Control of endothelial cell function and arteriogenesis by MEG3:EZH2 epigenetic regulation of integrin expression

Epigenetic processes involving long non-coding RNAs regulate endothelial gene expression. However, the underlying regulatory mechanisms causing endothelial dysfunction remain to be elucidated. Enhancer of zeste homolog 2 (EZH2) is an important rheostat of histone H3K27 trimethylation (H3K27me3) that represses endothelial targets, but EZH2 RNA binding capacity and EZH2:RNA functional interactions have not been explored in post-ischemic angiogenesis. We used formaldehyde/UV-assisted crosslinking ligation and sequencing of hybrids and identified a new role for maternally expressed gene 3 (MEG3). MEG3 formed the predominant RNA:RNA hybrid structures in endothelial cells. Moreover, MEG3:EZH2 assists recruitment onto chromatin. By EZH2-chromatin immunoprecipitation, following MEG3 depletion, we demonstrated that MEG3 controls recruitment of EZH2/H3K27me3 onto integrin subunit alpha4 (ITGA4) promoter. Both MEG3 knockdown or EZH2 inhibition (A-395) promoted ITGA4 expression and improved endothelial cell migration and adhesion to fibronectin in vitro. The A-395 inhibitor re-directed MEG3-assisted chromatin remodeling, offering a direct therapeutic benefit by increasing endothelial function and resilience. This approach subsequently increased the expression of ITGA4 in arterioles following ischemic injury in mice, thus promoting arteriogenesis. Our findings show a context-specific role for MEG3 in guiding EZH2 to repress ITGA4. Novel therapeutic strategies could antagonize MEG3:EZH2 interaction for pre-clinical studies.

Trichoplein binds PCM1 and controls endothelial cell function by regulating autophagy

Autophagy is an essential cellular quality control process that has emerged as a critical one for vascular homeostasis. Here, we show that trichoplein (TCHP) links autophagy with endothelial cell (EC) function. TCHP localizes to centriolar satellites, where it binds and stabilizes PCM1. Loss of TCHP leads to delocalization and proteasome-dependent degradation of PCM1, further resulting in degradation of PCM1's binding partner GABARAP. Autophagic flux under basal conditions is impaired in THCP-depleted ECs, and SQSTM1/p62 (p62) accumulates. We further show that TCHP promotes autophagosome maturation and efficient clearance of p62 within lysosomes, without affecting their degradative capacity. Reduced TCHP and high p62 levels are detected in primary ECs from patients with coronary artery disease. This phenotype correlates with impaired EC function and can be ameliorated by NF-κB inhibition. Moreover, Tchp knock-out mice accumulate of p62 in the heart and cardiac vessels correlating with reduced cardiac vascularization. Taken together, our data reveal that TCHP regulates endothelial cell function via an autophagy-mediated mechanism.

MicroRNA-148b Targets the TGF-β Pathway to Regulate Angiogenesis and Endothelial-to-Mesenchymal Transition during Skin Wound Healing

Transforming growth factor beta (TGF-β) is crucial for regulation of the endothelial cell (EC) homeostasis. Perturbation of TGF-β signaling leads to pathological conditions in the vasculature, causing cardiovascular disease and fibrotic disorders. The TGF-β pathway is critical in endothelial-to-mesenchymal transition (EndMT), but a gap remains in our understanding of the regulation of TGF-β and related signaling in the endothelium. This study applied a gain- and loss-of function approach and an in vivo model of skin wound healing to demonstrate that miR-148b regulates TGF-β signaling and has a key role in EndMT, targeting TGFB2 and SMAD2. Overexpression of miR-148b increased EC migration, proliferation, and angiogenesis, whereas its inhibition promoted EndMT. Cytokine challenge decreased miR-148b levels in ECs while promoting EndMT through the regulation of SMAD2. Finally, in a mouse model of skin wound healing, delivery of miR-148b mimics promoted wound vascularization and accelerated closure. In contrast, inhibition of miR-148b enhanced EndMT in wounds, resulting in impaired wound closure that was reversed by SMAD2 silencing. Together, these results demonstrate for the first time that miR-148b is a key factor controlling EndMT and vascularization. This opens new avenues for therapeutic application of miR-148b in vascular and tissue repair.

The value of cardiac MRI versus echocardiography in the pre-operative assessment of patients with Duchenne muscular dystrophy

BACKGROUND/PURPOSE

Duchenne Mmuscular Ddystrophy (DMD) related cardiomyopathy is associated with significant perioperative mortality. Cardiac MRI (CMR) has not previously been systematically evaluated as pre-operative assessment tool for heart function in DMD. Our aim was to establish whether CMR versus echocardiography contributes to pre-operative DMD assessment.

METHODS

Case records were retrospectively reviewed of 35 consecutive DMD boys who underwent evaluation for surgical procedures between 2010 and 2013.

RESULTS

Echocardiography revealed a median left ventricular (LV) shortening fraction (SF) of 29/% (range: 7-44). 37% of boys (13/35) had abnormal SF <25%, 66% (23/35) showed hypokinesia and 26% (9/35) had LV dilatation. CMR revealed a median left ventricular ejection fraction (LVEF) of 52% (range: 27-67%). 57% of boys (20/35) had abnormal LVEF <55%, 71% (25/35) had hypokinesia, and 82% late gadolinium enhancement. Extensive versus minimal late gadolinium enhancement was associated with reduced left ventricular ejection fraction (48% vs 58%; p = 0.003) suggesting more severe cardiomyopathy. Although echocardiography shortening fraction correlated with CMR ejection fraction (rs = 0.67; p < 0.001), three-quarter of echocardiography studies had suboptimal scanning windows and in 26% measurements significantly over- or underestimated left-ventricular function compared to CMR.

CONCLUSION

Our findings clearly demonstrate the added value of CMR versus echocardiography in assessing DMD-cardiomyopathy. Particularly when echocardiographic scanning windows are suboptimal, CMR should be considered to allow accurate pre-operative cardiac assessment.