Perivascular innate immune events modulate early murine vein graft adaptations

Abstract

Objective: Innate immunity drives numerous cardiovascular pathologies. Vein bypass grafting procedures are frequently accompanied by low-grade wound contamination. We hypothesized that a peri-graft innate immune challenge, via an outside-in route, augments inflammatory responses, which subsequently drive a component of negative vein graft wall adaptations; moreover, adipose tissue mediates this immune response.

Methods: The inferior vena cava from a donor mouse was implanted into the common carotid artery of a recipient mouse utilizing a validated cuff technique (9-week-old male C57BL/6J mice). Slow-release low-dose (5 μg) lipopolysaccharide (LPS) (n = 9) or vehicle (n = 9) was applied peri-graft; morphologic analysis was completed (day 28). In parallel, vein-grafted mice received peri-graft LPS (n = 12), distant subcutaneous LPS (n = 6), or vehicle (n = 12), then day-1 and -3 harvest of grafts and adipose tissue for cytokines and toll-like receptor (TLR) signaling mRNA expression (qRT-PCR).

Results: All recipient mice survived, and all vein grafts were patent. Acute low-dose local LPS challenge enhanced vein graft lumen loss (P = .04) and tended to augment intimal hyperplasia (P = .06). The surgical trauma of vein grafting universally upregulated key pro- and anti-inflammatory mediators within the day-1 graft wall, but varied on TLR signaling gene expression. Local and distant LPS accentuated these patterns until at least postoperative day 3. LPS challenge enhanced the inflammatory response in adipose tissue (locally > distantly); local LPS upregulated adipose TLR-4 dramatically.

Conclusions: Perivascular and distant inflammatory challenges potentiate the magnitude and duration of inflammatory responses in the early vein graft wall, negatively modulating wall adaptations, and thus, potentially contribute to vein graft failure. Furthermore, surgery activates innate immunity in adipose tissue, which is augmented (regionally > systemically) by LPS. Modulation of these local and distant inflammatory signaling networks stands as a potential strategy to enhance the durability of vascular interventions such as vein grafts.

Copyright © 2013 Society for Vascular Surgery. Published by Mosby, Inc. All rights reserved.

Figures

Fig 1

Morphologic analysis of day 28 mouse vein grafts. A-B, Representative Masson’s trichrome stained images. A, Normal saline suspended in pluronic F-127 gel (gNS) vein graft. B, Lipopolysaccharide suspended in pluronic F-127 gel (gLPS) vein graft. Scale bar = 200 μm. C, The comparison of vein graft lumen area, intimal thickness, media + adventitia thickness, the perimeter of internal elastic lamina, and the perimeter of outside boundary, based on Masson’s stained images. Values are shown as mean ± standard error of the mean.

Fig 2

mRNA expression of inflammatory mediators. Data are shown as fold induction ± standard error of the mean. A, Vein graft (VG) wall at baseline day 0, and postoperative days 1 and 3. §Relative to normal saline suspended in pluronic F-127 gel (gNS) VG at the same time point, P < .05. B, VG wall at postoperative day 3. *Relative to normal inferior vena cava (IVC), P <.05; §Relative to gNS VG (with gNS adipose), P < .05; †Relative to gNS VG (with lipopolysaccharide suspended in pluronic F-127 gel [gLPS] adipose), P < .05. C, Distant (flank) adipose tissue at postoperative day 3. *Relative to normal adipose, P < .05; §Relative to gNS adipose (with gNS VG), P < .05; †Relative to gNS adipose (with gLPS VG), P < .05. IL, Interleukin; TNFα, tumor necrosis factor-alpha.