Leptin upregulates COX-2 and its downstream products in aortic endothelial cells

The adipocyte-derived hormone leptin is associated with hypertension. The involvement of cyclooxygenase-2 (COX-2) and its downstream vasomotor products prostaglandin (PG) and thromboxane (TX)A₂ in the mechanisms of action of leptin have remained elusive. The aim of the present study was to investigate the effects of leptin on the expression of COX-2 by rat aortic endothelial cells (RAECs) and the concentration of its products, represented by 6-keto PGF_1α and TXB₂, in the culture media. RAECs were isolated, cultured and identified by immunofluorescence staining. The RAECs were incubated with different concentrations of leptin (10^-10, 10^-9 and 10^-8 M) for various durations (36 or 48 h). COX-2 mRNA and protein expression in the cells was detected by reverse-transcription quantitative PCR and western blot analysis, respectively. The vasodilator 6-keto PGF_1α and the vasoconstrictor TXB₂ were detected in the supernatant by ELISA. The cultured cells displayed specific factor VIII expression in the cytoplasm. Compared with the PBS-treated control group, leptin significantly increased the expression of COX-2 mRNA and protein in a time- and dose-dependent manner (P<0.01). Furthermore, the vasodilator 6-keto PGF_1α was increased and the TXB₂/6-keto PGF_1α ratio decreased only with relatively high concentrations of leptin (10^-9 or 10^-8 M; P<0.01), but TXB₂ levels were not affected (P>0.05). In conclusion, leptin significantly increased the expression of inflammatory marker COX-2 and its downstream product 6-keto PGF_1α, while also decreasing the TXB₂/6-keto PGF_1α ratio in vitro. These observations suggested that COX-2 may have an important role in the effects of leptin on inflammation, such as the low-inflammatory disease hypertension. However, selective COX-2 inhibitors may increase the risk of hypertension due to inhibiting 6-keto PGF_1α, the vasodilator product of COX-2.