Antimicrobial activities and membrane‐active mechanism of CPF‐C1 against multidrug‐resistant bacteria,a novel antimicrobial peptide derived from skin secretions of the tetraploid frog Xenopus clivii

Hospital‐acquired infections caused by multidrug‐resistant bacteria pose significant challenges for treatment, which necessitate the development of new antibiotics. Antimicrobial peptides are considered potential alternatives to conventional antibiotics. The skin of Anurans (frogs and toads) amphibians is an extraordinarily rich source of antimicrobial peptides. CPF‐C1 is a typical cationic antimicrobial peptide that was originally isolated from the tetraploid frog Xenopus clivii. Our results showed that CPF‐C1 has potent antimicrobial activity against both sensitive and multidrug‐resistant bacteria. It disrupted the outer and inner membranes of bacterial cells. CPF‐C1 induced both propidium iodide uptake into the bacterial cell and the leakage of calcein from large liposome vesicles, which suggests a mode of action that involves membrane disturbance. Scanning electron microscopy and transmission electron microscopy verified the morphologic changes of CPF‐C1‐treated bacterial cells and large liposome vesicles. The membrane‐dependent mode of action signifies that the CPF‐C1 peptide functions freely and without regard to conventional resistant mechanisms. Additionally, it is difficult for bacteria to develop resistance against CPF‐C1 under this action mode. Other studies indicated that CPF‐C1 had low cytotoxicity against mammalian cell. In conclusion, considering the increase in multidrug‐resistant bacterial infections, CPF‐C1 may offer a new strategy that can be considered a potential therapeutic agent for the treatment of diseases caused by multidrug‐resistant bacteria. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

骨髓间充质细胞联合PDMS支架构建移植胰岛微环境的实验研究

目的为了提高移植胰岛的活性和功能,构建适合移植胰岛生存的微环境。 方法采用聚二甲基硅氧烷（PDMS）和氯化钠晶体构建三维支架,联合骨髓间充质细胞（MSCs）、纤维蛋白和胰岛共同构建迷你"人工胰腺"。采用链脲佐菌素（STZ）诱导的糖尿病大鼠移植模型评价效果,将"人工胰腺"移植到糖尿病大鼠大网膜内,对照组行假手术,术后隔天监测移植大鼠血糖水平;数据采用t检验和曼-惠特尼U检验。 结果用PDMS构建的三维巨孔支架,支架内可见大量不规则孔洞空间。胰岛和MSCs可成功装载入支架内,HE染色结果显示,支架孔内存在胰岛,胰岛周围包绕有MSCs。糖尿病大鼠大网膜内移植结果显示,移植后各时间点（1,3,5,7 d）,"人工胰腺"移植组糖尿病大鼠血糖水平分别为（278.70±86.06）mg/ dl、（323.50±44.29）mg/ dl、（283.30±74.00）mg/dl、（304.80±13.33）mg/dl,较假手术对照组（606.00±52.40）mg/dl、（589.70±55.78）mg/dl、（615.00±54.84）mg/dl、（630.30±48.17）mg/ dl均降低,差异具有统计学意义（t = 7.96、9.15、8.82,U = 0.00,P均< 0.01）。 结论MSCs联合PDMS三维支架构建的微环境,可为移植胰岛提供生存的环境,为临床开展胰岛移植提供新的策略。     

A novel selenium-containing glutathione transferase zeta1-1, the activity of which surpasses the level of some native glutathione peroxidases

Glutathione peroxidase (GPX) is a critical antioxidant selenoenzyme in organisms that protects cells against oxidative damage by catalyzing the reduction of hydroperoxides by glutathione (GSH). Thus, some GPX mimics have been generated because of their potential therapeutic value. The generation of a semisynthetic selenoenzyme with peroxidase activity, which matches the catalytic efficiencies of naturally evolved GPX, has been a great challenge. Previously, we semisynthesized a GPX mimetic with high catalytic efficiency using a rat theta class glutathione transferase (rGST T2-2) as a scaffold, in which the highly specific GSH-binding site is adjacent to an active site serine residue that can be chemically modified to selenocysteine (Sec). In this study, we have taken advantage of a new scaffold, hGSTZ1-1, in which there are two serine residues in the active site, to achieve both high thiol selectivity and highly catalytic efficiency. The GPX activity of Se-hGSTZ1-1 is about 1.5 times that of rabbit liver GPX, indicating that the selenium content at the active site plays an important role in enhancement of catalytic performance. Kinetic studies revealed that the catalytic mechanism of Se-hGSTZ1-1 belong in a ping-pong mechanism similar to that of the natural GPX.     

Protective effects of circulating microvesicles derived from ischemic preconditioning on myocardial ischemia/reperfusion injury in rats by inhibiting endoplasmic reticulum stress

Microvesicles (MVs) have been shown to be involved in pathophysiology of ischemic heart diseases. However, the underlying mechanisms are still unclear. Here we investigated the effects of MVs derived from ischemic preconditioning (IPC-MVs) on myocardial ischemic/reperfusion (I/R) injury in rats. Myocardial IPC model was elicited by three cycles of ischemia and reperfusion of the left anterior descending (LAD) coronary artery. IPC-MVs from the peripheral blood of the above animal model were isolated by ultracentrifugation and characterized by flow cytometry and transmission electron microscopy. IPC-MVs were administered intravenously (7 mg/kg) at 5 min before reperfusion procedure in I/R injury model which was induced by 30-min ischemia and 120-min reperfusion of LAD in rats. We found that total IPC-MVs and different phenotypes, including platelet-derived MVs (PMVs), endothelial cell-derived MVs (EMVs), leucocyte-derived MVs and erythrocyte-derived MVs (RMVs) were all isolated which were identified membrane vesicles (<?1 µm) with corresponding antibody positive. The numbers of PMVs, EMVs and RMVs were significantly increased in circulation of IPC treated rats respectively. Additionally, treatment with IPC-MVs significantly alleviated damage of myocardium, and restored cardiac function of I/R injury rats, as evidenced by increased heart rate, and decreased the elevation of ST-segment. The size of myocardial infarction, lactate dehydrogenase activity, and the number of apoptotic cardiomyocytes were also reduced significantly with IPC-MVs treatment, coincident with the above function amelioration. Moreover, IPC-MVs decreased the activity of caspase 3, and the expression of endoplasmic reticulum stress (ERS) markers, GRP78, CHOP and caspase 12 indicating the involvement of ERS-specific apoptosis in I/R injury, and cardioprotective effects of IPC-MVs. In summary, our study demonstrated a novel mechanism of IPC in which circulating IPC-MVs could protect hearts from I/R injury in rats through attenuation of ERS-induced apoptosis. These findings provide new insight into therapeutic potential of IPC-induced MVs in cardioprotection against I/R injury.     

Interaction between residues in the Mg2+-binding site regulates BK channel activation

As a unique member of the voltage-gated potassium channel family, a large conductance, voltage- and Ca²⁺-activated K⁺ (BK) channel has a large cytosolic domain that serves as the Ca²⁺ sensor, in addition to a membrane-spanning domain that contains the voltage-sensing (VSD) and pore-gate domains. The conformational changes of the cytosolic domain induced by Ca²⁺ binding and the conformational changes of the VSD induced by membrane voltage changes trigger the opening of the pore-gate domain. Although some structural information of these individual functional domains is available, how the interactions among these domains, especially the noncovalent interactions, control the dynamic gating process of BK channels is still not clear. Previous studies discovered that intracellular Mg²⁺ binds to an interdomain binding site consisting of D99 and N172 from the membrane-spanning domain and E374 and E399 from the cytosolic domain. The bound Mg²⁺ at this narrow interdomain interface activates the BK channel through an electrostatic interaction with a positively charged residue in the VSD. In this study, we investigated the potential interdomain interactions between the Mg²⁺-coordination residues and their effects on channel gating. By introducing different charges to these residues, we discovered a native interdomain interaction between D99 and E374 that can affect BK channel activation. To understand the underlying mechanism of the interdomain interactions between the Mg²⁺-coordination residues, we introduced artificial electrostatic interactions between residues 172 and 399 from two different domains. We found that the interdomain interactions between these two positions not only alter the local conformations near the Mg²⁺-binding site but also change distant conformations including the pore-gate domain, thereby affecting the voltage- and Ca²⁺-dependent activation of the BK channel. These results illustrate the importance of interdomain interactions to the allosteric gating mechanisms of BK channels.     

Variation in russet sparrow (Passer cinnamomeus) breeding biology in relation to small-scale altitudinal differences in China

Evolution of avian life histories is typically strongly influenced by both altitude and latitude. To date, most studies have investigated the effects of extreme differences in altitude and latitude on variation in reproductive traits. Studies based on small altitude and latitude spans are needed to better understand the resolution of selective pressures. We compared several aspects of russet sparrow (Passer cinnamomeus) breeding biology between a low-altitude (200 m) and a high-altitude (1,500 m) population in China, representing a relatively small altitudinal gradient (1,300 m). High-altitude birds initiated breeding significantly later compared to their low-altitude counterparts. Interestingly, breeding season was significantly longer in the high-altitude site (57 vs. 84 d). Lowland sparrows laid larger clutches (4.92 vs. 4.09 eggs) and showed greater fledging success (4.20 vs. 3.46 fledgings) than did upland birds. Variation in life history traits thus appears to occur even along a small scale altitudinal gradient. We suggest that the longer breeding season and smaller clutch size in the highland population may be an adaptation or acclimation to compensate for the reduced annual productivity resulting from unfavourable or sub-optimal habitats for these sparrows.     

Construction of the active site of glutathione peroxidase on polymer-based nanoparticles

A new nanoenzyme model with glutathione peroxidase-like active site was constructed on polystyrene nanoparticle (PN1) via microemulsion polymerization. In this model system, two functional monomers were designed: one is a tellurium-containing compound that was introduced on the surface of the nanoparticle and acts as a catalytic center, and the other one is an arginine-containing compound designed as a binding site for the complexation of the carboxyl group of substrate 3-carboxy-4-nitrobenzenethiol (ArSH, 1). As a new glutathione peroxidase (GPx) mimic, it demonstrated excellent catalytic activity and substrate specificity. In ArSH assay system, it was at least 316,000-fold more efficient than PhSeSePh for the reduction of cumene hydroperoxide (CUOOH) by ArSH. In contrast to model PN2, which lacks of substrate binding site, PN1 exhibits an obvious enhancement in catalytic activity. To further promote the catalytic efficiency, a substrate ArSH surface-imprinted nanoenzyme model (I-PN) was developed. By correctly incorporating and positioning the catalytic center tellurium and functional binding factor guanidinium, a continuative activity enhancement of 596,000-fold for the reduction of CUOOH by catalyst I-PN compared with diphenyl diselenide (PhSeSePh) was observed. The results clearly show that polymeric nanoparticle can be developed as an excellent model for combining most of catalytic factors of enzyme into one scaffold.     

化学修饰抗体增加模拟酶的GPX活性

将丝氨酸共价偶联到兔抗人ＩｇＭ（Ｆｃμ）抗体上,以增加抗体结合部位丝氨酸残基含量．在中性条件下,丝氨酸被对苯甲基磺酰氟活化,再经ＮａＨＳｅ亲核取代,将丝氨酸诱变为硒代半胱氨酸（ＳｅＣｙｓ）．其谷胱甘肽过氧化物酶（ＧＰＸ）活性由未增加丝氨酸前的诱变抗体的７０Ｕ／μｍｏｌ提高到２１８Ｕ／μｍｏｌ,其活性为模拟物ＰＺ５１的２００多倍．     

Increased sustainable electricity generation in up-flow air-cathode microbial fuel cells

Sustainable electricity was generated from glucose in up-flow air-cathode microbial fuel cells (MFCs) with carbon cloth cathode and carbon granular anode. Plastic sieves rather than membrane were used to separate the anode and cathode. Based on 1g/l glucose as substrate, a maximum volumetric power density of 25+/-4 W/m(3) (89 A/m(3)) was obtained for the MFC with a sieve area of 30 cm(2) and 49+/-3 W/m(3) (215 A/m(3)) for the MFC with a sieve area of 60 cm(2). The increased power density with larger sieve area was mainly due to the decrease of internal resistance according to the electrochemistry impedance spectroscopy analysis. Increasing the sieve area from 30 cm(2) to 60 cm(2) resulted in a decrease of overall internal resistance from 41 ohm to 27.5 ohm and a decrease of ohmic resistance from 24.3 ohm to 14 ohm. While increasing operational recirculation ratio (RR) decreased internal resistance and increased power output at low substrate concentration, the effect of RR on cell performance was negligible at higher substrate concentration.     

CHOP双重调控衣霉素诱导的DU-145细胞凋亡及自噬的研究

目的研究内质网应激分子CHOP调控细胞凋亡与自噬的作用和机制。 方法利用衣霉素诱导DU-145细胞产生内质网应激,Western Blot法检测内质网应激相关分子Grp78、Grp94、p-eIF2α和CHOP及自噬蛋白LC3Ⅱ、Atg5和Beclin1的表达;用流式细胞术检测细胞凋亡水平;沉默CHOP基因,用Western Blot法检测凋亡蛋白PARP、Caspase3的表达,流式细胞术检测细胞凋亡;并利用免疫荧光检测自噬标志性蛋白LC3B的表达。 结果衣霉素诱导DU-145细胞内质网应激能诱导一定程度的细胞凋亡,衣霉素处理8、12、24?h的细胞凋亡率分别为3.27﹪±1.02﹪,8.97﹪±0.71﹪和11.67﹪±1.41﹪,处理12?h及24?h的细胞凋亡率与对照组相比差异具有统计学意义（P < 0.01）。同时也能通过抑制PI3K/AKt/mTOR信号通路激活DU-145细胞自噬。CHOP基因沉默抑制细胞凋亡,shCtrl组细胞凋亡率为32.17﹪±3.93﹪,shCHOP-1组细胞凋亡率为23.53﹪±3.41﹪,两组相比差异具有统计学意义（P < 0.05）。且CHOP基因沉默能促进细胞自噬分子LC3B的表达。 结论衣霉素诱导DU-145细胞内质网应激状态下,CHOP在细胞凋亡与自噬之间发挥双重调控作用。