Multi-subunit assembly of the Pyrococcus furiosus small heat shock protein is essential for cellular protection at high temperature

The hyperthermophilic archaeon, Pyrococcus furiosus, expresses a small, alpha-crystallin-like protein in response to exposure to extreme temperatures, above 103 degrees C. The P. furiosus small heat shock protein (Pfu-sHSP) forms large oligomeric complexes. Based on the available crystal structures of the Methanocaldococcus jannaschii and wheat sHSPs, the protruding carboxy terminal domain is probably involved in subunit interactions. We constructed Pfu-sHSP mutants to analyze chaperone function and to study multi-subunit assembly. The results confirmed that the carboxy terminus of Pfu-sHSP is involved in inter-dimer interactions, whereas the amino terminal deletion mutant still exhibited the wild-type assembly characteristics. The ability to form oligomeric complexes via the carboxy terminal domain was shown to be necessary for thermotolerance of Escherichia coli overexpressing Pfu-sHSP. The amino terminal domain was not required for inter-species thermotolerance.     

Redundant and nonredundant functions of ATM and H2AX in αβ T-lineage lymphocytes

The ataxia telangiectasia mutated (ATM) kinase and H2AX histone tumor suppressor proteins are each critical for maintenance of cellular genomic stability and suppression of lymphomas harboring clonal translocations. ATM is the predominant kinase that phosphorylates H2AX in chromatin around DNA double-strand breaks, including along lymphocyte Ag receptor loci cleaved during V(D)J recombination. However, combined germline inactivation of Atm and H2ax in mice causes early embryonic lethality associated with substantial cellular genomic instability, indicating that ATM and H2AX exhibit nonredundant functions in embryonic cells. To evaluate potential nonredundant roles of ATM and H2AX in somatic cells, we generated and analyzed Atm-deficient mice with conditional deletion of H2ax in αβ T-lineage lymphocytes. Combined Atm/H2ax inactivation starting in early-stage CD4(-)/CD8(-) thymocytes resulted in lower numbers of later-stage CD4(+)/CD8(+) thymocytes, but led to no discernible V(D)J recombination defect in G1 phase cells beyond that observed in Atm-deficient cells. H2ax deletion in Atm-deficient thymocytes also did not affect the incidence or mortality of mice from thymic lymphomas with clonal chromosome 14 (TCRα/δ) translocations. Yet, in vitro-stimulated Atm/H2ax-deficient splenic αβ T cells exhibited a higher frequency of genomic instability, including radial chromosome translocations and TCRβ translocations, compared with cells lacking Atm or H2ax. Collectively, our data demonstrate that both redundant and nonredundant functions of ATM and H2AX are required for normal recombination of TCR loci, proliferative expansion of developing thymocytes, and maintenance of genomic stability in cycling αβ T-lineage cells.     

血红蛋白的化学修饰与血液代用品

血液代用品系指具有携氧扩容功效的溶液,包括：氟碳化合物、脂质体包封血红蛋白（hemoglobin,Hb)、微囊化血红蛋白和无细胞基质血红蛋白（化学修饰Ｈb、基因重组Ｈb、化学合成Ｈb和转基因动物人Ｈb）。通过化学修饰稳定血红蛋白结构以避免其肾毒性,并延长循环半寿期是利用无基质血红蛋白制备血液代用品的主要研究内容,通常采用交联、聚合、偶联等方法完成。     

Shear stress regulates endothelial cell autophagy via redox regulation and Sirt1 expression

Disturbed cell autophagy is found in various cardiovascular disease conditions. Biomechanical stimuli induced by laminar blood flow have important protective actions against the development of various vascular diseases. However, the impacts and underlying mechanisms of shear stress on the autophagic process in vascular endothelial cells (ECs) are not entirely understood. Here we investigated the impacts of shear stress on autophagy in human vascular ECs. We found that shear stress induced by laminar flow, but not that by oscillatory or low-magnitude flow, promoted autophagy. Time-course analysis and flow cessation experiments confirmed that this effect was not a transient adaptive stress response but appeared to be a sustained physiological action. Flow had no effect on the mammalian target of rapamycin-ULK pathway, whereas it significantly upregulated Sirt1 expression. Inhibition of Sirt1 blunted shear stress-induced autophagy. Overexpression of wild-type Sirt1, but not the deacetylase-dead mutant, was sufficient to induce autophagy in ECs. Using both of gain- and loss-of-function experiments, we showed that Sirt1-dependent activation of FoxO1 was critical in mediating shear stress-induced autophagy. Shear stress also induced deacetylation of Atg5 and Atg7. Moreover, shear stress-induced Sirt1 expression and autophagy were redox dependent, whereas Sirt1 might act as a redox-sensitive transducer mediating reactive oxygen species-elicited autophagy. Functionally, we demonstrated that flow-conditioned cells are more resistant to oxidant-induced cell injury, and this cytoprotective effect was abolished after inhibition of autophagy. In summary, these results suggest that Sirt1-mediated autophagy in ECs may be a novel mechanism by which laminar flow produces its vascular-protective actions.Vascular endothelial cells (ECs) are fundamentally important in maintaining structural and functional homeostasis of blood vessels. Normal biological functions of ECs are highly sensitive to the biomechanical stimuli induced by blood flow, of which shear stress acting on the surface of EC has been recognized to be one of the most important vasoactive factors in EC.^{1, 2} A relatively high level of laminar shear stress is cytoprotective, whereas abnormal (low-magnitude or oscillatory) shear stress is a detrimental cellular stress to ECs.¹ Transduction of the mechanical signals involves multiple messenger molecules and signaling proteins, which collectively regulate important endothelial functions, such as gene expression, proliferation, migration, morphogenesis, permeability, thrombogenicity, and inflammation.²Autophagy (also known as macroautophagy) is an evolutionarily conserved cellular stress response.^{3, 4} Autophagy is a cellular self-digestion process, which is responsible for degradation of misfolded proteins and damaged organelles. Autophagic process is mainly mediated by the formation of autophagosome, a double-membrane vacuole structure containing engulfed cellular components. This process requires expression of a group of key genes involved in autophagy, including LC3A, beclin-1, Atg5, Atg7, and Atg12, for example.^{3, 5} Autophagosomes fuse with lysosomes, forming autolysosomes, where the cellular components are degraded by various hydrolases in an acidified environment.^{4, 5} In ECs, an autophagic response can be initiated by different stress stimuli.^{6, 7, 8} It is noted that the cellular outcome following autophagy induction in ECs varies depending on the nature of stimuli and specific experimental settings.^{6, 7, 9, 10} Moreover, there is evidence showing that autophagy may also be involved in modulating other EC functions such as angiogenesis and cellular senescence.^{11, 12} Therefore, understanding the regulatory mechanisms of autophagy in ECs will be important for discovery of strategies to protect normal endothelial functions. Recently, Guo et al. provided some evidence indicating that the autophagic process in EC might be affected by shear stress.¹³ This argument, however, was only based on observations of changed expression levels of LC3 and beclin-1; further experimental evidence is needed to confirm such an effect of shear stress on autophagy. More importantly, the mechanisms underlying this phenomenon are not understood. Different signaling pathways may be involved in modulating autophagy in ECs.^{14, 15, 16} For example, inhibition of the mTOR (mammalian target of rapamycin) pathway by rapamycin-induced endothelial autophagy and prevented energy stress-triggered cell damage.¹⁶ There is also evidence indicating a potential role of Sirt1.¹⁴ Moreover, accumulating evidence has suggested that reactive oxygen species (ROS) are closely implicated in modulating autophagic responses via complex interactions with other autophagy-related factors.¹⁵ Despite of these results, the signaling mechanisms of shear stress-regulated autophagy in EC remain to be defined. Hence, here we aim to delineate the impacts and underlying mechanisms of shear stress on autophagy in human vascular ECs.     

脂多糖对脊髓前角运动神经元的损伤作用

研究脂多糖(LPS)诱导的炎症反应对运动神经元的损伤作用及其机制.采用SD乳鼠脊髓器官型培养,分为单纯培养液组和不同浓度LPS组,应用免疫组化、酶活性测定、电镜等技术衡量神经元损伤程度.对LPS组分别给予细胞内钙离子螯合剂BAPTA-AM和NADPH氧化酶抑制剂apocynin,观察运动神经元数量和形态变化.结果显示LPS可以引起剂量和时间依赖性的运动神经元数量减少和培养液中乳酸脱氢酶含量增高,运动神经元超微结构改变明显,中间神经元损伤相对较轻.运动神经元缺乏钙网膜蛋白表达,而BAPTA-AM减轻运动神经元损伤,提示钙离子缓冲能力较低是其较易受损的原因之一.LPS可以引起NADPH氧化酶活性增高,而apocynin对LPS引起的运动神经元丢失有保护作用,说明NADPH氧化酶在炎症介导的运动神经元损伤中发挥着关键作用.     

Analysis of Antioxidant and Anti-inflammatory Activity of Silicon in Murine Macrophages

The purpose of this study is to investigate the antioxidant and anti-inflammatory properties of silicon (Si) in the RAW 264.7 murine macrophage cell line. Lipopolysaccharide (LPS) was used to induce inflammatory conditions, and cells were treated with 0, 1, 5, 10, 25, 50, and 100 μM Si in the form of sodium metasilicate. Tert-butylhydroquinone (TBHQ), a well-known antioxidative substance, was used as a positive control to assess the degree of antioxidative and anti-inflammatory properties of Si. Sodium metasilicate at 100 μM suppressed LPS-induced nitric oxide generation from macrophages 36 h after treatment. In addition, 50 μM sodium metasilicate decreased interleukin-6 production, and the degree of suppression was comparable to that of 10 μM TBHQ treatment. LPS-induced messenger RNA (mRNA) expression of tumor necrosis factor-α and inducible nitric oxide synthase was significantly decreased by 1, 5, 10, and 50 μM sodium metasilicate. Cyclooxygenase-2 mRNA expression was also suppressed by 1, 5, 25, and 50 μM sodium metasilicate. Based on these data, Si has the ability to suppress the production of inflammatory cytokines and mediators, possibly through the suppression of radical scavenger activity and down-regulation of gene expression of inflammatory mediators.     

Digital image analysis of chromatin fibre phenotype after "in situ" digestion with restriction endonucleases

Restriction Endonucleases (REs) may recognize, cleave and remove DNA from fixed chromatin producing specific chromosome banding patterns. However, the modifications produced in the chromatin fibre are not easy to evaluate and compare. The aim of the present investigation was to visualize differences resulting in the texture of the chromatin fibre from metaphase chromosomes after each digestion using digital image analysis (DIA) facilities. To this purpose, metaphase chromosomes derived from a L-929 mouse cell line were digested with different REs (AluI, HpaII and HaeIII). Since light microscopy does not permit the observation of the chromatin fibre, DIA was performed on digitalized images of metaphase chromosomes under electron microscopy. The application of a LUT (Look Up Table) within the DIA software assigns a colour to each grey level of a digital image. The results obtained using a particular LUT, which permits the discrimination of specific chromatin fibre phenotypes resulting from each digestion, are reported and compared with those obtained under the light microscope.     

高羊茅植株再生体系的研究与建立

利用幼苗下胚轴建立了高羊茅(FestucaarundinaceaSchreb.)植株再生体系。当高羊茅种子以次氯酸钠为主要消毒剂时,其最适的浓度和时间分别为次氯酸钠50%(V/V)处理20min,种子发芽率为80%,污染率为0%。研究发现用高羊茅下胚轴诱导愈伤组织时,下胚轴的不同的切法对愈伤组织诱导有影响,从一端切的下胚轴诱导愈伤率74.7%高于从两端切55.8%。以下胚轴为外植体,2,4D的浓度为9mg·L1时,愈伤组织诱导率最高。高羊茅愈伤组织的分化再生率可达80.7%。     

Comparison of HMOX1 expression and enzyme activity in blue-shelled chickens and brown-shelled chickens

Blue egg coloring is attributed to biliverdin derived from the oxidative degradation of heme through catalysis by heme oxygenase (HO). The pigment is secreted into the eggshell by the shell gland. There is uncertainty as to whether the pigment is synthesized in the shell gland or in other tissues. To investigate the site of pigment biosynthesis, the expression of heme oxygenase (decycling) 1 (HMOX1), a gene encoding HO, and HO activity in liver and spleen were compared between blue-shelled chickens (n = 12) and brown-shelled chickens (n = 12). There were no significant differences in HMOX1 expression and HO activity in these tissues between the two groups. Since the liver and spleen, two important sites outside the shell gland where heme is degraded into biliverdin, CO and Fe²⁺, did not differ in HO expression and activity we conclude that the pigment is most likely synthesized in the shell gland.