alpha-Synuclein, oxidative stress and apoptosis from the perspective of a yeast model of Parkinson's disease

The neuronal protein α-synuclein (α-syn) has been suggested to be one of the factors linked to Parkinson's disease (PD). Several organisms, including the rat, mouse, worm, and fruit fly, are being used to study α-syn pathobiology. A new model organism was recently added to this armamentarium: the budding yeast Saccharomyces cerevisiae . The yeast system recapitulates many of the findings made with higher eukaryotes. For example, yeast cells expressing α-syn accumulate lipid droplets, have vacuolar/lysosomal defects, and exhibit markers of apoptosis, including the externalization of phosphatidylserine, the release of cytochrome c , and the accumulation of reactive oxygen species. This MiniReview focuses on the mechanisms by which α-syn induces oxidative stress and the mechanisms by which yeast cells respond to this stress. Three classes of therapeutics are discussed.     

Capsaicin stimulates glucose uptake in C2C12 muscle cells via the reactive oxygen species (ROS)/AMPK/p38 MAPK pathway

Capsaicin has been reported to regulate blood glucose levels and to ameliorate insulin resistance in obese mice. This study demonstrates that capsaicin increases glucose uptake directly by activating AMP-activated protein kinase (AMPK) in C2C12 muscle cells, which manifested as an attenuation of glucose uptake when compound C, an AMPK inhibitor, was co-administered with capsaicin. However, the insulin signaling molecules insulin receptor substrate-1 (IRS-1) and Akt were not affected by capsaicin. Additional results showed that p38 mitogen-activated protein kinase (MAPK) is also involved in capsaicin-induced glucose transport downstream of AMPK because capsaicin increased p38 MAPK phosphorylation significantly and its specific inhibitor SB203580 inhibited capsaicin-mediated glucose uptake. Treatment with an AMPK inhibitor reduced p38 MAPK phosphorylation, but the p38 MAPK inhibitor had no effect on AMPK. Capsaicin stimulated ROS generation in C2C12 muscle cells, and when ROS were captured using the nonspecific antioxidant NAC, the increase in both capsaicin-induced AMPK phosphorylation and capsaicin-induced glucose uptake was attenuated, suggesting that ROS function as an upstream activator of AMPK. Taken together, these results suggest that capsaicin, independent of insulin, increases glucose uptake via ROS generation and consequent AMPK and p38 MAPK activations.     

Melatonin protects hepatocytes against bile acid-induced mitochondrial oxidative stress via the AMPK-SIRT3-SOD2 pathway

Abstract

Mitochondrial oxidative damage is hypothesized to contribute to the pathogenesis of chronic cholestatic liver diseases. Melatonin, an indolamine synthesized in the pineal gland, shows a wide range of physiological functions, and is under clinical investigation for expanded applications. Melatonin has demonstrated efficient protective effects against various types of oxidative damage in the liver system. This study investigates the protective effects of melatonin pretreatment on glycochenodeoxycholic acid (GCDCA)-induced hepatotoxicity and elucidates the potential mechanism of melatonin-mediated protection. Melatonin markedly decreased mitochondrial ROS (mROS) production in L02 cells treated with 100 μM GCDCA, and inhibited GCDCA-stimulated cytotoxicity. Notably, melatonin exerted its hepatoprotective effects by upregulating sirtuin 3 (SIRT3) activity and its expression level, thus regulating superoxide dismutase 2 (SOD2) acetylation and inhibiting the production of mROS induced by GCDCA. Moreover, siRNA targeting SIRT3 blocked the melatonin-mediated elevation in mitochondrial function by inhibiting SIRT3/SOD2 signaling. Importantly, melatonin-activated SIRT3 activity was completely abolished by AMP-activated, alpha 1 catalytic subunit (AMPK) siRNA transfection. Similar results were obtained in rat with bile duct ligation or BDL. In summary, our findings indicate that melatonin is a novel hepatoprotective small molecule that functions by elevating SIRT3, stimulating SOD2 activity, and suppressing mitochondrial oxidative stress at least through AMPK, and that SIRT3 may be of therapeutic value in liver cell protection for GCDCA-induced hepatotoxicity.     

Silibinin activates AMP-activated protein kinase to protect neuronal cells from oxygen and glucose deprivation-re-oxygenation

In this study, we explored the cytoprotective potential of silibinin against oxygen–glucose deprivation (OGD)-induced neuronal cell damages, and studied underling mechanisms. In vitro model of ischemic stroke was created by keeping neuronal cells (SH-SY5Y cells and primary mouse cortical neurons) in an OGD condition followed by re-oxygenation. Pre-treatment of silibinin significantly inhibited OGD/re-oxygenation-induced necrosis and apoptosis of neuronal cells. OGD/re-oxygenation-induced reactive oxygen species (ROS) production and mitochondrial membrane potential (MMP) reduction were also inhibited by silibinin. At the molecular level, silibinin treatment in SH-SY5Y cells and primary cortical neurons led to significant AMP-activated protein kinase (AMPK) signaling activation, detected by phosphorylations of AMPKα1, its upstream kinase liver kinase B1 (LKB1) and the downstream target acetyl-CoA Carboxylase (ACC). Pharmacological inhibition or genetic depletion of AMPK alleviated the neuroprotective ability of silibinin against OGD/re-oxygenation. Further, ROS scavenging ability by silibinin was abolished with AMPK inhibition or silencing. While A-769662, the AMPK activator, mimicked silibinin actions and suppressed ROS production and neuronal cell death following OGD/re-oxygenation. Together, these results show that silibinin-mediated neuroprotection requires activation of AMPK signaling.     

Elevated Levels of the Reactive Metabolite Methylglyoxal Recapitulate Progression of Type 2 Diabetes

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马里苷、黄诺玛苷对db/db小鼠肠道菌群的影响及相关性

目的探索两色金鸡菊中黄酮类成分马里苷、黄诺玛苷对db/db小鼠肠道菌群的影响。方法将db/m小鼠作为正常对照组,db/db小鼠分为db/db模型组、db/db+恩格列净(db/db+Empagliflozin)组、db/db+马里苷(db/db+Marein)组、db/db+黄诺玛苷(db/db+Flavanomarein)组,每组8只。采用实时荧光定量PCR(RT-qPCR)的方法检测小鼠粪样中Bacteroides ovatus、Ruminococcus gnavus的变化,并运用Pearson检验分析Bacteroides ovatus、Ruminococcus gnavus的变化与2型糖尿病相关表型的相关性。结果 (1)干预12周后与db/m组相比,db/db组小鼠粪样中Bacteroides ovatus水平显著降低(P0.010);恩格列净(P0.001)、马里苷(P0.050)、黄诺玛苷(P0.001)干预后能显著升高其含量,差异具有统计学意义。(2)与db/m组相比,db/db组小鼠粪样中Ruminococcus gnavus水平显著升高(P0.050);恩格列净(P0.050)、马里苷(P0.050)干预后能显著降低其含量,差异具有统计学意义。(3)Bacteroides ovatus水平与空腹血糖(FBG)、三酰甘油(TG)呈负相关(r=-0.420,P=0.021;r=-0.474,P=0.008);Ruminococcus gnavus水平与FBG、TG呈正相关(r=0.397,P=0.030;r=0.404,P=0.027)。结论马里苷、黄诺玛苷可以调节小鼠肠道菌群的变化,这可能是其抗糖尿病的重要机制。     

AMPKα1 Deletion Shortens Erythrocyte Life Span in Mice: ROLE OF OXIDATIVE STRESS*

AMP-activated protein kinase (AMPK) is an energy sensor essential for maintaining cellular energy homeostasis. Here, we report that AMPKα1 is the predominant isoform of AMPK in murine erythrocytes and mice globally deficient in AMPKα1 (AMPKα1^−/−), but not in those lacking AMPKα2, and the mice had markedly enlarged spleens with dramatically increased proportions of Ter119-positive erythroid cells. Blood tests revealed significantly decreased erythrocyte and hemoglobin levels with increased reticulocyte counts and elevated plasma erythropoietin concentrations in AMPKα1^−/− mice. The life span of erythrocytes from AMPKα1^−/− mice was less than that in wild-type littermates, and the levels of reactive oxygen species and oxidized proteins were significantly increased in AMPKα1^−/− erythrocytes. In keeping with the elevated oxidative stress, treatment of AMPKα1^−/− mice with the antioxidant, tempol, resulted in decreased reticulocyte counts and improved erythrocyte survival. Furthermore, the expression of Foxo3 and reactive oxygen species scavenging enzymes was significantly decreased in erythroblasts from AMPKα1^−/− mice. Collectively, these results establish an essential role for AMPKα1 in regulating oxidative stress and life span in erythrocytes.