Increased Fibronectin Deposition in Embryonic Hearts of Retinol-Binding Protein–Null Mice

Abstract

Abstract-Precise regulation of retinoid levels is critical for normal heart development. Retinol-binding protein (RBP), an extracellular retinol transporter, is strongly secreted by cardiogenic endoderm. This study addresses whether RBP gene ablation affects heart development. Despite exhibiting an Ͼ85% decrease in serum retinol, adult RBP-null mice are viable, breed, and have normal vision when maintained on a vitamin A-sufficient diet. Comparison of RBP-null with wild-type (WT) hearts from embryos at day 9.0 (E9.0) through E12.5 revealed an RBP-null phenotype similar to that of other retinoid-deficient models. At an early stage, RBP-null hearts display retarded trabecular development, which recovers by E9.5. This is accompanied at E9.5 and E10.5 by precocious differentiation of subepicardial cardiac myocytes. Most remarkably, RBP-null hearts display augmented deposition of fibronectin protein in the cardiac jelly at E9.0 through E10.5 and in the outflow tract at E12.5. This phenomenon, which was detected by immunohistochemistry and Western blotting without increased fibronectin transcript levels, is accompanied by increased numbers of mesenchymal cells in the outflow tract but not in the atrioventricular canal. RBP-null cardiac myocytes, especially in the subepicardial layer, display increased cell proliferation. This phenotype may present a model of subclinical retinoid insufficiency characterized by alteration of an extracellular matrix component and altered cellular differentiation and proliferation, changes that may have functional consequences for adult cardiac function. This murine model may have relevance to fetal development in human populations with inadequate retinoid intake. Key Words: retinol-binding protein knockout Ⅲ retinoic acid Ⅲ mouse heart development Ⅲ cardiac jelly Ⅲ fibronectin T he biologically active derivative of vitamin A, retinoic acid (RA), plays an essential role in regulating the homeostasis of adult organs as well as the development of numerous embryonic tissues. Precisely regulated retinoid levels are crucial for normal development of the cardiovascular system: too much or too little RA causes profound cardiac teratogenicity. 1,2 For example, excess RA causes effects ranging from diminished cardiac jelly and outflow tract (OFT) disruption 3,4 to the total and specific absence of the embryonic heart. 5 On the other hand, vitamin A deficiency (VAD) causes aortic arch anomalies, ventricular septal defects, and retarded myocardial development 6 reflecting cellular deficits, including hypoplastic myocardial walls that contain precociously differentiated cardiac myocytes. 7,8 Most deficits caused by VAD are recapitulated by ablation of the genes involved in retinoid synthesis, such as retinaldehydeoxidizing dehydrogenase (RALDH2), 9 or genes in the retinoid signaling pathway, including the RA receptor (RAR) and retinoid X receptor (RXR) genes. 7,8,10,11 These findings suggest that the ablation of genes that regulate retinoid delivery, such as the retinol-binding protein (RBP) gene, m...

A1 adenosine receptors play an essential role in protecting the embryo against hypoxia

“…Apoptosis was assessed with the in situ cell death detection kit (Roche, Mannheim, Germany) according to the manufacturer's instructions as described previously (42)(43)(44).…”

Pathways of Vitamin A Delivery to the Embryo: Insights from a New Tunable Model of Embryonic Vitamin A Deficiency

“…Within the rodent placenta, RBP is localized on the maternal side in the decidua basalis and the embryonic yolk sac endoderm from 7.0 d post coitum (dpc) (24). Starting from 11.5 dpc, RBP is also expressed in fetal liver (25). We recently demonstrated that maternal RBP does not cross the placenta (26).…”

“…However, when maintained on a vitamin A-sufficient diet, mice lacking RBP (RBP Ϫ/Ϫ ) yield viable embryos that display only relatively mild and transient cardiac embryonic developmental anomalies (25,29). The unremarkable phenotype of RBP Ϫ/Ϫ embryos reflects the existence of an alternative pathway(s) of vitamin A delivery to the fetus.…”

Postnatal Development of Spinal Cord and Liver Antioxidant Status in the Young of Retinol-Overdosed Female Rats

“…As in the studies cited, we administered RA to pregnant female rats at high doses at days 8, 9, and 10 post coitum, i.e. in the period when molecules of retinol carriers are present not only in the mother's placental decidua basalis but also in the embryo -from day 7 in the embryonic yolk sac (Sapin et al, 1998) and from day 11.5 post coitum in the liver (Wendler et al, 2003). Therefore, the binding ability of retinol carriers increased at the time of dietary RA administration.…”