Tumor risk by tissue engineering: cartilaginous differentiation of mesenchymal stem cells reduces tumor growth

OBJECTIVE

Implantation of autologous chondrocytes (AC) is a promising option for the treatment of cartilage defects, but problems with cell harvesting, dedifferentiation, or the donor age limit the clinical outcome. Mesenchymal stem cells (MSC) gain much interest because of their simple isolation and multipotential differentiation capacity along with their immunosuppressive properties. The latter might introduce tumor manifestation. The influence of undifferentiated and chondrogenically differentiated MSC or AC on tumor growth and metastasis formation was investigated in a murine melanoma model.

METHODS

Allogeneic melanoma cells and either syngeneic MSC (C3H10T1/2, transduced with enhanced green fluorescent protein gene) or AC were co-injected at a distance of 3 cm into the contra lateral groins of five mice/group, and evaluated macroscopically and histologically after 4 weeks.

RESULTS

Undifferentiated MSC migrated to the tumor site and induced strong tumor growth and metastasis formation. Even avital MSC promoted tumor growth and spreading, but insignificantly without detectable MSC at the tumor site. Chondrogenically differentiated MSC did not migrate and had a significantly lower impact on tumor growth and spreading; AC had no measurable influence on melanoma cells.

CONCLUSIONS

Our data suggest that differentiation of MSC reduces MSC-dependent promotion of latent tumors and that native AC do not introduce any increased risk of tumor growth. The question of how far MSC should be differentiated prior to clinical application should be addressed in further studies.

The role of human beta-defensin-2 in bone

Osteomyelitis often causes functional impairment due to tissue destruction. This report demonstrates a novel previously unappreciated role of osteoblasts. Samples of osteomyelitic bone and bacterially challenged osteoblasts produce increased amounts of antimicrobial peptides in order to combat bacterial bone infection. An osteomyelitis mouse model confirmed the osseous induction of the murine homologue of human beta-defensin-2, suggesting a central role in the prevention of bacterial bone infection. Antimicrobial peptides are effectors of the innate defence system and play a key role in host protection at cellular surfaces. Some of them are produced constitutively, whereas others are induced during infection. Human beta-defensins represent a major subclass of antimicrobial peptides and act as a first line of defence through their broad spectrum of potent antimicrobial activity. The aim of the present in-vitro and in-vivo investigations was to study the expression and regulation of human beta-defensin-2 in the case of bacterial bone infection and to analyse the effects of immunosuppressive drugs on bone-derived antimicrobial peptide expression. Samples of healthy human bone, osteomyelitic bone and cultured osteoblasts (hFOB cells) were assessed for the expression of human beta-defensin-2. Regulation of human beta-defensin-2 was studied in hFOB cells after exposure to bacterial supernatants, proinflammatory cytokines and immunosuppressive drugs (glucocorticoids and methotrexate) and was assayed by enzyme-linked immunosorbent assay. An osteomyelitis mouse model was performed to demonstrate the regulation of the murine homologue of human beta-defensin-2, named murine beta-defensin-3, by real-time reverse transcription-polymerase chain reaction and immunohistochemistry. Healthy human bone and cultured osteoblasts are able to produce human beta-defensin-2 under standard conditions. Samples of infected bone produce higher levels of endogenous antibiotics, such as human beta-defensin-2, when compared with samples of healthy bone. A clear induction of human beta-defensin-2 was observed after exposure of cultured osteoblasts to gram-positive bacteria or proinflammatory cytokines. Additional treatment with glucocorticoids or methotrexate prevented bacteria-mediated antimicrobial peptide induction in cultured osteoblasts. The osteomyelitis mouse model demonstrated transcriptional upregulation of the murine homologue of human beta-defensin-2, namely murine beta-defensin-3, in bone after intraosseous contamination of the tibia. Human and murine bone have the ability to produce broad-spectrum endogenous antibiotics when challenged by micro-organisms in vitro and in vivo. Immunosuppressive drugs, such as glucocorticoids or methotrexate, may increase the susceptibility to bone infection by decreasing antimicrobial peptide expression levels in case of microbial challenge. The induction of human beta-defensin-2 following bacterial contact suggests a central role of antimicrobial peptides in the prevention of bacterial bone infection.

Effects of pleiotrophin, a heparin-binding growth factor, on human primary and immortalized chondrocytes

OBJECTIVE

Pleiotrophin (PTN) is a secreted heparin-binding peptide expressed in mesodermal and neuroectodermal cells during development, but rarely in adult tissues. In fetal and juvenile, but not in mature cartilage, PTN is abundant. Furthermore, PTN is re-expressed in chondrocytes in early stages of osteoarthritis (OA). Since little is known about the functions of PTN in cartilage, we investigated the occurrence of PTN receptors in human articular cartilage in situ and PTN effects on human primary and immortalized chondrocytes in vitro.

METHODS

Receptor expression and regulation was monitored by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. PTN effects and signal transduction were studied by electrophoretic mobility shift, Boyden chamber cell migration and proliferation assays, effects on gene expression by real time RT-PCR and that on nitric oxide (NO) by the Griess reaction.

RESULTS

Of the putative PTN signaling receptors, immortalized and primary chondrocytes (pc) expressed the anaplastic lymphoma kinase (ALK), less the receptor-type protein tyrosine phosphatase zeta/beta (PTPzeta). ALK expression was upregulated upon ligand exposure. PTN stimulation activated the AP-1 (activator protein-1) transcription factor and altered gene expression. Prolonged stimulation induced PTN mRNA expression slightly, reduced vascular endothelial growth factor (VEGF) mRNA as well as NO production. Whereas mRNA expression of matrix metalloproteinases (MMPs) MMP-1 and MMP-13 was reduced, their inhibitors TIMP-1 and TIMP-2 were induced. Furthermore, PTN stimulated chondrocyte migration and proliferation.

CONCLUSIONS

These results show that PTN is an autocrine growth factor in cartilage. We suggest that PTN may be involved in the clustering and proliferation of chondrocytes observed in the early stages of OA.

TLR-2-mediated induction of vascular endothelial growth factor (VEGF) in cartilage in septic joint disease

Bacterial arthritis is a progressive joint disease which includes rapid destruction of articular cartilage even after clearance of the causal factor. The resulting post-infectious arthropathy is mainly characterized by self-perpetuating joint destruction and extensive angiogenesis in the emerging pannus-like synovial membrane, but the underlying molecular mechanisms of the bacteria-initiated process remain incompletely understood. This study was conducted to elucidate the expression and regulation of angiogenic and cartilage-destructive vascular endothelial growth factor (VEGF) in septic arthritis. For that purpose, aspirates of synovial fluid from patients with pyogenic arthritis were examined for VEGF levels by ELISA. In vitro studies with primary and immortalized chondrocytes were performed to determine whether Gram-positive and Gram-negative bacteria induce VEGF expression, by using real-time RT-PCR, ELISA, and immunohistochemistry. Activation of the transcription factor AP-1 was assessed by EMSA experiments. The necessity of the Toll-like receptor-2 (TLR-2), ERK-1/-2, and AP-1 pathway for infectious VEGF induction in chondrocytes was examined by using specific blocking reagents. ELISA experiments revealed that aspirates of synovial fluid from patients with pyogenic arthritis contain elevated levels of VEGF. The in vitro results confirmed the transcriptional induction of VEGF in chondrocytes after bacterial challenge by real-time RT-PCR, ELISA, and immunohistochemistry. This activation was mediated by a TLR-2-, ERK-1/-2-, and AP-1-dependent pathway. The findings demonstrate the expression of Toll-like receptors on mesenchymal articular chondrocytes and reveal TLR-2-mediated VEGF induction in human chondrocytes after Gram-positive bacterial sensing. Since VEGF is a potent angiogenic and tissue remodelling factor, evidence that Toll-like receptors contribute to destructive arthropathy after microbial joint infection is provided. VEGF may be a therapeutic target in the future for the prevention of post-infectious cartilage degradation in articular joints.

Expression and regulation of human β-defensin-2 in osteoarthritic cartilage

Defensins are antibiotic peptides that are involved in host defence at epithelial and mesenchymal surfaces. Previous studies have shown the induction of human beta-defensin-3 (HBD-3) in osteoarthritic joints, suggesting that these molecules have functions in addition to their ability to kill microbes. The aim of this study was to investigate the production of a further human beta-defensin, named HBD-2, in osteoarthritis (OA) and to determine its regulation by inflammatory cytokines. Healthy and osteoarthritic cartilage was assessed for HBD-2 expression by RT-PCR, immunohistochemistry, and ELISA. C28/I2 chondrocytes, primary chondrocytes, and cartilage explants were cultured for in vitro studies. After 24 h of stimulation with tumour necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1) or IL-6, real-time RT-PCR and ELISA experiments were performed to evaluate the effect of these cytokines on the production of HBD-2. In contrast to healthy cartilage, HBD-2 expression was identified in most of the OA samples examined (eight of ten). Cytokines that are potentially involved in the pathogenesis of OA, namely TNF-alpha, IL-1, and IL-6, were transcriptional inducers of HBD-2 in cultured chondrocytes and cartilage explants in vitro, as measured by real-time RT-PCR and ELISA. These results illustrate the induction of HBD-2 in osteoarthritic cartilage and suggest that it is a further factor in the pathogenesis of OA. However, further studies are required to elucidate the role played by HBD-2 in osteoarthritic cartilage.

The role of vasculature and angiogenesis for the pathogenesis of degenerative tendons disease

More than 100 years ago Wilhelm Roux (1895) introduced the term "functional adaptation to anatomy and physiology". Compared with other organ systems the functional adaptation processes are best identifiable in the locomotor system, like for example in the two types of tendons: traction and gliding tendons. Traction tendons are tendons where the direction of pull is in line with the direction of the muscle (e.g. Achilles tendon). Gliding tendons (e.g. tibialis posterior tendon) change direction by turning around a bony or fibrous hypomochlion. In this region the tendon is subjected to intermittent compressive and shear forces and the extracellular matrix consists of avascular fibrocartilage. Avascularity is considered to be a key factor for the etiology of degenerative tendon disease. The repair capability after repetitive microtrauma is strongly compromised in avascular tissue of gliding tendons. Reduced vascularity is not a specific feature of gliding tendons; several studies have shown that the number and size of blood vessels are largely shortened in the waist of the Achilles tendon. However, histological biopsies from degenerated Achilles tendons and Doppler flow examinations revealed a high blood vessel density in patients with degenerative tendon disease. Angiogenesis is mediated by angiogenic factors and recent studies have shown that the vascular endothelial growth factor (VEGF) is highly expressed in degenerative Achilles tendons, whereas VEGF expression is nearly completely downregulated in healthy tendons. Several factors are able to upregulate VEGF expression in tenocytes: hypoxia, inflammatory cytokines and mechanical load. Since VEGF has the potential to stimulate the expression of matrix metalloproteinases and inhibit the expression of tissue inhibitors of matrix metalloproteinases tissue inhibitor of metalloproteinases (TIMP) in various cell types (e.g. endothelial cells, fibroblasts, chondrocytes), this cytokine might play a significant role for the pathogenetic processes during degenerative tendon disease. An animal experiment in the rabbit has shown that local injection of VEGF reduced the material properties of the Achilles tendon. These experimental findings are in accordance with clinical results that a locally administered (in the area with neovascularization) sclerosing drug (Polidocanol) has a beneficial effect on chronic mid-portion Achilles tendinosis. In conclusion, decreased and increased vascularity might be involved in the pathogenesis of degenerative Achilles tendon disease.

Dipeptidyl peptidase inhibitors as new drugs for the treatment of type 2 diabetes

Inhibitors of the regulatory protease dipeptidyl peptidase-IV (DPP-IV) are currently under development in preclinical and clinical studies (several pharmaceutical companies, now in Phase III) as potential drugs for the treatment of type 2 diabetes. Their development is based on the observation that DPP-IV rapidly inactivates the incretin hormone glucagon-like peptide-1 (GLP-1), which is released postprandially from the gut and increases insulin secretion. DPP-IV inhibitors stabilise endogenous GLP-1 at physiological concentrations, and induce insulin secretion in a glucose-dependent manner; therefore, they do not demonstrate any hypoglycaemic effects. Furthermore, they are orally bioavailable. In addition to their ability to protect GLP-1 against degradation, DPP-IV inhibitors also stabilise other incretins, including gastric inhibitory peptide and pituitary adenylate cyclase-activating peptide. They also reduce the antagonistic and desensitising effects of the fragments formed by truncation of the incretins. In clinical studies, when used for the treatment of diabetes over a 1-year period, DPP-IV inhibitors show improved efficacy over time. This finding can be explained by a GLP-1-induced increase in the number of beta cells. Potential risks associated with DPP-IV inhibitors include the prolongation of the action of other peptide hormones, neuropeptides and chemokines cleaved by the protease, and their interaction with DPP-IV-related proteases. Based on their mode of action, DPP-IV inhibitors seem to be of particular value in early forms of type 2 diabetes, either alone or in combination with other types of oral agents.

Expression of vascular endothelial growth factor during healing of the meniscus in a rabbit model

Our aim was to investigate vascular endothelial growth factor (VEGF) expression after lacerations of a meniscus in a rabbit model. Specimens of meniscus were examined using immunohistochemistry, enzyme-linked immunoassay and the reverse transcription polymerase chain reaction after one, two, five or ten weeks. In the periphery of the meniscus 90% of the lacerations had healed after five and ten weeks, but no healing was observed in the avascular area. Expression of VEGF protein and VEGF mRNA was found in the meniscus of both the operated and the contralateral sites but both were absent in control rabbits which had not undergone operation. The highest expression of VEGF was found in the avascular area after one week (p < 0.001). It then lessened at both the vascular and avascular areas, but still remained greater in comparison with the control meniscus (p < 0.05). Despite greater expression of VEGF, angiogenesis failed at the inner portion. These findings demonstrated the poor healing response in the avascular area which may not be caused by an intrinsic cellular insufficiency to stimulate angiogenesis.

Pleiotrophin, an embryonic differentiation and growth factor, is expressed in osteoarthritis

OBJECTIVE

Pleiotrophin (PTN) is a 15.3 kDa heparin-binding peptide, which is expressed in mesodermal and neuroectodermal cells during development, but rarely in adult tissues. In fetal or juvenile cartilage, PTN is an abundant protein and appears to be involved in chondrocyte differentiation. Since developmentally regulated factors often re-appear in the disease state, we examined PTN expression in cartilage and synovial fluid of patients with osteoarthritis (OA).

METHODS

PTN mRNA and protein expression was assayed by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot, the protein was localized by immunohistochemistry and quantified by enzyme-linked immunoassay (ELISA).

RESULTS

PTN was undetectable in normal adult cartilage, but PTN mRNA and protein were found in OA. In cartilage from the tibial plateaus of OA patients, PTN could be immunostained in clusters of superficial chondrocytes. In the synovial fluids of OA patients, PTN concentrations were elevated in earlier OA stages, but rarely in late OA stages. Chondrosarcomas were PTN-immunonegative.

CONCLUSIONS

In addition to certain types of cancer, the embryonic growth and differentiation factor PTN is found also in adults in inflammatory diseases. In OA, PTN is especially expressed in early stages, and PTN concentrations in the synovial fluid could serve as a marker for the progress of the disease. PTN might be involved in cartilage repair in OA, in particular, in earlier stages.

Stromal cell-derived factor 1 is secreted by meningeal cells and acts as chemotactic factor on neuronal stem cells of the cerebellar external granular layer

The cerebellar external granular layer (EGL) is an unusually long-lasting neural proliferative zone positioned immediately beneath the pial surface. Its position and stability critically depend on meningeal cells, as their selective destruction leads to its rapid dispersal, creating massive cortical ectopia. Similar ectopias have recently been described as a side effect of deficiency for stromal cell-derived factor 1 (SDF-1), a chemoattractant for haematopoietic precursor cell migration. Here we show that SDF-1 is present in meningeal cells in vivo and in vitro, where it is secreted in functionally relevant concentrations into the medium. Correspondingly, the SDF-1 receptor (termed CXCR4) can be demonstrated on stem cells of the external granular layer, but is absent on postmitotic cells commencing their final inward migration. We show that SDF-1 is concentrated by heparan sulphate proteoglycans highly expressed in the EGL in a laminar fashion, which thus might act to locally restrict SDF-1 action to the EGL in a kind of step gradient. In vitro, SDF-1 chemotactically attracts neuronal cells isolated from the external, but not from the internal granular layer, in a Boyden chamber assay in concentrations found in meningeal cell-conditioned medium. Selective removal of SDF-1 from conditioned media by immunoprecipitation abolishes their chemoattractive action, which can be reconstituted again by the addition of recombinant SDF-1. Meningeal cells are thus an important source for the expression of SDF-1 during brain development, which--comparable to its role in haematopoiesis--appears to be a key factor attracting precursor cells to their proliferative compartment.

The angiogenic peptide vascular endothelial growth factor is expressed in foetal and ruptured tendons

The Achilles tendon is one of the most common sites of injury and rupture. Evidence suggests that local vascularisation is involved in this aetiology. We investigated the expression of one important angiogenic factor, the vascular endothelial growth factor (VEGF), in normal and pathologic human Achilles tendons using immunohistochemical, biochemical, molecular and cell biology methods. VEGF could be immunostained in tenocytes of ruptured and foetal Achilles tendons, but not in normal adult ones. In microvessels, the VEGF receptor VEGFR-1 (flt-1) could be visualised as well. High VEGF levels were measured in homogenates from ruptured adult, lower ones in foetal and negligible concentrations in normal adult Achilles tendons using enzyme-linked immunoassay (ELISA) and Western blot experiments. Reverse transcriptase-polymerase chain reaction (RT-PCR) showed that the splice variants VEGF121 and VEGF165 are exclusively expressed. In tenocytes cultivated from newborn rat Achilles tendons, hypoxia or epidermal growth factor (EGF) raised VEGF production moderately whereas their combination resulted in a strong, synergistic induction. These results prove the presence of an angiogenic peptide and vascularisation in ruptured and foetal tendons and support the view that microtrauma or degeneration in the Achilles tendon precedes its rupture.

Splice variants VEGF121 and VEGF165 of the angiogenic peptide vascular endothelial cell growth factor are expressed in the synovial tissue of patients with rheumatoid arthritis

OBJECTIVE

To determine the expression of the angiogenic peptide vascular endothelial growth factor (VEGF, also known as vascular permeability factor, VPF) in the synovium of patients with rheumatoid arthritis (RA).

METHODS

Expression of VEGF protein from the synovial tissue of 10 patients with RA was monitored by ELISA and visualized by immunocytochemistry, and by double-staining with the VEGFR-1/flt-1. VEGF mRNA and its splice variants were determined by reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

VEGF protein was strongly increased in rheumatoid synovium and localized at the synovial surface, whereas the VEGF receptor flt-1 (VEGFR-1) was visualized on microvessels in close vicinity. In synovial tissues from all 10 patients with RA, VEGF121 and VEGF165 were identified at the mRNA level as the only VEGF splice forms expressed.

CONCLUSION

Since VEGF165 and VEGF121 are differently diffusible due to their opposite heparan sulfate-binding properties, they act at different distances. The presence of VEGF121 may explain induction of the VEGFR-1 on infiltrating blood vessels near the synovial surface.

Somatostatin inhibits the production of vascular endothelial growth factor in human glioma cells

In various cell types, the neuro- and endocrine peptide somatostatin induces inhibitory and anti-secretory effects. Since somatostatin receptors, especially of the subtype sst2A, are constantly over-expressed in gliomas, we investigated the influence of somatostatin and the receptor subtype-selective peptide/non-peptide agonists octreotide and L-054,522 on the secretion of the most important angiogenesis factor produced by gliomas, vascular endothelial growth factor (VEGF). Cultivated cells from solid human gliomas of different stages and glioma cell lines secreted variable amounts of VEGF, which could be lowered to 25% to 80% by co-incubation with somatostatin or sst2-selective agonists (octreotide and L-054,522). These effects were dose-dependent at nanomolar concentrations. Stimulation with different growth factors (EGF, bFGF) or hypoxia considerably increased VEGF production over basal levels. Growth factor-induced VEGF synthesis could be suppressed to <50% by co-incubation with somatostatin or an sst2-selective agonist; this was less pronounced in hypoxia-induced VEGF synthesis. The effects were detected at the protein and mRNA levels. These experiments indicate a potent anti-secretory action of somatostatin or sst2 agonists on human glioma cells that may be useful for inhibiting angiogenesis in these tumors.

ATP and adenosine induce ramification of microglia in vitro

Microglial cells in the healthy adult brain possess a characteristic ramified morphology with multiple branched processes, small somata and down-regulated inflammatory properties. In contrast, microglial cells isolated from new-born rat brain inevitably show a non-ramified amoeboid phenotype, which is observed in vivo after pathologic activation or during development. To identify factors that control microglial morphology we investigated the effects of purines alone or in combination with astrocyte-conditioned medium (ACM). Under optimized culture conditions postnatal rat microglial cells developed an amoeboid to ovoid phenotype. Addition of 0.6-1 mM ATP or adenosine induced the outgrowth of numerous processes after 2-3 days that could be observed also in the presence of ACM as previously reported. Culture in ACM plus ATP or adenosine yielded an optimized ramified phenotype. ATP or adenosine, but not ACM alone, also prevented the formation of a flat, amoeboid morphology induced by lipopolysaccharide (LPS); however, at 0.6-1 mM they did not reduce the initial LPS-induced activation of the transcription factor NF-kappaB. By using specific agonists or antagonists the morphological transformations could not be confined to a distinct purinoreceptor subtype, but appeared to be mediated by long-term presence of adenosine in the medium to which phosphorylated purines were rapidly hydrolyzed by microglial cells. Since ACM did not contain sufficient concentrations of ATP or adenosine, purines are not the only ramification-inducing factors present in ACM; however, they are a valuable tool to induce microglial ramification in vitro.

Influence of the somatostatin receptor sst2 on growth factor signal cascades in human glioma cells

The somatostatin receptor subtype sst2A is highly expressed, non-mutated and functionally active in gliomas. After stimulation of cultivated human U343 glioma cells with somatostatin, octreotide (sst2-, sst3- and sst5-selective peptide agonist) or the sst2-selective non-peptide agonist L-054,522 multiple signal transduction pathways are induced: elevated cAMP levels are reduced, protein tyrosine phosphatases (especially SHP2) are activated and mitogen-activated protein kinases are inhibited. Stimulation of the phosphatases resulted in dephosphorylation of activated receptors for EGF and PDGF (epidermal and platelet-derived growth factor), and as a consequence the mitogen-activated protein kinases ERK 1 and 2 (p42/p44) were de-phosphorylated in co-stimulation experiments. Furthermore, somatostatin or sst2-selective agonists reduced EGF-stimulated expression of the AP-1 complex (c-jun/c-jun) on the transcriptional and translational level. These experiments show that the interaction of stimulatory and inhibitory receptors are important mechanisms for the regulation of signal cascades and gene expression.

Topology of the signal transduction of the G protein-coupled somatostatin receptor sst2 in human glioma cells

By a dual approach, using electron microscopy and biochemical techniques, we investigated the topology of the somatostatin receptor sst2 with its inhibitory G protein Gialpha after ligand-induced stimulation and internalization in human glioma cells. On intact cells, the sst2 was labeled at 8 degrees C by an antibody directed to its extracellular sequence followed by a 15-nm gold-labeled secondary antibody. In the presence of the ligand, internalization was induced by exposure to 37 degrees C for 5-10 min. Then, cells were either fixed for immunoelectron-microscopic analysis or homogenized for density gradient separation. After post-embedding staining of the sst2-labeled sections with anti-Gialpha1- 3 or anti-caveolin, a co-localization of sst2, Gialpha and caveolin was detected in endosomal vesicles after 5 min of internalization, but not after 10 min. Furthermore, the gold-labeled organelles containing the internalised receptor were separated from the non-labeled ones on sucrose gradients (density shift separation) and analyzed by Western blotting. Also here, in fractions with higher densities, sst2 could be costained with Gialpha and caveolin after 5 min. From these congruent results from both methods, it can be concluded that, in human glioma cells, the receptor sst2 (1) is internalised in caveolin-positive vesicles and (2) is neighboured to its Gialpha proteins at the plasma membrane and early endosomes.

The splice variants VEGF121 and VEGF189 of the angiogenic peptide vascular endothelial growth factor are expressed in osteoarthritic cartilage

OBJECTIVE

Vascular endothelial growth factor (VEGF) has recently been shown to play an important role during endochondral bone formation in hypertrophic cartilage remodeling, ossification, and angiogenesis, but it is not expressed in normal adult cartilage. Since genes expressed during development often reappear in the disease state, we investigated whether VEGF and its receptors (VEGFRs) are expressed in osteoarthritic (OA) cartilage.

METHODS

VEGF production in OA cartilage from the tibial plateau was measured by enzyme-linked immunosorbent assay. Deposition of VEGF and VEGFR was determined by immunohistochemistry. Expression of messenger RNA for the different VEGF splice forms and for VEGFR was analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

Increased VEGF concentrations were measured in OA cartilage from the tibial plateau, while VEGF was almost undetectable in normal cartilage but could be immunostained within the intracellular and pericellular matrices of OA chondrocytes. In analyses of cartilage samples from all 10 OA patients evaluated, VEGF121 and VEGF189 were identified as the only VEGF splice forms expressed. RT-PCR and immunohistochemistry for VEGF in normal hyaline cartilage yielded negative findings. In addition to VEGF, VEGFR-2 (kinase domain region/fetal liver kinase 1), but not VEGFR-1 (fms-like tyrosine kinase 1), could be detected by RT-PCR in OA cartilage and immunostained on OA chondrocytes.

CONCLUSION

Apart from its production in hypertrophic chondrocytes, VEGF is also produced in chondrocytes of OA cartilage. While the splice variant VEGF189 binds to extracellular matrix proteoglycans, VEGF121 is diffused freely. Both proteins should contribute to the inflammatory process by autocrine/paracrine stimulation of chondrocytes, chemotaxis of macrophages, and promotion of angiogenesis.

CD30 shedding from Karpas 299 lymphoma cells is mediated by TNF-alpha-converting enzyme

CD30 is a costimulatory receptor on activated lymphocytes and a number of human lymphoma cells. Specific ligation of membrane-bound CD30 or cellular stimulation by PMA results in a metalloproteinase-mediated down-regulation of CD30 and release of its soluble ectodomain (sCD30). In this report, it is demonstrated that PMA-induced CD30 cleavage from Karpas 299 cells was mediated by a membrane-anchored metalloproteinase which was active on intact cells following 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate extraction of membrane preparations. Moreover, CD30 shedding was blocked by the synthetic hydroxamic acid-based metalloproteinase inhibitor BB-2116 (IC(50), 230 nM) and the natural tissue inhibitor of metalloproteinases (TIMP)-3 (IC(50), 30 nM), but not by the matrix metalloproteinase inhibitors TIMP-1 and TIMP-2. This inhibition profile is similar to that of the TNF-alpha- converting enzyme (TACE) and, indeed, mRNA transcripts of the membrane-bound metalloproteinase-disintegrin TACE could be detected in Karpas 299 cells. The ectodomain of TACE was expressed in bacteria as a GST fusion protein (GST-TACE) which cleaved CD30 from the surface of Karpas 299 cells and concomitantly increased the level of sCD30 in the cell supernatants. Hence, TACE does not only control the release of TNF-alpha, but also that of sCD30.

What happens to tears inside the efferent lacrimal passage? An animal experimental study

BACKGROUND

To determine whether absorption of protein components of the tear fluid occurs in normal efferent tear ducts, an animal experiment was carried out.

METHODS

Iodinated albumin was dropped into eyes of female rats. After 10, 20 or 60 min the rats were killed, blood collected and the heads embedded for histological examination. Serum was obtained from the clotted blood and the radioactivity in a protein sediment and the combined supernatants counted. In a second approach, serum was fractionated by molecular mass and radioactivity in the fractions measured. Furthermore, autoradiographs of rat head sections were performed.

RESULTS

Uptake of radioactivity into the serum was low, but increased with time. After 60 min maximal incorporation of the applied radioactivity into the blood was 0.13%; most (70-80%) of the incorporated radioactivity was not protein bound. Gel chromatographic separation according to molecular mass yielded fractionated peaks of radioactivity corresponding to albumin with maximal 4.8 Bq/ml serum, iodinated tyrosine (5.5 Bq/ml), and free iodine (237 Bq/ml; each after 60 min). Histologically the rat efferent lacrimal tear ducts showed a multilayered lining epithelium with integrated goblet cells in a characteristic arrangement of several cells. In autoradiographs of rat head sections no transport of radioactivity could be visualized.

CONCLUSION

In rats only traces of iodinated albumin are incorporated from the efferent lacrimal tear ducts into the blood. A higher proportion of the radioactivity is taken up as the proteolytic degradation product of bovine serum albumin to free amino acids, and 96% of the radioactivity incorporated was free iodine, probably as a contaminant of the iodinated preparation.

Somatostatin receptors in gliomas

Gliomas differ from non-malignant glial cells in the overexpression or mutations of genes involved in cell cycle or growth regulation. One example is the overexpression of the somatostatin receptor subtype 2 (sst2), especially of the splice variant sst2A. The reasons for this overexpression are not known. However, the coding sequence and part of the promoter region is not mutated. In accordance to this, the sst2 is functionally active and is internalised upon agonist stimulation. Immunoelectronmicroscopic studies show that the activated sst2 is internalised via caveolin-positive endosomal vesicles and later accumulates in multivesicular bodies and lysosomal compartments. The activated sst2 is found to be co-localised with the inhibitory G-protein Gialpha at the plasma membrane and in early endosomal vesicles. Multiple signal transduction pathways are induced. Stimulation of sst2 lowers cAMP levels elicited by forskolin and activates the protein tyrosine phosphatase SHP-2. In contrast to other sst2-expressing cells a long term antiproliferative effect of somatostatin or sst2-selective agonists are not detected in cultivated glioma cells. However, continuous stimulation of sst2 decreases the expression of genes promoting tumour survival.

The brain and thymus have much in common: a functional analysis of their microenvironments

Research into the neural and immune systems has begun to converge. Since the first reports that interleukins play important roles in both systems and that lymphocytes secrete neuronal factors, scientists have been surprised by the ever-increasing list of interactions. Here, Rolf Mentlein and Marion Kendall examine the major supporting cells of the brain and thymus - astrocytes and thymic epithelial cells - the similar neuroectodermal origin of which could explain such fundamental analogies.

Proline-specific dipeptidyl peptidase activity in the cockroach brain and intestine: partial characterization, distribution, and inactivation of tachykinin-related peptides

Proline-specific dipeptidyl peptidase (DPP IV) is an established enzyme known to degrade neuropeptides and peptide hormones in vertebrate tissues. DPP IV cleaves peptides at the Pro2 residue. Because several neuropeptides of the cockroach Leucophaea maderae, such as LemTRP-1 (APSGFLGVRamide), are potential substrates for this peptidase, we investigated the occurrence of proline-specific DPP activity in cockroach tissues. Partly purified DPP activity was characterized from the brain and midgut of L. maderae by using Gly-Pro-4-nitroanilide as a substrate. The highest activity was obtained from the membrane fraction of intestine; about 10 times less activity (per milligram protein) was obtained from brain membranes. A smaller amount of soluble DPP activity could also be identified in both tissues. Gel chromatography of the solubilized intestinal DPP activity revealed a molecular mass of about 75 kDa. The enzyme had a pH optimum of 8.5. Diprotin A (Ile-Pro-Ile) was an efficient competitive inhibitor of the cockroach DPP, whereas other known DPP inhibitors were found to be less potent. When incubated with human and cockroach DPP IV, the cleavage products of LemTRP-1 were AP and SGFLGVRamide (des-AP-LemTRP-1) as determined by mass spectrometry of high-performance liquid chromatography (HPLC)-purified peptide fragments. The AP fragment was biologically inactive and the des-AP fragment had a drastically reduced myostimulatory activity on the hindgut of L. maderae. The blowfly TRP callitachykinin-I (CavTK-I; APTAFYGVRamide) was cleaved in two steps to des-AP-CavTK-I and desAPTA-CavTK-I, showing that cockroach DPP does not only liberate Xaa-Pro, but also Xaa-Ala dipeptides. The fragment desAPTA-CavTK-I was completely inactive on the cockroach hindgut. To compare, LemTRP-3 and CavTK-II, which lack a Pro2, were not cleaved by DPP IV. Enzyme histochemistry for DPP IV was performed on cryostat sections of brain and intestine with Gly-Pro-4-methoxy-2-naphthylamide as the substrate and Fast Blue B as the chromogen. Strong histochemical labeling was seen in specific neuropils of the brain such as the calyces of the mushroom bodies, the antennal glomeruli, and the central body. Also, the inner lining of the midgut (the peritrophic membrane) and the malpighian tubules were strongly labeled by reaction product. In both the brain and intestine, the enzyme-histochemical reaction was inhibited by diprotin A.

GLP-1-analogues resistant to degradation by dipeptidyl-peptidase IV in vitro

Glucagon-like peptide-1 (GLP-1) stimulates insulin secretion and improves glycemic control in type 2 diabetes. In serum the peptide is degraded by dipeptidyl peptidase IV (DPP IV). The resulting short biological half-time limits the therapeutic use of GLP-1. DPP IV requires an intact alpha-amino-group of the N-terminal histidine of GLP-1 in order to perform its enzymatic activity. Therefore, the following GLP- analogues with alterations in the N-terminal position 1 were synthesized: N-methylated- (N-me-GLP-1), alpha-methylated (alpha-me-GLP-1), desamidated- (desamino-GLP-1) and imidazole-lactic-acid substituted GLP-1 (imi-GLP-1). All GLP-1 analogues except alpha-me-GLP-1 were hardly degraded by DPP IV in vitro. The GLP-1 analogues showed receptor affinity and in vitro biological activity comparable to native GLP-1 in RINm5F cells. GLP-1 receptor affinity was highest for imi-GLP-1, followed by alpha-me-GLP-1 and N-me-GLP-1. Only desamino-GLP-1 showed a 15-fold loss of receptor affinity compared to native GLP-1. All analogues stimulated intracellular cAMP production in RINm5F cells in concentrations comparable to GLP-1. N-terminal modifications might therefore be useful in the development of long-acting GLP-1 analogues for type 2 diabetes therapy.

Dipeptidyl-peptidase IV (CD26)--role in the inactivation of regulatory peptides

Dipeptidyl-peptidase IV (DPP IV/CD26) has a dual function as a regulatory protease and as a binding protein. Its role in the inactivation of bioactive peptides was recognized 20 years ago due to its unique ability to liberate Xaa-Pro or Xaa-Ala dipeptides from the N-terminus of regulatory peptides, but further examples are now emerging from in vitro and vivo experiments. Despite the minimal N-terminal truncation by DPP IV, many mammalian regulatory peptides are inactivated--either totally or only differentially--for certain receptor subtypes. Important DPP IV substrates include neuropeptides like neuropeptide Y or endomorphin, circulating peptide hormones like peptide YY, growth hormone-releasing hormone, glucagon-like peptides(GLP)-1 and -2, gastric inhibitory polypeptide as well as paracrine chemokines like RANTES (regulated on activation normal T cell expressed and secreted), stromal cell-derived factor, eotaxin and macrophage-derived chemokine. Based on these findings the potential clinical uses of selective DPP IV inhibitors or DPP IV-resistant analogues, especially for the insulinotropic hormone GLP-1, have been tested to enhance insulin secretion and to improve glucose tolerance in diabetic animals. Thus, DPP IV appears to be a major physiological regulator for some regulatory peptides, neuropeptides, circulating hormones and chemokines.

Comparison of the effect of native glucagon-like peptide 1 and dipeptidyl peptidase IV-resistant analogues on insulin release from rat pancreatic islets

BACKGROUND

Glucagon-like peptide 1 (GLP-1) stimulates insulin secretion and may improve glycaemic control in type 2 diabetes. Therapeutic use is limited by its rapid degradation, primarily by dipeptidyl peptidase IV.

MATERIALS AND METHODS

Five GLP-1 analogues with alterations at cleavage positions were synthesized according to the Fmoc strategy and tested for metabolic stability by incubation with rat kidney membranes containing dipeptidyl peptidase IV activity. Their insulinotropic effect was compared in isolated rat pancreatic islets after 24 h maintenance in tissue culture. Ten islets per vial were incubated for 30 min; insulin was measured radioimmunologically. Each analogue was compared with GLP-1 in the same experiment.

RESULTS

All analogues were biologically active in isolated islets in the potency order da2d8 = da2 > d2d9 > da2ds8 > desamino. At 16.7 mmol L-1 glucose, GLP-1 and GLP-1 analogues altered as position 2, or 2 and 8 significantly (P < 0.05) increased insulin release at 10(-9) mol L-1. N-terminal modification of GLP-1 confers resistance to dipeptidyl peptidase IV degradation in rat kidney membranes in vitro.

CONCLUSIONS

The analogues tested are biologically active and resistant to degradation by dipeptidyl peptidase IV. Their greater metabolic stability may help to realize the potential of GLP-1 analogues in diabetes therapy.

Biological activity of GLP-1-analogues with N-terminal modifications

Glucagon-like peptide-1 (GLP-1) stimulates insulin secretion and improves glycemic control in type 2 diabetes. In serum the peptide is degraded by dipeptidyl peptidase IV (DPP IV). The resulting short biological half-time limits the therapeutic use of GLP-1. Therefore, various GLP-1 analogues with alterations in cleavage positions were synthesized. GLP-1-receptor binding was investigated in RINm5F cells. Biological activity of the GLP-1 analogues was investigated in vitro by measuring cAMP production in RINm5F cells. GLP-1 analogues with modifications in position 2 were not cleaved by DPP IV and showed receptor affinity and in vitro biological activity comparable to native GLP-1. Analogues with alterations in positions 2 and 8, 2 and 9 or 8 and 9 showed a significant decrease in receptor affinity and biological activity. In vivo biological activity was tested in pigs. GLP-1 analogues were administered subcutaneously followed by an intravenous bolus injection of glucose. Plasma glucose and insulin were monitored over 4 h. Compared to native GLP-1, analogues with an altered position 2 showed similar or increased potency and biological half-time. Other GLP-1 analogues were less active. Despite the lack of degradation of these GLP-1 analogues by DPP IV in vitro, their biological action is as short as that of GLP-1, except for desamino-GLP-1, indicating that other degradation enzymes are important in vivo. Alterations of GLP-1 in positions 8 or 9 result in a loss of biological activity without extending biological half-time.

Molecular analysis of the somatostatin receptor subtype 2 in human glioma cells

Gliomas constantly overexpress the receptor subtype SST2 for the inhibitory peptide somatostatin. Since somatostatin or metabolically stable agonists like octreotide have an antiproliferative and antisecretory potential for the treatment of SST2-expressing tumors, we evaluated the molecular integrity of SST2 in gliomas on the DNA, mRNA and protein levels. Sequencing of about 1800 bases from the SST2 gene in nine gliomas and five control samples revealed no mutations, but polymorphisms were detected in the 5'-region irrespective of the malignancy of the sample. Gliomas and the human glioma cell line U343 expressed mRNA for the receptor splice variant SST2A with a size of about 4.2 kb. A novel antibody generated against an extracellular part of the SST2 amino acid sequence strongly reacted with an 75-kDa protein in membranes from glioma or meningioma cells and-much weaker-normal rat astrocytes. The receptor could be immunostained on the surface of intact glioma cells or (weaker) astrocytes at the light and electron microscopic level. These results show that the somatostatin receptor SST2 is non-mutated in gliomas and has similar molecular properties as in non-malignant cells.

Effect of transmitters and co-transmitters of the sympathetic nervous system on interleukin-6 synthesis in thymic epithelial cells

In the thymus, sympathetic nerves run in septa in close connection to subcapsular/perivascular thymic epithelial cells (TEC). Since TEC are supposed to create a microenvironment of cytokines necessary for the development of thymocytes to T cells, we investigated the influence of sympathetic transmitters and co-transmitters on interleukin-6 (IL-6) synthesis in cultivated rat TEC that express markers of perivascular/subcapsular TEC. Noradrenaline and ATP stimulated IL-6 production in the culture supernatants 14- and 23-fold over basal values after 24 h. Co-stimulation with noradrenaline and ATP yielded an additive effect. Synthesis of IL-6 was concentration-dependent upon ATP and appeared to be mediated by P2 purinoceptors. During 24 h stimulation with 1 mM ATP, two thirds of the ligand was degraded mainly to ADP, production of AMP and adenosine was minor or negligible. Thus, in TEC, transmitters and co-transmitters of the sympathetic nervous system have a co-stimulatory effect on synthesis of IL-6 that is an important factor for thymocyte differentiation and proliferation.

Rapid progesterone actions on thymulin-secreting epithelial cells cultured from rat thymus

Many soluble factors of neural, endocrine, paracrine and autocrine origin are present in the thymus and modulate its function. Long-term effects of sex steroids have been documented for thymocytes and cells of the thymic microenvironment. In this report we examine rapid actions of progesterone upon aspects of epithelial cell physiology. Progesterone (0.1-10 microM) was applied to cultured thymulin-secreting thymic epithelial cells (TS-TEC) and changes in transmembrane potential, transmembrane current, intracellular calcium levels and thymulin secretion were assessed. Rapid changes in electrophysiology and intracellular calcium provide evidence for a membrane-bound progesterone receptor in these cells, in addition to classical cytoplasmic receptors. Application of progesterone to TS-TEC caused electrophysiological changes in 56% of cells (n = 40), activating an inward current (-24 +/- 9 pA at 1 microM, n = 7, p < 0.02) and dose-dependent depolarization (7.1 +/- 1.8 mV at 1 microM, n = 19, p < 0.01). Intracellular calcium levels, monitored by the ratiometric fluorescent calcium indicator fura-2, increased within seconds of progesterone (1 microM) application. Progesterone (1 microM) increased thymulin levels in supernatant, as measured by ELISA, above the levels in the preapplication period (142 +/- 16% of the preapplication period, n = 3, p < 0.02). This effect was reduced in the presence of cobalt chloride which blocks voltage-dependent calcium channels. In addition, TS-TEC in culture were immunoreactive to antibody AG7. This antibody was raised to a membrane-bound antigen involved in calcium influx subsequent to progesterone binding in sperm. Thus we suggest that progesterone acts upon many aspects of TS-TEC physiology through both cytoplasmic and membrane-bound receptors.

Immunoelectronmicroscopic analysis of the ligand-induced internalization of the somatostatin receptor subtype 2 in cultured human glioma cells

We analyzed the internalization of the receptor subtype 2 (sst2) for the neuropeptide somatostatin in glioma cells at the ultrastructural level using an antibody against an extracellular amino acid sequence. Intact cells derived from solid human gliomas or those of the human glioma cell line U343 were receptor-labeled (a) by classical gold immunocytochemistry using a 15-nm gold-labeled second antibody, (b) directly with the sst2 antibody adsorbed to 5-nm colloidal gold, and (c) with the physiological ligand somatostatin conjugated to 5-nm colloidal gold. The receptor was predominantly internalized via uncoated vesicles budding from the cell membrane but only rarely via coated pits, which has been mostly reported for G-protein-coupled, seven transmembrane-domain receptors. In the presence of ligand and sst2 antibody vesicles, tubule-like structures, and multivesicular bodies were labeled in superficial and in perinuclear portions of the cells within the first 30 min. Lysosomal labeling was observed after 30 min and especially after an hour of internalization time. This internalization route is also used to study the directly labeled sst2 antibody or the labeled ligand. However, the late endosomal compartment appears to be reached more rapidly in these latter experiments.

Receptors and effects of the inhibitory neuropeptide somatostatin in microglial cells

The expression of receptors for the neuropeptide somatostatin was investigated in cultured immunocytochemically pure rat microglial cells. By the reverse transcriptase-polymerase chain reaction, the mRNAs for the receptor subtypes sst2, sst3 and sst4, but not sst1 and sst5 could be detected. To show that these receptors were functionally active, the effects of somatostatin and the metabolically stable, receptor subtype (2, 3 and 5) selective derivative octreotide (SMS 201-995, Sandostatin) on protein phosphorylation and proliferation were evaluated. Somatostatin induced the tyrosine phosphorylation of a 95 kDa protein in microglia. Furthermore, somatostatin or octreotide inhibited the basal as well as the GM-CSF-(granulocyte macrophage colony-stimulating factor) or the IL-3-(interleukin-3)-stimulated proliferation of microglial cells. This effect was dose-dependent, with a half maximum activity of about 0.2-0.3 nM. Somatostatin was relatively stable in the cultures due to protease inhibitors in the serum. The results indicate that microglial cells are targets for the widespread neuropeptide somatostatin and that its receptors can transduce complex signals to microglia.

Isoforms of an N-acetyl-beta-D-glucosaminidase from the Antarctic krill, Euphausia superba: purification and antibody production

Two forms of the chitinolytic enzyme N-acetyl-beta-D-glucosaminidase (NAGase, EC 3.2.1.52) have been isolated from the Antarctic krill, Euphausia superba, in order to study their potential role in temperature adaptation processes. A chromatographic protocol was developed that allowed complete separation of the two enzyme forms, named NAGase B and NAGase C. The latter was purified to homogeneity with 600-fold enrichment and a yield of 17%. The molecular mass was 150 kDa. NAGase B showed characteristics of a glycoprotein due to affinity towards concanavalin A sepharose, while NAGase C did not. Highly specific polyclonal antibodies to NAGase C [anti-(E. superba-NAGase C)-IgG] showed only negligible cross-reactivity with NAGase B isoforms. A comparison with the Northern krill, Meganyctiphanes norvegica, revealed a corresponding chromatographic pattern with two main activity peaks, for differentiation named NAGase II and NAGase III. Application of the antibody on M. norvegica revealed a high specificity toward NAGase III and a low cross-reactivity with NAGase II. First indication is given that the two forms are no isoenzymes in a strict sense but instead may have different functions in the metabolism of krill.

Catecholamines and lipopolysaccharide synergistically induce the release of interleukin-6 from thymic epithelial cells

The thymus as the major site of T-cell development is exposed to circulating hormones as well as to neurotransmitters released from peripheral nerves. We investigated the influence of catecholamines on the synthesis of interleukin-1 (IL-1) and IL-6 by cultured rat thymic epithelial cells. Basal or lipopolysaccharide (LPS)-stimulated production of IL-1 was not affected by catecholamines. Release of IL-6 was stimulated only scarcely by catecholamines or tumor necrosis factor-alpha (TNF-alpha) and moderately by LPS alone. However, co-stimulation with adrenaline, noradrenaline, or the beta-adrenoceptor agonist isoproterenol (isoprenaline) had an additive (TNF-alpha) or synergistic (LPS) effect on IL-6 release. The synergistic effect was dose-dependent on catecholamine or LPS concentrations. It was mediated by beta-adrenoceptors that are linked to elevation of intracellular cAMP levels, since it was promoted by beta-adrenoceptor agonists and could be blocked by beta-adrenoceptor antagonists. Co-incubation of LPS with agents directly raising cAMP-levels like forskolin or dibutyryl cAMP yielded even stronger IL-6 induction. After co-stimulation IL-6 mRNA was first detected after 3-4 h and a constant increase of IL-6 bioactivity in the culture supernatant was measured for up to 48 h. Since IL-6 is an important factor for thymocyte differentiation and proliferation, the findings demonstrate an influence of neuronal or hormonal catecholamines on the thymic microenvironment that is created by thymic epithelial cells.

Riboflavin-mediated axonal degeneration of postnatal retinal ganglion cells in vitro is related to the formation of free radicals

It is well known that glial cells produce several neurotrophic factors. We detected a neurogedegenerative/neurite growth inhibiting activity in serum-free astrocyte-conditioned medium (ACM). After high performance liquid chromatography (HPLC)-purification, spectral analysis and test of biologic activity in tissue cultures of postnatal retinal explants we isolated a fraction containing a riboflavin-(vitamin B2)-like compound which caused the neuronal degeneration. We therefore investigated the influence of pure riboflavin on axonal regeneration in vitro. Riboflavin is a normal compound of Dulbecco's modified Eagle medium (DMEM) and other tissue culture media in various concentrations. The removal of riboflavin from ACM by reversed phase chromatography abolished the neurite growth inhibiting effect and enhanced the regenerative response of axonal outgrowth from postnatal rat retinal explants. However, doubling of the normal medium concentration (1 microM) of riboflavin lead to strong degenerative alteration of the outgrowing axons in a dose-dependent manner, even under maximal growth stimulation by cultivating the explants in astrocyte-conditioned medium. To check the possibility that riboflavin-mediated cytotoxicity is related to the production of free radicals through photoabsorption from daylight, we irradiated culture medium with UV light, and induced radical stress by incubating the explants with Fe2+/3+. In an other set of experiments, we proofed, if antioxidants/free radical scavengers like pyruvate or vitamin C and E are able to overcome the neurite growth inhibiting influence of riboflavin or the radical stress. Our findings suggest an involvement of riboflavin-mediated formation of free radicals/reactive oxygen species and subsequent neurite degeneration in in vitro-assays of neuronal regeneration or neuronal cell cultures. How far the riboflavin/free radical-induced axonal degeneration could be an explanation for neurological degenerative disorders has to be elucidated.

Purification and characterization of retinyl ester hydrolase as a member of the non-specific carboxylesterase supergene family

Hepatic retinyl ester hydrolase (REH) activity was isolated from porcine and human liver and characterized, and some of its properties were compared with those of other retinyl-ester-splitting enzymes. Sequence analysis revealed that the REH proteins are structurally similar to non-specific carboxylesterases and distinct from bile salt-activated lipases and cholesterol esterases. Pig REH, a 64-kDa protein, hydrolyzed retinyl palmitate at a rate of 595 nmol x h(-1) x mg(-1) protein in the presence of 100 mM Chaps with an apparent Km value for retinyl palmitate of 27.5 microM. The pH optimum was 7.0-9.2. Its human counterpart has a molecular mass of 65 kDa and a pH optimum near 6.5. In the presence of Chaps, pig REH activity was stimulated up to 1.7-fold by various non-ionic detergents. The ranking order of retinyl palmitate cleavage initiated by the stimuli was n-dodecylglucoside > octanoyl-N-methylglucamide > n-octyglucoside > n-dodecylmaltoside > Triton X-114 > Triton X-100. Porcine REH was effectively inhibited by alpha-tocopherol and bis-(4-nitrophenyl) phosphate [(Np)2P]. The structural, immunological and catalytic features, pH dependence, and the effect of (Np)2P on enzyme activity of pig REH are similar to those reported for the non-specific carboxylesterase ES-4. However, ES-4 differed from REH in molecular mass and the requirement of Chaps or Chaps-like detergents as cofactor. Judging from these results, pig REH may be a non-specific carboxylesterase isoform.

Proteolytic degradation of Alzheimer's disease amyloid beta-peptide by a metalloproteinase from microglia cells

The cerebral deposition of amyloid beta-peptide (A beta) is a histopathological characteristic of Alzheimer's disease. Because an impaired clearance of A beta might be involved in the disease, we investigated the proteolytic degradation of synthetic A beta (40-residue peptide) in cultures of glial cells and characterized a protease involved. Whereas rat astrocytes had a very low degradation capacity, cultivated rat microglia cells cleaved A beta. Microglia activity was considerably enhanced by stimulation with lipopolysaccharide and to a lesser extent by phorbol esters. Most of the A beta-degrading activity was released into the medium. By use of selective inhibitors the protease was characterized as a metalloprotease of approximately 200 kDa that was different from neutral endopeptidase (a neuropeptide-degrading enzyme), matrix metalloproteases, or macrophage elastase. Its activity was efficiently reduced by four hydroxamic acid-based zinc-metalloprotease inhibitors that have been shown to inhibit membrane protein secretases (disintegrins). We conclude that activated microglia cells might impair amyloid plaque formation by release of a metalloprotease that degrades soluble A beta, before polymerization.

Proline-specific dipeptidyl peptidase from the blue blowfly Calliphora vicina hydrolyzes in vitro the ecdysiostatic peptide trypsin-modulating oostatic factor (Neb-TMOF)

To elucidate the mechanisms of inactivation of the ecdysiostatic peptide trypsin-modulating oostatic factor (Neb-TMOF) in the blue blowfly Calliphora vicina, we investigated its proteolytic degradation. In homogenates and membrane and soluble fractions, this hexapeptide (sequence: NPTNLH) was hydrolyzed into two fragments, NP and TNLH, suggesting the involvement of a proline-specific dipeptidyl peptidase. The dipeptidyl peptidase activity was highest in the late larval stage. It was purified 240-fold from soluble fractions of pupae of mixed age and classified on the basis of several catalytic properties as an invertebrate homologue of mammalian dipeptidyl peptidase IV (EC 3.4.14.5). Fly dipeptidyl peptidase IV has a molecular mass of 200 kDa, showed a pH optimum of 7.5-8.0 with the chromogenic substrate Gly-Pro-4-nitroanilide, and cleaved other chromogenic substrates with penultimate Pro or, with lower activity, Ala. It liberated Xaa-Pro dipeptides from the N-terminus of several bioactive peptides including substance P, neuropeptide Y, and peptide YY but not from bradykinin, indicating that the peptide bond between the two proline residues was resistant to cleavage. Fly dipeptidyl peptidase belongs to the serine class of proteases as the mammalian enzyme does; the fly enzyme, however, is not inhibited by several selective or nonselective inhibitors of its mammalian counterpart. It is suggested that dipeptidyl peptidases exert a regulatory role for the clearance not only of TMOF in files but for other bioactive peptides in various invertebrates.

Neuropeptides exert direct effects on rat thymic epithelial cells in culture

To determine if major thymic neuropeptides and neurotransmitters can directly influence the functional activity of cultured rat thymic epithelium, neuropeptides and neurotransmitters were applied, and intercellular communication, proliferation, and thymulin secretion assessed. After injections of a mixture of lucifer yellow dextran (too large to pass gap junctions) and cascade blue (which does) into single cells, some neuropeptides decrease dye coupling: 0.1 mM GABA (P < 0.0001), 100 nM NPY (P < 0.0001), 100 nM VIP (P < 0.001), 100 nM CGRP (P < 0.001), 100 nM SP (P < 0.01), and 0.1 mM histamine (P < 0.01), whereas 0.1 mM 5-HT, 1 mM acetylcholine, and 1 microM isoproterenol (beta-adrenergic agonist) had no effect. Proliferation (incorporation of tritiated thymidine) was increased by CGRP (P = 0.004) and histamine (P < 0.02), but decreased by isoproterenol (P = 0.002), 5-HT (P = 0.003), and acetylcholine (P < 0.05). The percentage of multinucleate cells was decreased after isoproterenol (2.5%), and increased after 5-HT (21.3%), GABA (15%), and histamine (15.1%). Compared to controls, thymulin in the supernatant was decreased after challenge with acetylcholine (52%), isoproterenol (71%), 5-HT (73%), and histamine (84%). This study demonstrates direct effects of neuropeptides and neurotransmitters on functional aspects of cultured thymic epithelial cells.

Modulation of dye-coupling and proliferation in cultured rat thymic epithelium by factors involved in thymulin secretion

Cultures of rat thymic epithelium were used to measure the effect of thymulin secretagogues on dye-coupling and proliferation. Dye-coupling was assessed after the injection of lucifer yellow dextran which cannot permeate the connexin pore of gap junctions and the smaller, permeant cascade blue. In addition to gap junctional communication, larger intercellular bridges were demonstrated by the transfer of lucifer yellow dextran between cells. The extent of intercellular communication was found to be influenced by both cell density and the number of passages. In control cultures, intercellular communication was reduced in cell groups of low (< 20 cells/group) or high cell densities (> 100 cells/group) compared with groups of 20-60 cells. The highest coupling indices were found in subcultures 20-30. Taking these factors into account, significant decreases in coupling index were observed after pretreatment of test cultures with factors known to influence the secretion of thymulin (5 U/ml interleukin 1 (alpha and beta), 1 microM progesterone, 1 microM oestrogen, 1 microM testosterone, 1 ng/ml adrenocorticotropic hormone, 100 nM rat growth hormone) but 7.5 ng/ml thymulin had no effect on dye-coupling. The nonspecific gap junction uncoupler, octanol, abolished dye-coupling. Cellular proliferation, as measured by the uptake of tritiated thymidine, showed that the same factors that reduced coupling also increased proliferation. None of these factors affected the number of multinucleate cells present, except interleukin-1beta which caused a significant reduction in the average number of nuclei per cell. Thus rat thymic epithelium in vitro provides a model for the study of the direct action of factors on cells of the thymic microenvironment.

Methods for the investigation of neuropeptide catabolism and stability in vitro

The protocol describes (i) methods for the investigation of neuropeptide catabolism in the central nervous system (CNS), (ii) the identification of the neuropeptidases involved, and (iii) methods for the determination of neuropeptide stability in vitro. These methods are applicable also to study the degradation of peptide hormones by peripheral cells or tissues. To identify peptide degradation products, nanomolar amounts (micromolar concentrations) of peptides are incubated in synthetic media with cell or tissue cultures. Aliquots of the supernatants are withdrawn after different times, peptide fragments separated and fractionated by reversed-phase HPLC, and identified by peptide chemical methods. The peptidases responsible for this degradation can be identified by the use of specific inhibitors listed in the protocol. For receptor binding assays or the study of peptide effects in physiological, nanomolar concentrations the stability of the peptides in an in vitro system should be checked by addition of radiolabeled peptides (femtomolar or nanomolar concentrations) and monitoring the peptide degradation by a procedure analogous to that established for unlabeled peptides. The addition of more or less specific peptidase inhibitors enhances peptide stability in vitro, and thus it can be assured that a given peptide concentration is maintained during biological assays.

Beta-adrenoceptor-mediated effects in rat cultured thymic epithelial cells

1. Sympathetic nerves were visualized in sections from rat thymus by immunostaining of tyrosine hydroxylase, the rate-limiting enzyme of catecholamine biosynthesis, and by glyoxylic acid-induced fluorescence of catecholamines. Catecholaminergic nerve fibres were detected in close connection to thymic epithelial cells which therefore might be preferred target cells. To evaluate this, rat immunocytochemically defined, cultured thymic epithelial cells were investigated for adrenoceptors and adrenergic effects. 2. In rat cultured thymic epithelial cells mRNA for beta 1- and beta 2-adrenoceptors was detected by reverse transcription-polymerase chain reaction by use of sequence-specific primers. Specific, saturable binding to the cultivated cells was observed with the beta-adrenoceptor agonist CGP 12177. 3. Adrenaline, noradrenaline or the beta-adrenoceptor agonist, isoprenaline, increased intracellular adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels in cultivated thymic epithelial cells dose-dependently about 25 fold. The pharmacological properties revealed that this response was mediated by receptors of the beta 1- and the beta 2-subtypes. The selective beta 3-adrenoceptor agonist BRL 37344 had no effect on cyclic AMP levels. The increase in cyclic AMP was downregulated by preincubation with glucocorticoids like dexamethasone or cortisol which also changed the relative importance of beta 1-/beta 2-adrenoceptors to the response. 4. Incubation with isoprenaline or the adenylate cyclase activator forskolin decreased basal and serum-stimulated proliferation of thymic epithelial cells. However, adrenergic stimulation of thymic epithelial cells did not induce interleukin 1 production. Since thymic epithelial cells create a microenvironment which influences the maturation and differentiation of thymocytes to T-lymphocytes, their observed capacity to respond to catecholamines provides novel evidence for the suggestion that adrenergic stimulation may interfere with the regulation of immune functions.

Meningeal cells are targets and inactivation sites for the neuropeptide somatostatin

Transcripts of the somatostatin receptor subtypes sst3 and sst2 are expressed in meninges from rat brain as well as in immunocytochemical pure rat meningeal cells and rat fibroblasts in culture. mRNA of three other subtypes tested are absent or detected in trace amounts by reverse transcription-polymerase chain reaction. Presence of active receptors on the surface of meningeal cells and fibroblasts could be verified by direct visualisation of binding sites by affinity labelling with a somatostatin gold conjugate. The metabolically stable somatostatin agonist SMS 201-995 (octreotide) had a time-dependent effect on the [3H]thymidine incorporation by meningeal cells: after 2-5 h, the agonist inhibited cell proliferation to about 80% of controls, after 24 h proliferation was stimulated to about 150% of controls. Apart from being targets for somatostatin, meningeal cells had a high capacity to inactivate the peptide by proteolytic degradation. By analysis of cleavage sites and use of specific inhibitors, endopeptidase-24.11 ('enkephalinase', neutral endopeptidase, neprilysin, EC 3.4.24.11) was identified to be responsible for the initial catabolism of the peptide whereas aminopeptidase(s) truncated the fragments. Thus, meningeal cells express transcripts of multiple somatostatin receptor subtypes and produce peptidases that inactivate the neuropeptide somatostatin.

Time-dependent influence of the somatostatin analogue octreotide on the proliferation of rat astrocytes and glioma cells

The somatostatin receptor subtype sst2 was visualized by immunostaining on cultivated rat astrocytes and C6 rat glioma cells. Octreotide, a metabolically stable sst2 agonist reduced [3H]thymidine incorporation into DNA of both cell types dose-dependently only after short-time application (2-5 h), after prolonged incubation (> 12 h) no antiproliferative effect was measurable. We conclude that sst2 receptors may be desensitized. Thus, desensitization might hinder application of octreotide to reduce glial tumour growth.

Metabolism of neuropeptide Y and calcitonin gene-related peptide by cultivated neurons and glial cells

Neuropeptide Y and calcitonin gene-related peptide are abundant neuropeptides in the mammalian central and peripheral nervous systems. Their enzymatic degradation by cultivated neurons, astrocytes, and microglia, as well as by purified urokinase-type plasminogen activator, plasmin, thrombin, and trypsin, was investigated in an in vitro approach to elucidate the role of matrix-degrading serine proteinases for inactivation of neuropeptides, especially those of higher amino acid chain length, in the brain. Astrocytes were almost unable to catabolize the peptides. Cultivated neurons and microglia digested neuropeptide Y through cleavage after Arg19, Arg25, Arg33, and Arg35, calcitonin gene-related peptide was cleaved after Arg11 and Arg18. The same cleavage pattern was observed, when neuropeptide Y and calcitonin gene-related peptide were degraded by purified urokinase-type plasminogen activator, plasmin, thrombin, and trypsin. For further characterization of the neuropeptide-degrading serine proteinase activities from cell cultures, urokinase-type plasminogen activator was identified on microglia by immunostaining, whereas tissue-type plasminogen activator mRNA occurred in neurons and astrocytes, but not in microglia. The data are consistent with the possibility that the neuropeptide-degrading serine proteinase activity on neurons and microglia is due to a mixture of plasmin and plasminogen activator activities.