Transforming growth factor-beta1 promotes the morphological and functional differentiation of the myofibroblast

The myofibroblast is responsible for the generation of contractile force associated with wound contraction and pathological contractures and is characterized by the presence of alpha-smooth muscle (alpha-sm) actin-containing stress fibers, vinculin-containing fibronexus adhesion complexes, and fibronectin fibrils containing the ED-A splice variant. Transforming growth factor-beta1 (TGF-beta1) can promote the expression of alpha-sm actin in myofibroblasts, but the functional significance of this increased expression is unclear. In this study, we demonstrate, using the stress-relaxed collagen lattice contraction assay, that TGF-beta1 promoted a dose-dependent increase in the generation of contractile force in myofibroblasts and a concomitant increase in the expression of alpha-sm actin. We also demonstrate that TGF-beta1 enhanced the formation of the structural elements important in myofibroblast contractile force generation and transmission, including stress fibers, vinculin-containing fibronexus adhesion complexes, and fibronectin fibrils, and that this enhancement occurred prior to, and independent of, alpha-sm actin expression. This differentiated myofibroblast phenotype was not stable. Removal of TGF-beta1 resulted in reduced expression of alpha-sm actin as well as a decreased assembly of stress fibers and vinculin-containing adhesion complexes; however, there was no reduction in fibronectin fibrils. We conclude that TGF-beta1 promotes the morphological and functional differentiation of the myofibroblast by first enhancing the formation of the structural elements characteristic of the myofibroblast followed by increased expression of alpha-sm actin and contractile force generation.     

Transforming growth factor-beta 1 expression in irradiated liver

The expression of transforming growth factor-beta 1 (TGF-beta 1) in the liver of irradiated rats was increased in a dose-dependent fashion 9 months after irradiation. Expression of TGF-beta 1 was confined primarily to hepatocytes in the pericentral region of the liver, and the percentage of hepatocytes strongly positive for TGF-beta 1 was significantly correlated with the extent of fibrosis. We further showed that a localized injection of TGF-beta 1 into normal rat liver elicited a strong fibrotic reaction at the injection site. These results suggest that the increased hepatic concentration of TGF-beta 1 in response to radiation injury may be important in the pathogenesis of radiation hepatitis. TGF-beta 1 was also found to be present at a significantly higher concentration in unirradiated human hepatocytes than in normal rat hepatocytes, implying that the propensity for humans to develop radiation hepatitis may result in part from the elevated levels of TGF-beta 1 normally found in human liver.     

Transforming growth factor-beta 1 binds to immobilized fibronectin

We have characterized the interaction of homodimeric porcine transforming growth factor-beta 1 (TGF-beta 1) with affinity-purified human plasma fibronectin. Using a solid-phase binding assay, we have demonstrated that TGF-beta 1 binds to fibronectin immobilized on Immunlon ITM microtiter plates. TGF-beta 1 binding increased with time, reaching a plateau after 4-6 h, and was dependent upon the concentration of both labeled TGF-beta 1 and immobilized fibronectin present. The binding of radiolabeled TGF-beta 1 to fibronectin was saturable and was reduced 75% in the presence of a 100-fold excess of unlabeled TGF-beta 1. TGF-beta 1 bound to fibronectin with an association rate constant (Ka) of 2.96 x 10(3) M-1 s-1 and did not readily dissociate under various conditions. The binding of TGF-beta 1 to fibronectin was insensitive to variations in ionic strength over a range of 0.1-1.0 M NaCl and was relatively insensitive to divalent cation concentration in the range of 0.1-10.0 mM as well. These data suggest that the binding of TGF-beta 1 to fibronectin may not be dependent upon the interaction of charged amino acids within these two molecules. However, the binding of TGF-beta 1 to fibronectin was strongly pH-dependent and binding decreased dramatically below pH 4.0 and above pH 10.0, suggesting that charged amino acids may influence TGF-beta 1/fibronectin interactions. The association of TGF-beta 1 with immobilized fibronectin or other extracellular matrix components and subsequent dissociation under acidic conditions or by an as-yet-unidentified mechanism may play a role in the distribution and/or activity of this potent growth regulator at sites of tissue injury and inflammation in vivo.     

Transforming growth factor-beta in T-cell biology

Strict control of T-cell homeostasis is required to permit normal immune responses and prevent undesirable self-targeted responses. Transforming growth factor-beta (TGF-beta) has been shown to have an essential role in that regulation. Owing to its broad expression, and inhibitory effects on multiple cell types of the immune system, TGF-beta regulation is complex. Through advances in cell-specific targeting of TGF-beta signalling in vivo, the role of TGF-beta in T-cell regulation has become clearer. Recent in vitro studies provide a better understanding of how TGF-beta regulates T-cell homeostasis, through multiple mechanisms involving numerous cell types.     

Transforming growth factor-beta 3.

Transforming Growth Factor-Beta (TGF-β) is the general name for a family of naturally-occurring polypeptides which have multiple regulatory effects on cell proliferation and differentiation. Over the last decade it has become apparent that TGF-βs can be produced by most cell types and exert a wide range of effects in a context-dependent autocrine, paracrine or endocrine fashion via interactions with distinct receptors on the cell surface. This review summarizes current knowledge concerning the molecular and cellular biology of TGF-β3, the most recently described mammalian isoform, and focuses on those physiological actions which may lead to clinical applications, particularly in the indication areas of wound healing and chemoprotection.     

Transforming growth factor-beta 1 acts cooperatively with sodium n-butyrate to induce differentiation of normal human keratinocytes.

Growth factors with established biological activity toward cultured normal human epidermal keratinocytes (NHEKs) (e.g., transforming growth factor-beta, TGF-beta; retinoic acid, RA) initiate programmed changes in cellular maturation which differ with regard to the specific differentiation pathway (normal or abnormal) analyzed. Sodium butyrate (NaB) initiates one form of epidermal differentiation leading to enhanced cornified envelope (CE) formation which involves abrogation of the normally inhibitory effect of RA on NHEK maturation. NaB also induces TGF-beta mRNA in the maturing suprabasal compartment, suggesting that TGF-beta may play a role in NaB-initiated NHEK differentiation. Treatment with TGF-beta 1 alone, however, only marginally increased (by twofold) the number of detergent-resistant CEs compared to control NHEKs and did not alter the prevalence of fully mature enucleated CEs. TGF-beta 1 was quite effective in inducing significant levels of CE expression when used simultaneously with suboptimal concentrations of NaB. The cooperative action of suboptimal NaB and TGF-beta 1 generated numbers of CEs which, in fact, exceeded the incidence of mature CEs formed in response to optimal levels of NaB alone. Neutralizing antibodies to TGF-beta, moreover, effectively reduced the incidence of CE formation in cultures treated with optimal NaB concentrations, further implicating endogenous TGF-beta activity in the NaB-initiated NHEK differentiation model. It is suggested, therefore, that within the NaB-induced pathway of NHEK differentiation, TGF-beta can positively modulate expression of the differentiated phenotype but alone is insufficient for generation of mature CEs.     

Transforming growth factor-beta signalling in brain disorders

Transforming growth factor-beta (TGF-beta) has been characterized as an injury-related factor, based on the observation that it is strongly up-regulated in many acute or chronic central nervous system disorders. TGF-beta is generally thought to be neuroprotective and several mechanisms have been proposed to explain this beneficial action. For instance, TGF-beta protects neurons against the potentiating effect of tissue-type plasminogen activator on NMDA receptor-mediated excitotoxicity, by up-regulating type-1 plasminogen activator inhibitor expression in astrocytes. TGF-beta has also anti-apoptotic properties, through a recruitment of a mitogen-activated protein kinase pathway and a concomitant activation of anti-apoptotic members of the Bcl-2 family. These multiple mechanisms might reflect the pleiotropic nature of TGF-beta, reinforcing the potential therapeutic value of this cytokine in several central nervous system disorders.     

Transforming growth factor-beta 1 is a costimulator for IgA production

Transforming growth factor-beta 1 (TGF-beta 1) belongs to a family of polypeptides involved in the regulation of cell growth and differentiation. We have examined the ability of TGF-beta 1 to regulate isotype specific Ig secretion by murine spleen B cells. TGF-beta 1, in the presence of rIL-2, induced a synergistic 10-fold or greater increase in IgA secretion by LPS-stimulated spleen B cells. TGF-beta 1 alone had little to no effect on IgA secretion. In contrast, TGF-beta 1, with or without rIL-2, markedly inhibited IgG1 and IgM secretion under the same conditions. The costimulatory activity of TGF-beta 1 and rIL-2 on IgA secretion was seen in cultures of surface IgA negative B cells and was inhibited by anti-TGF-beta 1 antibody in a dose dependent manner. Vicia villosa agglutinin non-adherent Peyer's patch T cells, which secrete IL-2, also synergized with TGF-beta 1 and could substitute for the activity of LPS and rIL-2 on the IgA response. Finally, IL-5 added after 2 days of culture, but not at the beginning of culture, synergized with TGF-beta 1 on the IgA response. These studies indicate that TGF-beta 1 can interact with other lymphokines and selectively modulate the IgA response.     

Transforming growth factor-beta1 inhibits thrombin activation of endothelial cells

Transforming growth factor-beta1 (TGF-beta1) is reported to exert both pro- and anti-inflammatory effects on the chronic activation of endothelial cells (ECs) in vitro by cytokines such as tumour necrosis factor-alpha (TNF-alpha). However, the effects of TGF-beta1 on acute inflammatory responses of ECs in vitro (e.g. to thrombin) have not been characterised. Pretreatment with TGF-beta1 (10 ng/mL) effectively inhibited all the thrombin-stimulated responses in rat aortic endothelial cells (RAECs) examined: adhesion and migration of polymorphonuclear leukocytes, adhesion of platelets and lymphocytes. Substantial inhibition of thrombin stimulation occurred after 30 min of pretreatment with TGF-beta1 and maximal inhibition was obtained after 1-20 h of pretreatment. Inhibition by TGF-beta1 pretreatment for 30 min was not affected by cycloheximide and was therefore independent of protein synthesis. Treatment with TGF-beta1 for 20 h did not affect the total levels of P-selectin and von Willebrand factor (vWF) in RAECs, but reduced thrombin-stimulated recruitment of P-selectin and vWF to the cell surface. The data demonstrate that TGF-beta1 exerts a potent anti-thrombin effect on ECs, effective after long and short pretreatment times.     

Transforming growth factor-beta 1 modulates the expression of vascular endothelial growth factor by osteoblasts

Angiogenesis is essential to both normal and pathological bonephysiology. Vascular endothelial growth factor (VEGF) has been implicated in angiogenesis, whereas transforming growth factor-1 (TGF-1) modulates bone differentiation, matrixformation, and cytokine expression. The purpose of this study was toinvestigate the relationship between TGF-1 and VEGF expression inosteoblasts and osteoblast-like cells. Northern blot analysis revealedan early peak of VEGF mRNA (6-fold at 3 h) in fetal rat calvarial cellsand MC3T3-E1 osteoblast-like cells after stimulation with TGF-1 (2.5 ng/ml). The stability of VEGF mRNA in MC3T3-E1 cells was not increasedafter TGF-1 treatment. Actinomycin D inhibited the TGF-1-inducedpeak in VEGF mRNA, whereas cycloheximide did not. Blockade of TGF-1signal transduction via a dominant-negative receptor II adenovirussignificantly decreased TGF-1 induction of VEGF mRNA. Additionally,TGF-1 induced a dose-dependent increase in VEGF protein expressionby MC3T3-E1 cells (P < 0.01).Dexamethasone similarly inhibited VEGF protein expression. BothTGF-1 mRNA and VEGF mRNA were concurrently present in rat membranousbone, and both followed similar patterns of expression during ratmandibular fracture healing (mRNA and protein). In summary,TGF-1-induced VEGF expression by osteoblasts and osteoblast-likecells is a dose-dependent event that may be intimately related to bonedevelopment and fracture healing.

     

Transforming growth factor-beta1 enhanced vascular endothelial growth factor synthesis in mesenchymal stem cells

Angiogenesis is essential for transplantation of mesenchymal stem cells (MSCs). Vascular endothelial growth factor (VEGF) is one of the most potent angiogenic factors identified to date. Elevated VEGF levels in MSCs correlate with the potential of MSCs transplantation. As an indirect angiogenic agent, transforming growth factor-β1 (TGF-β1) plays a pivotal role in the regulation of vasculogenesis and angiogenesis. However, the effect of TGF-β1 on VEGF synthesis in MSCs is still unknown. Besides, the intracellular signaling mechanism by which TGF-β1 stimulates this process remains poorly understood. In this article, we demonstrated that exposure of MSCs to TGF-β1 stimulated the synthesis of VEGF. Meanwhile, TGF-β1 stimulated the phosphorylation of Akt and extracellular signal-regulated kinase 1/2 (ERK1/2). Moreover, Ly 294002, a specific inhibitor of phosphatidylinositol-3-kinase (PI3K)/Akt significantly attenuated the VEGF synthesis stimulated by TGF-β1. Additionally, U0126, a specific inhibitor of ERK1/2, also significantly attenuated the TGF-β1-stimulated VEGF synthesis. These results indicated that TGF-β1 enhanced VEGF synthesis in MSCs, and the Akt and ERK1/2 activation were involved in this process.     

Transforming growth factor-beta 1 inhibits cytokine-mediated induction of human metalloelastase in macrophages

Matrix metalloproteinases (MMP) have been identified in vulnerable areas of atherosclerotic plaques and may contribute to plaque instability through extracellular matrix degradation. Human metalloelastase (MMP-12) is a macrophage-specific MMP with broad substrate specificity and is capable of degrading proteins found in the extracellular matrix of atheromas. Despite its potential importance, little is known about the regulation of MMP-12 expression in the context of atherosclerosis. In this study, we report that in human peripheral blood-derived macrophages, MMP-12 mRNA was markedly up-regulated by several pro-atherosclerotic cytokines and growth factors including interleukin-1beta, tumor necrosis factor-alpha, macrophage colony-stimulating factor, vascular endothelial growth factor, and platelet-derived growth factor-BB. In contrast, the pleiotropic anti-inflammatory growth factor transforming growth factor-beta1 (TGF-beta1) inhibited cytokine-mediated induction of MMP-12 mRNA, protein, and enzymatic activity. Analyses of MMP-12 promoter through transient transfections and electrophoretic mobility shift assays indicated that both its induction by cytokines and its inhibition by TGF-beta1 depended on signaling through an AP-1 site at -81 base pairs. Moreover, the inhibitory effect of TGF-beta1 on MMP-12 was dependent on Smad3. Taken together, MMP-12 is induced by several factors implicated in atherosclerosis. The inhibition of MMP-12 expression by TGF-beta1 suggests that TGF-beta1, acting via Smad3, may promote plaque stability.     

Transforming growth factor-beta inhibits endothelial cell proliferation

Transforming growth factor-beta (TGF-beta) is an inhibitor of the proliferation of bovine aortic endothelial cells in culture. Basal cell growth in serum-containing medium and cell proliferation stimulated by fibroblast growth factor (FGF) are inhibited by TGF-beta in a dose-dependent manner. Half-maximal inhibition occurs at an inhibitor concentration of 0.5-1.0 ng/ml. TGF-beta does not appear to be cytotoxic and cells treated with the inhibitor grow normally after removal of TGF-beta. High concentrations of FGF are ineffective in overcoming TGF-beta-induced inhibition of cell proliferation, suggesting that antagonism of growth factor-induced cell proliferation by TGF-beta is of a noncompetitive nature.