Is HMGB1 an osteocyte alarmin?

The death of osteocytes, the terminally differentiated cells of the osteoblast lineage that are embedded in bone and regulate remodeling, is significant to both normal and pathological bone resorption. Apoptotic osteocytes putatively release a clarion signal that enhances the development of the bone-resorbing osteoclasts and targets their migration to the breach in the osteocyte network. This phenomenon is thought to underlie normal repair of bone microdamage and contribute to the etiologies of inflammatory bone loss. The chromatin protein high mobility group box 1 protein (HMGB1) has been identified as an "alarmin" in other tissues. An alarmin is an endogenous molecule released by dead and dying cells that alert the innate immune system to damage and the need for tissue repair. Wang and colleagues presented evidence in a landmark 1999 study showing that released HMGB1 is a lethal mediator of sepsis. Extracellular HMGB1 is a ligand for the toll-like receptors (TLRs) and for the receptor for advanced glycation end products (RAGE) all of which amplify inflammation. Recent studies by our lab and others have shown that HMGB1 is a bone-active cytokine. It is released by apoptotic osteoblasts in vitro, including the MLO-Y4 osteocyte-like cells. Extracellular HMGB1 enhances the expression of RANKL, TNFalpha, and IL6 in osteoblastogenic bone marrow stromal cell cultures, and it is chemotactic to osteoclasts. In this prospectus we will review HMGB1 activity at the immune-bone interface and propose a role for HMGB1 as an osteocyte alarmin and mediator of normal remodeling and inflammatory bone loss.     

Temporin/VesCP (T/V)-like antibiotic peptides, derived from frogs and wasps, induce migration of human monocytes and neutrophils

Summary  Several naturally occurring antimicrobial peptides, from mammals and insects, have previously been shown to be chemotactic for human inflammatory cells. Based on this evidence, ten synthetic analogs of naturally occurring antibiotic peptides from the skin secretions of three species of Ranid frogs and the venom of one species of Vespid wasp (i.e., T/V-like peptides) were tested for their abilities to induce migration of human neutrophils and monocytes. These included temporin A (TA fromRana temporaria), temporin 1P (T1P fromR. pipens), ranateurin 6 (Rana-6 fromR. catesbeiana)], three TA analogs [all D-amino acids (D-TA), reversed sequence (Rev-TA), and Pro3→Gly (G3-TA)], two frog skin-related T/V-like peptide consensus sequences (I4S10-Con and I4G10-Con), VesCP-M (VCP-M fromVespa mandarinia), and a hybrid peptide composed of portions of the insect antibiotic peptide, cecropin A (CA), and TA (CATA). TA, T1P, Rana-6, VCP-M, G3-TA, I4S10-Con, I4G10-Con, and CATA all induced cell migration at micromolar concentrations. D-TA and Rev-TA did not induce cell migration, suggesting that this process involves a chiral interaction, such as receptor binding, and also depends on the order of amino acids within TA. The results demonstrate, for the first time, that certain T/V-like antibiotic peptides are capable of inducing chemotaxis of human phagocytes and suggest that these peptides are multifunctional molecules with antimicrobial, hemolytic, and chemotactic capabilities.     

Temporin/VesCP (T/V)-like antibiotic peptides,derived from frogs and wasps,induce migration of human monocytes and neutrophils

Summary Several naturally occurring antimicrobial peptides, from mammals and insects, have previously been shown to be chemotactic for human inflammatory cells. Based on this evidence, ten synthetic analogs of naturally occurring antibiotic peptides from the skin secretions of three species of Ranid frogs and the venom of one species of Vespid wasp (i.e., T/V-like peptides) were tested for their abilities to induce migration of human neutrophils and monocytes. These included temporin A (TA fromRana temporaria), temporin 1P (T1P fromR. pipens), ranateurin 6 (Rana-6 fromR. catesbeiana)], three TA analogs [all D-amino acids (D-TA), reversed sequence (Rev-TA), and Pro3→Gly (G3-TA)], two frog skin-related T/V-like peptide consensus sequences (I4S10-Con and I4G10-Con), VesCP-M (VCP-M fromVespa mandarinia), and a hybrid peptide composed of portions of the insect antibiotic peptide, cecropin A (CA), and TA (CATA). TA, T1P, Rana-6, VCP-M, G3-TA, I4S10-Con, I4G10-Con, and CATA all induced cell migration at micromolar concentrations. D-TA and Rev-TA did not induce cell migration, suggesting that this process involves a chiral interaction, such as receptor binding, and also depends on the order of amino acids within TA. The results demonstrate, for the first time, that certain T/V-like antibiotic peptides are capable of inducing chemotaxis of human phagocytes and suggest that these peptides are multifunctional molecules with antimicrobial, hemolytic, and chemotactic capabilities.     

Molecular modeling of flexible arm‐mediated interactions between bacterial chemoreceptors and their modification enzyme

Sensory adaptation in bacterial chemotaxis is mediated by methylation and demethylation of specific glutamyl residues in the cytoplasmic domain of chemoreceptors. Methylation is catalyzed by methyltransferase CheR. In E. coli and related organisms, methylation sufficiently rapid to be physiologically effective requires a carboxyl terminal pentapeptide sequence on the receptor being modified or, via adaptational assistance, on a neighboring homodimer in a receptor cluster. Pentapeptide‐enhanced methylation is thought to be mediated by a ～30 residue, potentially disordered sequence that serves as a flexible arm connecting the receptor body and pentapeptide‐bound methyltransferase, thus allowing diffusionally restricted enzyme to reach methyl‐accepting sites. However, it was not known how many or which sites on the same or neighboring receptors were accessible to the tethered enzyme. We investigated using molecular modeling and found that, in a hexagonal array of trimers of receptor dimers, CheR tethered to a dimer of chemoreceptor Tar by its native 30‐residue flexible‐arm sequence could reach all methyl‐accepting sites on the dimer to which it was tethered plus 48 methyl‐accepting sites distributed among nine neighboring dimers, equivalent to the total sites carried by six receptors. This modeling‐determined methylation neighborhood of one enzyme‐binding dimer and six neighbors corresponds precisely with the experimentally identified neighborhood of seven. Thus, the experimentally observed adaptational assistance can occur by docking of pentapeptide‐bound, diffusionally restricted enzyme to methyl‐accepting sites on neighboring receptors. Our analysis introduces the notion that physiologically relevant adaptational assistance could occur even if only a subset of sites on a particular receptor are within reach.     

鱼类趋化因子的研究进展

趋化因子(Chemokine)是由多种细胞在致病因子刺激后分泌的一类低分子量的细胞因子,它们都具有激活和趋化白细胞的作用。趋化因子从结构上可分为四类:CC型、CXC型、CX3C型和C型;从功能上可分为两种类型:一类主要诱导白细胞到炎症部位;另一类主要是对肌体起免疫监控作用。目前,有关鱼类趋化因子的研究主要集中于CXC型和CC型两类,以及其在非特异性免疫中的作用。     

壳聚糖薄膜成球培养对脐带间充质干细胞迁徙趋化的影响

基于细胞实验研究壳聚糖（chitosan,CS）薄膜成球培养技术对间充质干细胞(mesenchymal stem cells, MSCs)迁徙趋化特性的影响。从脐带组织中分离原代MSCs采取CS成球法培养,以常规贴壁培养MSCs作为对照,72 h后收集两组细胞分别进行划痕实验、Tranthwell迁徙实验观察并拍照记录,RT-PCR方法检测两种培养方式中MSCs迁徙相关基因表达水平的差异。研究结果显示,相较常规贴壁培养方式,CS培养组MSCs体外迁徙趋化能力增强,差异具有显著统计学意义（P<0.01）;CS成球培养组MSCs 中CXCR4、CXCR7、MCP-1、MMP-1、MMP-2、MMP-9、TIMP-2等迁徙相关基因表达均明显上调（P<0.01）。实验表明CS成球培养可显著促进MSCs的迁移趋化特性。     

细菌趋化信号通路中的磷酸酯酶CheZ

细菌通过趋化系统获得在复杂环境中的生存优势。趋化性在细菌致病性、病菌定殖、固氮细菌与宿主共生、植物与微生物互作等方面有重要的作用。作为趋化信号适应中不可或缺的调节蛋白,对CheZ的深入研究具有重要意义。本文主要对CheZ的结构、作用机制、功能调节、蛋白定位以及进化地位等方面的研究现状进行了综述,旨在为其它细菌中趋化系统的研究提供有益参考。     

Mouse sperm exhibit chemotaxis to allurin, a truncated member of the cysteine-rich secretory protein family

Allurin, a 21 kDa protein isolated from egg jelly of the frog Xenopus laevis, has previously been demonstrated to attract frog sperm in two-chamber and microscopic assays. cDNA cloning and sequencing has shown that allurin is a truncated member of the Cysteine-Rich Secretory Protein (CRISP) family, whose members include mammalian sperm-binding proteins that have been postulated to play roles in spermatogenesis, sperm capacitation and sperm–egg binding in mammals. Here, we show that allurin is a chemoattractant for mouse sperm, as determined by a 2.5-fold stimulation of sperm passage across a porous membrane and by analysis of sperm trajectories within an allurin gradient as observed by time-lapse microscopy. Chemotaxis was accompanied by an overall change in trajectory from circular to linear thereby increasing sperm movement along the gradient axis. Allurin did not increase sperm velocity although it did produce a modest increase in flagellar beat frequency. Oregon Green 488-conjugated allurin was observed to bind to the sub-equatorial region of the mouse sperm head and to the midpiece of the flagellum. These findings demonstrate that sperm have retained the ability to bind and respond to truncated Crisp proteins over 300 million years of vertebrate evolution.