Zhijuan Ge

Erythropoietin (EPO) has beneficial effects on glucose metabolism and insulin resistance. However, the mechanism underlying these effects has not yet been elucidated. This study aimed to investigate how EPO affects hepatic glucose metabolism. Here, we report that EPO administration promoted phosphatidylinositol 3-kinase (PI3K)/AKT pathway activation in palmitic acid (PA)-treated HepG2 cells and in the liver of high-fat diet (HFD)-fed mice, whereas adenovirus-mediated silencing of the erythropoietin receptor (EPOR) blocked EPO-induced AKT signalling in HepG2 cells. Importantly, a peroxisome proliferator-activated receptor γ (PPARγ) antagonist and PPARγ small interfering RNA (siRNA) abrogated the EPO-induced increase in p-AKT in HepG2 cells. Lentiviral vector-mediated hepatic PPARγ silencing in HFD-fed C57BL/6 mice impaired EPO-mediated increases in glucose tolerance, insulin sensitivity and hepatic AKT activation. Furthermore, EPO activated the AMP-activated protein kinase (AMPK)/sirtuin 1 (SIRT1) signalling pathway, and AMPKα and SIRT1 knockdown each attenuated the EPO-induced PPARγ expression and deacetylation and PPARγ-dependent AKT activation in HepG2 cells. In summary, these findings suggest that PPARγ is involved in EPO/EPOR-induced AKT activation, and targeting the PPARγ/AKT pathway via EPO may have therapeutic implications for hepatic insulin resistance and type 2 diabetes.

Cancer cachexia as a metabolic syndrome can lead to at least 25% of cancer deaths. The inhibition of muscle atrophy is a main strategy to treat cancer cachexia. In this process, myostatin (MSTN) can exert a dual effect on protein metabolism, including inhibition of protein biosynthesis and enhancement of protein degradation. In this study, we will test the effect on muscle atrophy induced by cancer cachexia of IMB0901, a MSTN inhibitor. Two high-throughput screening models against MSTN were developed. By screening, IMB0901, 2-((1-(3,4-dichlorophenyl)-1H-pyrazolo [3,4-d] pyrimidin-4-yl) amino) butan-1-ol, was picked out from the compound library. The in vitro cell model and the C26 animal model of muscle atrophy induced by cancer cachexia were used to determine the pharmacological activity of IMB0901. Whether IMB0901 could inhibit the aggravating effect of doxorubicin on muscle wasting was examined in vitro and in vivo. IMB0901 inhibited the MSTN promoter activity, the MSTN signaling pathway, and the MSTN positive feedback regulation. In atrophied C2C12 myotubes, IMB0901 had a potent efficiency of decreasing MSTN expression and modulating MSTN signaling pathway which was activated by C26-conditioned medium (CM). In C2C12 myotubes, the expressions of three common myotube markers, myosin heavy chain (MyHC), myogenic differentiation 1 (MyoD), and myogenin (MyoG), were downregulated by CM, which could be efficiently reversed by IMB0901 via reduction of ubiquitin-mediated proteolysis and enhancement of AKT/mTOR-mediated protein synthesis. In the C26 animal model, IMB0901 mitigated the weight loss of body, quadricep and liver, and protected the quadriceps cell morphology. Furthermore, IMB0901 decreased the expression of two E3 ligases Atrogin-1 and MuRF-1 in the quadriceps in vivo. At the cellular level, IMB0901 had no influence on anti-tumor effect of three chemotherapeutic agents (cisplatin, doxorubicin, and gemcitabine) and lowered doxorubicin-induced upregulation of MSTN in C2C12 myotubes. IMB0901 did not affect the inhibitory effect of doxorubicin on C26 tumor and delayed the weight loss of muscle and adipose tissue caused by C26 tumor and doxorubicin. IMB0901 inhibits muscle atrophy induced by cancer cachexia by suppressing ubiquitin-mediated proteolysis and promoting protein synthesis. These findings collectively suggest that IMB0901 is a promising leading compound for the management of muscle atrophy induced by cancer cachexia.