Ribosomal protein S6 kinase 1 partakes hepatic insulin resistance by regulating expression of inflammatory cytokines

Abstract

Objective To study the effect of S6K1 silencing to hepatic inflammatory cytokines factors expression and explore the mechanism of S6K1 in the hepatic insulin resistance. Methods Forty eight male C57BL/6J mice (six-week old ) with body weight 12.6 to 14.8 g were randomly divided into four groups by using random number table: normal chow control group(ND+ pU6Ax), normal chow study group(ND+ S6K1Ax), high fat diet control group (HFD+ pU6Ax) and high fat diet study group(HFD+ S6K1Ax). For the depletion of S6K1 in the liver, C57BL/6J male mice by high fat diet and normal chow feeding for16 weeks were injected via the tail vein with S6K1shRNA recombinant adenovirus (S6K1Ax), U6 promoter recombinant adenovirus(pU6Ax) were injected into the control mice. Six days after virus injection, mice were killed and livers were obtained. Hepatic inflammatory cytokines expressions of Monocyte chemotactic protein 1(MCP-1), Tumor Necrosis Factor-α (TNF-α), Interleukin-1β(IL-1β), Interleukin-6(IL-6), Interleukin-10(IL-10) mRNA were examined by reverse transcription polymerase chain reaction, Hepatic protein expressions of S6K1, S6K1-thr389, IRS1-ser1101, IRS1-ser636/639, Akt-ser473, JNK-thr183/tyr185 were detected by western blotting. Results Comparing with the high fat diet control group, inflammatory factors of MCP-1, TNF-a, IL-1β mRNA in HFD+ S6K1Ax group showed lower expressions after hepatic S6K1 silencing(MCP-1 0.871±0.081 vs 0.549±0.016, TNF-α 0.905±0.059 vs 0.635±0.079, IL-1β 1.327±0.025 vs 0.642±0.042, t=9.55, 6.71, 34.07, all P 0.05). Anti-inflammatory factor of IL-10 mRNA in the HFD+ S6K1Ax group increased after hepatic S6K1 silencing (0.773±0.076 vs 0.436±0.046, t=9.27, P<0.05). Compared with the HFD+ pU6Ax group, the protein expressions of ISR1-ser1101, IRS1-ser636/639, S6K1-thr389, JNK-thr183/tyr185 decreased and protein expression of Akt-ser473 increased in the HFD+ S6K1Ax group by Western blotting detection after hepatic S6K1 silencing(t=6.59, 8.44, 5.37, 3.15, 6.52, all P<0.05). Conclusions High fat diet feeding can cause low grade inflammation and medicate insulin resistance in the liver. Hepatic S6K1 maybe participate hepatic insulin resistance by promoting inflammatory cytokines and inhibiting anti-inflammatory cytokine production. Key words: Ribosomal protein S6 kinase 1; Insulin resistance; Inflammatory cytokine; Liver; High fat diet