Changes in proteoglycan synthesis of chondrocytes in articular cartilage are associated with the time-dependent changes in their mechanical environment

Explant loading experiments were conducted to investigate the effect of load duration on proteoglycan synthesis. A compressive load of 0.1 MPa applied for 10 min was found to stimulate proteoglycan synthesis, while the same load applied for 20 h suppressed synthesis. This bimodal response suggests that the cells are responding to different mechanical stimuli as time progresses. A theoretical model has therefore been developed to describe the mechanical environment perceived by cells within soft hydrated tissues (e.g. articular cartilage) while the tissue is being loaded. The cells are modeled, using the biphasic theory, as fluid-solid inclusions embedded in and attached to a biphasic extracellular matrix of distinct material properties. A method of solution is developed which is valid for any axisymmetric loading configuration, provided that the cell radius, a, is small relative to the tissue height, h (i.e. h/a 1). A closed-form analytical solution for this inclusion problem is then presented for the confined compression configuration. Results from this model show that the mechanical environment in and around the cells is time dependent and inhomogeneous, and can be significantly influenced by differences in properties between the cell and the extracellular matrix.     

Modulation of insulin action by vanadate: evidence of a role for phosphotyrosine phosphatase activity to alter cellular signaling

A number of vanadium compounds (vanadate, vanadyl sulfate, metavanadate) have insulin-mimicking actions bothin vitro andin vivo. They have multiple biological effects in cultured cells and interact directly with various enzymes. The inhibitory action on phosphoprotein tyrosine phosphatases (PTPs) and enhancement of cellular tyrosine phosphorylation appear to be the most relevant to explain the ability to mimic insulin. We demonstrated that in rat adipocytes both acute insulin effects, e.g. stimulation of IGF-II and transferrin binding and a chronic effect, insulin receptor downregulation, were stimulated by vanadate. Vanadate also enhanced insulin binding, particularly at very low insulin concentrations, associated with increased receptor affinity. This resulted in increased adipocyte insulin sensitivity. Finally vanadate augmented the extent of activation of the insulin receptor kinase by submaximal insulin concentrations. This was associated with a prolongation of the insulin biological response, lipogenesis, after removal of hormone.In conclusion: in rat adipocytes vanadate promotes insulin action by three mechanisms, 1) a direct insulin-mimetic action, 2) an enhancement of insulin sensitivity and 3) a prolongation of insulin biological response. These data suggest that PTP inhibitors have potential as useful therapeutic agents in insulin-resistant and relatively insulin-deficient forms of diabetes mellitus.     

Hepatitis C virus core protein interacts with the cytoplasmic tail of lymphotoxin-beta receptor.

Hepatitis C virus (HCV) core protein is a multifunctional protein. We examined whether it can interact with cellular proteins, thus contributing to viral pathogenesis. Using the HCV core protein as a bait to screen a human liver cDNA library in a yeast two-hybrid screening system, we have isolated several positive clones encoding cellular proteins that interact with the HCV core protein. Interestingly, more than half of these clones encode the cytoplasmic domain of lymphotoxin-beta receptor (LT betaR), which is a member of the tumor necrosis factor receptor family. Their binding was confirmed by in vitro glutathione S-transferase fusion protein binding assay and protein-protein blotting assay to be direct and specific. The binding sites were mapped within a 58-amino-acid region of the cytoplasmic tail of LT betaR. The binding site in the HCV core protein was localized within amino acid residues 36 to 91 from the N terminus, corresponding to the hydrophilic region of the protein. In mammalian cells, the core protein was found to be associated with the membrane-bound LT betaR. Since the LT betaR is involved in germinal center formation and developmental regulation of peripheral lymphoid organs, lymph node development, and apoptotic signaling, the binding of HCV core protein to LT betaR suggests the possibility that this viral protein has an immunomodulating function and may explain the mechanism of viral persistence and pathogenesis of HCV.     

Determination of the secondary structure of and cellular protein binding to the 3'-untranslated region of the hepatitis C virus RNA genome.

Hepatitis C virus (HCV) contains a positive-stranded RNA genome of approximately 9.5 kb. Despite the overall sequence diversity among individual HCV isolates, the 3'-end 98 nucleotides (nt) of the HCV RNA, which constitute part of the 3'-untranslated region (3'-UTR), are highly conserved. This conserved region may contain the cis-acting signals for RNA replication involving possibly both viral and cellular proteins. We carried out RNase digestion studies, which revealed that this 98-nt region contains three stem-loops but may also assume alternative structures. We further performed UV cross-linking experiments to detect cellular proteins that bound to this region. A 58-kDa cellular protein (p58) was detected. Its binding site was mapped to the stem-loops 2 and 3, which are the most conserved region of the 3'-UTR. Site-directed mutagenesis studies revealed that both stem structures and specific nucleotide sequence within the two loops are important for p58 binding. Mutations that disrupted stem structures abolished protein binding, while the compensatory mutations restored its binding. This region also contains partial sequence similarity to the reported consensus binding sequence for polypyrimidine tract-binding protein (PTB) (a 57-kDa protein). The UV-cross-linked protein could be immunoprecipitated with the anti-PTB antibody, and the recombinant PTB bound to the HCV 3'-UTR with the same binding specificity as p58, establishing that this protein is PTB. However, the reported PTB-binding sequence was not sufficient, but rather the entire stem-loops 2 and 3 were required, for PTB binding; thus, its binding specificity is significantly different from the reported PTB-binding sequence requirement. This protein was detected in both the nuclei and cytoplasm of most mammalian cell lines tested and human primary hepatocytes. PTB may participate in the regulation of HCV RNA synthesis or translation.     

拉萨郊区藏族的指纹研究

本文报道了拉萨郊区５１７例（男２２６人,女２９１人）藏族健康人的指纹参数正常值、调查分析了指纹类型、指纹组合、指纹指数和指嵴纹计数。比较了藏族不同居群、不同民族和人种间的差异。结果表明,藏族有自己的指纹特点,又显著蒙古人种的一般特征。     

超临界CO2技术萃取蛋黄磷脂

采用新型物理分离技术──超临界CO₂萃取法,提取天然蛋黄粉中的磷脂.在40MPa,先去除蛋黄粉中甘油三酯和胆固醇,再萃取磷脂.结果显示,磷脂纯度为95%,N/P比值为1.003,λ_max=214nm,薄层层析显示磷脂着色点清晰,并去除了绝大部分甘油三酯和胆固醇.此法操作简单、产品质量高、安全和不污染环境,还可得到天然纯蛋黄油和蛋白.     

新型平均势函数在蛋白质反向折叠中的应用

利用蛋白质主链的极性分数及主链二面角为参量,构建了一种基于蛋白质结构数据库的势函数。将该势函数应用于蛋白质反向折叠研究中,发现该函数可成功地将蛋白质分子的天然构象从构建的构象库中识别出来;将一目标序列与构象库的每一可能的构象匹配,并用该势函数计算相应的能量,结果表明对绝大多数蛋白质分子来说,天然的构象的能量值总是最低。此外,该函数还将一些序列相似性较低,而结构相似性较高的蛋白质分子识别出来。我们认     

An analysis of the unconfined compression of articular cartilage

Analytical solutions have been obtained for the internal deformation and fluid-flow fields and the externally observable creep, stress relaxation, and constant strain-rate behaviors which occur during the unconfined compression of a cylindrical specimen of a fluid-filled, porous, elastic solid, such as articular cartilage, between smooth, impermeable plates. Instantaneously, the "biphasic" continuum deforms without change in volume and behaves like an incompressible elastic solid of the same shear modulus. Radial fluid flow then allows the internal fluid pressure to equilibrate with the external environment. The equilibrium response is controlled by the Young's modulus and Poisson's ratio of the solid matrix.