Neuregulin 4 Attenuates Podocyte Injury and Proteinuria in Part by Activating AMPK/mTOR-Mediated Autophagy in Mice.

In this study, we investigate the effect of neuregulin 4 (NRG4) on podocyte damage in a mouse model of diabetic nephropathy (DN) and we elucidate the underlying molecular mechanisms. In vivo experiments were conducted using a C57BL/6 mouse model of DN to determine the effect of NRG4 on proteinuria and podocyte injury, and in vitro experiments were performed with conditionally immortalized mouse podocytes treated with high glucose and NRG4 to assess the protective effects of NRG4 on podocyte injury. Autophagy-related protein levels and related signaling pathways were evaluated both in vivo and in vitro. The involvement of the adenosine monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway was detected using chloroquine or AMPK inhibitors. The results showed that the AMPK/mTOR pathway was involved in the protective roles of NRG4 against high glucose-mediated podocyte injury. Also, NRG4 significantly decreased albuminuria in DN mice. PAS staining indicated that NRG4 mitigated glomerular volume and mesangium expansion in DN mice. Consistently, western blot and RT-PCR analyses confirmed that NRG4 decreased the expression of pro-fibrotic molecules in the glomeruli of DN mice. The immunofluorescence results showed that NRG4 retained expression of podocin and nephrin, whereas transmission electron microscopy revealed that NRG4 alleviated podocyte injury. In DN mice, NRG4 decreased podocyte apoptosis and increased expression of nephrin and podocin, while decreasing the expression of desmin and HIF1α. Overall, NRG4 improved albuminuria, glomerulosclerosis, glomerulomegaly, and hypoxia in DN mice. The in vitro experiments showed that NRG4 inhibited HG-induced podocyte injury and apoptosis. Furthermore, autophagy of the glomeruli decreased in DN mice, but reactivated following NRG4 intervention. NRG4 intervention was found to partially activate autophagy via the AMPK/mTOR signaling pathway. Consequently, when the AMPK/mTOR pathway was suppressed or autophagy was inhibited, the beneficial effects of NRG4 intervention on podocyte injury were diminished. These results indicate that NRG4 intervention attenuates podocyte injury and apoptosis by promoting autophagy in the kidneys of DN mice, in part, by activating the AMPK/mTOR signaling pathway.

Deng J ，Yang Q ，Zhu W ，Zhang Y ，Lin M ，She J ，Li J ，Xiao Y ，Xiao J ，Xu X ，He H ，Zhu B ，Ding Y ... -  《-》

Sweroside attenuates podocyte injury and proteinuria in part by activating Akt/BAD signaling in mice.

Huang M ，Yang Y ，Chen Y ，Li Y ，Qin S ，Xiao L ，Long X ，Hu K ，Li Y ，Ying H ，Ding Y ... -  《-》

Mangiferin prevents diabetic nephropathy progression and protects podocyte function via autophagy in diabetic rat glomeruli.

Diabetic nephropathy (DN) is one of the most severe microangiopathies of diabetes mellitus and is a leading cause of end stage renal disease. Numerous studies suggest that podocyte injury contributes to progressive proteinuria. Podocytes are highly specialized, terminally differentiated cells that are unable to proliferate, autophagy plays a key role in maintaining the structure and function of podocytes. Autophagy impairment is involved in the pathogenesis of podocyte loss, which leads to massive proteinuria in DN. In the present study, we investigated the effects of mangiferin on nephropathy in streptozotocin (STZ)-induced diabetic rats; we focused on pathological factors related to autophagy in podocytes and the AMPK-mTOR-ULK1 pathway. The results showed that chronic treatment with mangiferin significantly decreased albuminuria, inhibited glomerular extracellular matrix expansion and restored the expression of nephrin, a podocyte marker, in diabetic rats; these results suggest that mangiferin delayed the process of DN and protected the podocytes. In addition, mangiferin induced autophagy, as shown by the up-regulation of LC3 II and the down-regulation of p62 in both DN rats and podocytes. Transmission electron microscope analyses showed that mangiferin increased the number of autophagosomes in the podocytes of DN rats. This underlying mechanism was associated with the up-regulation of AMPK phosphorylation, the down-regulation of mTOR phosphorylation and the up-regulation of p-ULK1. Taken together, mangiferin delayed the progression of DN and protected the podocytes by enhancing autophagy under diabetic conditions via the AMPK-mTOR-ULK1 pathway. These findings provide new insights into the molecular mechanisms underlying the renoprotective effects of mangiferin in DN.

Wang X ，Gao L ，Lin H ，Song J ，Wang J ，Yin Y ，Zhao J ，Xu X ，Li Z ，Li L ... -  《-》

Inhibition of high mobility group box 1 (HMGB1) attenuates podocyte apoptosis and epithelial-mesenchymal transition by regulating autophagy flux.

Podocyte injury, characterized by podocyte hypertrophy, apoptosis, and epithelial-mesenchymal transition (EMT), is the major causative factor of diabetic nephropathy (DN). Autophagy dysfunction is regarded as the major risk factor for podocyte injury including EMT and apoptosis. High mobility group box 1 (HMGB1) is involved in the progression of DN through the induction of autophagy. However, the underlying mechanism remains unknown. Plasma HMGB1 concentrations were determined in DN patients using ELISA. Apoptosis of DN serum-treated podocytes was evaluated by flow cytometry. Podocyte autophagy flux was measured using immunofluorescence. Western blotting analysis was used to investigate HMGB1 expression, EMT, and autophagy-related signaling pathways. Upregulation of HMGB1 was found in DN patients and DN serum-treated podocytes. Removal of HMGB1 inhibited DN serum-mediated podocyte apoptosis by inhibiting autophagy and activating AKT/mammalian target of rapamycin (mTOR) signaling. In addition, HMGB1 depletion repressed the progression of podocyte EMT by inhibiting transforming growth factor (TGF)-β/smad1 signaling in vitro and in vivo. The combination of HMGB1 short interference (si) RNA and the autophagy activator rapamycin protected against podocyte apoptosis and EMT progression by inhibiting the AKT/mTOR and TGF-β/smad signaling pathway, respectively. Although HMGB1 siRNA and rapamycin treatment had opposite effects on autophagy and AKT/mTOR signaling, there was no contradiction about the role of HMGB1 siRNA and rapamycin on AKT/mTOR pathway because autophagy and AKT/mTOR signaling play dual roles in intracellular biological processes. Based on the findings of this study, we may assume that HMGB1-initiated autophagy is harmful, whereas rapamycin is beneficial to podocyte survival. Possibly combined treatment with HMGB1 siRNA and rapamycin improved podocyte damage and EMT by regulating autophagy homeostasis.

Jin J ，Gong J ，Zhao L ，Zhang H ，He Q ，Jiang X ... -  《-》

Neuregulin 4 alleviates hepatic steatosis via activating AMPK/mTOR-mediated autophagy in aged mice fed a high fat diet.

Neuregulin 4 (Nrg4) is a brown fat-enriched endocrine factor that exerts beneficial metabolic effects on insulin resistance and hepatic steatosis. Autophagy is a mechanism that is essential for preventing hepatic steatosis. The aim of this study was to explore whether Nrg4 ameliorates hepatic steatosis by inducing autophagy. Aged C57BL/6 mice were maintained on a high fat diet with or without Nrg4 intervention for 3 months. Lipid accumulation in the liver was investigated. Autophagy related protein levels along with related signaling pathways that regulate autophagy were evaluated. In addition, the effects of Nrg4 on autophagy were also determined in cultured L-02 cells. Nrg4 decreased high-fat induced intrahepatic lipid content both in vivo and in vitro. Autophagy level in the liver also decreased in obese mice and Nrg4 intervention reactivated autophagy. Further, Nrg4 intervention was found to have activated autophagy via the adenosine monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) signaling pathway. Moreover, when the AMPK/mTOR pathway was suppressed or autophagy was inhibited, the beneficial effects of Nrg4 intervention on hepatic steatosis were diminished. These results indicated that Nrg4 intervention attenuated hepatic steatosis by promoting autophagy in the liver of aged obese mice. Additionally, Nrg4 induced autophagy via the AMPK/mTOR signaling pathway.

Zhu B ，Mei W ，Jiao T ，Yang S ，Xu X ，Yu H ，Ding Y ，Guo S ，Meng B ，Zhao L ，He M ，Dong K ，Guo H ，Guo X ，Zhang H ，Dang R ，Xiang G ，Wen N ... -  《-》