Pulling apart pulmonary hypertension

Lack of CCM1 induces hypersprouting and impairs response to flow

Cerebral cavernous malformation (CCM) is a disease of vascular malformations known to be caused by mutations in one of three genes: CCM1, CCM2 or CCM3. Despite several studies, the mechanism of CCM lesion onset remains unclear. Using a Ccm1 knockout mouse model, we studied the morphogenesis of early lesion formation in the retina in order to provide insight into potential mechanisms. We demonstrate that lesions develop in a stereotypic location and pattern, preceded by endothelial hypersprouting as confirmed in a zebrafish model of disease. The vascular defects seen with loss of Ccm1 suggest a defect in endothelial flow response. Taken together, these results suggest new mechanisms of early CCM disease pathogenesis and provide a framework for further study.

Tryptophan hydroxylase 1 knockout and tryptophan hydroxylase 2 polymorphism: effects on hypoxic pulmonary hypertension in mice

Serotonin [5-hydroxytryptamine (5-HT)] biosynthesis depends on two rate-limiting tryptophan hydroxylases (Tph): Tph1, which is expressed in peripheral organs, and Tph2, which is expressed in neurons. Because 5-HT is involved in pulmonary hypertension (PH), we investigated whether genetic variations in Tph1 and/or Tph2 affected PH development in mice. To examine the functional impact of peripheral Tph1 deficiency on hypoxic PH, we used Tph1(-/-) mice characterized by very low 5-HT synthesis rates and contents in the gut and lung and increased 5-HT synthesis in the forebrain. With chronic hypoxia, 5-HT synthesis in the forebrain increased further. Hypoxic PH, right ventricular hypertrophy, and distal pulmonary artery muscularization were less severe (P < 0.001) than in wild-type controls. The Tph inhibitor p-chlorophenylalanine (100 mgxkg(-1)xday(-1)) further improved these parameters. We then investigated whether mouse strains harboring the C1473G polymorphism of the Tph2 gene showed different PH phenotypes during hypoxia. Forebrain Tph activity was greater and hypoxic PH was more severe in C57Bl/6 and 129X1/SvJ mice homozygous for the 1473C allele than in DBA/2 and BALB/cJ mice homozygous for the 1473G allele. p-Chlorophenylalanine reduced PH in all groups and abolished the difference in PH severity across mouse strains. Hypoxia increased 5-hydroxytryptophan accumulation but decreased 5-HT contents in the forebrain and lung, suggesting accelerated 5-HT turnover during hypoxia. These results provide evidence that dysregulation of 5-HT synthesis is closely linked to the hypoxic PH phenotype in mice and that Tph1 and Tph2 may contribute to PH development.

A new recessive syndrome with VATER-like defects, pulmonary hypertension, abnormal ears, blue sclera, laryngeal webs, and persistent growth deficiency

VATER association is a term frequently used to describe children with multiple malformations. However, occasionally these children have malformations that are not typical of VATER defects and may represent unique multiple malformation syndromes with specific prognoses and recurrence risks. Two siblings with a heretofore previously undescribed multiple malformation syndrome are presented whose features include vertebral defects, cardiac abnormalities, pulmonary hypertension, laryngeal webs, blue sclerae, and persistent growth deficiency. Autosomal recessive inheritance is suggested. These cases suggest that other individuals labeled VATER association with multiple other defects should be reviewed more closely to give accurate prognosis and recurrence risk information to families.

Clinical and therapeutical follow-up of HIV-associated pulmonary hypertension: prospective study of 10 patients

OBJECTIVE

To determine the clinical course and prognosis of pulmonary hypertension (PH) in HIV-infected patients in comparison with a group of PH patients without HIV infection. The secondary objective was to ascertain whether more powerful antiretroviral treatments (highly active antiretroviral therapy) could modify the course of PH in HIV-infected patients.

DESIGN

Patients with PH and HIV (HIV-PH, group 1) and patients without HIV (PPH, group 2) were prospectively followed.

SETTING

A tertiary care institution.

PATIENTS

Group 1 included 10 patients, and group 2 included 25 patients.

INTERVENTIONS

In group 1, HIV infection was staged according to Centers for Disease Control and Prevention (CDC) classification when patients entered the study, and was re-staged every fourth month. In both groups, PH functional classes and right heart catheterization (RHC) were determined at baseline.

RESULTS

In group 1, one of 10 patients was assigned to New York Heart Association (NYHA) class II, seven patients to NYHA class III, and two patients to NYHA class IV. CDC stages ranged from A1 (three patients) to C3 (one patient). No patient showed progression of HIV disease during follow-up. By May 2001, six patients had died. The median survival by the time of RHC was 15.1 months. Causes of death were heart failure in three cases, sepsis in two, and suicide in one case. In seven patients, epoprostenol was started; three patients survived and four died. The cause of death was heart failure in one patient, suicide in one, non-catheter-related sepsis in one patient and catheter-related sepsis in the last patient. In group 2, 11 patients out of 25 were assigned to NYHA class II, 11 patients to NYHA class III, and three patients to NYHA class IV. RHC was not statistically different in the two groups. By May 2001, nine of 25 patients died and one underwent a double-lung transplant. The median survival from the time of RHC was 6.86 months. Cumulative survival rates by RHC were not statistically different (hazard ratio close to 1).

CONCLUSIONS

In HIV-infected patients, the onset of PH adversely affects the prognosis at any stage of infection. Clinically adverse progression of PH is not correlated with HIV initial stage and evolution. Moreover, prognosis in patients with sporadic or familial PPH and in patients with HIV-PH with similar RHC is so similar as to strengthen the concept that pulmonary vascular disease overshadows the overall clinical problem in HIV-infected patients.

Tempting fate: BMP signals for cardiac morphogenesis

Heart muscle cell specification (cardiac myogenesis) and creating the four-chambered heart (cardiac morphogenesis) are subject to regulation, in certain model organisms, by bone morphogenetic proteins and their receptors. Extrapolation to mammals from organisms that develop outside the mother (flies, fish, frogs, and avians) has been confounded by very early lethality-at gastrulation-of many null alleles needed to prove cause-effect relations in this pathway. Here, we describe the use of lineage- or compartment-restricted null alleles as well as hypomorphic alleles, which circumvent these limitations and pinpoint novel essential functions for the bone morphogenetic protein cascade in mammalian cardiac development.

Endocardial cushion and myocardial defects after cardiac myocyte-specific conditional deletion of the bone morphogenetic protein receptor ALK3

Receptors for bone morphogenetic proteins (BMPs), members of the transforming growth factor-beta (TGFbeta) superfamily, are persistently expressed during cardiac development, yet mice lacking type II or type IA BMP receptors die at gastrulation and cannot be used to assess potential later roles in creation of the heart. Here, we used a Cre/lox system for cardiac myocyte-specific deletion of the type IA BMP receptor, ALK3. ALK3 was specifically required at mid-gestation for normal development of the trabeculae, compact myocardium, interventricular septum, and endocardial cushion. Cardiac muscle lacking ALK3 was specifically deficient in expressing TGFbeta2, an established paracrine mediator of cushion morphogenesis. Hence, ALK3 is essential, beyond just the egg cylinder stage, for myocyte-dependent functions and signals in cardiac organogenesis.

Genetic aspects of pulmonary arterial hypertension

This paper concentrates on the genetic aspects of pulmonary arterial hypertension (PAH), a diagnostically based subclass of pulmonary hypertension that includes primary pulmonary hypertension (PPH). During the past year, patients with familial and sporadic PPH were found to have germline heterozygous missense, nonsense and frameshift mutations in bone morphogenetic protein receptor II (BMPR2). Mutations in BMPR2, a member of the transforming growth factor-beta (TGF-beta) receptor superfamily, are predicted to interrupt the bone morphogenetic protein (BMP) signalling pathway, resulting in proliferation, rather than apoptosis of cells within small arterioles. Mechanistically, haploinsufficiency was found by using in vitro gene expression experiments, but a dominant-negative mechanism has not been excluded. The failure to find BMPR2 mutations in all families with familial PPH and in all patients with sporadic PPH suggests that other genes remain to be identified. Mutations in ALK1, a TGF-beta type 1 receptor, previously known to cause type 2 hereditary haemorrhagic telangiectasia (HHT), have also been reported in a few HHT families with clinical and histological features of PPH. The clinical development of PPH, as in neoplasia, appears to require 'two hits' The two hits can be provided either by genetic or environmental factors.

Molecular determinants of left and right outflow tract obstruction

Congenital heart defects represent the most common group of human birth defects; they occur in 0.8-1% of live births and in 10% of spontaneously aborted fetuses. Heart defects seen in newborns typically represent specific morphogenetic defects of individual chambers or regions of the heart, with the remaining portions of the heart developing relatively normally. These developmental defects are commonly compatible with the intrauterine circulation, where the pulmonary circulation and systemic circulation work in concert, resulting in adequate embryonic growth and development. After delivery, however, significant cardiac symptoms develop. In many of these disorders, cyanosis is the earliest feature, while in others, cardiovascular collapse occurs before diagnosis. In this review, obstruction of the left and right sides of the heart are discussed. In these disorders, ventricular hypoplasia resulting in single ventricle physiologic characteristics is typical. The unaffected ventricle in these cases is usually morphologically and physiologically normal. These conditions include hypoplastic left heart syndrome and aortic coarctation on the left side, pulmonary stenosis, tetralogy of Fallot, and other complex right ventricle obstructive disorders. Many of these disorders occur in association with genetic syndromes identifiable by dysmorphic features. In some cases, the gene(s) has been identified or the genetic pathway has been defined. The purpose of this review is to discuss the molecular determinants of these obstructive disorders.