Semaphorin 3d signaling defects are associated with anomalous pulmonary venous connections

Semaphorins in cardiovascular medicine

During organogenesis, patterning is primarily achieved by the combined actions of morphogens. Among these, semaphorins represent a general system for establishing the appropriate wiring architecture of biological nets. Originally discovered as evolutionarily conserved steering molecules for developing axons, subsequent studies on semaphorins expanded their functions to the cardiovascular and immune systems. Semaphorins participate in cardiac organogenesis and control physiological vasculogenesis and angiogenesis, which result from a balance between pro- and anti-angiogenic signals. These signals are altered in several diseases. In this review, we discuss the role of semaphorins in vascular biology, emphasizing the mechanisms by which these molecules control vascular patterning and lymphangiogenesis, as well as in genetically inherited and degenerative vascular diseases.

Semaphorin 3d and semaphorin 3e direct endothelial motility through distinct molecular signaling pathways

Class 3 semaphorins were initially described as axonal growth cone guidance molecules that signal through plexin and neuropilin coreceptors and since then have been established to be regulators of vascular development. Semaphorin 3e (Sema3e) has been shown previously to repel endothelial cells and is the only class 3 semaphorin known to be capable of signaling via a plexin receptor without a neuropilin coreceptor. Sema3e signals through plexin D1 (Plxnd1) to regulate vascular patterning by modulating the cytoskeleton and focal adhesion structures. We showed recently that semaphorin 3d (Sema3d) mediates endothelial cell repulsion and pulmonary vein patterning during embryogenesis. Here we show that Sema3d and Sema3e affect human umbilical vein endothelial cells similarly but through distinct molecular signaling pathways. Time-lapse imaging studies show that both Sema3d and Sema3e can inhibit cell motility and migration, and tube formation assays indicate that both can impede tubulogenesis. Endothelial cells incubated with either Sema3d or Sema3e demonstrate a loss of actin stress fibers and focal adhesions. However, the addition of neuropilin 1 (Nrp1)-blocking antibody or siRNA knockdown of Nrp1 inhibits Sema3d-mediated, but not Sema3e-mediated, cytoskeletal reorganization, and siRNA knockdown of Nrp1 abrogates Sema3d-mediated, but not Sema3e-mediated, inhibition of tubulogenesis. On the other hand, endothelial cells deficient in Plxnd1 are resistant to endothelial repulsion mediated by Sema3e but not Sema3d. Unlike Sema3e, Sema3d incubation results in phosphorylation of Akt in human umbilical vein endothelial cells, and inhibition of the PI3K/Akt pathway blocks the endothelial guidance and cytoskeletal reorganization functions of Sema3d but not Sema3e.

Genetic basis of congenital cardiovascular malformations

Cardiovascular malformations are a singularly important class of birth defects and due to dramatic improvements in medical and surgical care, there are now large numbers of adult survivors. The etiologies are complex, but there is strong evidence that genetic factors play a crucial role. Over the last 15 years there has been enormous progress in the discovery of causative genes for syndromic heart malformations and in rare families with Mendelian forms. The rapid characterization of genomic disorders as major contributors to congenital heart defects is also notable. The genes identified encode many transcription factors, chromatin regulators, growth factors and signal transduction proteins- all unified by their required roles in normal cardiac development. Genome-wide sequencing of the coding regions promises to elucidate genetic causation in several disorders affecting cardiac development. Such comprehensive studies evaluating both common and rare variants would be essential in characterizing gene-gene interactions, as well as in understanding the gene-environment interactions that increase susceptibility to congenital heart defects.