Identical or overlapping sequences in the primary structure of human alpha(2)-macroglobulin are responsible for the binding of nerve growth factor-beta, platelet-derived growth factor-BB, and transforming growth factor-beta

Toll-like Receptor 4, Osteoblasts and Leukemogenesis; the Lesson from Acute Myeloid Leukemia

Toll-like receptor 4 (TLR4) is a pattern-recognizing receptor that can bind exogenous and endogenous ligands. It is expressed by acute myeloid leukemia (AML) cells, several bone marrow stromal cells, and nonleukemic cells involved in inflammation. TLR4 can bind a wide range of endogenous ligands that are present in the bone marrow microenvironment. Furthermore, the TLR4-expressing nonleukemic bone marrow cells include various mesenchymal cells, endothelial cells, differentiated myeloid cells, and inflammatory/immunocompetent cells. Osteoblasts are important stem cell supporting cells localized to the stem cell niches, and they support the proliferation and survival of primary AML cells. These supporting effects are mediated by the bidirectional crosstalk between AML cells and supportive osteoblasts through the local cytokine network. Finally, TLR4 is also important for the defense against complicating infections in neutropenic patients, and it seems to be involved in the regulation of inflammatory and immunological reactions in patients treated with allogeneic stem cell transplantation. Thus, TLR4 has direct effects on primary AML cells, and it has indirect effects on the leukemic cells through modulation of their supporting neighboring bone marrow stromal cells (i.e., modulation of stem cell niches, regulation of angiogenesis). Furthermore, in allotransplant recipients TLR4 can modulate inflammatory and potentially antileukemic immune reactivity. The use of TLR4 targeting as an antileukemic treatment will therefore depend both on the biology of the AML cells, the biological context of the AML cells, aging effects reflected both in the AML and the stromal cells and the additional antileukemic treatment combined with HSP90 inhibition.

Alpha-2-Macroglobulin in Inflammation, Immunity and Infections

Alpha-2-macroglobulin is an extracellular macromolecule mainly known for its role as a broad-spectrum protease inhibitor. By presenting itself as an optimal substrate for endopeptidases of all catalytic types, alpha-2-macroglobulin lures active proteases into its molecular cage and subsequently ‘flags’ their complex for elimination. In addition to its role as a regulator of extracellular proteolysis, alpha-2-macroglobulin also has other functions such as switching proteolysis towards small substrates, facilitating cell migration and the binding of cytokines, growth factors and damaged extracellular proteins. These functions appear particularly important in the context of immune-cell function. In this review manuscript, we provide an overview of all functions of alpha-2-macroglobulin and place these in the context of inflammation, immunity and infections.

Proteomic Analysis of Retinal Tissue in an S100B Autoimmune Glaucoma Model

Glaucoma is a neurodegenerative disease that leads to damage of retinal ganglion cells and the optic nerve. Patients display altered antibody profiles and increased antibody titer, e.g., against S100B. To identify the meaning of these antibodies, animals were immunized with S100B. Retinal ganglion cell loss, optic nerve degeneration, and increased glial cell activity were noted. Here, we aimed to gain more insights into the pathophysiology from a proteomic point of view. Hence, rats were immunized with S100B, while controls received sodium chloride. After 7 and 14 days, retinae were analyzed through mass spectrometry and immunohistology. Using data-independent acquisition-based mass spectrometry, we identified more than 1700 proteins on a high confidence level for both study groups, respectively. Of these 1700, 43 proteins were significantly altered in retinae after 7 days and 67 proteins revealed significant alterations at 14 days. For example, α2-macroglobulin was found significantly increased not only by mass spectrometry analysis, but also with immunohistological staining in S100B retinae at 7 and 14 days. All in all, the identified proteins are often associated with the immune system, such as heat shock protein 60. Once more, these data underline the important role of immunological factors in glaucoma pathogenesis.

Proteomic analysis of extracellular vesicles enriched serum associated with future ischemic stroke

Identifying new biomarkers beyond the established risk factors that make it possible to predict and prevent ischemic stroke has great significance. Extracellular vesicles are powerful cell‒cell messengers, containing disease-specific biomolecules, which makes them powerful diagnostic candidates. Therefore, this study aimed to identify proteins derived from extracellular vesicles enriched serum related to future ischemic stroke events, using a proteomic method. Of Japanese subjects who voluntarily participated in health checkups at our institute a number of times, 10 subjects (6 males and 4 females, age: 64.2 ± 3.9 years) who developed symptomatic ischemic stroke (7.3 ± 4.4 years’ follow-up) and 10 age‒sex matched controls without brain lesions (6.7 ± 2.8 years’ follow-up) were investigated. Extracellular vesicles enriched fractions were derived from serum collected at the baseline visit. Differentially expressed proteins were evaluated using isobaric tagging for relative and absolute protein quantification (iTRAQ)-based proteomic analysis. Of the 29 proteins identified, alpha-2-macroglobulin, complement C1q subcomponent subunit B, complement C1r subcomponent, and histidine-rich glycoprotein were significantly upregulated (2.21-, 2.15-, 2.24-, and 2.16-fold, respectively) in subjects with future ischemic stroke, as compared with controls. Our study supports the concept of serum-derived extracellular vesicles enriched fractions as biomarkers for new-onset stroke. These proteins may be useful for prediction or for targeted therapy.

Serum complement C3 and α2-macroglobulin are potentially useful biomarkers for inflammatory bowel disease patients

Aims

Ulcerative colitis (UC), characterized by chronic inflammation and its recurrence in the large intestine, is well known as inflammatory bowel disease (IBD). Suitable biomarkers specific for UC are poorly understood till date. We aimed to discover novel serum biomarkers for UC and identify good indicators that reflected the severity of UC.

Main methods

Serum samples were obtained from out-patients with IBD (n = 101) and healthy volunteers (HVs, n = 101). Serum proteins were subjected to high performance liquid chromatography (HPLC) and sodium dodecyl sulfate-electrophoresis (SDS-PAGE) analysis. After electrophoresis, proteins in the gel were identified by mass spectrometry. Further, the protein concentration was measured by enzyme-linked immunosorbent assays (ELISAs). Based on the results, correlations between the serum levels of these proteins and the disease activity index scores for UC were statistically evaluated.

Principal findings

HPLC showed that chromatograms of serum proteins from HVs apparently differed from those of patients with IBD. Eleven protein bands, which were different in their protein concentrations from those in HVs, were separated by SDS-PAGE accordingly. Among them, complement C3 (c-C3) and α₂-macroglobulin (α₂-MG), with high protein scores, were identified by mass spectrometry. The serum concentration of c-C3 in patients with IBD was higher than that in HVs. However, the level of α₂-MG in patients with IBD was significantly lower than that in HVs. Hence, the serum levels of c-C3 and α₂-MG could be good indicators of the severity of UC.

Conclusion

Serum c-C3 and α₂-MG are suitable biomarkers for monitoring the condition of patients with UC.

Failure of in vitro-cultured schistosomes to produce eggs: how does the parasite meet its needs for host-derived cytokines such as TGF-β?

When adult schistosome worm pairs are transferred from experimental hosts to in vitro culture they cease producing viable eggs within a few days. Female worms in unisexual infections fail to mature, and when mature adult females are separated from male partners they regress sexually. Worms cultured from the larval stage are also permanently reproductively defective. The cytokine transforming growth factor beta derived from the mammalian host is considered important in stimulating schistosome female worm maturation and maintenance of fecundity. The means by which schistosomes acquire TGF-β have not been elucidated, but direct uptake in vivo seems unlikely as the concentration of free, biologically active cytokine in host blood is very low. Here we review the complexities of schistosome development and male-female interactions, and we speculate about two possibilities on how worms obtain the TGF-β they are assumed to need: (i) worms may have mechanisms to free active cytokine from the latency-inducing complex of proteins in which it is associated, and/or (ii) they may obtain the cytokine from alpha 2-macroglobulin, a blood-borne protease inhibitor to which TGF-β can bind. These ideas are experimentally testable.

Alpha-2-Macroglobulin, a Hypochlorite-Regulated Chaperone and Immune System Modulator

Alpha-macroglobulins are ancient proteins that include monomeric, dimeric, and tetrameric family members. In humans, and many other mammals, the predominant alpha-macroglobulin is alpha-2-macroglobulin (α₂M), a tetrameric protein that is constitutively abundant in biological fluids (e.g., blood plasma, cerebral spinal fluid, synovial fluid, ocular fluid, and interstitial fluid). α₂M is best known for its remarkable ability to inhibit a broad spectrum of proteases, but the full gamut of its activities affects diverse biological processes. For example, α₂M can stabilise and facilitate the clearance of the Alzheimer's disease-associated amyloid beta (Aβ) peptide. Additionally, α₂M can influence the signalling of cytokines and growth factors including neurotrophins. The results of several studies support the idea that the functions of α₂M are uniquely regulated by hypochlorite, an oxidant that is generated during inflammation, which induces the native α₂M tetramer to dissociate into dimers. This review will discuss the evidence for hypochlorite-induced regulation of α₂M and the possible implications of this in neuroinflammation and neurodegeneration.

PSA-alpha-2-macroglobulin complex is enzymatically active in the serum of patients with advanced prostate cancer and can degrade circulating peptide hormones

BACKGROUND

Prostate cancer cells produce high levels of the serine protease Prostate-Specific Antigen (PSA). PSA is enzymatically active in the tumor microenvironment but is presumed to be enzymatically inactive in the blood due to complex formation with serum protease inhibitors α-1-antichymotrypsin and α-2-macroglobulin (A2M). PSA-A2M complexes cannot be measured by standard ELISA assays and are also rapidly cleared from the circulation. Thus the exact magnitude of PSA production by prostate cancer cells is not easily measured. The PSA complexed to A2M is unable to cleave proteins but maintains the ability to cleave small peptide substrates. Thus, in advanced prostate cancer, sufficient PSA-A2M may be in circulation to effect total A2M levels, levels of cytokines bound to A2M and hydrolyze small circulating peptide hormones.

METHODS

Total A2M levels in men with advanced prostate cancer and PSA levels above 1000 ng/mL were measured by ELISA and compared to controls. Additional ELISA assays were used to measure levels of IL-6 and TGF-beta which can bind to A2M. The ability of PSA-A2M complexes to hydrolyze protein and peptide substrates was analyzed ± PSA inhibitor. Enzymatic activity of PSA-A2M in serum of men with high PSA levels was also assayed.

RESULTS

Serum A2M levels are inversely correlated with PSA levels in men with advanced prostate cancer. Il-6 Levels are significantly elevated in men with PSA >1000 ng/mL compared to controls with PSA <0.1 ng/mL. PSA-A2M complex in serum of men with PSA levels >1000 ng/mL can hydrolyze small fluorescently labeled peptide substrates but not large proteins that are PSA substrates. PSA can hydrolyze small peptide hormones like PTHrP and osteocalcin. PSA complexed to A2M retains the ability to degrade PTHrP.

CONCLUSIONS

In advanced prostate cancer with PSA levels >1000 ng/mL, sufficient PSA-A2M is present in circulation to produce enzymatic activity against circulating small peptide hormones. Sufficient PSA is produced in advanced prostate cancer to alter total A2M levels, which can potentially alter levels of a variety of growth factors such as IL-6, TGF-beta, basic FGF, and PDGF. Alterations in levels of these cytokines and proteolytic degradation of small peptide hormones may have profound effect on host-cancer interaction.

Ceruloplasmin and other copper binding components of blood plasma and their functions: an update

We know that blood plasma contains many proteins and also other components that bind copper. The largest contributor to copper in the plasma is ceruloplasmin, which accounts for 40-70 percent. Apart from ceruloplasmin and albumin, most of these components have not been studied extensively, and even for ceruloplasmin and albumin, much remains to be discovered. New components with new functions, and new functions of known components are emerging, some warranting reconsideration of earlier findings. The author's laboratory has been actively involved in research on this topic. This review summarizes and updates our knowledge of the nature and functions of ceruloplasmin and the other known and emerging copper-containing molecules (principally proteins) in this fluid, to better understand how they contribute to copper homeostasis and consider their potential significance to health and disease.

Targeted Therapies in Liver Fibrosis: Combining the Best Parts of Platelet-Derived Growth Factor BB and Interferon Gamma

Cytokines, growth factors, and other locally produced mediators play key roles in the regulation of disease progression. During liver fibrosis, these mediators orchestrate the balance between pro- and antifibrotic activities as exerted by the hepatic cells. Two important players in this respect are the profibrotic mediator platelet-derived growth factor BB (PDGF-BB) and the antifibrotic cytokine interferon gamma (IFNγ). PDGF-BB, produced by many resident and infiltrating cells, causes extensive proliferation, migration, and contraction of hepatic stellate cells (HSCs) and myofibroblasts. These cells are the extracellular matrix-producing hepatic cells and they highly express the PDGFβ receptor. On the other hand, IFNγ is produced by natural killer cells in fibrotic livers and is endowed with proinflammatory, antiviral, and antifibrotic activities. This cytokine attracted much attention as a possible therapeutic compound in fibrosis. However, clinical trials yielded disappointing results because of low efficacy and adverse effects, most likely related to the dual role of IFNγ in fibrosis. In our studies, we targeted the antifibrotic IFNγ to the liver myofibroblasts. For that, we altered the cell binding properties of IFNγ, by delivery of the IFNγ-nuclear localization sequence to the highly expressed PDGFβ receptor using a PDGFβ receptor recognizing peptide, thereby creating a construct referred to as “Fibroferon” (i.e., fibroblast-targeted interferon γ). In recent years, we demonstrated that HSC-specific delivery of IFNγ increased its antifibrotic potency and improved its general safety profile in vivo, making Fibroferon highly suitable for the treatment of (fibrotic) diseases associated with elevated PDGFβ receptor expression. The present review summarizes the knowledge on these two key mediators, PDGF-BB and IFNγ, and outlines how we used this knowledge to create the cell-specific antifibrotic compound Fibroferon containing parts of both of these mediators.

Hepcidin bound to α2-macroglobulin reduces ferroportin-1 expression and enhances its activity at reducing serum iron levels

Hepcidin regulates iron metabolism by down-regulating ferroportin-1 (Fpn1). We demonstrated that hepcidin is complexed to the blood transport protein, α2-macroglobulin (α2M) (Peslova, G., Petrak, J., Kuzelova, K., Hrdy, I., Halada, P., Kuchel, P. W., Soe-Lin, S., Ponka, P., Sutak, R., Becker, E., Huang, M. L., Suryo Rahmanto, Y., Richardson, D. R., and Vyoral, D. (2009) Blood 113, 6225-6236). However, nothing is known about the mechanism of hepcidin binding to α2M or the effects of the α2M·hepcidin complex in vivo. We show that decreased Fpn1 expression can be mediated by hepcidin bound to native α2M and also, for the first time, hepcidin bound to methylamine-activated α2M (α2M-MA). Passage of high molecular weight α2M·hepcidin or α2M-MA·hepcidin complexes (≈725 kDa) through a Sephadex G-25 size exclusion column retained their ability to decrease Fpn1 expression. Further studies using ultrafiltration indicated that hepcidin binding to α2M and α2M-MA was labile, resulting in some release from the protein, and this may explain its urinary excretion. To determine whether α2M-MA·hepcidin is delivered to cells via the α2M receptor (Lrp1), we assessed α2M uptake and Fpn1 expression in Lrp1(-/-) and Lrp1(+/+) cells. Interestingly, α2M·hepcidin or α2M-MA·hepcidin demonstrated similar activities at decreasing Fpn1 expression in Lrp1(-/-) and Lrp1(+/+) cells, indicating that Lrp1 is not essential for Fpn1 regulation. In vivo, hepcidin bound to α2M or α2M-MA did not affect plasma clearance of α2M/α2M-MA. However, serum iron levels were reduced to a significantly greater extent in mice treated with α2M·hepcidin or α2M-MA·hepcidin relative to unbound hepcidin. This effect could be mediated by the ability of α2M or α2M-MA to retard kidney filtration of bound hepcidin, increasing its half-life. A model is proposed that suggests that unlike proteases, which are irreversibly bound to activated α2M, hepcidin remains labile and available to down-regulate Fpn1.

Activated α2-macroglobulin induces Müller glial cell migration by regulating MT1-MMP activity through LRP1

In retinal proliferative diseases, Müller glial cells (MGCs) acquire migratory abilities. However, the mechanisms that regulate this migration remain poorly understood. In addition, proliferative disorders associated with enhanced activities of matrix metalloprotease 2 (MMP-2) and MMP-9 also present increased levels of the protease inhibitor α2-macroglobulin (α2M) and its receptor, the low-density lipoprotein receptor-related protein 1 (LRP1). In the present work, we investigated whether the protease activated form of α2M, α2M*, and LRP1 are involved with the MGC migratory process. By performing wound-scratch migration and zymography assays, we demonstrated that α2M* induced cell migration and proMMP-2 activation in the human Müller glial cell line, MIO-M1. This induction was blocked when LRP1 and MT1-MMP were knocked down with siRNA techniques. Using fluorescence microscopy and biochemical procedures, we found that α2M* induced an increase in LRP1 and MT1-MMP accumulation in early endosomes, followed by endocytic recycling and intracellular distribution of MT1-MMP toward cellular protrusions. Moreover, Rab11-dominant negative mutant abrogated MT1-MMP recycling pathway, cell migration, and proMMP-2 activation induced by α2M*. In conclusion, α2M*, through its receptor LRP1, induces cellular migration of Müller glial cells by a mechanism that involves MT1-MMP intracellular traffic to the plasma membrane by a Rab11-dependent recycling pathway.

In vivo role of platelet-derived growth factor-BB in airway smooth muscle proliferation in mouse lung

Airway smooth muscle (ASM) hyperplasia in asthma likely contributes considerably to functional changes. Investigating the mechanisms behind proliferation of these cells may lead to therapeutic benefit. Platelet-derived growth factor (PDGF)-BB is a well known ASM mitogen in vitro but has yet to be directly explored using in vivo mouse models in the context of ASM proliferation and airway responsiveness. To determine the in vivo influence of PDGF-BB on gene transcripts encoding contractile proteins, ASM proliferation, and airway physiology, we used an adenovirus overexpression system and a model of chronic allergen exposure. We used adenovirus technology to selectively overexpress PDGF-BB in the airway epithelium of mice. Outcome measurements, including airway physiology, real time RT-PCR measurements, proliferating cell nuclear antigen staining, and airway smooth muscle quantification, were performed 7 days after exposure. The same outcome measurements were performed 24 hours and 4 weeks after a chronic allergen exposure model. PDGF-BB overexpression resulted in airway hyperresponsiveness, decreased lung compliance, increased airway smooth muscle cell numbers, positive proliferating cell nuclear antigen-stained airway smooth muscle cells, and a reduction in genes encoding contractile proteins. Chronic allergen exposure resulted in elevations in lung lavage PDGF-BB, which were observed in conjunction with changes in gene transcript expression encoding contractile proteins and ASM proliferation. We demonstrate for the first time in vivo that PDGF-BB induces ASM hyperplasia and changes in lung mechanics in mice and that, during periods of allergen exposure changes in lung, PDGF-BB are associated with changes in airway structure and function.

Hepcidin, the hormone of iron metabolism, is bound specifically to alpha-2-macroglobulin in blood

Hepcidin is a major regulator of iron metabolism. Hepcidin-based therapeutics/diagnostics could play roles in hematology in the future, and thus, hepcidin transport is crucial to understand. In this study, we identify alpha2-macroglobulin (alpha2-M) as the specific hepcidin-binding molecule in blood. Interaction of 125I-hepcidin with alpha2-M was identified using fractionation of plasma proteins followed by native gradient polyacrylamide gel electrophoresis and mass spectrometry. Hepcidin binding to nonactivated alpha2-M displays high affinity (Kd 177 +/- 27 nM), whereas hepcidin binding to albumin was nonspecific and displayed nonsaturable kinetics. Surprisingly, the interaction of hepcidin with activated alpha2-M exhibited a classical sigmoidal binding curve demonstrating cooperative binding of 4 high-affinity (Kd 0.3 microM) hepcidin-binding sites. This property probably enables efficient sequestration of hepcidin and its subsequent release or inactivation that may be important for its effector functions. Because alpha2-M rapidly targets ligands to cells via receptor-mediated endocytosis, the binding of hepcidin to alpha2-M may influence its functions. In fact, the alpha2-M-hepcidin complex decreased ferroportin expression in J774 cells more effectively than hepcidin alone. The demonstration that alpha2-M is the hepcidin transporter could lead to better understanding of hepcidin physiology, methods for its sensitive measurement and the development of novel drugs for the treatment of iron-related diseases.

Alpha2-macroglobulin is a mediator of retinal ganglion cell death in glaucoma

Glaucoma is defined as a chronic and progressive optic nerve neuropathy, characterized by apoptosis of retinal ganglion cells (RGC) that leads to irreversible blindness. Ocular hypertension is a major risk factor, but in glaucoma RGC death can persist after ocular hypertension is normalized. To understand the mechanism underlying chronic RGC death we identified and characterized a gene product, alpha2-macroglobulin (alpha2M), whose expression is up-regulated early in ocular hypertension and remains up-regulated long after ocular hypertension is normalized. In ocular hypertension retinal glia up-regulate alpha2M, which binds to low-density lipoprotein receptor-related protein-1 receptors in RGCs, and is neurotoxic in a paracrine fashion. Neutralization of alpha2M delayed RGC loss during ocular hypertension; whereas delivery of alpha2M to normal eyes caused progressive apoptosis of RGC mimicking glaucoma without ocular hypertension. This work adds to our understanding of the pathology and molecular mechanisms of glaucoma, and illustrates emerging paradigms for studying chronic neurodegeneration in glaucoma and perhaps other disorders.

Prostate stem cells and benign prostatic hyperplasia

Pharmacological approaches are available to medically-managed patients with symptomatic BPH before surgical intervention is required. These include daily treatment with alpha-blockers and 5-alpha-reductase inhibitors alone or in combination. These medical approaches have two major problems. First, treatments are chronic and must be taken daily. Second, there are significant financial costs and quality of life issues for such chronic treatments. Is it possible to develop effective acute therapy for symptomatic BPH without the long-term androgen deprivation-induced side effects? Two seminal but rarely cited studies of Walsh [Peters, Walsh: N Engl J Med 317:599-604, 1987] and Coffey et al. [Sufrin et al.: Invest Urol 13:418-423, 1976], combined with the growing understanding of the stem cell organization of the prostate stromal (S) and epithelial (E) compartments and their reciprocal paracrine and autocrine interactions provides the rationale for an acute approach.The Walsh study documents that: (1) androgen deprivation disrupts the reciprocal interaction between the prostate S and E thereby decreasing the weight of both compartments and (2) once BPH develops, androgen deprivation does not decrease the number of stem cell units in either the S or E compartments since subsequent androgen restoration fully restores the enlarged gland. The Coffey study documents that acute androgen deprivation sensitizes S-E interactions to radiation induced disruptions so that following radiation, androgen restoration does not induce full gland regrowth. Therefore, effective therapy for symptomatic BPH should be achievable by acute treatment with reversible androgen deprivation for a limited period followed by a single dose of conformal external beam radiation before allowing the man to recovery his normal serum testosterone.

Molecular dissection of the human alpha2-macroglobulin subunit reveals domains with antagonistic activities in cell signaling

alpha(2)-Macroglobulin (alpha(2)M) is a plasma protease inhibitor, which reversibly binds growth factors and, in its activated form, binds to low density lipoprotein receptor-related protein (LRP-1), an endocytic receptor with cell signaling activity. Because distinct domains in alpha(2)M are responsible for its various functions, we hypothesized that the overall effects of alpha(2)M on cell physiology reflect the integrated activities of multiple domains, some of which may be antagonistic. To test this hypothesis, we expressed the growth factor carrier site and the LRP-1 recognition domain (RBD) as separate GST fusion proteins (FP3 and FP6, respectively). FP6 rapidly and robustly activated Akt and ERK/MAP kinase in Schwann cells and PC12 cells. This response was blocked by LRP-1 gene silencing or by co-incubation with the LRP-1 antagonist, receptor-associated protein. The activity of FP6 also was blocked by mutating Lys(1370) and Lys(1374), which precludes LRP-1 binding. FP3 blocked activation of Akt and ERK/MAP kinase in response to nerve growth factor-beta (NGF-beta) but not FP6. In PC12 cells, FP6 promoted neurite outgrowth and expression of growth-associated protein-43, whereas FP3 antagonized the same responses when NGF-beta was added. The ability of FP6 to trigger LRP-1-dependent cell signaling in PC12 cells was reproduced by the 18-kDa RBD, isolated from plasma-purified alpha(2)M by proteolysis and chromatography. We propose that the effects of intact alpha(2)M on cell physiology reflect the degree of penetration of activities associated with different domains, such as FP3 and FP6, which may be regulated asynchronously by conformational change and by other regulatory proteins in the cellular microenvironment.

Differential transcription of multiple forms of alpha-2-macroglobulin in carp (Cyprinus carpio) infected with parasites

Alpha-2-macroglobulin (a2M) is a non-specific protease inhibitor involved in host defense mechanisms, inhibiting both endogenous and exogenous proteases. It is unique among the plasma anti-proteases with respect to the diversity of proteases that it can inactivate. Carp a2M consists of an alpha and beta chain of which the first includes the bioactive regions. Previously, three a2M alpha chain sequences were reported for East-Asian common carp. We studied a2M alpha chain variability in European common carp and report the cloning of a fourth a2M alpha chain with distinct sequence diversity in the bait region. The role of a2M in the immune response to parasites was studied in the liver of carp infected with Trypanoplasma borreli or with Ichthyophthirius multifiliis. Quantitative gene transcription analysis showed a differential regulation of the four isoforms, most clearly seen in infections with I. multifiliis. A2M3 was the only a2M isoform with a highly upregulated transcription during infection, suggesting that this particular isoform is of foremost biological importance.

Does PSA play a role as a promoting agent during the initiation and/or progression of prostate cancer?

Prostate cancer cells, like normal prostate epithelial cells, produce high levels of the differentiation marker and serine protease prostate-specific antigen (PSA). PSA is used extensively as a biomarker to screen for prostate cancer, to detect recurrence following local therapies, and to follow response to systemic therapies for metastatic disease. While much is known about PSA's role as a biomarker, only a relatively few studies address the role played by PSA in the pathobiology of prostate cancer. Autopsy studies have documented that not only do prostate cancer cells maintain production of high amounts of PSA but they also maintain the enzymatic machinery required to process PSA to an enzymatically active form. A variety studies performed over the last 10 years have hinted at a role for PSA in growth, progression, and metastases of prostate cancer. A fuller understanding of PSA's functional role in prostate cancer biology, however, has been hampered by the lack of appropriate models and tools. Therefore, the purpose of this review is not to address issues related to PSA as a biomarker. Instead, by reviewing what is known about the genetics, biochemistry, and biology of PSA in normal and malignant prostate tissue, insights may be gained into the role PSA may be playing in the pathobiology of prostate cancer that can connect measurement of this biomarker to an understanding of the underlying etiology and progression of the disease.

Limited Mutations in Full-length Tetrameric Human α2-Macroglobulin Abrogate Binding of Platelet-derived Growth Factor-BB and Transforming Growth Factor-β1

alpha2-Macroglobulin (alpha2M) inhibits diverse extracellular proteases, binds growth factors such as platelet-derived growth factor-BB (PDGF-BB) and transforming growth factor-beta1 (TGF-beta1), and carries beta-amyloid peptide. alpha2M may also trigger cell signaling by binding to the low density lipoprotein receptor-related protein (LRP-1) and/or other cell surface receptors. Based on studies with recombinant alpha2M fragments expressed in bacteria and synthetic peptides, we previously localized a growth factor-binding site near the center of the alpha2M subunit. However, because intact alpha2M forms a hollow cylinder structure, an alternative model for growth factor binding involves nonspecific entrapment within the alpha2M core. To distinguish between these two models, we engineered mutations in the putative growth factor binding sequence of full-length alpha2M. These mutations did not perturb the tetrameric structure of alpha2M, reaction with proteases, the thiol ester bonds, or binding to LRP-1. A single mutation (E730R) completely blocked binding of platelet-derived growth factor-BB to intact alpha2M. E730R did not alter TGF-beta1 binding; however, this mutation in combination with mutations at Glu714 and Asp719 eliminated the increase in TGF-beta1 binding associated with alpha2M conformational change. These studies demonstrate that growth factor binding to intact alpha2M is specific, involving a defined region of the alpha2M subunit. The exact sequences required for binding different growth factors may be non-identical, mimicking the model of the bait region in which different proteases target adjacent and sometimes overlapping sequences.

Macrophage Migration Inhibitory Factor is Increased in the Urine of Patients With Urinary Tract Infection: Macrophage Migration Inhibitory Factor-Protein Complexes in Human Urine

PURPOSE

MIF is a proinflammatory cytokine present in preformed stores in human urothelium. In animal models of bladder inflammation, including bacterial cystitis, MIF is up-regulated in the bladder and released from the bladder as a high molecular weight complex. We compared urine MIF amounts in patients with UTI to that in patients without UTI, and we examined and identified MIF-protein complexes in urine.

MATERIALS AND METHODS

Using enzyme-linked immunosorbent assay we compared MIF levels in the urine of 14 patients with UTI to levels in 16 controls with no UTI. Western blotting under native, denaturing and reducing conditions was done to examine MIF complexes found in urine. Mass spectrometry identified MIF associated proteins in urine, while co-immunoprecipitation confirmed the associations.

RESULTS

Mean urine MIF amounts +/- SEM determined by enzyme-linked immunosorbent assay were significantly greater in 14 patients with UTI compared to that in 16 controls (1.96 +/- 0.40 vs 0.59 +/- 0.09 ng/mg creatinine, p <0.01). Western blotting under denaturing conditions showed several high molecular weight complexes (100 to 165 kDa) that increased in UTI urine as well as typical, monomeric MIF (12 kDa). Mass spectrometry identified associated MIF proteins, including ceruloplasmin, albumin and uromodulin. Co-immunoprecipitation confirmed mass spectrometry findings and also identified MIF interaction with alpha-2-macroglobulin.

CONCLUSIONS

Increased urine MIF amounts in patients with bacterial cystitis support our experimental evidence showing a role for MIF in pelvic visceral inflammation. The novel finding of an association of MIF with other urine proteins suggest that the physiologically relevant form of MIF may be an MIF-protein complex.

A novel protease inhibitor of the alpha2-macroglobulin family expressed in the human epidermis

In the course of a large scale analysis of late-expressed genes in the human epidermis, we identified a new member of the alpha(2)-macroglobulin (alpha2M) protease inhibitor family, A2ML1 (for alpha(2)-macroglobulin-like 1). Like A2M and PZP, A2ML1 is located on chromosome 12p13.31. A2ML1 encodes a protein of 1454 amino acids, which fits the characteristics of alpha2Ms: 1) strong conservation in amino acid sequence including most of cysteine positions with alpha2M; 2) a putative central bait domain; 3) a typical thiol ester sequence. Northern blot and reverse transcriptase-PCR studies revealed a single 5-kb A2ML1 mRNA, mainly in the epidermis granular keratinocytes. A2ML1 is also transcribed in placenta, thymus, and testis. By Western blot analysis, alpha2ML1 is detected as a monomeric, approximately 180-kDa protein in human epidermis. In vitro keratinocyte differentiation is associated with increased expression levels. By immunohistochemistry, alpha2ML1 was detected within keratinosomes in the granular layer of the epidermis, and as a secreted product in the extracellular space between the uppermost granular layer and the cornified layer. Recombinant alpha2ML1 displayed inhibitory activity toward chymotrypsin, papain, thermolysin, subtilisin A, and to a lesser extent, elastase but not trypsin. Incubation with chymotrypsin and the chymotrypsin-like kallikrein 7 protease indicated that alpha2ML1 binds covalently to these proteases, a feature shared with other members of the family. Therefore, alpha2ML1 is the first alpha2M family member detected in the epidermis. It may play an important role during desquamation by inhibiting extracellular proteases.

Further evidence for increased macrophage migration inhibitory factor expression in prostate cancer

Background

Macrophage migration inhibitory factor (MIF) is a cytokine associated with prostate cancer, based on histologic evidence and circulating (serum) levels.

Recent studies from another laboratory failed to document these results. This study's aims were to extend and confirm our previous data, as well as to define possible mechanisms for the discrepant results. Additional aims were to examine MIF expression, as well as the location of MIF's receptor, CD74, in human prostatic adenocarcinoma compared to matched benign prostate.

Methods

MIF amounts were determined in random serum samples remaining following routine PSA screening by ELISA. Native, denaturing and reducing polyacrylamide gels and Western blot analyses determined the MIF form in serum. Prostate tissue arrays were processed for MIF in situ hybridization and immunohistochemistry for MIF and CD74. MIF released into culture medium from normal epithelial, LNCaP and PC-3 cells was detected by Western blot analysis.

Results

Median serum MIF amounts were significantly elevated in prostate cancer patients (5.87 ± 3.91 ng/ml; ± interquartile range; n = 115) compared with patients with no documented diagnosis of prostate cancer (2.19 ± 2.65 ng/ml; n = 158). ELISA diluent reagents that included bovine serum albumin (BSA) significantly reduced MIF serum detection (p < 0.01). MIF mRNA was localized to prostatic epithelium in all samples, but cancer showed statistically greater MIF expression. MIF and its receptor (CD74) were localized to prostatic epithelium. Increased secreted MIF was detected in culture medium from prostate cancer cell lines (LNCaP and PC-3).

Conclusion

Increased serum MIF was associated with prostate cancer. Diluent reagents that included BSA resulted in MIF serum immunoassay interference. In addition, significant amounts of complexed MIF (180 kDa under denaturing conditions by Western blot) found in the serum do not bind to the MIF capture antibody. Increased MIF mRNA expression was observed in prostatic adenocarcinoma compared to benign tissue from matched samples, supporting our earlier finding of increased MIF gene expression in prostate cancer.

MACROPHAGE MIGRATION INHIBITORY FACTOR IS RELEASED AS A COMPLEX WITH α1-INHIBITOR-3 IN THE INTRALUMINAL FLUID DURING BLADDER INFLAMMATION IN THE RAT

PURPOSE

Macrophage migration inhibitory factor (MIF) is released into intraluminal fluid (ILF) during bladder inflammation in the rat. We investigated the forms of MIF that are released. We examined MIF release after subcutaneous substance P (SP) or intravesical capsaicin and studied proteins associated with excreted MIF in ILF.

MATERIALS AND METHODS

Anesthetized male rats with the bladder isolated from the kidneys were injected with SP subcutaneously (saline vehicle) or with intravesical capsaicin (vehicle, 0.1 mM and 1 mM). After 1 hour the ILF was removed and MIF levels were determined using enzyme-linked immunosorbent assay or Western blotting procedures under native, nonreducing and reducing conditions. Mass spectrometry was used to identify proteins associated with MIF in ILF and results were verified by immunoprecipitation.

RESULTS

SP and intravesical capsaicin increased the total amount of MIF in ILF. MIF was found in high molecular weight complexes that resolved into 2 bands under nonreducing conditions. SP and capsaicin differentially increased the MIF bands. Mass spectrometry determined that MIF was complexed with acute phase proteins. MIF immunoprecipitation followed by Western blotting confirmed that MIF was complexed to alpha1-inhibitor-3.

CONCLUSIONS

MIF is complexed with alpha1-inhibitor-3, a member of the alpha-2-macroglobulin proteinase inhibitor family, in the rat. Although SP and capsaicin increased the total amount of MIF detected by enzyme-linked immunosorbent assay in ILF, the patterns of MIF complexes elicited by these 2 treatments were different. These findings suggest that in association with other proteins MIF forms part of a complex elicited by bladder inflammation.

β-Amyloid Peptide Binds Equivalently to Binary and Ternary α2-Macroglobulin–protease Complexes

alpha2-Macroglobulin (alpha2M) is a protease inhibitor that has separate binding sites for transforming growth factor-beta (TGF-beta) and beta-amyloid peptide (Abeta), both of which have been identified in the beta2M sequence. In the 3D-structure of alpha2M, TGF-beta occupies the alpha2M central cavity, overlapping with the space that can accommodate up to two molecules of protease. As a result, ternary alpha2M-protease complexes (2 mol protease/mol alpha2M) have been reported to not bind TGF-beta. The goal of the present study was to test whether binding of Abeta to alpha2M is controlled by steric constraints imposed by associated proteases, similarly to TGF-beta. We confirmed that binary alpha2M-trypsin complex (1 mol trypsin/mol alpha2M) binds increased amounts of TGF-beta1, compared with native alpha2M, while ternary alpha2M-trypsin complex binds substantially decreased amounts of TGF-beta1. By contrast, Abeta-binding to binary and ternary alpha2M trypsin complex was equivalent. In both cases, binding was substantially increased compared with the negligible level observed with native alpha2M. Plasmin is a large protease (Mr approximately 82,000) that substantially occupies the alpha2M central cavity; however, alpha2M-plasmin complex also bound increased amounts of Abeta, compared with native alpha2M. We conclude that Abeta accesses its binding site, in alpha2M, from outside the alpha2M central cavity. The TGF-beta- and Abeta-binding sites are spatially separated not only in the primary sequence of alpha2M, but also in the 3D-structure.

Identification and characterization of CPAMD8, a novel member of the complement 3/alpha2-macroglobulin family with a C-terminal Kazal domain

We have identified and characterized a novel member of the complement 3/alpha(2)-macroglobulin (C3/alpha(2)M) family named CPAMD8 (complement 3 and pregnancy zone protein-like, alpha2-macroglobulin domain-containing 8). The gene maps to chromosome 19p13.2-p13.3 and spans approximately 130 kb. The gene partially overlaps with the protease-activated receptor-4 (PAR4) gene in the reverse orientation. The cDNA consists of 40 exons ( approximately 6 kb) and encodes a protein of 1885 amino acids. Similar to other proteins in this family, CPAMD8 contains a signal sequence, an RXXR processing site, and a thioester motif. In addition, CPAMD8 has a Kazal-type serine proteinase inhibitor/follistatin-like domain at the C-terminus. The intact CPAMD8 protein generated by in vitro transcription and translation resolved as a single band of about 200 kDa on SDS-PAGE. RT-PCR and immunoblot assays showed that CPAMD8 is expressed in a number of human tissues, most abundantly in the kidney, brain, and testis and at lower levels in heart, liver, and small intestine. CPAMD8 is also expressed in several types of cells in culture, in which it is proteolytically processed into two chains of about 70 and 130 kDa. The Kazal domain of CPAMD8 binds to heparin, and subcellular fractionation shows that CPAMD8 is membrane associated via ionic interaction. In response to immune stimulants, CPAMD8 expression is markedly up-regulated in cells in culture. Thus, CPAMD8 may, like other members of the C3/alpha(2)M family, function in innate immunity but in a localized manner.

Regulation of PDGF and its receptors in fibrotic diseases

Platelet-derived growth factor (PDGF) isoforms play a major role in stimulating the replication, survival, and migration of myofibroblasts during the pathogenesis of fibrotic diseases. During fibrogenesis, PDGF is secreted by a variety of cell types as a response to injury, and many pro-inflammatory cytokines mediate their mitogenic effects via the autocrine release of PDGF. PDGF action is determined by the relative expression of PDGF alpha-receptors (PDGFRalpha) and beta-receptors (PDGFRbeta) on the surface of myofibroblasts. These receptors are induced during fibrogenesis, thereby amplifying biological responses to PDGF isoforms. PDGF action is also modulated by extracellular binding proteins and matrix molecules. This review summarizes the literature on the role of PDGF and its receptors in the development of fibrosis in a variety of organ systems, including lung, liver, kidney, and skin.

TGF-beta impairs renal autoregulation via generation of ROS

Impaired autoregulation in chronic kidney disease can result in elevation of glomerular capillary pressure and progressive glomerular damage; however, the factors linking chronic glomerular disorders to impaired autoregulation have not been identified. We tested the hypothesis that the cytokine most closely associated with progressive glomerular disease, transforming growth factor (TGF)-beta, may also attenuate autoregulation. Kidneys from normal rats were prepared for videomicroscopy, using the blood-perfused juxtamedullary nephron technique. Autoregulatory responses were measured under control conditions and during superfusion with TGF-beta1 (10 ng/ml). Control afferent arteriolar diameter averaged 18.4 +/- 1 microm and significantly decreased to 16.3 +/- 0.9 and 13.2 +/- 0.8 microm at perfusion pressures of 130 and 160 mmHg, respectively. In the presence of TGF-beta1, autoregulatory responses were completely blocked. In similar experiments performed using PDGF-BB (10 ng/ml) and HGF (25 ng/ml), the normal autoregulatory response was not affected. In vitro studies, using isolated preglomerular vascular smooth muscle cells, revealed that exposure to TGF-beta1 stimulated a rapid increase in reactive oxygen species (ROS) that was inhibited by NADPH oxidase inhibitors. In situ studies, with dihydroethidium staining, revealed a marked increase in renal vessel ROS production on exposure to TGF-beta1. Pretreatment of the juxtamedullary afferent arterioles with tempol, a ROS scavenger, or with apocynin, a NADPH oxidase inhibitor, prevented the impaired autoregulation induced by TGF-beta1. These data reveal a novel hemodynamic pathway by which TGF-beta could lead to progressive glomerular injury by impairing normal renal microvascular function.

The mosaic receptor sorLA/LR11 binds components of the plasminogen-activating system and platelet-derived growth factor-BB similarly to LRP1 (low-density lipoprotein receptor-related protein), but mediates slow internalization of bound ligand

The type-1 receptor sorLA/LR11, a member of the Vps10p-domain receptor family that also contains domains characterizing members of the LDL (low-density lipoprotein) receptor family, has been shown to induce increased uPAR (urokinase receptor) expression as well as enhanced migration and invasion activities in smooth muscle cells in the presence of PDGF-BB (platelet-derived growth factor-BB). Here we show that sorLA interacts with both components of the plasminogen activating system and PDGF-BB similarly to LRP1 (LDL receptor-related protein/alpha2-macroglobulin receptor), which is an important clearance receptor with established functions in controlling uPAR expression as well as PDGF-BB signalling. In contrast with LRP1, sorLA does not interact with alpha2-macroglobulin, which is a binding protein for several growth factors, including PDGF-BB. By using LRP1-deficient cells transfected with sorLA, we demonstrate that sorLA-bound ligand is internalized at a much lower rate than LRP1-bound ligand, and that sorLA is inefficient in regulating cell surface uPAR expression, which depends on rapid internalization of the ternary complex between urokinase-type plasminogen activator, its type-1 inhibitor, and uPAR. Thus, although overlapping with regard to binding profiles, sorLA is substantially less efficient as a clearance receptor than LRP1. We propose that sorLA can divert ligands away from LRP1 and thereby inhibit both their clearance and signalling events mediated by LRP1.

Binding of alpha2-macroglobulin to GRAB (Protein G-related alpha2-macroglobulin-binding protein), an important virulence factor of group A streptococci, is mediated by two charged motifs in the DeltaA region

GRAB (Protein G-related alpha2M-binding protein) is a surface protein of group A streptococci and exhibits high affinity for alpha2-macroglobulin (alpha2M), a broad-range protease inhibitor. It is the sole alpha2M-binding protein of group A streptococci that has been shown to promote bacterial virulence in a mouse model of skin infection. The binding site for alpha2M was predicted to be in the N-terminal A domain of GRAB. In the present study, the alpha2M-binding domain was first narrowed down to 34 amino acids (amino acids 34-67) using variable truncated N-terminal GRAB fusion proteins. The sequence of the identified domain was used to design overlapping synthetic peptides of different sizes, which were then immobilized on a membrane and assayed for their alpha2M-binding activity. The peptide screening revealed two binding motifs of ten amino acids length, located in the DeltaA (N-terminal part of the A domain) region (amino acids 34-67) with the sequences PRIIPNGGTL (amino acids 41-50) and NAPEKLALRN (amino acids 56-65) respectively. These motifs were used for systematic mutational analysis by generating synthetic peptides containing individual amino acid substitutions at every position of the mapped binding regions. The results indicated a critical role for the arginine residue at position 42 in the first binding domain and at position 64 in the second binding region. Validation of arginine residues as the critical amino acids for alpha2M binding was achieved by site-directed mutagenesis and binding assays. Competitive inhibition assays with GRAB containing amino acid substitutions R42G (Arg42-->Gly), R64G and R42G/R64G indicated differential contribution of the arginine residues at positions 42 and 64 to alpha2M-binding activity and, thus, their involvement in GRAB-induced virulence.

Functional analysis of plasma α2-macroglobulin from Alzheimer's disease patients with the A2M intronic deletion

alpha(2)-Macroglobulin (alpha(2)M) is an abundant plasma/extracellular space protein implicated in clearance of amyloid beta (Abeta), a key constituent of Alzheimer's disease (AD) plaques. alpha(2)M also regulates proteinase and growth factor activities. In recent years, there have been >30 genetic studies debating the controversial role of a five-base-pair intronic deletion in the A2M gene in late-onset AD. However, little is known about potential effects of the deletion upon alpha(2)M function. In this study, we examined the subunit and conformational structure of alpha(2)M in AD plasma samples, and its capacity to bind trypsin, transforming growth factor-beta1, and Abeta. Plasma from patients homozygous for the deletion (DD) showed normal alpha(2)M subunit size, conformation, and proteinase inhibitory activity. Interestingly, plasma alpha(2)M from two DD patients showed markedly increased TGF-beta1 binding. Moreover, methylamine-treated DD plasma samples showed modest, but significant, elevations in Abeta binding to alpha(2)M* compared with samples from patients lacking the deletion. These observations suggest a possible functional basis by which the A2M deletion may influence multifactorial AD pathogenesis.

Characterization of the interaction between alpha2-macroglobulin and fibroblast growth factor-2: the role of hydrophobic interactions

Basic fibroblast growth factor (FGF-2) is important in development, wound healing and angiogenesis. The human plasma proteinase inhibitor alpha2-macroglobulin (alpha2M) binds to and regulates the biological activity of various growth factors, including FGF-2. FGF-2 binds specifically and saturably to native alpha2M and conformationally modified alpha2M (alpha2M*); however, the KD for FGF-2 binding to alpha2M* is 10-fold lower. This study investigates the biochemical nature of the interaction between FGF-2 and alpha2M* and localizes a possible FGF-2 binding site in the alpha2M subunit. FGF-2 binding to alpha2M* was not affected by shifts in pH between 6.5 and 10; however, increasing temperature decreased the KD for this interaction. The binding affinity of FGF-2 for alpha2M* also increased with increasing ionic strength. These results are consistent with the hypothesis that hydrophobic interactions predominate in promoting FGF-2 association with alpha2M*. Consistent with this hypothesis, FGF-2 bound to a glutathione S-transferase fusion protein containing amino acids 591-774 of the alpha2M subunit (FP3) and to a hydrophobic 16-amino-acid peptide (amino acids 718-733) within FP3. Specific binding of FGF-2 to the 16-amino-acid peptide was inhibited by excess transforming growth factor-beta1. When the 16-amino-acid peptide was chemically modified to neutralize the only two charged amino acids, FGF-2-binding activity was unaffected, supporting the predominant role of hydrophobic interactions. FGF-2 presentation to signalling receptors is influenced by growth factor binding to heparan sulphate proteoglycans (HSPGs), which is electrostatic in nature. Our results demonstrate that the interactions of FGF-2 with alpha2M* and HSPGs are biochemically distinct, suggesting that different FGF-2 sequences are involved.

Growth factor-binding sequence in human alpha2-macroglobulin targets the receptor-binding site in transforming growth factor-beta

alpha(2)-Macroglobulin (alpha(2)M) binds transforming growth factor-beta1 (TGF-beta1) and TGF-beta2, forcing these growth factors into a state of latency. The mechanism by which this occurs remains unclear. In this paper, we demonstrate that peptides, derived from the structure of human alpha(2)M (amino acids 714-729), bind directly to TGF-beta1 and block the binding of TGF-beta1 to the type I and II TGF-beta receptors. The alpha(2)M-derived peptides are notable for hydrophobic tripeptide sequences (WIW or VVV) and acidic residues (Glu(714) and Asp(719) in the mature alpha(2)M subunit), which may function analogously to the structural elements that mediate TGF-beta-binding in the type II receptor. Mutating Glu(714) and Asp(719) in the alpha(2)M-peptide-GST fusion protein, FP3, which contains the putative growth factor-binding site, significantly decreased the binding affinity of FP3 for TGF-beta1. The alpha(2)M-derived peptides, which bind TGF-beta1, inhibited the interaction of TGF-beta1 with its receptors in fetal bovine heart endothelial cells. The same peptides also inhibited the activity of TGF-beta1 in endothelial cell proliferation assays. These results demonstrate that alpha(2)M-derived peptides target the receptor-binding sequence in TGF-beta.

Sex-related variations in serum nerve growth factor concentration in humans

A role of nerve growth factor (NGF) in the neuro-endocrine-immune interactions has been recently suggested by the presence of NGF and its receptors in cells of the immune and endocrine systems. The improvement in the comprehension of the role played by NGF in humans is linked to the availability of a sensitive and reliable method to quantify NGF concentrations in body fluids and tissues. As a consequence of different methods used, normal levels of human serum NGF reported in the literature show wide differences. The present results indicate that ELISA appears very sensitive (detection limit 1.4pg/ml) and allows the discrimination of subtle variations of serum NGF concentrations. ELISA performed in serum obtained from men indicated that NGF concentration was 40.8+/-10.8pg/ml, whereas women showed significantly lower levels that were influenced by the menstrual cycle. In particular, the mean value of this neurotrophin during the follicular phase was 8.2+/-1.4pg/ml; the luteal phase, in turn, showed levels up to 14.4+/-2.9pg/ml. The difference of serum NGF concentrations between the follicular and luteal phase in each woman was statistically significant. Differences in NGF concentrations between men and women (in both phases of the menstrual cycles) were also statistically significant. In conclusion, a possible role of sex steroids as modulators of NGF secretion in humans is strongly supported by the present paper. However, mechanisms underlying this phenomenon are still unknown. The evidence indicating physiological sex hormone-related variations in NGF levels would be of interest in view of the possible use of circulating NGF modifications as a laboratory biomarker in different diseases.

Molecular basis of endothelial cell morphogenesis in three-dimensional extracellular matrices

Although many studies have focused on blood vessel development and new blood vessel formation associated with disease processes, the question of how endothelial cells (ECs) assemble into tubes in three dimensions (i.e., EC morphogenesis) remains unanswered. EC morphogenesis is particularly dependent on a signaling axis involving the extracellular matrix (ECM), integrins, and the cytoskeleton, which regulates EC shape changes and signals the pathways necessary for tube formation. Recent studies reveal that genes regulating this matrix-integrin-cytoskeletal (MIC) signaling axis are differentially expressed during EC morphogenesis. The Rho GTPases represent an important class of molecules involved in these events. Cdc42 and Rac1 are required for the process of EC intracellular vacuole formation and coalescence that regulates EC lumen formation in three-dimensional (3D) extracellular matrices, while RhoA appears to stabilize capillary tube networks. Once EC tube networks are established, supporting cells, such as pericytes, are recruited to further stabilize these networks, perhaps by regulating EC basement membrane matrix assembly. Furthermore, we consider recent work showing that EC morphogenesis is balanced by a tendency for newly formed tubes to regress. This morphogenesis-regression balance is controlled by differential gene expression of such molecules as VEGF, angiopoietin-2, and PAI-1, as well as a plasmin- and matrix metalloproteinase-dependent mechanism that induces tube regression through degradation of ECM scaffolds that support EC-lined tubes. It is our hope that this review will stimulate increased interest and effort focused on the basic mechanisms regulating capillary tube formation and regression in 3D extracellular matrices.

Adipocyte-derived plasma protein adiponectin acts as a platelet-derived growth factor-BB-binding protein and regulates growth factor-induced common postreceptor signal in vascular smooth muscle cell

BACKGROUND

Vascular smooth muscle cell proliferation plays an important role in the development of atherosclerosis. We previously reported that adiponectin, an adipocyte-specific plasma protein, accumulated in the human injured artery and suppressed endothelial inflammatory response as well as macrophage-to-foam cell transformation. The present study investigated the effects of adiponectin on proliferation and migration of human aortic smooth muscle cells (HASMCs). Methods and Results- HASMC proliferation was estimated by [(3)H] thymidine uptake and cell number. Cell migration assay was performed using a Boyden chamber. Physiological concentrations of adiponectin significantly suppressed both proliferation and migration of HASMCs stimulated with platelet-derived growth factor (PDGF)-BB. Adiponectin specifically bound to (125)I-PDGF-BB and significantly inhibited the association of (125)I-PDGF-BB with HASMCs, but no effects were observed on the binding of (125)I-PDGF-AA or (125)I-heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) to HASMCs. Adiponectin strongly and dose-dependently suppressed PDGF-BB-induced p42/44 extracellular signal-related kinase (ERK) phosphorylation and PDGF beta-receptor autophosphorylation analyzed by immunoblot. Adiponectin also reduced PDGF-AA-stimulated or HB-EGF-stimulated ERK phosphorylation in a dose-dependent manner without affecting autophosphorylation of PDGF alpha-receptor or EGF receptor.

CONCLUSIONS

The adipocyte-derived plasma protein adiponectin strongly suppressed HASMC proliferation and migration through direct binding with PDGF-BB and generally inhibited growth factor-stimulated ERK signal in HASMCs, suggesting that adiponectin acts as a modulator for vascular remodeling.

Decrease of TGF-beta1 plasma levels and increase of nitric oxide synthase activity in leukocytes as potential biomarkers of Alzheimer's disease

A variety of inflammatory proteins have been identified in brains of Alzheimer's disease (AD) patients, including inflammatory cytokines, acute phase proteins and complement components. In the present paper we have investigated the levels of circulating inflammatory mediators as potential biomarkers of this disease, concentrating mostly on transforming growth factor beta (TGF-beta1) in plasma and on nitric oxide synthase (NOS) activity in leukocytes. Plasma and leukocytes were isolated from 48 sporadic AD and 23 healthy control subjects of same age and sex. Since alpha2-Macroglobulin (alpha2M), an acute phase protein possibly involved in AD, is an important modulator of TGF-beta1 activity, binding and targeting this cytokine to its appropriate site of action, we have investigated the possible complex between TGF-beta1 and alpha2M in plasma of the same subjects. The results demonstrate a significant reduction of TGF-beta1 levels in plasma of AD patients. A complex between alpha2M and TGF-beta1 occurred in AD as well as healthy elderly control subjects, however, with no significant differences. Moreover, alpha2M appeared to bind only the inactive form of this cytokine. In contrast, NOS activity increased significantly in leukocytes of AD patients. Therefore, we suggest the combined determination of TGF-beta1 in the plasma and of NOS activity in the leukocytes as biomarkers of AD.

Distinct binding sites in the structure of alpha 2-macroglobulin mediate the interaction with beta-amyloid peptide and growth factors

Alpha(2)-macroglobulin (alpha(2)M) and its receptor, low density lipoprotein receptor-related protein (LRP), function together to facilitate the cellular uptake and degradation of beta-amyloid peptide (Abeta). In this study, we demonstrate that Abeta binds selectively to alpha(2)M that has been induced to undergo conformational change by reaction with methylamine. Denatured alpha(2)M subunits, which were immobilized on polyvinylidene difluoride membranes, bound Abeta, suggesting that alpha(2)M tertiary and quaternary structure are not necessary. To determine whether a specific sequence in alpha(2)M is responsible for Abeta binding, we prepared and analyzed defined alpha(2)M fragments and glutathione S-transferase-alpha(2)M peptide fusion proteins. A single sequence, centered at amino acids (aa) 1314-1365, was identified as the only major Abeta-binding site. Importantly, Abeta did not bind to the previously characterized growth factor-binding site (aa 718-734). Although the Abeta binding sequence is adjacent to the binding site for LRP, the results of experiments with mutated fusion proteins indicate that the two sites are distinct. Furthermore, a saturating concentration of Abeta did not inhibit LRP-mediated clearance of alpha(2)M-MA in mice. Using various methods, we determined that the K(D) for the interaction of Abeta with its binding site in the individual alpha(2)M subunit is 0.7-2.4 microm. The capacity of alpha(2)M to bind Abeta and deliver it to LRP may be greater than that predicted by the K(D), because each alpha(2)M subunit may bind Abeta and the bound Abeta may multimerize. These studies suggest a model in which alpha(2)M has three protein interaction sites with distinct specificities, mediating the interaction with Abeta, growth factors, and LRP.

Delivery of neurotrophic factors to the central nervous system: pharmacokinetic considerations

Neurotrophic factors are proteins with considerable potential in the treatment of central nervous system (CNS) diseases and traumatic injuries. However, a significant challenge to their clinical use is the difficulty associated with delivering these proteins to the CNS. Neurotrophic factors are hydrophilic, typically basic, monomeric or dimeric proteins, mostly in the size range of 5 to 30 kDa. Neurotrophic factors potently support the development, growth and survival of neurons, eliciting biological effects at concentrations in the nanomolar to femtomolar range. They are not orally bioavailable and the blood-brain and blood-cerebrospinal fluid barriers severely limit their ability to enter into and act on sites in the CNS following parenteral systemic routes of administration. Most neurotrophic factors have short in vivo half-lives and poor pharmacokinetic profiles. Their access to the CNS is restricted by rapid enzymatic inactivation, multiple clearance processes, potential immunogenicity and sequestration by binding proteins and other components of the blood and peripheral tissues. The development of targeted drug delivery strategies for neurotrophic factors will probably determine their clinical effectiveness for CNS conditions. Achieving significant CNS target site concentrations while limiting systemic exposure and distribution to peripheral sites of action will lessen unwanted pleiotropic effects and toxicity. Local introduction of neurotrophic factors into the CNS intraparenchymally by direct injection/infusion or by implantation of delivery vectors such as polymer matrices or genetically modified cells yields the highest degree of targeting, but is limited by diffusion restrictions and invasiveness. Delivery of neurotrophic factors into the cerebrospinal fluid (CSF) following intracerebroventricular or intrathecal administration is less invasive and allows access to a much wider area of the CNS through CSF circulation pathways. However, diffusional and cellular barriers to penetration into surrounding CNS tissue and significant clearance of CSF into the venous and lymphatic circulation are also limiting. Unconventional delivery strategies such as intranasal administration may offer some degree of CNS targeting with minimal invasiveness. This review presents a summary of the neurotrophic factors and their indications for CNS disorders, their physicochemical characteristics and the different approaches that have been attempted or suggested for their delivery to the CNS. Future directions for further research such as the potential for CNS disease treatment utilising combinations of neurotrophic factors, displacement strategies, small molecule mimetics, chimaeric molecules and gene therapy are also discussed.

Identification of the high affinity binding site in transforming growth factor-beta involved in complex formation with alpha 2-macroglobulin. Implications regarding the molecular mechanisms of complex formation between alpha 2-macroglobulin and growth factors, cytokines, and hormones

The biological activities of transforming growth factor-beta isoforms (TGF-beta(1,2)) are known to be modulated by alpha(2)-macroglobulin (alpha(2)M). alpha(2)M forms complexes with numerous growth factors, cytokines, and hormones, including TGF-beta. Identification of the binding sites in TGF-beta isoforms responsible for high affinity interaction with alpha(2)M many unravel the molecular basis of the complex formation. Here we demonstrate that among nine synthetic pentacosapeptides with overlapping amino acid sequences spanning the entire TGF-beta(1) molecule, the peptide (residues 41-65) containing Trp-52 exhibited the most potent activity in inhibiting the formation of complexes between (125)I-TGF-beta(1) and activated alpha(2)M (alpha(2)M*) as determined by nondenaturing polyacrylamide gel electrophoresis and by plasma clearance in mice. TGF-beta(2) peptide containing the homologous sequence and Trp-52 was as active as the TGF-beta(1) peptide, whereas the corresponding TGF-beta(3) peptide lacking Trp-52, was inactive. The replacement of the Trp-52 with alanine abolished the inhibitory activities of these peptides. (125)I-TGF-beta(3), which lacks Trp-52, bound to alpha(2)M* with an affinity lower than that of (125)I-TGF-beta(1). Furthermore, unlabeled TGF-beta(3) and the mutant TGF-beta(1)W52A, in which Trp-52 was replaced with alanine, were less potent than unlabeled TGF-beta(1) in blocking I(125)-TGF-beta(1) binding to alpha(2)M*. TGF-beta(1) and TGF-beta(2) peptides containing Trp-52 were also effective in inhibiting I(125)-nerve growth factor binding to alpha(2)M*. Tauhese results suggest that Trp-52 is involved in high affinity binding of TGF-beta to alpha(2)M*. They also imply that TGF-beta and other growth factors/cytokines/hormones may form complexes with alpha(2)M* via a common mechanism involving the interactions between topologically exposed Trp and/or other hydrophobic residues and a hydrophobic region in alpha(2)M*.

Differential gene expression during capillary morphogenesis in 3D collagen matrices

We have performed a screening analysis of differential gene expression using a defined in vitro model of human capillary tube formation. Gene array, differential display and cDNA library screening were used to identify both known and novel differentially expressed genes. Major findings include: the upregulation and functional importance of genes associated with basement membrane matrix assembly; the upregulation of growth factors, transcription factors, anti-apoptotic factors, markers of endothelial cell differentiation, JAK-STAT signalling molecules, adhesion receptors, proteinase inhibitors and actin regulatory proteins; and expression changes consistent with inhibition of cell cycle progression, increased cholesterol biosynthesis, decreased ubiquitin-proteasome mediated degradation, and activation of G-protein signaling pathways. Using DNA microarray analysis, the most induced genes at 8, 24 and 48 hours compared with those at 0 hours were jagged-1, stanniocalcin and angiopoietin-2, whereas the most repressed genes were connective tissue growth factor, fibulin-3 and RGS-5. In addition, the full length coding sequence of two novel regulated capillary morphogenesis genes (CMGs) are presented. CMG-1 encodes a predicted intracellular 65 kDa protein with coiled-coil domains. A CMG-1-green fluorescent protein (GFP) chimera was observed to target to an intracellular vesicular compartment. A second novel gene, CMG-2, was found to encode a predicted intracellular protein of 45 kDa containing a transmembrane segment and a CMG-2-GFP chimera was observed to target to the endoplasmic reticulum. A recombinant portion of CMG-2 was found to bind collagen type IV and laminin, suggesting a potential role in basement membrane matrix synthesis and assembly. These data further elucidate the genetic events regulating capillary tube formation in a 3D matrix environment.

A 16-amino acid peptide from human alpha2-macroglobulin binds transforming growth factor-beta and platelet-derived growth factor-BB

Alpha2-macroglobulin (alpha2M) is a major carrier of transforming growth factor-beta (TGF-beta) in vitro and in vivo. By screening glutathione S-transferase (GST) fusion proteins with overlapping sequences, we localized the TGFbeta-binding site to aa 700-738 of the mature human alpha2M subunit. In separate experiments, we screened overlapping synthetic peptides corresponding to aa 696-777 of alpha2M and identified a single 16-mer (718-733) that binds TGF-beta1. Platelet-derived growth factor-BB (PDGF-BB) bound to the same peptide, even though TGF-beta and PDGF-BB share almost no sequence identity. The sequence of the growth factor-binding peptide, WDLVVVNSAGVAEVGV, included a high proportion of hydrophobic amino acids. The analogous peptide from murinoglobulin, a human alpha2M homologue that does not bind growth factors, contained only three nonconservative amino acid substitutions; however, the MUG peptide failed to bind TGF-beta1 and PDGF-BB. These results demonstrate that a distinct and highly-restricted site in alpha2M, positioned near the C-terminal flank of the bait region, mediates growth factor binding. At least part of the growth factor-binding site is encoded by exon 18 of the alpha2M gene, which is notable for a 5' splice site polymorphism that has been implicated in Alzheimer's Disease.