Connection between Elastin Haploinsufficiency and Increased Cell Proliferation in Patients with Supravalvular Aortic Stenosis and Williams-Beuren Syndrome

Abstract

To elucidate the pathomechanism leading to obstructive vascular disease in patients with elastin deficiency, we compared both elastogenesis and proliferation rate of cultured aortic smooth-muscle cells (SMCs) and skin fibroblasts from five healthy control subjects, four patients with isolated supravalvular aortic stenosis (SVAS), and five patients with Williams-Beuren syndrome (WBS). Mutations were determined in each patient with SVAS and in each patient with WBS. Three mutations found in patients with SVAS were shown to result in null alleles. RNA blot hybridization, immunostaining, and metabolic labeling experiments demonstrated that SVAS cells and WBS cells have reduced elastin mRNA levels and that they consequently deposit low amounts of insoluble elastin. Although SVAS cells laid down approximately 50% of the elastin made by normal cells, WBS cells deposited only 15% of the elastin made by normal cells. The observed difference in elastin-gene expression was not caused by a difference in the stability of elastin mRNA in SVAS cells compared with WBS cells, but it did indicate that gene-interaction effects may contribute to the complex phenotype observed in patients with WBS. Abnormally low levels of elastin deposition in SVAS cells and in WBS cells were found to coincide with an increase in proliferation rate, which could be reversed by addition of exogenous insoluble elastin. We conclude that insoluble elastin is an important regulator of cellular proliferation. Thus, the reduced net deposition of insoluble elastin in arterial walls of patients with either SVAS or WBS leads to the increased proliferation of arterial SMCs. This results in the formation of multilayer thickening of the tunica media of large arteries and, consequently, in the development of hyperplastic intimal lesions leading to segmental arterial occlusion.

Identification and characterization of seven novel mutations of elastin gene in a cohort of patients affected by supravalvular aortic stenosis

“…1,4,5,9,[11][12][13] Reduction of ELN expression has been reported in the skin fibroblast and aortic smooth muscle cells of SVAS patients, with premature truncation mutations in ELN resulting in haploinsufficiency of elastin. 5,10 In an attempt to molecularly characterize our SVAS patient group, we performed a mutation screening of the ELN gene. We detected seven novel mutations, of which five result in PTC and two affect the natural splicing of the ELN gene.…”

Dexamethasone normalizes aberrant elastic fiber production and collagen 1 secretion by Loeys–Dietz syndrome fibroblasts: a possible treatment?

“…At the end of the incubation period, the quadruplicate cultures were used for the quantitative assessment of metabolically labeled (radioactive) insoluble elastin as previously described. 13 Cell layers containing newly deposited matrix were boiled in 0.5 ml of 0.1 N NaOH for 45 min to solubilize all matrix components except elastin. The collected insoluble radioactive elastin was then solubilized by boiling in 200 ml of 5.7 N HCl for 1 h and quantified in scintillation counter.…”

Peripheral Pulmonary Artery Stenosis as a Cause of Pulmonary Hypertension in Adults

“…19 WBS is due to a microdeletion of a portion of chromosome 7q11.23, 20 which includes parts of the elastin gene and leads to reduced elastin synthesis and increased proliferation of vascular smooth muscle cells and fibroblasts. 21 Vascular involvement is common (60%-80% of affected individuals) in WBS and is characterized by nar- Figure 1. Balloon angioplasty of the right lobar pulmonary artery in a patient with peripheral pulmonary artery stenosis.…”

“…CRAN: cranial; LAO: left anterior oblique. rowing of medium-and large-sized elastic arteries due to thickening of the media, 21,22 which leads to supravalvular aortic stenosis and PPAS. PPAS is sometimes severe and bilateral, involving the main pulmonary arteries as well as the branching points of the lobar vessels.…”