Myocardium-specific deletion of rac1 causes ventricular noncompaction and outflow tract defects

Background: Left ventricular noncompaction (LVNC) is a cardiomyopathy that can lead to arrhythmias, embolic events and heart failure. Despite our current knowledge of cardiac development, the mechanisms underlying noncompaction of the ventricular myocardium are still poorly understood. The small GTPase Rac1 acts as a crucial regulator of numerous developmental events. The present study aimed to investigate the cardiomyocyte specific role of Rac1 in embryonic heart development. Methods and Results: The Nkx2.5-Cre transgenic mice were crossed with Rac1f/f mice to generate mice with a cardiomyocyte specific deletion of Rac1 (Rac1Nkx2.5 ) during heart development. Embryonic Rac1Nkx2.5 hearts at E12.5–E18.5 were collected for histological analysis. Overall, Rac1Nkx2.5 hearts displayed a bifid apex, along with hypertrabeculation and a thin compact myocardium. Rac1Nkx2.5 hearts also exhibited ventricular septal defects (VSDs) and double outlet right ventricle (DORV) or overriding aorta. Cardiomyocytes had a rounded morphology and were highly disorganized, and the myocardial expression of Scrib, a planar cell polarity protein, was reduced in Rac1Nkx2.5 hearts. In addition, cell proliferation rate was significantly decreased in the Rac1Nkx2.5 ventricular myocardium at E9.5. Conclusions: Rac1 deficiency in the myocardium impairs cardiomyocyte elongation and organization, and proliferative growth of the heart. A spectrum of CHDs arises in Rac1Nkx2.5 hearts, implicating Rac1 signaling in the ventricular myocardium as a crucial regulator of OFT alignment, along with compact myocardium growth and development

Maternal voluntary exercise mitigates oxidative stress and incidence of congenital heart defects in pre-gestational diabetes

Women with pre-gestational diabetes have a higher risk of producing children with congenital heart defects (CHDs), caused predominantly by hyperglycemia-induced oxidative stress. In this study, we evaluated if exercise during pregnancy could mitigate oxidative stress and reduce the incidence of CHDs in the offspring of diabetic mice. Female mice were treated with streptozotocin to induce pre-gestational diabetes, then mated with healthy males to produce offspring. They were also given access to running wheels 1 week before mating and allowed to exercise voluntarily until E18.5. Heart morphology, gene expression, and oxidative stress were assessed in foetal hearts. Maternal voluntary exercise results in a significantly lower incidence of CHDs from 59.5% to 25%. Additionally, diabetes-induced defects in coronary artery and capillary morphogenesis were also lower with exercise. Myocardial cell proliferation and epithelial-mesenchymal transition at E12.5 was significantly lower with pre-gestational diabetes which was mitigated with maternal exercise. Cardiac gene expression of Notch1, Snail1, Gata4 and Cyclin D1 was significantly higher in the embryos of diabetic mice that exercised compared to the non-exercised group. Furthermore, maternal exercise produced lower reactive oxygen species (ROS) and oxidative stress in the foetal heart. In conclusion, maternal exercise mitigates ROS and oxidative damage in the foetal heart, and results in a lower incidence of CHDs in the offspring of pre-gestational diabetes. Exercise may be an effective intervention to compliment clinical management and further minimize CHD risk in mothers with diabetes

Myocardium-Specific Deletion of Rac1 Causes Ventricular Noncompaction and Outflow Tract Defects

Background: Left ventricular noncompaction (LVNC) is a cardiomyopathy that can lead to arrhythmias, embolic events and heart failure. Despite our current knowledge of cardiac development, the mechanisms underlying noncompaction of the ventricular myocardium are still poorly understood. The small GTPase Rac1 acts as a crucial regulator of numerous developmental events. The present study aimed to investigate the cardiomyocyte specific role of Rac1 in embryonic heart development. Methods and Results: The Nkx2.5-Cre transgenic mice were crossed with Rac1f/f mice to generate mice with a cardiomyocyte specific deletion of Rac1 (Rac1Nkx2.5) during heart development. Embryonic Rac1Nkx2.5 hearts at E12.5–E18.5 were collected for histological analysis. Overall, Rac1Nkx2.5 hearts displayed a bifid apex, along with hypertrabeculation and a thin compact myocardium. Rac1Nkx2.5 hearts also exhibited ventricular septal defects (VSDs) and double outlet right ventricle (DORV) or overriding aorta. Cardiomyocytes had a rounded morphology and were highly disorganized, and the myocardial expression of Scrib, a planar cell polarity protein, was reduced in Rac1Nkx2.5 hearts. In addition, cell proliferation rate was significantly decreased in the Rac1Nkx2.5 ventricular myocardium at E9.5. Conclusions: Rac1 deficiency in the myocardium impairs cardiomyocyte elongation and organization, and proliferative growth of the heart. A spectrum of CHDs arises in Rac1Nkx2.5 hearts, implicating Rac1 signaling in the ventricular myocardium as a crucial regulator of OFT alignment, along with compact myocardium growth and development

Maternal voluntary exercise mitigates oxidative stress and incidence of congenital heart defects in pre‐gestational diabetes

Women with pre-gestational diabetes have a higher risk of producing children with congenital heart defects (CHDs), caused predominantly by hyperglycemia-induced oxidative stress. In this study, we evaluated if exercise during pregnancy could mitigate oxidative stress and reduce the incidence of CHDs in the offspring of diabetic mice. Female mice were treated with streptozotocin to induce pre-gestational diabetes, then mated with healthy males to produce offspring. They were also given access to running wheels 1 week before mating and allowed to exercise voluntarily until E18.5. Heart morphology, gene expression, and oxidative stress were assessed in foetal hearts. Maternal voluntary exercise results in a significantly lower incidence of CHDs from 59.5% to 25%. Additionally, diabetes-induced defects in coronary artery and capillary morphogenesis were also lower with exercise. Myocardial cell proliferation and epithelial-mesenchymal transition at E12.5 was significantly lower with pre-gestational diabetes which was mitigated with maternal exercise. Cardiac gene expression of Notch1, Snail1, Gata4 and Cyclin D1 was significantly higher in the embryos of diabetic mice that exercised compared to the non-exercised group. Furthermore, maternal exercise produced lower reactive oxygen species (ROS) and oxidative stress in the foetal heart. In conclusion, maternal exercise mitigates ROS and oxidative damage in the foetal heart, and results in a lower incidence of CHDs in the offspring of pre-gestational diabetes. Exercise may be an effective intervention to compliment clinical management and further minimize CHD risk in mothers with diabetes

Sapropterin reduces coronary artery malformation in offspring of pregestational diabetes mice

Endothelial nitric oxide synthase (eNOS) and oxidative stress are critical to embryonic coronary artery development. Maternal diabetes increases oxidative stress and reduces eNOS activity in the fetal heart. Sapropterin (Kuvan®) is an orally active, synthetic form of tetrahydrobiopterin (BH4) and a co-factor for eNOS with antioxidant properties. The aim of the present study was to examine the effects of sapropterin on fetal coronary artery development during pregestational diabetes in mice. Diabetes was induced by streptozotocin to adult female C57BL/6 mice. Sapropterin (10 mg/kg/day) was orally administered to pregnant mice from E0.5 to E18.5. Fetal hearts were collected at E18.5 for coronary artery morphological analysis. Sapropterin treatment to diabetic dams reduced the incidence of coronary artery malformation in offspring from 50.0% to 20.6%. Decreases in coronary artery luminal diameter, volume and abundance in fetal hearts from diabetic mothers, were prevented by sapropterin treatment. Maternal diabetes reduced epicardial epithelial-to-mesenchymal transition (EMT) and expression of transcription and growth factors critical to coronary artery development including hypoxia-inducible factor 1a (Hif1a), Snail1, Slug, β-catenin, retinaldehyde dehydrogenase 2 (Aldh1a2), basic fibroblast growth factor (bFGF) and vascular endothelial group factor receptor 2 (Vegfr2) in E12.5 hearts. Additionally, eNOS phosphorylation was lower while oxidative stress was higher in E12.5 hearts from maternal diabetes. Notably, these abnormalities were all restored to normal levels after sapropterin treatment. In conclusion, sapropterin treatment increases eNOS activity, lowers oxidative stress and reduces coronary artery malformation in offspring of pregestational diabetes. Sapropterin may have therapeutic potential in preventing coronary artery malformation in maternal diabetes