Defective neuromuscular synaptogenesis in agrin-deficient mutant mice

During neuromuscular synapse formation, motor axons induce clustering of acetylcholine receptors (AChRs) in the muscle fiber membrane. The protein agrin, originally isolated from the basal lamina of the synaptic cleft, is synthesized and secreted by motoneurons and triggers formation of AChR clusters on cultured myotubes. We show here postsynaptic AChR aggregates are markedly reduced in number, size, and density in muscles of agrin-deficient mutant mice. These results support the hypothesis that agrin is a critical organizer of postsynaptic differentiation does occur in the mutant, suggesting the existence of a second-nerve-derived synaptic organizing signal. In addition, we show that intramuscular nerve branching and presynaptic differentiation are abnormal in the mutant, phenotypes which may reflect either a distinct effect of agrin or impaired retrograde signaling from a defective postsynaptic apparatus.

High surface energy enhances cell response to titanium substrate microstructure

Titanium (Ti) is used for implantable devices because of its biocompatible oxide surface layer. TiO2 surfaces that have a complex microtopography increase bone-to-implant contact and removal torque forces in vivo and induce osteoblast differentiation in vitro. Studies examining osteoblast response to controlled surface chemistries indicate that hydrophilic surfaces are osteogenic, but TiO2 surfaces produced until now exhibit low surface energy because of adsorbed hydrocarbons and carbonates from the ambient atmosphere or roughness induced hydrophobicity. Novel hydroxylated/hydrated Ti surfaces were used to retain high surface energy of TiO2. Osteoblasts grown on this modified surface exhibited a more differentiated phenotype characterized by increased alkaline phosphatase activity and osteocalcin and generated an osteogenic microenvironment through higher production of PGE2 and TGF-beta1. Moreover, 1alpha,25OH2D3 increased these effects in a manner that was synergistic with high surface energy. This suggests that increased bone formation observed on modified Ti surfaces in vivo is due in part to stimulatory effects of high surface energy on osteoblasts.

Enhancing surface free energy and hydrophilicity through chemical modification of microstructured titanium implant surfaces

Roughness-induced hydrophobicity, well-known from natural plant surfaces and intensively studied toward superhydrophobic surfaces, has currently been identified on microstructured titanium implant surfaces. Studies indicate that microstructuring by sandblasting and acid etching (SLA) enhances the osteogenic properties of titanium. The undesired initial hydrophobicity, however, presumably decelerates primary interactions with the aqueous biosystem. To improve the initial wettability and to retain SLA microstructure, a novel surface modification was tested. This modification differs from SLA by its preparation after acid etching, which was done under protective gas conditions following liquid instead of dry storage. We hypothesized that this modification should have increased wettability due to the prevention of contaminations that occurs during air contact. The main outcome of dynamic wettability measurements was that the novel modification shows increased surface free energy (SFE) and increased hydrophilicity with initial water contact angles of 0 degrees compared to 139.9 degrees for SLA. This hydrophilization was kept even after any drying. Reduced hydrocarbon contaminations were identified to play a possible role in altered surface thermodynamics. Such surfaces aim to retain the hydrophilicity and natural high surface energy of the Ti dioxide surface until surgical implants' insertion and are compared in this in vitro study with structural surface variants of titanium to compare roughness and chemically induced wettability.

Structure and expression of a rat agrin

Agrin is a component of the basal lamina that causes the aggregation of acetylcholine receptors on cultured muscle fibers. An agrin cDNA clone isolated from electromotor neurons of a marine ray was used to characterize the corresponding cDNAs from a rat embryonic spinal cord library. Analysis of a set of clones predicts a 1940 amino acid protein containing 141 cysteine residues. The predicted protein has nine domains homologous to protease inhibitors, a region similar to domain III of laminin, and four epidermal growth factor repeats. The agrin gene is expressed in rat embryonic nervous system and muscle. The rat agrin protein is concentrated at synapses, where it may play a role in development and regeneration.

Roughness induced dynamic changes of wettability of acid etched titanium implant modifications

Dynamic contact angle analysis (DCA) was used to investigate time-dependent wettability changes of sandblasted and acid-etched commercially pure (cp) titanium (Ti) implant modifications during their initial contact with aqueous systems compared to a macrostructured reference surface. Surface topography was analyzed by scanning electron microscopy and by contact stylus profilometry. The microstructured Ti surfaces were found to be initially extremely hydrophobic. This hydrophobic configuration can shift to a completely wettable surface behavior with water contact angles of 0 degrees after the first emersion loop during DCA experiments. It is suggested that a hierarchically structured surface topography could be responsible for this unexpected wetting phenomenon. Roughness spatial and hybrid parameters could describe topographical features interfering with dynamic wettability significantly better than roughness height parameters. The Ti modifications which shift very sudden from a hydrophobic to a hydrophilic state adsorbed the highest amount of immunologically assayed fibronectin. The results suggest that microstructuring greatly influences both the dynamic wettability of Ti implant surfaces during the initial host contact and the initial biological response of plasma protein adsorption. The microstructured surfaces, once in the totally wettable configuration, may improve the initial contact with host tissue after implantation, due to the drastically increased hydrophilicity.

RNA splicing regulates agrin-mediated acetylcholine receptor clustering activity on cultured myotubes

Agrin is a component of the synaptic basal lamina that induces the clustering of acetylcholine receptors (AChRs) on muscle fibers. A region near the carboxyl terminus of the protein exists in four forms that are generated by alternative RNA splicing. All four alternatively spliced forms of agrin are active in inducing AChR clusters on rat primary and C2-derived muscle fibers. In contrast, only two forms of the protein, each containing an 8 amino acid insert, are capable of inducing clusters on myotubes of S27 cells, a C2 variant that has defective proteoglycans. These two forms are also most active in inducing clusters on chick myotubes. This pattern of differential activity suggests that RNA splicing of agrin transcripts and interactions with proteoglycans or other components of basal lamina have important roles in regulating the localization of neurotransmitter receptors at synaptic sites.

Biomechanical evaluation of the interfacial strength of a chemically modified sandblasted and acid-etched titanium surface

The functional capacity of osseointegrated dental implants to bear load is largely dependent on the quality of the interface between the bone and implant. Sandblasted and acid-etched (SLA) surfaces have been previously shown to enhance bone apposition. In this study, the SLA has been compared with a chemically modified SLA (modSLA) surface. The increased wettability of the modSLA surface in a protein solution was verified by dynamic contact angle analysis. Using a well-established animal model with a split-mouth experimental design, implant removal torque testing was performed to determine the biomechanical properties of the bone-implant interface. All implants had an identical cylindrical shape with a standard thread configuration. Removal torque testing was performed after 2, 4, and 8 weeks of bone healing (n = 9 animals per healing period, three implants per surface type per animal) to evaluate the interfacial shear strength of each surface type. Results showed that the modSLA surface was more effective in enhancing the interfacial shear strength of implants in comparison with the conventional SLA surface during early stages of bone healing. Removal torque values of the modSLA-surfaced implants were 8-21% higher than those of the SLA implants (p = 0.003). The mean removal torque values for the modSLA implants were 1.485 N m at 2 weeks, 1.709 N m at 4 weeks, and 1.345 N m at 8 weeks; and correspondingly, 1.231 N m, 1.585 N m, and 1.143 N m for the SLA implants. The bone-implant interfacial stiffness calculated from the torque-rotation curve was on average 9-14% higher for the modSLA implants when compared with the SLA implants (p = 0.038). It can be concluded that the modSLA surface achieves a better bone anchorage during early stages of bone healing than the SLA surface; chemical modification of the standard SLA surface likely enhances bone apposition and this has a beneficial effect on the interfacial shear strength.

Physiological regulation of the immunological synapse by agrin

T cell activation is dependent on both a primary signal delivered through the T cell receptor and a secondary costimulatory signal mediated by coreceptors. Although controversial, costimulation is thought to act through the specific redistribution and clustering of membrane and intracellular kinase-rich lipid raft microdomains at the contact site between T cells and antigen-presenting cells. This site has been termed the immunological synapse. Endogenous mediators of raft clustering in lymphocytes have not been identified, although they are essential for T cell activation. We now demonstrate that agrin, an aggregating protein crucial for formation of the neuromuscular junction, is also expressed in lymphocytes and is important in reorganization of membrane lipid microdomains and setting the threshold for T cell signaling. Our data show that agrin induces the aggregation of signaling proteins and the creation of signaling domains in both immune and nervous systems through a common lipid raft pathway.

T cell-specific gamma genes in C57BL/10 mice. Sequence and expression of new constant and variable region genes

The T cell-specific gamma genes in C57BL/10 (B10) mice have been analyzed. Based on the cDNA sequences of these genes from antigen-specific MHC-restricted cytotoxic T cells, we found that the repertoire of these genes is not as limited as previously postulated (8). T cells from the B10 mice express an identical copy of V gamma J gamma C gamma (V gamma 10.8A-JC gamma 10.5) transcript previously found in T cells of BALB/c mice. In addition, a potentially functional mRNA using V gamma 10.8B and newly identified J gamma and C gamma gene segments were found. The new J gamma C gamma (JC gamma 10.8) is located 5' to the inverted V gamma 10.8B in the germline DNA of both B10 and BALB/c mice. This new C gamma is only 77 and 66% homologous to the C gamma 10.5 at the nucleotide and deduced protein sequences, respectively, thus making it a potential isotype of the C gamma genes reported previously. The V gamma 5.7, J gamma 2.3 gene segments and pseudogene C gamma 7.5 found in the germline DNA of BALB/c mice are absent in B10 mice. The loss of this gamma chain pseudogene in the B10 mouse strain, and the retention of all potentially functional V gamma, J gamma, and C gamma genes with highly conserved coding sequences supports the importance of these genes.

Hydrothermal carbonization of anaerobically digested maize silage

Hydrochars were prepared by hydrothermal carbonization (HTC) of maize silage previously treated at 55 °C in a two-stage solid-state reactor system. The HTC was carried out in a 1-L stirred pressure reactor with pH regulation by citric acid. The treated silage carbonized at relatively mild conditions (190 °C, 2 h), and the hydrochars showed mainly amorphous macro-size features with a carbon content of 59-79% (ash-free, dry) and a higher heating value of 25-36 MJ kg⁻¹. Temperature was the main influencing factor. The surface area according to Brunauer-Emmett-Teller (BET) analysis was highest at 190 °C (12.3 m²) g⁻¹). Based on these results, the hydrochars are potentially interesting for applications such as an alternative fuel or a soil conditioner.

Repetitive transcranial magnetic stimulation activates specific regions in rat brain

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive technique to induce electric currents in the brain. Although rTMS is being evaluated as a possible alternative to electroconvulsive therapy for the treatment of refractory depression, little is known about the pattern of activation induced in the brain by rTMS. We have compared immediate early gene expression in rat brain after rTMS and electroconvulsive stimulation, a well-established animal model for electroconvulsive therapy. Our result shows that rTMS applied in conditions effective in animal models of depression induces different patterns of immediate-early gene expression than does electroconvulsive stimulation. In particular, rTMS evokes strong neural responses in the paraventricular nucleus of the thalamus (PVT) and in other regions involved in the regulation of circadian rhythms. The response in PVT is independent of the orientation of the stimulation probe relative to the head. Part of this response is likely because of direct activation, as repetitive magnetic stimulation also activates PVT neurons in brain slices.

Agrin mediates cell contact-induced acetylcholine receptor clustering

One of the important events in synapse formation is the accumulation of neurotransmitter receptors beneath the presynaptic nerve terminal. Agrin is a component of the synaptic basal lamina that induces the clustering of acetylcholine receptors when bath-applied to muscle fibers in culture. When a cDNA encoding a putative agrin protein is transfected into cells, the molecule is secreted and concentrated on the extracellular surface. Coculture of transfected cells with muscle fibers induces the formation of receptor patches at contact sites. These results demonstrate that expression of a single gene encoding agrin confers receptor clustering that is restricted to specific sites of cell-muscle contact.

Cloning, analysis, and expression of murine perforin 1 cDNA, a component of cytolytic T-cell granules with homology to complement component C9

The nucleotide sequence coding for the cytotoxic T-lymphocyte (CTL) protein perforin 1 (P1) has been determined and the corresponding protein sequence has been derived. Murine CTL cDNA libraries contained in the vector lambda gt11 were screened by using a monospecific antiserum to purified P1. Three recombinant phages were isolated and their cDNA inserts were sequenced. The derived protein sequence contains 554 amino acids and displays, as expected, considerable homology with certain functional domains in the complement components C9, C8 alpha, C8 beta, and C7. The identity of P1 cDNA clones was verified by prokaryotic expression and the reactivities of antisera produced to the expressed proteins. In addition, antisera were produced to two synthetic peptides located in the center and C-terminal portions of P1. All antisera reacted with purified P1. In Northern blot analyses, P1 cDNA probes recognized a 2.9-kilobase mRNA only in CTL. Perforin mRNA was found in all cloned CTL and in all mixed lymphocyte reactions that gave rise to cytotoxic cells. Perforin mRNA was also detected in virus-specific CTL that had been generated in vivo and isolated from liver tissue of mice infected with lymphocytic choriomeningitis virus. The cell-specific expression of perforin is consistent with its postulated role in cytolysis.

Identical V beta T-cell receptor genes used in alloreactive cytotoxic and antigen plus I-A specific helper T cells

T lymphocytes involved in the cellular immune response carry cell-surface receptors responsible for antigen and self recognition. This T-cell receptor molecule is a heterodimeric protein consisting of disulphide-linked alpha- and beta-chains with variable (V) and constant (C) regions. Several complementary DNA and genomic DNA clones have been isolated and characterized. These analyses showed that the genomic arrangement and rearrangement of T-cell receptor genes using VT, diversity (DT), joining (JT) and CT gene segments is very similar to the structure of the known immunoglobulin genes. We have isolated two cDNA clones from an allospecific cytotoxic T cell, one of which shows a productive V beta-J beta-C beta 1 rearrangement without an intervening D beta segment. This V beta gene segment is identical to the V beta gene expressed in a helper T-cell clone specific for chicken red blood cells and H-21. The other clone carries the C beta 2 gene of the T-cell receptor, but the C beta 2 sequence is preceded by a DNA sequence that does not show any similarity to V beta or J beta sequences.

Expression of agrin in the developing and adult rat brain

Agrin, a synaptic basal lamina protein, is essential for the formation of the vertebrate neuromuscular junction. Agrin's role in synaptogenesis in the central nervous system has, however, not been elucidated. Therefore, we performed immunohistochemical analysis of agrin localization in adult rat brain using agrin-specific polyclonal antibodies. Our results show that agrin immunoreactivity is detected in neuronal cells throughout the brain, and that agrin is expressed in many morphologically and neurochemically distinct neuronal populations. Within neurons, agrin-immunoreactive material is present in dendrites. To determine agrin isoform expression in the central nervous system, we analysed the pattern of expression of several isoforms during development of the rat brain. Our results indicate that alternative splicing of agrin is specifically regulated in the nervous system; isoforms of the Y=4 (i.e. Ag x,4,0, Ag x,4,8 and Ag x,4,19), Z=8 and Z=19 type are expressed exclusively in the nervous system. Agrin expression precedes synaptogenesis and is developmentally regulated in neural tissues. To evaluate stimuli that may be involved in the regulation of agrin expression, we monitored the patterns of isoform expression following a depolarizing stimulus. Our results show that agrin expression in the adult hippocampus is regulated in an activity-dependent manner, with kinetics of induction resembling a delayed early response gene.

T cell receptor variable gene usage in a specific cytotoxic T cell response. Primary structure of the antigen-MHC receptor of four hapten-specific cytotoxic T cell clones

The primary structure of the alpha and beta chains of the T cell antigen receptor in four cytotoxic T cell clones specific for N-iodoacetyl-sulfonic-naphthyl-ethylene-diamine (AED)-haptenated target cells displaying a particular class I MHC molecule has been determined. Two of the T cell clones, 8/10-2 and 5/10-20K, recognize AED-modified targets in association with H-2Kb, while the other two clones 5/10-20D and C9 react with AED-modified cells in the context of H-2Db. Comparison of the nucleotide sequences of both the alpha and beta chain cDNAs and their deduced protein sequences indicates that a specific variable gene segment was not used to recognize the hapten and/or class I gene products. Furthermore, there does not appear to be any conserved amino acid residues used in the AED-specific response other than the framework amino acids. However, when the two clones 8/10-2 and 5/10-20D were compared, a striking similarity was seen in the J segments. These two clones that recognize AED in the context of different MHC epitopes used identical J alpha (J alpha 810) and J beta (J beta 2.6) gene segments. C9, specific for AED-Db, shared identical V beta (V beta 6) and J beta gene segments (J beta 1.1) as those of a cytotoxic T cell that recognizes allogeneic targets expressing Db. These data indicate that a simple rule governing the usage of the variable regions of either the alpha or beta T cell receptor (TcR) genes in the recognition of antigen and MHC gene products cannot be formulated. However, subtle similarities can be detected in some situations between the primary structures of the TcR and the targets they recognize.

No functional gamma-chain transcripts detected in an alloreactive cytotoxic T-cell clone

Three groups of genes that undergo rearrangements during T-cell maturation have been isolated from T cells. Two of them encode the alpha- and beta-subunits of the T-cell antigen receptor and are shared between antigen-specific, major histocompatibility (MHC) class I-restricted cytotoxic T cells and antigen-specific, MHC class II-restricted helper T cells. The third group of genes, called gamma, is preferentially transcribed in cytotoxic T cells. This led to the hypothesis that the unidentified gamma-gene products could be part of a putative T-cell receptor responsible for MHC class I recognition. We report here on the isolation of three different types of gamma-gene transcripts of an alloreactive cytotoxic T-cell clone (3F9). Two are derived from two rearrangements that have occurred at the same locus (V gamma 10.8A to J gamma 10.5 and transcribed with C gamma 10.5), while the third involves a new V gamma-gene segment that is joined to J gamma 13.4 and transcribed with C gamma 13.4. All these rearrangements are abortive and lead to the formation of non-functional gamma-chain genes because the proper translational reading frame is not maintained. Because the second copy of the C gamma 13.4 gene segment is deleted and as C gamma 7.5 is considered to be a pseudogene and has not undergone any rearrangements in 3F9, we conclude that the alloreactive cytotoxic T-cell clone 3F9 does not contain a functional transcript of a known gamma-chain gene.

Adsorption/desorption phenomena on pure and Teflon AF-coated titania surfaces studied by dynamic contact angle analysis

As a result of inflammatory processes, plaque formation on dental titanium implants often leads to clinically pathogenic situations. This special biofilm formation on (bio)materials in contact with saliva is initiated by ionic and protein interactions. In this interfacial process, albumin becomes a main constituent of dental pellicle. Interfacial reactions change the surface characteristics. They determine the following steps of macromolecular adsorption and bacterial adhesion. This work focuses on the dynamic contact angle analysis (DCA), which is a tool for online measurements of dynamic changes of wettability without disturbing the interface during detection. Repeatability of the DCA method has been assessed according to the Bland and Altman method. The kinetics and equilibrium data of shifts in the wetting tension hysteresis indicate ionic influences at the titanium/bovine serum albumin (BSA) interface: the Ca-mediated increase of the BSA adsorption on titanium and the adsorption maximum at the isoelectric point (IEP) of BSA. Ti was surface modified by Teflon AF polymeric coatings. The result of the assessment gives reason to consider Teflon AF as a reference material for DCA repeatability studies. This surface modification caused drastic changes in the dynamic interfacial reactions. Shifts in the wetting tensions during DCA adsorption-desorption experiments clearly demonstrated the partially irreversible adsorption of BSA on Teflon AF. In contrast, reversible adsorption behavior was detected on pure Ti surfaces. These findings strengthen the hypothesis that the analysis of dynamic changes in wetting tension and wetting tension hysteresis is a sensitive analytical method for the detection of dynamic interfacial changes at biomaterial/biosystem interfaces during the initial steps of biofilm formation.

A luminescent Pt2Fe spin crossover complex

A heterotrinuclear luminescent [Pt₂Fe] spin crossover (SCO) complex was developed, synthesized, and investigated.

Multifunctional nature of UV-irradiated nanocrystalline anatase thin films for biomedical applications

Anatase is known to decompose organic material by photocatalysis and to enhance surface wettability once irradiated by ultraviolet (UV) light. In this study, pulse magnetron-sputtered anatase thin films were investigated for their suitability with respect to specific biomedical applications, namely superhydrophilic and biofilm degrading implant surfaces. UV-induced hydrophilicity was quantified by static and dynamic contact angle analysis. Photocatalytic protein decomposition was analyzed by quartz crystal microbalance with dissipation. The surfaces were characterized by X-ray diffraction, atomic force microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The radical formation on anatase, responsible for photocatalytic effects, was analyzed by electron spin resonance spectroscopy. Results have shown that the nanocrystalline anatase films, in contrast to reference titanium surfaces, were sensitive to UV irradiation and showed rapid switching towards superhydrophilicity. The observed decrease in carbon adsorbents and the increase in the fraction of surface hydroxyl groups upon UV irradiation might contribute to this hydrophilic behavior. UV irradiation of anatase pre-conditioned with albumin protein layers induces the photocatalytic decomposition of these model biofilms. The observed degradation is mainly caused by hydroxyl radicals. It is concluded that nanocrystalline anatase films offer different functions at implant interfaces, e.g. bedside hydrophilization of anatase-coated implants for improved osseointegration or the in situ decomposition of conditioning films forming the basal layer of biofilms in the oral cavity.

T-cell antigen receptors with identical variable regions but different diversity and joining region gene segments have distinct specificities but cross-reactive idiotypes

The T-cell antigen receptor alpha-chain genes of an alloreactive, H-2Db-specific cytotoxic T-cell clone (3F9) are described. This study and our work on the 3F9 beta-chain genes reveal that the variable region gene segments for the alpha and beta chains expressed in 3F9 are identical to the ones used by a chicken erythrocyte-specific, I-Ab-restricted helper T-cell clone (LB2). These two clones differ, however, in the diversity and joining portions of the alpha and beta chains of their T-cell receptor molecules. The analysis of 3F9 and LB2 with monoclonal antibodies specific for the 3F9 T-cell receptor shows that these two T-cell clones share the same idiotype; however, 3F9 and LB2 do not exhibit any antigen and/or major histocompatibility complex cross-reactivity. This suggests that the diversity and joining regions of the T-cell receptor may play a key role in antigen and/or major histocompatibility complex recognition.

Time-resolved IR spectroscopy of a trinuclear palladium complex in solution

Time-resolved IR spectroscopic methods covering the femto- to microsecond range in combination with (TD-)DFT computations were used to investigate the electronically excited state structure of a trinuclear Pd complex.