Liver fibrosis is a major cause of liver failure, but treatment remains ineffective. In the present study, we investigated the mechanisms and anti-hepatofibrotic activities of asiatic acid (AA) in a rat model of liver fibrosis induced by carbon tetrachloride (CCl4) and in vitro in TGF-beta1-stimulated rat hepatic stellate cell line (HSC-T6). Treatment with AA significantly attenuated CCl4-induced liver fibrosis and functional impairment in a dosage-dependent manner, including blockade of the activation of HSC as determined by inhibiting de novo alpha smooth muscle actin (a-SMA) and collagen matrix expression, and an increase in ALT and AST (all p<0.01). The hepatoprotective effects of AA on fibrosis were associated with upregulation of hepatic Smad7, an inhibitor of TGF-beta signaling, thereby blocking upregulation of TGF-beta1 and CTGF and the activation of TGF-beta/Smad signaling. The anti-fibrosis activity and mechanisms of AA were further detected in vitro in HSC-T6. Addition of AA significantly induced Smad7 expression by HSC-T6 cells, thereby inhibiting TGF-beta1-induced Smad2/3 activation, myofibroblast transformation, and collagen matrix expression in a dosage-dependent manner. In contrast, knockdown of Smad7 in HSC-T6 cells prevented AA-induced inhibition of HSC-T6 cell activation and fibrosis in response to TGF-beta1, revealing an essential role for Smad7 in AA-induced anti-fibrotic activities during liver fibrosis in vivo and in vitro. In conclusion, AA may be a novel therapeutic agent for liver fibrosis. Induction of Smad7-dependent inhibition of TGF-beta/Smad-mediated fibrogenesis may be a central mechanism by which AA protects liver from injury.
AIM: To explore the anti-fibrotic effect of Haobie Yangyin Ruanjian Decoction (HYRD) on CCl4-induced hepatic fibrosis in rats and its modulation on the transforming growth factor (TGF) β-Smad signaling pathway.
METHODS: Fifty-six healthy Wistar rats were randomly divided into five groups: normal control group (n = 6), CCl4-induced hepatic fibrosis group (n = 14) and three treatment groups (the treated rats received HYRD via oral administration at daily dosages of 8.2, 2.5 and 0.82 g/kg, respectively) of HYRD (n = 12, respectively). Experimental hepatic fibrosis was induced by subcutaneous injection of carbon tetrachloride solution (CCl4 dissolved in peanut oil, 4:6, V/V) with 0.5 mL/100 g body weight for the first time, and then 0.3 mL/100 g body weight twice a week for 8 wk. In the former 2 wk, rats were raised by feedstuff I (80% corn meal, 20% lard, 0.5% cholesterol). After 2 wk, they were raised by feedstuff II (corn meal and 0.5% cholesterol). Except for the control group, 30% alcohol solution was given orally to each rat every other day from the beginning, 1 mL for each rat. Liver function parameters and hepatic hydroxyproline content were detected by chromatometry. Serum levels of hyaluronic acid (HA), type IV collagen (CIV), type III precollagen (PCIII) and laminin (LN) were assayed with radioimmunoassay. Deposition of collagen was observed with hematoxylin-eosin staining and collagen staining. Gene expression of TGFβ1 and Smad3 were detected with real-time reverse transcriptase-polymerase chain reaction and Western blotting, respectively.
RESULTS: The serum levels of alanine transaminase and aspartate transaminase were increased in the model group compared with the control group (P < 0.01), and they were decreased in the three treatment groups compared with the model group. The serum levels of total protein and albumin were decreased in the model group and increased in the three treatment groups. The hepatic hydroxyproline content and serum levels of PCIII, HA, LN and CIV were markedly increased in the model group compared with the control group, and decreased in the treatment groups. The gene expression of TGFβ1 and Smad3 was enhanced in the model group compared with the control group, and HYRD could down regulate their expression.
CONCLUSION: HYRD can inhibit hepatic fibrosis induced by CCl4 in rats, which is probably associated with its down-regulation on fibrogenic signal transduction of TGFβ-Smad pathway.
Haobie Yangyin Ruanjian Decoction; Hepatic fibrosis; Transforming growth factor β-Smad signaling; Rat model; Carbon tetrachloride
AIM: To explore the anti-fibrotic effect of Oxymatrine on CCl4-induced liver fibrosis in rats and its modulation on the TGFbeta-Smad signaling pathway.
METHODS: One hundred healthy male SD rats were randomly divided into three groups: normal group (n = 20), treatment group of Oxymatrine (n = 40) and CCl4-induced fibrosis group (n = 40). Experimental hepatic fibrosis was induced by subcutaneous injection of carbon tetrachloride (CCl4 soluted in liquid paraffin with the concentration of 300 g/L, the dosage of injection was 3 mL/kg, twice per week for 8 wk). The treated rats received Oxymatrine via celiac injection at a dosage of 10 mg/kg twice a week at the same time. The deposition of collagen was observed with H&E and Masson staining. The concentration of serum TGF-β1 was assayed with ELISA. The gene expression of Smads and CBP (CREB binding protein) was detected with in situ hybridization (ISH) and immunohistochemistry (IH), respectively. All the experimental figures were scanned and analyzed with special figure-analysis software.
RESULTS: A significant reduction of collagen deposition and rearrangement of the parenchyma was noted in the liver tissue of Oxymatrine-treated rats. The semi-quantitative histological scores (2.43 ± 0.47 μm2 vs 3.76 ± 0.68 μm2, P < 0.05) and average area of collagen in those rats were significantly decreased when compared with hepatic cirrhosis model rats (94.41 ± 37.26 μm2 vs 290.86 ± 89.37 μm2, P < 0.05). The gene expression of Smad 3 mRNA was considerably decreased in the treated animals. The A value of Smad 3 mRNA was lower in the treated rats than the model rats (0.034 ± 0.090 vs 0.167 ± 0.092, P < 0.05). Contrarily, the A value of Smad 7 mRNA was increased considerably in the treated animals (0.175 ± 0.065 vs 0.074 ± 0.012, P < 0.05). There was an obvious decrease in the expression of CBP mRNA in treated rats as illuminated by a reduction of its A value when compared with model rats (0.065 ± 0.049 vs 0.235 ± 0.025, P < 0.001).
CONCLUSION: Oxymatrine is effective in reducing the production and deposition of collagen in the liver tissue of experimental rats. Oxymatrine could promote the expression of Smad 7 and inhibit the expression of Smad 3 and CBP in CCl4-induced hepatic fibrosis in SD rats, could modulate the fibrogenic signal transduction of TGFβ-Smad pathway.
Oxymatrine; Hepatic fibrosis; TGF-Smad signaling
Hepatic stellate cells (HSC) play a central role in the pathogenesis of liver fibrosis, transdifferentiating in chronic liver disease from “quiescent” HSC to fibrogenic myofibroblasts. Transforming growth factor-β (TGF-β), acting both directly and indirectly, is a critical mediator of this process. To characterize the function of the TGF-β signaling intermediates Smad2 and Smad3 in HSC, we infected primary rat HSC in culture with adenoviruses expressing wild-type and dominant negative Smads 2 and 3. Smad3-overexpressing cells exhibited increased deposition of fibronectin and type 1 collagen, increased chemotaxis, and decreased proliferation compared with uninfected cells and those infected with Smad2 or either dominant negative, demonstrating different biological functions for the two Smads. Additionally, coinfection experiments suggested that Smad2 and Smad3 signal via independent pathways. Smad3-overexpressing cells as well as TGF-β-treated cells demonstrated more focal adhesions and increased α-smooth muscle actin (α-SMA) organization in stress fibers, although all cells reached the same level of α-SMA expression, indicating that Smad3 also regulates cytoskeletal organization in HSC. We suggest that TGF-β, signaling via Smad3, plays an important role in the morphological and functional maturation of hepatic myofibroblasts.
AIM: To investigate the correlation between the antifibrotic effect of baicalin and serum cytokine production in rat hepatic fibrosis.
METHODS: Forty male Sprague-Dawley rats were divided randomly into four groups: normal control group, model group, baicalin-treated group, and colchicine-treated group. Except for the normal control group, all rats in the other groups were administered with carbon tetrachloride to induce hepatic fibrosis. At the same time, the last two groups were also treated with baicalin or colchicine. At the end of the 8 wk, all animals were sacrificed. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), transforming growth factor (TGF)-β1, tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-10 were measured. Liver index, hepatic hydroxyproline content and the degree of liver fibrosis were also evaluated.
RESULTS: The levels of ALT, AST and liver index in the baicalin-treated group were markedly lower than those in the model group (ALT: 143.88 ± 14.55 U/L vs 193.58 ± 24.35 U/L; AST: 263.66 ± 44.23 U/L vs 404.37 ± 68.29 U/L; liver index: 0.033 ± 0.005 vs 0.049 ± 0.009, P < 0.01). Baicalin therapy also significantly attenuated the degree of hepatic fibrosis, collagen area and collagen area percentage in liver tissue (P < 0.01). Furthermore, the levels of serum TGFβ1, TNF-α and IL-6 were strikingly reduced in the baicalin-treated group compared with the model group, while the production of IL-10 was up-regulated: (TGF-β1: 260.21 ± 31.01 pg/mL vs 375.49 ± 57.47 pg/mL; TNF-α: 193.40 ± 15.18 pg/mL vs 260.04 ± 37.70 pg/mL; IL-6: 339.87 ± 72.95 pg/mL vs 606.47 ± 130.73 pg/mL; IL-10: 506.22 ± 112.07 pg/mL vs 316.95 ± 62.74 pg/mL, P < 0.01).
CONCLUSION: Baicalin shows certain therapeutic effects on hepatic fibrosis, probably by immunoregulating the imbalance between profibrotic and antifibrotic cytokines.
Baicalin; Hepatic fibrosis; Hepatic stellate cell; Cytokines
Transforming growth factor type-β (TGF-β)/Smad pathway plays an essential role in vascular fibrosis. Reactive oxygen species (ROS) generation also mediates TGF-β signaling-induced vascular fibrosis, suggesting that some sort of interaction exists between Smad and redox pathways. However, the underlying molecular mechanism is largely unknown. This study aims to investigate the influence of poly(ADP-ribose) polymerase 1 (PARP1), a downstream effector of ROS, on TGF-β signaling transduction through Smad3 pathway in rat vascular smooth muscle cells (VSMCs).
Methods and Results
TGF-β1 treatment promoted PARP1 activation through induction of ROS generation in rat VSMCs. TGF-β1-induced phosphorylation and nuclear accumulation of Smad3 was prevented by treatment of cells with PARP inhibitor, 3-aminobenzamide (3AB) or N-(6-oxo-5,6-dihydrophenanthridin-2-yl)-2-(N,N-dimethylamino)acetami (PJ34), or PARP1 siRNA. TGF-β1 treatment promoted poly(ADP-ribosy)lation of Smad3 via activation of PARP1 in the nucleus. Poly(ADP-ribosy)lation enhanced Smad-Smad binding element (SBE) complex formation in nuclear extracts and increased DNA binding activity of Smad3. Pretreatment with 3AB, PJ34, or PARP1 siRNA prevented TGF-β1-induced Smad3 transactivation and expression of Smad3 target genes, including collagen Iα1, collagen IIIα1 and tissue inhibitor of metalloproteinase 1, in rat VSMCs.
PARP1 is indispensable for TGF-β1 induced Smad3 activation in rat VSMCs. Targeting PARP1 may be a promising therapeutic approach against vascular diseases induced by dysregulation of TGF-β/Smad3 pathway.
Transforming growth factor-β1 (TGF-β1) plays a key role in hypertrophic scar formation. A lot of studies have shown that TGF-β1 stimulates fibroblast proliferation, collagen production, and α-smooth muscle actin (α-SMA) expression, inhibits matrix degradation and eventually leads to scar formation. Smad proteins are important intracellular mediators of TGF-β1 signaling, and Smad ubiquitination regulatory factor 2 (Smurf2), an ubiquitin ligase for Smads, plays critical roles in the regulation of TGF-β1/Smad signaling. It was reported that Smurf2 was abnormally expressed during the process of liver fibrosis and lung fibrosis. Hypertrophic scarring is a fibroproliferative disorder of the dermis that occurs following wounding. However, little is known about the expression of Smurf2 in hypertrophic scarring. We hypothesized that TGF-β1 signaling cannot be disrupted after wound epithelialization probably due to abnormal expression of Smurf2 in hypertrophic scar fibroblasts. In the present study, we found that hypertrophic scar fibroblasts exhibited increased Smurf2 protein and mRNA levels compared with normal fibroblasts, and the expression of Smurf2 gradually increased in hypertrophic scar fibroblasts after TGF-β1 stimulation. Furthermore, we transfected Smurf2 siRNA into hypertrophic scar fibroblasts, and we found that silencing the expression of Smurf2 in hypertrophic scar fibroblasts dramatically reduced TGF-β1 production, inhibited TGF-β1-induced α-SMA expression and inhibited TGF-β1-induced collagen I synthesis. Our results suggest that the enhanced expression of Smurf2 is involved in the progression of hypertrophic scarring.
Smad ubiquitination regulatory factor 2; TGF-β1; Hypertrophic scar
Tubulointerstitial fibrosis is the final common result of a variety of progressive injuries leading to chronic renal failure. Transforming growth factor-β (TGF-β) is reportedly upregulated in response to injurious stimuli such as unilateral ureteral obstruction (UUO), causing renal fibrosis associated with epithelial-mesenchymal transition (EMT) of the renal tubules and synthesis of extracellular matrix. We now show that mice lacking Smad3 (Smad3ex8/ex8), a key signaling intermediate downstream of the TGF-β receptors, are protected against tubulointerstitial fibrosis following UUO as evidenced by blocking of EMT and abrogation of monocyte influx and collagen accumulation. Culture of primary renal tubular epithelial cells from wild-type or Smad3-null mice confirms that the Smad3 pathway is essential for TGF-β1–induced EMT and autoinduction of TGF-β1. Moreover, mechanical stretch of the cultured epithelial cells, mimicking renal tubular distention due to accumulation of urine after UUO, induces EMT following Smad3-mediated upregulation of TGF-β1. Exogenous bone marrow monocytes accelerate EMT of the cultured epithelial cells and renal tubules in the obstructed kidney after UUO dependent on Smad3 signaling. Together the data demonstrate that the Smad3 pathway is central to the pathogenesis of interstitial fibrosis and suggest that inhibitors of this pathway may have clinical application in the treatment of obstructive nephropathy.
We have recently described that in an experimental model of atherosclerosis and in vascular smooth muscle cells (VSMCs) statins increased the activation of the Smad pathway by transforming growth factor-β (TGF-β), leading to an increase in TGF-β-dependent matrix accumulation and plaque stabilization. Angiotensin II (AngII) activates the Smad pathway and contributes to vascular fibrosis, although the in vivo contribution of TGF-β has not been completely elucidated. Our aim was to further investigate the mechanisms involved in AngII-induced Smad activation in the vasculature, and to clarify the beneficial effects of statins on AngII-induced vascular fibrosis. Infusion of AngII into rats for 3 days activates the Smad pathway and increases fibrotic-related factors, independently of TGF-β, in rat aorta. Treatment with atorvastatin or simvastatin inhibited AngII-induced Smad activation and related-fibrosis. In cultured rat VSMCs, direct AngII/Smad pathway activation was mediated by p38 MAPK and ROCK activation. Preincubation of VSMCs with statins inhibited AngII-induced Smad activation at all time points studied (from 20 minutes to 24 hours). All these data show that statins inhibited several AngII-activated intracellular signaling systems, including p38-MAPK and ROCK, which regulates the AngII/Smad pathway and related profibrotic factors and matrix proteins, independently of TGF-β responses. The inhibitory effect of statins on the AngII/Smad pathway could explain, at least in part, their beneficial effects on hypertension-induced vascular damage.
Little is known about the involvement of Smad-related molecules in the regulation of the Transforming Growth Factor (TGF)-beta signaling pathway during hepatocarcinogenesis, particularly with respect to preneoplastic lesions of a rat liver. The aims of this study were to investigate the localizations and temporal expressions of TGF-beta Receptor Type 1 (TGR1) and Smads during the promotion stage of chemical hepatocarcinogenesis in rats. We investigated expressions and localizations of TGR1, Smad2, Smad4, and Smad7 by using semi-quantitative RT-PCR and immunohistochemistry in preneoplastic lesions during rat chemical hepatocarcinogenesis induced by Solt and Farber's method. The down-regulation of TGR1, Smad2, and Smad4 was evident during the later steps of the promotion stage of chemical hepatocarcinogenesis. In contrast with other Smads, increased Smad7 expression was evident during the later steps of the promotion stage. Also immunohistochemistry revealed that the main site of TGR1, Smad2, Smad4, and Smad7 expression was mainly in hepatocytes of the preneoplastic lesions of a rat liver. Dysregulation of the downstream effectors of TGF-beta such as TGR1, Smad2, Smad4 and, Smad7 might contribute to the progression of preneoplastic lesions during chemical hepatocarcinogenesis in a rat.
Notch signaling is essential to the regulation of cell differentiation, and aberrant activation of this pathway is implicated in human fibrotic diseases, such as pulmonary, renal, and peritoneal fibrosis. However, the role of Notch signaling in hepatic fibrosis has not been fully investigated. In the present study, we show Notch signaling to be highly activated in a rat model of liver fibrosis induced by carbon tetrachloride (CCl4), as indicated by increased expression of Jagged1, Notch3, and Hes1. Blocking Notch signaling activation by a γ-secretase inhibitor, DAPT, significantly attenuated liver fibrosis and decreased the expression of snail, vimentin, and TGF-β1 in association with the enhanced expression of E-cadherin. The study in vitro revealed that DAPT treatment could suppress the EMT process of rat hepatic stellate cell line (HSC-T6). Interestingly, DAPT treatment was found not to affect hepatocyte proliferation in vivo. In contrast, DAPT can inhibit hepatocyte apoptosis to some degree. Our study provides the first evidence that Notch signaling is implicated in hepatic fibrogenesis and DAPT treatment has a protective effect on hepatocytes and ameliorates liver fibrosis. These findings suggest that the inhibition of Notch signaling might present a novel therapeutic approach for hepatic fibrosis.
Although Smad3 has been considered as a downstream mediator of transforming growth factor-β (TGF-β) signaling in diabetes complications, the role of Smad7 in diabetes remains largely unclear. The current study tests the hypothesis that Smad7 may play a protective role and has therapeutic potential for diabetic kidney disease.
RESEARCH DESIGN AND METHODS
Protective role of Smad7 in diabetic kidney disease was examined in streptozotocin-induced diabetic mice that have Smad7 gene knockout (KO) and in diabetic rats given Smad7 gene transfer using an ultrasound-microbubble-mediated technique.
We found that mice deficient for Smad7 developed more severe diabetic kidney injury than wild-type mice as evidenced by a significant increase in microalbuminuria, renal fibrosis (collagen I, IV, and fibronectin), and renal inflammation (interleukin-1β [IL-1β], tumor necrosis factor-α [TNF-α], monocyte chemoattractant protein-1 [MCP-1], intracellular adhesion molecule-1 [ICAM-1], and macrophages). Further studies revealed that enhanced renal fibrosis and inflammation in Smad7 KO mice with diabetes were associated with increased activation of both TGF-β/Smad2/3 and nuclear factor-κB (NF-κB) signaling pathways. To develop a therapeutic potential for diabetic kidney disease, Smad7 gene was transferred into the kidney in diabetic rats by an ultrasound-microbubble-mediated technique. Although overexpression of renal Smad7 had no effect on levels of blood glucose, it significantly attenuated the development of microalbuminuria, TGF-β/Smad3-mediated renal fibrosis such as collagen I and IV and fibronectin accumulation and NF-κB/p65-driven renal inflammation including IL-1β, TNF-α, MCP-1, and ICAM-1 expression and macrophage infiltration in diabetic rats.
Smad7 plays a protective role in diabetic renal injury. Overexpression of Smad7 may represent a novel therapy for the diabetic kidney complication.
Progression of pancreatic ductal adenocarcinoma (PDAC) is largely the result of genetic and/or epigenetic alterations in the transforming growth factor-beta (TGF-β)/Smad signalling pathway, eventually resulting in loss of TGF-β-mediated growth arrest and an increase in cellular migration, invasion, and metastasis. These cellular responses to TGF-β are mediated solely or partially through the canonical Smad signalling pathway which commences with activation of receptor-regulated Smads (R-Smads) Smad2 and Smad3 by the TGF-β type I receptor. However, little is known on the relative contribution of each R-Smad, the possible existence of functional antagonism, or the crosstalk with other signalling pathways in the control of TGF-β1-induced growth inhibition and cell migration. Using genetic and pharmacologic approaches we have inhibited in PDAC cells endogenous Smad2 and Smad3, as well as a potential regulator, the small GTPase Rac1, and have analysed the consequences for TGF-β1-mediated growth inhibition and cell migration (chemokinesis).
SiRNA-mediated silencing of Smad3 in the TGF-β responsive PDAC cell line PANC-1 reduced TGF-β1-induced growth inhibition but increased the migratory response, while silencing of Smad2 enhanced growth inhibition but decreased chemokinesis. Interestingly, siRNA-mediated silencing of the small GTPase Rac1, or ectopic expression of a dominant-negative Rac1 mutant largely mimicked the effect of Smad2 silencing on both TGF-β1-induced growth inhibition, via upregulation of the cdk inhibitor p21WAF1, and cell migration. Inhibition of Rac1 activation reduced both TGF-β1-induction of a Smad2-specific transcriptional reporter and Smad2 C-terminal phosphorylation in PDAC cells while Smad3-specific transcriptional activity and Smad3 C-terminal phosphorylation appeared increased. Disruption of autocrine TGF-β signalling in PANC-1 cells rendered cells less susceptible to the growth-suppressive effect of Rac1 inhibition, suggesting that the decrease in "basal" proliferation upon Rac1 inhibition was caused by potentiation of autocrine TGF-β growth inhibition.
In malignant cells with a functional TGF-β signalling pathway Rac1 antagonizes the TGF-β1 growth inhibitory response and enhances cell migration by antagonistically regulating Smad2 and Smad3 activation. This study reveals that Rac1 is prooncogenic in that it can alter TGF-β signalling at the R-Smad level from a tumour-suppressive towards a tumour-promoting outcome. Hence, Rac1 might represent a viable target for therapeutic intervention to inhibit PDAC progression.
Liver fibrosis occurs in most types of chronic liver diseases and is characterized by excessive accumulation of extracellular matrix proteins, leading to disruption of tissue function and eventually organ failure. Transforming growth factor (TGF)-β represents an important pro-fibrogenic factor and aberrant TGF-β action has been implicated in many disease processes of the liver. Endoglin is a TGF-β co-receptor expressed mainly in endothelial cells that has been shown to differentially regulates TGF-β signal transduction by inhibiting ALK5-Smad2/3 signalling and augmenting ALK1-Smad1/5 signalling. Recent reports demonstrating upregulation of endoglin expression in pro-fibrogenic cell types such as scleroderma fibroblasts and hepatic stellate cells have led to studies exploring the potential involvement of this TGF-β co-receptor in organ fibrosis. A recent article by Meurer and colleagues now shows that endoglin expression is increased in transdifferentiating hepatic stellate cells in vitro and in two different models (carbon tetrachloride intoxication and bile duct ligation) of liver fibrosis in vivo. Moreover, they show that endoglin overexpression in hepatic stellate cells is associated with enhanced TGF-β-driven Smad1/5 phosphorylation and α-smooth muscle actin production without altering Smad2/3 signaling. These findings suggest that endoglin may play an important role in hepatic fibrosis by altering the balance of TGF-β signaling via the ALK1-Smad1/5 and ALK-Smad2/3 pathways and raise the possibility that targeting endoglin expression in transdifferentiating hepatic stellate cells may represent a novel therapeutic strategy for the treatment of liver fibrosis.
Endoglin, Liver fibrosis, TGF-β signaling; TGF-β co-receptor, Hepatic stellate cells
Transforming growth factor β (TGF-β) induces the process of epithelial-mesenchymal transition (EMT) through the Smad and JNK signaling. However, it is unclear how these pathways interact in the TGF-β1-induced EMT in rat peritoneal mesothelial cells (RPMCs). Here, we show that inhibition of JNK activation by introducing the dominant-negative JNK1 gene attenuates the TGF-β1-down-regulated E-cadherin expression, and TGF-β1-up-regulated α-SMA, Collagen I, and PAI-1 expression, leading to the inhibition of EMT in primarily cultured RPMCs. Furthermore, TGF-β1 induces a bimodal JNK activation with peaks at 10 minutes and 12 hours post treatment in RPMCs. In addition, the inhibition of Smad3 activation by introducing a Smad3 mutant mitigates the TGF-β1-induced second wave, but not the first wave, of JNK1 activation in RPMCs. Moreover, the inhibition of JNK1 activation prevents the TGF-β1-induced Smad3 activation and nuclear translocation, and inhibition of the TGF-β1-induced second wave of JNK activation greatly reduced TGF-β1-induced EMT in RPMCs. These data indicate a crosstalk between the JNK1 and Samd3 pathways during the TGF-β1-induced EMT and fibrotic process in RPMCs. Therefore, our findings may provide new insights into understanding the regulation of the TGF-β1-related JNK and Smad signaling in the development of fibrosis.
Cardiac fibroblasts are key effector cells in the pathogenesis of cardiac fibrosis. Transforming Growth Factor (TGF)-βSmad3 signaling is activated in the border zone of healing infarcts and induces fibrotic remodeling of the infarcted ventricle contributing to the development of diastolic dysfunction.
Our study explores the mechanisms responsible for the fibrogenic effects of Smad3 by dissecting its role in modulating cardiac fibroblast phenotype and function.
Methods and results
Smad3 null mice and corresponding wildtype (WT) controls underwent reperfused myocardial infarction protocols. Surprisingly, reduced collagen deposition in Smad3 −/− infarcts was associated with increased infiltration with myofibroblasts. In vitro studies demonstrated that TGF-β1 inhibited murine cardiac fibroblast proliferation; these anti-proliferative effects were mediated via Smad3. Smad3 −/− fibroblasts were functionally defective, exhibiting impaired collagen lattice contraction when compared to wildtype cells. Decreased contractile function was associated with attenuated TGF-β-induced expression of α-smooth muscle actin. In addition, Smad3 −/− fibroblasts had decreased migratory activity upon stimulation with serum, and exhibited attenuated TGF-β-induced upregulation of extracellular matrix protein synthesis. Upregulation of connective tissue growth factor (CTGF), an essential downstream mediator in TGF-β-induced fibrosis, was in part dependent on Smad3. CTGF stimulation enhanced extracellular matrix protein expression by cardiac fibroblasts in a Smad3-independent manner.
Disruption of Smad3 results in infiltration of the infarct with abundant, hypofunctional fibroblasts that exhibit impaired myofibroblast transdifferentiation, reduced migratory potential, and suppressed expression of fibrosis-associated genes.
fibroblasts; myocardial infarction; transforming growth factor-β; growth factors; fibrosis
Huangqi decoction was first described in Prescriptions of the Bureau of Taiping People's Welfare Pharmacy in Song Dynasty (AD 1078), and it is an effective recipe that is usually used to treat consumptive disease, anorexia, and chronic liver diseases. Transforming growth factor beta 1 (TGFβ1) plays a key role in the progression of liver fibrosis, and Huangqi decoction and its ingredients (IHQD) markedly ameliorated hepatic fibrotic lesions induced by ligation of the common bile duct (BDL). However, the mechanism of IHQD on hepatic fibrotic lesions is not yet clear. The purpose of the present study is to elucidate the roles of TGFβ1 activation, Smad-signaling pathway, and extracellular signal-regulated kinase (ERK) in the pathogenesis of biliary fibrosis progression and the antifibrotic mechanism of IHQD.
A liver fibrosis model was induced by ligation of the common bile duct (BDL) in rats. Sham-operation was performed in control rats. The BDL rats were randomly divided into two groups: the BDL group and the IHQD group. IHQD was administrated intragastrically for 4 weeks. At the end of the fifth week after BDL, animals were sacrificed for sampling of blood serum and liver tissue. The effect of IHQD on the TGFβ1 signaling pathway was evaluated by western blotting and laser confocal microscopy.
Decreased content of hepatic hydroxyproline and improved liver function and histopathology were observed in IHQD rats. Hepatocytes, cholangiocytes, and myofibroblasts in the cholestatic liver injury released TGFβ1, and activated TGFβ1 receptors can accelerate liver fibrosis. IHQD markedly inhibited the protein expression of TGFβ1, TGFβ1 receptors, Smad3, and p-ERK1/2 expression with no change of Smad7 expression.
IHQD exert significant therapeutic effects on BDL-induced fibrosis in rats through inhibition of the activation of TGFβ1-Smad3 and TGFβ1-ERK1/2 signaling pathways.
Ingredients of Huangqi decoction; Cholestatic liver fibrosis; Transforming growth factor beta 1; Smad-signaling pathway, Extracellular signal-regulated kinase
Tachycardia-induced atrial fibrosis is a hallmark of structural remodeling of atrial fibrillation (AF). The molecular mechanisms underlying the AF-induced atrial fibrosis remain unclear.
To determine the role of angiotensin II (AngII)/AT1 receptor-coupled transforming growth factor β1 (TGF-β1)/Smads signaling pathway in the AF-induced atrial fibrosis.
Methods and Results
Rapid atrial pacing (RAP, 1000 ppm) was applied to the left atrium of rabbit heart to induce atrial fibrillation and fibrosis. Quantitative PCR and Western blot analysis revealed that RAP caused a marked increase in the expression of AngII, TGF-β1, phosphorylated Smad2/3 (P-Smad2/3), Arkadia, and hydroxyproline synthesis. But the expression of Smad7, a key endogenous antagonist of the TGF-β1/Smads-mediated fibrosis, was significantly decreased. These changes were dose-dependently reversed by AT1 receptor antagonist losartan, implicating the involvement of AF-induced release of AngII and activation of AT1-receptor specific pathway. In the adult rabbit cardiac fibroblasts, AngII increased the expression of TGF-β1, P-Smad2/3, Smad4, Arkadia, and collagen I synthesis and significantly reduced Smad7 expression. These effects of AngII were reversed by losartan, but not by the AT2 antagonist (PD123319). In addition, extracellular signal-regulated kinase (ERK) inhibitor and anti-TGF-β1 antibody also blocked the AngII-induced downregulation of Smad7. Silencing of Smad7 gene by siRNA abolished losartan's antagonism on AngII's fibrogenic effects in cardiac fibroblasts while overexpression of Smad7 blocked AngII-induced increase in collagen I synthesis.
AngII/AT1-receptor specific activation of Arkadia-mediated poly-ubiquitination and degradation of Smad7 may decrease the inhibitory feedback regulation of TGF-β1/Smads signaling and serves as a key mechanism for AF-induced atrial fibrosis.
atrial remodeling; atrial fibrillation; atrial fibrosis; transforming growth factor; Smads; Angiotensin II; Arkadia
Connective tissue growth factor (CTGF/CCN2) is induced by transforming growth factor beta 1(TGF-β1) where it acts as a downstream mediator of TGF-β1 induced matrix production in osteoblasts. We have shown the requirement of Src, Erk and Smad signaling for CTGF induction by TGF-β1 in osteoblasts, however the potential interaction among these signaling pathways remains undetermined. In this study we demonstrate that TGF-β1 activates Src kinase in ROS17/2.8 cells and that treatment with the Src family kinase inhibitor PP2 prevents Src activation and CTGF induction by TGF-β1. Additionally, inhibiting Src activation prevented Erk activation, Smad 2 & 3 activation and nuclear translocation by TGF-β1, demonstrating that Src is an essential upstream signaling partner of both Erk and Smads in osteoblasts. MAPKs such as Erk can modulate the Smad pathway through directly mediating the phosphorylation of Smads or indirectly through activation/inactivation of required nuclear co-activators that mediate Smad DNA binding. When we treated cells with the Erk inhibitor, PD98059 it inhibited TGF-β1-induced CTGF protein expression but had no effect on Src activation, Smad activation or Smad nuclear translocation. However PD98059 impaired transcriptional complex formation on the Smad binding element (SBE) on the CTGF promoter, demonstrating that Erk activation was required for SBE transactivation. This data demonstrates that Src is an essential upstream signaling transducer of Erk and Smad signaling with respect to TGF-β1 in osteoblasts and that Smads and Erk function independently but are both essential for forming a transcriptionally active complex on the CTGF promoter in osteoblasts.
SRC; Osteoblasts; CTGF; TGF-β1; MAPK; Smads
The aim of this study was to investigate the hepatoprotective effect of Matrine salvianolic acid B salt on carbon tetrachloride (CCl4)-induced hepatic fibrosis in rats. Salvianolic acid B and Matrine has long been used to treat liver fibrosis. Matrine salvianolic acid B salt is a new compound containing Salvianolic acid B and Matrine. Hepatic fibrosis induced by CCl4 was studied in animal models using Wistar rats. Organ coefficient, serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), hexadecenoic acid (HA), laminin (LN), hydroxyproline (Hyp), and glutathione (GSH), malondialdehyde (MDA), superoxide dismutase (SOD) in liver tissues were measured, respectively. Histopathological changes in the livers were studied by hematoxylin-eosin (H&E) staining and Masson Trichrome (MT) examination. The expression of transforming growth factor-β1 (TGF-β1) and α-smooth muscle actin (α-SMA) was observed by immunohistochemical analysis. A significant reduction in serum levels of AST, ALT, HA, LN and Hyp was observed in the Matrine salvianolic acid B salt treated groups, suggesting that the salt had hepatoprotective effects. The depletion of GSH and SOD, as well as MDA accumulation in liver tissues was suppressed by Matrine salvianolic acid B salt too. The expression of TGF-β1 and α-SMA measured by immunohistology was significantly reduced by Matrine salvianolic acid B salt in a dose-dependent manner. Matrine salvianolic acid B salt treatment attenuated the necro-inflammation and fibrogenesis induced by CCl4 injection, and thus it is promising as a therapeutic anti-fibrotic agent against hepatic fibrosis.
Carbon tetrachloride; Hepatic fibrosis; Matrine salvianolic acid B salt
The cellular distribution and temporal expression of transcripts from transforming growth factor-beta 1 (TGF-beta 1) and procollagen alpha 1(I), alpha 1(III), and alpha 1(IV) genes were studied in carbon tetrachloride (CCl4)-induced rat liver fibrosis by using in situ hybridization technique. During the fibrotic process, TGF-beta 1 and procollagen genes were similarly and predominantly expressed in Desmin-positive perisinusoidal cells (e.g., fat-storing cells and myofibroblasts) and fibroblasts and their expression continued to be higher than those observed in control rats. These transcripts were also observed in inflammatory cells mainly granulocytes and macrophage-like cells at the early stages of liver fibrosis. The production of extracellular matrix along small blood vessels and fibrous septa coincided with the expression of these genes. Expression of TGF-beta 1 and procollagen genes were not detected in hepatocytes throughout the experiment. No significant differences in cellular distribution or time course of gene expression among procollagen alpha 1(I), alpha 1(III), and alpha 1(IV) were observed. Desmin-positive perisinusoidal cells and fibroblasts appeared to play the principal role in synthesis of collagens in CCl4-induced hepatic fibrosis. The simultaneous expression of TGF-beta 1 and procollagen genes in mesenchymal cells, including Desmin-positive perisinusoidal cells, during hepatic fibrosis suggests the possibility that TGF-beta 1 may have an important role in the production of fibrosis.
Recent advances in fibrosis biology have identified transforming growth factor (TGF)‐β type I receptor‐mediated activation of Smads as playing a central part in the development of fibrosis. However, to date, there have been few studies that examined the localisation and distribution of receptor‐activated Smads protein (R‐Smads: Smad2 and 3) during the fibrosis progression.
To histopathologically assess the time‐course change of the localisation and distribution of the Smads protein in pulmonary fibrosis.
Pulmonary fibrosis was induced by intranasal injection of bleomycin (0.3 U/mouse). Lungs were isolated 2, 5, 7, 9 and 14 days after bleomycin treatment. Histological changes in the lungs were evaluated by haematoxylin‐eosin stain or Masson's trichrome stain, and scored. TGF‐β1, Smad3 and phosphorylated Smad2 localisations in lung tissues were determined by immunohistochemistry.
The bleomycin treatment led to considerable pulmonary fibrotic changes accompanied by marked increase in TGF‐β1 expression in infiltrating macrophages. With the progression in fibrosis (day 7–14), marked increases in Smad3‐positive and pSmad2‐positive cells were observed. There were intense Smad3‐positive and pSmad2‐positive signals localised to the nuclei of the infiltrating macrophages and to type II epithelial cells, and less intense signals in fibroblasts and hyperplastic alveolar/bronchiolar epithelial cells.
The time‐course data of TGF‐β1 and R‐Smads indicate that progressive enhancement of TGF‐β1 signalling via R‐Smad is activated in the process of fibrosis progression.
Considerable evidence has demonstrated that transforming growth factor β (TGF-β) plays a key role in hepatic fibrosis, the final common pathway for a variety of chronic liver diseases leading to liver insufficiency. Although a few studies have reported that blocking TGF-β with soluble receptors or siRNA can prevent the progression of hepatic fibrosis, as yet no evidence has been provided that TGF-β antagonism can improve pre-existing hepatic fibrosis. The aim of this study was to examine the effects of a murine neutralizing TGF-β monoclonal antibody (1D11), in a rat model of thioacetamide (TAA)-induced hepatic fibrosis. TAA administration for 8 weeks induced extensive hepatic fibrosis, whereupon 1D11 dosing was initiated and maintained for 8 additional weeks. Comparing the extent of fibrosis at two time points, pre- and post-1D11 dosing, we observed a profound regression of tissue injury and fibrosis upon treatment, as reflected by a reduction of collagen deposition to a level significantly less than that observed before 1D11 dosing. Hepatic TGF-β1 mRNA, tissue hydroxyproline, and plasminogen activator inhibitor 1 (PAI-1) levels were significantly elevated at the end of the 8 week TAA treatment. Vehicle and antibody control groups demonstrated progressive injury through 16 weeks, whereas those animals treated for 8 weeks with 1D11 showed striking improvement in histologic and molecular endpoints. During the course of tissue injury, TAA also induced cholangiocarcinomas. At the end of study, the number and area of cholangiocarcinomas were significantly diminished in rats receiving 1D11 as compared to control groups, presumably by the marked reduction of supporting fibrosis/stroma. The present study demonstrates that 1D11 can reverse pre-existing hepatic fibrosis induced by extended dosing of TAA. The regression of fibrosis was accompanied by a marked reduction in concomitantly developed cholangiocarcinomas. These data provide evidence that therapeutic dosing of a TGF-β antagonist can diminish and potentially reverse hepatic fibrosis and also reduce the number and size of attendant cholangiocarcinomas.
To understand the role of TGF-β related signals in the repair of a corneal endothelium defect and also to evaluate the therapeutic effect of Smad7 gene transfer on injury induced fibrosis of the corneal endothelium in rats.
(1) Japanese albino rabbits (n=108) were used. Blocks of central cornea (4×4 mm) were prepared. After partially scraping the endothelium to produce a defect, the blocks were organ cultured for 24 h in the presence of either exogenous growth factors, transforming growth factor β (TGF-β)-neutralizing antibody, or inhibitors of each TGF-β related signal. Endothelium repair was assayed under light microscopy. (2) Adult Wistar rats (n=62) were then used. Smad7 expressing adenoviral vector (Smad7-Ad) or non-functioning control vector (Cre-Ad) was administered to the anterior chamber of an eye. The cornea was burned with topical 1 N NaOH (10 μl) three days later. After specific intervals, the eye was histologically observed.
(1) The endothelial layer that elongated toward the defect lacked proliferation after 24 h in organ culture. Endogenous TGF-β was required for endothelium defect repair. Inhibition of p38 and Erk but not c-Jun NH2-terminal kinase (JNK) and ALK5 signal (Smad) retarded such cell spreading. (2) Adenoviral Smad7 overexpression suppressed fibrogenic reaction of the endothelium of an alkali-burned cornea as evaluated by immunohistochemistry for phospho-Smad2, collagen I, and α-smooth muscle actin, a marker for endothelial-mesenchymal transition (EnMT), and by electron microscopy.
Inhibition of Smad and JNK signals do not affect corneal endothelium defect repair. Inhibition of Smad suppresses fibrogenic reaction via EnMT of corneal endothelium in vivo.
In addition to the activation of hepatic stellate cells TGF-β govern apoptosis and growth control of hepatocytes in liver injury. In non-parenchymal cells, TGF-β induces plasminogen activator inhibitor 1 (PAI-1) and connective tissue growth factor (CTGF) expression, which are involved in extra cellular matrix formation. Both genes were also regulated by glucocorticoids, which in certain cases showed antagonistic effects to the TGF-β-Smad 3 pathway. The purpose of our work was to investigate the influence of TGF-β and dexamethasone on PAI-1 and CTGF expression and secretion in primary hepatocytes.
By examining PAI-1 and CTGF mRNA and protein expression in cell lysates and cell-conditioned media under the influence of TGF-β and dexamethasone, we analysed signalling pathways controlling their expression. TGF-β and dexamethasone significantly co-induce PAI-1 and CTGF protein expression. On the other hand, we showed that TGF-β diminished a glucocorticoid receptor dependent luciferase reporter signal in Hep-G2. Inhibition of Erk downstream activation decreased TGF-β induced CTGF and PAI-1 expression to a basal level. PAI-1 was directly secreted by hepatocytes, whereas secretion of CTGF was retarded.
The data provide evidence that beside the TGF-β-Smad 3 pathway CTGF and PAI-1 expression is additionally dependent on Erk activity in hepatocytes giving new insights into regulation of the profibrogenic proteins.