Classification of alpha 2-macroglobulin-cytokine interactions based on affinity of noncovalent association in solution under apparent equilibrium conditions

A2M inhibits inflammatory mediators of chondrocytes by blocking IL-1β/NF-κB pathway

A hallmark of osteoarthritis (OA) is cartilage degeneration, which has been previously correlated with dramatic increases in inflammatory enzymes. Specifically, interleukin-1β (IL-1β) and subsequent upregulation of nuclear factor kappa B (NF-κB) is implicated as an important player in the development of posttraumatic osteoarthritis (PTOA). Alpha 2-macroglobulin (A2M) can inhibit this inflammatory pathway, making it a promising therapy for PTOA. Herein, we demonstrate that A2M binds and neutralizes IL-1β, blocking downstream NF-κB-induced catabolism seen in in vitro. Human chondrocytes (cell line C28) were incubated with A2M protein and then treated with IL-1β. A2M was labeled with VivoTag™ 680 to localize the protein postincubation. The degree of binding between A2M and IL-1β was evaluated through immunoprecipitation (IP). Catabolic proteins, including IL-1β and NF-kB, were detected by Western blot. Pro-inflammatory and chondrocyte-related gene expression was examined by qRT-PCR. VivoTag™ 680-labeled A2M was observed in the cytoplasm of C28 human chondrocytes by fluorescence microscopy. IP experiments demonstrated that A2M could bind IL-1β. Additionally, western blot analysis revealed that A2M neutralized IL-1β and NF-κB in a dose-dependent manner. Moreover, A2M decreased levels of MMPs and TNF-α and increased the expression of cartilage protective genes Col2, Type2, Smad4, and aggrecan. Mostly importantly, A2M was shown to directly neutralize IL-1β to downregulate the pro-inflammatory responses mediated by the NF-kB pathway. These results demonstrate a mechanism by which A2M reduces inflammatory catabolic activity and protects cartilage after joint injury. Further in vivo studies are needed to fully understand the potential of A2M as a novel PTOA therapy.

The conformational change of the protease inhibitor α2-macroglobulin is triggered by the retraction of the cleaved bait region from a central channel

The protease inhibitor α₂-macroglobulin (A2M) is a member of the ancient α₂-macroglobulin superfamily (A2MF), which also includes structurally related proteins, such as complement factor C3. A2M and other A2MF proteins undergo an extensive conformational change upon cleavage of their bait region by proteases. However, the mechanism whereby cleavage triggers the change has not yet been determined. We have previously shown that A2M remains functional after completely replacing its bait region with glycine and serine residues. Here, we use this tabula rasa bait region to investigate several hypotheses for the triggering mechanism. When tabula rasa bait regions containing disulfide loops were elongated by reducing the disulfides, we found that A2M remained in its native conformation. In addition, cleavage within a disulfide loop did not trigger the conformational change until after the disulfide was reduced, indicating that the introduction of discontinuity into the bait region is essential to the trigger. Previously, A2MF structures have shown that the C-terminal end of the bait region (a.k.a. the N-terminal region of the truncated α chain) threads through a central channel in native A2MF proteins. Bait region cleavage abolishes this plug-in-channel arrangement, as the bait region retracts from the channel and the channel itself collapses. We found that mutagenesis of conserved plug-in-channel residues disrupted the formation of native A2M. These results provide experimental evidence for a structural hypothesis in which retraction of the bait region from this channel following cleavage and the channel’s subsequent collapse triggers the conformational change of A2M and other A2MF proteins.

Alpha-2-macroglobulin in hemostasis and thrombosis: An underestimated old double-edged sword

Antiproteinases such as alpha-2-macroglobulin (A2M) play a role in hemostasis. A2M is highly conserved throughout evolution and is a high molecular weight homo-tetrameric glycoprotein. A2M proteinase inhibitor activity is possible via a unique cage structure leading to proteinase entrapment without direct enzymatic activity inhibition. Following this entrapment, proteinase clearance is possible through A2M binding to the low-density lipoprotein receptor-related protein 1. A2M synthesis is regulated by pro-inflammatory cytokines and increases during several chronic or acute inflammatory diseases and varies with age. For instance, A2M plasma levels are known to be increased in patients with diabetes mellitus, nephrotic syndrome, or sepsis. Concerning hemostasis, A2M can trap many proteinases involved in coagulation and fibrinolysis. Because of its pleiotropic effects A2M can be seen as both anti- and pro-hemostatic. A2M can inhibit thrombin, factor Xa, activated protein C, plasmin, tissue-plasminogen activator, and urokinase. Through its many different functions A2M is generally put apart in the balanced regulation of hemostasis. In addition, the fact that A2M plasma levels are differently regulated during inflammatory-related diseases and that A2M can neutralize cytokines that also modify hemostasis could explain why it is difficult to link common proteins and parameters of hemostasis with the mechanisms of thrombosis in such diseases. Thus, we propose in the present review to summarize known functions of A2M, give a brief overview about diseases, and then to focus on the roles of this antiproteinase in hemostasis and thrombosis.

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.

Anti-inflammatory Effect of Juniperus Procera Extract in Rats Exposed to Streptozotocin Toxicity

BACKGROUND

Chronic inflammation is a critical health issue and implicated in several chronic health problems such as tumors, auto-immune disorder, hypertension or diabetes. However, Juniperus procera is one of the famous ancient plants that has been traditionally used to treat several diseases such as hyperglycemia, hepatitis, jaundice, bronchitis, and pneumonia.

OBJECTIVE

Current study is an attempt to investigate the anti-inflammatory effect of Juniperus procera extract on rats exposed to cytotoxicity caused experimentally by streptozotocin injections.

METHODS

Five groups of adult Wistar rats (10 rats each) were examined as (Normal control, Normal rats treated with Juniperus procera extract, rats administrated with streptozotocin, rats administrated with streptozotocin and treated with insulin and, rats administrated with streptozotocin and Juniperus procera extract). At the end of the experiment, blood was collected from experimented rats. Animals then were killed and small parts of both pancreas and liver were collected for gene expression and histopathological examination.

RESULTS

Serum analysis showed a significant increase in glucose, IL-6, IL-2 and TNF-α levels in rats exposed to streptozotocin. That change was reduced in rats cotreated with insulin or Juniperus procera extract. Moreover, streptozotocin showed a significant upregulation of IL-6, TNF-α and A2M genes, while, either insulin or Juniperus procera treatment was restored to normal status. Streptozotocin induced inflammation within hepatic tissues which clearly reduced in hepatic tissues of both insulin and junipers cotreated groups.

CONCLUSION

Streptozotocin toxicity induces acute inflammation and increases serum glucose, IL-6, IL-2 and TNF-α levels. However, Juniperus procera extract was found to significantly prevent that reaction within four weeks experimented frame time.

Screening for protein adducts of naphthalene and chrysene in plasma of exposed Atlantic cod (Gadus morhua)

Polycyclic aromatic hydrocarbons (PAHs) are well known contaminants, ubiquitously present in the habitat and spawning areas for Atlantic cod (Gadus morhua). The Atlantic cod is a key species and a globally important food source, thus continuous monitoring of PAHs is considered highly valuable to ensure ecosystem sustainability and human food safety. PAH adducts to plasma proteins are applied as sensitive biomarkers of PAH exposure in humans and other species, thus the presence of PAH protein adducts in Atlantic cod plasma was investigated to identify PAH protein adduct biomarker candidates of exposure to PAHs. Blood plasma samples were collected from Atlantic cod (n = 66) one week after exposure by intramuscular injection of single PAHs (i.e. naphthalene and chrysene), and their corresponding dihydrodiol metabolites (i.e. (-)-(1R,2R)-1,2-dihydronaphthalene-1,2-diol and (-)-(1R,2R)-1,2-dihydrochrysene-1,2-diol). The samples were analyzed by shotgun tandem mass spectrometry (MS) and the resulting MS data were analyzed in Byonic™ to screen for proteins susceptible to adduct formation with naphthalene and chrysene. Furthermore, a wildcard modification search was performed to obtain additional information regarding potential modifications other than the targeted metabolites. The amino acid adductation sites and the metabolites involved in PAH adductation are reported. Forty-four proteins were found to bind PAHs. Alpha-2-macroglobulin-like proteins, apolipoproteins B-100-like proteins and an alpha-2-HS-glycoprotein were detected with the highest number of bound PAHs. This first insight into PAH protein adducts of Atlantic cod plasma generates valuable knowledge for the development of highly sensitive biomarkers of PAH exposure.

Morgagnian cataract resulting from a naturally occurring nonsense mutation elucidates a role of CPAMD8 in mammalian lens development

To investigate the genetic basis of hereditary lens opacities we analyzed 31 cases of bilateral congenital cataract in Red Holstein Friesian cattle. A genome-wide association study revealed a significant association on bovine chromosome 7 at positions 6,166,179 and 12,429,691. Whole genome re-sequencing of one case and four relatives showed a nonsense mutation (g.5995966C>T) in the PZP-like, alpha-2-macroglobulin domain containing 8 (CPAMD8) gene leading to a premature stop codon (CPAMD8 p.Gln74*) associated with cataract development in cattle. With immunohistochemistry we confirmed a physiological expression of CPAMD8 in the ciliary body epithelium of the eye in unaffected cattle, while the protein was not detectable in the ciliary body of cattle with cataracts. RNA expression of CPAMD8 was detected in healthy adult, fetal and cataractous lenses.

Mutations in CPAMD8 Cause a Unique Form of Autosomal-Recessive Anterior Segment Dysgenesis

Anterior segment dysgeneses (ASDs) comprise a spectrum of developmental disorders affecting the anterior segment of the eye. Here, we describe three unrelated families affected by a previously unclassified form of ASD. Shared ocular manifestations include bilateral iris hypoplasia, ectopia lentis, corectopia, ectropion uveae, and cataracts. Whole-exome sequencing and targeted Sanger sequencing identified mutations in CPAMD8 (C3 and PZP-like alpha-2-macroglobulin domain-containing protein 8) as the cause of recessive ASD in all three families. A homozygous missense mutation in the evolutionarily conserved alpha-2-macroglobulin (A2M) domain of CPAMD8, c.4351T>C (p. Ser1451Pro), was identified in family 1. In family 2, compound heterozygous frameshift, c.2352_2353insC (p.Arg785Glnfs^∗23), and splice-site, c.4549-1G>A, mutations were identified. Two affected siblings in the third family were compound heterozygous for splice-site mutations c.700+1G>T and c.4002+1G>A. CPAMD8 splice-site mutations caused aberrant pre-mRNA splicing in vivo or in vitro. Intriguingly, our phylogenetic analysis revealed rodent lineage-specific CPAMD8 deletion, precluding a developmental expression study in mice. We therefore investigated the spatiotemporal expression of CPAMD8 in the developing human eye. RT-PCR and in situ hybridization revealed CPAMD8 expression in the lens, iris, cornea, and retina early in development, including strong expression in the distal tips of the retinal neuroepithelium that form the iris and ciliary body, thus correlating CPAMD8 expression with the affected tissues. Our study delineates a unique form of recessive ASD and defines a role for CPAMD8, a protein of unknown function, in anterior segment development, implying another pathway for the pathogenicity of ASD.

Alpha-2-Macroglobulin Is Acutely Sensitive to Freezing and Lyophilization: Implications for Structural and Functional Studies

Alpha-2-macroglobulin is an abundant secreted protein that is of particular interest because of its diverse ligand binding profile and multifunctional nature, which includes roles as a protease inhibitor and as a molecular chaperone. The activities of alpha-2-macroglobulin are typically dependent on whether its conformation is native or transformed (i.e. adopts a more compact conformation after interactions with proteases or small nucleophiles), and are also influenced by dissociation of the native alpha-2-macroglobulin tetramer into stable dimers. Alpha-2-macroglobulin is predominately present as the native tetramer in vivo; once purified from human blood plasma, however, alpha-2-macroglobulin can undergo a number of conformational changes during storage, including transformation, aggregation or dissociation. We demonstrate that, particularly in the presence of sodium chloride or amine containing compounds, freezing and/or lyophilization of alpha-2-macroglobulin induces conformational changes with functional consequences. These conformational changes in alpha-2-macroglobulin are not always detected by standard native polyacrylamide gel electrophoresis, but can be measured using bisANS fluorescence assays. Increased surface hydrophobicity of alpha-2-macroglobulin, as assessed by bisANS fluorescence measurements, is accompanied by (i) reduced trypsin binding activity, (ii) increased chaperone activity, and (iii) increased binding to the surfaces of SH-SY5Y neurons, in part, via lipoprotein receptors. We show that sucrose (but not glycine) effectively protects native alpha-2-macroglobulin from denaturation during freezing and/or lyophilization, thereby providing a reproducible method for the handling and long-term storage of this protein.

Physical interaction of CCN2 with diverse growth factors involved in chondrocyte differentiation during endochondral ossification

CCN family member 2 (CCN2) has been shown to promote the proliferation and differentiation of chondrocytes, osteoblasts, osteoclasts, and vascular endothelial cells. In addition, a number of growth factors and cytokines are known to work in harmony to promote the process of chondrogenesis and chondrocyte differentiation toward endochondral ossification. Earlier we showed that CCN2 physically interacts with some of them, suggesting that multiple effects of CCN2 on various differentiation stages of chondrocytes may be attributed to its interaction with these growth factors and cytokines. However, little is known about the functional interaction occurring between CCN2 and other growth factors and cytokines in promoting chondrocyte proliferation and differentiation. In this study we sought to shed light on the binding affinities between CCN2 and other essential growth factors and cytokines known to be regulators of chondrocyte differentiation. Using the surface plasmon resonance assay, we analyzed the dissociation constant between CCN2 and each of the following: TGF-β1, TGF-β3, IGF-I, IGF-II, PDGF-BB, GDF5, PTHrP, and VEGF. We found a strong association between CCN2 and VEGF, as well as a relatively high association with TGF-β1, TGF-β3, PDGF-BB, and GDF-5. However, the sensorgrams obtained for possible interaction between CCN2 and IGF-I, IGF-II or PTHrP showed no response. This study underlines the correlation between CCN2 and certain other growth factors and cytokines and suggests the possible participation of such interaction in the process of chondrogenesis and chondrocyte differentiation toward endochondral ossification.

Proinflammatory status in the aqueous humor of high myopic cataract eyes

High myopia has long been recognized as an inflammation-related disease, and high myopic eyes are thought to have a proinflammatory internal microenvironment, which might predispose to the occurrence of certain inflammation-related complications such as fibrotic capsular contraction syndrome after cataract surgery. Therefore, the purpose of this study was to detect inflammatory cytokines expressed in the aqueous humor (AH) of high myopic cataract (HMC) patients. The cytokines were screened using a RayBio Human Cytokine Antibody Array in AH samples from 15 age-related cataract (ARC) patients and 15 HMC patients. Those detected by the screening assays were verified using a Bio-Plex Suspension Array System in AH samples from 35 ARC patients and 45 HMC patients. The cytokine antibody array showed that the expression level of interleukin-1 receptor antagonist (IL-1ra) in the AH was higher in ARC than in HMC, whereas opposite trends were found for monocyte chemoattractant protein-1 (MCP-1), regulated on activation, normal T-cell expressed and presumably secreted (RANTES), IL-8, platelet-derived growth factor-BB, and IL-6 (all P < 0.05). In the verification assay using the suspension cytokine array, only the expression levels of IL-1ra and MCP-1 were significantly different between the ARC and HMC groups (P = 0.014 and 0.038, respectively); these results were confirmed by western blot assays. Our results demonstrated that the expression of IL-1ra was significantly lower and the expression of MCP-1 was significantly higher in the AH of HMC than in ARC, suggestive of a proinflammatory status in the anterior chamber of HMC eyes.

Multiplex cytokine concentration measurement: how much do the medium and handling matter?

Cytokine concentrations are thought to be affected by methods of sampling and processing and by storage conditions. In this study we compared 17 cytokine concentrations obtained from plasma and serum at baseline and after a controlled thaw condition. We found that absolute agreement was poor between concentrations of cytokines in plasma and serum, except for MIP1β. A thaw condition significantly changed the concentrations of most cytokines, but serum appeared less affected by this than plasma was. Closer examination using Bland-Altman analyses revealed that for each comparison, agreement was moderately good for many cytokine concentrations. This is important because measures of agreement must be interpreted based on the required precision, which may differ between clinical and research demands. We also identified that for some cytokines, the relationship between serum and plasma is affected by concentration, thus advocating for the use of appropriate methods when performing such comparisons in studies such as systematic reviews and meta-analyses.

Characterization of alpha-2-macroglobulin from groupers

Alpha-2-macroglobulin (α-2-M) is a protease inhibitor broadly present in the plasma of vertebrates and invertebrates, and is an important non-specific humoral factor in defence system of the animals. This study conducted the immuno-analysis and mass spectrometric analysis methods to investigate the characteristics of the protease inhibitor, α-2-M, among groupers and related species. Rabbit antiserum to the purified α-2-M of Epinephelus coioides was used in different immunological methods to determine the immune cross-reactions of the α-2-M in samples. Plasma of Epinephelus bruneus, Epinephelus fuscoguttatus, Epinephelus lanceolatus, and Epinephelus quoyanus exhibited high protease inhibitory activities by BAPNA-trypsin assay. To purify the α-2-M protein, plasma protein of grouper E. coioides was first precipitated by using PEG 6000, then Blue Sepharose 6 Fast Flow, DEAE Sephacel, Con A Separose 4B and Phenyl Sepharose High Performance columns were used on FPLC system for purification. The molecular mass of grouper plasma α-2-M was determined as a 180 kDa protein on non-reduced SDS-PAGE. In addition, it was determined as 97 and 80 kDa protein on reduced SDS-PAGE. Enzymatic and chemical deglycosylation of glycogen revealed that the contents of glycogen in 97 and 80 kDa subunits were 12.4% and 15%, respectively, and were all belonging to N-linked type. Only one precipitation arc was visualized in all plasma of Epinephelus spp. using the rabbit antiserum to the purified α-2-M of E. coioides, on crossed immunoelectrophoresis (CIE) gels. The plasma of Epinephelus spp. and seawater fish species showed stronger responses than freshwater fish species while that of other animal species showed no response by dot-blot assay. One single band was detected on Native PAGE-Western blotting assay, one single 180 kDa band was detected on non-reduced SDS-PAGE-Western blotting, and four bands (80, 97, 160, 250 kDa) were detected on reduced SDS-PAGE when various grouper plasma was performed respectivity. However, no band was detected using plasma from the freshwater fish species and other animal species. Thus, further indicates that the protein structure of α-2-M of Epinephelus spp. was closely related among seawater fish species. In addition the identity of the two subunits was identified using LC/MS/MS which was similar to α-2-M of grass carp (Ctenopharyngodon idella) and bluegill sunfish (Lepomis macrochirus) on the protein hit.

Effect of implantation of Augment(®) Bone Graft on serum concentrations of platelet-derived growth factors: a pharmacokinetic study

BACKGROUND

Augment(®) Bone Graft is a bone graft substitute intended to be used as an alternative to autologous bone graft in the fusion of hindfoot and ankle joints. Augment(®) Bone Graft is a combination device comprised of beta-tricalcium phosphate (β-TCP) and recombinant human platelet-derived growth factor BB homodimer (rhPDGF-BB).

OBJECTIVE

This human pharmacokinetic study was undertaken to assess the effect of Augment(®) Bone Graft implantation on the serum concentration of platelet-derived growth factors (PDGFs).

METHODS

Under the terms of a Research Ethics Board-approved protocol, Augment(®) Bone Graft was implanted in patients (n = 7) undergoing hindfoot and ankle arthrodesis procedures requiring graft material. The control cohort of the study (n = 4) received autologous bone graft. The serum concentrations of PDGF isoforms AA, AB and BB in blood samples, obtained prior to and at ten time points (up to 7 days) after surgery, were measured using enzyme-linked immunosorbent assays (ELISA).

RESULTS

The serum concentration of PDGF-BB did not vary significantly from baseline (median of the combined cohorts 3.89 ng/mL) throughout the course of the study. The serum concentrations of PDGF-AA, PDGF-AB and total PDGF did not deviate from their baseline values (medians of the combined cohorts were 2.87, 14.95 and 20.19 ng/mL for PDGF-AA, PDGF-AB and total PDGF, respectively) except for the last time point in which they were increased (medians for the combined cohorts were 4.71, 20.42 and 30.29 ng/mL for PDGF-AA, PDGF-AB and total PDGF, respectively). There were no differences between the two treatment groups with regard to changes in the serum concentrations of PDGF. None of the samples tested contained anti-PDGF-BB antibodies.

CONCLUSION

Analysis of the data demonstrated that the serum concentrations of all three PDGF isoforms analysed were unaffected by implantation of Augment(®) Bone Graft.

Secreted phosphoprotein-24 kDa (Spp24) attenuates BMP-2-stimulated Smad 1/5 phosphorylation and alkaline phosphatase induction and was purified in a protective complex with alpha2 -Macroglobulins From Serum

Secreted phosphoprotein-24 kDa (Spp24) binds cytokines of the bone morphogenetic protein/transforming growth factor-β (BMP/TGFβ) superfamily and is one of the most abundant serum phosphoproteins synthesized by the liver. Little is known about how Spp24 binding affects BMP signal transduction and osteoblastic differentiation or how this labile protein is transported from the liver to remote tissues, such as bone. When Spp24 was administered to W-20-17 mesenchymal stem cells with rhBMP-2, short-term Smad1/5 phosphorylation was inhibited, intermediate-term alkaline phosphatase (ALP) induction was blunted, and long-term mineralization was unaffected. This supports the hypothesis that Spp24 proteolysis restricts the duration of its regulatory effects, but offers no insight into how Spp24 is transported intact from the liver to bone. When Spp24 was immunopurified from serum and subjected to native PAGE and Western blotting, a high molecular weight band of >500 kDa was found. Under reducing SDS-PAGE, a 24 kDa band corresponding to monomeric Spp24 was liberated, suggesting that Spp24 is bound to a complex linked by disulfide bonds. However, such a complex cannot be disrupted by 60 mM EDTA under non-reducing condition or in purification buffers containing 600 mM NaCl and 0.1% Tween-20 at pH 2.7-8.5. LC-MS/MS analysis of affinity-purified, non-reducing SDS-PAGE separated, and trypsin digested bands showed that the Spp24 was present in a complex with three α(2) -macroglobulins (α(2) -macroglobulin [α(2) M], pregnancy zone protein [PZP] and complement C3 [C3]), as well as ceruloplasmin and the protease inhibitor anti-thrombin III (Serpin C1), which may protect Spp24 from proteolysis.

Regulation of cytokine expression by Schwann cells in response to α2-macroglobulin binding to LRP1

Binding of activated α(2)-macroglobulin (α(2)M) to LDL receptor-related protein-1 (LRP1) in Schwann cells activates ERK/MAP kinase and Akt and thereby promotes cell survival and migration. The goal of this study was to determine whether α(2)M binding to LRP1 regulates expression of cytokines and chemokines. To assess the LRP1 response selectively, we studied primary cultures of rat Schwann cells. In a screening assay that detects 84 gene products, monocyte chemoattractant protein-1 (MCP-1/CCL2) mRNA expression was increased more than 13-fold in Schwann cells treated with activated α(2)M. The effects of α(2)M on MCP-1 expression were selective, because expression of the general proinflammatory cytokine tumor necrosis factor-α (TNF-α) was not induced. We confirmed that α(2)M selectively induces expression of MCP-1 and not TNF-α in single-target qPCR assays. MCP-1 protein accumulated at increased levels in conditioned medium of α(2)M-treated cells. LRP1 was necessary for induction of MCP-1 expression, as determined in experiments with the LRP1 antagonist receptor-associated protein, a mutated form of full-length α(2)M that does not bind LRP1, and in studies with Schwann cells in which LRP1 was silenced. Inhibiting ERK/MAP kinase activation blocked expression of MCP-1. These studies support a model in which LRP1 regulates multiple aspects of Schwann cell physiology in the response to PNS injury.

Extracellular chaperones

The maintenance of the levels and correct folding state of proteins (proteostasis) is a fundamental prerequisite for life. Life has evolved complex mechanisms to maintain proteostasis and many of these that operate inside cells are now well understood. The same cannot yet be said of corresponding processes in extracellular fluids of the human body, where inappropriate protein aggregation is known to underpin many serious diseases such as Alzheimer's disease, type II diabetes and prion diseases. Recent research has uncovered a growing family of abundant extracellular chaperones in body fluids which appear to selectively bind to exposed regions of hydrophobicity on misfolded proteins to inhibit their toxicity and prevent them from aggregating to form insoluble deposits. These extracellular chaperones are also implicated in clearing the soluble, stabilized misfolded proteins from body fluids via receptor-mediated endocytosis for subsequent lysosomal degradation. Recent work also raises the possibility that extracellular chaperones may play roles in modulating the immune response. Future work will better define the in vivo functions of extracellular chaperones in proteostasis and immunology and pave the way for the development of new treatments for serious diseases.

Extracellular Chaperones

The maintenance of the levels and correct folding state of proteins (proteostasis) is a fundamental prerequisite for life. Life has evolved complex mechanisms to maintain proteostasis and many of these that operate inside cells are now well understood. The same cannot yet be said of corresponding processes in extracellular fluids of the human body, where inappropriate protein aggregation is known to underpin many serious diseases such as Alzheimer's disease, type II diabetes and prion diseases. Recent research has uncovered a growing family of abundant extracellular chaperones in body fluids which appear to selectively bind to exposed regions of hydrophobicity on misfolded proteins to inhibit their toxicity and prevent them from aggregating to form insoluble deposits. These extracellular chaperones are also implicated in clearing the soluble, stabilized misfolded proteins from body fluids via receptor-mediated endocytosis for subsequent lysosomal degradation. Recent work also raises the possibility that extracellular chaperones may play roles in modulating the immune response. Future work will better define the in vivo functions of extracellular chaperones in proteostasis and immunology and pave the way for the development of new treatments for serious diseases.

ELISA and multiplex technologies for cytokine measurement in inflammation and aging research

Over the last decade there has been an enormous expansion of research focused on defining the role of inflammation in aging, age-related diseases, disability, and frailty. The availability of methods to measure cytokines and other inflammatory mediators or markers with high sensitivity and specificity is critically important. Enzyme-linked immunosorbent assay (ELISA), the most widely used and best validated method, is limited by its ability to measure only a single protein in each sample. Recent developments in serum cytokine quantification technology include multiplex arrays, which offer the potential of better evaluating the complexity and dynamic nature of inflammatory responses and offer substantial cost and sample savings over traditional ELISA measurements. Despite potential advantages of this new technology, experience with these techniques is limited, and it has not emerged to date as the gold standard in inflammatory mediator measurement. This article reviews ELISA and the emerging multiplex technologies, compares the cost and effectiveness of recently developed multiplex arrays with traditional ELISA technology, and provides specific recommendations for investigators interested in measuring serum inflammatory mediators in older adults.

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.

Protease activation of alpha2-macroglobulin modulates a chaperone-like action with broad specificity

Alpha2-macroglobulin (alpha2M) is a major human blood glycoprotein best known for its ability to inhibit a broad spectrum of proteases by a unique trapping method. This action induces an "activated" conformation of alpha2M with an exposed binding site for the low-density lipoprotein receptor, facilitating clearance of alpha2M/protease complexes from the body. This report establishes that protease activation also modulates a potent chaperone-like action of alpha2M that has broad specificity for proteins partly unfolded as a result of heat or oxidative stress. Protease-mediated activation of alpha2M abolishes its chaperone-like activity. However, native alpha2M is able to form soluble complexes with stressed proteins and then subsequently become activated by interacting with a protease, providing a potential mechanism for the in vivo clearance of alpha2M/stressed protein/protease complexes. We propose that alpha2M is a newly discovered and unique member of a small group of abundant extracellular proteins with chaperone properties that patrol extracellular spaces for unfolded/misfolded proteins and facilitate their disposal.

Antisense therapeutics for tumor treatment: the TGF-beta2 inhibitor AP 12009 in clinical development against malignant tumors

Overexpression of the cytokine transforming growth factor-beta 2 (TGF-beta2) is a hallmark of various malignant tumors including pancreatic carcinoma, malignant glioma, metastasizing melanoma, and metastatic colorectal carcinoma. This is due to the pivotal role of TGF-beta2 as it regulates key mechanisms of tumor development, namely immunosuppression, metastasis, angiogenesis, and proliferation. The antisense technology is an innovative technique offering a targeted approach for the treatment of different highly aggressive tumors and other diseases. Antisense oligonucleotides are being developed to inhibit the production of disease-causing proteins at the molecular level. The immunotherapeutic approach with the phosphorothioate oligodeoxynucleotide AP 12009 for the treatment of malignant tumors is based on the specific inhibition of TGF-beta2. After providing preclinical proof of concept, the safety and efficacy of AP 12009 were assessed in clinical phase I/II open-label dose-escalation studies in recurrent or refractory high-grade glioma patients. Median survival time after recurrence exceeded the current literature data for chemotherapy. Currently, phase I/II study in advanced pancreatic carcinoma, metastatic melanoma, and metastatic colorectal carcinoma and a phase IIb study in recurrent or refractory high-grade glioma are ongoing. The preclinical as well as the clinical results implicate targeted TGF-beta2 suppression as a promising therapeutic approach for malignant tumor therapy.

Serum neurotrophins—A study on the time course and influencing factors in a large old age sample

The neurotrophins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are important mediators of brain and neuronal development, the maintenance of homeostatic conditions in the adult nervous system, and the complex interplay of central and peripheral physiological and pathophysiological factors. To date there are few studies examining blood concentrations of neurotrophic factors in large samples of healthy and diseased individuals and no published study specifically addresses peripheral BDNF and NGF levels in late life. Using improved highly sensitive and specific fluorometric two-site enzyme-linked immunosorbent assays we examined BDNF (n=465) and NGF (n=175) serum levels in a large cohort of elderly individuals (age range: 70-103 years). Neither BDNF nor NGF serum levels proved to be normally distributed, indicating that previously published studies with small sample sizes using parametric testing may be misleading. A significant correlation was found between BDNF and platelet count (r=0.344, p<0.01), age and BDNF protein (r=-0.101, p=0.029) and BDNF and NGF serum levels (r=0.152, p=0.04). No other major influencing factors were found including gender, depression, and dementia.

A derivative of the plasma protease inhibitor alpha(2)-macroglobulin regulates the response to peripheral nerve injury

Peripheral nerve injury induces endoneural inflammation, controlled by diverse cytokines and extracellular mediators. Although inflammation is coupled to axonal regeneration, fulminant inflammation may increase nerve damage and neuropathic pain. alpha(2)-Macroglobulin (alpha2M) is a plasma protease inhibitor, cytokine carrier, and ligand for cell-signaling receptors, which exists in two well-characterized conformations and in less well-characterized intermediate states. Previously, we generated an alpha2M derivative (alpha(2)-macroglobulin activated for cytokine binding; MAC) similar in structure to alpha(2)M conformational intermediates, which binds tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta), and inhibits endotoxin toxicity. In this study, we report that the continuum of cytokines that bind to MAC includes IL-6 and IL-18. MAC inhibited TNF-alpha-induced p38 mitogen-activated protein kinase activation and cell death in cultured Schwann cells. When administered by i.p. injection to mice with sciatic nerve crush injury, MAC decreased inflammation and preserved axons. Macrophage infiltration and TNF-alpha expression also are decreased. MAC inhibited TNF-alpha expression in the chronic constriction injury model of nerve injury. When MAC was prepared using a mutated recombinant alpha2M, which does not bind to the alpha2M receptor, low-density lipoprotein receptor-related protein-1, activity in the chronic constriction injury model was blocked. These studies demonstrate that an alpha2M derivative is capable of regulating the response to peripheral nerve injury by a mechanism that requires low-density lipoprotein receptor-related protein-1.

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.

Functions of alpha 2 macroglobulins in pregnancy

The alpha 2 macroglobulins (A2M) are a family of abundant plasma proteins produced predominantly by the mammalian liver. Pregnancy zone proteins (PZP) of humans and rats are A2M family members that bind a wide variety of macromolecules including the important pregnancy-associated molecules such as vascular endothelial growth factor, placenta growth factor and glycodelin (also called PP14). Recently, a mouse gene analogous to PZP (A2M of pregnancy or A2Mp) was cloned. A2Mp has a unique pattern of expression in reproductive and cardiovascular tissues and, unexpectedly, is not expressed by liver. Since changes in heart function and remodeling of renal and uterine vasculature are amongst the earliest maternal responses to pregnancy, the product of the A2Mp gene has been postulated to systemically regulate these changes. A2Ms with and without non-covalently bound ligands also down regulate immune cell activation but promote immune cell migration, additional features associated with gestational success. Here, we review the A2M gene families of mice and humans, the predicted structural relationships between A2M and its pregnancy induced forms and the postulated roles for this gene family in normal pregnancy.

alpha2-Macroglobulin in the marine fish Sparus aurata

The alpha2-macroglobulin proteinase inhibitors (alpha2Ms) are a family of plasma proteins with the unique ability to inhibit a broad spectrum of proteinases, but are also known as binding proteins for many growth factors and cytokines, including growth hormone and members of the transforming growth factor-beta superfamily. A partial cDNA (475 amino acids) encoding the C-terminus of alpha2M was cloned from the liver of the marine teleostean fish Sparus aurata. The deduced amino acid sequence of the cloned fragment showed 58-60% similarity to carp alpha2Ms. Northern blot analysis of hepatic alpha2M revealed a transcript of about 5 kb. A transcript of a similar size was detected in 1-day larvae. Steady state levels of alpha2M in larvae increased gradually on subsequent days post-hatching. alpha2M expression in embryos was determined by RT-PCR and started in embryos aged 8 h post-fertilization, but not earlier. RT-PCR of muscle RNA detected alpha2M also in fish muscle, albeit with a lower expression than in the liver. Immunoreactive-alpha2M was found in yolk syncytial layer of 3-day larvae and in livers from larvae and adults. Immunoreactive-alpha2M was also identified in soluble total proteins from young larvae with a pattern resembling that of plasma. These data demonstrate that the alpha2M gene is expressed early in fish development. Moreover, in addition to its major expression in liver, alpha2M is expressed also in fish muscle.

Alpha1-antitrypsin deficiency in 26-year-old subjects: lung, liver, and protease/protease inhibitor studies

BACKGROUND

Clinical and biochemical signs of lung and liver disease have been followed prospectively in a birth cohort of individuals with alpha1-antitrypsin (AAT) deficiency.

OBJECTIVE

At age 26 years, the focus was on clinical health, lung and liver function tests, and plasma markers of the protease/antiprotease balance. The effect of early childhood environment and symptoms was also studied.

METHODS

Eligible individuals were 26-year-old subjects with AAT deficiency (PiZ, n = 122; PiZ -, n = 2; PiSZ/S-, n = 53) and control subjects (PiMM, n = 44). Of the original AAT-deficient subjects, 119 completed the clinical examination and 134 answered the questionnaire.

RESULTS

The prevalence of respiratory symptoms did not differ between the PiZ and SZ groups. Sixteen percent of PiZ and 14% of PiSZ subjects had asthma. Four current smokers (67%) and 22% of ex-smokers/never-smokers reported recurrent wheezing (p = 0.03). No difference in FEV1 or FEV1/FVC ratio was found between the PiZ, SZ (5% being smokers), and MM individuals (all nonsmokers). A decreased FEV1/FVC ratio was found in PiZ subjects with neonatal cholestasis, compared to remaining PiZ subjects (p = 0.02). Recurrent wheezers at age 2 years with AAT deficiency had decreased FEV1/FVC ratio (p = 0.025) at age 26 years. None had clinical symptoms of liver disease. Six percent of PiZ and 9% of PiSZ subjects had a marginal increase of serum alanine aminotransferase; 7% of PiZ and 4% of PiSZ had abnormal gamma-glutamyl transferase test results. The PiZ and SZ individuals had decreased plasma albumin (p = 0.0002). Secretory leukocyte protease inhibitor (SLPI) was increased in PiZ and SZ subjects compared to PiMM subjects (p = 0.0001). Neutrophil lipocalin was decreased in PiZ subjects (p = 0.0004) and PiSZ subjects (p = 0.001) compared to PiMM individuals. The elastase/AAT complex concentration was lower in AAT-deficient subjects (p = 0.0001).

CONCLUSION

Twenty-six-year-old PiZ and SZ individuals (5% smokers) had normal lung function test results, and 4 to 9% had marginal deviations in liver test results. Analyses of SLPI and neutrophil lipocalin, a marker of neutrophil activity, indicate compensatory changes in the AAT-deficiency state.

Prediction of acute graft-versus-host disease and detection of distinct end-organ targets by enumeration of peripheral blood cytokine spot-forming cells

BACKGROUND

Acute graft-versus-host disease (aGVHD) remains a significant cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. It was hypothesized that type 1 cytokines promoted aGVHD and type 2 cytokines inhibited it. However, recent publications demonstrated contradictory results in murine models. Type 1/2 paradigm in aGVHD remains to be determined in human.

METHODS

Using enzyme-linked immunospot assay that reflects ongoing immune status in vivo, we measured spot-forming cells (SFCs) for interferon (IFN)-gamma, interleukin (IL)-12, IL-4, and IL-10 in peripheral blood from 56 patients with hematological disorders who underwent allogeneic hematopoietic stem cell transplantation.

RESULTS

The numbers of IFN-gamma and IL-4 SFCs in patients with grade II approximately IV aGVHD were significantly higher than those in patients with grade 0 approximately I aGVHD. The enumeration of cytokine SFCs predicted aGVHD approximately 4 days before it became clinically evident, since IFN-gamma SFCs in asymptomatic phase that later progressed into grade II approximately IV aGVHD were elevated in 8 out of 8 evaluable patients. Similarly, IL-4 SFCs were elevated in 6 of 8 patients. In addition, Type 1 cytokine SFCs contributed to the intestinal, but not skin and hepatic aGVHD.

CONCLUSIONS

Enzyme-linked immunospot assay is clinically useful for predicting aGVHD and detecting distinct end-organ targets following allogeneic hematopoietic stem cell transplantation.

Alpha(2) macroglobulin, a PSA binding protein, is expressed in human prostate stroma

BACKGROUND

Benign prostatic hyperplasia (BPH) is characterized as a stromal process. The stroma smooth muscle (SM) may alter its phenotype during the progression of BPH. We have identified gene transcripts that may be differentially expressed in BPH using a differential display method. Among the fragments isolated, alpha(2) macroglobulin (alpha(2)-M) is one of the most interesting. alpha(2)-M is a binding protein of a variety of proteinases, including prostatic specific antigen (PSA). It also plays roles in molecular trapping and targeting. In this study, we characterized alpha(2)-M expression in the human prostate.

METHODS

Differential display was used to identify and isolate the differentially expressed transcripts between normal prostate and BPH tissues. RT-PCR, Western blot, in situ hybridization, and immunohistochemistry were utilized to confirm and characterize alpha(2)-M expression in the prostate.

RESULTS

Real-time RT-PCR results revealed that a 3.2-fold increase in alpha(2)-M mRNA expression is observed in BPH compared with normal prostate tissue. A 1.9-fold increase at protein level was also observed. In situ hybridization and immunohistochemistry showed that alpha(2)-M expression is primarily localized to the stromal compartment. Cultured primary stroma cells maintained alpha(2)-M expression, while prostate epithelial cells had a significantly lower level of alpha(2)-M expression. Furthermore, stromal cells in culture produce and secrete alpha(2)-M in the medium.

CONCLUSIONS

We identified alpha(2)-M expression in the human prostate. An increased alpha(2)-M expression appears to be associated with BPH. Considering the unique features of its protein binding and targeting properties, alpha(2)-M expressed in the prostate may play an important role in regulating benign and malignant prostatic growth.

Mutation of lysine 1370 in full-length human alpha2-macroglobulin blocks binding to the low density lipoprotein receptor-related protein-1

alpha2-Macroglobulin (alpha2M) regulates cell physiology by binding to cellular receptors; however, residues that contribute to receptor-binding have not been elucidated in the full-length protein. In alpha2M fragments, expressed in bacteria, Lys(1370) and Lys(1374) are critical for binding to the low density lipoprotein receptor-related protein-1 (LRP-1) and a distinct alpha2M-signaling receptor. We expressed full-length recombinant human alpha2M (r(alpha)2M) and mutants in which Lys(1370) or Lys(1374) was converted to alanine in K-562 cells. The r(alpha)2M species demonstrated intact structure and function, as determined by subunit size, intersubunit disulfide bonds, reaction with trypsin or methylamine, and ability to undergo conformational change. Binding of transforming growth factor-beta1 was unaltered. Mutation of Lys(1370) almost entirely inhibited specific binding of methylamine-activated r(alpha)2M to RAW 264.7 cells. Mutation of Lys(1374) had no effect. Binding of r(alpha)2M to RAW 264.7 cells was blocked by receptor-associated protein, indicating an essential role for LRP-1. These studies demonstrate that a single mutation in full-length r(alpha)2M is sufficient to block binding to LRP-1.

A chemically modified preparation of alpha2-macroglobulin binds beta-amyloid peptide with increased affinity and inhibits Abeta cytotoxicity

Macromolecules that bind beta-amyloid peptide (Abeta) and neutralize Abeta cytotoxicity offer a promising new approach for treating Alzheimer's disease. When the plasma protein, alpha2-macroglobulin (alpha2M), is treated with methylamine (alpha2M-MA), it undergoes conformational change and acquires Abeta-binding activity. In this study, we demonstrate that a chemically stabilized preparation of human alpha2M conformational intermediates (alpha2M-cis-Pt/MA) binds Abeta with greatly increased affinity, compared with alpha2M-MA. alpha2M-cis-Pt/MA was generated by reacting alpha2M with the protein cross-linking reagent, cis-Pt, followed by methylamine. Increased Abeta-binding to alpha2M-cis-Pt/MA was demonstrated by co-migration of radio-iodinated proteins in non-denaturing PAGE, chemical cross-linking, and co-immunoprecipitation. The apparent K(D) for Abeta-binding to alpha2M-cis-Pt/MA was decreased 10-fold, compared with alpha2M-MA, to 29 nm. Native alpha2M demonstrated negligible Abeta-binding, as anticipated. alpha2M-cis-Pt/MA markedly counteracted Abeta-induced C6 cell apoptosis. Essentially complete inhibition of apoptosis was observed even when the Abeta was present at fourfold molar excess to alpha2M-cis-Pt/MA. Under equivalent conditions, alpha2M-MA inhibited apoptosis by 25 +/- 6%. When Abeta and alpha2M-cis-Pt/MA were added to human plasma in vitro, significant binding was detected. No binding was observed when an equivalent concentration of native alpha2M or alpha2M-MA was added to plasma. We propose that alpha2M-cis-Pt/MA is a novel alternative to Abeta-specific antibodies, for studying the efficacy of Abeta-binding agents in vitro and in vivo.

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.

Significantly increased fractions of transformed to total α2-macroglobulin concentrations in plasma from patients with multiple sclerosis

We examined the proteinase inhibitor alpha2-macroglobulin (alpha2M) in plasma from patients with multiple sclerosis (MS); a neurological disease of the central nervous system. The plasma concentrations of native and transformed alpha2M were measured in 90 patients with clinically definite MS, 73 with relapsing-remitting and 17 with secondary progressive MS, and 132 healthy individuals. Significantly lower concentrations of native alpha2M and significantly higher concentrations of transformed alpha2M were found in MS patients. A significant correlation between the concentrations of native and transformed alpha2M was found. The fraction of transformed to total alpha2M in the MS patients was 36% higher than in the healthy individuals. The results suggest an important involvement of alpha2M in regulation of increased proteolytic activity occurring in MS disease.

mRNA level of alpha-2-macroglobulin as an aging biomarker of human fibroblasts in culture

Cellular senescence is a well-established model system for studying the molecular basis of aging. To identify a reliable biomarker for cellular age and further study the gene expression of aging, we profiled the gene expression difference between aged and young cultured human embryonic lung fibroblasts by high-density complementary deoxyribonucleic acid (cDNA) arrays. Among the differentially expressed genes, alpha-2-macroglobulin (alpha(2)M) was selected for further study. Its gene expression level as a function of population doubling level (PDL) in cultured fibroblasts was determined by RT-PCR and northern hybridization. mRNA level of alpha(2)M showed a positive linear-correlation with cumulative PDL. Additional assays revealed that the levels of alpha(2)M increased in irreversible growth arrest induced by sublethal H(2)O(2), but not in quiescent state of cultured fibroblasts induced by serum-deprivation, and remained stable in Hela cells. These results suggest that mRNA level of alpha(2)M can be used as a biomarker of aging in cultured fibroblasts. mRNA level of alpha(2)M showed significant difference between newborn and old human leucocytes, which suggest that the mRNA level of alpha(2)M may be used as a biomarker of aging in vivo.

Cytokine-mediated inflammation in acute lung injury

Clinical acute lung injury (ALI) is a major cause of acute respiratory failure in critically ill patients. There is considerable experimental and clinical evidence that pro- and anti-inflammatory cytokines play a major role in the pathogenesis of inflammatory-induced lung injury from sepsis, pneumonia, aspiration, and shock. A recent multi-center clinical trial found that a lung-protective ventilatory strategy reduces mortality by 22% in patients with ALI. Interestingly, this protective ventilatory strategy was associated with a marked reduction in the number of neutrophils and the concentration of pro-inflammatory cytokines released into the airspaces of the injured lung. Further research is needed to establish the contribution of cytokines to both the pathogenesis and resolution of ALI.

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.

Fatty acids modulate transforming growth factor-beta activity and plasma clearance

The activity and plasma clearance of transforming growth factor (TGF)-beta are known to be regulated by activated alpha2-macroglobulin (alpha2M*). This has been implicated in pathophysiological processes, but no small molecule compounds have been reported to modulate TGF-beta activity by affecting the interaction of TGF-beta and alpha2M*. Here, we demonstrate that fatty acids are capable of inhibiting complex formation of TGF-beta isoforms and alpha2M* as demonstrated by nondenaturing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This is dependent on carbon chain length (C20, C18, C16, C14 > C12 > C10), degree of unsaturation (polyunsaturated > saturated), and TGF-beta isoforms (TGF-beta1 > TGF-beta2 > TGF-beta3). Arachidonic acid, which is one of the most potent inhibitors, is also capable of dissociating TGF-beta-alpha2M* complexes, but higher concentrations are required. Arachidonic acid appears to inhibit TGF-beta-alpha2M* complex formation by binding specifically to alpha2M* as demonstrated by gel filtration chromatography. Arachidonic acid reverses the inhibitory effect of alpha2M* on TGF-beta binding, TGF-beta-induced growth inhibition, and TGF-beta-induced transcriptional activation in mink lung epithelial cells and affects plasma clearance of TGF-beta-alpha2M* complexes in mice. These results show that fatty acids are effective modulators of TGF-beta activity and plasma clearance and may be useful in treating human diseases through their effects on the interaction of TGF-beta and alpha2M*.

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.

Role of alpha(2)-macroglobulin in fever and cytokine responses induced by lipopolysaccharide in mice

Alpha(2)-macroglobulin (alpha(2)M) is not only a proteinase inhibitor in mammals, but it is also a specific cytokine carrier that binds pro- and anti-inflammatory cytokines implicated in fever, including interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha (TNF-alpha). To define the role of alpha(2)M in regulation of febrile and cytokine responses, wild-type mice and mice deficient in alpha(2)M (alpha(2)M -/-) were injected with lipopolysaccharide (LPS). Changes in body temperature as well as plasma levels of IL-1beta, IL-6, and TNF-alpha and hepatic TNF-alpha mRNA level during fever in alpha(2)M -/- mice were compared with those in wild-type control mice. The alpha(2)M -/- mice developed a short-term markedly attenuated (ANOVA, P < 0.05) fever in response to LPS (2.5 mg/kg ip) compared with the wild-type mice. At 1.5 h after injection of LPS, the plasma concentration of TNF-alpha, but not IL-1beta or IL-6, was significantly lower (by 58%) in the alpha(2)M -/- mice compared with their wild-type controls (ANOVA, P < 0.05). There was no difference in hepatic TNF-alpha mRNA levels between alpha(2)M -/- and wild-type mice 1.5 h after injection of LPS. These data support the hypotheses that 1) alpha(2)M is important for the normal development of LPS-induced fever and 2) a putative mechanism of alpha(2)M involvement in fever is through the inhibition of TNF-alpha clearance. These findings indicate a novel physiological role for alpha(2)M.

Activity of pulmonary edema fluid interleukin-8 bound to alpha(2)-macroglobulin in patients with acute lung injury

The formation of alpha(2)-macroglobulin (alpha(2)-M)/interleukin-8 (IL-8) complexes may influence the biological activity of IL-8 and the quantitative assessment of IL-8 activity. Therefore, in this study, concentrations of free IL-8 and IL-8 complexes with alpha(2)-M were measured in pulmonary edema fluid samples from patients with acute lung injury/acute respiratory distress syndrome (ALI/ARDS) and compared with control patients with hydrostatic pulmonary edema. Patients with ALI/ARDS had significantly higher concentrations of alpha(2)-M (P < 0.01) as well as alpha(2)-M/IL-8 complexes (P < 0.05). Because a substantial amount of IL-8 is complexed to alpha(2)-M, standard assays of free IL-8 may significantly underestimate the concentration of biologically active IL-8 in the distal air spaces of patients with ALI/ARDS. Furthermore, IL-8 bound to alpha(2)-M retained its biological activity, and this fraction of IL-8 was protected from proteolytic degradation. Thus complex formation may modulate the acute inflammatory process in the lung.

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.

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*.

Interaction of lecithin:cholesterol acyltransferase (LCAT).alpha 2-macroglobulin complex with low density lipoprotein receptor-related protein (LRP). Evidence for an alpha 2-macroglobulin/LRP receptor-mediated system participating in LCAT clearance

The reaction of lecithin:cholesterol acyltransferase (LCAT) with high density lipoproteins (HDL) is of critical importance in reverse cholesterol transport, but the structural and functional pathways involved in the regulation of LCAT have not been established. We present evidence for the direct binding of LCAT to alpha(2)-macroglobulin (alpha(2)M) in human plasma to form a complex 18.5 nm in diameter. Forty percent of plasma LCAT-HDL was associated with alpha(2)M; moreover, most of the LCAT in cerebrospinal fluid and in the medium of cultured human hepatoma cell line was associated with alpha(2)M. Purified recombinant human LCAT (rLCAT) labeled with (125)I bound to native and methylamine-activated alpha(2)M (alpha(2)M-MA) in vitro in a time- and concentration-dependent manner, and this binding did not depend on the presence of lipid. rLCAT bound to alpha(2)M-MA with greater affinity than to alpha(2)M. Furthermore, rLCAT did not activate alpha(2)M as phosphatidylcholine-specific phospholipase C does. Reconstituted HDL particles (LpA-I) inhibited the binding of rLCAT to alpha(2)M more efficiently than native HDL(3) did. LCAT associated with alpha(2)M was enzymatically inactive under both endogenous and exogenous assay conditions. Purified rLCAT alone did not bind to low density lipoprotein receptor-related protein (LRP) as lipoprotein lipase (LPL) does; however, when rLCAT was combined with alpha(2)M-MA to form a complex, binding, internalization, and degradation of rLCAT took place in LRP-expressing cells (LRP (+/+)) but not in cells deficient in LRP (LRP (-/-)). It is concluded that the binding of LCAT to alpha(2)M inhibits its enzymatic activity. Furthermore, the finding supports the possibility that the LRP receptor can act in vivo to mediate clearance of the LCAT-alpha(2)M complex and may significantly influence the bioavailability of LCAT.

Differential regulation of the fibroblast growth factor (FGF) family by alpha(2)-macroglobulin: evidence for selective modulation of FGF-2-induced angiogenesis

The fibroblast growth factor (FGF) family has an important role in processes such as angiogenesis, wound healing, and development in which precise control of proteinase activity is important. The human plasma proteinase inhibitor alpha(2)-macroglobulin (alpha(2)M) regulates cellular growth by binding and modulating the activity of many cytokines and growth factors. These studies investigate the ability of native and activated alpha(2)M (alpha(2)M*) to bind to members of the FGF family. Both alpha(2)M and alpha(2)M* bind specifically and saturably to FGF-1, -2, -4, and -6, although the binding to alpha(2)M* is of significantly higher affinity. Neither alpha(2)M nor alpha(2)M* bind to FGF-5, -7, -9, or -10. FGF-2 was chosen for more extensive study in view of its important role in angiogenesis. It was demonstrated that FGF-2 binds to the previously identified TGF-beta binding site. The alpha(2)M* inhibits FGF-2-dependent fetal bovine heart endothelial cell proliferation in a dose-dependent manner. Unexpectedly, alpha(2)M* does not affect FGF-2-induced vascular tubule formation on Matrigel basement membrane matrix or collagen gels. Further studies demonstrate that FGF-2 partitions between fluid-phase alpha(2)M* and solid-phase Matrigel or collagen. These studies suggest that the ability of alpha(2)M* to modulate the activity of FGF-2 is dependent on an interplay with extracellular matrix components. (Blood. 2001;97:3450-3457)

Stabilization of homogeneous preparations of pregnancy zone protein lyophilized in the presence of saccharose. Structural and functional studies

Human pregnancy zone protein (PZP) is a macromolecule of 360 kDa, organized as a disulfide-linked homodimer of two 180 kDa subunits, with an amino acid sequence and structure remarkably similar to that of human alpha2-Macroglobulin. Homogeneous PZP samples undergo fast aging forming oligomeric aggregates of high molecular weight. This aged PZP loses its ability to interact with proteinases and consequently, non-recognition of receptors occurs. In the present work, we assessed the effect of saccharose on the stability of native PZP on lyophilized samples kept for a long period of time. Herein, we demonstrate that the addition of 0.25 M saccharose to homogeneous PZP and further lyophilization is enough to prevent aging and preserve functional activity for more than 1 year. Hence, high quality samples, in terms of purity, stability and functional activity will allow to develop biochemical studies in order to know the PZP role in physiological and pathological states where the protein levels are increased, such as pregnancy and tumoral disorders.