Comprehensive ultrasound imaging of right ventricular remodeling under surgically induced pressure overload in mice.

This study reports a new methodology for right heart imaging by ultrasound in mice under right ventricular (RV) pressure overload. Pulmonary artery constriction (PAC) or sham surgeries were performed on C57BL/6 male mice at 8 wk of age. Ultrasound imaging was conducted at 2, 4, and 8 wk postsurgery using both classical and advanced ultrasound imaging modalities including electrocardiogram (ECG)-based kilohertz visualization, anatomical M-mode, and strain imaging. Based on pulsed Doppler, the PAC group demonstrated dramatically enhanced pressure gradient in the main pulmonary artery (MPA) as compared with the sham group. By the application of advanced imaging modalities in novel short-axis views of the ventricles, the PAC group demonstrated increased thickness of RV free wall, enlarged RV chamber, and reduced RV fractional shortening compared with the sham group. The PAC group also showed prolonged RV contraction, asynchronous interplay between RV and left ventricle (LV), and passive leftward motion of the interventricular septum (IVS) at early diastole. Consequently, the PAC group exhibited prolongation of LV isovolumic relaxation time, without change in LV wall thickness or systolic function. Significant correlations were found between the maximal pressure gradient in MPA measured by Doppler and the RV systolic pressure by catheterization, as well as the morphological and functional parameters of RV by ultrasound.NEW & NOTEWORTHY The established protocol overcomes the challenges in right heart imaging in mice, thoroughly elucidating the changes of RV, the dynamics of IVS, and the impact on LV and provides new insights into the pathophysiological mechanism of RV remodeling.

Deficiency in DDR1 Induces Pulmonary Hypertension and Impaired Alveolar Development.

Pulmonary hypertension (PH) is a multifaceted condition characterized by elevated pulmonary arterial pressure, which can result in right ventricular dysfunction and failure. Disorders of lung development can present with secondary PH, which is a leading cause of mortality in infants with bronchopulmonary dysplasia (BPD). DDR1 (discoidin domain receptor 1) is a collagen-binding receptor that regulates tissue fibrosis and inflammation and controls cellular growth and migration. However, the roles of DDR1 in lung development or the pathogenesis of PH are unknown. Studying mice with a DDR1 deletion (Ddr1-/-), we have noted 35% mortality between 1 and 4 months of age, and we demonstrate that DDR1 deficiency results in reduced right ventricular contractility and muscularization of distal pulmonary arteries, consistent with PH. Pathology analysis revealed enlarged alveolar spaces in Ddr1-/- mice by Postnatal Day 7, consistent with impaired alveolar development. Gene expression analysis showed that Ddr1-/- mice have reduced concentrations of alveologenesis factors and epithelial-to-mesenchymal transition markers. Mechanistic studies in vitro confirmed that DDR1 mediated epithelial-to-mesenchymal transition, migration, and growth of alveolar epithelial cells. Taken together, these data suggest that DDR1 plays important roles mediating alveolarization during lung development. Our studies also describe a new model of spontaneous PH and bronchopulmonary dysplasia in mice.

Epigenetic modification of intestinal smooth muscle cell phenotype during proliferation.

Inflammation causes proliferation of intestinal smooth muscle cells (ISMC), contributing to a thickened intestinal wall and to stricture formation in Crohn's disease. Proliferation of ISMC in vitro and in vivo caused decreased expression of marker proteins, but the underlying cause is unclear. Since epigenetic change is important in other systems, we used immunocytochemistry, immunoblotting, and quantitative PCR to examine epigenetic modification in cell lines from rat colon at low passage or after extended growth to evaluate phenotype. Exposure to the histone deacetylase (HDAC) inhibitor trichostatin A or the DNA methyltransferase inhibitor 5-azacytidine reversed the characteristic loss of phenotypic markers among high-passage cell lines of ISMC. Expression of smooth muscle actin and smooth muscle protein 22, as well as functional expression of the neurotrophin glial cell line-derived neurotrophic factor, was markedly increased. Increased expression of muscarinic receptor 3 and myosin light chain kinase was correlated with an upregulated response to cholinergic stimulation. In human ISMC (hISMC) lines from the terminal ileum, phenotype was similarly affected by extended proliferation. However, in hISMC from resected Crohn's strictures, we observed a significantly reduced contractile phenotype compared with patient-matched intrinsic controls that was associated with increased patient-specific expression of DNA methyltransferase 1, HDAC2, and HDAC5. Therefore, protracted growth causes epigenetic alterations that account for an altered phenotype of ISMC. A similar process may promote stricture formation in Crohn's disease, where the potential for halting progression, or even reversal, of disease through control of phenotypic modulation may become a novel treatment option.