Abdominal aortic aneurysm (AAA) is a vascular asymptomatic disease responsible for 4% of mortality in the elderly population. MicroRNAs (miRNA) have recently been shown to be potential biomarkers due to their stability in plasma.
The aim of this study was to investigate the potentiality of miRNAS as biomarkers of AAA by identifying miRNAs specifically expressed in the key cells present in the human AAA tissue.
The distribution of inflammatory cells such as smooth muscle cells (SMC), M1 and M2 macrophages, neutrophils, B and T lymphocytes and mast cells were located by immunohistochemistry in 20 human AAA biopsies, showing a specific distribution towards the aneurysmal aortic wall and the presence of adventitial tertiary lymphoid organs (ATLOs) in 10 samples. We isolated by laser microdissection (LMD) area enriched in aneurysmal SMC, M1 and M2 macrophages, and ATLOs and SMC from control aorta. RNA extracted from 2 samples of LMD-isolated cells was screened on human miRNAs microarray.
Out of the 850 human miRNAs, more than 200 miRNAs were detected in LMD-isolated aneurysmal cells, with 164 detected in ATLOs, 49 in SMC, and 87 miRNAs in macrophages. We selected the 3 miRs with the highest expression for ATLOs and 10 miRs (based on their miR-29b levels) for SMC and macrophages for validation by qRT-PCR in LMD-isolated samples (n=4).
We found that miR-15a-3p (0.1 fold) and miR-30a-5p (0.2 fold) were down-regulated and miR-489-3p up-regulated (2 fold) in ATLOs which was inversed for miR-489-3p in the whole aneurysmal aorta. Of the 10 miRNAs selected, six (miR-199a-3p and miR-451 upregulated and miR-24, miR-29a, miR-29b, and miR-29c downregulated) were modulated similarly in SMC and macrophages and whole aneurysmal aorta, except for miR-199-3p. Let-7f and miR-34a were similarly upregulated ed in both subtypes of macrophages and aneurysmal aorta.
Expression in the plasma of AAA (n=24) compared to PAD (n=18) patients was significantly down-regulated for miR-15a-3p (p = 0.03) and miR-30a-5p (p = 0.04) and upregulated for let-7f (p=0.048) and miR-29b (p=0.035).
In conclusion, this non-hypothesis driven screening of miRNAs expressed in isolated aneurysmal cells allowed to identify four miRNAs as potential AAA biomarkers.
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