Murine Model of Neointimal Formation and Stenosis in Vein Grafts

Abstract

Objective-Previous studies have suggested that neointimal formation, a central cause of vein graft stenosis, has several potential cell sources. It was hypothesized that neointimal cells arise primarily from the cells of the vein graft. Methods and Results-This study investigated vein graft neointimal cell origins using a model of vein-to-artery cross-transplantation between transgenic Rosa26 mice (constitutive expression of bacterial ␤-galactosidase marker gene) and wild-type mice. Vein-originating cells survived and make a major contribution to neointimal formation within the vein graft, mostly adjacent to the lumen/endothelium, suggesting an intimate association with endothelial cells. Key Words: bypass graft Ⅲ neointima Ⅲ Rosa26 Ⅲ thrombomodulin Ⅲ stenosis V ascular bypass surgery using vein grafts has become an established procedure for treating many conditions, most notably myocardial infarction (eg, coronary bypass) and limb claudication (eg, femoral-popliteal bypass grafting). 1,2 Despite high early success rates of these procedures, it is estimated that 20% to 50% of cases undergo stenotic occlusion of the graft within 5 years, 3-5 caused by an inward growth of neointimal cells. 6 Experimental models that mimic clinical vein grafting show a characteristic burst of neointimal cell proliferation early after grafting (3 to 7 days), which leads to a thickened intimal layer by 1 month. 7,8 This neointimal growth appears to stabilize beyond 1 to 2 months in animal models 9,10 and does not create significant graft stenosis at any time, thus differing from the clinical progression of this complication. See page 1147The source of neointimal cells remains controversial. Studies using arterial injury models (eg, balloon angioplasty) have presented evidence for medial smooth muscle cells, adventitial (myo)fibroblasts, and blood-borne stem cells as major contributors to the neointima. 11-15 Studies using vein graft models have supported adjacent arterial media as a major source for neointimal cells. 7,16 Arterial and organ allotransplantation models have found that circulating progenitor cells and adjacent (recipient) arterial media are the major contributors to transplant-associated neointimal formation. 15,[17][18][19] A recent study using a murine vein graft model demonstrated that the neointimal cells within the graft arise from both the vein graft and the recipient artery. 20 The following study confirms this result using a new murine model that has direct analogy to clinical vein grafting and stenosis. Furthermore, the findings show that neointima cells from the vein graft arise from and proliferate predominantly at the innermost (luminal) aspect, suggesting involvement of vein-derived endothelial cells. Methods Vein Graft ModelA new model of vein graft transplantation in mice was developed by the author and is similar to recently described murine vein graft models 20 -22 but uses a smaller-diameter graft, a branch of the jugular vein, interpositioned to the femoral artery. This model has more clinical analogy...

Mouse Strain Differential Neointimal Response in Vein Grafts and Wire-Injured Arteries

“…This manipulation was done to provide a closer parallel between the arterial and venous neointimal conditions. Previous results found that uninjured arterial grafts in mice develop very little neointima, 12 which, together with the present findings, shows an independent effect of wire-injury neointimal formation across mouse models. 13,14 The incidence of calcified tissue in the vein graft wall of FVB mice is intriguing, but may have little bearing on graft stenosis or clinically relevant complications, and may simply be a strain-dependent difference in inflammatory response after vein graft surgery.…”

“…(50 mg/kg body weight ip). A murine syngenic vein graft (same-strain) transplantation model 12 was used in 1 experiment, grafting a branch of the jugular vein (2-mm length) from a donor mouse to the femoral artery of a syngenic recipient mouse. A single intravenous bolus of heparin (5 units in 100 l) was given immediately before reflow of the femoral artery to prevent thrombosis.…”

“…Arterial grafts were harvested after 14 days and vein grafts after 30 days by double ligation outside the graft margins, resection, and immersion-fixation in 4% formaldehyde in phosphatebuffered saline for at least 24 h. Samples were processed through ascending ethanol and xylene, paraffin-embedded, cross-sectioned at 6 microns, and stained with either hematoxylin -eosin or Masson trichrome. Histomorphometry was accomplished on digitized images using NIH ImageTool 3.0 software as described previously, 12 analyzing representative sections from the proximal, middle and distal portions of each graft. Neointimal thickness and luminal area were measured.…”

Lumen Loss in the First Year in Saphenous Vein Grafts Is Predominantly a Result of Negative Remodeling of the Whole Vessel Rather Than a Result of Changes in Wall Thickness

“…7,19,20 These data support our observations. Moreover, some animal studies indicate that neointimal growth may stabilize after the first few weeks 21 and human studies have not followed wall thickness serially in the same patients. 6,18 The high usage of statins (81%) in this study may also have influenced wall thickness, because statins may reduce neointima formation in vein grafts via multiple mechanisms.…”

The Source of Neointimal Cells in Vein Grafts: Does the Origin Matter?

“…7,17 These data indicate that the vein graft itself is also a major source for neointimal cells, although the exact source of these cells remains to be elucidated. However, potential sources of these graft-intrinsic cells include adventitial myofibroblasts, 18 but also, recently identified localized vascular progenitor cells residing in the media 19 Taken together, these experimental data indicate that neointimal VSMCs in vein grafts can be recruited from various anatomical locations, including the BM, the adjacent arterial media, the circulation (containing also vascular progenitors that originate from non-BM compartments), and the vein graft vascular wall itself.…”