This study indicates that circulating progenitors of bone marrow origin give rise to cells with smooth muscle-like properties during formation of neointimal thickenings in the arterial wall after allotransplantation and after balloon injury. A segment of abdominal aorta was transplanted from female F344 to male LEW rats, and the grafts were analyzed for male cells by using the gene as a marker. Immunostaining demonstrated that CD45-positive leukocytes made up 35-45% of the neointimal cells during the 8-week period examined. Concurrently, up to 70% of the neointimal cells were of host origin, as shown by real-time polymerase chain reaction for the gene (Y chromosome). This suggests that the neointima contained host cells also of noninflammatory character. Accordingly, many cells positive for smooth-muscle alpha-actin were detected in this layer. To explore the possible bone marrow origin of allograft cells, female LEW rats were irradiated and substituted with bone marrow from male LEW rats. Subsequently, the animals received an aortic transplant from female F344 rats or were exposed to a balloon injury of the carotid artery. Immunostaining and real-time polymerase chain reaction confirmed the above findings, but the fractions of leukocytes and -positive cells were lower in the carotids than in the allografts. Combined primed in situ labeling and immunostaining verified that not only inflammatory but also smooth muscle-like cells of male origin appeared in the vessel wall in both situations. These observations suggest that the smooth-muscle cells that participate in the development of neointimal lesions during vascular disease may, in part, originate from circulating progenitors.

Development of intimal thickenings during transplant vasculopathy involves an allogenic immune response, which promotes accumulation of host-derived SMCs and apoptosis of resident graft SMCs.

Summary. Background: Growing evidence implicates the involvement of extracellular nucleotides in the regulation of platelet, leukocyte, endothelial cell (EC) and vascular smooth muscle cell (VSMC) phenotype and function. Within the quiescent vasculature, extracellular nucleotides are rapidly hydrolyzed by CD39, the dominant endothelial nucleoside triphosphate diphosphohydrolase (NTPDase-1). However, vascular CD39/NTPDase-1 activity is lost in EC activated by oxidative stress or proinflammatory mediators, and upon denudation of the endothelium following balloon injury. The consequent increase in extracellular nucleotide concentrations triggers signaling events leading to prothrombotic responses and increased VSMC proliferation. Objectives: To investigate the effect of overexpressed CD39/NTPDase-1 in injured aorta. Methods: Using adenoviral-mediated gene transfer we expressed CD39/NTPDase-1 in mechanically denudated rat aortas. We measured intima formation by morphometry and VSMC proliferation by the [ 3 H]-thymidine incorporation assay. Results: Targeted expression of CD39 in injured vessels increased NTPDase activity (from 2.91 ± 0.31 to 22.07 ± 6.7 nmols Pi mg )1 protein, 4 days after exposure to the adenovirus) and prevented the formation of neointima. The thickness of the intimal layer in injured aortas exposed to Ad-CD39 was 26.2 ± 3.9 lm vs. 51.8 ± 6.1 lm and 64.4 ± 22.2 lm (P < 0.001) in vessels treated with Ad-b-gal and saline, respectively. Moreover, targeted expression of CD39/NTPDase-1 caused a 70% (P < 0.01) decrease in proliferation of VSMC isolated from transduced rat aortas as compared with VSMC derived from control vessels. Conclusions: The presented data suggest that increasing CD39/ NTPDase-1 activity in VSMC could represent a novel therapeutic approach for the prevention of stenosis associated with angioplasty and other occlusive vascular diseases.

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