Disruption of the Smad7 gene enhances CCI4-dependent liver damage and fibrogenesis in mice

Peptidoglycan isolated from the fruit of Lycium barbarum alleviates liver fibrosis in mice by regulating the TGF-β/Smad7 signaling and gut microbiota

The hepatoprotective effect of the fruit of Lycium barbarum has been documented in China over millennia. Lycium barbarum polysaccharides (LBPs) were the first macromolecules reported to mitigate liver fibrosis in carbon tetrachloride (CCl4)-treated mice. Herein, a neutral peptidoglycan, named as LBPW, was extracted from the fruit of Lycium barbarum. In this study, we investigated the hepatoprotective mechanisms of LBPW. CCl4-induced liver fibrosis mice were administered LBPW (50, 100, 200 mg ·kg-1 ·d-1, i.p.) or (100, 200, 300 mg· kg-1 ·d-1, i.g.) for 6 weeks. We showed that either i.p. or i.g. administration of LBPW dose-dependently attenuated liver damage and fibrosis in CCl4-treated mice. Pharmacokinetic analysis showed that cyanine 5.5 amine (Cy5.5)-labeled LBPW (Cy5.5-LBPW) could be detected in the liver through i.p. and i.g. administration with i.g.-administered Cy5.5-LBPW mainly accumulating in the intestine. In TGF-β1-stimulated LX-2 cells as well as in the liver of CCl4-treated mice, we demonstrated that LBPW significantly upregulated Smad7, a negative regulator of TGF-β/Smad signaling, to retard the activation of hepatic stellate cells (HSCs) and prevent liver fibrosis. On the other hand, LBPW significantly boosted the abundance of Akkermansia muciniphila (A. muciniphila) and fortified gut barrier function. We demonstrated that A. muciniphila might be responsible for the efficacy of LBPW since decreasing the abundance of this bacterium by antibiotics (Abs) blocked the effectiveness of LBPW. Overall, our results show that LBPW may exert the hepatoprotective effect via rebalancing TGF-β/Smad7 signaling and propagating gut commensal A. muciniphila, suggesting that LBPW could be leading components to be developed as new drug candidates or nutraceuticals against liver fibrosis.

Macrophage expression of constitutively active TβRI alleviates hepatic injury in a mouse model of concanavalin A-induced autoimmune hepatitis

Transforming growth factor-β (Tgf-β) contributes to the development of liver diseases through its regulation of various cell types. While Tgf-β signaling to hepatic stellate cells (HSCs) and hepatocytes was shown to mediate hepatic damage, the effect of Tgf-β on other cells in liver is yet to be clearly defined. Herein we identified a regulatory function of macrophage Tgf-β signaling in liver injury. We found that transgenic mice expressing constitutively active Tgf-β receptor type I (TβRI CA ) under the control of Fsp1-Cre (TβRI CA /Fsp1-Cre mice) were less susceptible to concanavalin A (conA)-induced autoimmune hepatitis. Liver tissue examination showed a decrease of necrotic area in conA-treated TβRI CA /Fsp1-Cre liver compared to those of wild-type mice. Blood test revealed that serum aminotransferases were significantly reduced in conA-treated TβRI CA /Fsp1-Cre mice as compared to those of wild-type mice. Immunohistochemistry for CD3 and myeloperoxidase demonstrated that there was a decreased accumulation of T cells and neutrophils, respectively, whereas ELISA showed that IL-4, IL-5, IL-10, IL-12 and IFN-γ was increased in livers of conA-treated TβRI CA /Fsp1-Cre mice. Alternatively activated macrophage (M2) polarization was significantly elevated in livers of conA-treated TβRI CA /Fsp1-Cre mice as indicated by enhanced hepatic expression of CCR2 and CD206 as well as increased numbers of liver macrophages expressing M2 subtype marker, CD163. qPCR analysis indicated an increased expression of TβRI CA , Arg1, Ym1, CD206, Snail1, Foxo1 and IRF4 as well as a decreased expression of MHC class II and CD1d in liver macrophages that were isolated from TβRI CA /Fsp1-Cre mice. Moreover, flow cytometry analysis showed a lower number of NKT cells in livers of conA-treated TβRI CA /Fsp1-Cre mice when compared to those of wild-type mice. In conclusion, Fsp1-Cre-mediated expression of TβRI CA lead to a decreased conA-induced liver injury that was associated with enhanced M2 macrophage polarization and reduced NKT cell recruitment.

Ursodeoxycholic acid ameliorates erectile dysfunction and corporal fibrosis in diabetic rats by inhibiting the TGF-β1/Smad2 pathway

Corporal tissue fibrosis is critical in diabetes-associated erectile dysfunction. Transforming growth factor-β1/Small mothers against decapentaplegic-2 (TGF-β1/Smad2) contributes to the induction of fibrosis in corporal tissue. Smad7 is accepted as a general negative regulator of Smad signaling, although its role in corporal fibrosis is unknown. Ursodeoxycholic acid (UDCA) is a hydrophilic bile acid used for biliary and liver related disorders and has antifibrotic effects in the liver. This study investigated the effects of UDCA on diabetic erectile dysfunction. Forty-eight male Spraque Dawley rats were divided into six groups: nondiabetic (n = 6), nondiabetic+20 mg/kg UDCA (n = 6), nondiabetic+80 mg/kg UDCA (n = 6), diabetic (n = 10), diabetic+20 mg/kg UDCA (n = 10), diabetic+80 mg/kg UDCA (n = 10). Diabetes was induced by intraperitoneal injection of 60 mg/kg Streptozocin. UDCA (20 and 80 mg/kg/day) or saline was subsequently administered via oral gavage for 56 days. Erectile function was evaluated as measurement of maximum intracavernosal pressure (m-ICP)/mean arterial pressure (MAP) and total ICP/MAP. Corporal tissues were evaluated by Western blotting and Masson's trichrome staining. Electrical stimulation-induced m-ICP/MAP responses were higher in UDCA-treated diabetic rats compared to untreated diabetic rats, respectively (20 mg/kg; 4 V: 0.77 ± 0.11 vs 0.45 ± 0.09, p = 0.0001 and 80 mg/kg; 4 V: 0.78 ± 0.11 vs 0.45 ± 0.09, p = 0.0001) UDCA prevented the increase in phospho-Smad2 and fibronectin protein expressions in diabetic corporal tissue both at 20 mg/kg (p = 0.0002, p = 0.002 respectively) and 80 mg/kg doses (p < 0.0001 for both). Smad7 protein expressions were significantly increased in the UDCA-treated diabetic groups compared to the untreated diabetic group (20 mg/kg: p = 0.0079; 80 mg/kg: p = 0.004). Furthermore, UDCA significantly prevented diabetes-induced increase in collagen (20 mg/kg: p = 0.0172; 80 mg/kg: p = 0.0003) and smooth muscle loss (20 mg/kg: p = 0.044; 80 mg/kg: p = 0.039). In conclusion, UDCA has a potential protective effect on erectile function in diabetic rats by altering fibrotic pathways via inhibition of TGF-β1/Smad2 and activation of Smad7.

Epithelial-mesenchymal transition in tissue repair and degeneration

Epithelial-mesenchymal transitions (EMTs) are the epitome of cell plasticity in embryonic development and cancer; during EMT, epithelial cells undergo dramatic phenotypic changes and become able to migrate to form different tissues or give rise to metastases, respectively. The importance of EMTs in other contexts, such as tissue repair and fibrosis in the adult, has become increasingly recognized and studied. In this Review, we discuss the function of EMT in the adult after tissue damage and compare features of embryonic and adult EMT. Whereas sustained EMT leads to adult tissue degeneration, fibrosis and organ failure, its transient activation, which confers phenotypic and functional plasticity on somatic cells, promotes tissue repair after damage. Understanding the mechanisms and temporal regulation of different EMTs provides insight into how some tissues heal and has the potential to open new therapeutic avenues to promote repair or regeneration of tissue damage that is currently irreversible. We also discuss therapeutic strategies that modulate EMT that hold clinical promise in ameliorating fibrosis, and how precise EMT activation could be harnessed to enhance tissue repair.

Ergothioneine suppresses hepatic stellate cell activation via promoting Foxa3-dependent potentiation of the Hint1/Smad7 cascade and improves CCl4-induced liver fibrosis in mice

Ergothioneine (EGT) is a bioactive compound derived from certain edible mushrooms. The activation of hepatic stellate cells (HSCs) is critically involved in the etiology of liver fibrosis (LF). Here, we report that in LX-2 HSCs, EGT upregulates the expression of Hint1 and Smad7 and suppresses their activation provoked by TGFβ1. The EGT-triggered inhibition of HSC activation is abolished by knocking down the expression of Hint1. Overexpression of Hint1 increases Smad7 and represses TGFβ1-provoked activation of LX-2 HSCs. In silico predictions unveiled that in the promoter region of the human Hint1 gene, there are two conserved cis-acting elements that have the potential to interact with the transcription factor Foxa3 termed hFBS1 and hFBS2, respectively. The knockdown of Foxa3 obviously declined Hint1 expression at both mRNA and protein levels. Transfection of Foxa3 or EGT treatment increased the activity of the luciferase reporter driven by the Hint1 promoter in an hFBS2-dependent manner. The knockdown of Foxa3 eliminated EGT-mediated upregulation of Hint1 promoter activity. Additionally, EGT triggered the nuclear translocation of Foxa3 without obviously affecting its expression level. Molecular docking analysis showed that EGT has the potential to directly interact with the Foxa3 protein. Moreover, Foxa3 played a critical role in EGT-mediated hepatoprotection. EGT modulated the Foxa3/Hint1/Smad7 signaling in mouse primary HSCs and inhibited their activation. The gavage of EGT considerably relieved CCl4-induced LF in mice. Our data provide new insights into the anti-LF activity of EGT. Mechanistically, EGT triggers the nuclear translocation of Foxa3 in HSCs, which promotes Hint1 transcription and subsequently elevates Smad7.

Global Transcriptomics of Congenital Hepatic Fibrosis in Autosomal Recessive Polycystic Kidney Disease using PCK rats

Congenital hepatic fibrosis / Autosomal recessive polycystic kidney disease (CHF/ARPKD) is an inherited neonatal disease induced by mutations in the PKHD1 gene and characterized by cysts, and robust pericystic fibrosis in liver and kidney. The PCK rat is an excellent animal model which carries a Pkhd1 mutation and exhibits similar pathophysiology. We performed RNA-Seq analysis on liver samples from PCK rats over a time course of postnatal day (PND) 15, 20, 30, and 90 using age-matched Sprague-Dawley (SD) rats as controls to characterize molecular mechanisms of CHF/ARPKD pathogenesis. A comprehensive differential gene expression (DEG) analysis identified 1298 DEGs between PCK and SD rats. The genes overexpressed in the PCK rats at PND 30 and 90 were involved cell migration (e.g. Lamc2, Tgfb2 , and Plet1 ), cell adhesion (e.g. Spp1, Adgrg1 , and Cd44 ), and wound healing (e.g. Plat, Celsr1, Tpm1 ). Connective tissue growth factor ( Ctgf ) and platelet-derived growth factor ( Pdgfb ), two genes associated with fibrosis, were upregulated in PCK rats at all time-points. Genes associated with MHC class I molecules (e.g. RT1-A2 ) or involved in ribosome assembly (e.g. Pes1 ) were significantly downregulated in PCK rats. Upstream regulator analysis showed activation of proteins involved tissue growth (MTPN) and inflammation (STAT family members) and chromatin remodeling (BRG1), and inhibition of proteins involved in hepatic differentiation (HNF4α) and reduction of fibrosis (SMAD7). The increase in mRNAs of four top upregulated genes including Reg3b, Aoc1, Tm4sf20 , and Cdx2 was confirmed at the protein level using immunohistochemistry. In conclusion, these studies indicate that a combination of increased inflammation, cell migration and wound healing, and inhibition of hepatic function, decreased antifibrotic gene expression are the major underlying pathogenic mechanisms in CHF/ARPKD.

Established new compound IMB16-4 self-emulsifying drug delivery systems for increasing oral bioavailability and enhancing anti-hepatic fibrosis effect

Liver fibrosis results from the chronic liver injury and no specific medical therapy is approved so far. Recently, new compound, N-(3,4,5-trichlorophenyl) - 2 (3-nitrobenzenesulfonamido) benzamide, referred to as IMB16-4, was developed to resist liver fibrosis. However, IMB16-4 displays poor aqueous solubility and poor oral bioavailability. To increase the dissolution rate, improve the oral bioavailability and enhance the anti-hepatic fibrosis action of IMB16-4, IMB16-4 self-emulsifying drug delivery systems (SEDDS) with negative charge or positive charge were prepared using simple stirring, respectively. Their stability, oral bioavailability and anti-liver fibrosis effect were evaluated. The results showed IMB16-4 SEDDS in simulated gastric juice were nearly spherical with the diameter of 100～200 nm and possessed good stability in 30 days. The oral bioavailability of IMB16-4 SEDDS with negative charge and positive charge were increased to 33 folds and 58 folds compared with that of pure IMB16-4, respectively. In bile duct ligation (BDL) rats, IMB16-4 SEDDS attenuated the degree of liver damage and decreased collagen accumulation. In addition, IMB16-4 SEDDS with negative charge easily accumulated in the liver and alleviated hepatic fibrosis by TGF-β/Smad signaling. These findings indicate that IMB16- 4 SEDDS may be a potential therapy for the treatment of liver fibrosis.

Limonin relieves TGF-β-induced hepatocyte EMT and hepatic stellate cell activation in vitro and CCl4-induced liver fibrosis in mice via upregulating Smad7 and subsequent suppression of TGF-β/Smad cascade

Liver fibrosis is a pathological process as a result of intrahepatic deposition of excessive extracellular matrix. Epithelial-mesenchymal transition (EMT) of hepatocytes and activation of hepatic stellate cells (HSCs) both play important roles in the etiology of liver fibrosis. Here, we found that limonin repressed transforming growth factor-β1 (TGF-β)-induced EMT in AML-12 hepatocytes and activation of LX-2 HSCs. In both kinds of cells, limonin suppressed TGF-β-provoked Smad2/3 C-terminal phosphorylation and subsequent nuclear translocation. Transcription of Smad2/3-downstream genes was in turn reduced. However, limonin exerted few effects on Smad2/3 phosphorylation at linker region. Mechanistically, limonin increased Smad7 at mRNA level in both AML-12 and LX-2 cells. Knockdown of Smad7 abrogated inhibitory effects of limonin on TGF-β-induced EMT in AML-12 cells and activation of LX-2 cells. Further studies revealed that limonin alleviated mouse liver fibrosis induced by CCl₄. In livers of model mice, limonin upregulated Smad7 and declined C-terminal phosphorylation and nuclear translocation of Smad2/3. Transcription of Smad2/3-responsive genes was also attenuated. Our findings indicated that limonin inhibits TGF-β-induced EMT of hepatocytes and activation of HSCs in vitro and CCl₄-induced liver fibrosis in mice. Upregulated Smad7 which suppresses Smad2/3-dependent gene transcription is implicated in the hepatoprotective activity of limonin.

Smad7 effects on TGF-β and ErbB2 restrain myofibroblast activation and protect from postinfarction heart failure

Repair of the infarcted heart requires TGF-β/Smad3 signaling in cardiac myofibroblasts. However, TGF-β-driven myofibroblast activation needs to be tightly regulated in order to prevent excessive fibrosis and adverse remodeling that may precipitate heart failure. We hypothesized that induction of the inhibitory Smad, Smad7, may restrain infarct myofibroblast activation, and we examined the molecular mechanisms of Smad7 actions. In a mouse model of nonreperfused infarction, Smad3 activation triggered Smad7 synthesis in α-SMA+ infarct myofibroblasts, but not in α-SMA-PDGFRα+ fibroblasts. Myofibroblast-specific Smad7 loss increased heart failure-related mortality, worsened dysfunction, and accentuated fibrosis in the infarct border zone and in the papillary muscles. Smad7 attenuated myofibroblast activation and reduced synthesis of structural and matricellular extracellular matrix proteins. Smad7 effects on TGF-β cascades involved deactivation of Smad2/3 and non-Smad pathways, without any effects on TGF-β receptor activity. Unbiased transcriptomic and proteomic analysis identified receptor tyrosine kinase signaling as a major target of Smad7. Smad7 interacted with ErbB2 in a TGF-β-independent manner and restrained ErbB1/ErbB2 activation, suppressing fibroblast expression of fibrogenic proteases, integrins, and CD44. Smad7 induction in myofibroblasts serves as an endogenous TGF-β-induced negative feedback mechanism that inhibits postinfarction fibrosis by restraining Smad-dependent and Smad-independent TGF-β responses, and by suppressing TGF-β-independent fibrogenic actions of ErbB2.

Targeting of Smad7 in Mesenchymal Cells Does Not Exacerbate Fibrosis During Experimental Chronic Pancreatitis

OBJECTIVES

Transforming growth factor-β (TGF-β)-mediated accumulation of extracellular matrix proteins such as collagen I is a common feature of fibrosis. Pancreatic stellate cells play an integral role in the pathogenesis of pancreatitis, and their profibrotic ability is mainly mediated by TGF-β signaling. To specifically address the role of fibrogenic cells in experimental pancreatic fibrosis, we deleted Smad7, the main feedback inhibitor of TGF-β signaling in this cell type in mice.

METHODS

A mouse strain harboring a conditional knockout allele of Smad7 (Smad7fl/fl) with the tamoxifen-inducible inducible Col1a2-CreERT allele was generated and compared with wild-type mice challenged with the cerulein-based model of chronic pancreatitis.

RESULTS

Pancreatic stellate cells lacking Smad7 had significantly increased collagen I and fibronectin production and showed a higher activation level in vitro. Surprisingly, the fibrotic index in the pancreata of treated conditional knockout mice was only slightly increased, without statistical significance. Except for fibronectin, the expression of different extracellular matrix proteins and the numbers of fibroblasts and inflammatory cells were similar between Smad7-mutant and control mice.

CONCLUSIONS

There was no clear evidence that the lack of Smad7 in pancreatic stellate cells plays a major role in experimental pancreatitis, at least in the mouse model investigated here.

Smad7 Deficiency in Myeloid Cells Does Not Affect Liver Injury, Inflammation or Fibrosis after Chronic CCl4 Exposure in Mice

Myeloid cells play an essential role in the maintenance of liver homeostasis, as well as the initiation and termination of innate and adaptive immune responses. In chronic hepatic inflammation, the production of transforming growth factor beta (TGF-β) is pivotal for scarring and fibrosis induction and progression. TGF-β signalling is tightly regulated via the Smad protein family. Smad7 acts as an inhibitor of the TGF-β-signalling pathway, rendering cells that express high levels of it resistant to TGF-β-dependent signal transduction. In hepatocytes, the absence of Smad7 promotes liver fibrosis. Here, we examine whether Smad7 expression in myeloid cells affects the extent of liver inflammation, injury and fibrosis induction during chronic liver inflammation. Using the well-established model of chronic carbon tetrachloride (CCl₄)-mediated liver injury, we investigated the role of Smad7 in myeloid cells in LysM-Cre Smad^fl/fl mice that harbour a myeloid-specific knock-down of Smad7. We found that the chronic application of CCl₄ induces severe liver injury, with elevated serum alanine transaminase (ALT)/aspartate transaminase (AST) levels, centrilobular and periportal necrosis and immune-cell infiltration. However, the myeloid-specific knock-down of Smad7 did not influence these and other parameters in the CCl₄-treated animals. In summary, our results suggest that, during long-term application of CCl₄, Smad7 expression in myeloid cells and its potential effects on the TGF-β-signalling pathway are dispensable for regulating the extent of chronic liver injury and inflammation.

MicroRNA-503 Targets Mothers Against Decapentaplegic Homolog 7 Enhancing Hepatic Stellate Cell Activation and Hepatic Fibrosis

BACKGROUND

The hyper-accumulation of extracellular matrix (ECM) is the leading cause of hepatic fibrosis, and TGF-β-induced activation of hepatic stellate cells (HSCs) is the central event of hepatic fibrosis pathogenesis. The deregulation and dysfunction of miRNAs in hepatic fibrosis have been reported previously.

AIMS

To identify miRNA(s) playing a role in HSC activation and the underlying mechanism.

METHODS

We analyzed online microarray expression datasets from Gene Expression Omnibus (GEO) for differentially expressed miRNAs in hepatic fibrosis-related disease liver tissues, examined the specific effects of the candidate miRNA on TGF-β-induced HSC activation, and screened for the targets of the candidate miRNA in the TGF-β/SMAD signaling. Then, the predicted miRNA-mRNA binding, the specific effects of the target mRNA, and the dynamic effects of miRNA and mRNA on TGF-β-induced HSC activation were investigated.

RESULTS

The miR-503 expression was upregulated in TGF-β-activated HSCs. miR-503 overexpression enhanced, while miR-503 inhibition attenuated TGF-β-induced HSC proliferation and ECM accumulation in HSCs. miR-503 targeted SMAD7 to inhibit SMAD7 expression. SMAD7 knockdown also aggravated TGF-β-induced HSC proliferation and ECM accumulation in HSCs. The effects of miR-503 overexpression on TGF-β-induced HSC activation were partially reversed by SMAD7 overexpression. In CCl₄-induced hepatic fibrosis model in rats, miR-503 overexpression aggravated, whereas SMAD7 overexpression improved CCl₄-induced fibrotic changes in rats' liver tissues. The effects of miR-503 overexpression on CCl₄-induced fibrotic changes were partially reversed by SMAD7 overexpression.

CONCLUSION

miR-503 acts on HSC activation and hepatic fibrosis through SMAD7. The miR-503/SMAD7 axis enhances HSC activation and hepatic fibrosis through the TGF-β/SMAD pathway.

Histone deacetylase‑2: A potential regulator and therapeutic target in liver disease (Review)

Histone acetyltransferases are responsible for histone acetylation, while histone deacetylases (HDACs) counteract histone acetylation. An unbalanced dynamic between histone acetylation and deacetylation may lead to aberrant chromatin landscape and chromosomal function. HDAC2, a member of class I HDAC family, serves a crucial role in the modulation of cell signaling, immune response and gene expression. HDAC2 has emerged as a promising therapeutic target for liver disease by regulating gene transcription, chromatin remodeling, signal transduction and nuclear reprogramming, thus receiving attention from researchers and clinicians. The present review introduces biological information of HDAC2 and its physiological and biochemical functions. Secondly, the functional roles of HDAC2 in liver disease are discussed in terms of hepatocyte apoptosis and proliferation, liver regeneration, hepatocellular carcinoma, liver fibrosis and non-alcoholic steatohepatitis. Moreover, abnormal expression of HDAC2 may be involved in the pathogenesis of liver disease, and its expression levels and pharmacological activity may represent potential biomarkers of liver disease. Finally, research on selective HDAC2 inhibitors and non-coding RNAs relevant to HDAC2 expression in liver disease is also reviewed. The aim of the present review was to improve understanding of the multifunctional role and potential regulatory mechanism of HDAC2 in liver disease.

Current perspectives on inhibitory SMAD7 in health and disease

Transforming growth factor β (TGF-β) family members play an extensive role in cellular communication that orchestrates both early development and adult tissue homeostasis. Aberrant TGF-β family signaling is associated with a pathological outcome in numerous diseases, and in-depth understanding of molecular and cellular processes could result in therapeutic benefit for patients. Canonical TGF-β signaling is mediated by receptor-regulated SMADs (R-SMADs), a single co-mediator SMAD (Co-SMAD), and inhibitory SMADs (I-SMADs). SMAD7, one of the I-SMADs, is an essential negative regulator of the pleiotropic TGF-β and bone morphogenetic protein (BMP) signaling pathways. In a negative feedback loop, SMAD7 inhibits TGF-β signaling by providing competition for TGF-β type-1 receptor (TβRI), blocking phosphorylation and activation of SMAD2. Moreover, SMAD7 recruits E3 ubiquitin SMURF ligases to the type I receptor to promote ubiquitin-mediated proteasomal degradation. In addition to its role in TGF-β and BMP signaling, SMAD7 is regulated by and implicated in a variety of other signaling pathways and functions as a mediator of crosstalk. This review is focused on SMAD7, its function in TGF-β and BMP signaling, and its role as a downstream integrator and crosstalk mediator. This crucial signaling molecule is tightly regulated by various mechanisms. We provide an overview of the ways by which SMAD7 is regulated, including noncoding RNAs (ncRNAs) and post-translational modifications (PTMs). Finally, we discuss its role in diseases, such as cancer, fibrosis, and inflammatory bowel disease (IBD).

Acute Liver Injury after CCl4 Administration is Independent of Smad7 Expression in Myeloid Cells

Myeloid cells are essential for the initiation and termination of innate and adaptive immunity that create homeostasis in the liver. Smad7 is an inhibitor of the transforming growth factor β (TGF-β) signaling pathway, which regulates inflammatory cellular processes. Knockdown of Smad7 in hepatocytes has been shown to promote liver fibrosis, but little is known about the effects of Smad7 in myeloid cells during inflammatory responses in the liver. Using mice with a myeloid-specific knockdown of Smad7 (LysM-Cre Smad7^fl/fl), we investigated the impact of Smad7 deficiency in myeloid cells on liver inflammation and regeneration using the well-established model of CCl₄-mediated liver injury. Early (24/48 h) and late (7 d) time points were analyzed. We found that CCl₄ induces severe liver injury, with elevated serum ALT levels, centrilobular and periportal necrosis, infiltrating myeloid cells and an increase of inflammatory cytokines in the liver. Furthermore, as expected, inflammation peaked at 24 h and subsided after 7 d. However, the knockdown of Smad7 in myeloid cells did not affect any of the investigated parameters in the CCl₄-treated animals. In summary, our results suggest that the inhibition of TGF-β signaling via Smad7 expression in myeloid cells is dispensable for the induction and control of acute CCl₄-induced liver injury.

CD147 mediates intrahepatic leukocyte aggregation and determines the extent of liver injury

Background

Chronic inflammation is the driver of liver injury and results in progressive fibrosis and eventual cirrhosis with consequences including both liver failure and liver cancer. We have previously described increased expression of the highly multifunctional glycoprotein CD147 in liver injury. This work describes a novel role of CD147 in liver inflammation and the importance of leukocyte aggregates in determining the extent of liver injury.

Methods

Non-diseased, progressive injury, and cirrhotic liver from humans and mice were examined using a mAb targeting CD147. Inflammatory cell subsets were assessed by multiparameter flow cytometry.

Results

In liver injury, we observe abundant, intrahepatic leukocyte clusters defined as ≥5 adjacent CD45⁺ cells which we have termed “leukocyte aggregates”. We have shown that these leukocyte aggregates have a significant effect in determining the extent of liver injury. If CD147 is blocked in vivo, these leukocyte aggregates diminish in size and number, together with a marked significant reduction in liver injury including fibrosis. This is accompanied by no change in overall intrahepatic leukocyte numbers. Further, blocking of aggregation formation occurs prior to an appreciable increase in inflammatory markers or fibrosis. Additionally, there were no observed, “off-target” or unpredicted effects in targeting CD147.

Conclusion

CD147 mediates leukocyte aggregation which is associated with the development of liver injury. This is not a secondary effect, but a cause of injury as aggregate formation proceeds other markers of injury. Leukocyte aggregation has been previously described in inflammation dating back over many decades. Here we demonstrate that leukocyte aggregates determine the extent of liver injury.

Smad7 deficiency decreases iron and haemoglobin through hepcidin up-regulation by multilayer compensatory mechanisms

To maintain iron homoeostasis, the iron regulatory hormone hepcidin is tightly controlled by BMP-Smad signalling pathway, but the physiological role of Smad7 in hepcidin regulation remains elusive. We generated and characterized hepatocyte-specific Smad7 knockout mice (Smad7^Alb/Alb ), which showed decreased serum iron, tissue iron, haemoglobin concentration, up-regulated hepcidin and increased phosphor-Smad1/5/8 levels in both isolated primary hepatocytes and liver tissues. Increased levels of hepcidin lead to reduced expression of intestinal ferroportin and mild iron deficiency anaemia. Interestingly, we found no difference in hepcidin expression or phosphor-Smad1/5/8 levels between iron-challenged Smad7^Alb/Alb and Smad7^flox/flox , suggesting other factors assume the role of iron-induced hepcidin regulation in Smad7 deletion. We performed RNA-seq to identify differentially expressed genes in the liver. Significantly up-regulated genes were then mapped to pathways, revealing TGF-β signalling as one of the most relevant pathways, including the up-regulated genes Smad6, Bambi and Fst (Follistatin). We found that Smad6 and Bambi-but not Follistatin-are controlled by the iron-BMP-Smad pathway. Overexpressing Smad6, Bambi or Follistatin in cells significantly reduced hepcidin expression. Smad7 functions as a key regulator of iron homoeostasis by negatively controlling hepcidin expression, and Smad6 and Smad7 have non-redundant roles. Smad6, Bambi and Follistatin serve as additional inhibitors of hepcidin in the liver.

Effect of Compound 21, a Selective Angiotensin II Type 2 Receptor Agonist, in a Murine Xenograft Model of Dupuytren Disease

BACKGROUND

Although surgical excision and intralesional collagenase injection are mainstays in Dupuytren disease treatment, no effective medical therapy exists for recurrent disease. Compound 21, a selective agonist of the angiotensin II type 2 receptor, has been shown to protect against fibrosis in models of myocardial infarction and stroke. The authors investigated the potential use of compound 21 in the treatment of Dupuytren disease.

METHODS

Human dermal fibroblasts were treated in vitro with compound 21 and assessed for viability using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, migration by means of scratch assay, and profibrotic gene transcription by means of quantitative reverse transcription polymerase chain reaction. Compound 21 effects in vivo were assessed using a xenograft model. Dupuytren disease cord specimens from patients undergoing open partial fasciectomy were divided into two segments. Segments were implanted under the dorsal skin of nude mouse pairs. Beginning on day 5, one mouse from each pair received daily intraperitoneal injections of compound 21 (10 μg/kg/day), and the other received vehicle. On day 10, segments were explanted and submitted for immunohistochemistry.

RESULTS

Human dermal fibroblasts treated with compound 21 displayed decreased migration and decreased gene expression of connective tissue growth factor, fibroblast specific protein-1, transforming growth factor-β1, Smad3, and Smad4. Dupuytren disease segments from compound 21-treated mice demonstrated significantly reduced alpha-smooth muscle actin and Ki67 staining, with increased density of CD31 staining vessels.

CONCLUSIONS

Compound 21 significantly decreases expression of profibrotic genes and decreases myofibroblast proliferation as indicated by reduced Ki67 and alpha-smooth muscle actin expression. These findings support compound 21 as a potential novel treatment modality for Dupuytren disease.

MiR-21-Mediated Suppression of Smad7 Induces TGFβ1 and Can Be Inhibited by Activation of Nrf2 in Alcohol-Treated Lung Fibroblasts

BACKGROUND

We previously demonstrated that chronic alcohol ingestion augments TGFβ1 expression in the lung fibroblast and increases the risk of fibroproliferative disrepair in a mouse model of acute lung injury. The effect of alcohol on TGFβ1 is mitigated by treatment with sulforaphane (SFP), which can activate nuclear factor (erythroid-derived 2)-like 2 (Nrf2). However, the mechanisms by which alcohol amplifies, or SFP attenuates, TGFβ1 expression in the fibroblast are not known. MicroRNA (miR)-21 has been shown to inhibit Smad7, a TGFβ1 signaling inhibitor. In this study, we hypothesized that alcohol augments TGFβ1 expression through up-regulation of miR-21, which subsequently inhibits Smad7.

METHODS

Primary mouse lung fibroblasts were cultured ± alcohol ± SFP and assessed for gene expression of miR-21, and gene and/or protein expression of Nrf2, Nrf2-regulated antioxidant enzymes, Smad7, STAT3, and TGFβ1. NIH 3T3 fibroblasts were transfected with a miR-21 inhibitor and cultured ± alcohol. α-SMA, Smad7, and TGFβ1 protein expression were then assessed. In parallel, NIH 3T3 lung fibroblasts were transfected with Nrf2 silencing RNA (siRNA) and cultured ± alcohol ± SFP. Gene expression of miR-21, Nrf2, Smad7, and TGFβ1 was assessed.

RESULTS

MiR-21 gene expression was increased by 12-fold at 48 hours, and Smad7 gene expression and protein expression were reduced by ~30% in alcohol-treated fibroblasts. In parallel, inhibition of miR-21 attenuated alcohol-mediated decrease in Smad7 and increase in TGFβ1 and α-SMA protein expression. Treatment with SFP mitigated the effect of alcohol on miR-21, Smad7 and total and phosphorylated STAT3, and restored Nrf2-regulated antioxidant gene expression. Silencing of Nrf2 prevented the effect of SFP on miR-21, Smad7, and TGFβ1 gene expression in alcohol-treated NIH 3T3 fibroblasts.

CONCLUSIONS

Alcohol treatment increases TGFβ1 in fibroblasts, at least in part, through augmentation of miR-21, which then inhibits Smad7 expression. These effects can be attenuated by activation of Nrf2 with SFP.

Hepatocyte-specific expression of constitutively active Alk5 exacerbates thioacetamide-induced liver injury in mice

While Transforming growth factor-βs (Tgf-βs) have been known to play an important role in liver fibrosis through an activation of Hepatic Stellate Cells (HSC), their fibrotic role on hepatocytes in liver damage has not been addressed thoroughly. To shed more light on the hepatocyte-specific role of Tgf-β signaling during liver fibrosis, we generated transgenic mice expressing constitutively active Tgf-β type I receptor Alk5 under the control of albumin promoter. Uninjured mice with increased Tgf-β/Alk5 signaling in hepatocytes (caAlk5/Alb-Cre mice) did not show characteristics related to hepatocyte death, fibrosis and inflammation. When subjected to thioacetamide (TAA) treatment, caAlk5/Alb-Cre mice exhibited more severe liver injury, when compared to control littermates. After TAA administration for 12 weeks, an increase in pathological changes was evident in caAlk5/Alb-Cre livers, with higher number of infiltrating cells in the portal and periportal area. Immunohistochemistry for F4/80, myeloperoxidase and CD3 showed that there was an increased accumulation of macrophages, neutrophils and T-lymphocytes, respectively, in caAlk5/Alb-Cre livers. Coincidently, we observed an exacerbated liver damage as seen by increases in serum aminotransferase level and number of apoptotic hepatocytes in caAlk5/Alb-Cre mice. Sirius staining of collagen demonstrated that the fibrotic response was worsened in caAlk5/Alb-Cre mice. The enhanced fibrosis in mutant livers was associated with marked production of α-SMA-positive myofibroblast. Hepatic expression of genes indicative of HSC activation was greater in caAlk5/Alb-Cre mice. In conclusion, our data indicated that elevation of Tgf-β signaling via Alk5 in hepatocytes is not sufficient to induce liver pathology but plays an important role in amplifying TAA-induced liver damage.

Regulation of TGF-β Family Signaling by Inhibitory Smads

Inhibitory Smads (I-Smads) have conserved carboxy-terminal MH2 domains but highly divergent amino-terminal regions when compared with receptor-regulated Smads (R-Smads) and common-partner Smads (co-Smads). Smad6 preferentially inhibits Smad signaling initiated by the bone morphogenetic protein (BMP) type I receptors ALK-3 and ALK-6, whereas Smad7 inhibits both transforming growth factor β (TGF-β)- and BMP-induced Smad signaling. I-Smads also regulate some non-Smad signaling pathways. Here, we discuss the vertebrate I-Smads, their roles as inhibitors of Smad activation and regulators of receptor stability, as scaffolds for non-Smad signaling, and their possible roles in the nucleus. We also discuss the posttranslational modification of I-Smads, including phosphorylation, ubiquitylation, acetylation, and methylation.

Regulation of TGF-β Family Signaling by Inhibitory Smads

Inhibitory Smads (I-Smads) have conserved carboxy-terminal MH2 domains but highly divergent amino-terminal regions when compared with receptor-regulated Smads (R-Smads) and common-partner Smads (co-Smads). Smad6 preferentially inhibits Smad signaling initiated by the bone morphogenetic protein (BMP) type I receptors ALK-3 and ALK-6, whereas Smad7 inhibits both transforming growth factor β (TGF-β)- and BMP-induced Smad signaling. I-Smads also regulate some non-Smad signaling pathways. Here, we discuss the vertebrate I-Smads, their roles as inhibitors of Smad activation and regulators of receptor stability, as scaffolds for non-Smad signaling, and their possible roles in the nucleus. We also discuss the posttranslational modification of I-Smads, including phosphorylation, ubiquitylation, acetylation, and methylation.

Role of histone deacetylases(HDACs) in progression and reversal of liver fibrosis

Liver fibrosis refers to a reversible wound healing process response to chronic liver injuries. Activation of hepatic stellate cells (HSCs) is closely correlated with the development of liver fibrosis. Histone deacetylases(HDACs) determine the acetylation levels of core histones to modulate expression of genes. To demonstrate the link between HDACs and liver fibrosis, CCl4-induced mouse liver fibrosis model and its spontaneous reversal model were established. Results of the current study demonstrated that deregulation of liver HDACs may involved in the development of liver fibrosis. Among 11 HDACs tested in our study (Class I, II, and IV HDACs), expression of HDAC2 was maximally increased in CCl4-induced fibrotic livers but decreased after spontaneous recovery. Moreover, expression of HDAC2 was elevated in human liver fibrotic tissues. In this regard, the potential role of HDAC2 in liver fibrosis was further evaluated. Our results showed that administration of HSC-T6 cells with transforming growth factor-beta1 (TGF-β1) resulted in an increase of HDAC2 protein expression in dose- and time-dependent manners. Moreover, HDAC2 deficiency inhibited HSC-T6 cell proliferation and activation induced by TGF-β1. More importantly, the present study showed HDAC2 may regulate HSCs activation by suppressing expression of Smad7, which is a negative modulator in HSCs activation and liver fibrosis. Collectively, these observations revealed that HDAC2 may play a pivotal role in HSCs activation and liver fibrosis while deregulation of HDACs may serve as a novel mechanism underlying liver fibrosis.

Effect of SMAD7 gene overexpression on TGF-β1-induced profibrotic responses in fibroblasts derived from Peyronie's plaque

Transforming growth factor-β1 (TGF-β1) has been identified as one of the most important fibrogenic cytokines associated with Peyronie's disease (PD). The mothers against decapentaplegic homolog 7 (SMAD7) is an inhibitory Smad protein that blocks TGF-β signaling pathway. The aim of this study was to examine the anti-fibrotic effect of the SMAD7 gene in primary fibroblasts derived from human PD plaques. PD fibroblasts were pretreated with the SMAD7 gene and then stimulated with TGF-β1. Treated fibroblasts were used for Western blotting, fluorescent immunocytochemistry, hydroxyproline determination, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assays. Overexpression of the SMAD7 gene inhibited TGF-β1-induced phosphorylation and nuclear translocation of SMAD2 and SMAD3, transdifferentiation of fibroblasts into myofibroblasts, and quashed TGF-β1-induced production of extracellular matrix protein and hydroxyproline. Overexpression of the SMAD7 gene decreased the expression of cyclin D1 (a positive cell cycle regulator) and induced the expression of poly (ADP-ribose) polymerase 1, which is known to terminate Smad-mediated transcription, in PD fibroblasts. These findings suggest that the blocking of the TGF-β pathway by use of SMAD7 may be a promising therapeutic strategy for the treatment of PD.

TGF-β/SMAD Pathway and Its Regulation in Hepatic Fibrosis

Transforming growth factor-beta1 (TGF-β1), a key member in the TGF-β superfamily, plays a critical role in the development of hepatic fibrosis. Its expression is consistently elevated in affected organs, which correlates with increased extracellular matrix deposition. SMAD proteins have been studied extensively as pivotal intracellular effectors of TGF-β1, acting as transcription factors. In the context of hepatic fibrosis, SMAD3 and SMAD4 are pro-fibrotic, whereas SMAD2 and SMAD7 are protective. Deletion of SMAD3 inhibits type I collagen expression and blocks epithelial-myofibroblast transition. In contrast, disruption of SMAD2 upregulates type I collagen expression. SMAD4 plays an essential role in fibrosis disease by enhancing SMAD3 responsive promoter activity, whereas SMAD7 negatively mediates SMAD3-induced fibrogenesis. Accumulating evidence suggests that divergent miRNAs participate in the liver fibrotic process, which partially regulates members of the TGF-β/SMAD signaling pathway. In this review, we focus on the TGF-β/SMAD and other relative signaling pathways, and discussed the role and molecular mechanisms of TGF-β/SMAD in the pathogenesis of hepatic fibrosis. Moreover, we address the possibility of novel therapeutic approaches to hepatic fibrosis by targeting to TGF-β/SMAD signaling.

miR-33a levels in hepatic and serum after chronic HBV-induced fibrosis

BACKGROUND

Chronic hepatitis B virus (HBV) infection, which can lead to hepatic disease, has become a critical national healthcare problem, and many people die each year as a result of HBV infection and its complications. Although microRNA-33a (miR-33a) is a novel modulator of lipid and cholesterol metabolism, the role of miR-33a in the hepatic fibrogenesis is still unknown. Here, we aimed to explore the roles and mechanisms of miR-33a in liver fibrosis.

METHODS

miR-33a expression in whole liver and serum samples was measured from chronic hepatitis B (CHB) patients by quantitative real-time PCR (qRT-PCR). In addition, different murine hepatic fibrosis models were produced to consolidate the results in human tissue. Human and murine primary liver fibrosis-associated cells were isolated and treated with transforming growth factor-β1 (TGF-β1).

RESULTS

miR-33a expression levels in liver tissue significantly increased with a fibrosis progression manner in the human liver. Furthermore, serum miR-33a levels associated positively with progressing process of hepatic fibrosis. miR-33a was in particular increased in hepatic stellate cells (HSC) than other liver fibrosis-associated cells. Stimulation of HSCs with TGF-β1 leads to a critical increase of miR-33a. Increasing miR-33a levels increased (whereas inhibiting miR-33a weakened) the activation role of TGF-β1 in LX-2 cells, which might be a potential mechanism through moderating Smad7 expression.

CONCLUSIONS

miR-33a may be a novel marker for HSC activation and hepatic fibrosis progress, suggesting a new therapeutic target in liver fibrosis.

Mistletoe alkaloid fractions alleviates carbon tetrachloride-induced liver fibrosis through inhibition of hepatic stellate cell activation via TGF-β/Smad interference

ETHNOPHARMACOLOGICAL RELEVANCE

Mistletoe (Viscum coloratum (Kom.) Nakai) has long been categorized as a traditional herbal medicine in Asia. In addition to its application in cancer therapy, mistletoe has also been used in the treatment of chronic hepatic disorders in China. In the present study, we investigated the antifibrotic effect and mechanisms of action of mistletoe extracts in a rat model of carbon tetrachloride (CCl4)-induced hepatotoxicity.

MATERIALS AND METHODS

An experimental model of hepatic fibrosis was established by intraperitoneal injection of rats with CCl4 for 8 weeks. Rats were subsequently treated with a mistletoe alkaloid fraction preparation via oral administration (120mg/kg daily for 8 weeks) or with distilled water as a control. Histopathological changes were observed by hematoxylin and eosin staining and Masson׳s trichrome staining. The expression of markers relevant to hepatic stellate cell (HSC) activation in the liver was assessed by real-time reverse transcription-polymerase chain reaction, immunohistochemistry and western blotting. The anti-fibrosis activity and mechanisms of action of mistletoe alkaloid fractions were further investigated in the HSC-T6 HSC line, following treatment with mistletoe alkaloid fractions (12mg/ml) for 48h.

RESULTS

Hepatic fibrosis decreased markedly in CCl4-treated animals following treatment with mistletoe alkaloid fractions, compared to controls. The mRNA levels of transforming growth factor-β1 (TGF-β1), procollagen I and tissue inhibitors of metalloproteinases (TIMPs) were significantly downregulated, by about 40%, 40% and 45%, respectively, in liver tissues from rats treated with mistletoe alkaloid fractions. Furthermore, significant downregulation of TGF-β1, TGF-β1 receptor, phosphorylated Smad 2 and alpha smooth muscle actin (α-SMA) proteins, by about 45%, 30% and 40%, respectively, was also observed in liver tissues from mistletoe alkaloid fractions-treated rats. In contrast, Smad 7 levels were significantly increased by about 30% in mistletoe alkaloid fractions-treated rats. Treatment of HSC-T6 cells with mistletoe alkaloid fractions significantly induced Smad 7 expression and inhibited the expression of α-SMA, TGFβ1, TGF-β1 receptor, Smad 2 and TIMP-1, in vitro.

CONCLUSION

We demonstrate that mistletoe alkaloid fractions decrease extracellular matrix accumulation by inhibiting HSC activation. Mechanistically, this may occur via inhibition of TGF-β1/Smad 2 and Smad 7 signal transduction, thereby blocking the synthesis of procollagen I and TIMP-1. These findings suggest that mistletoe alkaloid fractions may be a potential therapeutic agent for the treatment of hepatic fibrosis.

Astragalus and Paeoniae Radix Rubra extract (APE) inhibits hepatic stellate cell activation by modulating transforming growth factor-β/Smad pathway

Previous studies have shown that Astragalus and Paeoniae Radix Rubra extract (APE) is capable of protecting against liver fibrosis in rats. The hypothesis of the present study was that APE exerts its anti‑fibrotic effect by mediating the transforming growth factor β (TGF‑β)/Smad signaling pathway. In order to investigate this hypothesis, a series of assays were designed to detect the effects of APE on cell proliferation, cell invasion and the activation of hepatic stellate cells (HSCs). In addition, the effects of APE on the TGF‑β/Smad signaling pathway were explored, with the aim of elucidating the underlying mechanisms. HSCs were initially isolated from normal rat liver. A number of assays were then employed in order to evaluate the effects of APE on the function of these cells. Cell proliferation was investigated using an MTT assay and cell invasion was observed with the use of transwell invasion chambers. Collagen synthesis was measured with a 3H‑proline incorporation assay and expression of α‑smooth muscle actin was used to determine the extent of HSC activation. Protein expression induced by TGF‑β1 in HSCs was investigated by western blot and immunofluorescence analyses. Plasminogen activator inhibitor type1 (PAI‑1) and urokinase‑type plasminogen activator (uPA) transcriptional activity was measured using reverse transcription polymerase chain reaction. The results demonstrated that APE (5‑80 µg/ml) significantly inhibited fetal bovine serum‑induced cell proliferation in a dose‑dependent manner. Cell invasion and activation of HSCs induced by TGF‑β1 were disrupted by treatment with APE in a dose‑dependent manner. TGF‑β1 was observed to increase the phosphorylation of Smad2/3, while APE administered at higher doses produced inhibitory effects on Smad2/3 phosphorylation. In addition, administration of APE abrogated the TGF‑β1‑induced reduction in Smad‑7 expression in a dose‑dependent manner. The results further indicated that APE treatment not only reduced PAI‑1 expression, but also increased uPA expression in a dose‑dependent manner. In conclusion, APE exerted inhibitory effects on cell proliferation, invasion and activation of HSCs, and the mechanisms underlying these effects may involve the TGF‑β1/Smad pathway.

Hepatocyte produced matrix metalloproteinases are regulated by CD147 in liver fibrogenesis

BACKGROUND

The classical paradigm of liver injury asserts that hepatic stellate cells (HSC) produce, remodel and turnover the abnormal extracellular matrix (ECM) of fibrosis via matrix metalloproteinases (MMPs). In extrahepatic tissues MMP production is regulated by a number of mechanisms including expression of the glycoprotein CD147. Previously, we have shown that CD147 is expressed on hepatocytes but not within the fibrotic septa in cirrhosis [1]. Therefore, we investigated if hepatocytes produce MMPs, regulated by CD147, which are capable of remodelling fibrotic ECM independent of the HSC.

METHODS

Non-diseased, fibrotic and cirrhotic livers were examined for MMP activity and markers of fibrosis in humans and mice. CD147 expression and MMP activity were co-localised by in-situ zymography. The role of CD147 was studied in-vitro with siRNA to CD147 in hepatocytes and in-vivo in mice with CCl4 induced liver injury using ãCD147 antibody intervention.

RESULTS

In liver fibrosis in both human and mouse tissue MMP expression and activity (MMP-2, -9, -13 and -14) increased with progressive injury and localised to hepatocytes. Additionally, as expected, MMPs were abundantly expressed by activated HSC. Further, with progressive fibrosis there was expression of CD147, which localised to hepatocytes but not to HSC. Functionally significant in-vitro regulation of hepatocyte MMP production by CD147 was demonstrated using siRNA to CD147 that decreased hepatocyte MMP-2 and -9 expression/activity. Further, in-vivo α-CD147 antibody intervention decreased liver MMP-2, -9, -13, -14, TGF-β and α-SMA expression in CCl4 treated mice compared to controls.

CONCLUSION

We have shown that hepatocytes produce active MMPs and that the glycoprotein CD147 regulates hepatocyte MMP expression. Targeting CD147 regulates hepatocyte MMP production both in-vitro and in-vivo, with the net result being reduced fibrotic matrix turnover in-vivo. Therefore, CD147 regulation of hepatocyte MMP is a novel pathway that could be targeted by future anti-fibrogenic agents.

Chronic CCl4 intoxication causes liver and bone damage similar to the human pathology of hepatic osteodystrophy: a mouse model to analyse the liver-bone axis

Patients with chronic liver diseases frequently exhibit decreased bone mineral densities (BMD), which is defined as hepatic osteodystrophy (HOD). HOD is a multifactorial disease whose regulatory mechanisms are barely understood. Thus, an early diagnosis and therapy is hardly possible. Therefore, the aim of our study consisted in characterizing a mouse model reflecting the human pathomechanism. Serum samples were collected from patients with chronic liver diseases and 12-week old C57Bl6/N mice after 6-week treatment with carbon tetrachloride (CCl4). Repetitive injections of CCl4 induced liver damage in mice, resembling liver fibrosis in patients, as assessed by serum analysis and histological staining. Although CCl4 did not affect primary osteoblast cultures, μCT analysis revealed significantly decreased BMD, bone volume, trabecular number and thickness in CCl4-treated mice. In both HOD patients and CCl4-treated mice, an altered vitamin D metabolism with decreased CYP27A1, CYP2R1, vitamin D-binding protein GC and increased 7-dehydrocholesterol reductase hepatic gene expression, results in decreased 25-OH vitamin D serum levels. Moreover, both groups exhibit excessively high active transforming growth factor-beta (TGF-β) serum levels, inhibiting osteoblast function in vitro. Summarizing, our mouse model presents possible mediators of HOD, e.g. altered vitamin D metabolism and increased active TGF-β. Liver damage and significant changes in bone structure and mineralization are already visible by μCT analysis after 6 weeks of CCl4 treatment. This fast response and easy transferability makes it an ideal model to investigate specific gene functions in HOD.

Inhibitory role of Smad7 in hepatocarcinogenesis in mice and in vitro

Smad7 is a principal inhibitor of the TGFβ-Smad signalling pathway. We have investigated the functional significance of Smad7 in hepatocellular carcinoma (HCC). Smad7 knockout (KO) and wild-type (WT) mice were injected with diethylnitrosamine (DEN) to induce HCC. The effects of Smad7 on cellular features were examined in HCC cells, using a Smad7 over-expression or deletion approach. Signalling pathway components modulated by Smad7 in HCC were evaluated using luciferase reporter assay and co-immunoprecipitation. Smad7 was down-regulated in human HCCs compared with the adjacent normal tissues (p < 0.001). Smad7 KO mice were more susceptible to DEN-induced HCC than WT mice (78% versus 22%, p < 0.05). HCCs from KO mice displayed a greater proliferation activity (p < 0.05) and a reduced apoptotic index compared with WT littermates (p < 0.05). Deletion of Smad7 promoted cell proliferation in primary cultured HCC cells. In addition, over-expression of Smad7 in HCC cell lines markedly suppressed cell growth (p < 0.0001) and colony formation (p < 0.01). Cell cycle analysis revealed an increase in the G1 phase and a reduction in the S-phase populations, accompanied by up-regulation of p27(Kip1) and down-regulation of cyclin D1. Smad7 increased cell apoptosis (p < 0.01) by mediating an intrinsic [caspase-9, caspase-3 and poly(ADP-ribose) polymerase] apoptotic pathway. Moreover, Smad7 inhibited NF-κB signalling by interacting with TAB2, an upstream activator of NF-κB, and inhibited TGFβ signalling by suppressing phosphorylation of Smad3. In conclusion, loss of Smad7 enhances susceptibility to HCC. Smad7 suppresses HCC cell growth by inhibiting proliferation and G1 -S phase transition and inducing apoptosis through attenuation of NF-κB and TGFβ signalling. Smad7 acts as a potential tumour suppressor in liver.

Asiatic acid inhibits liver fibrosis by blocking TGF-beta/Smad signaling in vivo and in vitro

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.

Animal models of cutaneous and hepatic fibrosis

Fibrosis occurs as a part of normal wound healing. However, excessive or dysregulated fibrosis can lead to severe organ dysfunction and is a feature of a variety of diseases. Due to its insidious onset, fibrosis tends to go undetected in its early stages. This is in part why these diseases remain so poorly understood. Animal models have provided a means to examine these early stages and to isolate and understand the effect of perturbations in signaling pathways, chemokines, and cytokines. Here, we summarize recent progress in the understanding of the molecular pathogenesis of fibrosis, both its initiation and its maintenance phases, from animal models of fibrosis in the skin and liver. Due to these organs' properties, modeling fibrosis in them poses unique challenges. Elegant solutions have therefore been developed for modeling fibrosis in each, and now, great potential for animal models to contribute to our understanding appears scientifically imminent.

Cell signals influencing hepatic fibrosis

Liver fibrosis is the result of the entire organism responding to a chronic injury. Every cell type in the liver contributes to the fibrosis. This paper first discusses key intracellular signaling pathways that are induced during liver fibrosis. The paper then examines the effects of these signaling pathways on the major cell types in the liver. This will provide insights into the molecular pathophysiology of liver fibrosis and should identify therapeutic targets.

Unraveling the biological functions of Smad7 with mouse models

Smad7 is a key negative regulator of the transforming growth factor β (TGF-β) signaling and plays an important role in modulating a large array of biological processes. The physiological actions of Smad7 have been extensively investigated by using various mouse models. These studies have pinpointed numerous important in vivo functions of Smad7, including its activity in early embryonic development, fibrosis of many organs, skin cell differentiation, regulation of immune response and inflammation, tumorigenesis, and metabolic control. As most biological activities modulated by Smad7 are closely related to human disorders, it is anticipated that Smad7 will continue to be an intriguing molecule that will be vigorously investigated in the future to strengthen our understanding about the pathogenesis of human diseases.

Animal models for the study of liver fibrosis: new insights from knockout mouse models

Fibrosis arises as part of a would-healing response that maintains organ structure and integrity following tissue damage but also contributes to a variety of human pathologies such as liver fibrosis. Liver fibrosis is an abnormal response of the liver to persistent injury with the excessive accumulation of collagenous extracellular matrices. Currently there is no effective treatment, and many patients end up with a progressive form of the disease, eventually requiring a liver transplant. The clarification of mechanisms underlying pathogenesis of liver fibrosis and the development of effective therapy are of clinical importance. Experimental animal models, in particular targeted gene knockouts (loss of function) in mice, have become a powerful resource to address the molecular mechanisms or significance of the targeted gene in hepatic functions and diseases. This review will focus on the recent advances in knowledge obtained from genetically engineered mice that provide novel insights into the pathophysiology of liver fibrosis.

Hepatic deletion of Smad7 in mouse leads to spontaneous liver dysfunction and aggravates alcoholic liver injury

Background

TGF-β has been known to play an important role in various liver diseases including fibrosis and alcohol-induced fatty liver. Smad7 is an intracellular negative regulator of TGF-β signaling. It is currently unclear whether endogenous Smad7 has an effect on liver function and alcoholic liver damage.

Methodology/Principal Findings

We used Cre/loxP system by crossing Alb-Cre mice with Smad7^loxP/loxP mice to generate liver-specific deletion of Smad7 with loss of the indispensable MH2 domain. Alcoholic liver injury was achieved by feeding mice with a liquid diet containing 5% ethanol for 6 weeks, followed by a single dose of ethanol gavage. Deletion of Smad7 in the liver was associated with increased Smad2/3 phosphorylation in the liver or upon TGF-β treatment in primary hepatocytes. The majority of mice with liver specific deletion of Smad7 (Smad7^liver-KO) were viable and phenotypically normal, accompanied by only slight or no reduction of Smad7 expression in the liver. However, about 30% of Smad7^liver-KO mice with high efficiency of Smad7 deletion had spontaneous liver dysfunction, demonstrated as low body weight, overall deterioration, and increased serum levels of AST and ALT. Degeneration and elevated apoptosis of liver cells were observed with these mice. TGF-β-induced epithelial to mesenchymal transition (EMT) was accelerated in Smad7-deleted primary hepatocytes. In addition, alcohol-induced liver injury and steatosis were profoundly aggravated in Smad7 deficient mice, associated with upregulation of critical genes involved in lipogenesis and inflammation. Furthermore, alcohol-induced ADH1 expression was significantly abrogated by Smad7 deletion in hepatocytes.

Conclusion/Significance

In this study, we provided in vivo evidence revealing that endogenous Smad7 plays an important role in liver function and alcohol-induced liver injury.

Enhanced transforming growth factor-beta signaling and fibrogenesis in ovine fetal skeletal muscle of obese dams at late gestation

Maternal obesity (MO) is increasing at an alarming rate. The objective of this study was to evaluate the effect of MO on fibrogenesis in fetal skeletal muscle during maturation in late gestation. Nonpregnant ewes were assigned to a control diet (Con; fed 100% of NRC nutrient recommendations, n = 6) or obesogenic diet (OB; fed 150% of NRC recommendations, n = 6) from 60 days before conception, and fetal semitendenosus (St) muscle was sampled at 135 days of gestation (term 148 days). Total concentration and area of collagen in cross-sections of muscle increased by 27.0 +/- 6.0 (P < 0.05) and 105.1 +/- 5.9% (P = 0.05) in OB compared with Con fetuses. The expression of precursor TGF-beta was 177.3 +/- 47.6% higher, and concentration of phospho-p38 74.7 +/- 23.6% was higher (P < 0.05) in OB than in CON fetal muscle. Increases of 327.9 +/- 168.0 (P < 0.05) and 188.9 +/- 82.1% (P < 0.05), respectively, were observed for mRNA expression of Smad7 and fibronectin in OB compared with Con muscles. In addition, enzymes involved in collagen synthesis, including lysyl oxidase, lysyl hydroxylase 2b, and prolyl 4-hydroxylase-alpha1, were increased by 350.2 +/- 90.0 (P < 0.05), 236.5 +/- 25.2 (P < 0.05), and 82.0 +/- 36.2% (P = 0.05), respectively, in OB muscle. In conclusion, MO-enhanced fibrogenesis in fetal muscle in late gestation was associated with upregulation of the TGF-beta/p38 signaling pathway. Enhanced fibrogenesis at such an early stage of development is expected to negatively affect the properties of offspring muscle because muscle fibrosis is a hallmark of aging.

Smad7 regulates the adult neural stem/progenitor cell pool in a transforming growth factor beta- and bone morphogenetic protein-independent manner

Members of the transforming growth factor beta (TGF-beta) family of proteins modulate the proliferation, differentiation, and survival of many different cell types. Neural stem and progenitor cells (NPCs) in the adult brain are inhibited in their proliferation by TGF-beta and by bone morphogenetic proteins (BMPs). Here, we investigated neurogenesis in a hypomorphic mouse model for the TGF-beta and BMP inhibitor Smad7, with the hypothesis that NPC proliferation might be reduced due to increased TGF-beta and BMP signaling. Unexpectedly, we found enhanced NPC proliferation as well as an increased number of label-retaining cells in vivo. The enhanced proliferation potential of mutant cells was retained in vitro in neurosphere cultures. We observed a higher sphere-forming capacity as well as faster growth and cell cycle progression. Use of specific inhibitors revealed that these effects were independent of TGF-beta and BMP signaling. The enhanced proliferation might be at least partially mediated by elevated signaling via epidermal growth factor (EGF) receptor, as mutant cells showed higher expression and activation levels of the EGF receptor. Conversely, an EGF receptor inhibitor reduced the proliferation of these cells. Our data indicate that endogenous Smad7 regulates neural stem/progenitor cell proliferation in a TGF-beta- and BMP-independent manner.

Smad signaling in skeletal development and regeneration

Smad proteins are intracellular molecules that mediate the canonical signaling cascade of TGFbeta superfamily growth factors. The TGFbeta superfamily comprises two groups of growth factors, BMPs and TGFbetas. Both groups can be further divided into several sub-groups based on sequence homologies and functional similarities. Ligands of the TGFbeta superfamily bind to cell surface receptors to activate Smad proteins in the cytoplasm; then the activated Smad proteins translocate into the nucleus to activate or repress specific target gene transcription. Both groups of growth factors play important roles in skeletal development and regeneration. However, whether these effects reflect signaling through canonical Smad pathways, or other non-canonical signaling pathways in vivo remains a mystery. Moreover, the mechanisms utilized by Smad proteins to initiate nuclear events and their interactions with cytoplasmic proteins are still under intensive investigation. This review will discuss the most recent progress understanding Smad signaling in the context of skeletal development and regeneration.

TGF-beta enhances alcohol dependent hepatocyte damage via down-regulation of alcohol dehydrogenase I

BACKGROUND & AIMS

Adverse alcohol effects in the liver involve oxidative metabolism, fat deposition and release of fibrogenic mediators, including TGF-beta. The work presents an assessment of liver damaging cross-talk between ethanol and TGF-beta in hepatocytes.

METHODS

To investigate TGF-beta effects on hepatocytes, microarray analyses were performed and validated by qRT-PCR, Western blot analysis and immunohistochemistry. The cellular state was determined by assessing lactate dehydrogenase, cellular glutathione, reactive oxygen species, lipid peroxidation and neutral lipid deposition. RNA interference was used for gene silencing in vitro.

RESULTS

TGF-beta is induced in mouse livers after chronic ethanol insult, enhances ethanol induced oxidative stress and toxicity towards cultured hepatocytes plus induces lipid-, oxidative stress metabolism- and fibrogenesis-gene expression signatures. Interestingly, TGF-beta down-regulates alcohol metabolizing enzyme Adh1 mRNA in cultured hepatocytes and liver tissue from TGF-beta transgenic mice via the ALK5/Smad2/3 signalling branch, with Smad7 as a potent negative regulator. ADH1 deficiency is a determining factor for the increased lipid accumulation and Cyp2E1 dependent toxicity in liver cells upon alcohol challenge. Further, ADH1 expression was decreased during liver damage in an intragastric ethanol infusion mouse model.

CONCLUSION

In the presence of ethanol, TGF-beta displays pro-steatotic action in hepatocytes via decreasing ADH1 expression. Low ADH1 levels are correlated with enhanced hepatocyte damage upon chronic alcohol consumption by favoring secondary metabolic pathways.

A rapid and easy to handle thermoluminescence based technique for evaluation of carbon tetrachloride-induced oxidative stress on rat hepatocytes

Oxidative stress has become one of the most intensively studied topics in biomedical research and is an often observed mechanism of non-genotoxic carcinogens like carbon tetrachloride. To monitor the oxidative stress status in in vitro hepatocytes, we compared thermoluminescence (TL) measurements with biochemical standard methods for oxidative stress markers. In contrast to biochemical analysis, TL measurements can be performed without any time-consuming extraction procedures by using directly collected cell material. After incubation with CCl(4) (24 h), thermo-induced light emission increased with rising concentration of CCl(4) up to eightfold at 10 mM CCl(4). Simultaneously, we determined the content of different secondary oxidative stress products, like thiobarbituric acid reactive substances and malondialdehyde. The rise of all biochemical markers complied with the increasing concentration of CCl(4). Finally, we could show that the CCl(4)-induced increase of oxidative stress markers determined by time-consuming biochemical methods perfectly correlates with the increase of high temperature bands in rapid TL measurements.

Disruption of the Smad7 gene promotes renal fibrosis and inflammation in unilateral ureteral obstruction (UUO) in mice

BACKGROUND

The present study tested the hypothesis that disruption of Smad7 function may accelerate renal fibrosis and inflammation.

METHODS

This was investigated in a unilateral ureteral obstruction (UUO) model induced in wild-type (WT) and Smad7DeltaE1 mice in which functional Smad7 is disrupted by deleting exon I in the Smad7 gene. Renal fibrosis and inflammation after UUO were examined by histology, real-time PCR, western blot analyses and immunohistochemistry.

RESULTS

Seven days after UUO, severe tubulointerstitial fibrosis developed in WT mice as evidenced by a marked increase in alpha-SMA, collagen I and III extracellular matrix. This was associated with a significant upregulation of renal TGF-beta1 and CTGF and activation of Smad2/3. Interestingly, compared to WT UUO mice, Smad7DeltaE1 mice with UUO exhibited a further increase in TGF-beta/Smad2/3-dependent renal fibrosis. Moreover, compared to WT UUO mice, deletion of the Smad7 gene also sustained NF-kappaB activation and thus enhanced further renal inflammation such as macrophage infiltration and upregulation of TNF-alpha, MCP-1, OPN and ICAM-1.

CONCLUSION

Smad7 is a critical negative regulator of TGF-beta/Smad2/3 and NF-kappaB signalling and plays a negative regulating role in both renal fibrosis and inflammation after UUO. Results from this study further support the notion that Smad7 may be a therapeutic agent for kidney diseases.