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Bo Li, Zhiguo Zhang, Huizhi Zhang, Kai Quan, Yan Lu, Dongsheng Cai and Guang Ning

The prevalence of non-alcoholic fatty liver disease (NAFLD), a condition characterized by an excessive accumulation of triglycerides (TGs) in hepatocytes, has dramatically increased globally during recent decades. MicroRNAs (miRs) have been suggested to play crucial roles in many complex diseases and lipid metabolism. Our results indicated that miR199a-5p was remarkably upregulated in free fatty acid (FA)-treated hepatocytes. To investigate the role of miR199a-5p in the pathogenesis of fatty liver and the potential mechanism by which miR199a-5p regulates NAFLD, we first transfected two hepatocyte cell lines, HepG2 and AML12 cells, with agomiR199a-5p or antagomiR199a-5p. Our results indicated that miR199a-5p overexpression exacerbated deposition of FA and inhibited ATP levels and mitochondrial DNA (mtDNA) contents. Consistently, suppression of miR199a-5p partially alleviated deposition of FA and increased ATP levels and mtDNA contents. Moreover, miR199a-5p suppressed the expression of mitochondrial FA β-oxidation-related genes through inhibition of caveolin1 (CAV1) and the related peroxisome proliferator-activated receptor alpha (PPAR α) pathway. Furthermore, suppression of CAV1 gene expression by CAV1 siRNA inhibited the PPARα signalling pathway. Finally, we examined the expression of miR199a-5p in liver samples derived from mice fed a high-fat diet, db/db mice, ob/ob mice and NAFLD patients, and found that miR199a-5p was upregulated while CAV1 and PPARA were downregulated in these systems, which was strongly indicative of the essential role of miR199a-5p in NAFLD. In summary, miR199a-5p plays a vital role in lipid metabolism, mitochondrial activity and mitochondrial β-oxidation in liver. Upregulated miR199a-5p in hepatocytes may contribute to impaired FA β-oxidation in mitochondria and aberrant lipid deposits, probably via CAV1 and the PPARα pathway.

Free access

Shaoqian Zhao, Wen Liu, Jiqiu Wang, Juan Shi, Yingkai Sun, Weiqing Wang, Guang Ning, Ruixin Liu and Jie Hong

Abnormal shifts in the composition of gut microbiota contribute to the pathogenesis of metabolic diseases, including obesity and type 2 diabetes (T2DM). The crosstalk between gut microbes and the host affects the inflammatory status and glucose tolerance of the individuals, but the underlying mechanisms have not been elucidated completely. In this study, we treated the lean chow diet-fed mice with Akkermansia muciniphila, which is thought to be inversely correlated with inflammation status and body weight in rodents and humans, and we found that A. muciniphila supplementation by daily gavage for five weeks significantly alleviated body weight gain and reduced fat mass. Glucose tolerance and insulin sensitivity were also improved by A. muciniphila supplementation compared with the vehicle. Furthermore, A. muciniphila supplementation reduced gene expression related to fatty acid synthesis and transport in liver and muscle; meanwhile, endoplasmic reticulum (ER) stress in liver and muscle was also alleviated by A. muciniphila. More importantly, A. muciniphila supplementation reduced chronic low-grade inflammation, as reflected by decreased plasma levels of lipopolysaccharide (LPS)-binding protein (LBP) and leptin, as well as inactivated LPS/LBP downstream signaling (e.g. decreased phospho-JNK and increased IKBA expression) in liver and muscle. Moreover, metabolomics profiling in plasma also revealed an increase in anti-inflammatory factors such as α-tocopherol, β-sitosterol and a decrease of representative amino acids. In summary, our study demonstrated that A. muciniphila supplementation relieved metabolic inflammation, providing underlying mechanisms for the interaction of A. muciniphila and host health, pointing to possibilities for metabolic benefits using specific probiotics supplementation in metabolic healthy individuals.

Free access

Qinyun Ma, Jianxia Fan, Jiqiu Wang, Shuai Yang, Qing Cong, Rui Wang, Qianqian Lv, Ruixin Liu and Guang Ning

Gestational diabetes mellitus (GDM) presents with moderate inflammation, insulin resistance and impaired glucose uptake, which may result from increased maternal fat mass and increased circulation of placental hormones and adipokines. In this study, we set out to test whether the surge in chorionic gonadotrophin (CG) secretion is a cause of inflammation and impaired insulin sensitivity in GDM. We first found that LH/chorionic gonadotrophin receptors (CG/LHR) were expressed at low levels in insulin-sensitive murine 3T3-L1 adipocytes and murine C2C12 myocytes. CG treatment not only directly reduced insulin-responsive gene expression, including that of glucose transporter 4 (GLUT4), but also impaired insulin-stimulated glucose uptake in 3T3-L1 cells. Moreover, CG treatment increased the expression of the proinflammatory cytokine monocyte chemotactic protein 1 (MCP1) and upregulated nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) activity in 3T3-L1 cells. Clinically, pregnant women who had higher CG levels and elevated MCP1 developed GDM. Above all, apart from prepregnancy BMI and MCP1 level, CG level was associated with abnormal glucose tolerance. In summary, our findings confirmed that higher CG levels in pregnancy possibly played a role in GDM development partly by impairing the functions of insulin, such those involved in as glucose uptake, while promoting inflammation in adipocyte.

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Qianqian Lu, Yuying Yang, Sheng Jia, Shaoqiang Zhao, Bin Gu, Peng Lu, Yang He, Ruixin Liu, Jiqiu Wang, Guang Ning and Qinyun Ma

Appetite is tightly controlled by neural and hormonal signals in animals. In general, steroid receptor coactivator 1 (SRC1) enhances steroid hormone signalling in energy balance and serves as a common coactivator of several steroid receptors, such as oestrogen and glucocorticoid receptors. However, the key roles of SRC1 in energy balance remain largely unknown. We first confirmed that SRC1 is abundantly expressed in the hypothalamic arcuate nucleus (ARC), which is a critical centre for regulating feeding and energy balance; it is further co-localised with agouti-related protein and proopiomelanocortin neurons in the arcuate nucleus. Interestingly, local SRC1 expression changes with the transition between sufficiency and deficiency of food supply. To identify its direct role in appetite regulation, we repressed SRC1 expression in the hypothalamic ARC using lentivirus shRNA and found that SRC1 deficiency significantly promoted food intake and body weight gain, particularly in mice fed with a high-fat diet. We also found the activation of the AMP-activated protein kinase (AMPK) signalling pathway due to SRC1 deficiency. Thus, our results suggest that SRC1 in the ARC regulates appetite and body weight and that AMPK signalling is involved in this process. We believe that our study results have important implications for recognising the overlapping and integrating effects of several steroid hormones/receptors on accurate appetite regulation in future studies.

Free access

Guojun Shi, Chen Sun, Weiqiong Gu, Minglan Yang, Xiaofang Zhang, Nan Zhai, Yan Lu, Zhijian Zhang, Peishun Shou, Zhiguo Zhang and Guang Ning

Recent reports have highlighted the roles of free fatty acid receptor 2 (FFAR2) in the regulation of metabolic and inflammatory processes. However, the potential function of FFAR2 in type 1 diabetes (T1D) remains unexplored. Our results indicated that the mRNA level of FFAR2 was upregulated in peripheral blood mononuclear cells of T1D patients. The human FFAR2 promoter regions were cloned, and luciferase reporter assays revealed that NFκB activation induced FFAR2 expression. Furthermore, we showed that FFAR2 activation by overexpression induced cell apoptosis through ERK signaling. Finally, treatment with the FFAR2 agonists acetate or phenylacetamide 1 attenuated the inflammatory response in multiple-low-dose streptozocin-induced diabetic mice, and improved the impaired glucose tolerance. These results indicate that FFAR2 may play a protective role by inducing apoptosis of infiltrated macrophage in the pancreas through its feedback upregulation and activation, thus, in turn, improving glucose homeostasis in diabetic mice. These findings highlight FFAR2 as a potential therapeutic target of T1D, representing a link between immune response and glucose homeostasis.

Free access

Rui Wang, Jie Hong, Ruixin Liu, Maopei Chen, Min Xu, Wiqiong Gu, Yifei Zhang, Qinyun Ma, Feng Wang, Juan Shi, Jiqiu Wang, Weiqing Wang and Guang Ning

WNT/β-catenin signalling is involved in regulating adipogenesis, and its dysregulation occurs in obesity. Secreted frizzled-related protein 5 (SFRP5) is a WNT protein inhibitor; however, its role in adipogenesis and obesity is controversial. In this study, we observed that SFRP5 mRNA levels were increased in the fat tissues of obese humans and mice. Sfrp5 expression was gradually induced during differentiation of white and brown adipocytes and was highly increased in mature adipocytes rather than preadipocytes. However, the effects of the exogenous overexpression of Sfrp5 indicated that Sfrp5 may not directly regulate adipogenesis in vitro under the conditions studied. Moreover, SFRP5 did not inhibit the canonical WNT/β-catenin signalling pathway in preadipocytes. Subsequently, we measured the levels of circulating SFRP5 in obese patients and non-obese subjects using ELISA and did not find any significant difference. Collectively, these findings indicate that Sfrp5 represents a candidate for a mature adipocyte marker gene. Our data provide new evidence concerning the role of SFRP5 in adipogenesis of white and brown adipocytes and obesity.

Free access

Feng Wang, Xianfeng Zhang, Jiqiu Wang, Maopei Chen, Nengguang Fan, Qinyun Ma, Ruixin Liu, Rui Wang, Xiaoying Li, Mingyao Liu and Guang Ning

The circadian clock plays an important role in the liver by regulating the major aspects of energy metabolism. Currently, it is assumed that the circadian clock regulates metabolism mostly by regulating the expression of liver enzymes at the transcriptional level, but the underlying mechanism is not well understood. In this study, we showed that L gr4 homozygous mutant (L gr4 m/m) mice showed alteration in the rhythms of the respiratory exchange ratio. We further detected impaired plasma triglyceride rhythms in L gr4 m/m mice. Although no significant changes in plasma cholesterol rhythms were observed in the L gr 4 m/m mice, their cholesterol levels were obviously lower. This phenotype was further confirmed in the context of ob/ob mice, in which lack of LGR4 dampened circadian rhythms of triglyceride. We next demonstrated that Lgr 4 expression exhibited circadian rhythms in the liver tissue and primary hepatocytes in mice, but we did not detect changes in the expression levels or circadian rhythms of classic clock genes, such as C lock, Bmal1 (Arntl), P ers, Rev-erbs, and C rys, in L gr 4 m/m mice compared with their littermates. Among the genes related to the lipid metabolism, we found that the diurnal expression pattern of the M ttp gene, which plays an important role in the regulation of plasma lipid levels, was impaired in L gr 4 m/m mice and primary L gr 4 m/m hepatocytes. Taken together, our results demonstrate that LGR4 plays an important role in the regulation of plasma lipid rhythms, partially through regulating the expression of microsomal triglyceride transfer protein. These data provide a possible link between the peripheral circadian clock and lipid metabolism.

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Yingkai Sun, Rui Wang, Shaoqian Zhao, Wen Li, Wen Liu, Lingyun Tang, Zhugang Wang, Weiqing Wang, Ruixin Liu, Guang Ning, Jiqiu Wang and Jie Hong

Browning of white adipose tissue has been proven to be a potential target to fight against obesity and its metabolic commodities, making the exploration of molecules involved in browning process important. Among those browning agents reported recently, FGF21 play as a quite promising candidate for treating obesity for its obvious enhancement of thermogenic capacity in adipocyte and significant improvement of metabolic disorders in both mice and human. However, whether other members of fibroblast growth factor (FGF) family play roles in adipose thermogenesis and obese development is still an open question. Here, we examined the mRNA expression of all FGF family members in three adipose tissues of male C57BL/6 mice and found that FGF9 is highly expressed in adipose tissue and decreased under cold stress. Furthermore, FGF9 treatment inhibited thermogenic genes in the process of beige adipocytes differentiation from stromal vascular fraction (SVF) in a dose-dependent manner. Similar results were obtained with FGF9 overexpression. Consistently, knockdown of FGF9 in SVF cells by using lentiviral shRNA increased thermogenic genes in differentiated beige adipocytes. RNA sequencing analysis revealed a significant increment of hypoxia-inducible factor (HIF) pathway in the early stage of beige adipocytes differentiation under FGF9 treatment, which was validated by real-time PCR. FGF9 expression was increased in subcutaneous WAT of obese human and mice. This study shows that adipose-derived FGF9 play as an inhibitory role in the browning of white adipocytes. Activation of hypoxia signaling at early stage of adipose browning process may contribute to this anti-thermogenic effect of FGF9.