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 (β) 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 μm ² versus control, 218±21 μm ² ; 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 200%; P _interaction <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.

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 (AT₁) receptor expression and signaling. In addition, local RAAS up-regulation was associated with increased pulmonary artery smooth muscle cell proliferation via enhanced AT₁ 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 AT₁ 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.

Rationale: Inflammation and endothelial dysfunction are considered two primary instigators of pulmonary arterial hypertension (PAH). CD74 is a receptor for the proinflammatory cytokine macrophage migration inhibitory factor (MIF). This ligand/receptor complex initiates survival pathways and cell proliferation, and it triggers the synthesis and secretion of major proinflammatory factors and cell adhesion molecules. Objectives: We hypothesized that the MIF/CD74 signaling pathway is overexpressed in idiopathic PAH (iPAH) and contributes to a proinflammatory endothelial cell (EC) phenotype. Methods: Primary early passage cultures of human ECs isolated from lung tissues obtained from patients with iPAH and controls were examined for their ability to secrete proinflammatory mediators and bind inflammatory cells with or without modulation of the functional activities of the MIF/CD74 complex. In addition, we tested the efficacies of curative treatments with either the MIF antagonist ISO-1 or anti-CD74 neutralizing antibodies on the aberrant proinflammatory EC phenotype in vitro and in vivo and on the progression of monocrotaline-induced pulmonary hypertension. Measurements and Main Results: In human lung tissues, intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin expressions are markedly up-regulated in the endothelium of distal iPAH pulmonary arteries. Circulating MIF levels are increased in the serum of patients with PAH compared with control subjects, and T-cell lymphocytes represent a source of this overabundance. In addition, CD74 is highly expressed in the endothelium of muscularized pulmonary arterioles and in cultured pulmonary ECs from iPAH, contributing to an exaggerated recruitment of peripheral blood mononuclear cells to pulmonary iPAH ECs. Finally, we found that curative treatments with the MIF antagonist ISO-1 or anti-CD74 neutralizing antibodies partially reversed development of pulmonary hypertension in rats and substantially reduced inflammatory cell infiltration. Conclusions: We report here that CD74 and MIF are markedly increased and activated in patients with iPAH, contributing to the abnormal proinflammatory phenotype of pulmonary ECs in iPAH.

Background— Exercise training in pulmonary arterial hypertension (PH) is a promising adjunct to medical treatment. However, it is still unclear whether training is beneficial for all PH patients. We hypothesized that right ventricular adaptation plays a pivotal role in the response to training. Methods and Results— Two different dosages of monocrotaline were used in rats to model stable PH with preserved cardiac output and progressive PH developing right heart failure. Two weeks after injection, PH was confirmed by echocardiography, and treadmill training was initiated. Rats were trained for 4 weeks unless manifest right heart failure developed earlier. At the end of the study protocol, all rats were functionally assessed by endurance testing, echocardiography, and invasive pressure measurements. Lungs and hearts were further analyzed in quantitative histomorphologic analyses. In stable PH, exercise training was well tolerated and markedly increased exercise endurance (from 25±3.9 to 62±3.9 minutes; P <0.001). Moreover, capillary density increased significantly (from 1.21±0.12 to 1.51±0.07 capillaries per cardiomyocyte; P <0.05). However, in progressive PH, exercise training worsened survival (hazard ratio, 2.7; 95% confidence interval, 1.1 to 14.2) and increased pulmonary vascular remodeling. In addition, training induced widespread leukocyte infiltration into the right ventricle (from 135±14 to 276±18 leukocytes per 1 mm ² ; P <0.001). Conclusions— In our rat model, exercise training was found to be beneficial in stable PH but detrimental in progressive PH. Future studies are necessary to address the clinical implications of our findings.

We determined the physiological effects of exercise training on exercise capacity and quadriceps muscle function in patients with idiopathic pulmonary arterial hypertension (iPAH).In total, 19 clinically stable iPAH patients (New York Heart Association II-III) underwent a supervised exercise training programme for the duration of 12 weeks. Maximal capacity, endurance capacity and quadriceps function were assessed at baseline and after 12 weeks. In 12 patients, serial quadriceps muscle biopsies were obtained.6-min walk distance and peak exercise capacity did not change after training. However, endurance capacity improved significantly after training, demonstrated by a shift of the anaerobic threshold to a higher workload (from 32±5 to 46±6 W; p = 0.003) together with an increase in exercise endurance time (p<0.001). Moreover, exercise training increased quadriceps strength by 13% (p = 0.005) and quadriceps endurance by 34% (p = 0.001).Training enhanced aerobic capacity of the quadriceps, by increasing capillarisation (1.36±0.10 to 1.78±0.13 capillaries per muscle fibre; p<0.001) and oxidative enzyme activity, especially of the type-I (slow) muscle fibres. No changes were found in cross-sectional area and fibre type distribution.Exercise training in iPAH improves exercise endurance and quadriceps muscle function, which is also reflected by structural changes of the quadriceps.