In situ expression of transforming growth factor beta in streptococcal cell wall-induced granulomatous inflammation and hepatic fibrosis

Inhibition of hepatic stellate cell activation and liver fibrosis by fat-specific protein 27

In order to explore the effects of fat-specific protein 27 (Fsp27) on regulation of hepatic stellate cell (HSC) activation and liver fibrosis. HSCs were isolated from rat liver tissues and cultivated in vitro for gene expression and lentivirus infection. CCK-8 cell viability assay, immunofluorescence staining, qRT-PCR, and western blot assays were used to assess phenotypic changes and gene expression in HSCs. The rat liver fibrosis model was produced by intraperitoneal injection of carbon tetrachloride for assessing the effects of Fsp27 in the rat liver. Gene expression was then detected by immunohistochemistry and ELISA assays. The results of the study showed that Fsp27 was constitutively expressed in primary quiescent HSCs, but was absent in activated HSCs. Ectopic expression of Fsp27 significantly inhibited HSC proliferation and activation, as well as expression of α-smooth muscle actin. Fsp27 expression also significantly reduced collagen I production and matrix metalloproteinases 2 protein levels, and to a lesser degree, reduced tissue inhibitors of metalloproteinases 1 expression. In vivo data showed that ectopic expression of Fsp27 protein significantly reduced levels of hydroxyproline in liver tissue, and decreased serum levels of collagen III and hyaluronic acid, which in turn, suppressed liver fibrosis in rats. From these findings, it can be concluded that Fsp27 expression suppressed HSC activation in vitro and liver fibrogenesis in vivo. Further studies are needed to explore whether expression of Fsp27 can be selected as a potential novel strategy for anti-fibrotic therapy against liver fibrosis.

The gene transfer of soluble VEGF type I receptor (Flt-1) attenuates peritoneal fibrosis formation in mice but not soluble TGF-beta type II receptor gene transfer

Peritoneal fibrosis formation is a consequence of inflammation/injury and a significant medical problem to be solved. The effects of soluble VEGF receptor type I (sFlt-1) gene transfer on experimental peritoneal fibrosis were examined and compared with soluble transforming growth factor-beta (TGF-beta) receptor type II (sTGF beta RII) gene transfer. Male C57BL/6 mice were injected with 1.5 x 10(8) plaque-forming unit of adenovirus encoding active TGF-beta (AdTGF beta) intraperitoneally. Some mice had been treated with sTGF betaRII or sFlt-1 plasmid injection into skeletal muscle with electroporation 4 days before virus administration. Mice were euthanized at day 14 after virus administration. AdTGF beta induced significant elevation of serum active TGF-beta, caused significant inflammatory response [weight loss, elevation of serum amyloid-P (SAP) and IL-12, increased expression of monocyte chemoattractant protein-1 (MCP-1) mRNA], and induced marked thickening of the peritoneum and collagen deposition. Gene transfer of sFlt-1 reduced the collagen deposition approximately 81% in mesenteric tissue. Treatment with sFlt-1 decreased ICAM-1 and MCP-1 mRNA expression significantly. Significant negative correlation between serum sFlt-1 and placental growth factor level was observed, whereas there was no significant negative correlation between sFlt-1 and VEGF. On the other hand, sTGF beta RII treatment enhanced the AdTGF beta-induced inflammation (significant elevation of SAP, TNF-alpha, and IL-12 levels and upregulation of ICAM-1 and MCP-1 mRNA expressions) and failed to prevent collagen deposition. These observations indicate that sFlt-1 gene transfer might be of therapeutic benefit in peritoneal fibrosis.

Kupffer-cell depletion attenuates colonic and extracolonic granulomatous inflammation in chronic colitis

Intramural injection of peptidoglycan-polysaccharide polymers into the distal colon in rats induces granulomatous colitis associated with extracolonic manifestations. We sought to clarify the effects of Kupffer-cell depletion induced by the intravenous administration of gadolinium on colonic and extracolonic inflammation in this model. The effects of Kupffer-cell depletion on acute and chronic inflammation were evaluated 3 days and 3 weeks after injection of peptidoglycan-polysaccharide, respectively. We assessed the effects of gadolinium on colonic cytokine levels in vivo and the viability of elicited peritoneal macrophages and peptidoglycan-polysaccharide-induced production of nitrite, an indirect index of nitric oxide production, by these cells in vitro. A single injection of gadolinium caused a marked decrease in the number of Kupffer cells stained with antibodies within 3 days. Gadolinium treatment did not alter acute inflammation at 3 days. Repeated treatment with gadolinium dramatically attenuated grossly observed chronic inflammation, including thickening of colon wall, hepatic and splenic nodules, and swelling of foot joints; and significantly reduced the proportional areas occupied by granulomas in the colon, liver, and spleen at 3 weeks. These protective effects were reflected in significant reduction in colon and liver weights; gross scores; colonic myeloperoxidase activity, an indirect quantitative index of granulocyte infiltration; colonic interleukin-1beta levels; plasma nitrite and nitrate levels; and decreased tendency toward arthritis. Although gadolinium did not cause injury in elicited peritoneal macrophages in vitro, the compound dose-dependently attenuated peptidoglycan-polysaccharide-induced production of nitrite by these cells. Chronic Kupffer-cell depletion attenuates peptidoglycan-polysaccharide-induced granulomatous inflammation in the colon, liver, and spleen and reduces the incidence of arthritis, possibly by suppressing the production of interleukin-1beta and nitric oxide.

Inhibition of Bacterial Cell Wall-Induced Leukocyte Recruitment and Hepatic Granuloma Formation by TGF-β Gene Transfer

Intraperitoneal injection of streptococcal cell walls (SCW) into Lewis rats results in dissemination of SCW to the liver, spleen, bone marrow, and peripheral joints. The uptake of SCW by Kupffer cells in the liver initiates a chain of events largely mediated by T lymphocytes and macrophages. Local synthesis and secretion of cytokines and growth factors in response to the persistent SCW lead to the evolution and maintenance of a chronic T cell-dependent granulomatous response and result in granuloma formation and irreversible hepatic fibrosis. In an attempt to impede the development of the chronic granulomatous lesions in the liver, we injected a plasmid DNA encoding TGF-β1 i.m. to the SCW animals to determine the effect of TGF-β1 gene transfer on the course of liver inflammation and fibrosis. A single injection of plasmid DNA encoding TGF-β1 resulted in virtual abolition of the development of the SCW-induced hepatic granuloma formation and matrix expansion. TGF-β1 DNA not only reduced key proinflammatory cytokines including TNF-α, IL-1β, IFN-γ, and IL-18, but also inhibited both CXC and CC chemokine production, thereby blocking inflammatory cell recruitment and accumulation in the liver. Moreover, TGF-β1 gene delivery inhibited its own expression in the liver tissue, which is otherwise up-regulated in SCW-injected animals. Our study suggests that TGF-β1 gene transfer suppresses hepatic granuloma formation by blocking the recruitment of inflammatory cells to the liver, and thus may provide a new approach to the control of hepatic granulomatous and fibrotic diseases.

Bacterial cell wall polymers promote intestinal fibrosis by direct stimulation of myofibroblasts

Normal luminal bacteria and bacterial cell wall polymers are implicated in the pathogenesis of chronic intestinal inflammation. To determine the direct involvement of bacteria and their products on intestinal fibrogenesis, the effects of purified bacterial cell wall polymers on collagen and cytokine synthesis were evaluated in intestinal myofibroblast cultures established from normal fetal and chronically inflamed cecal tissues. In this study, the intestines of Lewis rats were intramurally injected with peptidoglycan-polysaccharide polymers. Collagen and transforming growth factor (TGF)-beta1 mRNA levels were measured and correlated with mesenchymal cell accumulation by immunohistochemistry. The direct effects of cell wall polymers on fibrogenic cytokine and collagen alpha1 (type I) expression were evaluated in intestinal myofibroblast cultures. We found that intramural injections of bacterial cell wall polymers induced chronic granulomatous enterocolitis with markedly increased collagen synthesis and concomitant increased TGF-beta1 and interleukin (IL)-6 expression. Intestinal myofibroblast cultures were established, which both phenotypically and functionally resemble the mesenchymal cells that are involved in fibrosis in vivo. Bacterial cell wall polymers directly stimulated collagen alpha1 (I), TGF-beta1, IL-1beta, and IL-6 mRNA expression in the intestinal myofibroblasts derived from both normal and inflamed cecum. Neutralization of endogenous TGF-beta1 inhibited in vitro collagen gene expression. From our results, we conclude that increased exposure to luminal bacterial products can directly activate intestinal mesenchymal cells, which accumulate in areas of chronic intestinal inflammation, thus stimulating intestinal fibrosis in genetically susceptible hosts.

Amphiregulin and nerve growth factor expression are regulated by barrier status in murine epidermis

Disruption of the murine permeability barrier by solvents or tape stripping stimulates a homeostatic repair response that includes increased epidermal DNA synthesis. To identify potential mediators of the increase in DNA synthesis, we have measured epidermal levels of mRNAs encoding various growth factors after acute barrier disruption. In this study, mRNAs for amphiregulin and nerve growth factor were each shown to increase over controls at 30 min, reach peak levels of 12- to 30-fold at 1-2 h, and return to control levels by 6 h after tape stripping. A similar time course for the increase of amphiregulin and nerve growth factor mRNAs was observed after an unrelated form of barrier disruption, i.e., acetone treatment. Furthermore, artificial restoration of the barrier by Latex occlusion, immediately following barrier disruption by acetone treatment, inhibited the increase in epidermal amphiregulin and nerve growth factor mRNA levels, indicating that barrier status regulates the production of these growth factors. In contrast, mRNA levels of transforming growth factor-beta1, an inhibitory growth factor, were unchanged at early times and decreased by 53% (p < 0.02) 6 h after tape stripping, whereas mRNA levels of transforming growth factor-alpha remained unchanged at all times after acute barrier disruption. These results suggest that barrier disruption stimulates the expression of amphiregulin and nerve growth factor. Together, these regulators of keratinocyte growth and differentiation may be responsible for the increased proliferative response that is associated with barrier disruption.

The use of immunohistochemistry for evaluating the liver

Immunohistochemistry has been utilized in recent years primarily for diagnosis of infectious diseases of the liver, especially in humans. The utility of immunohistochemistry has extended to experimental and toxicologic pathology in a variety of areas: identification of cell phenotype, cell receptors, cytokine and chemikine production, and functional cell changes such as enzyme induction. In addition, markers for experimental carcinogenesis studies are detectable by immunohistochemical changes as well as novel antigen induction such as placental glutathione-S-transferase, oncofetal proteins, oncogene products, and typing of neoplasms. Immunohistochemistry is also used to detect the origin and function of various cell types in developmental and toxicity studies. Careful use of immunohistochemical procedures in conjunction with routine pathology and molecular techniques enhance the ability of the toxicologic pathologist to diagnose unique conditions and to understand mechanisms of lesion development.

Distribution of extracellular matrices, matrix receptors, and transforming growth factor-beta 1 in human and experimental lung granulomatous inflammation

Aberrant deposition of extracellular matrices (ECMs) may affect lung inflammation by influencing cell adhesion, migration, and activation. Little is known about the expression of ECMs in lungs with granulomatous inflammation. Therefore the authors investigated the distribution of ECMs, matrix receptors of the integrin family, and transforming growth factor-beta 1 (TGF-beta 1) in lungs from patients with pulmonary sarcoidosis and animals with experimental granulomatosis. Immunohistochemistry revealed increased deposition of type I collagen and fibronectin in human lung granulomas when compared with healthy human lungs. Procollagen type I and cellular fibronectin also were increased, suggesting local synthesis of ECM in sarcoid granulomas. These findings were accompanied by increased staining for fibronectin (alpha 5 beta 1) and collagen (alpha 2 beta 1) integrin receptors. The matrix-inducing cytokine TGF-beta 1 was co-distributed with the aforementioned molecules in the granulomas, whereas no significant staining for TGF-beta 1 was found in healthy lungs. Similar to sarcoid lungs, analysis of lung sections obtained from a murine model of granuloma formation revealed increased expression of fibronectin, collagen, integrin receptors, and TGF-beta 1 within granulomas. Based on these observations, there is increased expression of ECM and matrix receptors in both human and experimental lung granulomas. Such alterations may influence the recruitment and activation of inflammatory cells and fibroblasts, promoting granuloma formation and remodeling of tissue by fibrosis. Activation of mononuclear cells resulting in production of TGF-beta 1 is likely to contribute to the changes described.

Tumor necrosis factor alpha (TNF alpha) and transforming growth factor beta 1 (TGF beta 1) stimulate fibronectin synthesis and the transdifferentiation of fat-storing cells in the rat liver into myofibroblasts

Transforming growth factor-beta (TGF beta 1) and tumor necrosis factor alpha (TNF alpha) stimulate the transdifferentiation of fat-storing cells (FSC) in the rat liver into highly active and "synthetic" myofibroblast-like cells (MFBIC). This activation has been documented by differential-interference contrast and light microscopy using morphologic criteria (a reduction in the number and size of fat droplets, cell flattening and the development of long cytoplasmic extensions), by the loss of retinyl-palmitate (measured by HPLC) and by the enhanced expression of iso-alpha smooth muscle actin (demonstrated by immunofluorescence microscopy). Furthermore, while cell growth measured by the cell count and DNA content is slightly inhibited by TGF beta 1 (0.81 of the control), the combination of TGF beta 1 with TNF alpha stimulates cell proliferation to 1.44 times of the control. In addition the combination of TGF beta and TNF alpha potentiated the stimulatory effect on fibronectin synthesis (TGF beta alone: 1.4 times control; TNF alpha alone: 2.2 times control; TGF beta plus TNF alpha: 4.7 times control). The total protein synthesis was not altered by TGF beta or TNF alpha. In summary the results obtained identify TGF beta and TNF alpha as mediators stimulating key events in liver fibrogenesis (i.e. FSC proliferation, FSC transdifferentiation into MFBIC, and fibronectin synthesis).

Insulinlike growth factor I and interleukin 1 beta messenger RNA in a rat model of granulomatous enterocolitis and hepatitis

BACKGROUND

Insulinlike growth factor I (IGF-I) is mitogenic for fibroblasts and smooth muscle cells and stimulates collagen synthesis. The present study tested the hypothesis that IGF-I is important in the development of granulomatous inflammation and fibrosis.

METHODS

IGF-I messenger RNA (mRNA) was measured in bowel and liver of rats with peptidoglycan-polysaccharide-induced chronic granulomatous enterocolitis and hepatitis using RNase protection. Cellular sites of IGF-I mRNA and IGF-I peptide precursor were localized by in situ hybridization and immunohistochemistry, respectively. Sites of IGF-I synthesis were compared with sites of interleukin 1 beta mRNA expression.

RESULTS

IGF-I mRNA was increased 3.7-fold in cecal tissue from peptidoglycan-polysaccharide-injected rats compared with controls. IGF-I mRNA was up-regulated in fibroblastlike cells in the intensely fibrotic periphery of cecal and hepatic granulomas. This region also expressed IGF-I peptide precursor. Interleukin 1 mRNA localized to macrophage-like cells in the center of granulomas.

CONCLUSIONS

IGF-I may be important in the development of fibrosis in this model of Crohn's disease. The localization of IGF-I and interleukin 1 mRNAs to distinct but adjacent sites is consistent with a paracrine interaction between cells expressing IGF-I and interleukin 1.

A role for cytokines as regulators of hepatic fibrogenesis

It is evident that hepatic fibrogenesis is a complex process involving a cascade of cytokines which interact to enhance the expression of ECM. Cytokines involved early in this cascade may serve as proinflammatory agents or as stimulators of macrophage and Ito cell activation and proliferation, while those cytokines involved later in this process may be directly fibrogenic. Furthermore, we speculate that a balance between profibrogenic and antifibrogenic cytokines normally exists but in the presence of hepatic insults, a relative super-abundance of the fibrogenic factors promotes the development of liver fibrosis. To date, most of the evidence supporting a role for cytokines in liver fibrosis has been obtained in in vitro systems or in animal models. We now need to extend these findings to man in order to determine whether a similar cascade of cytokines is important in the development of this pathologic process in man. Further delineation of these cytokines (as well as other profibrogenic soluble factors), and the mechanisms by which they act, are critical to our development of more rational forms of therapy for liver fibrosis.

Role of proteoglycans and cytoskeleton in the effects of TGF-beta 1 on renal proximal tubule cells

Transforming growth factor-beta (TGF-beta) is a critical cell regulatory protein which influences cell growth, cell differentiation and cell chemotaxis. TGF-beta 1 has been previously shown to promote a migratory and adherent transformation of monolayers of renal proximal tubule cells in primary culture to form solid clusters of cells. To better understand the cellular basis of this TGF-beta 1 effect, these studies evaluated the influence of TGF-beta 1 on the synthesis of proteoglycans and on cytoskeleton rearrangement in rabbit renal proximal tubule cells in primary culture, and their role in this transformation effect of TGF-beta 1. Biosynthetic labeling of proteoglycans with 35S sulfate and enzyme digestion studies demonstrated that TGF-beta 1 promoted the synthesis of heparan sulfate proteoglycans in these cells. The importance of proteoglycan synthesis induced by TGF-beta 1 in this migration and aggregation process was demonstrated with the use of two chemically-dissimilar proteoglycan synthesis inhibitors: xyloside and galactosamine. Both compounds inhibited TGF-beta 1 stimulation of proteoglycan synthesis and diminished TGF-beta 1 promoted transformation of proximal tubule cells as assessed by quantitative morphometry. Further experiments evaluated the influence of TGF-beta 1 on actin microfilaments with the use of rhodamine conjugated phalloidin staining and immunofluorescent microscopy, and demonstrated that TGF-beta 1 provoked a dramatic rearrangement of actin microfilaments into stress fibers. The use of actin microfilament disrupting agents, cytochalasin B and D, attenuated the stress fiber formation promoted by TGF-beta 1 and inhibited the TGF-beta 1-induced morphologic transformation of these cells. Further studies evaluated these effects on the rate of DNA synthesis in these cells, as assessed with 3H-thymidine incorporation. Proteoglycan synthesis inhibitors significantly diminished the maximal proliferative response of these epithelial cells to epidermal growth factor (EGF). In contrast, actin microfilament disaggregation with cytochalasin B or D did not change the rate of DNA synthesis in response to EGF but did attenuate the antiproliferative effect of TGF-beta 1 on EGF-induced DNA synthesis cells. These studies demonstrate that the TGF-beta 1 promoted synthesis cells. These studies demonstrate that the TGF-beta 1 promoted an increase in the production of proteoglycans and a higher ordered structure of the cytoskeleton. Both effects were instrumental in the adhesive migratory response of proximal tubule cells to TGF-beta 1 as well as the DNA synthesis rate response to both EGF and TGF-beta 1.

Transforming growth factor beta (TGF-beta) in inflammation: a cause and a cure

As we continue to explore the biology of TGF-beta in the network of cells and mediators contributing to host defense, the mechanisms controlling whether the pro- or antiinflammatory effects of this peptide prevail will be unraveled. Understanding these basic mechanisms may offer new approaches for identifying agonists and/or antagonists and in which circumstances their use might be appropriate. The striking differences between local and systemic administration of this cytokine reaffirm that the functional consequences of any biologic mediator must be considered in context (9) and, furthermore, suggest avenues of therapeutic application (Table III). In summary, the central role of TGF-beta in normal and aberrant host defense has become indisputable.

Kupffer cells express type I TGF-beta receptors, migrate to TGF-beta and participate in streptococcal cell wall induced hepatic granuloma formation

Intraperitoneal injection of Group A streptococcal cell wall (SCW) fragments into female Lewis rats results in the induction of an acute hepatic inflammation that progresses to granulomatous lesions. Kupffer cells have been shown to rapidly clear circulating SCW which triggers production of TGF-beta. In this study, we examined Kupffer cells for the expression of TGF-beta receptors to determine if these cells might be modulated in an autocrine/paracrine fashion by TGF-beta during SCW-hepatic inflammation. By receptor crosslinking and subsequent SDS-PAGE analysis we demonstrate that Kupffer cells express Type I TGF-beta receptors, but not Types II and III. Scatchard analysis indicated a receptor density of approximately 1100 receptors per cell. Functionally, TGF-beta was found to be chemotactic for Kupffer cells in vitro and this chemotactic response was higher in cells isolated from rats 1-21 days post SCW-injection. Although TGF-beta 1 mRNA is constitutively expressed by Kupffer cells, in vitro stimulation of the cultures with purified TGF-beta augments the expression of TGF-beta 1 mRNA and protein synthesis suggesting autocrine/paracrine regulation. These results indicate that TGF beta secreted by Kupffer cells during SCW-induced hepatic inflammation may amplify its own expression and regulate Kupffer cell functions relevant to the formation of granulomatous lesions within the liver.

A second messenger RNA species of transforming growth factor beta 1 in infarcted rat heart

Transforming growth factor-beta 1 (TGF-beta 1) is encoded predominantly by a 2.4-kb mRNA in most tissues. However, an additional transcript of 1.9 kb can be detected in rat heart after experimental myocardial infarction caused by ligation of the left coronary artery. This transcript level is significantly higher in infarcted heart tissue than in normal heart tissue, suggesting an important role for this mRNA species in response to injury. Structural characterization of the 1.9-kb mRNA showed that it included the entire coding sequence present in the 2.4-kb TGF-beta 1 mRNA, but also contained an additional nonhomologous 3'-untranslated region (UTR). The junction between the shared and unique 3' sequence in the 1.9-kb mRNA occurred only two nucleotides before the proposed polyadenylation site of the rat TGF-beta 1 2.4-kb mRNA. The unique 3'-UTR and the deduced shortened 5'-UTR in the novel 1.9-kb TGF-beta 1 mRNA suggest different transcriptional and translational regulatory mechanisms under conditions of tissue injury.