Vascular calcification is a major risk factor for cardiovascular morbidity and mortality. Smooth muscle cells (SMCs) may play an important role in vascular cartilaginous metaplasia and calcification via reprogramming to the osteochondrogenic state. To study whether SM lineage reprogramming and thus matrix calcification is reversible and what the necessary regulatory factors are to reverse this process, we used cells isolated from calcifying arterial medias of 4-week-old matrix Gla protein knockout mice (MGP−/− SMCs). We found that vascular cells with an osteochondrogenic phenotype regained SMC properties (positive for SM22α and SM α-actin) and down-regulated osteochondrogenic gene expression (Runx2/Cbfa1 and osteopontin) upon culture in medium that favors SMC differentiation. Over time, the MGP−/− SMCs no longer expressed osteochondrogenic proteins and became indistinguishable from wild-type SMCs. Moreover, phenotypic switch of the restored SMCs to the osteochondrogenic state was re-induced by the pro-calcific factor, inorganic phosphate. Finally, loss- and gain-of-function studies of myocardin, a SM-specific transcription co-activator, and Runx2/Cbfa1, an osteochondrogenic transcription factor, revealed that upregulation of Runx2/Cbfa1, but not loss of myocardin, played a critical role in phosphate-induced SMC lineage reprogramming and calcification. These results are the first to demonstrate reversibility of vascular SMCs to an osteochondrogenic state in response to local environmental cues, and that myocardin-enforced SMC lineage allocation was not sufficient to block vascular calcification. On the other hand, Runx2/Cbfa1 was found to be a decisive factor identified in the process.

The transition from healthy myocardium to hypertensive heart disease is characterized by a series of poorly understood changes in myocardial tissue microstructure. Incremental alterations in the orientation and integrity of myocardial fibers can be assessed using advanced ultrasonic image analysis. We used a modified algorithm to investigate left ventricular myocardial microstructure based on analysis of the reflection intensity at the myocardial-pericardial interface on B-mode echocardiographic images. We evaluated the extent to which the novel algorithm can differentiate between normal myocardium and hypertensive heart disease in humans as well as in a mouse model of afterload resistance. The algorithm significantly differentiated between individuals with uncomplicated essential hypertension (N = 30) and healthy controls (N = 28), even after adjusting for age and sex (P = 0.025). There was a trend in higher relative wall thickness in hypertensive individuals compared to controls (P = 0.08), but no difference between groups in left ventricular mass (P = 0.98) or total wall thickness (P = 0.37). In mice, algorithm measurements (P = 0.026) compared with left ventricular mass (P = 0.053) more clearly differentiated between animal groups that underwent fixed aortic banding, temporary aortic banding, or sham procedure, on echocardiography at 7 weeks after surgery. Based on sonographic signal intensity analysis, a novel imaging algorithm provides an accessible, non-invasive measure that appears to differentiate normal left ventricular microstructure from myocardium exposed to chronic afterload stress. The algorithm may represent a particularly sensitive measure of the myocardial changes that occur early in the course of disease progression.

Background Noninvasive assessment of altered myocardial tissue in patients with genetic mutations associated with hypertrophic cardiomyopathy (HCM) remains a challenge. In this pilot study, we evaluated whether a novel echocardiography-based assessment of myocardial microstructure, the signal intensity coefficient (SIC), could detect tissue-level alterations in HCM sarcomere mutation carriers with and without left ventricular hypertrophy (LVH). Methods and Results We studied 3 groups of genotyped individuals: sarcomere mutation carriers with LVH (clinical HCM; N=36), mutation carriers with normal LV wall thickness (subclinical HCM; N=28), and healthy controls (N=10). We compared measurements of echocardiographic SIC with validated assessments of cardiac microstructural alteration, including CMR measures of interstitial fibrosis (extracellular volume fraction, ECV), as well as serum biomarkers (NTproBNP, hs-cTnI, and PICP). In age-, sex-, and familial relation-adjusted analyses, the SIC was quantitatively different in subjects with overt HCM, subclinical HCM, and healthy controls (P<0.001). Compared to controls, the SIC was 61% higher in overt HCM and 47% higher in subclinical HCM (P<0.001 for both). The SIC was significantly correlated with ECV (r=0.72; P<0.01), with LV mass and E’ velocity (r=0.45, −0.60, respectively; P<0.01 for both), as well as with serum NT-proBNP levels (r=0.36; P<0.001). Conclusions Our findings suggest that the SIC could serve as a non-invasive quantitative tool for assessing altered myocardial tissue characteristics in patients with genetic mutations associated with HCM. Further studies are needed to determine whether the SIC could be used to identify subclinical changes in patients at risk for HCM and evaluating the effects of interventions.