ABSTRACT
Objective: To investigate the mechanisms of telmisartan on delaying the course of type 2 diabetes. Methods: 3T3-L1 preadipocytes were induced to 80% mature adipocytes (control group) and stimulated with 50 ng/ml tumor necrosis factor (TNF-α) for 1 hour (TNF-α group). Then 0.1, 5, 10 µmol/L telmisartan was added to the culture medium for 24 h, respectively(T(0.1, )T(5) and T(10) group). The cells from each group was collected to detect peroxisome proliferator-activated receptors γ (PPARγ) and its phosphorylation level, as well as upstream kinase cell cycle dependent kinase 5 (CDK5) by Western blot. Adiponectin in the culture supernatant was detected by enzyme-linked immunosorbent assay (ELISA). PPARγ or CDK5 of undifferentiated 3T3-L1 adipocytes were silenced by using targeted short hairpin RNA (shRNA). Through infection of the cells with the retrovirus, stabled PPARγ or CDK5 knockdown cell lines were set up and screened by incubation with puromycin. 3T3-L1 adipocyte cell lines expressing serine mutant PPARγ (S273A, S112A, S186A) were obtained and thus their phosphorate sites were further determined. CDK5 knockdown cell lines were detected by oil red O staining to measure the lipid accumulation and differentiation efficiency. The 10 µmol/L telmisartan was used to treat mature CDK5 knockdown 3T3-L1 adipocytes, Western blot was used to detect PPARγ and its phosphorylation level, and ELISA was used to detect the release of adiponectin in the culture supernatant. Results: The TNF-α stimulation had no significant effect on the expression of PPARγ in each group (all P>0.05), but it could up-regulate the phosphorylation of PPARγ in the TNF-α group and down-regulate the release of adiponectin (all P<0.05). Compared with TNF-α group, telmisartan can reduce PPARγ phosphorylation levels and up-regulate adiponectin release in different degrees, among which T(5) group and T(10) group had statistically significant differences (all P<0.05), but for T(0.1) group, the difference was not significant (P>0.05). Compared with the 3T3-L1 wild type (WT) adipocytes, adiponectin in cell line with only S273A mutant did not respond to TNF-α stimulation and telmisartan intervention. Oil red O staining showed that silencing of CDK5 did not affect the differentiation of 3T3-L1 preadipocytes. Western blot results showed that silencing of CDK5 (shCDK5 group) had no significant effect on PPARγ expression (P>0.05), but it could down-regulate the phosphorylation of PPARγ and up-regulate release of adiponectin, compared with the randomized control group (shCon group) and the differences were statistically significant (all P<0.05). Conclusions: Telmisartan can alleviate the increased PPARγ phosphorylation and up-regulation of adiponectin content due to TNF-α stimulation. CDK5 mediates the effect of telmisartan on PPARγ signaling pathway in 3T3-L1 adipocytes. Additonally, it also demonstrated the action site of telmisartan was PPARγ Ser 273, and CDK5 is upstream kinases of PPARγ.
