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Peroxisome proliferator-activated receptor (PPAR)-γ agonists are emerging as potential protectors against inflammatory cardiovascular diseases including atherosclerosis and diabetic complications. However, their molecular mechanism of action within vasculature remains unclear. We report here that PPARγ agonists, thiazolidinedione class drugs (TZDs), or 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) were capable of activating diacylglycerol (DAG) kinase (DGK), resulting in attenuation of DAG levels and inhibition of protein kinase C (PKC) activation. The PPARγ agonist-induced DGK was completely blocked by a dominant-negative mutant of PPARγ, indicating an essential receptor-dependent action. Importantly, the suppression of DAG-PKC signaling pathway was functional linkage to the anti-inflammatory properties of PPARγ agonists in endothelial cells (EC), characterized by the inhibition of proinflammatory adhesion molecule expression and adherence of monocytes to the activated EC induced by high glucose. These findings thus demonstrate a novel molecular action of PPARγ agonists to suppress the DAG-PKC signaling pathway via upregulation of an endogenous attenuator, DGK.