Loss of mitofusin 2 links beta‐amyloid‐mediated mitochondrial fragmentation and Cdk5‐induced oxidative stress in neuron cells

Mitochondrial dysfunction is implicated in age‐related degenerative disorders such as Alzheimer's disease (AD). Maintenance of mitochondrial dynamics is essential for regulating mitochondrial function. Aβ oligomers (AβOs), the typical cause of AD, lead to mitochondrial dysfunction and neuronal loss. AβOs have been shown to induce mitochondrial fragmentation, and their inhibition suppresses mitochondrial dysfunction and neuronal cell death. Oxidative stress is one of the earliest hallmarks of AD. Cyclin‐dependent kinase 5 (Cdk5) may cause oxidative stress by disrupting the antioxidant system, including Prx2. Cdk5 is also regarded as a modulator of mitochondrial fission; however, a precise mechanistic link between Cdk5 and mitochondrial dynamics is lacking. We estimated mitochondrial morphology and alterations in mitochondrial morphology‐related proteins in Neuro‐2a (N2a) cells stably expressing the Swedish mutation of amyloid precursor protein (APP), which is known to increase AβO production. We demonstrated that mitochondrial fragmentation by AβOs accompanies reduced mitofusin 1 and 2 (Mfn1/2) levels. Interestingly, the Cdk5 pathway, including phosphorylation of the Prx2‐related oxidative stress, has been shown to regulate Mfn1 and Mfn2 levels. Furthermore, Mfn2, but not Mfn1, over‐expression significantly inhibits the AβO‐mediated cell death pathway. Therefore, these results indicate that AβO‐mediated oxidative stress triggers mitochondrial fragmentation via decreased Mfn2 expression by activating Cdk5‐induced Prx2 phosphorylation.

     

Glycerol‐3‐phosphate metabolism plays a role in stress response in the red alga Pyropia haitanensis

Glycerol‐3‐phosphate (G3P) has been suggested as a novel regulator of plant defense signaling, however, its role in algal resistance remains largely unknown. The glycerol kinase (also designated as NHO1) and NAD‐dependent G3P dehydrogenase (GPDH) are two key enzymes involved in the G3P biosynthesis. In our study, we cloned the full‐length cDNA of NHO1 (NHO1_Ph) and GPDH (GPDH_Ph) from the red alga Pyropia haitanensis (denoted as NHO1_Ph and GPDH_Ph) and examined their expression level under flagellin peptide 22 (flg22) stimulation or heat stress. We also measured the level of G3P and floridoside (a downstream product of G3P in P. haitanensis) under flg22 stimulation or heat stress. Both NHO1_Ph and GPDH_Ph shared high sequence identity and structural conservation with their orthologs from different species, especially from red algae. Phylogenetic analysis showed that NHO1s and GPDHs from red algae were closely related to those from animals. Under flg22 stimulation or heat stress, the expression levels of NHO1_Ph and GPDH_Ph were up‐regulated, G3P levels increased, and the contents of floridoside decreased. But the floridoside level increased in the recovery period after heat stress. Taken together, we found that G3P metabolism was associated with the flg22‐induced defense response and heat stress response in P. haitanensis, indicating the general conservation of defense response in angiosperms and algae. Furthermore, floridoside might also participate in the stress resistance of P. haitanensis.     

非生物胁迫下耐辐射异常球菌drB0118基因功能分析

【目的】鉴定和确定被预测为编码干燥相关蛋白的耐辐射异常球菌(Deinococcus radiodurans) drB0118基因功能,探讨该基因对盐、渗透和氧化胁迫抗性的作用。【方法】构建drB0118基因缺失突变株(ΔB0118),通过氯化钠、D-山梨糖醇和过氧化氢等胁迫冲击实验及氧化胁迫条件下qRT-PCR分析,研究drB0118突变对非生物胁迫反应及氧化胁迫相关基因表达的影响。【结果】drB0118突变导致菌株对NaCl和D-sorbitol胁迫的抗性降低;对氧化胁迫(H2O2)敏感;qRT-PCR分析显示,drB0118突变引起氧化胁迫抗性基因pod和oxyR分别下调4倍和10倍。【结论】D. radiodurans中drB0118参与了盐、渗透和氧化等多种非生物胁迫反应。     

敲除Nrf2促进高脂饮食诱导小鼠肝脏NF-kB的活化

目的：氧化应激和炎症反应是NASH进展的关键因素,同时二者之间存在着密切关系,而转录因子Nrf2和NF-kB分别是氧化应激和炎症信号通路的关键调控靶点,因此,研究Nrf2对高脂饮食诱导小鼠肝脏NF-kB信号通路的影响,对探讨NASH进展具有重要的意义。方法：雄性野生型（WT）和Nrf2基因敲除（Nrf2-/-）ICR小鼠各10只,随机分为WT对照组（Control）、Nrf2-/-对照组（KO）、WT高脂饮食组（HFD）和Nrf2-/-高脂饮食组（KOHFD）（n=5）。喂养8周后,观察肝脏光镜下改变,检测肝脏GSH、MDA、TNFα和IL-6水平。Western-Blot检测肝脏NF-kB蛋白表达水平,观察敲除Nrf2对肝脏NF-kB活性作用的影响。结果：1.光镜下观察,Control组与KO组小鼠肝脏结构无明显变化,HFD组小鼠肝脏呈现大片脂肪沉积和炎症细胞浸润,KOHFD组小鼠肝脏则呈现明显的大泡性变性,且炎症细胞浸润较HFD组明显加重;2.与Control组相比,KO组小鼠肝脏MDA轻度升高,GSH轻度降低,但无明显差异,而HFD组和KOHFD组小鼠肝脏MDA显著升高（P〈0.05）,GSH显著降低（P〈0.05）,且KOHFD组MDA明显高于HFD组（P〈0.05）,GSH明显低于HFD组（P〈0.05）。3.ELISA结果显示,与Control组相比,KO组小鼠肝脏TNFα和IL-6分泌轻度增加,而HFD组和KOHFD组小鼠肝脏TNFα与IL-6水平显著升高（P〈0.05）,且KOHFD组小鼠肝脏TNFα与IL-6显著高于HFD组（P〈0.05）;4.Western-Blot结果显示,Control组和KO组之间无明显差异,而KOHFD组和HFD组小鼠肝脏胞核NF-kB蛋白表达水平显著升高,且KOHFD组高于HFD组。结论：敲除Nrf2可以显著加重高脂饮食诱导的小鼠肝脏氧化应激水平,进而促进NF-kB的活化,从而为通过以Nrf2为靶点治疗NASH提供重要的实验依据。     

Proteomic analysis reveals tanshinone IIA enhances apoptosis of advanced cervix carcinoma CaSki cells through mitochondria intrinsic and endoplasmic reticulum stress pathways

Cervix cancer is the second most common cancer among women worldwide, whereas paclitaxel, the first line chemotherapeutic drug used to treat cervical cancer, shows low chemosensitivity on the advanced cervical cancer cell line. Tanshinone IIA (Tan IIA) exhibited strong growth inhibitory effect on CaSki cells (IC₅₀ = 5.51 μM) through promoting caspase cascades with concomitant upregulating the phosphorylation of p38 and JNK signaling. Comprehensive proteomics revealed the global protein changes and the network analysis implied that Tan IIA treatment would activate ER stress pathways that finally lead to apoptotic cell death. Moreover, ER stress inhibitor could alleviate Tan IIA caused cell growth inhibition and ameliorate C/EBP‐homologous protein as well as apoptosis signal‐regulating kinase 1 mediated cell death. The therapeutic interventions targeting the mitochondrial‐related apoptosis and ER stress responses might be promising strategies to conquer paclitaxel resistance.     

1O2-Mediated and EXECUTER-Dependent Retrograde Plastid-to-Nucleus Signaling in Norflurazon-Treated Seedlings of Arabidopsis thaliana

Chloroplast development depends on the synthesis and import of a large number of nuclear-encoded pro- teins. The synthesis of some of these proteins is affected by the functional state of the plastid via a process known as retrograde signaling. Retrograde plastid-to-nucleus signaling has been often characterized in seedlings of Arabidopsis thaliana exposed to norflurazon （NF）, an inhibitor of carotenoid biosynthesis. Results of this work suggested that, throughout seedling development, a factor is released from the plastid to the cytoplasm that indicates a perturbation of plastid homeostasis and represses nuclear genes required for normal chloroplast development. The identity of this factor is still under debate. Reactive oxygen species （ROS） were among the candidates discussed as possible retrograde signals in NF-treated plants. In the present work, this proposed role of ROS has been analyzed. In seedlings grown from the very beginning in the presence of NF, ROS-dependent signaling was not detectable, whereas, in seedlings first exposed to NF after light-dependent chloroplast formation had been completed, enhanced ROS production occurred and, among oth- ers, 1O2-mediated and EXECUTER-dependent retrograde signaling was induced. Hence, depending on the developmental stage at which plants are exposed to NF, different retrograde signaling pathways may be activated, some of which are also active in non-treated plants under light stress.     

Autophagy and ethanol neurotoxicity

Excessive ethanol exposure is detrimental to the brain. The developing brain is particularly vulnerable to ethanol such that prenatal ethanol exposure causes fetal alcohol spectrum disorders (FASD). Neuronal loss in the brain is the most devastating consequence and is associated with mental retardation and other behavioral deficits observed in FASD. Since alcohol consumption during pregnancy has not declined, it is imperative to elucidate the underlying mechanisms and develop effective therapeutic strategies. One cellular mechanism that acts as a protective response for the central nervous system (CNS) is autophagy. Autophagy regulates lysosomal turnover of organelles and proteins within cells, and is involved in cell differentiation, survival, metabolism, and immunity. We have recently shown that ethanol activates autophagy in the developing brain. The autophagic preconditioning alleviates ethanol-induced neuron apoptosis, whereas inhibition of autophagy potentiates ethanol-stimulated reactive oxygen species (ROS) and exacerbates ethanol-induced neuroapoptosis. The expression of genes encoding proteins required for autophagy in the CNS is developmentally regulated; their levels are much lower during an ethanol-sensitive period than during an ethanol-resistant period. Ethanol may stimulate autophagy through multiple mechanisms; these include induction of oxidative stress and endoplasmic reticulum stress, modulation of MTOR and AMPK signaling, alterations in BCL2 family proteins, and disruption of intracellular calcium (Ca2+) homeostasis. This review discusses the most recent evidence regarding the involvement of autophagy in ethanol-mediated neurotoxicity as well as the potential therapeutic approach of targeting autophagic pathways.     

Autophagy activity contributes to programmed cell death in Caenorhabditis elegans

The physiological relationship between autophagy and programmed cell death during C. elegans development is poorly understood. In C. elegans, 131 somatic cells and a large number of germline cells undergo programmed cell death. Autophagy genes function in the removal of somatic cell corpses during embryogenesis. Here we demonstrated that autophagy activity participates in germ-cell death induced by genotoxic stress. Upon γ ray treatment, fewer germline cells execute the death program in autophagy mutants. Autophagy also contributes to physiological germ-cell death and post-embryonic cell death in ventral cord neurons when ced-3 caspase activity is partially compromised. Our study reveals that autophagy activity contributes to programmed cell death during C. elegans development.