Progranulin (PGRN) has recently emerged as an important regulator for insulin resistance. However, the direct effect of PGRN in vivo and the underlying role of progranulin in adipose insulin resistance involving the autophagy mechanism is not fully understood. In this study, mice treated with PGRN for 21 days exhibited the impaired glucose tolerance and insulin sensitivity, remarkable adipose autophagy as well as attenuated insulin signaling via inhibition of mammalian target of rapamycin (mTOR) pathway. Furthermore, blockade of tumor necrosis factor receptor 1 (TNFR1) by TNFR1BP-Fc injection resulted in the restoration of impaired insulin sensitivity and insulin signaling induced by PGRN. Consistent with these findings in vivo, PGRN treatment induced defective insulin signaling, abnormal autophagic and mitochondrial activity in cultured adipocytes, while such effects were nullified by the blockade of TNFR1. In addition, PGRN-deficient adipocytes were more refractory to tunicamycin- or dexamethasone-induced insulin resistance, indicating the causative role of the TNFR1 pathway in the action of PGRN. Collectively, our findings support the notion that PGRN is a key regulator of insulin resistance and that PGRN may mediate its effects, at least in part, by inducing autophagy via the TNFR1-dependent mechanism.
Bo Zhou, Huixia Li, Jiali Liu, Lin Xu, Qinyue Guo, Hongzhi Sun, and Shufang Wu
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.
Bo Li, Yue Zhou, Jing Chen, Tingting Wang, Zhijuan Li, Yili Fu, Aixia Zhai, and Changlong Bi
Diabetic foot ulcer (DFU) is a chronic and non-healing complication of diabetes that leads to high hospital costs and, in extreme cases, to amputation. Recent studies have reported that long non-coding RNAs (lncRNAs) are linked to various diabetes-related symptoms. Thus, we aim to explore the role of lncRNA H19 in the wound healing process following DFU. Fibroblasts were isolated from the ulcer margin tissues of DFU patients, with the expression of lncRNA H19, connective tissue growth factor (CTGF) or serum response factor (SRF) altered by lentivirus infection. Next, rat models of DFU induced by high glucose and lipid diet were established, which was also infected with the corresponding lentivirus. The interaction among lncRNA H19, SRF and CTGF was determined. Afterward, cell proliferation and apoptosis, angiogenesis, ECM remodeling and wound healing in DFU tissues were evaluated to explore the effects of lncRNA H19/SRF/CTGF and MAPK signaling pathway on DFU. CTGF was poorly expressed in ulcer tissues from DFU rats and patients. CTGF overexpression was shown to activate the MAPK signaling pathway to promote cell proliferation, ECM remodeling, angiogenesis and wound healing while inhibiting cell apoptosis. lncRNA H19 was validated to elevate CTGF expression by recruiting SRF to the promoter region of CTGF, thus accelerating cell proliferation, ECM remodeling and wound healing while repressing cell apoptosis. Furthermore, MAPK signaling pathway activation is confirmed to be the underlying mechanism behind lncRNA H19/CTGF/SRF-induced results. Thus, lncRNA H19 accelerated wound healing in DFU through elevation of CTGF and activation of the MAPK signaling pathway.
Hui Juan Zhu, Hui Pan, Xu Zhe Zhang, Nai Shi Li, Lin Jie Wang, Hong Bo Yang, and Feng Ying Gong
Myostatin is a critical negative regulator of skeletal muscle development, and has been reported to be involved in the progression of obesity and diabetes. In the present study, we explored the effects of myostatin on the proliferation and differentiation of 3T3-L1 preadipocytes by using 3-[4,5-dimethylthiazol-2-yl] 2,5-diphenyl tetrazolium bromide spectrophotometry, intracellular triglyceride (TG) assays, and real-time quantitative RT-PCR methods. The results indicated that recombinant myostatin significantly promoted the proliferation of 3T3-L1 preadipocytes and the expression of proliferation-related genes, including Cyclin B2, Cyclin D 1, Cyclin E1, Pcna, and c-Myc, and IGF1 levels in the medium of 3T3-L1 were notably upregulated by 35.2, 30.5, 20.5, 33.4, 51.2, and 179% respectively (all P<0.01) in myostatin-treated 3T3-L1 cells. Meanwhile, the intracellular lipid content of myostatin-treated cells was notably reduced as compared with the non-treated cells. Additionally, the mRNA levels of Ppar γ, Cebp α, Gpdh, Dgat, Acs1, Atgl, and Hsl were significantly downregulated by 22–76% in fully differentiated myostatin-treated adipocytes. Finally, myostatin regulated the mRNA levels and secretion of adipokines, including Adiponectin, Resistin, Visfatin, and plasminogen activator inhibitor-1 (PAI-1) in 3T3-L1 adipocytes (all P<0.001). Above all, myostatin promoted 3T3-L1 proliferation by increasing the expression of cell-proliferation-related genes and by stimulating IGF1 secretion. Myostatin inhibited 3T3-L1 adipocyte differentiation by suppressing Ppar γ and Cebp α expression, which consequently deceased lipid accumulation in 3T3-L1 cells by inhibiting the expression of critical lipogenic enzymes and by promoting the expression of lipolytic enzymes. Finally, myostatin modulated the expression and secretion of adipokines in fully differentiated 3T3-L1 adipocytes.
Yousheng Xu, Yongshun Wang, Jingjin Liu, Wei Cao, Lili Li, Hongwei Du, Enbo Zhan, Ruoxi Zhang, Huimin Liu, Maoen Xu, Tao Chen, Yilin Qu, and Bo Yu
The prevalence of obesity is dramatic increased and strongly associated with cardiovascular disease. Adipokines, secreted from adipose tissues, are critical risk factors for the development of cardiomyopathy. Present study aimed to investigate the pathophysiological role of autotaxin in obesity-related cardiomyopathy. In high-fat diet-fed mice, autotaxin was mainly synthesized and secreted from adipocytes. The increased accumulation of cardiac autotaxin was positively associated with cardiac dysfunction in obese mice. Interestingly, specific blockage of adipose tissue autotaxin effectively protected against high-fat diet-induced cardiac structural disorders, left ventricular hypertrophy and dysfunction. Inhibition of autotaxin further improved high-fat diet-induced cardiac fibrosis and mitochondrial dysfunction, including improvement of mitochondrial structure, mass and activities. Our findings demonstrated intervention of adipose tissue biology could influence cardiac modification in obese mice, and adipocyte-derived autotaxin was a potential diagnostic marker and therapeutic target for obesity-related cardiomyopathy.
Jie Sun, Yan Liu, Jinhui Yu, Jin Wu, Wenting Gao, Liyuan Ran, Rujiao Jiang, Meihua Guo, Dongyu Han, Bo Liu, Ning Wang, Youwei Li, He Huang, Li Zeng, Ying Gao, Xin Li, and Yingjie Wu
Astragalus polysaccharide (APS) is the main component of Astragalus membranaceus, an anti-diabetic herb being used for thousands of years in Traditional Chinese medicine (TCM). In this study, we aimed to evaluate the impact of APS on hepatic insulin signaling, autophagy and ER stress response in high-fat-diet (HFD)-induced insulin resistance (IR) mice. APS was intra-gastrically administrated and metformin was used as a control medicine. Apart from monitoring the changes in the important parameters of IR progression, the gene and protein expression of the key factors marking the state of hepatic ER stress and autophagic flux were examined. We found that, largely comparable to the metformin regime, APS treatment resulted in an overall improvement of IR, as indicated by better control of body weight and blood glucose/lipid levels, recovery of liver functions and regained insulin sensitivity. In particular, the excessive and pro-apoptotic ER stress response and inhibition of autophagy, as a result of prolonged HFD exposure, were significantly corrected by APS administration, indicating a switch of the cellular fate in favor of cell survival. Using the HepG2/IR cell model, we demonstrated that APS modulated the insulin-initiated phosphorylation cascades in a similar manner to metformin. This study provides a rationale for exploiting the insulin-sensitizing potential of APS, which has a therapeutic performance almost equivalent to metformin, to enrich our options in the treatment of IR.