetal growth, brain development, and placental development when comparing euploid and trisomic embryos. For the Dp(16)1/Yey mouse model, genotype did not impact fetal growth, but there were differences in brain and placental development. For the Ts1Cje mouse model, no significant association was found between genotype and fetal growth, brain development, or placental development. Euploid mouse embryos had no congenital anomalies; however, 1 mouse embryo died. Hepatic necrosis was seen in 6 of 12 Dp(16)1/Yey (50%) and 1 of 12 Ts1Cje (8%) mouse embryos; hepatic congestion or inflammation was observed in 3 of 10 Ts65Dn mouse embryos (30%). Renal pelvis dilation was seen in 5 of 12 Dp(16)1/Yey (42%), 5 of 10 Ts65Dn (50%), and 3 of 12 Ts1Cje (25%) mouse embryos. In addition, 1 Ts65Dn mouse embryo and 1 Dp(16)1/Yey mouse embryo had an aortic outflow abnormality. Furthermore, 2 Ts1Cje mouse embryos had ventricular septal defects. Ts65Dn mouse placentas had increased spongiotrophoblast necrosis.

Conclusion: Fetal and placental growth showed varying trends across strains. Congenital anomalies were primarily seen in trisomic embryos. The presence of liver abnormalities in all 3 mouse models of Down syndrome (10 of 34 cases) is a novel finding. Renal pelvis dilation was also common (13 of 34 cases). Future research will examine human autopsy material to determine if these findings are relevant to infants with Down syndrome. Differences in placental histology were also observed among strains.

Keywords: Down syndrome; fetal phenotyping; liver abnormalities; mouse models; placenta.

Figure 1.. Liver Pathology

Hematoxylin and Eosin (H&E) stained sections of E18.5 embryonic liver. A sagittal section of normal liver in a euploid Dp16(1)/YeY embryo. Upper 2X magnification. Lower 10X magnification. B. Sagittal section of liver demonstrating hepatic necrosis in a Dp16(1)/Yey embryo. Upper 2X magnification. Lower 20X magnification. C. Ts65Dn embryo. Upper sagittal section of liver with hepatic congestion (2X magnification). Lower sagittal section of pancreatic fibrosis (10X magnification). Arrows indicate pathologic findings D. Sagittal section of liver with focal hepatitis in a Ts65Dn embryo. Upper 10X magnification. Lower 40X magnification. The red box in the low magnification section represents the location of the high magnification image.

Figure 2.. Renal Pathology

H&E stained sections of embryonic kidneys (E18.5). A. Sagittal section of normal kidney from a euploid Ts65Dn embryo at 2X magnification. B. Sagittal section of kidney with dilation of the renal pelvis from a trisomic Ts65Dn embryo at 2X magnification. C. Sagittal section of kidney with severe hydronephrosis with dilation of the proximal ureter from a trisomic Ts65Dn embryo at 2X magnification. C= Renal cortex, G = Glomeruli, RP = renal pelvis.

Figure 3.. Cardiac Pathology

H&E stained sections of embryonic hearts (E18.5). A. Sagittal section of a normal cardiac anatomy in a trisomic Ts65Dn embryo at 2X magnification. The normal orientation of the aortic valve and aorta can be seen arising from the left ventricle. B. Sagittal section of an aortic outflow abnormality in a trisomic Ts65Dn embryo at 2X magnification. The aorta and aortic valve are seen arising from the right ventricle. C. Sagittal section of normal interventricular septum in a trisomic Ts1Cje embryo at 2X magnification. The arrow points to the intact septum between the left and right ventricles. D. Sagittal section showing a ventricular septal defect in a trisomic Ts1Cje embryo. The arrow is pointing to a defect in the septum with blood flow between the left and right ventricles. The red box in the low magnification section represents the location of the high magnification image in E. Upper 2X magnification. Lower 10X magnification. LV= Left ventricle. RV = Right ventricle. LA = Left atrium. RA = right atrium. IVS = interventricular septum. Ao = Aorta. Aov = Aortic valve. VSD = Ventricular septal defect.

Figure 4.. Placental Abnormalities

Hematoxylin and eosin- stained sections of embryonic placentas (embryonic day 18.5). A. Sagittal section of placenta from a euploid littermate control from a Ts65Dn mating. Upper 2X magnification shows layers of the placenta. Decidua basalis (maternal side), Junctional zone (location of spongiotrophoblast cells and glycogen cells, with giant cells lining the periphery), labyrinth zone (fetal vasculature lined by multinucleated progenitor cells (syncytiotrophoblast), chorionic plate (fetal side). Lower 10X magnification. The arrows indicate layers and cell types. B. Sagittal section of a Ts65Dn placenta at 10X magnification showing evidence of syncytiotrophoblast necrosis. The box indicates the area of necrosis. The arrows are pointing to cells with both nuclear and cellular swelling, pale, eosinophilic cytoplasm, cellular debris and nuclear fragmentation. C. Sagittal section of Ts65Dn placenta at 10X magnification showing decreased number of giant cells. The outlined area shows the location of the spongiotrophopblast layer and absence of giant cells in the periphery. Jz = Junctional zone. Lb = Labyrinth. Dc = Decidua Basalis. STB = Syncytiotrophoblast. SpTb = Spongiotrophoblast. GC = Giant Cell. GlyC = Glycogen cell