Rationale Proteomics has been previously applied to vascular tissues, but few studies have specifically targeted the vascular extracellular matrix.
Methods and results In this study, we developed a novel methodology for the extraction and identification of extracellular proteins from human aortas. Our approach is based on (a) effective decellularisation to enrich for scarce extracellular proteins, (b) successful solubilisation and deglycosylation of matrix proteins and (c) relative estimation of protein abundance by liquid chromatography tandem mass spectrometry. This methodology resulted in the identification of 103 extracellular space proteins, of which one-third have never been reported in the proteomic literature of vascular tissues. In particular, our study revealed the presence of four novel glycoproteins in human aortas (podocan, sclerostin, agrin and asporin) and we confirmed their presence on the aortic extracellular matrix by independent methods. Although their function in the vasculature is currently unknown, we found that cholesterol loading regulated podocan and agrin expression in human aortic smooth muscle cells. Moreover, our methodology allowed us to investigate proteolytic activity within tissues, based on the identification of proteolytic enzymes and their corresponding degradation products. For instance, we were able to detect matrix metalloproteinase 9 by mass spectrometry and relate its presence to degradation of fibronectin.
Conclusions We expect this new proteomic method to shed light on the composition and breakdown of extracellular matrix within cardiovascular tissues and provide insights into important pathological processes, such as plaque rupture, aneurysm formation and restenosis.