Granulocyte-Macrophage Colony–Stimulating Factor Prevents the Progression of Atherosclerosis via Changes in the Cellular and Extracellular Composition of Atherosclerotic Lesions in Watanabe Heritable Hyperlipidemic Rabbits

Abstract

Background —A cytokine network is involved in atherogenesis. This study was conducted to investigate the effects of granulocyte-macrophage colony–stimulating factor (GM-CSF) on the development and composition of atherosclerotic lesions in Watanabe heritable hyperlipidemic (WHHL) rabbits. Methods and Results —GM-CSF (10 μg · kg −1 · d −1 ) was administered to 4-month-old WHHL rabbits (n=9) 5 days a week for 7.5 months, whereas an equal dose of human serum albumin was administered to controls (n=9). The cholesterol levels were not changed significantly by the treatment. Age-matched 4-month-old rabbits (n=7) had atheromatous plaques over 30.7±5.7% of the inner surface area of the aortic arch. After treatment, the percentages of surface atheromatous plaques to total aortic arch area were 45.0±12.6% in the GM-CSF group and 74.3±11.0% in controls ( P <0.0001). Histological examination demonstrated that GM-CSF reduced the ratio of intima to media ( P <0.01) and cross-sectional areas of atherosclerotic lesions ( P <0.0001). Quantitative analysis indicated a marked decrease in the areas of smooth muscle cells ( P =0.0001), collagen ( P =0.0001), and extracellular lipid deposits ( P <0.05) of atheromatous plaques in GM-CSF–treated rabbits compared with controls. The terminal deoxynucleotidyltransferase–mediated dUTP-digoxigenin nick end-labeling (TUNEL) method and immunohistochemistry were performed to examine the relationship between decreased atherosclerotic lesions and apoptosis. The percentage of TUNEL-positive cells increased in the GM-CSF group (GM-CSF, 24.1±4.4% versus control, 11.6±3.2%; P <0.0001). GM-CSF enhanced the apoptosis of smooth muscle cells in the shoulder region and the fibrous cap ( P <0.0001), suggesting one of the mechanisms for the antiatherogenic effect. Conclusions —GM-CSF altered the composition of atherosclerotic lesions and reduced the atherosclerosis in WHHL rabbits.