Peroxisome proliferator-activated receptor gamma agonists induce lipid sequesteration by rabbit vascular smooth muscle cells

Date

2002-08

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Publisher

Texas Tech University

Abstract

The hypothesis for this study is that peroxisome proliferator-activated receptor gamma (PPARy) agonists induce lipid sequestration in rabbit aortic vascular smooth muscle cells (VSMC). Davis et al. (unpublished) had demonstrated that treatment of these VSMC cultures with the thiazolidinedione (TZD), ciglitazone, induced lipid sequestration as indicated by the neutral lipid stain Oil Red O (ORO). The purpose of the current study was: (1) Confirm the studies performed by Davis et al. (2) Develop a method to quantify the ORO accumulation, (3) Determine if the response was specific for ciglitazone or if the phenomenon was inducible by other thiazolidinediones and/or an endogenous PPARy agonist, the metabolite of the prostaglandin J2, 15-deoxy-A-^^''"^-PGJ2 (15dPGJ2), and (4) Identify the cell type responsible for the lipid sequestration by staining with fluorescent antibodies. In the process of the current study, the preliminary observations by Davis et al. were confirmed. Reporting the ORO accumulation, as a percent of the image area, required the use of the computer assisted image analysis software, MetaMorph®. Ciglitazone was able to stimulate lipid sequestration in VSMC cultures time- and concentration-dependently and this response was independent of the concentration of vehicle, DMSO, used. Treatment with 60 pM ciglitazone for nine days induced lipid sequestration by almost 200% relative to control. The increased ORO accumulation was not a unique property of ciglitazone but was also inducible by other TZDs (rosiglitazone and troglitazone), as well as 15dPGJ2, supporting a role of PPARy in this response. The 15dPGJ2 showed a significant concentration dependent increase and was the most potent PPARy agonist tested. Rosiglitazone also showed a trend toward increased ORO accumulation in a concentration-dependent fashion, but only achieved significance at day seven. While troglitazone followed the same trend, it was not statistically significant. In a co-localization study of rabbit aortic VSMC cultures, cells were stained with ORO and bound anti-a-smooth muscle actin antibody after ciglitazone treatment for nine days. Evidence was found indicating that VSMC were phenotypically changed to induce lipid sequestration. In all, PPARy agonists can induce VSMC to sequester lipids in a concentration-dependent manner. Whether this process is pro- or anti-atherogenic remains to be determined.

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