MMP-9 Deletion Attenuates Arteriovenous Fistula Neointima through Reduced Perioperative Vascular Inflammation

Abstract

Matrix metalloproteinase 9 (MMP-9) expression is upregulated in vascular inflammation and participates in vascular remodeling, including aneurysm dilatation and arterial neointima development. Neointima at the arteriovenous (AV) fistula anastomosis site primarily causes AV fistula stenosis and failure; however, the effects of MMP-9 on perioperative AV fistula remodeling remain unknown. Therefore, we created AV fistulas (end-to-side anastomosis) in wild-type (WT) and MMP-9 knockout mice with chronic kidney disease to further clarify this. Neointima progressively developed in the AV fistula venous segment of WT mice during the four-week postoperative course, and MMP-9 knockout increased the lumen area and attenuated neointima size by reducing smooth muscle cell and collagen components. Early perioperative AV fistula mRNA sequencing data revealed that inflammation-related gene sets were negatively enriched in AV fistula of MMP-9 knockout mice compared to that in WT mice. qPCR results also showed that inflammatory genes, including tumor necrosis factor-a (TNF-α), monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1), were downregulated. In addition, Western blot results showed that MMP-9 knockout reduced CD44 and RAC-alpha serine/threonine-protein kinase (Akt) and extracellular signal-regulated kinases (ERK) phosphorylation. In vitro, MMP-9 addition enhanced IL-6 and MCP-1 expression in vascular smooth muscle cells, as well as cell migration, which was reversed by an MMP-9 inhibitor. In conclusion, MMP-9 knockout attenuated AV fistula stenosis by reducing perioperative vascular inflammation.

Roles of PI3K/AKT/mTOR Axis in Arteriovenous Fistula

“…Since AKT and ERK phosphorylation increases in neointimal lesions in AVF, the authors showed that, by western blot experiments, the AKT and ERK phosphorylation increase is attenuated by MMP-9 knockout [16]. Importantly, PI3K/AKT/mTOR signalling repression can be related to a decrease in the inflammation, migration and proliferation of VSMC cells.…”

“…A particular expression pattern of KI67 in the AVF vein wall has been observed: KI67 expression increases rapidly after AVF creation until it reaches a protein expression plateau. Moreover, matrix metalloproteinase 9 (MMP-9) expression also increases after AVF creation due to shear stress, the uremic environment, inflammation and hypoxia [16], and this increase contributes to an altered matrix deposition together with its degradation, leading to anomalous vascular wall remodelling and neointima formation [16]. Despite notable progress in the knowledge about AVF, causes of its failure are not clear, and the biology of the remodelling process is still not completely understood.…”

“…VSMCs dedifferentiation can be induced by growth factors and inflammatory cytokines locally released after vascular injury [16]: among these, platelet-derived growth factor (PDGF) is one of the most powerful mitogens that can induce a "phenotypic switch" from a contractile to a proliferative state, an essential step for neointima hyperplasia. PDGFinduced VSMC proliferation [45,46] is mediated by a signalling cascade that includes PI3K/AKT, mTOR/p70S6kinase and MEK1/ERK signalling downstream of the insulin receptor stimulus.…”

“…The PI3K/AKT/mTOR axis is also involved in extracellular matrix (ECM) formation: in fact, inflammation-released cytokines and growth factors can also influence extracellular matrix (ECM) degradation, which in turn helps VSMC infiltration and new matrix deposition. Notably, matrix metalloproteinase 9 (MMP-9) expression is upregulated in vascular inflammation and participates in vascular remodelling [16,49]. Recently, Shih et al used MMP-9 knock-out mice with CDK and observed a decrease in inflammation, an increase in AVF lumen diameter, and attenuated neointima formation due to a concomitant reduction in collagen factor and smooth muscle cell proliferation, compared to wt CDK mice [16].…”

“…Notably, matrix metalloproteinase 9 (MMP-9) expression is upregulated in vascular inflammation and participates in vascular remodelling [16,49]. Recently, Shih et al used MMP-9 knock-out mice with CDK and observed a decrease in inflammation, an increase in AVF lumen diameter, and attenuated neointima formation due to a concomitant reduction in collagen factor and smooth muscle cell proliferation, compared to wt CDK mice [16].…”