Mechanical stimulation of induced pluripotent stem derived cardiac fibroblasts.

Cardiac fibrosis contributes to the development of heart failure, and is the response of cardiac fibroblasts (CFs) to pressure or volume overload. Limiting factors in CFs research are the poor availability of human cells and the tendency of CFs to transdifferentiate into myofibroblasts when cultured in vitro. The possibility to generate CFs from induced pluripotent stem cells (iPSC), providing a nearly unlimited cell source, opens new possibilities. However, the behaviour of iPSC-CFs under mechanical stimulation has not been studied yet. Our study aimed to assess the behaviour of iPSC-CFs under mechanical stretch and pro-fibrotic conditions. First, we confirm that iPSC-CFs are comparable to primary CFs at gene, protein and functional level. Furthermore, iPSC-derived CFs adopt a pro-fibrotic response to transforming growth factor beta (TGF-ß). In addition, mechanical stretch inhibits TGF-ß-induced fibroblast activation in iPSC-CFs. Thus, the responsiveness to cytokines and mechanical stimulation of iPSC-CFs demonstrates they possess key characteristics of primary CFs and may be useful for disease modelling.

Right Atrial Adaptation to Precapillary Pulmonary Hypertension: Pressure-Volume, Cardiomyocyte, and Histological Analysis.

BACKGROUND: Precapillary pulmonary hypertension (precPH) patients have altered right atrial (RA) function and right ventricular (RV) diastolic stiffness. OBJECTIVES: This study aimed to investigate RA function using pressure-volume (PV) loops, isolated cardiomyocyte, and histological analyses. METHODS: RA PV loops were constructed in control subjects (n = 9) and precPH patients (n = 27) using magnetic resonance and catheterization data. RA stiffness (pressure rise during atrial filling) and right atrioventricular coupling index (RA minimal volume / RV end-diastolic volume) were compared in a larger cohort of patients with moderate (n = 39) or severe (n = 41) RV diastolic stiffness. Cardiomyocytes were isolated from RA tissue collected from control subjects (n = 6) and precPH patients (n = 9) undergoing surgery. Autopsy material was collected from control subjects (n = 6) and precPH patients (n = 4) to study RA hypertrophy, capillarization, and fibrosis. RESULTS: RA PV loops showed 3 RA cardiac phases (reservoir, passive emptying, and contraction) with dilatation and elevated pressure in precPH. PrecPH patients with severe RV diastolic stiffness had increased RA stiffness and worse right atrioventricular coupling index. Cardiomyocyte cross-sectional area was increased 2- to 3-fold in precPH, but active tension generated by the sarcomeres was unaltered. There was no increase in passive tension of the cardiomyocytes, but end-stage precPH showed reduced number of capillaries per mm2 accompanied by interstitial and perivascular fibrosis. CONCLUSIONS: RA PV loops show increased RA stiffness and suggest atrioventricular uncoupling in patients with severe RV diastolic stiffness. Isolated RA cardiomyocytes of precPH patients are hypertrophied, without intrinsic sarcomeric changes. In end-stage precPH, reduced capillary density is accompanied by interstitial and perivascular fibrosis.

Interplay of sex hormones and long-term right ventricular adaptation in a Dutch PAH-cohort.

BACKGROUND: To investigate the association between altered sex hormone expression and long-term right ventricular (RV) adaptation and progression of right heart failure in a Dutch cohort of Pulmonary Arterial Hypertension (PAH)-patients across a wide range of ages. METHODS: In this study we included 279 PAH-patients, of which 169 females and 110 males. From 59 patients and 21 controls we collected plasma samples for sex hormone analysis. Right heart catheterization (RHC) and/or cardiac magnetic resonance (CMR) imaging was performed at baseline. For longitudinal data analysis, we selected patients that underwent a RHC and/or CMR maximally 1.5 years prior to an event (death or transplantation, N = 49). RESULTS: Dehydroepiandrosterone-sulfate (DHEA-S) levels were reduced in male and female PAH-patients compared to controls, whereas androstenedione and testosterone were only reduced in female patients. Interestingly, low DHEA-S and high testosterone levels were correlated to worse RV function in male patients only. Subsequently, we analyzed prognosis and RV adaptation in females stratified by age. Females ≤45years had best prognosis in comparison to females ≥55years and males. No differences in RV function at baseline were observed, despite higher pressure-overload in females ≤45years. Longitudinal data demonstrated a clear distinction in RV adaptation. Although females ≤45years had an event at a later time point, RV function was more impaired at end-stage disease. CONCLUSIONS: Sex hormones are differently associated with RV function in male and female PAH-patients. DHEA-S appeared to be lower in male and female PAH-patients. Females ≤45years could persevere pressure-overload for a longer time, but had a more severe RV phenotype at end-stage disease.

Development of a 3-Dimensional Model to Study Right Heart Dysfunction in Pulmonary Arterial Hypertension: First Observations.

Pulmonary arterial hypertension (PAH) patients eventually die of right heart failure (RHF). Currently, there is no suitable pre-clinical model to study PAH. Therefore, we aim to develop a right heart dysfunction (RHD) model using the 3-dimensional engineered heart tissue (EHT) approach and cardiomyocytes derived from patient-induced pluripotent stem cells (iPSCs) to unravel the mechanisms that determine the fate of a pressure-overloaded right ventricle. iPSCs from PAH and healthy control subjects were differentiated into cardiomyocytes (iPSC-CMs), incorporated into the EHT, and maintained for 28 days. In comparison with control iPSC-CMs, PAH-derived iPSC-CMs exhibited decreased beating frequency and increased contraction and relaxation times. iPSC-CM alignment within the EHT was observed. PAH-derived EHTs exhibited higher force, and contraction and relaxation times compared with control EHTs. Increased afterload was induced using 2× stiffer posts from day 0. Due to high variability, there were no functional differences between normal and stiffer EHTs, and no differences in the hypertrophic gene expression. In conclusion, under baseline spontaneous conditions, PAH-derived iPSC-CMs and EHTs show prolonged contraction compared with controls, as observed clinically in PAH patients. Further optimization of the hypertrophic model and profound characterization may provide a platform for disease modelling and drug screening.