FOLIC ACID AND HOMOCYSTEINE: MECHANISMS OF HEART DEFECTS

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The central theme and overall objective of this program is to determine the biological mechanisms whereby folic acid insufficiency and hyperhomocysteinemia may contribute to abnormal development of the heart. This program project is designed to provide maximum focus upon this theme, and to optimize scientific and intellectual synergy among members of the research team. Discovery of the cellular mechanisms that provide this protection is the objective of the research program proposed here. Two hypotheses will be tested: Hyperhomocysteinemia that results from folic acid insufficiency may induce abnormal development of the conotruncal region of the heart, as well as other neural crest and neural tube derivatives, by inhibiting the function of N-methyl-D-aspartate receptors (NMDA). Folate insufficiency also may induce abnormal development by a direct effect upon the growth and differentiation of neural crest and neural tube cells directly, for example, by limiting the availability of methyl groups for gene methylation. A principle objective of this research program is to sort out the biological effects of low folate from those of hyperhomocysteinemia; and to determine how these two mechanisms may interact. It is inferred that they converge upon processes that are especially critical to the cardiac neural crest, other regions of the neural crest, and the neural tube. Project 1 will examine the teratogenic interaction of homocysteine with other NMDA antagonists, and will determine the degree to which embryos can be rescued by NMDA activation. Project 2 will investigate the impact of impaired folate binding and transport on the development of the heart, as well as other neural crest and neural tube derivatives, using transgenic mouse embryos models made for this purpose. Project 3 will concentrate upon the relative roles of hyperhomocysteinemia and the NMDA on the one hand, and folate insufficiency on the other, as they impact on neural crest cell migration and differentiation. Project 4 will test the elements of each of these hypotheses in a population-based study.