Electrostatic and non-electrostatic contributions of proteoglycans to the compressive equilibrium modulus of bovine articular cartilage

This study presents direct experimental evidence for assessing the electrostatic and non-electrostatic contributions of proteoglycans to the compressive equilibrium modulus of bovine articular cartilage. Immature and mature bovine cartilage samples were tested in unconfined compression and their depth-dependent equilibrium compressive modulus was determined using strain measurements with digital image correlation analysis. The electrostatic contribution was assessed by testing samples in isotonic and hypertonic saline; the combined contribution was assessed by testing untreated and proteoglycan-depleted samples.Though it is well recognized that proteoglycans contribute significantly to the compressive stiffness of cartilage, results demonstrate that the combined electrostatic and non-electrostatic contributions may add up to more than 98% of the modulus, a magnitude not previously appreciated. Of this contribution, about two thirds arises from electrostatic effects. The compressive modulus of the proteoglycan-depleted cartilage matrix may be as low as 3 kPa, representing less than 2% of the normal tissue modulus; experimental evidence also confirms that the collagen matrix in digested cartilage may buckle under compressive strains, resulting in crimping patterns. Thus, it is reasonable to model the collagen as a fibrillar matrix that can sustain only tension. This study also demonstrates that residual stresses in cartilage do not arise exclusively from proteoglycans, since cartilage remains curled relative to its in situ geometry even after proteoglycan depletion. These increased insights on the structure–function relationships of cartilage can lead to improved constitutive models and a better understanding of the response of cartilage to physiological loading conditions.     

Bicyclic α,ω-dicarboxylic acid derivatives from a colonial tunicate of the family Polyclinidae

In the course of our search for bioactive metabolites from a colonial tunicate of the family Polyclinidae, six new (1–6) cyclic fatty acid derivatives were isolated. Their planar structures were established on the basis of NMR and MS spectroscopic analyses. The relative configuration was determined by NOESY experiment. Compounds 1–6 represent a fused bicyclic skeleton possibly derived from α,ω-dicarboxylic acids such as eicosanedioic acid or docosanedioic acid via a Diels–Alder type of cyclization. Compounds 1–4 and 6 showed mild cytotoxicity against a panel of five human solid tumor cell lines.     

Alkaline phosphatase and OmpA protein can be translocated posttranslationally into membrane vesicles of Escherichia coli.

We previously described a system for translocating the periplasmic enzyme alkaline phosphatase and the outer membrane protein OmpA into inverted membrane vesicles of Escherichia coli. We have now optimized and substantially improved the translocation system by including polyamines and by reducing the amount of membrane used. Under these conditions, efficient translocation was seen even posttranslationally, i.e., when vesicles were not added until after protein synthesis was stopped. This was the case not only with the OmpA protein, which is synthesized by free polysomes and hence is presumably exported posttranslationally in the cell, but also with alkaline phosphatase, which is synthesized only by membrane-bound polysomes and has been shown to be secreted cotranslationally in the cells. Prolonged incubation rendered the precursors inactive for subsequent translocation. Posttranslational translocation was impaired, like cotranslational translocation, by inhibitors of the proton motive force and by treatment of the vesicles with protease. Since it appears that E. coli can translocate the same proteins either cotranslationally or posttranslationally, the cotranslational mode may perhaps be more efficient, but not obligatory, for the secretion of bacterial proteins.     

Beyond NF-κB activation: nuclear functions of IκB kinase α

IκB kinase (IKK) complex, the master kinase for NF-κB activation, contains two kinase subunits, IKKα and IKKβ. In addition to mediating NF-κB signaling by phosphorylating IκB proteins during inflammatory and immune responses, the activation of the IKK complex also responds to various stimuli to regulate diverse functions independently of NF-κB. Although these two kinases share structural and biochemical similarities, different sub-cellular localization and phosphorylation targets between IKKα and IKKβ account for their distinct physiological and pathological roles. While IKKβ is predominantly cytoplasmic, IKKα has been found to shuttle between the cytoplasm and the nucleus. The nuclear-specific roles of IKKα have brought increasing complexity to its biological function. This review highlights major advances in the studies of the nuclear functions of IKKα and the mechanisms of IKKα nuclear translocation. Understanding the nuclear activity is essential for targeting IKKα for therapeutics.     

黑线姬鼠两亚种(中国东北地区及俄罗斯远东地区的东北亚种和朝鲜半岛的朝鲜亚种) 的线粒体DNA 序列缺少趋异性

为了检测黑线姬鼠两亚种(来自中国东北地区、俄罗斯远东地区的东北亚种和朝鲜半岛的朝鲜亚种)线
粒体DNA 的变异水平并确定朝鲜亚种的分类地位,我们测序分析了两亚种的线粒体DNA 细胞色素b 的部分序列
(1 054 bp)和控制区的部分序列(860 bp),并与基因库中黑线姬鼠相应的单倍型序列进行了比较。可以看出东
北亚种的序列显示出某些分异,可以被分为2 或3 个亚群,所以我们提出需要更多标本的DNA 分析来确定东北
亚种的分类地位。另外,来自韩国的朝鲜亚种的序列,与来自中国东北地区龙江和哈尔滨的东北亚种的两个亚
群相似(1 个亚群是细胞色素b 的两个单倍型,另1 个是控制区的两个单倍型),表明基于线粒体DNA 序列的遗
传多样性与现今基于形态特征对这些姬鼠的分类所得结果是不一致的。因此我们认为来自韩国的朝鲜亚种是一
个只在形态特异上不同于东北亚种的地方亚种,我们建议通过其他DNA 标记来进一步验证其亚种地位。我们还
认为朝鲜半岛不是最近的冰川期黑线姬鼠残遗种的保护区。     

社会行为发育的行为神经内分泌效应

发育过程中行为神经内分泌环境能够调节解剖和生理的长期变化,产生深远的行为效应,所以神经内分泌环境在幼体发育及其行为生理特征的形成中起重要作用。本文综述了神经垂体激素、类固醇激素及它们的受体在社会行为发育中的行为神经内分泌效应;指出该领域有待解决的问题和进一步研究的方向;希望能使人们重视人类发育过程中双亲行为和激素作用对儿童社会行为及其相关神经内分泌特征的影响。     

Protein sorting to the cell wall envelope of Gram-positive bacteria

The covalent anchoring of surface proteins to the cell wall envelope of Gram-positive bacteria occurs by a universal mechanism requiring sortases, extracellular transpeptidases that are positioned in the plasma membrane. Surface protein precursors are first initiated into the secretory pathway of Gram-positive bacteria via N-terminal signal peptides. C-terminal sorting signals of surface proteins, bearing an LPXTG motif or other recognition sequences, provide for sortase-mediated cleavage and acyl enzyme formation, a thioester linkage between the active site cysteine residue of sortase and the C-terminal carboxyl group of cleaved surface proteins. During cell wall anchoring, sortase acyl enzymes are resolved by the nucleophilic attack of peptidoglycan substrates, resulting in amide bond formation between the C-terminal end of surface proteins and peptidoglycan cross-bridges within the bacterial cell wall envelope. The genomes of Gram-positive bacteria encode multiple sortase genes. Recent evidence suggests that sortase enzymes catalyze protein anchoring reactions of multiple different substrate classes with different sorting signal motif sequences, protein linkage to unique cell wall anchor structures as well as protein polymerization leading to the formation of pili on the surface of Gram-positive bacteria.     

Amyloid‐β‐induced occludin down‐regulation and increased permeability in human brain endothelial cells is mediated by MAPK activation

Vascular dysfunction is emerging as a key pathological hallmark in Alzheimer’s disease (AD). A leaky blood–brain barrier (BBB) has been described in AD patient tissue and in vivo AD mouse models. Brain endothelial cells (BECs) are linked together by tight junctional (TJ) proteins, which are a key determinant in restricting the permeability of the BBB. The amyloid β (Aβ) peptides of 1–40 and 1–42 amino acids are believed to be pivotal in AD pathogenesis. We therefore decided to investigate the effect of Aβ 1–40, the Aβ variant found at the highest concentration in human plasma, on the permeability of an immortalized human BEC line, hCMEC/D3. Aβ 1–40 induced a marked increase in hCMEC/D3 cell permeability to the paracellular tracer 70 kD FITC‐dextran when compared with cells incubated with the scrambled Aβ 1–40 peptide. Increased permeability was associated with a specific decrease, both at the protein and mRNA level, in the TJ protein occludin, whereas claudin‐5 and ZO‐1 were unaffected. JNK and p38MAPK inhibition prevented both Aβ 1–40‐mediated down‐regulation of occludin and the increase in paracellular permeability in hCMEC/D3 cells. Our findings suggest that the JNK and p38MAPK pathways might represent attractive therapeutic targets for preventing BBB dysfunction in AD.