Fibrogenesis. V. TGF-beta signaling pathways

Identification of transforming growth factors actively transcribed during the progress of liver fibrosis in biliary atresia

BACKGROUND/PURPOSE

Transforming growth factor-beta (TGF-beta) 1 and 2 and their receptors TbetaR-I, TbetaR-II, and TbetaR-III are powerful profibrogenic mediators in the body. Their expression has not been completely elucidated in the progress of liver fibrosis associated with biliary atresia (BA).

METHODS

The authors compared the cytokine expression in the liver of 3 patients with BA at Kasai's procedure (KP) and in 3 patients at liver transplantation (LT). Two liver samples from children with no liver disorders served as normal controls (CO). Real-time quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) was used to confirm the findings of relative mRNA expression of TGF-beta1 and 2 and their receptors. An immunohistochemistry and an enzyme-linked immunoassay (ELISA) were used to localize the liver cells that express TGF-beta2 and to quantitate the protein expression among groups.

RESULTS

Compared with controls, both TGF-beta1 and TGF-beta2 mRNA expression increased in the liver during the progress of liver fibrosis in patients with KP and LT on the array. Only TGF-beta2 showed a significant increase in expression in LT compared with KP and CO (P =.001 for TGF-beta2 and P = 0.054 for TGF-beta1). Both TbetaR-I and TbetaR-II showed no significant change among groups; TbetaR-III decreased significantly in LT compared with CO (P =.011). TGF-beta2 immunostaining was mainly localized in the bile duct epithelium and was remarkably higher in LT in which the proliferating bile ductules and the hepatocytes contributed to the increase in immunostaining and possibly to significantly higher plasma TGF-beta2 protein levels in LT than in KP.

CONCLUSIONS

This study identified TGF-beta2 as the most actively transcribed TGF-beta gene during the progress of liver fibrosis in BA and found a reciprocal relationship of upregulation of TGF-beta2 with downregulation of TbetaR-III in LT.

Autocrine release of TGF-beta by portal fibroblasts regulates cell growth

Portal fibroblasts (PF) are a newly isolated population of fibrogenic cells in the liver postulated to play a significant role in early biliary fibrosis. Because transforming growth factor-beta (TGF)-beta is a key growth factor in fibrosis, we characterized the response of PF to TGF-beta. We demonstrate that PF produce significant amounts of TGF-beta2 and, unlike activated hepatic stellate cells (HSC), express all three TGF-beta receptors and are growth inhibited by TGF-beta1 and TGF-beta2. Fibroblast growth factor (FGF)-2, but not platelet derived growth factor (PDGF), causes PF proliferation. These data suggest a mechanism whereby HSC eclipse PF as the dominant myofibroblast population in biliary fibrosis.

The role of transforming growth factor beta in lung development and disease

Transforming growth factor (TGF) beta plays an important role in normal pulmonary morphogenesis and function and in the pathogenesis of lung disease. The effect of TGFbeta is regulated via a selective pathway of TGFbeta synthesis and signaling that involves activation of latent TGFbeta, specific TGFbeta receptors, and intracellular signaling via Smad molecules. All three isoforms of TGFbeta are expressed at high levels during normal lung development, being particularly important for branching morphogenesis and epithelial cell differentiation with maturation of surfactant synthesis. Small amounts of TGFbeta are still present in the adult lung, and TGFbeta is involved in normal tissue repair following lung injury. However, in a variety of forms of pulmonary pathology, the expression of TGFbeta is increased. These include chronic lung disease of prematurity as well as several forms of acute and chronic adult lung disease. While TGFbeta1 appears to be the predominant isoform involved, elevated levels of all three isoforms have been demonstrated. The increase in TGFbeta precedes abnormalities in lung function and detectable lung pathology, but correlates with the severity of the disease. TGFbeta plays a key role in mediating fibrotic tissue remodeling by increasing the production and decreasing the degradation of connective tissue via several mechanisms.

Extracellular matrix molecules in chronic obstructive sialadenitis: an immunocytochemical and Western blot investigation

The exact pathomechanism of inflammation progress and fibrosis in chronic sialadenitis is unknown. Connective tissue growth factor (CTGF), matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) have been implicated in the pathogenesis of various fibrotic conditions. These factors are thought to be essential in the regulation of extracellular matrix turnover and the development of tissue fibrosis. In the present study, the expression of CTGF, MMP-2, -3, -9, -13 and TIMP-3 was examined in chronic obstructive sialadenitis. Tissue samples of 13 patients with chronic sialadenitis of the submandibular gland associated with sialolithiasis and 4 normal tissue samples of the submandibular gland were analyzed immunohistochemically and by Western blot analysis. An intense CTGF immunoreactivity was observed in the ductal system of inflamed salivary glands, whereas in normal glands no reactivity or a very low CTGF immunoreactivity was present. Immunohistochemical studies revealed a low to strong reactivity of MMP-2, -3, -9, -13, and TIMP-3 in the ductal system, in acinar cells and in lymphomonocytic infiltrates in normal and inflamed tissues. The expression of MMP-2, -3, -9, -13, and TIMP-3 was confirmed by Western blotting in all cases. Over-expression of CTGF in chronic obstructive sialadenitis suggests that this factor may play a role in glandular fibrosis. However, the physiological role of MMP-2, -3, -9, -13, and TIMP-3 in normal glands, as well as their possible role in inflammation progress and fibrosis in chronic obstructive sialadenitis, remains to be elucidated.

[Interstitial lung disease]

Molecular investigation into the physiopathology of interstitial lung diseases has gained special interest through the trials carried out in the last decade. These trials seem to point at the role played by certain molecules, such as cytokines (transforming growth factor, platelet derived growth factor) and integrins, in the processes that lead to pulmonary fibrosis during the course of interstitial lung disease. They also demonstrate the important role that angiotensin II plays in increasing the secretion of transforming growth factor by several cells. The above-mentioned studies allow new therapeutic approaches to be considered which will possibly improve the serious prognosis of such diseases once they have reached the last stage of their course: pulmonary fibrosis.

Kallikrein gene delivery attenuates cardiac remodeling and promotes neovascularization in spontaneously hypertensive rats

Hypertension that results in left ventricular (LV) hypertrophy and/or fibrosis can lead to cardiac dysfunction. Spontaneously hypertensive rats (SHR) develop high blood pressure and LV hypertrophy at an early age and are a popular model of human essential hypertension. To investigate the role of the tissue kallikrein-kinin system in cardiac remodeling, an adenovirus containing the human tissue kallikrein gene was injected intravenously into adult SHR and normotensive Wistar-Kyoto (WKY) rats. The blood pressure of WKY rats remained unchanged throughout the experiment. Alternatively, kallikrein gene transfer reduced blood pressure in SHR for the first 2 wk, but had no effect from 3 to 5 wk. Five weeks after kallikrein gene delivery, SHR showed significant reductions in LV-to-heart weight ratio, LV long axis, and cardiomyocyte size; however, these parameters were unaffected in WKY rats. Interestingly, cardiac collagen density was decreased in both SHR and WKY rats receiving the kallikrein gene. Kallikrein gene transfer also increased cardiac capillary density in SHR, but not in WKY rats. The morphological changes after kallikrein gene transfer were associated with decreases in JNK activation as well as transforming growth factor (TGF)-beta 1 and plasminogen activator inhibitor-1 levels in the heart. In addition, kallikrein gene delivery elevated LV nitric oxide and cGMP levels in both rat strains. These results indicate that kallikrein-kinin attenuates cardiac hypertrophy and fibrosis and enhances capillary growth in SHR through the suppression of JNK, TGF-beta 1, and plasminogen activator inhibitor-1 via the nitric oxide-cGMP pathway.

Effect of Sea buckthorn on liver fibrosis: A clinical study

AIM: To appraise the effect of sea buckthorn (Hippophae rhamnoides) on cirrhotic patients.

METHODS: Fifty cirrhotic patients of Child-Pugh grade A and B were randomly divided into two groups: Group A as the treated group (n = 30), taking orally the sea buckthorn extract, 15 g 3 times a day for 6 mo. Group B as the control group (n = 18), taking vitamin B complex one tablet, 3 times a day for 6 mo. The following tests were performed before and after the treatment in both groups to determine LN, HA, collagens types III and IV, cytokines IL-6 and TNFα, liver serum albumin, total bile acid, ALT, AST and prothrombin time.

RESULTS: The serum levels of TNFα, IL-6, laminin and type IV collagen in group A were significantly higher than those in the control group. After a course of sea buckthorn treatment, the serum levels of LN, HA, collagen types III and IV, total bile acid (TBA) decreased significantly as compared with those before and after treatment in the control group. The sea buckthorn notably shortened the duration for normalization of aminotransferases.

CONCLUSION: Sea buckthorn may be a hopeful drug for prevention and treatment of liver fibrosis.

TGF beta 1 signaling and stimulation of osteoadherin in human odontoblasts in vitro

Transforming growth factor beta 1 (TGF beta 1) is generally considered to be a potent inducer of dentin formation. In order to further assess this role, we studied the influence of this factor in human dental pulp cells on the expression of osteoadherin (OSAD), a newly described proteoglycan found in bone and dentin and suspected to play a role in mineralization events. We performed TGF beta 1 stimulation both in cultures of human tooth thick slices including mature odontoblasts and in pulp explant cultures giving rise to early secretory odontoblasts or pulpal fibroblasts. We first showed by immunohistochemistry that molecules involved in TGF beta 1 signal transduction, that is, membrane receptors T beta RI and T beta RII and intracellular proteins SMAD-2, SMAD-3, and SMAD-4, were present in human dental cells in vivo and were all maintained after culture of thick-sliced teeth in cells undergoing TGF beta 1 stimulation. In this culture system, OSAD synthesis was increased in mature odontoblasts close to the TGF beta 1 delivery system. In explant cultures, semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) analysis indicated that the growth factor stimulated OSAD gene expression in early secretory odontoblasts and in pulpal fibroblasts. Taken together, these results indicate that OSAD expression is stimulated by TGF beta 1 in pulpal fibroblasts and in early secretory and mature odontoblasts. We suggest that TGF beta 1 in this way could control the organization and the mineralization of the extracellular matrix deposited by these cells during dentin formation.

Transforming growth factor beta in chronic obstructive sialadenitis of human submandibular gland

BACKGROUND

The exact pathomechanism of inflammation progress and fibrosis in chronic obstructive sialadenitis is unknown. The aim of the present study was to assess whether there is an association between transforming growth factor beta (TGF-beta) and fibrogenic process of chronic sialadenitis.

METHODS

Tissue samples of 12 patients with chronic sialadenitis and 4 normal tissue samples of the submandibular gland were examined immunohistochemically for identification of TGF-beta. TGF-beta1 messenger RNA (mRNA) expression was analysed semiquantitatively using reverse transcription polymerase chain reaction and gel electrophoresis to correlate its expression levels with stages of the disease.

RESULTS

TGF-beta positive cells could be found in the secretory duct system of all examined samples. However, an intense TGF-beta immunoreactivity was observed in inflamed salivary glands. With progress of disease TGF-beta1 mRNA expression increases significantly.

CONCLUSION

Expression of TGF-beta in chronic sialadenitis and its apparent increase in advanced stages of the disease, suggests that this growth factor may play a role in glandular fibrosis.

The role of transforming growth factor beta in atherosclerosis: novel insights and future perspectives

PURPOSE OF REVIEW

Atherosclerosis is a disease of the arterial wall that seems to be tightly modulated by the local inflammatory balance. Transforming growth factors beta 1, 2 and 3 are cytokines/growth factors with broad activities on cells and tissues in the cardiovascular system, and have been suggested to play a role in the pathogenesis of atherosclerosis.

RECENT FINDINGS

In the present review, we discuss recent developments in the role of transforming growth factor beta in the regulation of the immuno-inflammatory balance that modulates atherosclerosis. Such studies strongly suggest that the inhibition of endogenous transforming growth factor beta signalling favours the development of atherosclerotic lesions with an increased inflammatory component (T cells and macrophages) and decreased collagen content, features that are characteristic of unstable atherosclerotic plaques.

SUMMARY

Transforming growth factor beta is identified as a critical modulator of the immuno-inflammatory balance in atherosclerosis, and a crucial plaque-stabilizing factor. Future studies should aim at defining the precise molecular mechanisms responsible for this protective effect, and developing immunomodulatory strategies based on the promotion of transforming growth factor beta activity (T regulatory T helper type 3 cells) to limit disease complications.

The role of hepatic stellate cells and transforming growth factor-beta(1) in cystic fibrosis liver disease

Liver disease causes significant morbidity and mortality from multilobular cirrhosis in patients with cystic fibrosis. Abnormal bile transport and biliary fibrosis implicate abnormal biliary physiology in the pathogenesis of cystic fibrosis-associated liver disease (CFLD), yet the mediators linking biliary events to fibrosis remain unknown. Activated hepatic stellate cells (HSCs) are the pre-eminent mediators of fibrosis in a range of hepatic disorders. The dominant stimulus for matrix production by HSCs is the cytokine transforming growth factor (TGF)-beta(1). In CFLD, the role of HSCs and the source of TGF-beta(1) have not been evaluated. Liver biopsy tissue obtained from 38 children with CFLD was analyzed. Activated HSCs, identified by co-localization of procollagen alpha(1)(I) mRNA and alpha-smooth muscle actin, were demonstrated as the cellular source of excess collagen production in the fibrosis surrounding the bile ducts and the advancing edge of scar tissue. TGF-beta protein and TGF-beta(1) mRNA expression were shown to be predominantly expressed by bile duct epithelial cells. TGF-beta(1) expression was significantly correlated with both hepatic fibrosis and the percentage of portal tracts showing histological abnormalities associated with CFLD. This study demonstrates a definitive role for HSCs in fibrogenesis associated with CFLD and establishes a potential mechanism for the induction of HSC collagen gene expression through the production of TGF-beta(1) by bile duct epithelial cells.

Transforming growth factor beta stimulates fibroblast-collagen matrix contraction by different mechanisms in mechanically loaded and unloaded matrices

Studies were carried out to test the idea that transforming growth factor beta (TGFbeta) stimulated fibroblast contraction of collagen matrices by different mechanisms depending on mechanical loading on the cells and matrix. Under mechanically unloaded conditions (floating matrices), TGFbeta stimulated contraction directly as an agonist and indirectly by preactivating cells to express the myofibroblast phenotype. Increased contraction of floating matrices by preactivated cells appeared to result in part from an autocrine mechanism. Under mechanically loaded conditions (stressed matrices), TGFbeta had no direct agonist effect on contraction. Fibroblasts preactivated to become myofibroblasts showed increased ability to transfer tension to stressed matrices, and tension persisted even after the cells' actin cytoskeleton was disrupted. Our findings are consistent with the idea that fibroblasts activated to become myofibroblasts in vitro have increased contractile activity and indicate that multiple mechanisms that differ depending on mechanical loading on the cells and matrix are involved.

Extraction and purification of TGFβ and its effect on the induction of apoptosis of hepatocytes

AIM: To extract and purify the transforming growth factor β (TGFβ), and to demonstrate its biological activity in vivo and induction of apoptosis of hepatocytes in vitro.

METHODS: TGFβ was isolated from fresh bovine platelets by acid/ethanol extraction method and purified with ion exchange and gel chromatography. The extracted TGFβ as injected subcutaneously to mice, and its biological activity in vivo was observed 72 hrs post-injection by HE staining. The morphological changes were observed by HE staining and the occurrence of apoptosis was detected by TUNEL method after the human normal hepatic cell line QZG was treated with 8 μg·L^-1TGFβ for 12 hrs in vitro.

RESULTS: The molecular mass 25 ku TGFβ protein was successfully extracted. It was able to induce localized granulation tissue formation in vivo. TGFβ-treated hepatocytes showed obvious apoptotic morphological changes, including the pyknosis and dense-stained nuclei and cytoplasm, the fragmentary, annular or crescent nuclei, and the “bubbling” cytoplasm. Moreover, its apoptotic rate was significantly higher than that of the control group (P < 0.05).

CONCLUSION: Biological active TGFβ protein is extracted and purified successfully from bovine platelets, and it is able to induce the apoptosis of hepatocytes.

The many faces of transforming growth factor-beta in pleural diseases

Transforming growth factor (TGF)-beta is responsible for critical regulatory functions in many physiologic and pathologic processes. Emerging evidence suggests that these roles also apply to a multitude of pleural diseases. Both mesothelial cells and infiltrating cells in the pleural space can produce TGFbeta, and elevated TGFbeta concentrations have been found in pleural effusions and in pleural tissues during disease processes. Recent animal studies have suggested that TGFbeta can induce significant pleurodesis and probably plays a central role in the pathogenesis of pleural fibrosis. Paradoxically, TGFbeta may also stimulate increased pleural fluid formation, in part by inducing the production of vascular endothelial growth factor. TGFbeta also participates in the regulation of pleural inflammation and cell proliferation. Further research into the roles of TGFbeta in the pathogenesis of various pleural diseases is needed and may lead to the development of novel treatment strategies.