Silvia Rain

Dysregulated Renin–Angiotensin–Aldosterone System Contributes to Pulmonary Arterial Hypertension

RATIONALE Patients with idiopathic pulmonary arterial hypertension (iPAH) often have a low cardiac output. To compensate, neurohormonal systems such as the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system are up-regulated, but this may have long-term negative effects on the progression of iPAH. OBJECTIVES Assess systemic and pulmonary RAAS activity in patients with iPAH and determine the efficacy of chronic RAAS inhibition in experimental PAH. METHODS We collected 79 blood samples from 58 patients with iPAH in the VU University Medical Center Amsterdam (between 2004 and 2010) to determine systemic RAAS activity. MEASUREMENTS AND MAIN RESULTS We observed increased levels of renin, angiotensin (Ang)I, and AngII, which were associated with disease progression (P < 0.05) and mortality (P < 0.05). To determine pulmonary RAAS activity, lung specimens were obtained from patients with iPAH (during lung transplantation, n = 13) and control subjects (during lobectomy or pneumonectomy for cancer, n = 14). Local RAAS activity in pulmonary arteries of patients with iPAH was increased, demonstrated by elevated angiotensin-converting enzyme activity in pulmonary endothelial cells and increased AngII type 1 (AT(1)) receptor expression and signaling. In addition, local RAAS up-regulation was associated with increased pulmonary artery smooth muscle cell proliferation via enhanced AT(1) receptor signaling in patients with iPAH compared with control subjects. Finally, to determine the therapeutic potential of RAAS activity, we assessed the chronic effects of an AT(1) receptor antagonist (losartan) in the monocrotaline PAH rat model (60 mg/kg). Losartan delayed disease progression, decreased right ventricular afterload and pulmonary vascular remodeling, and restored right ventricular-arterial coupling in rats with PAH. CONCLUSIONS Systemic and pulmonary RAAS activities are increased in patients with iPAH and are associated with increased pulmonary vascular remodeling. Chronic inhibition of RAAS by losartan is beneficial in experimental PAH.

Right Ventricular Diastolic Impairment in Patients With Pulmonary Arterial Hypertension

Background— The role of right ventricular (RV) diastolic stiffness in pulmonary arterial hypertension (PAH) is not well established. Therefore, we investigated the presence and possible underlying mechanisms of RV diastolic stiffness in PAH patients. Methods and Results— Single-beat RV pressure-volume analyses were performed in 21 PAH patients and 7 control subjects to study RV diastolic stiffness. Data are presented as mean±SEM. RV diastolic stiffness (&bgr;) was significantly increased in PAH patients (PAH, 0.050±0.005 versus control, 0.029±0.003; P<0.05) and was closely associated with disease severity. Subsequently, we searched for possible underlying mechanisms using RV tissue of PAH patients undergoing heart/lung transplantation and nonfailing donors. Histological analyses revealed increased cardiomyocyte cross-sectional areas (PAH, 453±31 &mgr;m2 versus control, 218±21 &mgr;m2; P<0.001), indicating RV hypertrophy. In addition, the amount of RV fibrosis was enhanced in PAH tissue (PAH, 9.6±0.7% versus control, 7.2±0.6%; P<0.01). To investigate the contribution of stiffening of the sarcomere (the contractile apparatus of RV cardiomyocytes) to RV diastolic stiffness, we isolated and membrane-permeabilized single RV cardiomyocytes. Passive tension at different sarcomere lengths was significantly higher in PAH patients compared with control subjects (>200%; Pinteraction<0.001), indicating stiffening of RV sarcomeres. An important regulator of sarcomeric stiffening is the sarcomeric protein titin. Therefore, we investigated titin isoform composition and phosphorylation. No alterations were observed in titin isoform composition (N2BA/N2B ratio: PAH, 0.78±0.07 versus control, 0.91±0.08), but titin phosphorylation in RV tissue of PAH patients was significantly reduced (PAH, 0.16±0.01 arbitrary units versus control, 0.20±0.01 arbitrary units; P<0.05). Conclusions— RV diastolic stiffness is significantly increased in PAH patients, with important contributions from increased collagen and intrinsic stiffening of the RV cardiomyocyte sarcomeres.

Protein changes contributing to right ventricular cardiomyocyte diastolic dysfunction in pulmonary arterial hypertension.

Background Right ventricular (RV) diastolic function is impaired in patients with pulmonary arterial hypertension (PAH). Our previous study showed that elevated cardiomyocyte stiffness and myofilament Ca2+ sensitivity underlie diastolic dysfunction in PAH. This study investigates protein modifications contributing to cellular diastolic dysfunction in PAH. Methods and Results RV samples from PAH patients undergoing heart‐lung transplantation were compared to non‐failing donors (Don). Titin stiffness contribution to RV diastolic dysfunction was determined by Western‐blot analyses using antibodies to protein‐kinase‐A (PKA), Cα (PKCα) and Ca2+/calmoduling‐dependent‐kinase (CamKIIδ) titin and phospholamban (PLN) phosphorylation sites: N2B (Ser469), PEVK (Ser170 and Ser26), and PLN (Thr17), respectively. PKA and PKCα sites were significantly less phosphorylated in PAH compared with donors (P<0.0001). To test the functional relevance of PKA‐, PKCα‐, and CamKIIδ‐mediated titin phosphorylation, we measured the stiffness of single RV cardiomyocytes before and after kinase incubation. PKA significantly decreased PAH RV cardiomyocyte diastolic stiffness, PKCα further increased stiffness while CamKIIδ had no major effect. CamKIIδ activation was determined indirectly by measuring PLN Thr17phosphorylation level. No significant changes were found between the groups. Myofilament Ca2+ sensitivity is mediated by sarcomeric troponin I (cTnI) phosphorylation. We observed increased unphosphorylated cTnI in PAH compared with donors (P<0.05) and reduced PKA‐mediated cTnI phosphorylation (Ser22/23) (P<0.001). Finally, alterations in Ca2+‐handling proteins contribute to RV diastolic dysfunction due to insufficient diastolic Ca2+ clearance. PAH SERCA2a levels and PLN phosphorylation were significantly reduced compared with donors (P<0.05). Conclusions Increased titin stiffness, reduced cTnI phosphorylation, and altered levels of phosphorylation of Ca2+ handling proteins contribute to RV diastolic dysfunction in PAH.

Clinical relevance of right ventricular diastolic stiffness in pulmonary hypertension

Right ventricular (RV) diastolic stiffness is increased in pulmonary arterial hypertension (PAH) patients. We investigated whether RV diastolic stiffness is associated with clinical progression and assessed the contribution of RV wall thickness to RV systolic and diastolic stiffness. Using single-beat pressure–volume analyses, we determined RV end-systolic elastance (Ees), arterial elastance (Ea), RV–arterial coupling (Ees/Ea), and RV end-diastolic elastance (stiffness, Eed) in controls (n=15), baseline PAH patients (n=63) and treated PAH patients (survival >5 years n=22 and survival <5 years n=23). We observed an association between Eed and clinical progression, with baseline Eed >0.53 mmHg·mL-1 associated with worse prognosis (age-corrected hazard ratio 0.27, p=0.02). In treated patients, Eed was higher in patients with survival <5 years than in patients with survival >5 years (0.91±0.50 versus 0.53±0.33 mmHg·mL-1, p<0.01). Wall-thickness-corrected Eed values in PAH patients with survival >5 years were not different from control values (0.76±0.47 versus 0.60±0.41 mmHg·mL-1, respectively, not significant), whereas in patients with survival <5 years, values were significantly higher (1.52±0.91 mmHg·mL-1, p<0.05 versus controls). RV diastolic stiffness is related to clinical progression in both baseline and treated PAH patients. RV diastolic stiffness is explained by the increased wall thickness in patients with >5 years survival, but not in those surviving <5 years. This suggests that intrinsic myocardial changes play a distinctive role in explaining RV diastolic stiffness at different stages of PAH. Right ventricular diastolic stiffness is related to clinical progression in both baseline and treated PAH patients http://ow.ly/K15me

Pressure-overload-induced right heart failure

Although pulmonary arterial hypertension originates in the lung and is caused by progressive remodeling of the small pulmonary arterioles, patients die from the consequences of pressure-overload-induced right heart failure. Prognosis is poor, and currently there are no selective treatments targeting the failing right ventricle. Therefore, it is of utmost importance to obtain more insights into the mechanisms of right ventricular adaptation and the transition toward right heart failure. In this review, we propose that the same adaptive mechanisms, which initially preserve right ventricular systolic function and maintain cardiac output, eventually initiate the transition toward right heart failure.

The striated muscles in pulmonary arterial hypertension: adaptations beyond the right ventricle

Pulmonary arterial hypertension (PAH) is a fatal lung disease characterised by progressive remodelling of the small pulmonary vessels. The daily-life activities of patients with PAH are severely limited by exertional fatigue and dyspnoea. Typically, these symptoms have been explained by right heart failure. However, an increasing number of studies reveal that the impact of the PAH reaches further than the pulmonary circulation. Striated muscles other than the right ventricle are affected in PAH, such as the left ventricle, the diaphragm and peripheral skeletal muscles. Alterations in these striated muscles are associated with exercise intolerance and reduced quality of life. In this Back to Basics article on striated muscle function in PAH, we provide insight into the pathophysiological mechanisms causing muscle dysfunction in PAH and discuss potential new therapeutic strategies to restore muscle dysfunction. RV, LV, diaphragm and peripheral muscle dysfunction contributes to reduced quality of life in PAH patients http://ow.ly/NAyZP