Pro-inflammatory cytokines and adipokines regulate PCSK9 expression in HepG2 cells

Background and aim: Clinical, genetic and experimental evidence indicates that proprotein convertase subtilisin/kexin 9 (PCSK9) may be either a cause or an effect of metabolic syndrome (MetS). We have recently demonstrated that PCSK9 is regulated by pro-inflammatory cytokine TNF-α in a SOCS3-dependent manner (Ruscica et al., JBC, 2016). Thus, the present work aimed to further extend this observation and studied the possible molecular mechanisms linking the effects of cytokines (TNF-α) and adipokines (leptin and resistin) on de novo lipogenesis and PCSK9 expression. Methods: Human hepatocellular liver carcinoma cell line (HepG2) and HepG2 overexpressing PCSK9 (HepG2_PCSK9) were used as in vitro tools. qPCR, Western blot, ELISA and luciferase reporter assays, together with siRNA directed to STAT3 and SOCS3, were used. Results: HepG2 cells express leptin (ObRb) and resistin (Adenylyl cyclase-associated protein 1, CAP1) receptors; the overexpression of PCSK9 in HepG2 (HepG2_PCSK9) does not alter that of ObRl and CAP-1. Fourty-eight-h treatment of HepG2 with TNF-α (10 ng/mL), leptin (200 ng/mL) and resistin (50 ng/mL) induced the expression of both PCSK9 (2.3-, 2.0- and 3.5-fold, respectively) and JAK/STAT pathway (3-, 1.8- and 1.9-fold, respectively). TNF-α and leptin increased the amount of secreted PCSK9 by 15%. Only leptin stimulated PCSK9 promoter activity after 24- and 48-h treatment (+52 and +26%, respectively). TNF-α, leptin and resistin induced the gene expression of apoB, sterol regulatory element-binding protein 1 (SREBP1), stearoyl-CoA desaturase-1 (SCD-1), fatty acid synthase (FAS) and microsomal triglyceride transfer protein (MTP). These effects, along with the activation of PCSK9, were inhibited by transfection with siRNA anti-STAT3, suggesting the involvement of the JAK/STAT pathway. Conclusions: Pro-inflammatory cytokines and adipokines up-regulate PCSK9 expression and the key genes involved in the de novo lipogenesis. Future analyses will investigate the potential role of JAK/STAT pathways in mediating these effects.