Human transforming growth factor beta.alpha 2-macroglobulin complex is a latent form of transforming growth factor beta

Profound Properties of Protein-Rich, Platelet-Rich Plasma Matrices as Novel, Multi-Purpose Biological Platforms in Tissue Repair, Regeneration, and Wound Healing

Autologous platelet-rich plasma (PRP) preparations are prepared at the point of care. Centrifugation cellular density separation sequesters a fresh unit of blood into three main fractions: a platelet-poor plasma (PPP) fraction, a stratum rich in platelets (platelet concentrate), and variable leukocyte bioformulation and erythrocyte fractions. The employment of autologous platelet concentrates facilitates the biological potential to accelerate and support numerous cellular activities that can lead to tissue repair, tissue regeneration, wound healing, and, ultimately, functional and structural repair. Normally, after PRP preparation, the PPP fraction is discarded. One of the less well-known but equally important features of PPP is that particular growth factors (GFs) are not abundantly present in PRP, as they reside outside of the platelet alpha granules. Precisely, insulin-like growth factor-1 (IGF-1) and hepatocyte growth factor (HGF) are mainly present in the PPP fraction. In addition to their roles as angiogenesis activators, these plasma-based GFs are also known to inhibit inflammation and fibrosis, and they promote keratinocyte migration and support tissue repair and wound healing. Additionally, PPP is known for the presence of exosomes and other macrovesicles, exerting cell-cell communication and cell signaling. Newly developed ultrafiltration technologies incorporate PPP processing methods by eliminating, in a fast and efficient manner, plasma water, cytokines, molecules, and plasma proteins with a molecular mass (weight) less than the pore size of the fibers. Consequently, a viable and viscous protein concentrate of functional total proteins, like fibrinogen, albumin, and alpha-2-macroglobulin is created. Consolidating a small volume of high platelet concentrate with a small volume of highly concentrated protein-rich PPP creates a protein-rich, platelet-rich plasma (PR-PRP) biological preparation. After the activation of proteins, mainly fibrinogen, the PR-PRP matrix retains and facilitates interactions between invading resident cells, like macrophages, fibroblast, and mesenchymal stem cells (MSCs), as well as the embedded concentrated PRP cells and molecules. The administered PR-PRP biologic will ultimately undergo fibrinolysis, leading to a sustained release of concentrated cells and molecules that have been retained in the PR-PRP matrix until the matrix is dissolved. We will discuss the unique biological and tissue reparative and regenerative properties of the PR-PRP matrix.

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.

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.

Agonists and Antagonists of TGF-β Family Ligands

The discovery of the transforming growth factor β (TGF-β) family ligands and the realization that their bioactivities need to be tightly controlled temporally and spatially led to intensive research that has identified a multitude of extracellular modulators of TGF-β family ligands, uncovered their functions in developmental and pathophysiological processes, defined the mechanisms of their activities, and explored potential modulator-based therapeutic applications in treating human diseases. These studies revealed a diverse repertoire of extracellular and membrane-associated molecules that are capable of modulating TGF-β family signals via control of ligand availability, processing, ligand-receptor interaction, and receptor activation. These molecules include not only soluble ligand-binding proteins that were conventionally considered as agonists and antagonists of TGF-β family of growth factors, but also extracellular matrix (ECM) proteins and proteoglycans that can serve as "sink" and control storage and release of both the TGF-β family ligands and their regulators. This extensive network of soluble and ECM modulators helps to ensure dynamic and cell-specific control of TGF-β family signals. This article reviews our knowledge of extracellular modulation of TGF-β growth factors by diverse proteins and their molecular mechanisms to regulate TGF-β family signaling.

Nodal·Gdf1 heterodimers with bound prodomains enable serum-independent nodal signaling and endoderm differentiation

The TGFβ family member Nodal is central to control pluripotent stem cell fate, but its use as a stem cell differentiation factor is limited by low specific activity. During development, Nodal depends on growth and differentiation factor (Gdf)-1 and on the shared co-receptor Cryptic to specify visceral left-right axis asymmetry. We therefore asked whether the functionality of Nodal can be augmented by Gdf1. Because Nodal and Gdf1 coimmunoprecipitate each other, they were predicted to form heterodimers, possibly to facilitate diffusion or to increase the affinity for signaling receptors. Here, we report that Gdf1 suppresses an unexpected dependence of Nodal on serum proteins and that it is critically required for non-autonomous signaling in cells expressing Cryptic. Nodal, Gdf1, and their cleaved propeptides copurified as a heterodimeric low molecular weight complex that stimulated Activin receptor (Acvr) signaling far more potently than Nodal alone. Although heterodimerization with Gdf1 did not increase binding of Nodal to Fc fusions of co-receptors or Acvr extracellular domains, it was essential for soluble Acvr2 to inhibit Nodal signaling. This implies that Gdf1 potentiates Nodal activity by stabilizing a low molecular weight fraction that is susceptible to neutralization by soluble Acvr2. Finally, in differentiating human ES cells, endodermal markers were more efficiently induced by Nodal·Gdf1 than by Nodal, suggesting that Nodal·Gdf1 is an attractive new reagent to direct stem cell differentiation.

Eosinophil activation and novel mediators in the aspirin-induced nasal response in AERD

BACKGROUND

Eosinophil activation is the key feature of upper and lower airway inflammation in aspirin-exacerbated respiratory disease (AERD).

OBJECTIVE

To investigate the mechanism of eosinophil activation and identify novel inflammatory mediators using proteomics.

METHODS

Thirty-two asthmatic subjects were enrolled: 18 AERD patients who showed positive responses to the lysine-aspirin nasal provocation test (L-ASA NPT) and 14 aspirin-tolerant asthma (ATA) patients who showed negative responses to the L-ASA NPT (control group). Nasal lavage fluid (NLF) was collected before (baseline), at 10, 30 and 60 min (early response), and at 3 h (late response) after the L-ASA NPT. Eosinophil cationic protein (ECP) and cysteinyl leucotriene (CysLT) levels were measured using an ImmunoCAP system and ELISA respectively. To identify proteins involved in AERD, comparative proteomics was applied using NLFs collected before and after L-ASA NPTs in AERD patients. The clinical relevance of identified novel proteins was evaluated by ELISA using NLFs from the AERD and ATA groups.

RESULTS

Eosinophil cationic protein and CysLT levels both increased significantly during the early response in AERD. ECP levels increased until the late response in AERD, while CysLT levels were not significantly increased during the late response. Proteomic analysis showed up-regulation of apolipoprotein A1 (ApoA1), α2-macroglobulin (α2M) and ceruloplasmin (CP), with significant increases in NLF of AERD patients, which was significantly higher in AERD patients with chronic rhinosinusitis. Significant correlations were noted between ECP and CysLT, ApoA1, α2M and CP levels during the early response in AERD patients.

CONCLUSION

Eosinophil activation occurred in early and late responses after L-ASA NPT in upper airway mucosa of AERD patients, where ApoA1, α2M and CP as well as CysLT may be involved in eosinophilic inflammation.

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.

Sulfated hyaluronan and chondroitin sulfate derivatives interact differently with human transforming growth factor-β1 (TGF-β1)

This study demonstrates that the modification of hyaluronan (hyaluronic acid; Hya) and chondroitin sulfate (CS) with sulfate groups leads to different binding affinities for recombinant human transforming growth factor-β1 (TGF-β1) for comparable average degrees of sulfation (DS). In general, Hya derivates showed higher binding strength than CS derivatives. In either case, a higher degree of sulfation leads to a stronger interaction. The high-sulfated hyaluronan sHya3 (average DS≈3) exhibited the tightest interaction with TGF-β1, as determined by surface plasmon resonance and enzyme-linked immunosorbent assay. The binding strength was significantly weakened by carboxymethylation. Unmodified Hya and low-sulfated, native CS showed weak or no binding affinity. The interaction characteristics of the different sulfated glycosaminoglycans are promising for incorporation into bioengineered coatings of biomaterials to modulate growth factor binding in medical applications.

Biological basis of bone formation, remodeling, and repair-part I: biochemical signaling molecules

The bony biochemical environment is an active and dynamic system that permits and promotes cellular functions that lead to matrix production and ossification. Each component is capable of conveying important regulatory cues to nearby cells, thus effecting gene expression and changes at the cytostructural level. Here, we review the various signaling molecules that contribute to the active and dynamic nature of the biochemical system. These components include hormones, cytokines, and growth factors. We describe their role in regulating bone metabolism. Certain growth factors (i.e., TGF-beta, IGF-1, and VEGF) are described in greater detail because of their potential importance in developing successful tissue-engineering strategies.

An intracellular trafficking pathway in the seminiferous epithelium regulating spermatogenesis: a biochemical and molecular perspective

During spermatogenesis in adult rat testes, fully developed spermatids (i.e. spermatozoa) at the luminal edge of the seminiferous epithelium undergo "spermiation" at stage VIII of the seminiferous epithelial cycle. This is manifested by the disruption of the apical ectoplasmic specialization (apical ES) so that spermatozoa can enter the tubule lumen and to complete their maturation in the epididymis. At the same time, the blood-testis barrier (BTB) located near the basement membrane undergoes extensive restructuring to allow transit of preleptotene spermatocytes so that post-meiotic germ cells complete their development behind the BTB. While spermiation and BTB restructuring take place concurrently at opposite ends of the Sertoli cell epithelium, the biochemical mechanism(s) by which they are coordinated were not known until recently. Studies have shown that fragments of laminin chains are generated from the laminin/integrin protein complex at the apical ES via the action of MMP-2 (matrix metalloprotease-2) at spermiation. These peptides serve as the local autocrine factors to destabilize the BTB. These laminin peptides also exert their effects on hemidesmosome which, in turn, further potentiates BTB restructuring. Thus, a novel apical ES-BTB-hemidesmosome regulatory loop is operating in the seminiferous epithelium to coordinate these two crucial cellular events of spermatogenesis. This functional loop is further assisted by the Par3/Par6-based polarity protein complex in coordination with cytokines and testosterone at the BTB. Herein, we provide a critical review based on the latest findings in the field regarding the regulation of these cellular events. These recent findings also open up a new window for investigators studying blood-tissue barriers.

Latent forms of TGF-beta: molecular structure and mechanisms of activation

TGF-beta proteins are produced as latent, high molecular weight complexes. The latent form of TGF-beta 1 (L-TGF-beta 1) in human platelets comprises three components: the mature TGF-beta 1 molecule, the N-terminal remnant of the TGF-beta 1 precursor in dimeric form and a novel component denoted TGF-beta 1-binding protein (TGF-beta 1-BP). Recombinant TGF-beta 1 expressed in CHO cells, which lacks TGF-beta 1-BP, is also produced as a latent form. Thus, the N-terminal remnant of the TGF-beta 1 precursor is sufficient for TGF-beta 1 latency, and it was denoted TGF-beta 1 latency-associated peptide (TGF-beta 1-LAP). The cDNA for TGF-beta 1-BP has been cloned. It is mainly composed of two different kinds of repeat sequences, i.e. 16 epidermal growth factor-like repeats and three copies of a cysteine-rich repeat hitherto not found in other proteins. The function of TGF-beta 1-BP remains to be elucidated. Activation of L-TGF-beta can be achieved by different chemical and enzymic treatments, or by incubation with certain cell types. Understanding of the physiological activation mechanisms and the in vivo roles of L-TGF-beta will be important for future clinical applications of TGF-beta.

Substance P induces localization of MIF/alpha1-inhibitor-3 complexes to umbrella cells via paracellular transit through the urothelium in the rat bladder

BACKGROUND

Macrophage migration inhibitory factor (MIF) is released into the intraluminal fluid during bladder inflammation in the rat complexed to alpha1-inhibitor-3 (A1-I3; a rodent proteinase inhibitor in the alpha-macroglobulin family). The location of A1-I3 in the bladder had not been investigated. Therefore, we examined the location of A1-I3 and MIF/A1-I3 complexes in the bladder and changes due to experimental inflammation.

METHODS

Anesthetized male rats had bladders removed with no treatment (intact) or were injected with Substance P (SP; s.c.; saline vehicle). After one hour intraluminal fluid was removed, bladder was excised and MIF and A1-I3 levels were determined using ELISA and/or western-blotting. MIF co-immunoprecipitation determined MIF/A1-I3 complexes in the bladder. Bladder sections were immunostained for A1-I3 and MIF/A1-I3.

RESULTS

A1-I3 immunostaining was observed in interstitial spaces throughout the bladder (including submucosa) but not urothelium in intact and saline-treated rats. RT-PCR showed that the bladder does not synthesize A1-I3, therefore, A1-I3 in the interstitial space of the bladder must be plasma derived. In SP-treated rats, A1-I3 in the bladder increased and A1-I3 was observed traversing through the urothelium. Umbrella cells that do not show MIF and/or A1-I3 immunostaining in intact or saline-treated rats, showed co-localization of MIF and A1-I3 after SP-treatment. Western blotting demonstrated that in the bladder MIF formed non-covalent interactions and also binds covalently to A1-I3 to form high molecular weight MIF/A1-I3 complexes (170, 130 and 75-kDa, respectively, verified by co-immunoprecipitation). SP-induced inflammation selectively reduced 170-kDa MIF/A1-I3 in the bladder while increasing 170 and 130-kDa MIF/A1-I3 in the intraluminal fluid.

CONCLUSION

A1-I3 and MIF/A1-I3 complexes are resident in bladder interstitium. During SP-induced inflammation, MIF/A1-I3 complexes are released from the bladder into the lumen. Binding of MIF/A1-I3 complexes to urothelial cells during inflammation suggests these complexes participate in the inflammatory reaction through activation of receptors for MIF and/or for A1-I3.

Mallory body forming cells express the preneoplastic hepatocyte phenotype

The livers of mice fed diethyl 1,4-dihydro-2,4,6,-trimethyl-3,5-pyridinedicarboxylate (DDC) for 10 weeks formed Mallory bodies (MBs) in clusters of hepatocytes. Mice withdrawn from DDC for 9 months developed liver tumors. In the present study, the phenotype of the hepatocytes that formed MBs and tumors was characterized. Immunoperoxidase and immunofluorescent stains were done on the DDC-treated mouse livers, as well as mouse liver tumors and a human hepatocellular carcinoma that formed MBs. Antibodies to markers of hepatocellular neoplasms such as alpha-fetoprotein (AFP), ubiquitin B (UbB) fatty acid synthase (FAS) and alpha2 macroglobulin (A2m) stained the MB forming cells positive. Quantitative real-time RT-PCR assay was used to measure AFP, UbB, FAS and GCP-3 A2m mRNA levels in the livers of DDC fed mice and the DDC-induced mouse liver tumors. The FAS, UbB, GPC-3 and AFP mRNA levels were significantly increased in the MB forming liver cells. The in vitro model of MB formation was used to correlate MB formation with gene and protein expression. Primary cultures of DDC-primed hepatocytes were compared with the controls. A2m and UbB expression increased in the primary cultures of DDC-primed hepatocytes when MBs formed. Thus, the tumor markers used to identify hepatocellular carcinoma were upregulated in cells forming MBs in vivo and in vitro, suggesting that MB forming cells express preneoplastic phenotypic features.

Microarray analysis of androgen-regulated gene expression in testis: the use of the androgen-binding protein (ABP)-transgenic mouse as a model

BACKGROUND

Spermatogenesis is an androgen-dependent process, yet the molecular mechanisms of androgens' actions in testis are poorly understood. Transgenic mice overexpressing rat androgen-binding protein (ABP) in their testes have reduced levels of intratesticular androgens and, as a result, show a progressive impairment of spermatogenesis. We used this model to characterize changes in global gene expression in testis in response to reduced bioavailability of androgens.

METHODS

Total RNA was extracted from testes of 30-day old transgenic and wild-type control mice, converted to cRNA, labeled with biotin, and hybridized to oligonucleotide microarrays. Microarray results were confirmed by real-time reverse transcription polymerase chain reaction.

RESULTS

Three-hundred-eighty-one genes (3.05% of all transcripts represented on the chips) were up-regulated and 198 genes (1.59%) were down-regulated by at least a factor of 2 in the androgen-deficient animals compared to controls. Genes encoding membrane proteins, intracellular signaling molecules, enzymes, proteins participating in the immune response, and those involved in cytoskeleton organization were significantly overrepresented in the up-regulated group. Among the down-regulated transcripts, those coding for extracellular proteins were overrepresented most dramatically, followed by those related to proteolysis, cell adhesion, immune response, and growth factor, cytokine, and ion channel activities. Transcripts with the greatest potential impact on cellular activities included several transcription factors, intracellular signal transducers, secreted signaling molecules and enzymes, and various cell surface molecules. Major nodes in the up-regulated network were IL-6, AGT, MYC, and A2M, those in the down-regulated network were IL-2, -4, and -10, MAPK8, SOCS1, and CREB1.

CONCLUSION

Microarray analysis followed by gene ontology profiling and connectivity analysis identified several functional groups of genes and individual genes responding to sustained reduction of androgen levels in the mouse testis. These include genes whose products function as transcription factors, cell surface molecules including ion channels, extra- and intracellular signaling molecules, and secreted enzymes with the potential of regulating cell-to-cell attachment. The transcription factors CREB1 (down-regulated) and MYC (up-regulated) may mediate the most important initial phases of the testicular response to reduced levels of androgens. These results suggest specific avenues for further research that will lead to a better understanding of how androgens regulate spermatogenesis.

Expression of Panza, an alpha2-macroglobulin, in a restricted dorsal domain of the primitive gut in Xenopus laevis

Alpha2-macroglobulin is a major serum protein with diverse functions, including inhibition of protease activity and binding of growth factors, cytokines, and disease factors. We have cloned and characterized Panza, a new Xenopus laevis alpha2-macroglobulin. Panza has 56-60% amino acid similarity with previously identified Xenopus, mouse, rat and human alpha2-macroglobulins, indicating that Panza is a new member of the alpha2-macroglobulin family. Panza mRNA is first detected at the beginning of neurulation in the dorsal endoderm lining the primitive gut (archenteron roof). At the completion of neurulation and continuing through the late tadpole stage, Panza is restricted to a dorsal domain of the gut endoderm adjacent to the notochord and extending along the entire anterior-posterior axis. With outgrowth of the tailbud, Panza expression persists in the chordaneural hinge at the posterior end of the differentiating notochord and extends into the floor plate of the posterior neural tube. As gut coiling commences, Panza expression is initiated in the liver, and the dorsal domain of Panza expression becomes limited to the midgut and hindgut. With further gut coiling, strong Panza expression persists in the liver, but is lost from other regions of the gut. The expression of Panza in endodermal cells adjacent to the notochord points to a potential role for Panza in signal modulation and/or morphogenesis of the primitive gut.

alpha(2)-Macroglobulin: a novel cytochemical marker characterizing preneoplastic and neoplastic rat liver lesions negative for hitherto established cytochemical markers

We tried to identify a novel marker characteristic for rat hepatocellular preneoplastic and neoplastic lesions, undetectable by well established cytochemical markers. Glutathione S-transferase placental (GST-P)-negative hepatocellular altered foci (HAF), hepatocellular adenoma (HCA), and hepatocellular carcinoma (HCC) were generated by two initiation-promotion models with N-nitrosodiethylamine (NDEN) and peroxisome proliferators, Wy-14,643 and clofibrate. Total RNAs isolated from laser-microdissected GST-P-negative HAF (amphophilic cell foci) and adjacent normal tissues were applied to microarray analysis. As a result, five up-regulated genes were identified, and further detailed examinations of the gene demonstrating most fluctuation, ie, that for alpha(2)-macroglobulin (alpha(2)M) were performed. In reverse transcriptase-polymerase chain reaction, alpha(2)M mRNA was overexpressed not only in amphophilic GST-P-negative HAF but also in amphophilic GST-P-negative HCA and HCC. In situ hybridization showed accumulation of alpha(2)M mRNA to be evenly distributed within GST-P-negative HAF (predominantly amphophilic cell foci). Distinctive immunohistochemical staining for alpha(2)M could be consistently demonstrated in GST-P-negative HAF, HCA, and HCC induced not only by peroxisome proliferators but also N-nitrosodiethylamine alone. Thus our findings suggest that alpha(2)M is an important novel cytochemical marker to identify hepatocellular preneoplastic and neoplastic lesions, particularly amphophilic cell foci, undetectable by established cytochemical markers and is tightly linked to rat hepatocarcinogenesis.

Sertoli-Sertoli and Sertoli-germ cell interactions and their significance in germ cell movement in the seminiferous epithelium during spermatogenesis

Spermatogenesis is the process by which a single spermatogonium develops into 256 spermatozoa, one of which will fertilize the ovum. Since the 1950s when the stages of the epithelial cycle were first described, reproductive biologists have been in pursuit of one question: How can a spermatogonium traverse the epithelium, while at the same time differentiating into elongate spermatids that remain attached to the Sertoli cell throughout their development? Although it was generally agreed upon that junction restructuring was involved, at that time the types of junctions present in the testis were not even discerned. Today, it is known that tight, anchoring, and gap junctions are found in the testis. The testis also has two unique anchoring junction types, the ectoplasmic specialization and tubulobulbar complex. However, attention has recently shifted on identifying the regulatory molecules that "open" and "close" junctions, because this information will be useful in elucidating the mechanism of germ cell movement. For instance, cytokines have been shown to induce Sertoli cell tight junction disassembly by shutting down the production of tight junction proteins. Other factors such as proteases, protease inhibitors, GTPases, kinases, and phosphatases also come into play. In this review, we focus on this cellular phenomenon, recapping recent developments in the field.

Endothelial–Mesenchymal Interactions In Vitro Reveal Molecular Mechanisms of Smooth Muscle/Pericyte Differentiation

Cell-cell interactions are central to vascular development. We have developed an in vitro system in which endothelial cells (EC) are co-cultured with 10T1/2 cells as smooth muscle cell (SMC)/pericyte precursors. 10T1/2 cells, in contact with EC, differentiate to SMC in a process mediated, at least in part, by a transforming growth factor-beta (TGF-beta)-mediated event. Co-culture with EC or TGF-beta treatment induced expression of SM22alpha, with co-culture inducing a significantly greater response. To dissect the molecular mechanisms of SMC/pericyte differentiation, reporter constructs containing the promoter for SM22alpha, a SMC-specific gene, were stably transfected into 10T1/2 cells and response to EC-co-culture and TGFbeta were compared. Co-culture with EC or TGFbeta treatment stimulated activity of a 441-bp SM22-alpha promoter to about the same extent, whereas co-culture induced the activity of a 3.7-kb promoter to about twice that of TGBbeta. Neutralization of TGFbeta in EC-10T1/2 co-cultures partially reduced the 3.7-kb SM22alpha promoter activity in 10T1/2 cells. Previously unidentified CArG and TCE elements near the 5' end of the promoter are responsible for full promoter activity. EC-mesenchymal contact appears to be required for full promoter activity of the SM22alpha gene in 10T1/2 and requires upstream CArG and TCE elements. The 3.7-kb SM22alpha promoter can direct expression of lacZ in vivo to SMC of the large vessels and the smaller intersomitic vessels. We have identified the expression of SM22alpha in pericytes of the retinal microvasculature in developing and remodeling vessels.

Identification and Characterization of the Acidic pH Binding Sites for Growth Regulatory Ligands of Low Density Lipoprotein Receptor-related Protein-1

The type V TGF-beta receptor (TbetaR-V) plays an important role in growth inhibition by IGFBP-3 and TGF-beta in responsive cells. Unexpectedly, TbetaR-V was recently found to be identical to the LRP-1/alpha(2)M receptor; this has disclosed previously unreported growth regulatory functions of LRP-1. Here we demonstrate that, in addition to expressing LRP-1, all cells examined exhibit low affinity but high density acidic pH binding sites for LRP-1 growth regulatory ligands (TGF-beta(1), IGFBP-3, and alpha(2)M(*)). These sites, like LRP-1, are sensitive to receptor-associated protein and calcium depletion but, unlike LRP-1, are also sensitive to chondroitin sulfate and heparin and capable of directly binding ligands, which do not bind to LRP-1. Annexin VI has been identified as a major membrane-associated protein capable of directly binding alpha(2)M(*) at acidic pH. This is evidenced by: 1) structural and Western blot analyses of the protein purified from bovine liver plasma membranes by alpha(2)M(*) affinity column chromatography at acidic pH, and 2) dot blot analysis of the interaction of annexin VI and (125)I-alpha(2)M(*). Cell surface annexin VI is involved in (125)I-TGF-beta(1) and (125)I-alpha(2)M(*) binding to the acidic pH binding sites and (125)I-alpha(2)M(*) binding to LRP-1 at neutral pH as demonstrated by the sensitivity of cells to pretreatment with anti-annexin VI IgG. Cell surface annexin VI is also capable of mediating internalization and degradation of cell surface-bound (125)I-TGF-beta(1) and (125)I-alpha(2)M(*) at pH 6 and of forming ternary complexes with (125)I-alpha(2)M(*) and LRP-1 at neutral pH as demonstrated by co-immunoprecipitation. Trifluoperazine and fluphenazine, which inhibit ligand binding to the acidic pH binding sites, block degradation after internalization of cell surface-bound (125)I-TGF-beta(1) or (125)I-alpha(2)M(*). These results suggest that cell surface annexin VI may function as an acidic pH binding site or receptor and may also function as a co-receptor with LRP-1 at neutral pH.

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.

LRP-1/TbetaR-V mediates TGF-beta1-induced growth inhibition in CHO cells

The type V transforming growth factor-beta (TGF-beta) receptor (TbetaR-V) is hypothesized to be involved in cellular growth inhibition by TGF-beta(1). Recently, TbetaR-V was found to be identical to low density lipoprotein receptor-related protein-1 (LRP-1). Here we demonstrate that TGF-beta(1) inhibits growth of wild-type CHO cells but not LRP-1-deficient mutant cells (CHO-LRP-1(-) cells). Stable transfection of CHO-LRP-1(-) cells with LRP-1 cDNA restores the wild-type morphology and the sensitivity to growth inhibition by TGF-beta(1). In addition, overexpression of LRP-1 minireceptors exerts a dominant negative effect and attenuates the growth inhibitory response to TGF-beta(1) in wild-type CHO cells. These results suggest that LRP-1/TbetaR-V is critical for TGF-beta(1)-mediated growth inhibition in CHO cells.

Human serum inactivates non-glycosylated but not glycosylated granulocyte colony stimulating factor by a protease dependent mechanism: significance of carbohydrates on the glycosylated molecule

It has previously been reported that the biological activity of the human hematopoetic cytokine granulocyte colony stimulating factor (G-CSF) was reduced following incubation with human serum. The mechanism of action of serum has remained elusive although a number of possible mechanisms have been suggested including inactivation due to binding to the serum protein alpha(2)-macroglobulin (alpha(2)M) and degradation by serum proteases. The aim of this study was to clarify the conditions required by serum to reduce the biological activity of the cytokine and to define the mechanism involved. It has also been noted that G-CSF obtained from a CHO expression system (and therefore considered a glycosylated molecule) was resistant to serum inactivation unlike G-CSF obtained from an E. coli expression system (considered to be non-glycosylated). We used an enzymatic approach to remove the carbohydrate residues from glycosylated G-CSF and tested this material for its stability in serum. We additionally used a mutated G-CSF lacking glycosylation sites. We concluded that glycosylation was important in protecting against serum inactivation. We observed that serum reduced the biological activity of non-glycosylated G-CSF in a dose, and temperature dependent manner and deduced that the mechanism of action was dependent upon alpha(2)M bound serum protease enzymes.

Cellular growth inhibition by IGFBP‐3 and TGF‐β1requires LRP‐1

The type V TGF-beta receptor (TbetaR-V)/IGFBP-3 receptor mediates the IGF-independent growth inhibition induced by IGFBP-3. It also mediates the growth inhibitory response to TGF-beta1 in concert with other TGF-beta receptor types, and its loss may contribute to the malignant phenotype of human carcinoma cells. Here we demonstrate that TbetaR-V is identical to LRP-1/alpha2M receptor as shown by MALDI-TOF analysis of tryptic peptides of TbetaR-V purified from bovine liver. In addition, 125I-IGFBP-3 affinity-labeled TbetaR-V in Mv1Lu cells is immunoprecipitated by antibodies to LRP-1 and TbetaR-V. RAP, an LRP-1 antagonist, inhibits binding of 125I-TGF-beta1 and 125I-IGFBP-3 to TbetaR-V and diminishes IGFBP-3-induced growth inhibition in Mv1Lu cells. Absent or low levels of LRP-1, as with TbetaR-V, have been linked to the malignant phenotype of carcinoma cells. Mutagenized Mv1Lu cells selected for reduced expression of LRP-1 have an attenuated growth inhibitory response to TGF-beta1 and IGFBP-3. LRP-1-deficient mouse embryonic fibroblasts lack a growth inhibitory response to TGF-beta1 and IGFBP-3. On the other hand, stable transfection of H1299 human lung carcinoma cells with LRP-1 cDNA restores the growth inhibitory response. These results suggest that the LRP-1/TbetaR-V/IGFBP-3 receptor is required for the growth inhibitory response to IGFBP-3 and TGF-beta1.

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*.

Role of tissue inhibitor of metalloproteases-1 in junction dynamics in the testis

Using multiple high-performance liquid chromatography steps, we have identified and purified a polypeptide to apparent homogeneity from primary Sertoli cell conditioned culture medium that consisted of 2 molecular variants of 31 and 29 kDa when electrophoresed on a sodium dodecyl sulfate-polyacrylamide gel run under reducing conditions. Partial N-terminal amino acid sequence analysis of these 2 proteins revealed a sequence of NH(2)-IKMAKMLKGFDAVGNATG, which is homologous to tissue inhibitor of metalloproteases-1 (TIMP-1). Studies by semiquantitative reverse transcription-polymerase chain reaction using a primer pair specific to rat TIMP-1 demonstrated that both Sertoli and germ cells express TIMP-1. During maturation, the steady-state TIMP-1 mRNA level in the testis increased significantly from 40 to 60 days of age, which suggests its role in the restructuring of the epithelium during spermiation. This increase in testicular TIMP-1 expression was apparently not due to the increase in germ cell number, because TIMP-1 expression decreased approximately fivefold in germ cells isolated from testes of aging rats. Using Sertoli cells cultured at low (0.05 x 10(6) cells/cm(2)) and high (0.5 x 10(6) cells/cm(2)) densities, it was found that TIMP-1 expression increased transiently but significantly during junction assembly. A similar induction of TIMP-1 mRNA was also detected in Sertoli-germ cell cocultures during germ cell adhesion onto Sertoli cells. More important, the inclusion of either alpha(2)-macroglobulin (a protease inhibitor produced by Sertoli cells) or aprotinin (a serine protease inhibitor) into an in vitro germ cell adhesion assay facilitated the attachment of fluorescently labeled germ cells onto the Sertoli cell epithelium when compared to control, which suggests that the assembly of adherens junctions may involve protease inhibitors.

Fibroproliferative scars

Fibroproliferative scars remain an ongoing clinical challenge. Both hypertrophic scars and keloids require multimodal therapy toachieve partally successful treatment. At the present time incomplete understanding about the pathogenesis of fibroproliferative scars makes targeted, mechanistic treatment impossible. As understanding of these abnormal wound problems increases, more effective treatments will likely be available. Until that time, clinicians must utilize existing knowledge to treat patients while continuing to experiment with new approaches.

Down-regulation of human type II collagen gene expression by transforming growth factor-beta 1 (TGF-beta 1) in articular chondrocytes involves SP3/SP1 ratio

Although transforming growth factor beta1 (TGF-beta1) is generally considered as a stimulator of type I collagen production in smooth organs, we found that it can inhibit type II collagen biosynthesis in primary rabbit articular chondrocytes (RAC) at transcriptional levels. Constructs of promoter and first intron sequences associated with the luciferase reporter gene were used to delineate the gene sequences involved in TGF-beta1 control of human COL2A1 gene transcription. Cotransfection of these DNA fragments with a TbetaRII/I cDNA hybrid receptor, capable of inducing a TGF-beta1 dominant negative effect, showed that TGF-beta1 inhibits specifically COL2A1 gene transcription in RAC by a 63-bp proximal promoter. Footprint and gel retardation analyses revealed that the TGF-beta1-induced inhibition effect exerted through the 63-bp promoter sequence implies a multimeric complex that binds to the -41/-33 sequence and involves Sp1 and Sp3 transcription factors. Transfection of decoy Sp-binding oligonucleotides corroborated the implication of the proximal promoter in the TGF-beta1-induced inhibition of COL2A1 gene transcription. In addition, TGF-beta1 was found to increase the expression of Sp3 without significant changes to its binding level, but repressed both the biosynthesis and binding activity of Sp1. In functional assays, Sp3 inhibited the 63-bp promoter activity and prevented Sp1 induction of transcription. These findings suggest that TGF-beta1 inhibition of COL2A1 gene transcription in RAC is mediated by an increase of the Sp3/Sp1 ratio and by the repression of Sp1 transactivating effects on that gene.

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*.

Inflammatory left ventricular microaneurysms as a cause of apparently idiopathic ventricular tachyarrhythmias

BACKGROUND

We sought to investigate the arrhythmogenic role, incidence, treatment, and prognosis of inflammatory left ventricular (LV) microaneurysms in patients with apparently idiopathic ventricular tachyarrhythmias. Methods and Results-- We studied 156 consecutive patients (71 men, 85 women; mean age, 44.1+/-11.8 years) with severe ventricular arrhythmias and normal 2D echo cardiac parameters by coronary and ventricular angiography, biventricular endomyocardial biopsy, and electrophysiological study. Polymerase chain reaction was used to detect genomic sequences of enterovirus, adenovirus, Epstein Barr virus, cytomegalovirus, herpes simplex viruses, influenza A and B viruses, and hepatitis C virus in frozen endomyocardial samples. Of these patients, 15 (9.6%) showed angiographic evidence of single or multiple LV microaneurysms. All 15 patients had recurrent episodes of ventricular tachycardia with right bundle-branch block morphology, and the arrhythmias originated within or close to the aneurysms in those patients (n=6) undergoing ventricular mapping. A lymphocytic myocarditis was observed in LV biopsies of all patients and in the right ventricles of 3 patients. Polymerase chain reaction analysis was performed in 12 and viral genomes were found in 5 (42%): hepatitis C virus in 2, enterovirus in 2, and influenza virus A in 1. The patients were treated with antiarrhythmics, and cardiac function was preserved for the next 47+/-39.5 months of follow-up. No major clinical event was registered, and arrhythmias were successfully treated by antiarrhythmics.

CONCLUSIONS

Inflammatory LV microaneurysms, often of viral origin, are a consistent cause of apparently idiopathic ventricular arrhythmias. Their prognosis so far has been benign, and aggressive therapeutic strategies have been unnecessary.

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)

Transforming growth factor-beta1 in the cerebrospinal fluid of patients with subarachnoid hemorrhage: titers derived from exogenous and endogenous sources

Transforming growth factor-beta1 (TGF-beta1) is a fibrogenic cytokine that is involved in postinjury repair and is implicated in the etiology of postsubarachnoid hemorrhage (SAH) chronic communicating hydrocephalus. TGF-beta1 was measured by enzyme-linked immunosorbant assay (ELISA) in sequential samples of cerebrospinal fluid (CSF) in 11 patients with hydrocephalus after SAH; levels were seen to be biphasically elevated and sources were investigated. TGF-beta1 levels were compared with albumin levels that estimated CSF blood content. Control samples from nonhemorrhagic hydrocephalics were tested similarly. Mean total TGF-beta1 levels were elevated to 4400+/-3435 (+/-SD) pg/mL greater than control levels of 97+/-42 at 1 to 2 days posthemorrhage. Thereafter, levels fell to 714+/-401 by 5 to 6 days posthemorrhage, then rose to a second peak of 1667+/-774 at 9 to 10 days posthemorrhage, remaining significantly increased until 19 days posthemorrhage (P = 0.007). The first peak probably derived from extravasated platelets and correlated with increased albumin levels in the CSF. The second TGF-beta1 peak rose greater than CSF albumin levels that had stabilized at this time, and thus was attributed to a tissue-specific response rather than a re-bleed. TGF-beta1 was detected in the choroid secretory epithelium from controls, but levels were greater in SAH patients at 10 to 12 days posthemorrhage. The authors conclude that the elevated levels of TGF-beta1 in CSF after SAH are derived initially from blood and later from endogenous sources such as the choroid plexus.

Measurement of cytokines in clinical samples using immunoassays: problems and pitfalls

With the explosion in interest in cytokines and an increasing understanding of their possible involvement in the pathogenesis of many diseases, the number of studies measuring cytokines in body fluids has increased markedly over the last 5 to 10 years. However, it is readily apparent from the literature that the level of awareness of the many factors that can potentially influence the results obtained is very low. Such factors are likely to contribute considerably to the disparities seen among similar types of study. These include assay properties such as standardization and specificity, type of sample and sample handling, and many biological influences such as age, sex, ethnic background, and diurnal rhythmicity. Clearly, it is not possible to control for all these factors, but a minimum evaluation of assays should be carried out as described, including recovery and parallelity studies using relevant samples and the establishment of reproducibility and normal healthy population levels. An awareness of these factors, which is the purpose of this review, may hopefully lead to an improvement in the quality of studies incorporating the measurement of cytokines in clinical samples and should aid in the interpretation of the data.

Interleukin-4 and IL-10 bind covalently to activated human alpha2-macroglobulin by a mechanism that requires Cys949

Alpha2-macroglobulin (alpha2M) functions as an extracellular carrier of diverse cytokines, including transforming growth factor-beta1 (TGF-beta1), that expresses anti-inflammatory activities. The results presented here demonstrate that interleukin-10 (IL-10) and IL-4, which also regulate the inflammatory response, bind to alpha2M. Unlike TGF-beta, IL-4 and IL-10 bind almost exclusively to the receptor-recognized, or activated, form of alpha2M. Purified IL-4-alpha2M complexes were predominantly covalent due to thiol disulfide exchange involving Cys949 in the alpha2M subunit. Blocking Cys949 with iodoacetamide significantly inhibited IL-4- and IL-10 binding. Bovine serum albumin (BSA), which possesses a free Cys residue and undergoes thiol disulfide exchange reactions, did not compete with alpha2M for the binding of IL-4 or IL-10. These results suggest a model in which IL-4 and IL-10 associate with activated alpha2M to form complexes that are initially noncovalent but unstable. In these complexes, Cys949 is properly aligned to undergo thiol disulfide exchange and generate stable, covalent IL-4-alpha2M and IL-10-alpha2M complexes.

TGF-beta is not the principal immunosuppressive component in coagulation factor concentrates

Coagulation factor concentrates are known to inhibit a variety of immune reactions when assessed in vitro. This study assessed the immunomodulatory activity of a wide range of coagulation factor concentrates by measuring their inhibition of PHA-stimulated lymphocyte proliferation and reduction in IL-2 secretion. The hypothesis that TGF-beta is responsible for most of these effects was tested by measuring biologically active TGF-beta and immunoreactive TGF-beta1 in the concentrates and comparing the levels recorded with immunosuppressive activity. In addition, the coagulation factors were compared directly with a standard preparation of TGF-beta in a TGF-beta-specific bioassay and in lymphocyte proliferation assays. Although there was a broad correlation between levels of total or active TGF-beta and immunosuppressive activity across all of the coagulation factors tested, individual data sets showed clear discrepancies. Implying that TGF-beta probably serves as a surrogate marker for other immunomodulatory contaminants and that neither TGF-beta nor any other single substance could account for all of the immunosuppressive activity observed. Furthermore, there was a difference of more than 100-fold in the relative potencies of coagulation factors and pure TGF-beta, when compared in immunosuppression assays, indicating that the different assays did not measure the same substance. Whereas anti-TGF-beta antibody almost completely blocked the activity of coagulation factor concentrates (TGF-beta-specific bioassay) and abrogated the effect of authentic TGF-beta (immunosuppression assays) at high concentrations it achieved <50% reversal of the immunosuppressive effects of coagulation factors in immunosuppression assays. These findings indicated that TGF-beta accounted for only a minor proportion of the immunosuppressive activity in most coagulation factor concentrates.

Growth factors VEGF and TGF-beta1 in peritoneal dialysis

The morphologic alterations in the kidney and the retina that can be present in patients with diabetic microangiopathy are mediated by growth factors. Vascular endothelial growth factor (VEGF) is a mediator of neoangiogenesis in diabetic retinopathy. Transforming growth factor-beta (TGF-beta) is involved in the extracellular matrix proliferation in diabetic nephropathy. The aim of the present study was to investigate the presence of VEGF and TGF-beta1 in peritoneal effluents of patients undergoing continuous ambulatory peritoneal dialysis who are being treated with glucose-containing dialysis solutions in relation to parameters of peritoneal transport. Standard peritoneal permeability analyses with 3.86% glucose dialysate were performed in 16 stable patients undergoing peritoneal dialysis (PD) (median duration of PD 39 months, range 1 to 104 months). The power relationship that is present between dialysate/serum (D/S) ratios of serum proteins that are transported only across the peritoneal membrane and their molecular weights was used to predict the D/S ratios when diffusion would be the only explanation for the measured dialysate concentration. It was assumed that all TGF-beta1 in the circulation was bound to alpha2-macroglobulin. The D/S ratios of VEGF (P < .0005) and TGF-beta1 (P < .015) were significantly higher than expected when VEGF and TGF-beta1 would have been transported from the circulation only by diffusion. No relationship was present between the effluent concentration attributed to the local production of VEGF (LVEGF) and that of TGF-beta1 (LTGF-beta1). LVEGF correlated with the mass transfer area coefficient (MTAC) creatinine value (r = 0.69, P < .007), MTAC urate value (r = 0.60, P < .02), and glucose absorption value (r = 0.75, P < .004), all reflections of the peritoneal vascular surface area. A negative correlation was observed between the transcapillary ultrafiltration (926 mL/4 h, 394 to 1262 mL/4 h) and LVEGF (r = -0.52, P < .045). This negative tendency was also observed between the net ultrafiltration (622 mL/4 h, -43 to 938 mL/4 h) and LVEGF (r = -0.48) but did not reach significance. LVEGF and the duration of treatment did not correlate, possibly because of the relatively small number of patients. LTGF-beta1 showed no relationship with transport parameters or duration of treatment. In conclusion, we found evidence for the local production of both VEGF and TGF-beta1 in the peritoneal membrane of patients undergoing long-term peritoneal dialysis with glucose-based dialysate solutions. The analogy with VEGF in diabetic retinopathy suggests a pathogenetic role of high dialysate glucose concentrations in the development of these alterations in the peritoneal membrane.

Augmentation of natural killer cell activity in mice by oral administration of transforming growth factor-beta

The latent form of transforming growth factor-beta (TGF-beta) in human milk and platelets was converted to the active form when conscious, pylorus-ligated mice were given human milk and platelets by intragastric intubation. Oral administration of TGF-beta exerted enhancing effects on the natural killer (NK)-cell activities in spleen and liver. Augmentation of NK-cell activities in spleen was observed for 7 days after oral administration of TGF-beta. TGF-beta at concentrations of 5 and 20 ng produced the greatest augmentation of NK-cell activities in spleen. However, NK-cell activities in spleen were unaffected when TGF-beta was given intravenously. Interleukin (IL)-12 production in spleen was enhanced by oral administration of TGF-beta, but not by intravenous administration of TGF-beta. These findings suggest that large amounts of TGF-beta in human milk are involved in early antiviral protection through the augmentation of NK-cell activities.

Oxidized α2-Macroglobulin (α2M) Differentially Regulates Receptor Binding by Cytokines/Growth Factors: Implications for Tissue Injury and Repair Mechanisms in Inflammation

α2M binds specifically to TNF-α, IL-1β, IL-2, IL-6, IL-8, basic fibroblast growth factor (bFGF), β-nerve growth factor (β-NGF), platelet-derived growth factor (PDGF), and TGF-β. Since many of these cytokines are released along with neutrophil-derived oxidants during acute inflammation, we hypothesize that oxidation alters the ability of α2M to bind to these cytokines, resulting in differentially regulated cytokine functions. Using hypochlorite, a neutrophil-derived oxidant, we show that oxidized α2M exhibits increased binding to TNF-α, IL-2, and IL-6 and decreased binding to β-NGF, PDGF-BB, TGF-β1, and TGF-β2. Hypochlorite oxidation of methylamine-treated α2M (α2M*), an analogue of the proteinase/α2M complex, also results in decreased binding to bFGF, β-NGF, PDGF-BB, TGF-β1, and TGF-β2. Concomitantly, we observed decreased ability to inhibit TGF-β binding and regulation of cells by oxidized α2M and α2M*. We then isolated α2M from human rheumatoid arthritis synovial fluid and showed that the protein is extensively oxidized and has significantly decreased ability to bind to TGF-β compared with α2M derived from plasma and osteoarthritis synovial fluid. We, therefore, propose that oxidation serves as a switch mechanism that down-regulates the progression of acute inflammation by sequestering TNF-α, IL-2, and IL-6, while up-regulating the development of tissue repair processes by releasing bFGF, β-NGF, PDGF, and TGF-β from binding to α2M.

Activated thyroglobulin possesses a transforming growth factor-beta activity

Thyroglobulin (Tg), the thyroid hormone precursor, is a major protein component in the thyroid gland and may have other important functions. Here, we show that bovine Tg inhibited 125I-labeled transforming growth factor-beta1 (125I-TGF-beta1) binding to cell-surface TGF-beta receptors in mink lung epithelial cells with an IC50 of approximately 300 nM. After disuccinimidyl suberate (DSS) modification, reduction/alkylation, treatment with 8 M urea, 0. 1% SDS, or acidic pH (pH 4-5), Tg exhibited a approximately 5-10-fold increase of 125I-TGF-beta1 binding inhibitory activity with IC50 of approximately 30-60 nM. This inhibitory activity was an intrinsic property of the Tg and could not be segregated from Tg protein by 5% SDS-polyacrylamide gel electrophoresis or by immunoprecipitation using antiserum to Tg. Untreated Tg did not affect DNA synthesis but blocked the TGF-beta-induced inhibition of DNA synthesis in mink lung epithelial cells. After DSS activation, Tg possessed TGF-beta agonist activity and inhibited DNA synthesis of mink lung epithelial cells and rat thyroid cells. The activated Tg also exerted a small but significant TGF-beta agonist activity in transcriptional activation of plasminogen activator inhibitor-1. These results suggest that Tg possesses an authentic TGF-beta activity which can be induced by chemical modifications and treatments with denaturing agents and acidic pH.

Regulation of alpha2-macroglobulin expression in rat Sertoli cells and hepatocytes by germ cells in vitro

Germ cells isolated from rat testes by trypsinization have been shown to yield unwanted artifacts in biological assays, since conditioned media derived from these germ cells (germ cell-conditioned media [GCCM]) can modulate Sertoli cell secretory function because of the presence of residual trypsin. To determine whether germ cells themselves can modulate Sertoli cell function, we isolated germ cells from tubules by a mechanical procedure and assessed the effect of these cells on Sertoli cell alpha2-macroglobulin (alpha2-MG) steady-state mRNA level. It was found that germ cells indeed could stimulate Sertoli cell alpha2-MG expression. This effect is probably mediated by a soluble factor(s) released from germ cells, since GCCM fractionated by HPLC contained multiple fractions that can stimulate Sertoli cell alpha2-MG expression dose-dependently. These results illustrate that germ cells play a role in regulating testicular alpha2-MG expression. Since Sertoli cells synthesize and secrete many of the serum proteins behind the blood-testis barrier that are also produced by hepatocytes, we sought to ascertain whether germ cells can affect hepatic alpha2-MG expression. When germ cells were cocultured with hepatocytes isolated from adult rats, the hepatocyte alpha2-MG steady-state mRNA level was shown to be stimulated by germ cells dose-dependently. Using different pools of fractions derived from GCCM after their fractionation by a preparative anion-exchange HPLC column, GCCM was found to contain a factor(s) that stimulated hepatocyte alpha2-MG expression dose-dependently. More importantly, the fractions that stimulated hepatocyte alpha2-MG expression had a retention time different from that of the factor(s) that affected Sertoli cell alpha2-MG expression. These data illustrate that germ cells secrete multiple biological factors capable of regulating alpha2-MG expression in the testis and the liver. In summary, this study reveals a possible physiological link between the testis and the liver in that germ cells may release a factor(s) capable of modulating alpha2-MG expression in both organs.

Localization of the binding site for transforming growth factor-beta in human alpha2-macroglobulin to a 20-kDa peptide that also contains the bait region

alpha2-Macroglobulin (alpha2M) functions as a major carrier of transforming growth factor-beta (TGF-beta) in vivo. The goal of this investigation was to characterize the TGF-beta-binding site in alpha2M. Human alpha2M, which was reduced and denatured to generate 180-kDa subunits, bound TGF-beta1, TGF-beta2, and NGF-beta in ligand blotting experiments. Cytokine binding was not detected with bovine serum albumin that had been reduced and alkylated, and only minimal binding was detected with purified murinoglobulin. To localize the TGF-beta-binding site in alpha2M, five cDNA fragments, collectively encoding amino acids 122-1302, were expressed as glutathione S-transferase (GST) fusion proteins. In ligand blotting experiments, TGF-beta2 bound only to the fusion protein (FP3) that includes amino acids 614-797. FP3 bound 125I-TGF-beta1 and 125I-TGF-beta2 in solution, preventing the binding of these growth factors to immobilized alpha2M-methylamine (alpha2M-MA). The IC50 values were 33 +/- 5 and 26 +/- 6 nM for TGF-beta1 and TGF-beta2, respectively; these values were comparable with or lower than those determined with native alpha2M or alpha2M-MA. A GST fusion protein that includes amino acids 798-1082 of alpha2M (FP4) and purified GST did not inhibit the binding of TGF-beta to immobilized alpha2M-MA. FP3 (0.2 microM) neutralized the activity of TGF-beta1 and TGF-beta2 in fetal bovine heart endothelial (FBHE) cell proliferation assays; FP4 was inactive in this assay. FP3 also increased NO synthesis by RAW 264.7 cells, mimicking an alpha2M activity that has been attributed to the neutralization of endogenously synthesized TGF-beta. Thus, we have isolated a peptide corresponding to 13% of the alpha2M sequence that binds TGF-beta and neutralizes the activity of TGF-beta in two separate biological assays.

The interaction of the transforming growth factor-betas with heparin/heparan sulfate is isoform-specific

We have undertaken a comparative study of the interaction of the three mammalian transforming growth factor-betas (TGF-beta) with heparin and heparan sulfate. TGF-beta1 and -beta2, but not -beta3, bind to heparin and the highly sulfated liver heparan sulfate. These polysaccharides potentiate the biological activity of TGF-beta1 (but not the other isoforms), whereas a low sulfated mucosal heparan sulfate fails to do so. Potentiation is due to antagonism of the binding and inactivation of TGF-beta1 by alpha2-macroglobulin, rather than by modulation of growth factor-receptor interactions. TGF-beta2.alpha2-macroglobulin complexes are more refractory to heparin/heparan sulfate, and those involving TGF-beta3 cannot be affected. Comparison of the amino acid sequences of the TGF-beta isoforms strongly implicates the basic amino acid residue at position 26 of each monomer as being a vital binding determinant. A model is proposed in which polysaccharide binding occurs at two distinct sites on the TGF-beta dimer. Interaction with heparin and liver heparan sulfate may be most effective because of the ability of the dimer to co-operatively engage two specific sulfated binding sequences, separated by a distance of approximately seven disaccharides, within the same chain.

Transforming growth factor-beta-induced collagen synthesis by human liver myofibroblasts is inhibited by alpha2-macroglobulin

BACKGROUND

Transforming growth factor-beta (TGFbeta) plays a central role in the stimulation of matrix production during liver fibrosis. The action of TGFbeta in different systems has been shown to be influenced by alpha2-macroglobulin (alpha2M), a serum protein with strong protease-scavenging and cytokine-binding properties.

AIMS

In the present study, alpha2M derived from normal human plasma has been tested for its ability to modulate the TGFbeta-induced collagen production by human liver fat-storing cells (FSC), which had transformed into alpha-smooth muscle actin-expressing myofibroblasts in culture.

METHODS

Alpha2M has been tested after activation with methylamine (alpha2M-Me), an in vitro equivalent of protease activated alpha2M. The binding of 125I-TGFbeta1 to activated forms of alpha2M was demonstrated by rate electrophoresis. Collagen synthesis was examined in human liver myofibroblast cultures obtained from three different human livers by incorporation of 3H-proline into TCA-precipitable, specific collagenase degradable proteins. Uptake of alpha2M was studied by means of immunofluorescence.

RESULTS

TGFbeta (1 ng/ml) significantly stimulated collagen synthesis of controls in the absence of TGFbeta. Alpha2M-Me reduced this TGFbeta-induced collagen synthesis dose-dependently, reaching significant inhibition from 10 microg/ml alpha2M-Me onward. Upon addition of 100 microg/ml alpha2M-Me the effect of TGFbeta was reduced by 60% to 128+/-31% (mean+/-SD) of control values in the absence of TGFbeta. Human liver myofibroblasts endocytosed alpha2M-Me added to the cultures as detected by immunofluorescence. Accordingly, reduction of TGFbeta-activity by alpha2M-Me may be explained by receptor-mediated clearance of alpha2M-TGFbeta complexes by the cells.

CONCLUSIONS

TGFbeta-induced collagen formation by human liver myofibroblasts obtained from three different livers is reduced in vitro by activated alpha2M. From these results, we hypothesize that alpha2M may have an antifibrogenic effect in vivo by interference with TGFbeta-induced matrix synthesis during liver fibrosis.

Alpha 2-macroglobulin protects some of the protein constituents of dialysis-associated amyloidosis from protease degradation

A crucial point to know in the prevention and treatment of beta 2-microglobulin (beta 2-m) amyloidosis is the putative resorption of amyloid fibrils in vivo. Although still controversial, long term clinical studies suggest that there is no resorption of amyloid fibrils in vivo, even after the suppression of the primary cause of amyloidosis. Two in vitro studies on murine and human AA amyloidosis as well as Alzheimer's disease suggest that protein constituents of amyloid fibrils may be resorbed. Protein resorption can be inhibited by the antiprotease amyloid P component. We extended these in vitro studies on beta 2-m amyloidosis, and assessed the effect of alpha 2-macroglobulin (alpha 2-M), a serum antiprotease previously found in this type of amyloidosis, on the putative protease induced protein resorption. Here, we show that amyloid proteins, beta 2-m and light chains of immunoglobulins, were degraded by trypsin. Preincubation of the amyloid proteins with alpha 2-M significantly inhibited the trypsin induced protein degradation of lambda chains. These data add further support to the hypothesis proposing a role for alpha 2-M and other antiproteases in the formation and/or persistence of beta 2-m amyloidosis.

Acute phase proteins and transformed cells

Acute phase proteins (APP) are plasma proteins whose concentration and glycosylation alters in response to tissue injury, inflammation, or tumor growth. Significant interspecies and sex differences in APP response exist. APP are produced mainly by hepatocytes, and their synthesis and glycosylation are controlled by a network consisting of cytokines, their soluble receptors, and glucocorticoids. The major cytokines involved in these processes belong to a group of interleukin-6-type cytokines that act through the hematopoietin receptor complex on hepatocytes and JAK-STAT signal transduction pathway. Transformed cells (hepatoma) display significant differences in synthesis of APP, cytokine responsiveness, expression of cytokine-receptor subunits and signal-transduction machinery. The most striking variability relates to the glycosylation alterations induced by cytokines. However, transformed cells (hepatoma) form a basic model for studying and understanding mechanisms controlling the synthesis and glycosylation of APP. Furthermore, APP may be secreted by transformed (tumor) cells of various origins and may display a growth factor-like function in certain cancer types.

Murine alpha-macroglobulins demonstrate divergent activities as neutralizers of transforming growth factor-beta and as inducers of nitric oxide synthesis. A possible mechanism for the endotoxin insensitivity of the alpha2-macroglobulin gene knock-out mouse

alpha2-Macroglobulin null mice demonstrate increased resistance to endotoxin challenge (Umans, L., Serneels, L., Overbergh, L., Van Leuven, F., and Van den Berghe, H. (1995) J. Biol. Chem. 270, 19778-19785). We hypothesized that this phenotype might reflect the function of murine alpha2M (malpha2M) as a neutralizer of transforming growth factor-beta (TGF-beta) and inducer of nitric oxide synthesis in vivo. When incubated with wild-type mouse plasma, TGF-beta1 and TGF-beta2 bound only to malpha2M. Alternative TGF-beta-binding proteins were not detected in plasma from alpha2M(-/-) mice. Wild-type mouse plasma, but not plasma from alpha2M(-/-) mice, inhibited TGF-beta1 binding to TGF-beta receptors on fibroblasts. Purified malpha2M bound TGF-beta1 and TGF-beta2 with similar affinity; the KD values were 28 +/- 4 and 33 +/- 4 nM, respectively. Murinoglobulin, the second murine alpha-macroglobulin, bound both TGF-beta isoforms with 30-fold lower affinity. Malpha2M counteracted the activities of TGF-beta1 and TGF-beta2 in an endothelial cell growth assay. Malpha2M also induced NO synthesis when incubated with RAW 264.7 cells, an activity which probably results from the neutralization of autocrine TGF-beta activity. Human alpha2M induced NO synthesis comparably to malpha2M; however, MUG had no effect. These studies demonstrate that the ability to neutralize TGF-beta is a property of malpha2M, which is not redundant in the murine alpha-macroglobulin family or in murine plasma. Malpha2M is the only murine alpha-macroglobulin that promotes NO synthesis. The absence of malpha2M, in alpha2M(-/-) mice, may allow TGF-beta to more efficiently suppress excessive iNOS expression following endotoxin challenge.

Elastase binding capacity of alpha 2-macroglobulin and its association with glucocorticoid concentration in southern African black patients with hepatocellular carcinoma

Thirty-three Southern African black patients with hepatocellular carcinoma (HCC) (7 women) and 43 black control individuals (14 women), all in the age group 18-45 years, were investigated for plasma alpha 2-macroglobulin (alpha 2M) elastase binding capacity (EBC). Cortisol levels were measured in 15 (3 women) of the HCC patients and 10 (5 women) of the control subjects. A significant difference in EBC was found between the HCC patients and the control subjects (P < 0.001). A significant difference was also found in cortisol levels between the two groups (P < 0.001). A significant correlation between EBC and cortisol levels was obtained (r = 0.57; P < 0.042). The significant increase in EBC of alpha 2M in HCC patients could be due to an increase in circulating cortisol.