Characterization of the spontaneous degenerative mitral valve disease in FVB mice

Figures

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  Fig 1. Platelet count in C57BL/6J and FVB/NJ mice at 12, 16, 20 and 24 weeks. Platelet count at different times points: W12, W16 and W20, that is significantly increased in pooled FVB compared to C57BL/6J at W16 and W20 (p = 0.0028 and p = 0.0031 respectively). Major blood clotting occurred in FVB mice at W24. Taking into account that platelet count was therefore underestimated due to platelet consumption, results are not presented.

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  Fig 2. Characteristics of mitral valve remodeling in FVB mice. A: Length of the mitral valve leaflets did not differ between FVB mice compared to C57BL/6J mice at any time-point (at 12-, 16-, 20- and 24-weeks) (p>0.05) indicating the absence of mitral valve prolapse in FVB mice. B: Thickness of the mitral valve leaflets in FVB mice substrains increases comparatively to C57BL/6J mice at 12-weeks (p = 0.0131 and p = 0.0375 for respectively FVB/NJ and FVB/NRj vs C57BL/6J), 16-weeks (FVB/NRj vs C57BL/6J, p = 0.0374), 20-weeks (FVB/NJ vs C57BL/6J, p = 0.0052) and 24-weeks (p = 0.0002 and p = 0.0011 for respectively FVB/NJ and FVB/NRj vs C57BL/6J).

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  Fig 3. Spontaneous mitral valve lesions in C57BL/6J and FVB mice. Hematoxylin and eosin staining shows thickened leaflets, called "cushions", with important cellular density, in FVB/NJ (C) and FVB/NRj (D) mice, in comparison to thin leaflets in C57BL/6J mice (A). However, some C57BL/6J mice may have highly cellularized valvular lesions (B), but with a prevalence of only 30% and a lower thickness. In C57BL/6J (E and F), as well as in FVB mice (G and H), Alcian blue staining shows severe deposition of glycosaminoglycans (blue) in the spongiosa and disrupted, disorganized collagen (pink); all features that are characteristics of fibromyxoid lesions. Finally, clusters of rounded shape cells bordering the valvular surface and penetrating the interstitial matrix were observed in all mice with lesion, but more prominent in FVB mice (I and J) (scale bar = 100μm).

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  Fig 4. Correlations between mitral valve thickness and either 5-HIAA or platelets. Left: correlations between mitral valve thickness and pooled urinary 5-HIAA at 12-, 16-, 20- and 24- weeks (Spearman r = 0.2280, p = 0.0130). Right: correlation between thickness and pooled platelets count at 12-, 16- and 20- weeks (Spearman r = 0.2428, p = 0.0251).

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  Fig 5. Echocardiographic evaluation showing left cardiac cavities and systolic left ventricular function. In FVB/NJ mice compared to C57BL/6J echocardiography identified the enlargement of the left atrium (A). Echocardiographic pictures are showing C57BL/6J (upper and left panel) and FVN/NJ (upper and right panel) left atrium obtained in a 2D apical view. An important dilation of the left-atrium is observed in the FVB/NJ mouse. We also observed a left-ventricular hypertrophy (B). At that stage, no reduction of the systolic function was observed (C). In D, the increased thickness of the ventricular walls can be observed on the 2D (upper picture) and the M-mode obtained in a mid-ventricular short axis section of the left ventricle in a C57BL/6J (left) and a FVB/NJ (right). A disorganization of papillary muscles can also be observed in the FVB/NJ mouse case.

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  Fig 6. Diastolic function and anatomo-pathologic parameters of the mitral apparatus. A trouble of the cardiomyocytes primary relaxation as attested by the isovolumetric relaxation time increase (A) was observed in FVB/NJ animals. This increase is shown in the FVB/NJ case #1 (blue arrows) (B). In the two FVB/NJ mice a mitral insufficiency is detected with a pulsed-Doppler window placed at the tip of the leaflets meaning that the insufficiency is originating at the valve’s commissure (yellow arrows). Mitral valve annulus is not enlarged (C) but leaflets are thickened (D).

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  Fig 7. Mitral valve insufficiency in FVB/NJ mice and correlation between left-ventricular dilatation and mitral valve thickening. The absence of mitral valve prolapse is demonstrated by the lack of systolic valvular protusion towards the atrium in FVB/NJ (right) compared to C57BL/6J (left) (apical view). Note the mitral lesions observed at the tip of mitral leaflets (arrow) in the FVB/NJ case (A). Some FVB mice show massive mitral valve insufficiency as shown by the systolic backflow from the ventricle to the atrium observed with color Doppler (yellow arrow). The red part in the middle of the blue backflow corresponds to aliasing due to high flow velocities (apical view) (B). The remodeling of the mitral valve is associated with the dilatation of the left ventricle (C). A: anterior leaflet of the mitral valve, P: posterior leaflet of the mitral valve, LA: left atrium, S: interventricular septum, RV: right ventricle, LW: lateral wall of the left ventricle, AMVLT: Anterior Mitral Valve Leaflet Thickness, EDLVD: End-Diastolic Left-Ventricular Diameter.