Laetitia Vanhoutte

Prospective cardiac MRI for the analysis of biventricular function in children undergoing cancer treatments

Cardiotoxicity is one of the most serious long‐term complications in childhood cancer survivors. Measurement of the left ventricular ejection and shortening fraction remains the most common screening tool for cardiac systolic dysfunction. However, M‐mode echocardiography can be viewed as a crude approach as refined strategies are now available. The aim of this prospective study was to determine the role of cardiac MRI in the detection of subclinical left or right ventricular dysfunction as well as the prevalence of myocardial scaring in patients undergoing cancer treatments.

MRI Assessment of Cardiomyopathy Induced by β1-Adrenoreceptor Autoantibodies and Protection Through β3-Adrenoreceptor Overexpression.

The cardiopathogenic role of autoantibodies (aabs) directed against β1-adrenoreceptors (β1-AR) is well established. In mouse models, they cause progressive dilated cardiomyopathy (DCM) whose characterization with echocardiography requires prolonged protocols with numerous animals, complicating the evaluation of new treatments. Here, we report on the characterization of β1-aabs-induced DCM in mice using 11.7T MRI. C57BL/6J mice (n = 10 per group) were immunized against the β1-AR and left ventricular (LV) systolic function was assessed at 10, 18 and 27 weeks. Increase in LV mass/tibial length ratio was detected as the first modification at 10 weeks together with dilation of cavities, thereby outperforming echocardiography. Significant impairment in diastolic index was also observed in immunized animals before the onset of systolic dysfunction. Morphometric and histological measurements confirmed these observations. The same protocol performed on β3-AR-overexpressing mice and wild-type littermates (n = 8–12 per group) showed that transgenic animals were protected with reduced LV/TL ratio compared to wild-type animals and maintenance of the diastolic index. This study demonstrates that MRI allows a precocious detection of the subtle myocardial dysfunction induced by β1-aabs and that β3-AR stimulation blunts the development of β1-aabs-induced DCM, thereby paving the way for the use of β3AR-stimulating drugs to treat this autoimmune cardiomyopathy.

Dnmt3a-mediated inhibition of Wnt in cardiac progenitor cells improves differentiation and remote remodeling after infarction

Adult cardiac progenitor cells (CPCs) display a low capacity to differentiate into cardiomyocytes in injured hearts, strongly limiting the regenerative capacity of the mammalian myocardium. To identify new mechanisms regulating CPC differentiation, we used primary and clonally expanded Sca-1+ CPCs from murine adult hearts in homotypic culture or coculture with cardiomyocytes. Expression kinetics analysis during homotypic culture differentiation showed downregulation of Wnt target genes concomitant with increased expression of the Wnt antagonist, Wnt inhibitory factor 1 (Wif1), which is necessary to stimulate CPC differentiation. We show that the expression of the Wif1 gene is repressed by DNA methylation and regulated by the de novo DNA methyltransferase Dnmt3a. In addition, miR-29a is upregulated early during CPC differentiation and downregulates Dnmt3a expression, thereby decreasing Wif1 gene methylation and increasing the efficiency of differentiation of Sca-1+ CPCs in vitro. Extending these findings in vivo, transient silencing of Dnmt3a in CPCs subsequently injected in the border zone of infarcted mouse hearts improved CPC differentiation in situ and remote cardiac remodeling. In conclusion, miR-29a and Dnmt3a epigenetically regulate CPC differentiation through Wnt inhibition. Remote effects on cardiac remodeling support paracrine signaling beyond the local injection site, with potential therapeutic interest for cardiac repair.

Intra-observer, inter-experiment and inter-observer variability of left ventricular volumes and mass measurements in mice using an 11.7 Tesla MRI

Background In cardiovascular research, there is an increasing interest in high-field MRI to characterize cardiac anatomy and function in small rodents. However, data on reproducibility of the method are scarce. Our aim was to evaluate the intra-observer, inter-experiment and inter-observer variability of left ventricular (LV) mass and volumes measurements in mice using an 11.7T MRI scanner. Methods Seven 10 weeks-old C57Bl6J male mice were studied, including 4 animals with a surgical transverse aortic constriction in order to produce cardiac hypertrophy. 3 were sham (control) mice. During the entire procedure, animals were anaesthetized with Isoflurane 1-3%, in a temperature-controlled setting. Scan were retrospectively gated for electrocardiogram (ECG) and respiration. Imaging was performed on a 11.7 Tesla Bruker MR scanner. Cardiac scout images were obtained in the conventional planes with a tripilot sequence. A 2D cine FLASH sequence was applied to acquire a set of 7 contiguous short axis images covering the entire ventricles, perpendicular to the LV long axis. One day after the procedure, mice were scanned again under the same conditions. The LV systolic function was assessed from each stack of images by tracing epicardial and endocardial borders, including papillary muscles, on the Segment software (Medviso, Sweden). End-diastolic (EDV), end-systolic (ESV) and stroke volume (SV) were determined (µl). LV ejection fraction (EF, in %) and LV mass (mg) were subsequently deduced. One stack of images was analyzed twice by the same person, and once by an independent observer. Results Accurate quantitative data were obtained in all animals. The Table 1 lists the mean ± SD values and the Bland-Altman and Pearson analysis results. The best reproducibility was obtained for the measurements of LV mass and EDV, with a coefficient of variability (Cov) between 1.70 and 12%. More variation was found in ESV measurement (CoV 1-70-22.40%). Results for SV and EF were the less reproducible, with a CoV between 14.52 and 31.45%. The Pearson correlation coefficient indicates good correlation between all methods for all parameters (r square between 0.81 and 0.99), except for the SV, particularly in terms of inter-experiment reproducibility (r square =0.03). Conclusions In our hands, reproducibility was excellent for LV mass and EDV, good for ESV and EF to al esser extent, and more limited for the stroke volume, with a bad inter-observer correlation. This highlights the need to interpret our results by taking into account these limitations, focusing on more reproducible parameters when interpreting data.