Specific biofunctional performances of the hydroxyapatite-sodium maleate copolymer hybrid coating nanostructures evaluated by in vitro studies

The nanohybrid structures consisting of hydroxyapatite (HA) and sodium maleate-vinyl acetate copolymer (MP) deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique on Ti surfaces were investigated for specific biological qualities required in bone implantology. The data from in vitro studies demonstrated that human primary osteoblasts (OBs) firmly adhered to Ti coated with HA-MP as indicated by cytoskeleton and vinculin dynamics. OBs spread onto biomaterial surface and formed groups of cells which during their biosynthetic activity expressed OB phenotype specific markers (collagen and non-collagenous proteins) and underwent controlled proliferation.

Folding and maturation of tyrosinase-related protein-1 are regulated by the post-translational formation of disulfide bonds and by N-glycan processing

In this study we have explored the endoplasmic reticulum associated events accompanying the maturation of the tyrosinase-related protein-1 (TRP-1) nascent chain synthesized in mouse melanoma cells. We show that TRP-1 folding process occurs much more rapidly than for tyrosinase, a highly homologous protein, being completed post-translationally by the formation of critical disulfide bonds. In cells pretreated with dithiothreitol (DTT), unfolded TRP-1 is retained in the endoplasmic reticulum by a prolonged interaction with calnexin and BiP before being targeted for degradation. The TRP-1 chain was able to fold into DTT-resistant conformations both in the presence or absence of alpha-glucosidase inhibitors, but folding occurred through different pathways. During the normal folding pathway, TRP-1 interacts with calnexin. In the presence of alpha-glucosidase inhibitors, the interaction with calnexin is prevented, with TRP-1 folding being assisted by BiP. In this case, the process has similar kinetics to that of untreated TRP-1 and yields a compact form insensitive to DTT as well. However, this form has different thermal denaturation properties than the native conformation. We conclude that disulfide bridge burring is crucial for the TRP-1 export. This suggests that although various folding pathways may complete this process, the native form may be acquired only through the normal unperturbed pathway.

Mutations at critical N-glycosylation sites reduce tyrosinase activity by altering folding and quality control

Tyrosinase is a copper-containing enzyme that regulates melanin biosynthesis in mammals. Mutations at a single N-glycosylation sequon of tyrosinase have been reported to be responsible for oculocutaneous albinism type IA in humans, characterized by inactive tyrosinase and the total absence of pigmentation. To probe the role that each N-glycosylation site plays in the synthesis of biologically active tyrosinase, we analyzed the calnexin mediated folding of tyrosinase N-glycosylation mutants. We have determined that four of the six potential N-glycosylation sites, including that associated with albinism, are occupied. Analysis of the folding pathway and activity of 15 tyrosinase mutants lacking one or more of the occupied N-glycosylation sites shows that glycans at any two N-glycosylation sites are sufficient to interact with calnexin and give partial activity, but a specific pair of sites (Asn(86) and Asn(371)) is required for full activity. The mutants with less than two N-glycosylation sites do not interact with calnexin and show a complete absence of enzyme activity. Copper analysis of selected mutants suggests that the observed partial activity is due to two populations with differential copper content. By correlating the degree of folding with the activity of tyrosinase, we propose a local folding mechanism for tyrosinase that can explain the mechanism of inactivation of tyrosinase N-glycosylation mutants found in certain pigmentation disorders.

Protein specific N-glycosylation of tyrosinase and tyrosinase-related protein-1 in B16 mouse melanoma cells

Tyrosinase and tyrosinase-related protein-1 (TRP-1) are two melanogenic enzymes that regulate melanin biosynthesis. Both are glycoproteins and belong to the TRP-1 gene family. They share a significant level of sequence similarity in several regions, including the catalytic domain and the potential N-glycosylation sites. We have recently shown that inhibition of the early steps of N-glycan processing in B16F1 cells dramatically affects tyrosinase activity and melanin synthesis. We present here results on N-glycan processing of TRP-1 and tyrosinase and compare the maturation process and activity of both glycoproteins in the presence of inhibitors of the endoplasmic reticulum stages of N-glycosylation. N-glycan analysis reveals that each of these two glycoproteins contains a mixture of high-mannose and sialylated complex N-glycans. However, in contrast to TRP-1, tyrosinase presents a homogeneous high-mannose glycoform, also. In the presence of alpha-glucosidases inhibitors, the maturation of tyrosinase N-glycans is completely inhibited, whereas TRP-1 is still able to acquire some complex glycans, indicating that endomannosidase acts preferentially on the later glycoprotein. In addition, the dopa-oxidase activity of tyrosinase is totally abolished, whereas for TRP-1 it is only partially affected. The results suggest that despite their structural similarity, tyrosinase is more sensitive than TRP-1 to perturbations of early N-glycan processing, in terms of maturation and catalytical activity.

Investigation of the intracellular transport of tyrosinase and tyrosinase related protein (TRP)-1. The effect of endoplasmic reticulum (ER)-glucosidases inhibition

Melanin biosynthesis is completely inhibited in the B16 melanoma cells following their incubation with inhibitors of the two ER glucosidases. This is primarily due to the inactivation of tyrosinase. Under the same conditions, the DOPA-oxidase activity of TRP-1 was only partially affected. In this report we investigate the effects of the perturbation of N-glycan processing in ER on the transport and activation of tyrosinase and TRP-1. We have localized the DOPA-oxidase activity in normal and inhibited cells and suggest that the first DOPA-reactive compartment of the secretory pathway (trans Golgi network) is also the site of tyrosinase activation. The inhibition of N-glycan processing does not affect the intracellular trafficking of the two melanogenic enzymes that are correctly transported to melanosomes. Immunoprecipitation experiments followed by analysis in SDS-PAGE under non-reducing conditions suggest that in inhibited cells, both tyrosinase and TRP-1 are synthesized in a modified conformation as compared to the normal proteins. These data suggest that the inhibition of melanin synthesis is not due to a defective transport but rather to conformational changes induced in the structure of tyrosinase and TRP-1 during their transit through the ER.

Critical roles of glycosaminoglycan side chains of cartilage proteoglycan (aggrecan) in antigen recognition and presentation

Systemic immunization of BALB/c mice with proteoglycan (aggrecan) from fetal human cartilage induces progressive polyarthritis, an experimental disease similar to human rheumatoid arthritis. The development of the disease in this genetically susceptible murine strain is based on cross-reactive immune responses between the immunizing fetal human and mouse self-proteoglycans. One of the cross-reactive and arthritogenic T cell epitopes (92GR/QVRVNSA/IY) is localized in the G1 domain of human/murine proteoglycan. Susceptible BALB/c mice, however, develop arthritis only if both the chondroitin sulfate (CS) and keratan sulfate (KS) side chains of the arthritogenic human proteoglycans are removed. The function of these two glycosaminoglycan side chains is opposite. The presence of a KS side chain in adult proteoglycan inhibits the recognition of arthritogenic T cell epitopes, prevents the development of T cell response, and protects animals from autoimmune arthritis. In contrast, the depletion of the CS side chain generates clusters of CS stubs and provokes a strong B cell response. These carbohydrate-specific B cells are the most important proteoglycan APC. Taken together, proteoglycan-induced progressive polyarthritis is dictated by three major components: genetic background of the BALB/c strain, highly specific T cell response to epitope(s) masked by a KS chain in aging tissue, and the presence of proteoglycan (CS stub)-specific B cells required for sufficient Ag presentation.

A proteoglycan (aggrecan)-specific T cell hybridoma induces arthritis in BALB/c mice

Aggrecan, the high buoyant density cartilage proteoglycan (PG), has been shown to induce progressive polyarthritis and ankylosing spondylitis in genetically susceptible BALB/c mice. To further characterize the nature of the autopathogenic effector T cells operating in these mice and to determine the region(s) of the PG molecule recognized by these T cells, we generated PG-specific T cell hybridomas from arthritic mice. One of the PG-specific T cell hybridomas (5/4E8), when injected into naive irradiated BALB/c mice, was capable of inducing clinical and histopathologic signs of arthritis. Massive swelling and redness of the paws dominated the clinical picture. A reactive synovial cell proliferation, the accumulation of hybridoma and inflammatory cells in the enlarged joint space, the loss of PG from the superficial layer of the articular cartilage, and the erosion of articular surface were identical histopathologic signs to those found either in primary or adoptive transfer of PG-induced arthritis. The PG-specific and arthritogenic T cell hybridoma (5/4E8) expressed TCR-alpha beta + (V beta 4), CD4+, and CD8- phenotypes and belonged to the Th1 subset, as the cells secreted IL-2 and IFN-gamma, but not IL-4 upon PG stimulation, and the response was MHC class II (I-Ad)-restricted. These observations provide direct evidence that PG-specific Th cells play crucial roles in autoimmune arthritic processes.

Antigen-specific B cells present cartilage proteoglycan (aggrecan) to an autoreactive T cell hybridoma derived from a mouse with proteoglycan-induced arthritis

Cartilage proteoglycan (aggrecan)-induced polyarthritis in BALB/c mice is characterized by chronic inflammation and destruction of joint tissues similar to that observed in human rheumatoid arthritis. The immunization of mice with fetal human proteoglycan (PG) elicits specific antibodies to the immunizing antigen of which a population cross-reacts with native mouse PG. This (auto)antibody production is immediately followed by an explosive proliferation of autoreactive T cells, suggesting that PG-specific B cells may participate in antigen presentation of PG to autoreactive T cells. We therefore isolated B cells from the spleens and lymph nodes of PG-immunized mice and examined their ability to present PG to a PG-specific T cell hybridoma. The antigen-specific T cell responses elicited by B cells from PG-immunized mice (both arthritic and clinically asymptomatic) were markedly higher than those of non-immune mice and keyhole limpet haemocyanin (KLH)-immunized mice, and these B cells could present low PG concentrations. Levels of B cell presentation corresponded with the serum levels of PG-specific antibodies, implying that these B cells were presenting the PG specifically via their surface immunoglobulin. This B cell-T cell interaction was strongly dependent on MHC class II/T cell receptor (TCR), LFA-1/intercellular adhesion molecule-1 (ICAM-1) and CD28/B7 interactions, as antibodies to Ia, ICAM-1 and B7-2 (but not to B7-1) markedly reduced presentation. These data indicate that PG-specific B cells may play an essential role in governing the development of PG-induced arthritis.

A proteoglycan (aggrecan)-specific T cell hybridoma induces arthritis in BALB/c mice

Aggrecan, the high buoyant density cartilage proteoglycan (PG), has been shown to induce progressive polyarthritis and ankylosing spondylitis in genetically susceptible BALB/c mice. To further characterize the nature of the autopathogenic effector T cells operating in these mice and to determine the region(s) of the PG molecule recognized by these T cells, we generated PG-specific T cell hybridomas from arthritic mice. One of the PG-specific T cell hybridomas (5/4E8), when injected into naive irradiated BALB/c mice, was capable of inducing clinical and histopathologic signs of arthritis. Massive swelling and redness of the paws dominated the clinical picture. A reactive synovial cell proliferation, the accumulation of hybridoma and inflammatory cells in the enlarged joint space, the loss of PG from the superficial layer of the articular cartilage, and the erosion of articular surface were identical histopathologic signs to those found either in primary or adoptive transfer of PG-induced arthritis. The PG-specific and arthritogenic T cell hybridoma (5/4E8) expressed TCR-alpha beta + (V beta 4), CD4+, and CD8- phenotypes and belonged to the Th1 subset, as the cells secreted IL-2 and IFN-gamma, but not IL-4 upon PG stimulation, and the response was MHC class II (I-Ad)-restricted. These observations provide direct evidence that PG-specific Th cells play crucial roles in autoimmune arthritic processes.

Presentation of cartilage proteoglycan to a T cell hybridoma derived from a mouse with proteoglycan-induced arthritis

Immunization of BALB/c mice with human fetal cartilage proteoglycan (PG) produces progressive polyarthritis, and T cells play key roles in the development of the disease. To gain an understanding of how PG is presented to autoreactive T cells by synovial antigen-presenting cells (APC), we examined the abilities of various syngeneic APC in presenting PG to a specific T cell hybridoma 5/4E8, derived from a mouse with PG-induced arthritis. A20 B lymphoma cells and spleen cells were strong presenters of PG, but synoviocytes and P388D1 macrophages could only present PG effectively after stimulation with interferon-gamma (IFN-gamma). The IFN-gamma exerted its effect by up-regulating both MHC class II and intercellular adhesion molecule-1 (ICAM-1) expression by these cells as neutralizing antibodies to Ia, LFA-1 and ICAM-1 inhibited presentation. Our studies also showed that synoviocytes and spleen cells took up and processed PG more rapidly than the cell lines. Cysteine and serine protease-dependent antigen presentation of PG was blocked at 4 degrees C, 18 degrees C and by chloroquine treatment, indicating that presentation required active uptake and processing in an acidic compartment, probably in lysosomes. Also, keratan sulphate-depleted and cyanogen bromide (CNBr) and 2-nitro-5-thiocyanobenzoic acid (NTCB)-cleaved PG elicited stronger T cell responses, as they were more easily processed than the native molecule. Furthermore, CNBr-generated peptides were presented by fixed APC, indicating that core protein fragments of cartilage PG can be presented directly by APC in context with MHC class II molecules.

The action of the collagen-Fe2+ complex at tissular level

The aim of this paper is to know the iron dynamics and action of the collagen-Fe2+ complex at tissular level. The results showed that the collagen-Fe2+ complex is biocompatible at tissular level and the ferrous iron entered the animal organism on the well-known metabolic pathways. When a high dose of the complex was administered, an overloading with hemosiderin of macrophages and hepatocytes was noticed.