Robert P. Garvin

Regional expression of HOXA4 along the aorta and its potential role in human abdominal aortic aneurysms

BackgroundThe infrarenal abdominal aorta exhibits increased disease susceptibility relative to other aortic regions. Allograft studies exchanging thoracic and abdominal segments showed that regional susceptibility is maintained regardless of location, suggesting substantial roles for embryological origin, tissue composition and site-specific gene expression.ResultsWe analyzed gene expression with microarrays in baboon aortas, and found that members of the HOX gene family exhibited spatial expression differences. HOXA4 was chosen for further study, since it had decreased expression in the abdominal compared to the thoracic aorta. Western blot analysis from 24 human aortas demonstrated significantly higher HOXA4 protein levels in thoracic compared to abdominal tissues (P < 0.001). Immunohistochemical staining for HOXA4 showed nuclear and perinuclear staining in endothelial and smooth muscle cells in aorta. The HOXA4 transcript levels were significantly decreased in human abdominal aortic aneurysms (AAAs) compared to age-matched non-aneurysmal controls (P < 0.00004). Cultured human aortic endothelial and smooth muscle cells stimulated with INF-γ (an important inflammatory cytokine in AAA pathogenesis) showed decreased levels of HOXA4 protein (P < 0.0007).ConclusionsOur results demonstrated spatial variation in expression of HOXA4 in human aortas that persisted into adulthood and that downregulation of HOXA4 expression was associated with AAAs, an important aortic disease of the ageing population.

Novel pathways in the pathobiology of human abdominal aortic aneurysms

Objectives: Abdominal aortic aneurysm (AAA), a dilatation of the infrarenal aorta, typically affects males >65 years. The pathobiological mechanisms of human AAA are poorly understood. The goal of this study was to identify novel pathways involved in the development of AAAs. Methods: A custom-designed ‘AAA-chip’ was used to assay 43 of the differentially expressed genes identified in a previously published microarray study between AAA (n = 15) and control (n = 15) infrarenal abdominal aorta. Protein analyses were performed on selected genes. Results: Altogether 38 of the 43 genes on the ‘AAA-chip’ showed significantly different expression. Novel validated genes in AAA pathobiology included ADCY7, ARL4C, BLNK, FOSB, GATM, LYZ, MFGE8, PRUNE2, PTPRC, SMTN, TMODI and TPM2. These genes represent a wide range of biological functions, such as calcium signaling, development and differentiation, as well as cell adhesion not previously implicated in AAA pathobiology. Protein analyses for GATM, CD4, CXCR4, BLNK, PLEK, LYZ, FOSB, DUSP6, ITGA5 and PTPRC confirmed the mRNA findings. Conclusion: The results provide new directions for future research into AAA pathogenesis to study the role of novel genes confirmed here. New treatments and diagnostic tools for AAA could potentially be identified by studying these novel pathways.

Role of Complement Cascade in Abdominal Aortic Aneurysms

Objective—The goal of this study was to investigate the role of complement cascade genes in the pathobiology of human abdominal aortic aneurysms (AAAs). Methods and Results—Results of a genome-wide microarray expression profiling revealed 3274 differentially expressed genes between aneurysmal and control aortic tissue. Interestingly, 13 genes in the complement cascade were significantly differentially expressed between AAA and the controls. In silico analysis of the promoters of the 13 complement cascade genes showed enrichment for transcription factor binding sites for signal transducer and activator of transcription (STAT)5A. Chromatin-immunoprecipitation experiments demonstrated binding of transcription factor STAT5A to the promoters of the majority of the complement cascade genes. Immunohistochemical analysis showed strong staining for C2 in AAA tissues. Conclusion—These results provide strong evidence that the complement cascade plays a role in human AAA. Based on our microarray studies, the pathway is activated in AAA, particularly via the lectin and classical pathways. The overrepresented binding sites of transcription factor STAT5A in the complement cascade gene promoters suggest a role for STAT5A in the coordinated regulation of complement cascade gene expression.

The potential role of DNA methylation in abdominal aortic aneurysms.

Abdominal aortic aneurysm (AAA) is a complex disorder that has a significant impact on the aging population. While both genetic and environmental risk factors have been implicated in AAA formation, the precise genetic markers involved and the factors influencing their expression remain an area of ongoing investigation. DNA methylation has been previously used to study gene silencing in other inflammatory disorders and since AAA has an extensive inflammatory component, we sought to examine the genome-wide DNA methylation profiles in mononuclear blood cells of AAA cases and matched non-AAA controls. To this end, we collected blood samples and isolated mononuclear cells for DNA and RNA extraction from four all male groups: AAA smokers (n = 11), AAA non-smokers (n = 9), control smokers (n = 10) and control non-smokers (n = 11). Methylation data were obtained using the Illumina 450k Human Methylation Bead Chip and analyzed using the R language and multiple Bioconductor packages. Principal component analysis and linear analysis of CpG island subsets identified four regions with significant differences in methylation with respect to AAA: kelch-like family member 35 (KLHL35), calponin 2 (CNN2), serpin peptidase inhibitor clade B (ovalbumin) member 9 (SERPINB9), and adenylate cyclase 10 pseudogene 1 (ADCY10P1). Follow-up studies included RT-PCR and immunostaining for CNN2 and SERPINB9. These findings are novel and suggest DNA methylation may play a role in AAA pathobiology.

Current Status of Endovascular Devices to Treat Abdominal Aortic Aneurysms

The introduction of endovascular abdominal aortic aneurysm (AAA) repair has revolutionized the therapeutic approach to patients with AAA. Due to an ongoing and prolific collaboration between vascular interventionalists and biomedical engineers, the devices used to perform endovascular AAA repair have also changed dramatically. The purpose of this publication is to provide an overview of the currently available and upcoming options for endovascular AAA repair.

The SAAAVE Act and Routine Ambulatory Medical Care Fail to Diagnose Patients with Abdominal Aortic Aneurysms prior to Rupture: A Single-Institution Experience

Objectives. To demonstrate that routine ambulatory medical evaluation in the outpatient setting and current utilization of the Screening Abdominal Aortic Aneurysms Very Efficiently (SAAAVE) Act are inadequate methods to diagnose abdominal aortic aneurysms (AAA) prior to rupture. Methods. A retrospective review was performed on patients with ruptured AAA (rAAA) at a single institution. All patients who were evaluated in an ambulatory care setting within 6 months of the date of rupture were identified, and clinical data were analyzed. Results. Between January 1, 2004 and December 31, 2010, there were 149 patients with rAAA. Fifty-two of 149 (34.9%) patients were evaluated in the outpatient setting within 6 months prior to the date of rupture, and these patients form the basis of this study. Thirty-six of 52 (70%) patients were male, average age was 73.5 years, average BMI was 28, and average aneurysm diameter was 76 mm. Only 5/52 (9.6%) patients had physical exam findings suspicious for AAA. Only 9/52 (17%) would have been eligible for the screening abdominal ultrasound under the SAAAVE Act. Conclusions. Routine medical evaluation in the ambulatory care setting and current utilization of AAA screening methods are inadequate at detecting AAA in the at-risk population prior to rupture.