Abstract 172: The Role of Activin A in Maternal Diabetes-Induced Cardiac Malformations

Abstract

Diabetes mellitus in pregnancy causes heart defects, especially atrioventricular septal defects (AVSDs), in infants. Manifestation of AVSDs results from dysmorphogenesis of the endocardial cushions in the embryo, which is regulated by members of the transforming growth factor (TGF) β family. Among the TGFβs, we have previously observed that the inhibin βA gene, which encodes a protein to form homodimers as activin A, is markedly downregulated by maternal diabetes. To further determine the involvement of inhibin βA and its signaling in diabetic embryopathy, the levels of inhibin βA protein and activation of its downstream transcription factors, Smad2 and Smad3, were examined using immunohistochemical, proximity ligation, and immunoblot assays, and shown to be decreased in the embryonic hearts of diabetic mice induced via intravenous injection of streptozotocin. To investigate the role of activin A in hyperglycemia-induced cardiac malformations, mouse embryos at embryonic day 9.5 (E9.5) cultured in high glucose (22 mM) were treated with activin A (50 ng/ml) for 24 hours. The treatment rescued the development of the endocardial cushions and cell proliferation (BrdU-incorporation assay) in the myocardium, similar to those in normal glucose control (8.3 mM). The role of activin A in endocardial cell migration, an important process for cellularization of the cardiac jelly, was investigated by treating E10.5 endocardial cushion explants cultured in high glucose with activin A (50 ng/ml) in a collagen matrix-based assay system. The treatment significantly increased the number of migrating cells, compared with that in high glucose-treated group, to the level in the control group. These effects were associated with restoration of the activation of Smad2/3. The results demonstrate that the activin-Smad2/3 signaling system plays an important role in cardiac malformation in diabetic embryopathy.