Effect of telmisartan on cyclin-dependent kinase 5-mediated peroxisome proliferator-activated receptors γ phosphorylation regulates adiponectin expression

Abstract

Objective To study the mechanism of telmisartan on peroxisome proliferator-activated receptors (PPAR) γ phosphorylation mediated by cyclin-dependent kinase (CDK) 5 and regulation of adiponectin expression in 3T3-L1 adipocytes. Methods 3T3-L1 with differentiation rate above 80% adipocytes were stimulated with different concentrations of tumor necrosis factor (TNF)-α (10, 50, 100 ng/ml for T10, T50, and T100 groups respectively) for 1 h. Different doses of telmisartan (0.1, 5, 10 μmol/L) treated T100 group for 24 h. The expression of CDK5 and p35 protein and the PPARγ phosphorylation levels were detected with Western blotting; Quantitative real-time polymerase chain reaction (qPCR) assessed CDK5, p35, PPARγ gene expression changes. Enzyme-linked immunosorbent assay (ELISA) was used to measure adiponectin concentration. 3T3-L1 cells were constructed and packaged with retroviruses carrying the p35 gene. The empty vector virus was used as a control and a CDK5 inhibitor group was set up to detect the CDK5, p35/p25, phosphorylation levels of PPARγ and the adiponectin level. Data were expressed in ±s, data among multiple groups were compared using One-Way ANOVA. Results Compared with untreated group, the relative expression levels of CDK5 mRNA and protein in the T10, T50, and T100 groups were not statistically different (all P>0.05). The relative expression of p35 mRNA (2.11±0.66, 2.71±0.59 vs 1.22±0.35, q=3.77, 4.91) and protein (0.32±0.02, 0.45±0.04 vs 0.09±0.01, q=2.19, 4.55) in the T50 and T100 groups were up-regulated, the differences were statistically significant (all P 0.05). pPPARγ/PPARγ was increased in the T50 and T100 groups (0.21±0.03, 0.47±0.04 vs 0.11±0.02, q=3.89, 6.91) while adiponectin concentration was decreased (1.56±0.34, 1.07±0.12 vs 2.36±0.55, q=6.32, 6.99, all P>0.05). After telmisartan intervention there was no significant difference in the relative mRNA and protein expression levels of CDK5 and p35 compared with the T100 group (all P>0.05). Tel5 and Tel10 groups had significant decreases in pPPARγ/PPARγ (0.11±0.03, 0.05±0.01 vs 0.38±0.02, q=4.91, 5.22) and increase in adiponectin release (1.71±0.06, 1.92±0.27 vs 1.11±0.05, q=5.77, 6.43) (all P<0.05). Over-expression of p35 led to p25 expression, elevation of pPPARγ/PPARγ (0.87±0.12 vs 0.07±0.02, q=9.13) and down-regulation of adiponectin (1.39±0.12 vs 2.21±0.33, q=5.67). In the inhibitor group, pPPARγ/PPARγ significantly decreased (0.15±0.01 vs 0.87±0.12, q=3.14) and adiponectin increased (1.95±0.24 vs 1.39±0.12, q=4.99) (all P<0.05). Conclusion Telmisartan regulates 3T3-L1 adipocyte adiponectin expression by inhibiting PPARγ phosphorylation induced by CDK5 overactivation. Key words: Peroxisome proliferator-activated receptors; Telmisartan; Cyclin-dependent kinase 5; p35; 3T3-L1