Molecular consequences of elastin gene mutations in autosomal dominant cutis laxa and supravalvular aortic stenosis

Elastic fibers are components of the extracellular matrix(ECM) that contribute resilience to tissues and bind and regulate transforming growth factor beta (TGFβ). Elastin gene (ELN) mutations cause several phenotypes including Williams-Beuren Syndrome (WBS), supravalvular aortic stenosis (SVAS) and autosomal dominant cutis laxa (ADCL). This work focused on the molecular consequences of the ELN gene mutations in ADCL and SVAS. \ud \ud ADCL is characterized by loose and inelastic skin, pulmonary emphysema, aortic root dilation, and peripheral pulmonary aortic stenosis. Our goal was to evaluate the impact of ELN mutations on TGFβ signaling and molecular pathology of ADCL. Dermal fibroblasts from four patients with ELN mutations in exon 34 or exon 30 and controls were used. Increased intracellular TGFβ signaling was found in patients with exon 30 mutations, despite unchanged extracellular TGFβ activity. TGFBR1 levels were increased at the protein and the RNA level. Patients with exon 34 mutations had normal TGFβ signaling. Our results indicate mutation-specific TGFβ signaling changes in ELN-related cutis laxa patients, which may influence to disease severity. Elastin assay showed decreased elastin deposition in ADCL cells and long-term TGFβ treatment improved elastin deposition. Semi-quantitative RT-PCR experiments showed increased expression of the mutant compared to the wild-type allele in ADCL cells under baseline conditions. Long-term TGFβ treatment normalized this allelic imbalance in expression. Therefore, we conclude that increased TGFβ signaling is a protective mechanism in ADCL at the molecular level.\ud \ud SVAS is characterized by narrowing of the ascending aorta. An SVAS family with a duplication in the ELN gene was analyzed genetically and functionally. Gene-dosage analysis showed that a tetranucleotide repeat in intron 1 was within the duplicated region. RT-PCR of pre-mRNA showed that a SNP in intron 23 of the mutant allele was not expressed. Decreased elastin deposition was found in affected individuals, supporting that this partial duplication yielded a null allele.\ud \ud Uncovering the nature of connections between elastin and TGFβ may help developing treatments for cutis laxa. Our findings are relevant to complex diseases characterized by elastin degradation and TGFβ dysregulation, including aneurysms and chronic obstructive pulmonary disease that have major public health impact