Pulmonary arterial hypertension associated with congenital heart disease and Eisenmenger syndrome: current practice in pediatrics.

Pulmonary arterial hypertension (PAH) is an uncommon but serious disease characterized by severe pulmonary vascular disease and significant morbidity and mortality. PAH associated with congenital heart disease (APAH-CHD) is one etiology of PAH that has innate characteristics delineating it from other forms of PAH. The patient with APAH-CHD presents with unique challenges consisting of not only pulmonary vascular disease but also the complexity of the cardiac lesion. Eisenmenger syndrome (ES) represents the severe end of the spectrum for disease in APAH-CHD. Over time, systemic-to-pulmonary shunting through cardiac defects increases pulmonary vascular resistance to levels significant enough to reverse shunting across the defect. Historically, ES patients have been reported to have better outcomes than IPAH despite similarities in pulmonary vascular disease. However, recent studies are challenging this notion. Nonetheless, APAH-CHD survival has improved with the advent of modern PAH targeted therapies. New therapeutic options have allowed us to reconsider the dogma of inoperability in APAH-CHD patients with unrepaired defects. Certainly advances have been made, however, investigators must continue to advance the field through controlled clinical trials in both adult and pediatric APAH-CHD patients.

Transforming growth factor-beta receptor-associated protein 1 is a Smad4 chaperone.

Members of the transforming growth factor-beta (TGF-beta) superfamily signal through unique cell membrane receptor serine-threonine kinases to activate downstream targets. TRAP1 is a previously described 96-kDa cytoplasmic protein shown to bind to TGF-beta receptors and suggested to play a role in TGF-beta signaling. We now fully characterize the binding properties of TRAP1, and show that it associates strongly with inactive heteromeric TGF-beta and activin receptor complexes and is released upon activation of signaling. Moreover, we demonstrate that TRAP1 plays a role in the Smad-mediated signal transduction pathway, interacting with the common mediator, Smad4, in a ligand-dependent fashion. While TRAP1 has only a small stimulatory effect on TGF-beta signaling in functional assays, deletion constructs of TRAP1 inhibit TGF-beta signaling and diminish the interaction of Smad4 with Smad2. These are the first data to identify a specific molecular chaperone for Smad4, suggesting a model in which TRAP1 brings Smad4 into the vicinity of the receptor complex and facilitates its transfer to the receptor-activated Smad proteins.

Sorting nexin 6, a novel SNX, interacts with the transforming growth factor-beta family of receptor serine-threonine kinases.

Sorting nexins (SNX) comprise a family of proteins with homology to several yeast proteins, including Vps5p and Mvp1p, that are required for the sorting of proteins to the yeast vacuole. Human SNX1, -2, and -4 have been proposed to play a role in receptor trafficking and have been shown to bind to several receptor tyrosine kinases, including receptors for epidermal growth factor, platelet-derived growth factor, and insulin as well as the long form of the leptin receptor, a glycoprotein 130-associated receptor. We now describe a novel member of this family, SNX6, which interacts with members of the transforming growth factor-beta family of receptor serine-threonine kinases. These receptors belong to two classes: type II receptors that bind ligand, and type I receptors that are subsequently recruited to transduce the signal. Of the type II receptors, SNX6 was found to interact strongly with ActRIIB and more moderately with wild type and kinase-defective mutants of TbetaRII. Of the type I receptors, SNX6 was found to interact only with inactivated TbetaRI. SNXs 1-4 also interacted with the transforming growth factor-beta receptor family, showing different receptor preferences. Conversely, SNX6 behaved similarly to the other SNX proteins in its interactions with receptor tyrosine kinases. Strong heteromeric interactions were also seen among SNX1, -2, -4, and -6, suggesting the formation in vivo of oligomeric complexes. These findings are the first evidence for the association of the SNX family of molecules with receptor serine-threonine kinases.