Synthetic fibronectin peptides interrupt inflammatory cell infiltration in transforming growth factor beta 1 knockout mice

The impact of inflammation and acute phase activation in cancer cachexia

The development of cachexia in the setting of cancer or other chronic diseases is a significant detriment for patients. Cachexia is associated with a decreased ability to tolerate therapies, reduction in ambulation, reduced quality of life, and increased mortality. Cachexia appears intricately linked to the activation of the acute phase response and is a drain on metabolic resources. Work has begun to focus on the important inflammatory factors associated with the acute phase response and their role in the immune activation of cachexia. Furthermore, data supporting the liver, lung, skeletal muscle, and tumor as all playing a role in activation of the acute phase are emerging. Although the acute phase is increasingly being recognized as being involved in cachexia, work in understanding underlying mechanisms of cachexia associated with the acute phase response remains an active area of investigation and still lack a holistic understanding and a clear causal link. Studies to date are largely correlative in nature, nonetheless suggesting the possibility for a role for various acute phase reactants. Herein, we examine the current literature regarding the acute phase response proteins, the evidence these proteins play in the promotion and exacerbation of cachexia, and current evidence of a therapeutic potential for patients.

Fibronectin-targeted FUD and PEGylated FUD peptides for fibrotic diseases

Tissue fibrosis is characterized by excessive deposition of extracellular matrix (ECM) molecules. Fibronectin (FN) is a glycoprotein found in the blood and tissues, a key player in the assembly of ECM through interaction with cellular and extracellular components. Functional Upstream Domain (FUD), a peptide derived from an adhesin protein of bacteria, has a high binding affinity for the N-terminal 70-kDa domain of FN that plays a crucial role in FN polymerization. In this regard, FUD peptide has been characterized as a potent inhibitor of FN matrix assembly, reducing excessive ECM accumulation. Furthermore, PEGylated FUD was developed to prevent rapid elimination of FUD and enhance its systemic exposure in vivo. Herein, we summarize the development of FUD peptide as a potential anti-fibrotic agent and its application in experimental fibrotic diseases. In addition, we discuss how modification of the FUD peptide via PEGylation impacts pharmacokinetic profiles of the FUD peptide and can potentially contribute to anti-fibrosis therapy.

Transcriptome analysis of human cholangiocytes exposed to carcinogenic 1,2-dichloropropane in the presence of macrophages in vitro

1,2-Dichloropropane (1,2-DCP), a synthetic organic solvent, has been implicated in causality of cholangiocarcinoma (bile duct cancer). 1,2-DCP-induced occupational cholangiocarcinoma show a different carcinogenic process compared to common cholangiocarcinoma, but its mechanism remains elusive. We reported previously that exposure of MMNK-1 cholangiocytes co-cultured with THP-1 macrophages, but not monocultured MMNK-1 cholangiocytes, to 1,2-DCP induced activation-induced cytidine deaminase (AID) expression, DNA damage and ROS production. The aim of this study was to identify relevant biological processes or target genes expressed in response to 1,2-DCP, using an in vitro system where cholangiocytes are co-cultured with macrophages. The co-cultured cells were exposed to 1,2-DCP at 0, 0.1 or 0.4 mM for 24 h, and then the cell lysates were assessed by transcriptome analysis. 1,2-DCP upregulated the expression of base excision repair genes in MMNK-1 cholangiocytes in the co-cultures, whereas it upregulated the expression of cell cycle-related genes in THP-1 macrophages. Activation of the base excision repair pathway might result from the previously observed DNA damage in MMNK-1 cholangiocytes co-cultured with THP-1 macrophages, although involvement of other mechanisms such as DNA replication, cell death or other types of DNA repair was not disproved. Cross talk interactions between cholangiocytes and macrophages leading to DNA damage in the cholangiocytes should be explored.

PEGylated pUR4/FUD peptide inhibitor of fibronectin fibrillogenesis decreases fibrosis in murine Unilateral Ureteral Obstruction model of kidney disease

Fibronectin is a blood and extracellular matrix glycoprotein that plays important roles in wound healing and fibrosis since it controls the deposition of collagen and other extracellular matrix molecules and is a substrate for infiltrating lymphocytes. Using a high-affinity fibronectin-binding peptide (FUD/pUR4) that inhibits fibronectin deposition into extracellular matrix (ECM), we tested the ability of a PEGylated FUD/pUR4 (PEG-FUD) to inhibit fibrosis in the Unilateral Ureteral Obstruction (UUO) kidney disease model. Fibronectin fibrillogenesis assays, using human fibroblasts and human proximal tubular epithelial cultures, showed that PEG-FUD can inhibit fibronectin fibrillogenesis in vitro with an IC50 similar to unconjugated FUD, in the order of 20–35 nM. In contrast, a mutated FUD (mFUD) conjugated to PEG that lacked activity did not inhibit fibronectin assembly, even at 20 μM. The in vivo activity of PEG-FUD was tested in the murine UUO model by daily subcutaneous injection of 12.5 mg/kg for 7 days until harvest at day 10. Control treatments included saline, PEG, unconjugated FUD, and PEG-mFUD. Immunoblotting studies showed that fibronectin was enriched in the extracellular matrix fractions of extracted UUO kidneys, compared to contralateral untreated kidneys. In vivo, PEG-FUD significantly decreased fibronectin by ~70% in UUO kidneys as determined by both IHC and immunoblotting, respectively. In contrast, neither PEG-mFUD, PEG, nor saline had any significant effect. PEG-FUD also decreased collagens I and III and CD45-expressing cells (leukocytes) by ~60% and ~50%, as ascertained by picrosirius red staining and IHC, respectively. Immunoblotting studies also showed that the fibronectin remaining after PEG-FUD treatment was intact. Utilizing a custom-made polyclonal antibody generated against pUR4/FUD, intact PEG-FUD was detected by immunoblotting in both the ECM and lysate fractions of UUO kidneys. No adverse reaction or event was noted with any treatment. In summary, these studies suggest that PEG-FUD reached the kidneys without degradation, and decreased fibronectin incorporation into interstitial tissue. Decreased fibronectin was accompanied by a decrease in collagen and leukocyte infiltration. We propose that PEG-FUD, a specific inhibitor of fibronectin assembly, may be a candidate therapeutic for the treatment of fibrosis in kidney diseases.

NF-κB pathways in the development and progression of colorectal cancer

Nuclear factor-κB (NF-κB) has been widely implicated in the development and progression of cancer. In colorectal cancer (CRC), NF-κB has a key role in cancer-related processes such as cell proliferation, apoptosis, angiogenesis, and metastasis. The role of NF-κB in CRC is complex, owed to the cross talk with other signaling pathways. Although there is sufficient evidence gained from cell lines and animal models that NF-κB is involved in cancer-related processes, because of a lack of studies in human tissue, the clinical evidence of its importance is limited in patients with CRC. This review summarizes evidence relating to how NF-κB is involved in the development and progression of CRC and comments on future work to be carried out.

High expression of fibronectin is associated with poor prognosis, cell proliferation and malignancy via the NF-κB/p53-apoptosis signaling pathway in colorectal cancer

Fibronectin is a glycoprotein of the extracellular matrix, and regulates the processes of self-renewal and cell cycle progression. This study aimed to investigate fibronectin expression in colorectal cancer (CRC) and elucidate the effects of fibronectin on CRC by using a knockdown approach. Immunohistochemistry was used to evaluate the expression of fibronectin in 107 CRC patient tissues and gene expression was detected by real-time quantitative PCR (qPCR) and western blot analysis. Based on the above findings, the association among fibronectin expression, clinicopathological features and prognosis was analyzed. Next, fibronectin expression was silenced by small-interfering RNAs (siRNAs) and the effects of fibronectin siRNA transfection on CRC cells and tumor growth in nude mice were assessed. Expression of genes in the NF-κB/p53-apoptosis signaling pathway were analyzed after fibronectin siRNA transfection both in vitro and in vivo. Based on the results, high expression of fibronectin was observed both in the CRC tissues and CRC cell lines. The expression level was positively correlated with TNM stage (P=0.0025) and distant metastasis (P=0.0013). By Kaplan-Meier analysis, the patients with low fibronectin expression had a longer survival time comparing to those with relatively high expression. Knockdown of fibronectin suppressed SW480 cell proliferation, migration and invasion. In addition, knockdown of fibronectin led to S phase cell cycle arrest. The following study showed that the NF-κB/p53-apoptosis signaling pathway in CRC was affected by fibronectin knockdown. Tumor formation was also depressed by fibronectin siRNA transfection of CRC cells. These results showed the significant role of fibronectin in CRC tissues and cell lines. Therefore, fibronectin may be regarded as a potential target for CRC treatment.

Embryonic Lethality Due to Arrested Cardiac Development in Psip1/Hdgfrp2 Double-Deficient Mice

Hepatoma-derived growth factor (HDGF) related protein 2 (HRP2) and lens epithelium-derived growth factor (LEDGF)/p75 are closely related members of the HRP2 protein family. LEDGF/p75 has been implicated in numerous human pathologies including cancer, autoimmunity, and infectious disease. Knockout of the Psip1 gene, which encodes for LEDGF/p75 and the shorter LEDGF/p52 isoform, was previously shown to cause perinatal lethality in mice. The function of HRP2 was by contrast largely unknown. To learn about the role of HRP2 in development, we knocked out the Hdgfrp2 gene, which encodes for HRP2, in both normal and Psip1 knockout mice. Hdgfrp2 knockout mice developed normally and were fertile. By contrast, the double deficient mice died at approximate embryonic day (E) 13.5. Histological examination revealed ventricular septal defect (VSD) associated with E14.5 double knockout embryos. To investigate the underlying molecular mechanism(s), RNA recovered from ventricular tissue was subjected to RNA-sequencing on the Illumina platform. Bioinformatic analysis revealed several genes and biological pathways that were significantly deregulated by the Psip1 knockout and/or Psip1/Hdgfrp2 double knockout. Among the dozen genes known to encode for LEDGF/p75 binding factors, only the expression of Nova1, which encodes an RNA splicing factor, was significantly deregulated by the knockouts. However the expression of other RNA splicing factors, including the LEDGF/p52-interacting protein ASF/SF2, was not significantly altered, indicating that deregulation of global RNA splicing was not a driving factor in the pathology of the VSD. Tumor growth factor (Tgf) β-signaling, which plays a key role in cardiac morphogenesis during development, was the only pathway significantly deregulated by the double knockout as compared to control and Psip1 knockout samples. We accordingly speculate that deregulated Tgf-β signaling was a contributing factor to the VSD and prenatal lethality of Psip1/Hdgfrp2 double-deficient mice.

A Comparative Study of Fibronectin Cleavage by MMP-1, -3, -13, and -14

Fibronectin fragments are important for synovial inflammation and the progression of arthritis, and thus, identifying potential enzymatic pathways that generate these fragments is of vital importance. The objective of this study was to determine the cleavage efficiency of fibronectin by matrix metalloproteinases (MMP-1, MMP-3, MMP-13, and MMP-14). Intact human plasma fibronectin was co-incubated with activated MMPs in neutral or acidic pH for up to 24 hours at 37 °C. The size and distribution of fibronectin fragments were determined by Western blot analysis using antibodies that recognized the N-terminals of fibronectin. All MMPs were able to cleave fibronectin at neutral pH. MMP-13 and -14 had the highest efficiency followed by MMP-3 and -1. MMP-3, -13, and -14 generated 70-kDa fragments, a known pro-inflammatory peptide. Further degradation of fibronectin fragments was only found for MMP-13 and -14, generating 52-kDa, 40-kDa, 32-kDa, and 29-kDa fragments. Fibronectin fragments of similar size were also found in the articular cartilage of femoral condyles of normal bovine knee joints. At acidic pH (5.5), the activities of MMP-1 and -14 were nearly abolished, while MMP-3 had a greater efficiency than MMP-13 even though the activities of both MMPs were significantly reduced. These findings suggest that MMP-13 and -14 may play a significant role in the cleavage of fibronectin and the production of fibronectin fragments in normal and arthritic joints.

Experimental autoimmune encephalomyelitis (EAE) as a model for multiple sclerosis (MS)

Experimental autoimmune encephalomyelitis (EAE) is the most commonly used experimental model for the human inflammatory demyelinating disease, multiple sclerosis (MS). EAE is a complex condition in which the interaction between a variety of immunopathological and neuropathological mechanisms leads to an approximation of the key pathological features of MS: inflammation, demyelination, axonal loss and gliosis. The counter-regulatory mechanisms of resolution of inflammation and remyelination also occur in EAE, which, therefore can also serve as a model for these processes. Moreover, EAE is often used as a model of cell-mediated organ-specific autoimmune conditions in general. EAE has a complex neuropharmacology, and many of the drugs that are in current or imminent use in MS have been developed, tested or validated on the basis of EAE studies. There is great heterogeneity in the susceptibility to the induction, the method of induction and the response to various immunological or neuropharmacological interventions, many of which are reviewed here. This makes EAE a very versatile system to use in translational neuro- and immunopharmacology, but the model needs to be tailored to the scientific question being asked. While creating difficulties and underscoring the inherent weaknesses of this model of MS in straightforward translation from EAE to the human disease, this variability also creates an opportunity to explore multiple facets of the immune and neural mechanisms of immune-mediated neuroinflammation and demyelination as well as intrinsic protective mechanisms. This allows the eventual development and preclinical testing of a wide range of potential therapeutic interventions.

Loss of protein kinase Cϵ results in impaired cutaneous wound closure and myofibroblast function

Cutaneous wound repair requires the de novo induction of a specialized form of fibroblast, the α-smooth muscle actin (α-SMA)-expressing myofibroblast, which migrates into the wound where it adheres to and contracts extracellular matrix (ECM), resulting in wound closure. Persistence of the myofibroblast results in scarring and fibrotic disease. In this report, we show that, compared with wild-type littermates, PKCϵ-/- mice display delayed impaired cutaneous wound closure and a reduction in myofibroblasts. Moreover, both in the presence and absence of TGFβ, dermal fibroblasts from PKCϵ-/- mice cultured on fibronectin show impaired abilities to form `supermature' focal adhesions and α-SMA stress fibers, and reduced pro-fibrotic gene expression. Smad3 phosphorylation in response to TGFβ1 was impaired in PKCϵ-/- fibroblasts. PKCϵ-/- fibroblasts show reduced FAK and Rac activation, and adhesive, contractile and migratory abilities. Overexpressing constitutively active Rac1 rescues the defective FAK phosphorylation, cell migration, adhesion and stress fiber formation of these PKCϵ-/- fibroblasts, indicating that Rac1 operates downstream of PKCϵ, yet upstream of FAK. These results suggest that loss of PKCϵ severely impairs myofibroblast formation and function, and that targeting PKCϵ may be beneficial in selectively modulating wound healing and fibrotic responses in vivo.

Transforming growth factor beta (TGF-beta) and autoimmunity

TGF-beta1 deficient mice develop multifocal inflammatory autoimmune disease and serve as a valuable animal model of autoimmunity. Transgenic expression of a dominant negative form of TGF-beta receptor type II in T cells have enabled the study of cell lineage specific effects of TGF-beta providing clues to the potential etiology of autoimmunity. These studies suggest that TGF-beta deficiency may induce autoimmune disease by influencing a number of immunological phenomena including lymphocyte activation and differentiation, cell adhesion molecule expression, regulatory T cell function, the expression of MHC molecules and cytokines, and cell apoptosis. The spectrum of effects appears to be significant in mucosal immunity and may contribute to the pathogenesis of inflammatory bowel disease.

Identification of fibronectin neoepitopes present in human osteoarthritic cartilage

OBJECTIVE

Fibronectin fragments are present at high concentrations in the cartilage of patients with rheumatoid arthritis and patients with osteoarthritis (OA) and have been shown to promote cartilage catabolism in human cartilage cultures, suggesting that fibronectin fragments participate in the initiation and progression of arthritic disease. This study was undertaken to 1) identify the major fibronectin fragments in human OA cartilage and confirm their ability to elicit cartilage catabolism, 2) identify the cleavage sites in fibronectin and generate the corresponding neoepitope antibodies, and 3) explore the utility of fibronectin neoepitopes as biomarkers.

METHODS

Fibronectin fragments were purified from human OA cartilage using affinity chromatography; their N-termini were then identified by sequencing. Bovine nasal cartilage was treated with affinity-purified fibronectin fragments and assayed for aggrecan breakdown by monitoring the release of glycosaminoglycans and the aggrecan neoepitope 1771AGEG. Fibronectin neoepitopes were detected by Western blotting in cytokine-treated media of human cartilage explants, and by immunohistochemical analyses of human OA cartilage.

RESULTS

Multiple fibronectin fragments were isolated from human OA cartilage, and all contained the N-terminus 272VYQP. These fragments induced aggrecanase-mediated cartilage catabolism in bovine cartilage explants. Fibronectin fragments with the N-terminus 272VYQP and fragments with the C-terminus VRAA271 were detected following cytokine treatment of human cartilage extracts. These neoepitopes localized with areas of aggrecan loss in OA cartilage.

CONCLUSION

Human OA cartilage contains fibronectin fragments with catabolic activity and a major cleavage site within fibronectin. This study is the first to characterize fibronectin neoepitopes in OA cartilage, suggesting that they may represent a novel biomarker of arthritis.

Aberrant Toll Receptor Expression and Endotoxin Hypersensitivity in Mice Lacking a Functional TGF-β1 Signaling Pathway

TGF-beta1 plays a central role in maintaining normal immune function and deficiency of this potent immunosuppressive molecule is linked to uncontrolled inflammation, cachexia, and multiorgan failure as seen in the TGF-beta1 null mouse. Infiltration of inflammatory cells into vital organs of the null mouse is accompanied by increased gene expression of inflammatory cytokines, including TNF-alpha and IL-1beta, as well as inducible NO synthase, each regulated by NF-kappaB. Treatment with the proteasome inhibitor MG132 to prevent NF-kappaB activation dramatically reduced NO production and expression of inflammatory cytokines. This inflammatory phenotype with NF-kappaB activation in the TGF-beta1 null mouse, in the absence of any identifiable pathogen, suggested activation of innate immune responses. Because Toll-like receptors (TLR) are essential in the activation of innate immunity, we examined inflamed tissue from TGF-beta1 null and wild-type mice for expression of TLR4, the receptor that interacts with bacterial cell wall LPS to initiate an NF-kappaB-dependent signaling pathway, leading to gene transcription of inflammatory mediators. Increased TLR4 mRNA expression observed in TGF-beta1 null mice as well as in mice lacking the TGF-beta transcription factor Smad3 was associated with LPS hyperresponsiveness leading to increased expression of inflammatory cytokines and NO and endotoxemia. Furthermore, mice lacking both TGF-beta1 and a functional TLR4 were resistant to endotoxin shock. Constitutive and/or environmental activation of TLR4 and downstream elements, in the absence of TGF-beta suppression, may impact on innate and adaptive immunity and contribute to massive uncontrolled inflammation.

Genetically altered mouse models: the good, the bad, and the ugly

Targeted gene disruption in mice is a powerful tool for generating murine models for human development and disease. While the human genome program has helped to generate numerous candidate genes, few genes have been characterized for their precise in vivo functions. Gene targeting has had an enormous impact on our ability to delineate the functional roles of these genes. Many gene knockout mouse models faithfully mimic the phenotypes of the human diseases. Because some models display an unexpected or no phenotype, controversy has arisen about the value of gene-targeting strategies. We argue in favor of gene-targeting strategies, provided they are used with caution, particularly in interpreting phenotypes in craniofacial and oral biology, where many genes have pleiotropic roles. The potential pitfalls are outweighed by the unique opportunities for developing and testing different therapeutic strategies before they are introduced into the clinic. In the future, we believe that genetically engineered animal models will be indispensable for gaining important insights into the molecular mechanisms underlying development, as well as disease pathogenesis, diagnosis, prevention, and treatment.

TGF-beta 1 regulates lymphocyte homeostasis by preventing activation and subsequent apoptosis of peripheral lymphocytes

TGF-beta1 plays an important role in the maintenance of immune homeostasis and self-tolerance. To determine the mechanism by which TGF-beta1 prevents autoimmunity we have analyzed T cell activation in splenic lymphocytes from TGF-beta1-deficient mice. Here we demonstrate that unlike wild-type splenic lymphocytes, those from Tgfb1(-/-) mice are hyporesponsive to receptor-mediated mitogenic stimulation, as evidenced by diminished proliferation and reduced IL-2 production. However, they have elevated levels of IFN-gamma and eventually undergo apoptosis. Receptor-independent stimulation of Tgfb1(-/-) T cells by PMA plus ionomycin induces IL-2 production and mitogenic response, and it rescues them from anergy. Tgfb1(-/-) T cells display decreased CD3 expression; increased expression of the activation markers LFA-1, CD69, and CD122; and increased cell size, all of which indicate prior activation. Consistently, mutant CD4(+) T cells have elevated intracellular Ca(2+) levels. However, upon subsequent stimulation in vitro, increases in Ca(2+) levels are less than those in wild-type cells. This is also consistent with the anergic phenotype. Together, these results demonstrate that the ex vivo proliferative hyporesponsiveness of Tgfb1(-/-) splenic lymphocytes is due to prior in vivo activation of T cells resulting from deregulated intracellular Ca(2+) levels.

TGF beta 1 inhibits Ca2+-calcineurin-mediated activation in thymocytes

TGFbeta1 is a polypeptide growth modulatory and differentiation factor involved in many biological processes including immune homeostasis and self-tolerance. Tgfb1 knockout mice die around weaning age due to severe inflammation in most major organ systems, but the mechanism underlying this disease is not understood. In this study we demonstrate that Tgfb1(-/-) CD4(+)CD8(+) and CD4(+)CD8(-) thymocytes are hyperresponsive to receptor-mediated and receptor-independent mitogenic stimulation. A suboptimal concentration of ionomycin in the presence of PMA fully activates Tgfb1(-/-) thymocytes, whereas the inhibitors of Ca(2+) influx and calcineurin, EGTA and FK506, eliminate the hyperresponsiveness. Hence, the hypersensitivity of Tgfb1(-/-) thymocytes is due to a lowered threshold for Ca(2+)-dependent activation. Further, we demonstrate that the hypersensitivity of thymocytes results from the absence of TGFbeta1 and not from the inflammatory environment because the thymocytes are hyperresponsive in preinflammatory-stage Tgfb1(-/-) mice. Our results suggest for the first time that TGFbeta1 functions to inhibit aberrant T cell expansion by maintaining intracellular calcium concentration levels low enough to prevent a mitogenic response by Ca(2+)-independent stimulatory pathways alone. Consequently, TGFbeta1 prevents autoimmune disease through a Ca(2+) regulatory pathway that maintains the activation threshold above that inducible by self-MHC-TCR interactions.

Effects of transforming growth factor-beta deficiency on bone development: a Fourier transform-infrared imaging analysis

Transforming growth factor-beta 1 (TGF-beta1) is a cytokine member of the TGF-beta superfamily involved in the control of proliferation and differentiation of various cell types. TGF-beta1 plays an important role in bone formation and resorption. To determine the effect of TGF-beta1 deficiency on bone mineral and matrix, tibias from mice in which TGF-beta1 expression had been ablated (TGF-beta1 null) were analyzed and compared with background- and age-matched wild-type (WT) control animals by Fourier transform-infrared imaging (FTIRI) and histochemistry. FTIRI allows the characterization of nondemineralized thin tissue sections at the ultrastructural level with a spatial resolution of approximately 7 microm. The spectroscopic parameters calculated were: mineral-to-matrix ratio (previously shown to correspond to ash weight); mineral crystallinity (related to the crystallographically determined crystallite size and perfection in the apatite c-axis direction); and collagen maturity (related to the ratio of pyridinoline:deH-DHLNL collagen cross-links). Several fields were selected to represent different stages of bone development within the same specimen from the secondary ossification center to the distal diaphysis. Anatomically equivalent areas were compared as a function of age and genotype. The spectroscopic results were expressed both as color-coded images and as pixel population distributions for each of the three parameters monitored. Based on comparisons of histochemistry and FTIRI, there were distinctive age and genotype variations. At all ages examined, in the TGF-beta1 null mice growth plates, alkaline phosphatase (ALP) activity and collagen maturity were reduced, but no effect on mineral content or crystallinity was noted. In the TGF-beta1 null mice metaphyses, there was a persistence of trabeculae, but no significant alterations in mineral content or crystallinity. In contrast, mineral content, mineral crystallinity, and collagen maturity were reduced in the secondary ossification center and cortical bone of the TGF-beta1 null mice. These results, consistent with a mechanism of impaired bone maturation in the TGF-beta1 null mice, may be directly related to TGF-beta1 deficiency and indirectly to increased expression of inflammatory cytokines in the TGFbeta1 null mice.

Dysregulation of IFN-gamma signaling pathways in the absence of TGF-beta 1

Deficiency of TGF-beta1 is associated with immune dysregulation and autoimmunity as exemplified by the multifocal inflammatory lesions and early demise of the TGF-beta1 null mice. Elevated NO metabolites (nitrite and nitrate) in the plasma of these mice suggest a participatory role of NO in the pathogenic inflammatory response. To determine the mechanism for this dysregulation, we examined upstream elements that could contribute to the overexpression of NO, including inducible NO synthase (iNOS) and transcription factors Stat1alpha and IFN-regulatory factor-1 (IRF-1). The coincident up-regulation of IFN-gamma, an iNOS inducer, and iNOS, before the appearance of inflammatory lesions, suggests that failed regulation of the IFN-gamma signaling pathway may underlie the immunological disorder in TGF-beta1 null mice. In fact, IFN-gamma-driven transcription factors IRF-1 and Stat1alpha, both of which act as transcriptional activators of iNOS, were elevated in the null mice. Treatment of mice with a polyclonal anti-IFN-gamma Ab reduced expression and activity not only of transcription factors Stat1alpha and IRF-1 but also of iNOS. Furthermore, anti-IFN-gamma treatment delayed the cachexia normally seen in TGF-beta1 null mice and increased their longevity. The global nature of immune dysregulation in TGF-beta1 null mice documents TGF-beta1 as an essential immunoregulatory molecule.

Endocrine expression of the active form of TGF-beta1 in the TGF-beta1 null mice fails to ameliorate lethal phenotype

TGF-beta1 null mice die by 3 to 4 weeks of age due to a severe autoimmune-mediated multifocal inflammation resulting in multi-organ failure. To assess the therapeutic potential of circulating levels of active TGF-beta1, we generated mice with endocrine expression of active TGF-beta1 on a TGF-beta1 null background (TGF-beta1 (-/-/TG)) by crossing TGF-beta1(+/-) mice with transgenic mice (TG) that express recombinant TGF-beta1 specifically in the liver and secrete it in the blood. The TGF-beta1 (-/-/TG) mice exhibit a survival profile similar to the TGF-beta1 (-/-) mice indicating a failure to rescue the lethal phenotype. However, serum TGF-beta1 levels in the TGF-beta1 (-/-/TG) mice were restored to near normal levels with expression in all the tissues, notably in the kidney and spleen. Histopathology showed reduced inflammation in the target tissues, especially in the heart. Interestingly, unlike TGF-beta1 (-/-) mice, the TGF-beta1 (-/-/TG) mice have glomerulonephritis in their kidneys similar to the TG mice. Thus, the phenotype of TGF-beta1 (-/-/TG) animal model indicates the potential role of circulating active-TGF-beta1 in reducing inflammation, but its failure to rescue lethality in TGF-beta1 null mice indicates a critical autocrine role of TGF-beta1.

alpha(4)beta(1) Integrin activation of L-type calcium channels in vascular smooth muscle causes arteriole vasoconstriction

A pathway for the regulation of vascular tone appears to involve coupling between integrins and extracellular matrix proteins or their fragments and the subsequent modulation of ion movement across the smooth muscle cell membrane. Here, we report that the activation of L-type voltage-activated Ca(2+) channels occurs through a novel interaction of alpha(4)beta(1) integrin with peptides containing the Leu-Asp-Val (LDV) integrin--binding sequence, which is found in the CS-1 region of an alternately spliced fibronectin variant. Experiments were conducted on arterioles isolated from rat skeletal muscle. Arterioles exhibited sustained concentration-dependent vasoconstriction to LDV peptides but not to Leu-Glu-Val (LEV) control peptides. The constriction was associated with increased smooth muscle cell [Ca(2+)](i), as measured by using fura 2. The response could be inhibited with a function-blocking anti--alpha(4) integrin antibody. Removal of the endothelium did not alter the vasoconstrictor response. Further experiments demonstrated that the vasoconstriction was abolished by the L-type Ca(2+) channel inhibitor nifedipine and the Src family kinase inhibitor PP2. In studies of isolated smooth muscle cells using whole-cell patch-clamp methods, the L-type current was enhanced by the LDV but not LEV peptide and was blocked by PP2 or antibodies to alpha(4) integrin. Collectively, these data indicate that activation of alpha(4)beta(1) integrin leads to enhanced influx of Ca(2+) through L-type channels by activating a tyrosine kinase pathway, leading to vasoconstriction. Involvement of integrins in the modulation of vascular tone may be particularly important in vascular responses to mechanical signals, such as pressure and flow, and to tissue injury after damage to the extracellular matrix.

TGF-beta1 null mutation leads to CD154 upregulated expression in affected tissues

The TGF-beta1(-/-) mouse is a murine model for systemic autoimmune disease. The aim of this study is to elucidate the immunological mechanism that leads to multifocal tissue inflammation and autoantibody production in TGF-beta1(-/-) mice. Heart, lung, liver, and salivary gland from TGF-beta1(-/-) were assessed for CD154 expression by RT-PCR and immunohistochemistry. Compared to wild-type littermates, CD154 expression was elevated in all tissues studied. Furthermore, IL-12 mRNA was expressed in the salivary gland and heart of TGF-beta1(-/-) mice and not in wild-type littermates. This suggests that the CD154 pathway is activated in these tissues. This shows that TGF-beta1 regulates CD154 expression leading to spontaneous IL-12 production and autoimmunity.

Activation of beta(1) integrins mediates proliferation and inhibits apoptosis of intestinal CD4-positive lymphocytes

A characteristic of lamina propria lymphocytes (LPL) is their low proliferative response to stimuli of the CD3 pathway. beta(1) integrins were expressed on LPL; however, their function is unknown. Therefore, we determined whether beta(1) integrins contribute to T cell responses by providing costimulatory signals. Integrins on CD4(+) LPL of controls and patients with inflammatory bowel disease were characterized by flow cytometry. Cells were stimulated by anti-CD3 or anti-CD2 antibodies either alone or in combination with a stimulatory beta(1) integrin antibody (12G10). Proliferation and apoptosis were measured by [(3)H]thymidine pulsing or flow cytometry. Cytokine mRNA and apoptosis-related transcripts were quantified by reverse transcriptase-PCR. We demonstrated that beta(1) integrin costimulation restored CD3-induced proliferation of CD4(+) LPL and reduced activation-induced apoptosis. Activation of beta(1) integrins by addition of 12G10 antibody to CD3-stimulated cells restored their capacity to express proinflammatory cytokine transcripts. Further, expression of the activated form of beta(1) integrins was significantly elevated on LPL from inflamed mucosa. These studies demonstrate that beta(1) integrin costimulation modulates the response of LPL after TCR stimulation. An increased expression of activated beta(1) integrins on LPL in intestinal inflammation may abolish their unresponsiveness to antigens and perpetuate the inflammatory process.

Enhancement of nigral graft survival in rat brain with the systemic administration of synthetic fibronectin peptide V

A major obstacle in neural transplantation is a severe loss of neurons in grafts soon after implantation. In the present study, we have investigated whether the systemic administration of synthetic fibronectin peptide V can increase the survival of neural grafts. Synthetic fibronectin peptide V is derived from the 33,000 mol. wt carboxyl-terminal heparin-binding domain of fibronectin. Previous studies have shown that these polypeptides possess anti-inflammatory properties. However, it is currently unknown whether this peptide has anti-apoptotic properties. Dissociated neural grafts were prepared from the ventral mesencephalon of pregnant Sprague-Dawley rats and were stereotaxically injected as a cell suspension into the striatum of adult Sprague-Dawley rats. A group of recipient rats received i.v. injections of peptide V (5mg/kg, dissolved in saline) at 24 and 4h prior to transplantation, at the time of transplantation, and 24, 48 and 72h post-transplantation. Saline-treated rats served as controls. The rats were killed at two, four and 42 days post-grafting and the brain tissue was immunologically processed for tyrosine-hydroxylase, major histocompatibility complex class I and class II antigens, complement receptor type 3 and leukocyte common antigen immunocytochemistry, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling assay. We found a significant increase (approximately twofold) in the number of dopamine neurons in the grafts for the peptide-treated group at four and 42 days compared with the controls. In contrast, there was no significant difference in the patterns of inflammation using different immunocytochemical markers in the two different groups. The levels of expression for these markers, however, were reduced over time. Interestingly, the number of apoptotic cells in the graft areas was significantly smaller in the peptide-treated group than in the control group two days after grafting. The results demonstrate that the systemic administration of synthetic fibronectin peptide V can dramatically increase the survival of nigral grafts in the brain and substantially reduce the number of apoptotic cells in the graft site, suggesting that this peptide may exert a beneficial effect on survival of nigral grafts through an anti-apoptotic mechanism.

Fibronectin-mononuclear cell interactions regulate type 1 helper T cell cytokine network in tolerant transplant recipients

Fibronectin (FN), expressed primarily by macrophages, endothelial cells, and smooth muscle cells, represents an integral feature of the rejection response in transplant recipients. Here we demonstrate a unique pattern of cellular FN expression in rat recipients of cardiac allografts rendered tolerant in an infectious manner with either nondepleting CD4 mAb or regulatory spleen cells. Unlike in rejecting controls, cellular FN in tolerant hosts was restricted to the graft vessels and no vascular cell adhesion molecule-1 or intercellular adhesion molecule-1 expression could be found, supporting the role of FN in leukocyte sequestration at the graft site. The lack of myocardial FN in tolerant rats, despite dense macrophage infiltration, correlated with profound depression of Th1 (interleukin-2 and interferon-gamma) cytokines. Treatment with CD4-depleting mAb prevented tolerance induction and restored myocardial expression of FN in parallel with marked increase in the expression of interleukin-2 and interferon-gamma mRNA/protein. Furthermore, connective segment-1 peptide-facilitated adjunctive blockade of FN-alpha4beta1 interactions in recipients conditioned with CD4 depleting mAb, significantly depressed intragraft expression of interleukin-2 and interferon-gamma mRNA/protein. Hence, the lack of FN associated with infiltrating leukocytes plays an important role in the maintenance of tolerance in transplant recipients by depressing local expression of Th1 cytokines that otherwise facilitate acute graft rejection.

Disruption of T cell homeostasis in mice expressing a T cell-specific dominant negative transforming growth factor beta II receptor

The immune system, despite its complexity, is maintained at a relative steady state. Mechanisms involved in maintaining lymphocyte homeostasis are poorly understood; however, recent availability of transgenic (Tg) and knockout mouse models with altered balance of lymphocyte cell populations suggest that cytokines play a major role in maintaining lymphocyte homeostasis. We show here that transforming growth factor (TGF)-beta plays a critical role in maintaining CD8(+) T cell homeostasis in a Tg mouse model that specifically overexpresses a dominant negative TGF-beta II receptor (DNRII) on T cells. DNRII T cell Tg mice develop a CD8(+) T cell lymphoproliferative disorder resulting in the massive expansion of the lymphoid organs. These CD8(+) T cells are phenotypically "naive" except for the upregulation of the cell surface molecule CD44, a molecule usually associated with memory T cells. Despite their dominance in the peripheral lymphoid organs, CD8(+) T cells appear to develop normally in the thymus, suggesting that TGF-beta exerts its homeostatic control in the peripheral immune system.

TGF-beta influences the life and death decisions of T lymphocytes

TGF-beta is a powerful mediator of immune cell phenotype and function. In TGF-beta1 homozygous null mice, aberrant regulation of the immune response culminates in lethal cardiopulmonary inflammation. In dissecting the underlying mechanisms leading to the attack of self, a role for TGF-beta1 in controlling apoptosis and T cell selection patterns was uncovered. Increased levels of apoptosis and TCR mediated cell death disrupted normal negative and positive T cell selection in the thymus. Moreover, in peripheral T cell populations, increased T lymphocyte death was associated with increased expression of apoptosis-inducing receptors. Persistent activation of T cells engendered unchecked apoptosis which, rather than reducing, further exacerbated, tissue inflammation due to the absence of TGF-beta1. TGF-beta, normally generated by macrophages during clearance of apoptotic cells contributes to dampening of inflammatory sequelae associated with phagocytosis. Collectively, these data demonstrate a pivotal role for TGF-beta in multiple stages of T cell apoptosis, selection, activation and clearance.

The inhibitory effects of transforming growth factor-beta-1 (TGF-beta1) in autoimmune diseases

The importance of transforming growth factor-beta-1 (TGF-beta1) in immunoregulation and tolerance has been increasingly recognized. It is now proposed that there are populations of regulatory T cells (T-reg), some designated T-helper type 3 (Th3), that exert their action primarily by secreting this cytokine. Here, we emphasize the following concepts: (1) TGF-beta1 has multiple suppressive actions on T cells, B cells, macrophages, and other cells, and increased TGF-beta1 production correlates with protection and/or recovery from autoimmune diseases; (2) TGF-beta1 and CTLA-4 are molecules that work together to terminate immune responses; (3) Th0, Th1 and Th2 clones can all secrete TGF-beta1 upon cross-linking of CTLA-4 (the functional significance of this in autoimmune diseases has not been reported, but TGF-beta1-producing regulatory T-cell clones can produce type 1 inflammatory cytokines); (4) TGF-beta1 may play a role in the passage from effector to memory T cells; (5) TGF-beta1 acts with some other inhibitory molecules to maintain a state of tolerance, which is most evident in immunologically privileged sites, but may also be important in other organs; (6) TGF-beta1 is produced by many cell types, is always present in the plasma (in its latent form) and permeates all organs, binding to matrix components and creating a reservoir of this immunosuppressive molecule; and (7) TGF-beta1 downregulates adhesion molecules and inhibits adhesion of leukocytes to endothelial cells. We propose that rather than being passive targets of autoimmunity, tissues and organs actively suppress autoreactive lymphocytes. We review the beneficial effects of administering TGF-beta1 in several autoimmune diseases, and show that it can be effectively administered by a somatic gene therapy approach, which results in depressed inflammatory cytokine production and increased endogenous regulatory cytokine production.

Transforming growth factor-beta1 regulates basement membrane formation by alveolar epithelial cells in vitro

Immortalized alveolar type II epithelial (SV40-T2) cells formed a continuous, thin lamina densa when they were cultured on collagen fibrils with the supplement of 1.0 ng/ml TGF-beta1. Corresponding to lamina densa formation, immunohistochemical analysis of laminin, type IV collagen, perlecan, and entactin (nidogen) indicated integration of these components in a linear array beneath the SV40-T2 cells. Synthesis of these basement membrane constituents was significantly enhanced by TGF-beta1 in a dose-dependent manner. On the other hand, TGF-beta1 did not affect the synthesis of extracellular matrix-regulatory enzymes and their inhibitors, such as type II transglutaminase, matrix metalloproteinase-2, plasminogen activator inhibitor-1, or tissue inhibitor of matrix metalloproteinase-1. These results indicate that basement membrane formation in the presence of 1.0 ng/ml TGF-beta1 is attributable to enhanced synthesis of basement membrane constituents. However, formation of a continuous basement membrane was inhibited at a TGF-beta1 concentration of 5.0 ng/ml. Synthesis of the basement membrane constituents was further enhanced at this concentration and the extracellular matrix-regulatory enzymes remained unchanged. The deposits of cellular fibronectin and type I collagen beneath SV40-T2 cells were significantly augmented. Thus excessive production of interstitial extracellular matrix components appears to obstruct the integration of basement membrane constituents into a continuous architecture. These results indicate that the basement membrane formation by SV40-T2 cells is achieved at the optimal TGF-beta1 concentration.

Bidirectional regulation of macrophage function by TGF-beta

The dual role of transforming growth factor-beta (TGF-beta) in modulating macrophage function is an important concept gaining increasing recognition. In addition to its role as a 'macrophage-deactivating' agent, TGF-beta functions as a monocyte activator, inducing cytoke production and mediating host defence. These functions are context-dependent, modulated by the differentiation state of the cell, the local cytokine environment, and the local levels of TGF-beta in itself. In general, during the initial stages of inflammation, TGF-beta locally acts as a proinflammatory agent by recruiting and activating resting monocytes. As these cells differentiate specific immunosuppressive actions of TGF-beta predominate, leading to resolution of the inflammatory response. Increasing our understanding of the bidirectional regulation of macrophage function will facilitate prediction of the ultimate outcome of modulating TGF-beta levels in vivo.

β2-Microglobulin-Deficient Background Ameliorates Lethal Phenotype of the TGF-β1 Null Mouse

TGF-β1 null (TGF-β1−/−) mice die at 3–4 wk of age and show an autoimmune inflammatory phenotype associated with enhanced expression of both class I and II MHC molecules. To determine the role of MHC class I Ags in the autoimmune manifestations and the inflammation observed in TGF-β1−/− mice, we generated TGF-β1−/− mice in the genetic background of β2-microglobulin deficiency (β2M−/−). TGF-β1−/−;β2M−/− mice had improved survival compared with TGF-β1−/− mice. Histopathological examination showed less severe inflammation, especially in the heart, where Mac-2 reactive macrophages were significantly decreased as compared with TGF-β1−/− mice. In vivo depletion of CD8+ T cells in TGF-β1−/− mice confirmed suppression of inflammation and reduction in the severity of the wasting syndrome. MHC class II mRNA expression in TGF-β1−/−;β2M−/− mice was also lower than that in TGF-β1−/− mice, suggesting reduced systemic inflammation. Autoimmune response as judged by serum Ab titers to ssDNA and 16/6 Id and by immune complex deposits in kidney was reduced in TGF-β1−/−;β2M−/− mice, when compared with that in TGF-β1−/− mice. Our data thus indicate that MHC class I molecules influence the development of the autoimmunity and the inflammation seen in TGF-β1−/− mice and CD8+ T cells may have a contribution to the inflammation in TGF-β1−/− mice.

Dependence of neurones on astrocytes in a coculture system renders neurones sensitive to transforming growth factor beta1-induced glutamate toxicity

Transforming growth factor beta1 (TGF-beta1) has been implicated in formation of astrocyte scars, which prevents axonal regeneration. A coculture system of astrocytes and cerebellar cells was used to investigate possible neurotoxic effects of TGF-beta1. Although not directly neurotoxic, TGF-beta1 was toxic to cerebellar cells in the presence of astrocytes. This toxicity is based on an effect of the cytokine on astrocytes, as conditioned medium from astrocyte cultures treated with TGF-beta1 was more toxic by a similar mechanism. This neurotoxicity was mediated by glutamate present in the culture medium as demonstrated by inhibition by MK-801. Astrocytic ability to metabolise glutamate was compromised by TGF-beta1, as this cytokine increased glutamate concentration. The astrocytes in the coculture system responded to the presence of neurones by secreting neuroprotective interleukin-6, which was partly protective against the TGF-beta1-induced toxicity. In the coculture system, neurones responded to the presence of astrocytes by a reduction in resistance to glutamate toxicity. On addition of TGF-beta1, which compromised astrocytic clearance of glutamate, this reduction in resistance to glutamate toxicity led to a reduction in neuronal survival. These results suggest that when neurones are cocultured with astrocytes they become dependent on astrocytes for survival. This dependence makes neurones susceptible to damage when astrocytes are activated by substances such as TGF-beta1.

TGF-beta: a balancing act

Regulation of developmental processes as well as host defense and repair mechanisms requires the maintenance of a delicate balance of positive and negative regulatory signals. TGF-beta, a molecule known for its many diverse activities, can promote or inhibit cell growth and function. Disruption of the balance between these opposing activities can contribute to aberrant development, malignancy, or pathogenic immune and inflammatory responses. TGF-beta transgenic mouse studies highlight the essential function(s) of TGF-beta and its receptors and provide insight to potential therapeutic approaches to manipulate TGF-beta expression.

Induction of Oral Tolerance in TGF-β1 Null Mice

Previous studies have suggested that oral tolerance induction by low doses of Ag is mediated by inhibitory cytokines, particularly TGF-β1. To examine the roles of TGF-β1 and other inhibitory cytokines in the induction of oral tolerance, TGF-β1 null mice and controls were gavaged with 10 to 20 mg (high dose) or 1 mg (low dose) of OVA for 3 days. After immunization with OVA, the in vitro proliferative response of OVA-specific popliteal lymph node cells was assessed. Lymphocytes from all TGF-β1 null mice fed high doses of OVA exhibited highly significant suppression compared with controls. A weaker, but still significant, suppression was observed in lymphocytes from the majority of TGF-β1 null mice fed low doses of OVA. In addition, supernatants from these lymphocytes exhibited lower levels of IL-4, IL-10, and IFN-γ than those from water-fed control animals. These results indicate that while TGF-β1 may play a role in suppression, inhibitory cytokines are not the exclusive mechanism by which low dose oral tolerance is induced.

Regulation of immune responses by TGF-beta

The transforming growth factor beta (TGF-beta) family of proteins are a set of pleiotropic secreted signaling molecules with unique and potent immunoregulatory properties. TGF-beta 1 is produced by every leukocyte lineage, including lymphocytes, macrophages, and dendritic cells, and its expression serves in both autocrine and paracrine modes to control the differentiation, proliferation, and state of activation of these immune cells. TGF-beta can modulate expression of adhesion molecules, provide a chemotactic gradient for leukocytes and other cells participating in an inflammatory response, and inhibit them once they have become activated. Increased production and activation of latent TGF-beta have been linked to immune defects associated with malignancy and autoimmune disorders, to susceptibility to opportunistic infection, and to the fibrotic complications associated with chronic inflammatory conditions. In addition to these roles in disease pathogenesis, TGF-beta is now established as a principal mediator of oral tolerance and can be recognized as the sine qua non of a unique subset of effector cells that are induced in this process. The accumulated knowledge gained through extensive in vitro functional analyses and from in vivo animal models, including newly established TGF-beta gene knockout and transgenic mice, supports the concept that clinical therapies based on modulation of this cytokine represent an important new approach to the treatment of disorders of immune function.

Blockade of very late antigen-4 integrin binding to fibronectin in allograft recipients. II. Treatment with connecting segment-1 peptides prevents chronic rejection by attenuating arteriosclerotic development and suppressing intragraft T cell and macrophage activation

BACKGROUND

Chronic rejection remains the leading obstacle to long-term allograft survival. We have shown that treatment of sensitized rats with rapamycin (RPM) does not prevent progressive chronic-type cardiac allograft failure. Having documented the role of fibronectin (FN) in the allograft rejection cascade, we hypothesized that treatment with synthetic peptides that specifically block adhesive interactions between the connecting segment-1 (CS1)-binding domain of FN and alpha4beta1 integrin on circulating cells may prevent the development of chronic rejection in transplant recipients.

METHODS AND RESULTS

Lewis rats were sensitized with Brown Norway skin grafts (day -7), followed by transplantation of LBNF1 hearts (day 0). Experimental animals were treated with RPM (day -7 to -1; 0.25 mg/kg/day i.p.), or RPM + CS1 peptides (day +7 to +13; 4 mg/kg/day i.v.), and euthanized at day 60. Unlike cardiac allografts in rats undergoing RPM monotherapy, those after adjunctive CS1 peptides had well preserved myocardial architecture and were free of arteriosclerotic lesions. Moreover, reverse transcription-polymerase chain reaction-based intragraft expression of transcripts for CD3, interferon-gamma, interleukin-12, monocyte chemoattractant protein-1, and transforming growth factor-beta were diminished in the CS1 group when compared with levels in the RPM group. The corresponding expression of cytokine proteins, as determined by immunoperoxidase labeling, was also depressed and correlated with decreased infiltration by T cells and macrophages.

CONCLUSION

CS1 peptide-facilitated blockage of alpha4beta1-FN interactions prevents the development of chronic rejection and depresses the expression of key T cell- and macrophage-associated cytokines/chemoattractants. Hence, local synthesis of FN is an ongoing feature of, and adhesive FN-alpha4beta1 associations are critical for, the development of chronic transplant rejection.

Blockade of very late antigen-4 integrin binding to fibronectin in allograft recipients: I. Treatment with connecting segment-1 peptides prevents acute rejection by suppressing intragraft mononuclear cell accumulation, endothelial activation, and cytokine expression

BACKGROUND

Allograft rejection is associated with infiltration of inflammatory cells and local deposition of fibronectin (FN). This study was carried out to examine the hypothesis that peptides known to specifically block adhesive interactions between the connecting segment-1 (CS1)-binding domain of FN and alpha4beta1 integrin on circulating cells may interfere with the immune cascade, which would lead to acute rejection in transplant recipients.

METHODS AND RESULTS

Cardiac allografts from Lewis x Brown Norway F1 hybrids were rejected in 7+/-1 days in Lewis rats. Treatment with bioactive CS1 peptides (4 mg/kg/day i.v. for 7 days) abrogated acute rejection and prolonged cardiac allograft survival to 13+/-1 days (P<0.001). This effect correlated with decreased expression of total fibronectin and cell adhesion molecules, such as alpha4beta1, vascular cell adhesion molecule-1, intercellular adhesion molecule-1, as well as reduced infiltration by CD4+ and CD8+ T cells at the graft site. Treatment with CS1 peptides decreased alloantigen activation, as evidenced by decreased intragraft infiltration by CD25+ cells, and diminished expression of mRNA coding for Th1 (interleukin [IL]-2, interferon-gamma)- and Th2 (IL-4, IL-5, IL-6)-type cytokines. CS1-mediated immunosuppressive effects could be reversed and acute rejection recreated after adjunctive treatment of rats with recombinant IL-2.

CONCLUSION

Our data are consistent with the model in which in vivo interaction between the alpha4beta1 integrin receptor and the cell-associated CS1 motif of FN is critical for rejection cascade. The novel therapeutic approach of selectively blocking the alpha4beta1-FN activation pathway with CS1 peptides prevents acute allograft rejection by inhibiting expansion of antigen-specific T cells and inducing a transient state of cytokine-responsive anergy in the residual T-cell population.

Effects of pravastatin on chronic rejection of rat cardiac allografts

BACKGROUND

Pravastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, inhibits coronary transplant vasculopathy in the clinical setting. To further delineate the immune modulatory effect of this agent, it was tested in a rat cardiac transplant model of chronic rejection.

METHODS

Rat heterotopic abdominal cardiac transplants were performed using a Lewis to Fischer 344 combination. Fischer 344 recipients received a brief course of cyclosporine to decrease the incidence of acute rejection. Experimental groups were treated with either high-dose (10 mg/kg) or low-dose (5 mg/kg) pravastatin for 120 days, while a control group did not receive pravastatin. The effect of pravastatin on chronic rejection of cardiac allografts was analyzed by histology, and the expression of laminin, fibronectin, macrophages, and T cells was assessed by immunohistochemistry.

RESULTS

Coronary transplant vasculopathy was inhibited in both groups of pravastatin-treated animals, as compared with controls. Immunohistochemistry revealed that control animals had degraded laminin and fibronectin which paralleled the degree of tissue necrosis. In contrast, pravastatin-treated animals had modest amounts of extracellular matrix proteins retained within intermyocytes and endothelium, a pattern seen in native cardiac tissue. The pravastatin-treated groups also had fewer graft-infiltrating macrophages, specifically within the arterial intima and perivascular areas.

CONCLUSIONS

Progressive chronic vascular rejection, a leading cause of allograft failure, can be inhibited by pravastatin in a well-defined rat cardiac transplant model. Pravastatin appears to inhibit the synthesis and subsequent degradation of extracellular matrix proteins and block the infiltration of macrophages to the graft, which emphasizes that this inflammatory cell plays a major role in the pathogenesis of transplant chronic rejection.

Lacrimal gland inflammation is responsible for ocular pathology in TGF-beta 1 null mice

Mice homozygous for a nonfunctional transforming growth factor-beta 1 gene develop rampant inflammation in vital organs that contributes to a shortened life span. The presence of circulating anti-nuclear anti-bodies, immune deposits in tissues, leukocyte infiltration, and increased major histocompatibility complex antigen expression resembles an autoimmune-like syndrome. One of the overt symptoms that appears in these mice lacking transforming growth factor-beta 1 is the development of dry crusty eyes that close persistently as their health declines. Histologically, the eyes appear normal with little or no inflammation. However, inflammatory lesions, predominantly lymphocytic, develop in the lacrimal glands, disrupting their structure and function and severely limiting their ability to generate tears. This histopathology and aberrant function mimic that of Sjögren's syndrome, a human autoimmune disease characterized by dry eyes and dry mouth. Impeding the leukocyte infiltration into the glands with synthetic fibronectin peptides, which block adhesion, not only prevents the inflammatory pathology but also prevents the persistent eye closure characteristic of these mice.

Interaction of the NH2-terminal domain of fibronectin with heparin. Role of the omega-loops of the type I modules

Determinants of the interaction of the 29-kDa NH2-terminal domain of fibronectin with heparin were explored by analysis of normal and mutant recombinant NH2-terminal fibronectin fragments produced in an insect cell Baculovirus host vector system. A genomic/cDNA clone was constructed that specified a secretable human fibronectin NH2 fragment. With the use of site-directed mutagenesis a set of 29 kDa fragments was obtained that contained glycine or glutamic acid residues in place of basic residues at various candidate sites for heparin binding in the five type I modules that make up the domain. The recombinant fragment containing the wild type sequence had a nearly normal circular dichroic spectra and a melting profile, as assayed by loss of ellipticity at 228 nm, that was indistinguishable from that of the native fragment obtained by trypsinization of plasma fibronectin. A substantial proportion of the wild type recombinant fragment bound to heparin-Sepharose, where it was eluted at the same NaCl concentration as the native fragment. The wild type fragment was capable of promoting matrix-driven translocation, a morphogenetic effect in artificial extracellular matrices that depends on the interaction of the fibronectin NH2 terminus with heparin-like molecules on the surfaces of particles. Mutant fragments in which arginines predicted to be most exposed in the folded fragment were converted to glycines retained the same affinity for heparin as the wild type fragment. In contrast, a mutant fragment in which the single basic residue (Arg99) in the minor loop ("Omega-loop") of the second type I module was converted to a glycine had an essentially normal melting profile but exhibited no binding to heparin and failed to promote matrix-driven translocation. A mutant fragment in which the single basic residue (Arg52) of the first type I module was converted to a glycine also completely lacked heparin binding activity, but one in which the single basic residue (Arg191) the fourth type I module was converted to a glycine retained the ability to bind heparin. A mutant fragment in which the single basic residue (Lys143) in the Omega-loop of the third type I module was converted to a glutamic acid lacked heparin binding activity but had a CD spectrum similar to the heparin-liganded native protein and was capable of promoting matrix-driven translocation. The results indicate that multiple residues in the Omega-loops of the fibronectin NH2-terminal domain participate in its interactions with heparin. In addition, the conformation of one of the nonbinding mutants may mimic the heparin-induced structural alteration in this fibronectin domain required for certain morphogenetic events.

Obliterative bronchiolitis

Obliterative bronchiolitis following lung transplantation is common and potentially devastating. Its exact cause is undefined, but multiple immune and nonimmune processes contribute to its pathogenesis. Severe acute rejection and recurrent acute rejection have been shown to confer the greatest risk for obliterative bronchiolitis, signifying the central importance of alloimmunity in the disease process. Treatment of established disease with intensification of immune suppression has been of limited benefit, so current clinical strategies include early detection and minimization of risk. As our understanding of the disease evolves, it is hoped that effective interventions targeted at specific pathogenetic steps will emerge. In the meantime, obliterative bronchiolitis remains the most important and sinister long-term complication of lung transplantation.

Cytokine regulation of schistosome-induced granuloma and fibrosis

Schistosomiasis mansoni, a major cause of hepatic fibrosis in many developing countries, triggers a granulomatous inflammatory reaction in response to its eggs that lodge in the liver. The egg antigens are eliminated slowly, and the persistent granulomatous response leads to prolonged matrix synthesis and hepatic fibrosis. In mice, soluble egg antigens (SEA) induce interleukin 4 synthesis, promoting a dominant T helper type 2 lymphocyte accumulation with the release of additional cytokines (IL-5, IL-10), which not only suppress Th1 lymphocyte subset cytokines, but mediate the characteristic pathophysiology. Manipulation of the cytokine profile with antagonists or exogenous cytokine delivery alters the course of the hepatic inflammation and fibrosis. In the evolution of the granulomatous response to the S. mansoni eggs, transforming growth factor beta (TGF-beta) is also produced that may modulate inflammation and regulate fibrogenesis. In TGF-beta 1-gene targeted mutant mice that over-express TGF-beta 1 (TGF-beta 1 transgenics) or in which TGF-beta 1 has been inactivated (TGF-beta 1-/-; null mutation) or partially inactivated (TGF-beta 1+/-; null mutation heterozygotes), the altered production of TGF-beta 1 impacts on S. mansoni granuloma and hepatic fibrosis. In addition to the Th1/Th2 cytokine balance, modulation of TGF-beta 1 may change the outcome of chronic inflammatory fibrotic disease.

Induction of liver-associated transforming growth factor beta 1 (TGF-beta 1) mRNA expression by carbon tetrachloride leads to the inhibition of T helper 2 cell-associated lymphokines

Acute treatment of B6C3F1 mice with a hepatotoxic dose (500 mg/kg) of carbon tetrachloride (CCl4) produced a marked but transient increase in transforming growth factor beta 1 (TGF-beta 1) mRNA expression in the liver within 24 hr. We have previously shown that an identical dose of CCl4 also produces a marked increase in serum TGF-beta 1 concentrations which peak at 48 hr and produce a marked inhibition of the anti-sRBC IgM antibody forming cell (AFC) response. Similar increases in TGF-beta 1 transcripts scripts in the liver were also induced by an acute hepatotoxic dose (600 mg/kg) of acetaminophen. No increase in TGF-beta 1 mRNA expression was detected in the spleen following treatment with either agent. Direct addition of TGF-beta 1 (0.05-1.0 ng/ml) to naive splenocyte cultures produced a marked and dose-related inhibition of the anti-sRBC IgM AFC response. Under the same conditions, TGF-beta 1 induced a marked decrease in IL-4 and IL-5 mRNA expression in sRBC-sensitized splenocytes. Concomitantly, TGF-beta 1 induced a rapid increase in NF-kappa B/Rel trans-acting factor binding within the first 24 hr post-sRBC sensitization of splenocytes. Conversely, NF-kappa B/Rel binding activity was inhibited on Days 2 through 4 in sRBC-sensitized splenocytes in the presence of TGF-beta 1. The increase in NF-kappa B/Rel binding within 24 hr following sRBC sensitization is consistent with the positive influence TGF-beta 1 exerts on Th1 cytokines such as IL-2 and IFN-gamma. Conversely the decrease in NF-kappa B/Rel binding at the later time period during the AFC response (Days 2-4) coincides with the inhibitory effects TGF-beta 1 exerted on IgM production by B cells.

Expression of fibronectin splicing variants in organ transplantation: a differential pattern between rat cardiac allografts and isografts

Allograft rejection is associated with infiltration of inflammatory cells and deposition of extracellular matrix proteins. The extent to which diversity in the extracellular matrix regulates inflammatory cell function in transplants remains unclear. One group of extracellular matrix proteins, termed fibronectins (FNs), exhibits inherent diversity as a consequence of alternative splicing in three segments: EIIIA, EIIIB, or V. Although the EIIIA segment has documented functions in mesenchymal cell differentiation, neither this segment nor the EIIIB segment have been tested for effects specific to leukocyte functions. By contrast, the V region can include the CS-1 segment to which leukocytes may adhere through alpha 4 beta 1 integrins. In this study, we demonstrate that EIIIA+, EIIIB+, and V+ FN variants are synthesized, primarily by macrophages in distinct temporal and spatial patterns in two rat cardiac transplant models: either with antigenic challenge, allografts, or without challenge, isografts. The ratio of EIIIA inclusion into FN increases by day 1 in allografts and isografts and remains high until allografts are rejected (approximately 7 days) but falls to normal levels in tolerated isografts (day 6). EIIIB+ FN ratios in allografts peak later than do EIIIA+ FNs (day 4). EIIIB+ FN ratios remain relatively low in isografts. Interestingly, EIIIA+ and EIIIB+ FNs are deposited prominently in the myocardium of rejecting allografts in close association with infiltrating leukocytes, and FN expression and deposition are prominent at sites of infarction. By contrast, these FNs are largely restricted to the epicardium and to a lesser degree in the immediately adjacent myocardium in isografts. CS-1+ FNs increase in allografts and isografts at 3 hours after transplantation but are particularly prominent in allografts 1 to 3 days before rejection. Our data suggest that FN splicing variants have a differential role in the effector functions of leukocytes in allografts and isografts and provide a foundation for testing their function on leukocytes and a rationale for FN-based therapeutics to modulate allograft rejection in transplant recipients.

Antagonism of leukocyte adherence by synthetic fibronectin peptide V in a rat model of transient focal cerebral ischemia

OBJECTIVE

Activated polymorphonuclear leukocytes (PMNs) seem to be directly involved in potentiating ischemic brain injury. Recent work in our laboratory demonstrated that synthetic fibronectin peptides significantly inhibit PMN accumulation in ischemic tissue, reduce the size of infarction, and reduce neurological dysfunction after transient focal cerebral ischemia in rats. The purpose of this study was to examine any dose-related effects (Experiment 1) and the optimal timing of the administration (Experiment 2) of synthetic fibronectin peptide V (FN-C/H-V) to further substantiate the role of the peptide in ameliorating cerebral ischemic damage.

METHODS

Fifty-six animals were included in the study. We evaluated the efficacy of FN-C/H-V on PMN accumulation in ischemic tissue, infarct size, and neurological outcomes in rats subjected to 1 hour of cerebral ischemia and 48 hours of reperfusion.

RESULTS

In Experiment 1, the animals receiving FN-C/H-V at a dose of 10 to 15 mg/kg of body weight per injection showed significant reduction of PMN accumulation, reduction of infarct size, and improvement of neurological outcomes at 48 hours after reperfusion compared to untreated animals (P < 0.05). In Experiment 2, the animals receiving FN-C/H-V within 3 hours after reperfusion also showed significantly better results than untreated animals (P < 0.05). Despite the treatment delay, the administration of FN-C/H-V inhibited PMN accumulation after reperfusion but did not reduce the size of infarction when administered 6 hours after reperfusion.

CONCLUSION

These data suggest that relatively late postischemic administration of FN-C/H-V is effective in brain protection after ischemia/reperfusion.