Absence of cardiovascular manifestations in a haploinsufficient TGFBR1 mouse model

Loeys-Dietz syndrome (LDS) is an autosomal dominant arterial aneurysm disease belonging to the spectrum of transforming growth factor beta (TGF beta)-associated vasculopathies. In its most typical form it is characterized by the presence of hypertelorism, bifid uvula/cleft palate and aortic aneurysm and/or arterial tortuosity. LDS is caused by heterozygous loss of function mutations in the genes encoding TGF beta receptor 1 and 2 (TGFBR1 and -2), which lead to a paradoxical increase in TGF beta signaling. To address this apparent paradox and to gain more insight into the pathophysiology of aneurysmal disease, we characterized a new Tgfbr1 mouse model carrying a p.Y378* nonsense mutation. Study of the natural history in this model showed that homozygous mutant mice die during embryonic development due to defective vascularization. Heterozygous mutant mice aged 6 and 12 months were morphologically and (immuno) histochemically indistinguishable from wild-type mice. We show that the mutant allele is degraded by nonsense mediated mRNA decay, expected to result in haploinsufficiency of the mutant allele. Since this haploinsufficiency model does not result in cardiovascular malformations, it does not allow further study of the process of aneurysm formation. In addition to providing a comprehensive method for cardiovascular phenotyping in mice, the results of this study confirm that haploinsuffciency is not the underlying genetic mechanism in human LDS

Absence of cardiovascular manifestations in a haploinsufficient Tgfbr1 mouse model

Loeys-Dietz syndrome (LDS) is an autosomal dominant arterial aneurysm disease belonging to the spectrum of transforming growth factor β (TGFβ)-associated vasculopathies. In its most typical form it is characterized by the presence of hypertelorism, bifid uvula/cleft palate and aortic aneurysm and/or arterial tortuosity. LDS is caused by heterozygous loss of function mutations in the genes encoding TGFβ receptor 1 and 2 (TGFBR1 and -2), which lead to a paradoxical increase in TGFβ signaling. To address this apparent paradox and to gain more insight into the pathophysiology of aneurysmal disease, we characterized a new Tgfbr1 mouse model carrying a p.Y378*nonsense mutation. Study of the natural history in this model showed that homozygous mutant mice die during embryonic development due to defective vascularization. Heterozygous mutant mice aged 6 and 12 months were morphologically and (immuno)histochemically indistinguishable from wild-type mice. We show that the mutant allele is degraded by nonsense mediated mRNA decay, expected to result in haploinsufficiency of the mutant allele. Since this haploinsufficiency model does not result in cardiovascular malformations, it does not allow further study of the process of aneurysm formation. In addition to providing a comprehensive method for cardiovascular phenotyping in mice, the results of this study confirm that haploinsuffciency is not the underlying genetic mechanism in human LDS

The heterozygous Lemd3+/GT mouse is not a murine model for osteopoikilosis in humans

Osteopoikilosis and the Buschke-Ollendorff syndrome are skeletal dysplasias with hyperostotic lesions in the long bones. These disorders are caused by heterozygous loss-of-function mutations in the LEMD3 gene. LEMD3 codes for a protein of the inner nuclear membrane that, through interaction with R-SMADs, antagonizes the BMP and TGF beta 1 pathway. It is suggested that the hyperostotic lesions in these disorders are caused by enhanced BMP and TGF beta 1 signaling. The exact mechanism by which mutations in the LEMD3 gene lead to these bone lesions has not yet been unraveled precisely. To further assess this, an Lemd3 gene-trapped mouse was created in a gene-trapping program by Baygenomics. To investigate whether the heterozygous gene-trapped mouse is a good model for osteopoikilosis in humans, we studied these mice radiologically with high-resolution micro-computed tomography (microCT) and histologically. X-ray images were evaluated by a trained radiologist, but no typical osteopoikilosis lesions could be recognized. On all microCT reconstructed images a 3D cortical and trabecular quantitative analysis was performed, investigating different histomorphometric parameters ranging from percent bone volume, bone surface/volume ratio over trabecular thickness, separation, number, and pattern factor to structure model index and fractal dimension. No significant differences were found after a t-test statistical analysis. Also, histological analysis did not reveal lesions typical for osteopoikilosis. We conclude that the heterozygous Lemd3 gene-trapped mouse is not a good model to study osteopoikilosis and the Buschke-Ollendorff syndrome