Background: Cell death-inducing DFF45-like effector C (CIDEC) is a novel lipid droplet-coating protein that promotes triglyceride accumulation and inhibits lipolysis. TNFα downregulates CIDEC levels to enhance basal lipolysis, while CIDEC overexpression could block this effect. However, the signalling mechanism by which TNFα regulates CIDEC expression in human is still unknown.
Objective and hypotheses: The aim of this study was to investigate the signalling pathway of TNFα-mediated CIDEC downregulation in human adipocytes.
Method: We first detected CIDEC expression by RT-PCR in human adipose tissue of lean and obese subjects. Next, using fully differentiated human adipocytes, we investigated the temporal and dose-dependent effects of TNFα on CIDEC levels. Both MAPK inhibitors and siRNA were used to suppress ERK cascade activated by TNFα. Furthermore, we resorted to subcellular fractionation technique and immunostaining to study PPARγ localisation after TNFα treatment. Reporter assay was performed to confirm the direct effects of TNFα on CIDEC promoter.
Results: CIDEC expression was markedly decreased in obese subjects and negatively correlated with adipose TNFα levels as well as systemic lipolysis. TNFα reduced CIDEC expression in both time and dose-dependent manner. However, suppression of MEK, either by selective inhibitors or siRNA, prevented TNFα-mediated CIDEC downregulation. Further results showed that PPARγ, the transcription factor of CIDEC, was phosphorylated and redistributed by TNFα in a MEK-dependent manner. Reporter assay confirmed that TNFα downregulated CIDEC expression by inhibiting its promoter activity.
Conclusion: TNFα downregulates CIDEC protein levels through phosphorylation and nuclear export of PPARγ by MEK/ERK cascade and this adds new aspects of TNFα-induced lipolysis in human.
Funding: This work was supported by National Natural Science Foundation of China No. 81172689.
01 - 03 Oct 2015
European Society for Paediatric Endocrinology