Lin Dou1, Shuyue Wang1,2, Libo Sun3, Xiuqing Huang1, Yang Zhang1, Tao Shen1, Jun Guo1, Yong Man1, Weiqing Tang1, Jian Li1. 1. The MOH Key Laboratory of Geriatrics, Beijing Hospital, National Center of Gerontology, Beijing, China. 2. Nation Engineering Laboratory for Druggable Gene and Protein Screening, Northeast Normal University, Changchun, China. 3. Department of Hepatobiliary Surgery and You-An Liver Transplantation Center, Beijing You-An Hospital, Capital Medical University, Beijing, China.
Abstract
OBJECTIVE: Insulin resistance is a critical factor contributing to the pathogenesis of type 2 diabetes and other metabolic diseases. Recent studies have indicated that miR-338-3p plays an important role in cancer. Here, we investigated whether miR-338-3p mediates tumour necrosis factor-α (TNF-α)-induced hepatic insulin resistance. METHODS: The activation of the insulin signalling pathway and the level of glycogenesis were examined in the livers of the db/db and high fat diet (HFD)-fed mice and in HEP1-6 cells transfected with miR-338-3p mimic or inhibitor. Computational prediction of microRNA target, luciferase assay and Western blot were used to assess the miR-338-3p target. Chromatin immunoprecipitation (ChIP) assay was used to determine the transcriptional regulator of miR-338-3p. RESULTS: miR-338-3p was down-regulated in the livers of the db/db, HFD-fed and TNF-α-treated C57BL/6J mice, as well as in mouse HEP1-6 hepatocytes treated with TNF-α. Importantly the down-regulation of miR-338-3p induced insulin resistance, as indicated by impaired glucose tolerance and insulin tolerance. Further research showed that the down-regulated miR-338-3p resulted in the impaired AKT/ glycogen synthase kinase 3 beta (GSl·Gβ) signalling pathway and glycogen synthesis. In contrast, hepatic over-expression of miR-338-3p rescued the TNF-α-induced insulin resistance. Moreover, protein phosphatase 4 regulator subunit 1 (PP4R1) was identified as a direct target of miR-338-3p that mediated hepatic insulin signalling by regulating protein phosphatase 4 (PP4). Finally we identified hepatic nuclear factor 4 alpha (HNF-4α) as the transcriptional regulator of miRNA-338-3p. CONCLUSIONS: Our studies provide novel insight into the critical role and molecular mechanism by which miR-338-3p is involved in TNF-α-induced hepatic insulin resistance. miR-338-3p might mediate TNF-α-induced hepatic insulin resistance by targeting PP4R1 to regulate PP4 expression.
OBJECTIVE: Insulin resistance is a critical factor contributing to the pathogenesis of type 2 diabetes and other metabolic diseases. Recent studies have indicated that miR-338-3p plays an important role in cancer. Here, we investigated whether miR-338-3p mediates tumour necrosis factor-α (TNF-α)-induced hepatic insulin resistance. METHODS: The activation of the insulin signalling pathway and the level of glycogenesis were examined in the livers of the db/db and high fat diet (HFD)-fed mice and in HEP1-6 cells transfected with miR-338-3p mimic or inhibitor. Computational prediction of microRNA target, luciferase assay and Western blot were used to assess the miR-338-3p target. Chromatin immunoprecipitation (ChIP) assay was used to determine the transcriptional regulator of miR-338-3p. RESULTS: miR-338-3p was down-regulated in the livers of the db/db, HFD-fed and TNF-α-treated C57BL/6J mice, as well as in mouseHEP1-6 hepatocytes treated with TNF-α. Importantly the down-regulation of miR-338-3p induced insulin resistance, as indicated by impaired glucose tolerance and insulin tolerance. Further research showed that the down-regulated miR-338-3p resulted in the impaired AKT/ glycogen synthase kinase 3 beta (GSl·Gβ) signalling pathway and glycogen synthesis. In contrast, hepatic over-expression of miR-338-3p rescued the TNF-α-induced insulin resistance. Moreover, protein phosphatase 4 regulator subunit 1 (PP4R1) was identified as a direct target of miR-338-3p that mediated hepatic insulin signalling by regulating protein phosphatase 4 (PP4). Finally we identified hepatic nuclear factor 4 alpha (HNF-4α) as the transcriptional regulator of miRNA-338-3p. CONCLUSIONS: Our studies provide novel insight into the critical role and molecular mechanism by which miR-338-3p is involved in TNF-α-induced hepatic insulin resistance. miR-338-3p might mediate TNF-α-induced hepatic insulin resistance by targeting PP4R1 to regulate PP4 expression.