Mechanisms of Diabetic Embryopathy and Molecular Pathways

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DESCRIPTION (provided by applicant): Diabetes mellitus in pregnancy is one of the maternal diseases that cause congenital defects in infants. Although control of glycemic level during pregnancy has been associated with reduced rate of malformed infants, nevertheless, achieving and maintaining satisfactory glycemic control is very difficult. Hence, prevention or reduction of maternal diabetes-associated fetal anomalies remains a major clinical challenge. This is in part because the period of vulnerability occurs during organogenesis, which is early in pregnancy and often before the mother is aware that she is pregnant. Thus, insufficient glycemic control or even transient loss of glycemic control during this developmental period may result in embryonic abnormalities and birth defects. To improve public health and prevent these birth defects, we need innovative and effective therapeutic approaches. To develop these therapies, it is critical to understand the mechanisms of embryonic malformations induced by hyperglycemia. Our published work and on-going studies lead us to hypothesize that hyperglycemia initiates a signaling cascade whereby increased activity of protein kinase C (PKC), activates cytosolic phospholipase A2 (cPLA2) and arachidonic acid release, resulting in increased membrane lipid peroxidation and reactive oxygen species (ROS) production. The resultant oxidative stress stimulates aberrant mitogen-activated protein kinase (MAPK) signaling pathways, such as extracellular signal-regulated kinases (ERKs) and jun N-terminal kinases (JNKs), leading to excessive apoptosis and embryonic dysmorphogenesis. To test these hypotheses, we will, in Specific Aim 1, investigate the mechanism of action of PKC as a mediator of hyperglycemia-dependent embryonic malformation. We will use PKC gene knockout mice to determine the role of PKC1, 22, and 4 in diabetic embryopathy. We will address the mechanisms whereby each PKC isoform regulates cPLA2 activation, phospholipid peroxidation, and ROS production. In Specific Aim 2, we will investigate the mechanisms of PKC and JNK activation by ROS. We will determine whether PKC and JNK are activated by oxidative stress, using a transgenic mouse model that carries the human SOD1 gene (converts oxygen free radicals into less reactive molecules). We will further investigate whether JNK upstream kinases, apoptosis signal-regulating kinase 1 (ASK1) and MAPK kinase 4 (MKK4), play a role in mediating the effect of oxidative stress on JNK activation. In Specific Aim 3, we will investigate the mechanisms by which JNK induces apoptosis in diabetic embryopathy. We will use a mouse model that lacks the jnk2 gene to determine the role of JNK in diabetic embryopathy. We will further delineate the JNK- regulated molecular pathway involving key apoptotic regulators, including p66Shc, a critical mediator of oxidative stress signaling, and members of the Bcl-2 family, which play essential roles in apoptosis. By carefully analyzing the signaling mechanisms altered by maternal hyperglycemia in the developing embryo, our proposed studies will have an enormous impact on understanding the molecular mechanisms of diabetic embryopathy, and provide important information for developing novel biochemical targets for potential therapeutic interventions. PUBLIC HEALTH RELEVANCE: Pregnant women with diabetes during the early gestation period have a high risk of having babies with birth defects. The aims of this study are to understand how hyperglycemia changes the molecular and biochemical events in the developing embryo, causing abnormalities in newborn infants. The results of the study will provide information that will serve as a basis for future development of therapeutic interventions to prevent maternal diabetes-associated birth defects.