Experimental Research on the Evaluation of Left Ventricular Function by Layered Speckle Tracking in a Constrictive Pericarditis Rat Model

Mechanical Interaction of the Pericardium and Cardiac Function in the Normal and Hypertensive Rat Heart

The pericardium is a thin connective tissue membrane that surrounds the heart and is an integral regulatory component of cardiopulmonary performance. Pathological growth and remodeling of the right ventricle (RV) stemming from structural heart diseases are thought to include a significant role of the pericardium, but its exact role remains unclear. The objective of this study was to investigate potential biomechanical adaptations of the pericardium in response to pulmonary hypertension and their effects on heart behavior. Integrated computational-experimental modeling of the heart offers a robust platform to achieve this objective. We built upon our recently developed high-fidelity finite-element models of healthy and hypertensive rodent hearts via addition of the pericardial sac. In-silico experiments were performed to investigate changes in pericardium reserve elasticity and their effects on cardiac function in hypertensive hearts. Our results suggest that contractile forces would need to increase in the RV and decrease in the left ventricle (LV) in the hypertensive heart to compensate for reductions in pericardium reserve elasticity. The discrepancies between chamber responses to pericardium addition result, in part, from differences in the impact of pericardium on the RV and LV preload. We further demonstrated the capability of our platform to predict the effect of pericardiectomy on heart function. Consistent with previous results, the effect of pericardiectomy on the chamber pressure-volume loop was the largest in the hypertensive RV. These insights are expected to motivate further computational investigations of the effect of pericardiectomy on cardiac function which remains an important factor in surgical planning of constrictive pericarditis and coronary artery bypass grafting.

MiR-146a mediates TLR-4 signaling pathway to affect myocardial fibrosis in rat constrictive pericarditis model

Background

Myocardial fibrosis (MF) is thought to be associated with constrictive pericarditis (CP). miR-146a has been reported to be related to the survival of myocardial fibroblasts and related signal transduction pathways. The aim of this study was to investigate the expression of miR-146a in CP with MF and the activation of the Toll-like receptor 4 (TLR-4) signaling pathway, to understand the molecular mechanism of MF involvement in CP.

Methods

Thirty rats with different disease duration were randomly divided into three groups: an 8-week model group (CP-8W group), a 16-week model group (CP-16W group) model, and a normal control group (N group). After the CP model was established in the rats, the myocardial tissues were collected. The expression of miR-146a, the key factors of TLR-4 signaling pathway, including IL-1 receptor-associated kinase 1 (IRAK1), tumor necrosis factor receptor-associated factor 6 (TRAF6), nuclear factor-κB (NF-κB) and p-NF-κB, and the MF indicator α-SMA in myocardial tissue were detected. After treatment with lipopolysaccharide (LPS), primary cultured rat cardiac fibroblasts (CFs) were transfected with miR-146a. RT-PCR and western blot were used to detect the expression of downstream effectors to further verify the function of miRNA-146a in regulating MF via the TLR-4 signaling pathway.

Results

miR-146a was increased in the CP-8W group but not in the CP-16W group. IRAK1 and TRAF6 in the CP-16W group were found to be higher than in the N group and CP-8W group. α-SMA in the model groups was higher than in the N group. Compared with the CP-8W group, α-SMA in the CP-16W model group was further increased. In the experiments using CFs, the expression of IRAK1, TRAF6, p-NF-κB and α-SMA increased in the LPS-treated group compared with the N group. After transfection of CFs with the miR-146a mimics, the expression of IRAK1, TRAF6, p-NF-κB and α-SMA decreased compared with the LPS-treated group. Following transfection of CFs with miR-146a inhibitors, the expression of IRAK1, TRAF6, p-NF-κB and α-SMA increased compared with the LPS-treated group.

Conclusions

The expression of miR-146a demonstrated a dynamic change in the CP model; it was increased at the early time point (CP-8W) and then decreased at the 16W time point. miR-146a suppressed MF by inhibiting the target genes TRAF6 and IRAK1 via the TLR-4 signaling pathway.