Candidate genes for abdominal aortic aneurysms

Genome-wide approach to finding abdominal aortic aneurysm susceptibility genes in humans

Familial aggregation of abdominal aortic aneurysms (AAAs) is now widely recognized, however, susceptibility genes have not yet been identified. Our approach to find susceptibility genes has been to collect families with AAAs and to perform DNA linkage analyses to identify regions on the human chromosomes that are linked to AAAs and could harbor susceptibility genes for AAAs. We identified 233 families with at least two individuals diagnosed with AAAs. These families had 653 AAA patients and an average of 2.8 cases per family. When evaluating mode of inheritance, 167 (72%) families were consistent with autosomal recessive inheritance, whereas 58 (25%) families were consistent with autosomal dominant inheritance and in 8 families the familial aggregation could be explained by autosomal dominant inheritance with incomplete penetrance. Blood samples from 235 affected relative pairs (ARPs) and their unaffected relatives were collected for DNA isolation and the DNA used for genotyping with highly variable microsatellite markers. We included covariates in the statistical analyses to allow for genetic heterogeneity. The results for chromosomes 19g13 and 4q31 were significant with sex, number of affected first-degree relatives, and their interaction as covariates. These chromosomal regions contain many plausible candidate genes, and the future research will include more detailed analyses of these positional candidate genes.

Differential gene expression in human abdominal aorta: aneurysmal versus occlusive disease

OBJECTIVE

Inflammation and atherosclerosis are present in both abdominal aortic aneurysm (AAA) and arterial occlusive disease (AOD). Changes in gene expression that underlie the development of AAA versus AOD are poorly defined. This study evaluated differences in gene expression in AAA, AOD, and control aortic tissue with human gene array technology.

METHODS

RNA was isolated from human aortic specimens (seven AAA, five AOD, and five control), and complementary DNA (cDNA) probes were generated. The cDNA probes were hybridized to a human cell interaction array of 265 genes and quantitated with phosphorimaging. The data were corrected for background and were standardized to housekeeping genes. Statistical differences in individual gene expression were determined with the Kruskal-Wallis test.

RESULTS

Of 265 genes studied, 11 showed statistically different expression in diseased aorta as compared with control. The following three genes were downregulated in AAA: collagen VI alpha1 (P <.037), glycoprotein IIIA (P <.006), and alpha2-macroglobulin (P <.020). The following two genes were upregulated in AOD: laminin alpha4 (P <.034) and insulin-like growth factor 2 receptor (P <.049). The following three genes were upregulated in both AAA and AOD: matrix metalloproteinase-9 (MMP-9; P <.005), intercellular adhesion molecule-1 (P <.012), and tumor necrosis factor--beta receptor (P <.022). The following three genes were downregulated in both AAA and AOD: integrin alpha5 (P <.012), ephrin A5 (P <.037), and rho/rac guanine nucleotide exchange factor (P <.028). Of 16 MMPs evaluated, only MMP-9 was significantly (P <.005) upregulated in both AAA and AOD. Evaluation results of four tissue inhibitors of metalloproteinases showed no significant difference in expression for all tissue types, although tissue inhibitor of metalloproteinase-1 trended toward upregulation in AAA (P =.053). Eight of the fifteen most highly expressed genes in all the groups were extracellular matrix or secreted proteins. Of these, only collagen VI alpha1 (P <.037) showed a significant change, although biglycan trended toward downregulation in AAA (P =.076).

CONCLUSION

This study used cDNA array technology in the comparison of human control and pathologic aortic tissue. Six genes had similar differential expression in both AAA and AOD as compared with control. Even more interesting were differences between AAA and AOD in the expression of five genes. These data suggest a similarity in genetic expression for both AAA and AOD, with altered expression of several genes playing a role in disease differentiation.

Expression and localization of macrophage elastase (matrix metalloproteinase-12) in abdominal aortic aneurysms

Elastolytic matrix metalloproteinases (MMPs) have been implicated in the pathogenesis of abdominal aortic aneurysms (AAA), a disorder characterized by chronic aortic wall inflammation and destruction of medial elastin. The purpose of this study was to determine if human macrophage elastase (HME; MMP-12) might participate in this disease. By reverse transcription-polymerase chain reaction, HME mRNA was consistently demonstrated in AAA and atherosclerotic occlusive disease (AOD) tissues (six of six), but in only one of six normal aortas. Immunoreactive proteins corresponding to proHME and two products of extracellular processing were present in seven of seven AAA tissue extracts. Total HME recovered from AAA tissue was sevenfold greater than normal aorta (P < 0.001), and the extracted enzyme exhibited activity in vitro. Production of HME was demonstrated in the media of AAA tissues by in situ hybridization and immunohistochemistry, but HME was not detected within the media of normal or AOD specimens. Importantly, immunoreactive HME was specifically localized to residual elastin fragments within the media of AAA tissue, particularly areas adjacent to nondilated normal aorta. In vitro, the fraction of MMP-12 sequestered by insoluble elastin was two- to fivefold greater than other elastases found in AAA tissue. Therefore, HME is prominently expressed by aneurysm-infiltrating macrophages within the degenerating aortic media of AAA, where it is also bound to residual elastic fiber fragments. Because elastin represents a critical component of aortic wall structure and a matrix substrate for metalloelastases, HME may have a direct and singular role in the pathogenesis of aortic aneurysms.