Florent Soubrier

An insertion/deletion polymorphism in the angiotensin I-converting enzyme gene accounting for half the variance of serum enzyme levels.

A polymorphism consisting of the presence or absence of a 250-bp DNA fragment was detected within the angiotensin I-converting enzyme gene (ACE) using the endothelial ACE cDNA probe. This polymorphism was used as a marker genotype in a study involving 80 healthy subjects, whose serum ACE levels were concomitantly measured. Allele frequencies were 0.6 for the shorter allele and 0.4 for the longer allele. A marked difference in serum ACE levels was observed between subjects in each of the three ACE genotype classes. Serum immunoreactive ACE concentrations were, respectively, 299.3 +/- 49, 392.6 +/- 66.8, and 494.1 +/- 88.3 micrograms/liter, for homozygotes with the longer allele (n = 14), and heterozygotes (n = 37) and homozygotes (n = 29) with the shorter allele. The insertion/deletion polymorphism accounted for 47% of the total phenotypic variance of serum ACE, showing that the ACE gene locus is the major locus that determines serum ACE concentration. Concomitant determination of the ACE genotype will improve discrimination between normal and abnormal serum ACE values by allowing comparison with a more appropriate reference interval.

Molecular basis of human hypertension: Role of angiotensinogen

Essential hypertension is a common human disease believed to result from the interplay of multiple genetic and environmental determinants. In genetic studies of two large panels of hypertensive sibships from widely separated geographical areas, we obtained evidence of genetic linkage between the angiotensinogen gene (AGT) and hypertension, demonstrated association of AGT molecular variants with the disease, and found significant differences in plasma concentrations of angiotensinogen among hypertensive subjects with different AGT genotypes. The corroboration and replication afforded by these results support the interpretation that molecular variants of AGT constitute inherited predispositions to essential hypertension in humans.

Synergistic effects of angiotensin-converting enzyme and angiotensin-II type 1 receptor gene polymorphisms on risk of myocardial infarction

We reported from our previous multicentre case-control study that the deletion (D) polymorphism of the gene encoding angiotensin-converting enzyme (ACE) was associated with increased risk of myocardial infarction. The main function of ACE is to convert angiotensin I into angiotensin II, which exerts its known cellular actions through the angiotensin II AT1 receptor subtype (AGT1R). We have now investigated the role of a common polymorphism of the AT1 receptor gene (an A-->C transversion at position 1166 of AGT1R) and looked for an interaction between ACE and AGT1R gene polymorphisms on the risk of myocardial infarction. We analysed DNA from 613 patients with myocardial infarction and 723 age-matched population controls. We found a significant interaction between ACE and AGT1R gene polymorphisms; the odds ratio for myocardial infarction associated with the ACE DD genotype was 1.05 (95% CI 0.75-1.49) for subjects without the AGT1R C allele, 1.52 (1.06-2.18) in AC heterozygotes, and 3.95 (1.26-12.4) in CC homozygotes (test for trend, p < 0.02). Among patients defined as low risk by traditional risk factors (serum apolipoprotein B < 1.25 g/L, body-mass index < 26 kg/m2) the interaction was even stronger (odds ratios 1.64 [0.68-3.92], 7.03 [2.61-19.0], and 13.3 [p = 0.05], respectively). These findings, if confirmed, could have clinical implications for the prevention and treatment of coronary heart disease.

Genetics and genomics of pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is a rare disorder that may be hereditable (HPAH), idiopathic (IPAH), or associated with either drug-toxin exposures or other medical conditions. Familial cases have long been recognized and are usually due to mutations in the bone morphogenetic protein receptor type 2 gene (BMPR2), or, much less commonly, 2 other members of the transforming growth factor-beta superfamily, activin-like kinase-type 1 (ALK1) and endoglin (ENG), which are associated with hereditary hemorrhagic telangiectasia. In addition, approximately 20% of patients with IPAH carry mutations in BMPR2. We provide a summary of BMPR2 mutations associated with HPAH, most of which are unique to each family and are presumed to result in loss of function. We review the finding of missense variants and variants of unknown significance in BMPR2 in IPAH/HPAH, fenfluramine exposure, and PAH associated with congenital heart disease. Clinical testing for BMPR2 mutations is available and may be offered to HPAH and IPAH patients but should be preceded by genetic counseling, since lifetime penetrance is only 10% to 20%, and there are currently no known effective preventative measures. Identification of a familial mutation can be valuable in reproductive planning and identifying family members who are not mutation carriers and thus will not require lifelong surveillance. With advances in genomic technology and with international collaborative efforts, genome-wide association studies will be conducted to identify additional genes for HPAH, genetic modifiers for BMPR2 penetrance and genetic susceptibility to IPAH. In addition, collaborative studies of BMPR2 mutation carriers should enable identification of environmental modifiers, biomarkers for disease development and progression, and surrogate markers for efficacy end points in clinical drug development, thereby providing an invaluable resource for trials of PAH prevention.

THE DELETION/ INSERTION POLYMORPHISM OF THE ANGIOTENSIN CONVERTING ENZYME GENE AND CARDIOVASCULAR- RENAL RISK

Objective This meta-analysis attempted to derive pooled estimates for the associations between various cardiovascular-renal disorders and the deletion/insertion (D/I) polymorphism of the angiotensin converting enzyme (ACE) gene. Methods Case–control studies were combined, using the Mantel–Haenszel approach. Joint P values for continuous variables were calculated by Stouffers method. Continuous measurements reported in different units were expressed on a percentage scale using the within-study mean of the II genotype as the denominator. Results The computerized database used for this analysis included 145 reports with an overall sample size of 49 959 subjects. Overall, possession of the D allele was associated with an increased risk of atherosclerotic and renal microvascular complications. In comparison with the II reference group, the excess risk in DD homozygotes (P < 0.001) was 32% for coronary heart disease (CHD; 30 studies), 45% for myocardial infarction (20 studies), 94% for stroke (five studies) and 56% for diabetic nephropathy (11 studies). The corresponding risk in DI heterozygotes amounted to 11% (P = 0.02), 13% (P = 0.02), 22% (P = 0.10) and 40% (P < 0.001), respectively. Hypertension (23 studies), left ventricular hypertrophy (five studies), hypertrophic or dilated cardiomyopathy (eight studies) and diabetic retinopathy (two studies) were not related to the DI polymorphism. Publication bias was observed for CHD, myocardial infarction and microvascular nephropathy, but not hypertension. In studies with DNA amplification in the presence of insertion-specific primers, the risk associated with the DD genotype increased to 150% [95% confidence interval (CI) 76–256; four studies] for diabetic nephropathy, but decreased to 12% (95% CI −3 to 28; seven studies) for CHD and 14% (95% CI −6 to 37; four studies) for myocardial infarction. On the other hand, the pooled odds ratios did not materially change if the meta-analysis was limited to articles published in journals with an impact factor of at least 4. Furthermore, compared with the II control group, the circulating ACE levels (29 studies) were raised 58 and 31% (P < 0.001) in DD and DI subjects, respectively. In contrast, plasma renin (10 studies), systolic and diastolic blood pressure (46 studies) and body mass index (30 studies) were not associated with the D allele. Conclusion The D allele is not associated with hypertension, but behaves as a marker of atherosclerotic cardiovascular complications and diabetic nephropathy. These associations do not necessarily imply a causal relationship and may have been inflated by publication bias. Nevertheless, their possible therapeutic implications may be subject to further investigation in prospective (intervention) studies.

Influence of Angiotensin-Converting Enzyme and Angiotensin II Type 1 Receptor Gene Polymorphisms on Aortic Stiffness in Normotensive and Hypertensive Patients

BACKGROUND Clinical and experimental studies have demonstrated a major role of the renin-angiotensin system in the functional and structural changes of the large arteries in hypertension. Because genetic studies may help us to understand the mechanisms underlying the involvement of this system in arterial regulation, the present study was designed to assess the contribution of polymorphisms of the ACE insertion/deletion (I/D) and angiotensin II type 1 receptor (AGTR1 A 1166C) genes on aortic stiffness regulation. METHODS AND RESULTS This study included 311 untreated hypertensive and 128 normotensive subjects. Aortic stiffness was evaluated by measurement of the carotid-femoral pulse-wave velocity (PWV). In normotensive subjects, the two polymorphisms did not influence any of the studied parameters. In hypertensive subjects, there was a decreasing trend of mean PWV with the number of ACE D alleles, but this association became significant only after adjustment for blood pressure (P < .05). Conversely, the AGTR1 A 1166C polymorphism was independently associated with aortic stiffness. Mean values of PWV were 11.6 +/- 2.7 m/s in AGTR1 AA homozygotes, 13.3 +/- 3.3 m/s in AC heterozygotes, and 15.3 +/- 4.3 m/s in CC homozygotes (P < .0001 and P < .00001 after adjustment for age and mean blood pressure, respectively). The percentage of variance of PWV explained by AGTR1 A 1166C polymorphism (11.6%) was much larger than that of ACE I/D polymorphism (1.7%). CONCLUSIONS These results suggest that in hypertensive but not normotensive subjects, the AGTR1 and ACE genotypes are involved in the regulation of aortic rigidity. The presence of the AGTR1 C allele is a strong independent determinant of aortic stiffness, whereas presence of the ACE 1 allele is weakly associated with increased stiffness.

Peptidyl dipeptidase A: angiotensin I-converting enzyme.

Publisher Summary This chapter discusses the tissue distribution and the substrate specificity of peptidyl-dipeptidase A/angiotensin I-converting enzyme. Angiotensin I-Converting Enzyme (ACE) is a zinc metallopeptidase that belongs to the gluzincin family (clan MA) of metalloproteases of which thermolysin is the prototype. ACE cleaves the C-terminal dipeptide from angiotensin I to produce the potent vasopressor octapeptide angiotensin II and inactivates bradykinin by the sequential removal of two C-terminal dipeptides. In addition to these two main physiological substrates, which are involved in blood pressure regulation and water and salt metabolism, ACE cleaves C-terminal dipeptides from various oligopeptides with a free C-terminus. ACE is also able to cleave a C-terminal dipeptide-amide. The maximum expression of ACE occurs during the acrosome phase in murine species. ACE is exclusively produced in haploid germ cells and belongs to the group of proteins whose expression during definite maturation steps of spermiogenesis appears to be correlated with the unique process of germ cell differentiation. The inactivation of the ACE gene by homologous recombination leads to homozygous male mice with markedly reduced blood pressure, severe renal abnormalities and severely reduced fertility.

Pulmonary veno-occlusive disease

Pulmonary veno-occlusive disease (PVOD) is a rare form of pulmonary hypertension (PH) characterised by preferential remodelling of the pulmonary venules. In the current PH classification, PVOD and pulmonary capillary haemangiomatosis (PCH) are considered to be a common entity and represent varied expressions of the same disease. The recent discovery of biallelic mutations in the EIF2AK4 gene as the cause of heritable PVOD/PCH represents a major milestone in our understanding of the molecular pathogenesis of PVOD. Although PVOD and pulmonary arterial hypertension (PAH) share a similar clinical presentation, with features of severe precapillary PH, it is important to differentiate these two conditions as PVOD carries a worse prognosis and life-threatening pulmonary oedema may occur following the initiation of PAH therapy. An accurate diagnosis of PVOD based on noninvasive investigations is possible utilising oxygen parameters, low diffusing capacity for carbon monoxide and characteristic signs on high-resolution computed tomography of the chest. No evidence-based medical therapy exists for PVOD at present and lung transplantation remains the preferred definitive therapy for eligible patients. Recent advances such as discovery of the genetic basis of PVOD will pave way for future translational research http://ow.ly/YldhC

Clinical outcomes of pulmonary arterial hypertension in carriers of BMPR2 mutation.

RATIONALE Germline mutations in the gene encoding for bone morphogenetic protein receptor 2 (BMPR2) are a cause of pulmonary arterial hypertension (PAH). OBJECTIVES We conducted a study to determine the influence, if any, of a BMPR2 mutation on clinical outcome. METHODS The French Network of Pulmonary Hypertension obtained data for 223 consecutive patients displaying idiopathic or familial PAH in whom point mutation and large size rearrangements of BMPR2 were screened for. Clinical, functional, and hemodynamic characteristics, as well as outcomes, were compared in BMPR2 mutation carriers and noncarriers. MEASUREMENTS AND MAIN RESULTS Sixty-eight BMPR2 mutation carriers (28 familial and 40 idiopathic PAH) were compared with 155 noncarriers (all displaying idiopathic PAH). As compared with noncarriers, BMPR2 mutation carriers were younger at diagnosis of PAH (36.5 +/- 14.5 vs. 46.0 +/- 16.1 yr, P < 0.0001), had higher mean pulmonary artery pressure (64 +/- 13 vs. 56 +/- 13 mm Hg, P < 0.0001), lower cardiac index (2.13 +/- 0.68 vs. 2.50 +/- 0.73 L/min/m(2), P = 0.0005), higher pulmonary vascular resistance (17.4 +/- 6.1 vs. 12.7 +/- 6.6 mm Hg/L/min/m(2), P < 0.0001), lower mixed venous oxygen saturation (59 +/- 9% vs. 63 +/- 9%, P = 0.02), shorter time to death or lung transplantation (P = 0.044), and younger age at death (P = 0.002), but similar overall survival (P = 0.51). CONCLUSIONS BMPR2 mutation carriers with PAH present approximately 10 years earlier than noncarriers, with a more severe hemodynamic compromise at diagnosis.

Sustained Increase in Aortic Endothelial Nitric Oxide Synthase Expression In Vivo in a Model of Chronic High Blood Flow

Physiological adaptation of normal blood vessels to acute or chronic changes in blood flow is endothelium dependent. In vitro studies have shown that, among other genes, NO synthase (NOS) 3 mRNA and protein expression is enhanced by acute elevation of shear stress in endothelial cells. We have investigated the effect of chronic high blood flow on NOS3 mRNA and protein expression in rat aorta. NOS3 mRNA levels were measured by quantitative polymerase chain reaction (PCR) in the aortas of 12 rats with arteriovenous fistulas and 9 sham-operated control rats. The PCR assay indicated that NOS3 mRNA levels were significantly enhanced (twofold) during high blood flow. Western blots showed that immunoreactive NOS3 levels were also increased to a similar extent. Furthermore, the Ca(2+)-dependent NOS activity, measured by the L-arginine to L-citrulline conversion assay, and the cGMP content were also significantly increased in the proximal aortic wall submitted to the arteriovenous shunt. These results indicate that NOS3 mRNA and protein expression is enhanced in vivo during chronic high blood flow.