Peroxisome proliferator-activated receptor gamma ligands inhibit development of atherosclerosis in LDL receptor-deficient mice

Abstract

The peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor that regulates fat-cell development and glucose homeostasis and is the molecular target of a class of insulin-sensitizing agents used for the management of type 2 diabetes mellitus. PPARgamma is highly expressed in macrophage foam cells of atherosclerotic lesions and has been demonstrated in cultured macrophages to both positively and negatively regulate genes implicated in the development of atherosclerosis. We report here that the PPARgamma-specific agonists rosiglitazone and GW7845 strongly inhibited the development of atherosclerosis in LDL receptor-deficient male mice, despite increased expression of the CD36 scavenger receptor in the arterial wall. The antiatherogenic effect in male mice was correlated with improved insulin sensitivity and decreased tissue expression of TNF-alpha and gelatinase B, indicating both systemic and local actions of PPARgamma. These findings suggest that PPARgamma agonists may exert antiatherogenic effects in diabetic patients and provide impetus for efforts to develop PPARgamma ligands that separate proatherogenic activities from antidiabetic and antiatherogenic activities.

Figure 1

Atherosclerosis in LDLR^–/– mice fed a high-fat, cholesterol-enriched Western diet for 10 weeks. (a) Sections through the aortic root at the levels of the aortic valves were stained for elastin to highlight the medial boundaries of atherosclerotic lesions. (b) Quantitative analysis of lesion areas in control mice (C), mice treated with rosiglitazone (Ro), and mice treated with GW7845 (GW). For male mice, means ± SEM were: C, 0.161 ± 0.067 mm²/section (n = 10); Ro, 0.037 ± 0.014 mm²/section (n = 12); GW, 0.063 ± 0.027 mm²/section (n = 10). For female mice, means ± SEM were: C, 0.131 ± 0.035 mm²/section (n = 10); Ro, 0.183 ± 0.0.088 mm²/section (n = 10); GW, 0.181±0.0091 mm²/section (n = 10). NS, not statistically significant.

Figure 2

Size distribution of lipoprotein particles in LDLR^–/– mice fed a high-fat, cholesterol-enriched diet and treated with solvent (control; diamonds), rosiglitazone (squares), or GW7845 (triangles) for 10 weeks. Plasma was pooled from four mice from each treatment group and fractionated by FPLC. Mean cholesterol content in each fraction was determined in duplicate.

Figure 3

Glucose and insulin responses to an oral glucose challenge in LDLR^–/– mice fed the normal chow (circles); high-fat, cholesterol-enriched diet and solvent (control; diamonds); rosiglitazone (squares); or GW7845 (triangles). Blood glucose and plasma insulin levels were determined at base line (after a 4-hour fast) and 15, 30, 60, and 90 minutes after oral administration of 0.75 mg glucose/g body weight. Samples were taken from eight animals per group. Data are expressed as the mean ± SEM. ^AP < 0.0001, ^BP < 0.002, ^CP < 0.015, and ^DP < 0.04, drug treatment group vs. control group.

Figure 4

Expression of TNF-α, MCP-1, VCAM-1, and gelatinase B mRNA in the aortic root. The mRNA levels were quantitated using real-time RT-PCR. Six to seven samples per group were analyzed. C, control; Ro, rosiglitazone; GW, GW7845. Data are expressed as mean ± SEM. ^AP < 0.05, ^BP < 0.01, and ^CP < 0.001, drug treatment groups vs. cholesterol group.

Figure 5

Expression of macrosialin, CD36, SR-A, MCP-1, TNF-α, and VCAM-1 mRNA in the aorta. Male LDLR^–/– mice were fed either a normal chow diet (N) or a high-cholesterol diet for 4 months to induce the development of atherosclerosis (Athero). Animals fed the high-cholesterol diet were then treated with either solvent control, rosiglitazone, or GW8745 for 2 weeks. The mRNA levels were quantitated using real-time RT-PCR. Data represent pooled aortas with an average weight of 3.86 ± 0.16 mg/aorta for normal chow (N) (n = 11); 5.75 ± 0.67 mg/aorta for high cholesterol (C)(n = 6); 5.67 ± 0.56 mg/aorta for high cholesterol/rosiglitazone (Ro) (n = 6); and 5.80 ± 0.70 mg/aorta for high cholesterol/GW7845 (GW) (n = 6). Data are in triplicates and expressed as mean ± SEM.