Aim:

Chronic kidney disease (CKD) and aortic aneurysm (AA) are tightly connected by a bi-directional relationship. While CKD is an independent risk factor for the development of AA as well as all-cause mortality following surgery, the incidence of acute kidney injury after aortic surgery or intervention is a striking indicator of persistent loss of kidney function and future cardiovascular events. While pathomechanisms initiating both diseases have been studied extensively, the influence of uremic conditions on aortic integrity is still poorly understood. As matrix metalloproteinases (MMPs) are concomitantly implicated in renal disease as well as AA, we aimed to identify whether uremic conditions expedite aneurysmal disease via these mediators.

Methods and results:

Human coronary artery endothelial cells (HCAEC) and human aortic endothelial cells (HAoEC, not shown) were subjected to simulated conditions of uremia via treatment with 250µM indoxyl sulfate (IS) for 24h. Proteomics analysis revealed significant upregulation of MMP-1 upon uremic injury (A). Increased transcription of MMP-1 as well as inflammatory cytokine IL-1β and cellular adhesion molecules ICAM and VCAM was validated via RTPCR as the expression of MMP-inhibitor TIMP- remained unchanged (B). While ELISA demonstrated elevated release of MMP-1 (C), collagenase assay showed increased degradation of collagen fibers after exposure to IS-treated cells (D). Proteomics analysis revealed MMP-1 to be encapsulated in microvesicles (E). Immunofluorescence (IFL)-stainings of the aorta of mice treated with IS exhibited a higher expression level of MMP-1 and increased collagen degradation in the staining against the product Col2 3/4C. Additionally, the circular intima-media area was augmented as a sign of aneurysmal degeneration, whereas monocyte infiltration as quantified by staining against CD 68 remained unchanged (F; DAPI: blue, tissue autofluorescence: green, protein of interest: red). Lastly, IFL-staining of paraffin sections of aortic specimens from patients undergoing replacement surgery for aneurysms of the ascending aorta demonstrated intensified co-localization of MMP-1 to the intimal and adventitial space (G; DAPI: blue, tissue autofluorescence: green, MMP-1: red).

Conclusions:

IS stimulates an inflammatory response characterized by increased release of MMP-1 by endothelial cells, facilitating degradation of collagen I and leading to signs of aneurysmal degeneration of the aorta.