Cardiac, mandibular and thymic phenotypical association indicates that cranial neural crest underlies bicuspid aortic valve formation in hamsters

<div><p>Bicuspid aortic valve (BAV) is the most prevalent human congenital cardiac malformation. It may appear isolated, associated with other cardiovascular malformations, or forming part of syndromes. Cranial neural crest (NC) defects are supposed to be the cause of the spectrum of disorders associated with syndromic BAV. Experimental studies with an inbred hamster model of isolated BAV showed that alterations in the migration or differentiation of the cardiac NC cells in the embryonic cardiac outflow tract are most probably responsible for the development of this congenital valvular defect. We hypothesize that isolated BAV is not the result of local, but of early alterations in the behavior of the NC cells, thus also affecting other cranial NC-derived structures. Therefore, we tested whether morphological variation of the aortic valve is linked to phenotypic variation of the mandible and the thymus in the hamster model of isolated BAV, compared to a control strain. Our results show significant differences in the size and shape of the mandible as well as in the cellular composition of the thymus between the two strains, and in mandible shape regarding the morphology of the aortic valve. Given that both the mandible and the thymus are cranial NC derivatives, and that the cardiac NC belongs to the cephalic domain, we propose that the causal defect leading to isolated BAV during embryonic development is not restricted to local alterations of the cardiac NC cells in the cardiac outflow tract, but it is of pleiotropic or polytopic nature. Our results suggest that isolated BAV may be the <i>forme fruste</i> of a polytopic syndrome involving the cranial NC in the hamster model and in a proportion of affected patients.</p></div

Hassall’s corpuscles.

<p>(A-C) Micrographs of the thymus stained with HE (A and C) or immunostained using KRT10 antibodies (B). B and C correspond to consecutive sections. The asterisks mark the Hassall’s corpuscles, the arrows point to epithelial reticular cells, and the arrowheads to lymphocytes. Scale bars: 17 μm (in A); 50 μm (in B and C). (D) Mean density of Hassall’s corpuscles in animals of the H (n = 15) and T (n = 11) strains. A significant (<i>p</i> = 0.020) 0.71-fold increase was found in the T strain.</p

Mahalanobis distances between the groups with distinct morphological variants of BAV and TAV in T strain.

<p>Mahalanobis distances between the groups with distinct morphological variants of BAV and TAV in T strain.</p

Mahalanobis distances between the groups with distinct morphological variants of TAV in T strain.

<p>Mahalanobis distances between the groups with distinct morphological variants of TAV in T strain.</p

Anatomy and size of the thymus.

<p>(A) Frontal view of the right thymic lobe of a specimen from the T strain. The arrows indicate the major and minor diameters used to estimate the volume. (B) Mean relative volume of the thymus of specimens of the H (n = 15) and the T (n = 11) strains. No statistically significant difference was found.</p

Two-factor ANOVA for centroid size conducted on the entire sample.

<p>Two-factor ANOVA for centroid size conducted on the entire sample.</p

Scatter plot of CV1 <i>vs</i>. CV2 scores according to strain and aortic valve phenotype.

<p>The CV1 axis especially differentiates between the two strains, whereas the CV2 axis differentiates between the specimens with TAV and BAV belonging to T strain.</p

Scatter plots of CV1 <i>vs</i>. CV2 scores according to the morphological variants of the aortic valve.

<p>(A) Morphological variants of TAV (0–2) in H strain; (B) morphological variants of TAV (0–2) and BAV (3–5) in T strain; (C) morphological variants of TAV (0–2) in T strain; (D) morphological variants of BAV (3–5) in T strain.</p

Mahalanobis distances between the groups with distinct morphological variants of BAV in T strain.

<p>Mahalanobis distances between the groups with distinct morphological variants of BAV in T strain.</p

Diagrams of mean mandible shape differences.

<p>(A) Mean mandible shape difference between H and T strains. Black: Mean shape of H strain. Grey: Mean shape of T strain. Scale factor: 1.0. (B) Mean mandible shape difference between BAV and TAV phenotypes. Black: Mean shape of BAV phenotype. Grey: Mean shape of TAV phenotype. Scale factor: 2.0.</p