Differential expression of elastin assembly genes in patients with Stanford Type A aortic dissection using microarray analysis

Objective: Pathologic studies have demonstrated that aortic dissection is initiated by an intimal tear, followed by the rapid growth of an intramural hematoma that dissects the media and is characterized by elastin degradation. Genetic extracellular matrix abnormalities and proteinases may be the predisposing factors in aortic dissection, but little is known about the role of elastic fiber assembly. Fibulin-1 is an extracellular protein that is expressed in the vascular basement membrane. It regulates elastic fiber assembly and hence provides integrity in aortic structure. This study investigates the expression profiles of genes responsible for the elastolysis in the dissected human aorta, especially those coding fibulin-1, matrix metalloproteinase-9 (MMP-9), and elastin.

Methods: Intraoperative aortic samples were obtained from Chinese patients with Stanford Type A aortic dissection. Both the ascending dissected aortas (primary tear) and the adjacent intact aortas were collected for comparison. Control aortic tissues were obtained from healthy organ donors. The gene profile study was determined by the Affymetrix HG-U133A GeneChip (Affymetrix, Santa Clara, Calif) and analyzed by GeneSpring GX11.0 (Agilent Technologies Inc, Palo Alto, Calif). Only the genes displaying a net signal intensity two-fold higher than the mean background were used for analysis. To evaluate elastin expression, aortic sections were stained with Movat pentachrome stain. Fibulin-1, MMP-9, and elastin mRNA and protein expression were further confirmed by reverse transcriptase polymerase chain reaction (RT-PCR) and immunoblotting, respectively.

Results: Eight male Chinese aortic dissection patients (mean age, 45.8 years) and eight gender- and age-matched organ donors were recruited for the study. On the Affymetrix platform, 2,250 of 22,283 genes (10.1%) were detectable. The dissected and adjacent macroscopically intact aorta displayed similar gene expression patterns. In contrast, 11.2% (252) of the detectable genes were differentially expressed in the dissected and control aortas. Of these, 102 genes were upregulated, and 150 genes were downregulated. Based on the gene ontology, genes that code for extracellular matrix protein components and regulating elastic fiber assembly, like fibulin-1 and elastin, were downregulated, while enzymes like MMP-9 and MMP-11 that degrade matrix proteins were upregulated in dissected aortas. RT-PCR and Western blot results further validated the results.

Conclusions: Our gender- and age-matched study demonstrated that the alternated genes in the elastin assembly of dissected aortas may predispose structural failure in the aorta leading to dissection. However, no significant gene alterations in the adjacent intact and dissected aortas of the same patient can be found. Therefore, the genetic changes found in the dissected aortas most likely developed before the dissection starts. The inhibition of the aberrant expression of the fibulin-1 gene and that of the related matrix proteinase may open a new avenue for preventing aortic dissection.