A potential mouse model for the erosive vitreoretinopathy of Wagner disease

Patients with the very rare eye pathology Wagner disease (OMIM #143200) present with an abnormal (empty) vitreous, retinal detachment and altered electroretinogram (ERG). The disease is progressive and can eventually lead to blindness. No therapy can be offered to date. The genetic basis is the presence of mutations in the VCAN gene, encoding the large extracellular matrix molecule versican, which is a component of the vitreous. All identified mutations map to the canonical splice sites flanking exon 8, resulting in low number of aberrant splice products and a severe increase in two (V2, V3) of the four naturally occurring splice variants. The pathomechanism of Wagner's disease is poorly understood and a mouse model may afford further insight. The hdf -/- mice, named for their initial phenotype of heart defects, carry a null allele for Vcan that leads to embryonic lethality when homozygous, but heterozygote animals are viable. Here we investigated a possible eye phenotype in the heterozygous animals. While the overall morphology of retina and ciliary body appears to be normal, older (17 months) mutant animals show a decrease in ERG signaling profiles affecting the a-, b- and c-waves. This aspect of altered ERG profile demonstrates similarities to the human disease manifestation and underlines the suitability of heterozygous hdf+/- mice as a model for Wagner disease

Fibulin-1 is required for morphogenesis of neural crest-derived structures

AbstractHere we report that mouse embryos homozygous for a gene trap insertion in the fibulin-1 (Fbln1) gene are deficient in Fbln1 and exhibit cardiac ventricular wall thinning and ventricular septal defects with double outlet right ventricle or overriding aorta. Fbln1 nulls also display anomalies of aortic arch arteries, hypoplasia of the thymus and thyroid, underdeveloped skull bones, malformations of cranial nerves and hemorrhagic blood vessels in the head and neck. The spectrum of malformations is consistent with Fbln1 influencing neural crest cell (NCC)-dependent development of these tissues. This is supported by evidence that Fbln1 expression is associated with streams of cranial NCCs migrating adjacent to rhombomeres 2–7 and that Fbln1-deficient embryos display patterning anomalies of NCCs forming cranial nerves IX and X, which derive from rhombomeres 6 and 7. Additionally, Fbln1-deficient embryos show increased apoptosis in areas populated by NCCs derived from rhombomeres 4, 6 and 7. Based on these findings, it is concluded that Fbln1 is required for the directed migration and survival of cranial NCCs contributing to the development of pharyngeal glands, craniofacial skeleton, cranial nerves, aortic arch arteries, cardiac outflow tract and cephalic blood vessels

Caveolin-1 Deletion Exacerbates Cardiac Interstitial Fibrosis by Promoting M2 Macrophage Activation in Mice after Myocardial Infarction

Adverse remodeling following myocardial infarction (MI) leading to heart failure is driven by an imbalanced resolution of inflammation. The macrophage cell is an important control of post-MI inflammation, as macrophage subtypes secrete mediators to either promote inflammation and extend injury (M1 phenotype) or suppress inflammation and promote scar formation (M2 phenotype). We have previously shown that the absence of caveolin-1 (Cav1), a membrane scaffolding protein, is associated with adverse cardiac remodeling in mice, but the mechanisms responsible remain to be elucidated. We explore here the role of Cav1 in the activation of macrophages using wild type C57BL6/J (WT) and Cav1tm1Mls/J (Cav1-/-) mice. By echocardiography, cardiac function was comparable between WT and Cav1-/- mice at 3days post-MI. In the absence of Cav1, there were a surprisingly higher percentage of M2 macrophages (arginase-1 positive) detected in the infarcted zone. Conversely, restoring Cav1 function after MI in WT mice by adding back the Cav1 scaffolding domain reduced the M2 activation profile. Further, adoptive transfer of Cav1 null macrophages into WT mice on d3 post-MI exacerbated adverse cardiac remodeling at d14 post-MI. In vitro studies revealed that Cav1 null macrophages had a more pronounced M2 profile activation in response to IL-4 stimulation. In conclusion, Cav1 deletion promotes an array of maladaptive repair processes after MI, including increased TGF-β signaling, increased M2 macrophage infiltration and dysregulation of the M1/M2 balance. Our data also suggest that cardiac remodeling can be improved by therapeutic intervention regulating Cav1 function during the inflammatory response phase

Imbalanced Expression of <i>Vcan</i> mRNA Splice Form Proteins Alters Heart Morphology and Cellular Protein Profiles

<div><p>The fundamental importance of the proteoglycan versican to early heart formation was clearly demonstrated by the <i>Vcan</i> null mouse called heart defect (<i>hdf</i>). Total absence of the <i>Vcan</i> gene halts heart development at a stage prior to the heart’s pulmonary/aortic outlet segment growth. This creates a problem for determining the significance of versican’s expression in the forming valve precursors and vascular wall of the pulmonary and aortic roots. This study presents data from a mouse model, <i>Vcan</i>^(tm1Zim), of heart defects that results from deletion of exon 7 in the <i>Vcan</i> gene. Loss of exon 7 prevents expression of two of the four alternative splice forms of the <i>Vcan</i> gene. Mice homozygous for the exon 7 deletion survive into adulthood, however, the inability to express the V2 or V0 forms of versican results in ventricular septal defects, smaller cushions/valve leaflets with diminished myocardialization and altered pulmonary and aortic outflow tracts. We correlate these phenotypic findings with a large-scale differential protein expression profiling to identify compensatory alterations in cardiac protein expression at E13.5 post coitus that result from the absence of <i>Vcan</i> exon 7. The <i>Vcan</i>^(tm1Zim) hearts show significant changes in the relative abundance of several cytoskeletal and muscle contraction proteins including some previously associated with heart disease. These alterations define a protein fingerprint that provides insight to the observed deficiencies in pre-valvular/septal cushion mesenchyme and the stability of the myocardial phenotype required for alignment of the outflow tract with the heart ventricles.</p></div

Histological comparison of cushions in the <i>Vcan</i>^(tm1Zim).

<p>Hematoxylin/eosin stained sections of postnatal day 1 (B, D) and <i>Vcan</i>^(tm1Zim) (A, C) hearts were compared. Boxed region in A and B of the cushion is shown higher magnification in C and D. Note the smaller cushions in the <i>Vcan</i>^(tm1Zim) heart. Panel A and B are the same magnification as are C and D; magnification bars = 200 µm.</p

Normal rotation and integration of the outflow tract (cardiac outlet) into the fused atrioventricular (AV) cushion in the final stages of looping and septal alignment.

<p>Upper panels are cross section dorsal views showing left and right AV canals, aorta and pulmonary trunks (Ao & P). Lower panels are depictions of the sagittal view. The dotted line indicates approximate section shown in upper panels. The myocardium (*inner curvature) between the outlet and AV cushion is removed and myocardial cells invade the proximal outlet cushion as in E12.5. P-pulmonary artery, Ao-aorta, LAV & RAV, left & right atrioventricular canals, M-mitral valve, T-tricuspid valve.</p

Whole-heart confocal optical imaging of defects in <i>Vcan</i>^(tm1Zim) E13.5 dpc mouse hearts.

<p>In the wild-type (Panel A), consecutively deeper optical section images showed the pulmonary outlet is ventral to the aortic outlet at the base of the heart. In the <i>Vcan</i>^(tm1Zim) (Panel B), the aorta and pulmonary outlets were within the same plane of optical section due to altered/defective outflow tract rotation and integration (−50 um). Hearts were treated to increase optical transparency and then perfused with FITC conjugated poly-L-lysine to visualize the endothelial lining of the vessels (yellow/green). Each optical section with each panel is a frontal image taken at sequentially deeper focal planes. Panels for the wild-type heart (panel A) span a total depth of 200 µm. The <i>Vcan</i>^(tm1Zim) heart (panel B) required imaging through a much shorter distance (125 µm) to image the same structures. RV-right ventricle; A-aorta; P-pulmonary; M-mitral; T-tricuspid.</p