Halofuginone inhibition of COL1A2 promoter activity via a c-Jun-dependent mechanism

A Novel HIF Inhibitor Halofuginone Prevents Neurodegeneration in a Murine Model of Retinal Ischemia-Reperfusion

Neurodegeneration caused with retinal ischemia or high intraocular pressure is irreversible in general. We have focused on the role of hypoxia-inducible factor (HIF) in retinal homeostasis and revealed that HIF inhibition may be effective against retinal neovascular and neurodegeneration. In this study, we performed in vitro screening of natural products and found halofuginone, which is a derivative of febrifugine extracted from hydrangea, as a novel HIF inhibitor. Administration of halofuginone showed a significant neuroprotective effect by inhibiting HIF-1α expression in a murine retinal ischemia-reperfusion model histologically and functionally. These results indicate that halofuginone can be a neuroprotective agent in ischemic retinal degenerative diseases.

Discovery and pharmacological characterization of a new class of prolyl-tRNA synthetase inhibitor for anti-fibrosis therapy

Scleroderma has clinical characteristics including skin and other tissue fibrosis, but there is an unmet need for anti-fibrotic therapy. Halofuginone (HF) is a well-known anti-fibrosis agent in preclinical and clinical studies which exerts its effect via inhibition of TGF-β/Smad3 signaling pathway. Recently, prolyl-tRNA synthetase (PRS) was elucidated as a target protein for HF that binds to the proline binding site of the catalytic domain of PRS. Here, we characterized a new class of PRS inhibitor (T-3833261) that is carefully designed in a way that binds to the ATP site of the catalytic domain and does not disrupt binding of proline. The anti-fibrotic activity and the mechanism of action for T-3833261 on TGF-β-induced fibrotic assay were compared with those of HF in primary human skin fibroblast. We evaluated in vivo effect of topical application of T-3833261 and HF on TGF-β-induced fibrotic genes expression in mice. We found that T-3833261 suppressed TGF-β-induced α-smooth muscle actin (α-SMA) and type I collagen α1 (COL1A1) expression through the Smad3 axis in a similar fashion to HF. In vivo topical application of T-3833261 reduced the increase of fibrotic genes expression such as α-Sma, Col1a1 and Col1a2 by TGF-β intradermal injection to the ear of a mouse. We revealed that T-3833261 is more effective than HF under the conditions of high proline concentration, as reported in fibrotic tissues. These results suggest the potential of ATP competitive PRS inhibitors for the treatment of fibrotic diseases such as scleroderma.

Regulation of renal fibrosis by Smad3 Thr388 phosphorylation

Transforming growth factor-β (TGF-β) promotes tissue fibrosis via receptor-mediated phosphorylation of the receptor-activated Smad2/3, together with Smad4. Of these, Smad3 plays a major profibrotic role in mouse models of tissue fibrosis. Transcriptional activity of the Smad3 protein is regulated by phosphorylation of residues in the C-terminal domain and the linker region. Herein, we examined the role of a novel phosphorylation site within the MH2 domain (T388) in the regulation of Smad3 activity. Confocal microscopy using an Smad3 phosphorylated T388-specific antibody identified phosphorylation of Smad3 T388 in myofibroblasts and tubular epithelial cells in human focal and segmental glomerulosclerosis and mouse models of unilateral ureteric obstruction and diabetic nephropathy, whereas phosphorylated T388 was largely absent in normal kidney. In vitro, TGF-β1 induced phosphorylation of Smad3 T388 in a biphasic pattern. A point mutation of T388/V in an Smad3 construct demonstrated that phosphorylation of T388 promotes Smad3 binding to Smad4 and CDK8, but was not necessary for nuclear translocation. Furthermore, T388 phosphorylation was required for TGF-β-induced collagen I gene promoter activity and extracellular matrix production in cultured fibroblasts. In conclusion, our study identifies phosphorylation of T388 in the Smad3 MH2 domain as an important mechanism that regulates the profibrotic TGF-β/Smad3 signaling pathway, which has direct relevance to human and experimental fibrotic kidney disease.

Endothelial dysfunction exacerbates renal interstitial fibrosis through enhancing fibroblast Smad3 linker phosphorylation in the mouse obstructed kidney

Endothelial dysfunction and enhanced transforming growth factor-β (TGF-β)/Smad3 signalling are common features of progressive renal fibrosis. This study investigated a potential link between these mechanisms. In unilateral ureteric obstruction (UUO) we observed an acute (6 hr) down-regulation of nitric oxide synthase 3 (NOS3/eNOS) levels and increased phosphorylation of the linker region of Smad3 at T179 and S208 in Smad3/JNK complexes. These events preceded Smad3 C-terminal domain phosphorylation and the induction of myofibroblast proliferation at 48 hrs. Mice deficient in NOS3 showed enhanced myofibroblast proliferation and collagen accumulation compared to wild type mice in a 7 day UUO model. This was associated with enhanced phosphorylation of Smad3 T179 and S208 by 92% and 88%, respectively, whereas Smad3-C-terminal phosphorylation was not affected. Resolvin D1 (RvD1) can suppress renal fibrosis in the UUO model, and further analysis herein showed that RvD1 protected against endothelial dysfunction and suppressed Smad3/JNK complex formation with a consequent reduction in phosphorylation of Smad3 T179 and S208 by 78% and 65%, respectively, while Smad3 C-terminal phosphorylation was unaltered. In vitro, conditioned media from mouse microvascular endothelial cells (MMEC) treated with a general inhibitor of nitric oxide synthase (L-NAME) augmented the proliferation and collagen production of renal fibroblasts (NRK49F cells) compared to control MMEC media and this was associated with increased phosphorylation of JNK and Smad3 T179 and S208, whereas Smad3-C-terminal domain phosphorylation was unaffected. The addition of RvD1 to L-NAME treated MMEC abrogated these effects of the conditioned media on renal fibroblasts. Finally, Smad3 T179/V and S208/A mutations significantly inhibit TGF-β1 induced up-regulation collagen I promoter. In conclusion, these data suggest that endothelial dysfunction can exacerbate renal interstitial fibrosis through increased fibroblast proliferation and collagen production via enhanced Smad3 linker phosphorylation.

Halofuginone inhibits multiple myeloma growth in vitro and in vivo and enhances cytotoxicity of conventional and novel agents

Multiple Myeloma (MM), a malignancy of plasma cells, remains incurable despite the use of conventional and novel therapies. Halofuginone (HF), a synthetic derivative of quinazolinone alkaloid, has recently been shown to have anti-cancer activity in various preclinical settings. This study demonstrated the anti-tumour activity of HF against a panel of human MM cell lines and primary patient-derived MM cells, regardless of their sensitivity to conventional therapy or novel agents. HF showed anti-MM activity in vivo using a myeloma xenograft mouse model. HF suppressed proliferation of myeloma cells alone and when co-cultured with bone marrow stromal cells. Similarly, HF induced apoptosis in MM cells even in the presence of insulin-like growth factor 1 or interleukin 6. Importantly, HF, even at high doses, did not induce cytotoxicity against CD40 activated peripheral blood mononuclear cells from normal donors. HF treatment induced accumulation of cells in the G(0) /G(1) cell cycle and induction of apoptotic cell death associated with depletion of mitochondrial membrane potential; cleavage of poly (ADP-ribose) polymerase and caspases-3, 8 and 9 as well as down-regulation of anti-apoptotic proteins including Mcl-1 and X-IAP. Multiplex analysis of phosphorylation of diverse components of signalling cascades revealed that HF induced changes in P38MAPK activation; increased phosphorylation of c-jun, c-jun NH(2)-terminal kinase (JNK), p53 and Hsp-27. Importantly, HF triggered synergistic cytotoxicity in combination with lenalidomide, melphalan, dexamethasone, and doxorubicin. Taken together, these preclinical studies provide the preclinical framework for future clinical studies of HF in MM.

Inhibition of transforming growth factor beta signaling by halofuginone as a modality for pancreas fibrosis prevention

OBJECTIVES

Chronic pancreatitis is characterized by inflammation and fibrosis. We evaluated the efficacy of halofuginone, an inhibitor of collagen synthesis and myofibroblast activation, in preventing cerulein-induced pancreas fibrosis.

METHODS

Collagen synthesis was evaluated by in situ hybridization and staining. Levels of prolyl 4-hydroxylase beta (P4Hbeta), cytoglobin/stellate cell activation-associated protein (Cygb/STAP), transgelin, tissue inhibitors of metalloproteinases, serum response factor, transforming growth factor beta (TGFbeta), Smad3, and pancreatitis-associated protein 1 (PAP-1) were determined by immunohistochemistry. Metalloproteinase activity was evaluated by zymography.

RESULTS

Halofuginone prevented cerulein-dependent increase in collagen synthesis, collagen cross-linking enzyme P4Hbeta, Cygb/STAP, and tissue inhibitors of metalloproteinase 2. Halofuginone did not affect TGFbeta levels in cerulein-treated mice but inhibited serum response factor synthesis and Smad3 phosphorylation. In culture, halofuginone inhibited pancreatic stellate cell (PSC) proliferation and TGFbeta-dependent increase in Cygb/STAP and transgelin synthesis and metalloproteinase 2 activity. Halofuginone increased c-Jun N-terminal kinase phosphorylation in PSCs derived from cerulein-treated mice. Halofuginone prevented the increase in acinar cell proliferation and further increased the cerulein-dependent PAP-1 synthesis.

CONCLUSIONS

Halofuginone inhibits Smad3 phosphorylation and increases c-Jun N-terminal kinase phosphorylation, leading to the inhibition of PSC activation and consequent prevention of fibrosis. Halofuginone increased the synthesis of PAP-1, which further reduces pancreas fibrosis. Thus, halofuginone might serve as a novel therapy for pancreas fibrosis.

Molecular aspects of regulation of collagen gene expression in fibrosis

Fibrosis, the hyper-accumulation of scar tissue, is characterized by the overproduction and deposition of type I and III collagen by fibroblasts and is the one of the main pathologic outcomes of the autoimmune disorder scleroderma. While the causes of fibrosis in scleroderma are unknown, cytokines such as TGF-beta, IL-4 and IL-13, play a crucial role in the stimulation of collagen production have been implicated in the disease process. In fibroblasts stimulation of collagen production by these cytokines is dependent on the Smad and STAT6 signaling pathways induced by TGF-beta and IL-4, IL-13 respectively. Furthermore, mounting evidence suggest cytokine crosstalk is relevant in the sclerotic process. Our laboratory demonstrated an increase in TGF-beta1 gene transcription from fibroblasts stimulated with IL-4. In addition, TSK/+ mice lacking the IL-4alpha receptor show impaired transcription of the TGF-beta1 gene and did not display fibrosis. Likewise, it appears that STAT6 plays a role in fibroblast TGF-beta1 transcription after IL-4 or IL-13 stimulation. These findings suggest that an epistatic interaction between IL-4 and TGF-beta may exist which is crucial for pathologic sclerotic activity.

Functional resolution of fibrosis in mdx mouse dystrophic heart and skeletal muscle by halofuginone

The effect of halofuginone (Halo) on established fibrosis in older mdx dystrophic muscle was investigated. Mice (8 to 9 mo) treated with Halo (or saline in controls) for 5, 10, or 12 wk were assessed weekly for grip strength and voluntary running. Echocardiography was performed at 0, 5, and 10 wk. Respiratory function and exercise-induced muscle damage were tested. Heart, quadriceps, diaphragm, and tibialis anterior muscles were collected to study fibrosis, collagen I and III expression, collagen content using a novel collagenase-digestion method, and cell proliferation. Hepatocyte growth factor and α-smooth muscle actin proteins were assayed in quadriceps. Halo decreased fibrosis (diaphragm and quadriceps), collagen I and III expression, collagen protein, and smooth muscle actin content after 10 wk treatment. Muscle-cell proliferation increased at 5 wk, and hepatocyte growth factor increased by 10 wk treatment. Halo markedly improved both cardiac and respiratory function and reduced damage and improved recovery from exercise. The overall impact of established dystrophy and dysfunction in cardiac and skeletal muscles was reduced by Halo treatment. Marked improvements in vital-organ functions implicate Halo as a strong candidate drug to reduce morbidity and mortality in Duchenne muscular dystrophy.

Involvement of ERK signaling in halofuginone-driven inhibition of fibroblast ability to contract collagen lattices

Halofuginone, an alkaloid isolated from the plant Dichroa febrifuga, has been shown to be a potent inhibitor of tissue fibrosis. We herein demonstrate that, at concentrations below 10(-7) M, halofuginone does not affect the cell cycle but efficiently induces extracellular signal-regulated kinases(1,2) (ERK(1,2)), p38 and Jun NH2-terminal kinases(1,2) (JNK(1,2)) phosphorylation. In addition, at these non cytotoxic concentrations, halofuginone diminishes the capacity of fibroblasts to contract mechanically unloaded collagen lattices, an effect that is specifically blocked by the ERK inhibitors PD98059 and U0126, not by inhibitors of the JNK or p38 pathways. These data thus indicate that the inhibitory effect of halofuginone on fibroblast contractile activity, a key function for wound healing implicated in the development of tissue fibrosis, is an ERK-mediated mechanism.

Effect of halofuginone, a collagen alpha1(I) inhibitor, on wound healing in normal and irradiated skin: implication for hematopoietic stem cell transplantation

It is a major interest in the field of hematopoietic stem cell transplantation to reduce scarring of healing wounds with overdeposition of collagen due to radiation injury or graft-versus-host disease. Halofuginone (HF) inhibits collagen alpha1(I) gene expression and overdeposition of collagen. We examined the effect of HF on the healing of full-depth incision wounds inflicted in normal skin or skin areas compromised by local preirradiation with 18 Gy. Preirradiation significantly decreased the tensile strength of the healing wounds at day 14 (by approximately 60%, p < 0.0001). In contrast, HF treatment did not significantly decrease the strength of wounds inflicted in both normal and preirradiated skin. Histological evaluation revealed that HF induced moderate thinning of the dermis accompanied by elevated thickness of the epidermis and enhanced rejoining of subdermal muscles in the wound area. HF only minimally reduced total collagen deposition in both groups, with minor changes in the level of more matured fibrillar collagen network. Our study demonstrates that HF does not significantly affect wound strength. This encourages the possible use of HF as an antifibrotic agent with minimal complications for post-hematopoietic stem cell transplantation complications including radiation toxicity and graft-versus-host disease.

Inhibition of fibroblast to myofibroblast transition by halofuginone contributes to the chemotherapy-mediated antitumoral effect

Stromal myofibroblasts play an important role in tumor progression. The transition of fibroblasts to myofibroblasts is characterized by expression of smooth muscle genes and profuse synthesis of extracellular matrix proteins. We evaluated the efficacy of targeting fibroblast-to-myofibroblast transition with halofuginone on tumor progression in prostate cancer and Wilms' tumor xenografts. In both xenografts, low doses of halofuginone treatment, independent of the route of administration, resulted in a trend toward inhibition in tumor development. Moreover, halofuginone synergizes with low dose of docetaxel in prostate cancer and vincristine and dactinomycin in Wilms' tumor xenografts, resulting in significant reduction in tumor volume and weight comparable to the effect observed by high doses of the respective chemotherapies. In prostate cancer and Wilms' tumor xenografts, halofuginone, but not the respective chemotherapies, inhibited the synthesis of collagen type I, alpha-smooth muscle actin, transgelin, and cytoglobin, all of which are characteristics of activated myofibroblasts. Halofuginone, as the respective chemotherapies, increased the synthesis of Wilms' tumor suppressor gene product (WT-1) and prostate apoptosis response gene-4 (Par-4), resulting in apoptosis/necrosis. These results suggest that targeting the fibroblast-to-myofibroblast transition with halofuginone may synergize with low doses of chemotherapy in achieving a significant antitumoral effect, avoiding the need of high-dose chemotherapy and its toxicity without impairing treatment efficacy.

Gene expression during chemically induced liver fibrosis: effect of halofuginone on TGF-beta signaling

Hepatic fibrosis is associated with the activation of stellate cells (HSCs), the major source of extracellular matrix (ECM) proteins. Transforming growth factor-beta (TGF-beta), signaling via Smad3, is the most profibrogenic cytokine and the major promoter of ECM synthesis. Halofuginone, an inhibitor of liver fibrosis, inhibits TGF-beta-dependent Smad3 phosphorylation in human HSCs in culture. We have used transcriptional profiling to evaluate the effect of halofuginone on gene expression during the progression of thioacetamide (TAA)-induced liver fibrosis in the rat and have focused on genes that are associated with TGF-beta. TAA treatment causes alterations in the expression of 7% of liver genes. Halofuginone treatment prevents the changes in the expression of 41% of these genes and results in the inhibition of HSC activation and collagen synthesis. During the early stages of the disease, halofuginone affects genes involved in alcohol, lipid, protein, and phosphate metabolism and cell adhesion and, at later stages, in the cell cycle (cell development, differentiation, cell proliferation, and apoptosis). The activation of TGF-beta-dependent genes, such as tartrate-resistant acid phosphatase, its putative substrate osteopontin, stellate cell activation-association protein, and fibrillin-1, during chemically induced fibrosis is prevented by halofuginone. This study thus highlights the role of TGF-beta signaling in liver fibrosis and especially its potential for pharmacological intervention. Halofuginone, which has demonstrated efficacy and tolerance in animals and humans, could become an effective and novel therapy for liver fibrosis.

Transcriptional regulation of the human alpha2(I) collagen gene (COL1A2), an informative model system to study fibrotic diseases

During the past two decades, the human pro-alpha2(I) collagen gene (COL1A2) has emerged as an informative model in which to study the general principles that govern the transcriptional control of extracellular matrix deposition in normal and fibrotic conditions. Multiple studies have in fact delineated the genomic regions, cis-acting elements and trans-acting factors implicated in constitutive, cytokine-modulated and tissue-specific expression of COL1A2. These functional components are integrated into a regulatory network that consists of the proximal promoter, far-upstream enhancer and downstream repressor, and which operates according to two mechanisms. The first mechanism is one in which combinatorial interactions among promoter-bound proteins determine transcriptional outcome in different cellular and experimental contexts. The other mechanism is one whereby cooperative assembly of protein complexes at distantly located DNA elements directs spatiotemporal specificity. These transcriptional studies have also an additional value in translational research, in that they are providing the conceptual means to develop new animal models of and therapeutic strategies for fibrotic diseases.

Involvement of the tyrosine phosphatase early gene of liver regeneration (PRL-1) in cell cycle and in liver regeneration and fibrosis effect of halofuginone

Tyrosine phosphatase PRL-1 is one of the immediate-early genes up-regulated during liver regeneration and is apparently involved in cell proliferation. Previously, we have demonstrated that halofuginone, an inhibitor of collagen type I synthesis, prevents liver fibrosis and improves cirrhotic liver regeneration. In this study, we evaluated the effect of halofuginone on PRL-1 expression, its cellular localization in vitro and during liver regeneration, and fibrosis progression in vivo. In culture, halofuginone increased PRL-1 expression in primary rat hepatocytes and in hepatocellular carcinoma (HCC) cell lines, the former being more sensitive to halofuginone. The halofuginone-dependent increase in PRL-1 gene expression was correlated with an increase in the transcription factor early growth response-1 (Egr-1) and inversely correlated with the inhibition of cell proliferation. Halofuginone arrested HepG2 and Huh7 cell lines at the G1 phase, whereas Hep3B cells were arrested at G2/M, probably because of a reduction in the synthesis of cyclins D1 and B1 in all HCC cells and increased cyclin A in Hep3B cells. Halofuginone also affected the PRL-1 sub-cellular localization that was cell-cycle-dependent. In addition, halofuginone augmented PRL-1 expression in the remnant liver after partial hepatectomy and in chemically induced fibrosis in rats; this was accompanied by increased expression of insulin-like growth factor binding protein 1 (IGFBP-1), another immediate-early gene of regeneration. The regulation of the expression of the early genes of regeneration such as PRL-1 and IGFBP-1 is thus part of the mode of action of halofuginone and results in the prevention of liver fibrosis and improved cirrhotic liver regeneration.

Halofuginone induces matrix metalloproteinases in rat hepatic stellate cells via activation of p38 and NFkappaB

The semisynthetic plant alkaloid halofuginone (HAL) was reported to prevent and partly reverse experimental liver fibrosis. However, its mechanisms of action are poorly understood. We therefore aimed to determine the antifibrotic potential of HAL and to characterize involved signal transduction pathways in hepatic stellate cells (HSCs). Results were compared with its in vivo effects in a rat model of reversal of established liver fibrosis induced by thioacetamide. In vitro HAL inhibited HSC proliferation and migration dose dependently at submicromolar concentrations. HAL (200 nm) up-regulated matrix metalloproteinase (MMP)-3 and MMP-13 expression between 10- and 50-fold, resulting in a 2- to 3-fold increase of interstitial collagenase activity. Procollagen alpha1(I) and MMP-2 transcript levels were suppressed 2- to 3-fold, whereas expression of other profibrogenic mRNAs remained unaffected. p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor kappaB(NFkappaB) pathways were activated by HAL, and specific inhibitors of p38 MAPK and NFkappaB dose dependently inhibited MMP-13 induction. Treatment with HAL did not affect HSC viability, and observed effects were reversible after its removal. In vivo HAL up-regulated MMP-3 and -13 mRNA expression 1.5- and 2-fold, respectively, in cirrhotic rats, whereas tissue inhibitor of metalloproteinase-1 was suppressed by 50%. In conclusion, submicromolar concentrations of HAL inhibit HSC proliferation and migration and up-regulate their expression of fibrolytic MMP-3 and -13 via activation of p38 MAPK and NFkappaB. The remarkable induction of MMP-3 and -13 makes HAL a promising agent for antifibrotic combination therapies.

Proteasome blockade exerts an antifibrotic activity by coordinately down-regulating type I collagen and tissue inhibitor of metalloproteinase-1 and up-regulating metalloproteinase-1 production in human dermal fibroblasts

Tissue fibrosis results when dysregulation of extracellular matrix (ECM) turnover favors deposition of collagen and other ECM proteins over degradation. Fibrosis may then lead to organ dysfunction and pathology as observed in systemic sclerosis (SSc). In the present study, we investigated the antifibrotic properties of proteasome blockade. A dose- and time-dependent reduction in type-I collagen and tissue inhibitor of metalloproteinase-1 (TIMP-1) production was observed in normal fibroblasts exposed to proteasome inhibitors (PI). In the same culture conditions, metalloproteinase-1 (MMP-1) protein and the collagenolytic activity on type I collagen was increased. The steady-state mRNA levels of COL1A1, TIMP-1, and MMP-1 paralleled protein levels. These effects were dominant over the profibrotic properties of TGF-beta and were observed with fibroblasts generated from normal and SSc skin. PI decreased type I collagen mRNA levels with kinetics similar to those observed with DRB, a specific RNA polymerase II inhibitor, thus indicating transcriptional inhibition. Of interest, PI induced c-Jun phosphorylation and c-Jun nuclear accumulation. The specific N-terminal Jun-kinase inhibitor SP-600125 selectively abrogated c-Jun phosphorylation and, in a dose-dependent fashion, the up-regulated synthesis of MMP-1 induced by PI. Finally, PI did not affect fibroblast viability. Thus, the coordinated down-regulation of collagen and TIMP-1 and up-regulation of MMP-1 renders proteasome blockade an attractive strategy for treating conditions as SSc, characterized by excessive fibrosis.

Roles of MAP kinases in the regulation of bone matrix gene expressions in human osteoblasts by oscillatory fluid flow

We investigated the effects of oscillatory flow in regulating the gene expressions of type I collagen (COL1, the main component of human bone tissues) and osteopontin (OPN, the key gene for calcium deposition) in human osteoblast-like (MG-63) cells, and the roles of mitogen-activated protein kinases (MAPKs) in this regulation. The cells were subjected to oscillatory flow (0.5 +/- 4 dyn/cm(2)) or kept under static condition for various time periods (15 min, 30 min, 1 h, 2 h, 4 h, 8 h, and 16 h). Oscillatory flow caused significant up-regulations of both COL1 and OPN gene expressions over the 16 h of study, and a transient activation of MAPKs was starting at 15 min and declining to basal level in 2 h. The flow-induction of COL1 was blocked by an ERK inhibitor (PD98059) and reduced by a JNK inhibitor (SP600125), whereas that of OPN was abolished by PD98059. Analysis of the cis-elements in the COL1 and OPN promoters suggests the involvement of transacting factors Elk-1 and AP-1 in the transcription regulation. The ERK inhibitor (PD98059) blocked Elk-1 phosphorylation, as well as COL1 and OPN gene expression. The JNK inhibitor (SP600125) abolished c-jun phosphorylation and COL1 expression. These results suggest that the flow-induction of OPN was mediated through the ERK-Elk1-OPN pathway, and that COL1 was regulated by both the ERK-Elk1-COL1 and JNK-c-JUN-COL1 pathway.

Scleroderma, fibroblasts, signaling, and excessive extracellular matrix

Excessive extracellular matrix (ECM) deposition in the skin, lung, and other organs is a hallmark of systemic sclerosis (SSc). The pathogenesis of SSc is still poorly understood, but increasing evidence suggests that various cytokines such as transforming growth factor (TGF)-beta and their signaling pathways are key mediators of tissue fibrosis as a consequence of ECM accumulation in the pathogenesis of fibrosis such as SSc. TGF-beta regulates diverse biologic activities including cell growth, cell death or apoptosis, cell differentiation, and ECM synthesis. TGF-beta is known to induce the expression of ECM proteins in mesenchymal cells, and to stimulate the production of protease inhibitors that prevent enzymatic breakdown of the ECM. This paper focuses on the possible role of ECM, various cytokines, especially TGF-beta signal transduction pathways in the pathogenesis of fibrosis in SSc.

[Drug treatments for idiopathic pulmonary fibrosis]

Idiopathic pulmonary fibrosis is a disease of unknown cause characterized by cough, progressive dyspnea, restrictive respiratory disorder, a typical honeycomb aspect on the high-resolution CT-scan, and usual interstitial pneumonia at histological examination of the lung biopsy. Most patients die 3 to 8 years after diagnosis. Current treatment is based on a combination of corticosteroids and immunosuppressants, but the efficacy of treatment remains a matter of debate. New therapeutics currently under evaluation in controlled clinical trials include interferon-gamma, pirfenidone, N-acetylcysteine, etanercept (anti-TNFalpha), bosentan (endothelin receptor antagonist), imatinib (tyrosine-kinases inhibitor of the PDGF receptor), etc. At the same time, new compounds showing efficacy in experimental models of fibrosis and the development of new pathophysiological concepts open new perspectives both in terms of concept and clinical practice.

Animal models of systemic sclerosis: insights into systemic sclerosis pathogenesis and potential therapeutic approaches

PURPOSE OF REVIEW

Animal models have been extremely valuable in contributing to a better understanding of the pathogenesis of systemic sclerosis. Discussed here are recent studies that have examined the molecular pathways and potential therapeutic approaches for systemic sclerosis using animal models.

RECENT FINDINGS

Reported evidence further indicates that the immune system plays a role in modulating the fibrosis observed in the tight skin-1/+ mouse model for systemic sclerosis. CD19, interleukin-6, and interleukin-4 are involved. The injection of spleen cells into immune-compromised mice resulted in fibrotic, vascular, and immunologic alterations quite similar to those of systemic sclerosis. Transforming growth factor-beta and its signaling pathway (JAK kinase and STAT-6, Smad2/3, and Smad7) appear to play a central role in the development of fibrosis as well as monocyte chemoattractant protein-1, CCR-2, platelet-derived growth factor C, and excessive apoptosis. Viruses were shown to be possible cofactors. The therapeutic agents hepatocyte growth factor and halofuginone were shown to prevent fibrosis in animal models of systemic sclerosis.

SUMMARY

The transforming growth factor-beta signaling pathway is a common mechanism of tissue fibrosis in animal models of systemic sclerosis, although numerous additional molecules modulate this pathway or have a direct effect on fibrosis.

Halofuginone Inhibits Serum-Stimulated Pericardial Tissue Retraction in Vitro

We developed an in vitro model of tissue contraction in which living pericardium, in response to serum, contracted and the cells in situ expressed proliferating cell nuclear antigen (PCNA) and synthesized collagen. Here we evaluated the effects of halofuginone on these serum-stimulated pericardial tissue responses. Parietal pericardium was incubated with media containing increasing doses of halofuginone and evaluated for tissue contraction, evident by tissue curling. Proliferation was measured by MTS metabolism and PCNA expression. Furthermore, collagen synthesis was compared between samples incubated with halofuginone, cytochalasin B, cytochalasin D, aphidicolin, or cytosine arabinoside (AraC), using Masson's trichrome and the monoclonal antibody to sheep type I procollagen, SP1. D8. Halofuginone inhibited tissue contraction, cellular proliferation, and collagen synthesis in a dose-dependent manner. In contrast, cytochalasin B, cytochalasin D, aphidicolin, and AraC, shown previously to prevent cellular proliferation, did not prevent type I collagen synthesis. Halofuginone has been implicated as an agent in the prevention of wound-healing fibrosis. This study suggests that halofuginone may have an added benefit in the inhibition of pericardial tissue contraction, which appeared to be related to the synthesis of type I procollagen.

Halofuginone, an inhibitor of collagen synthesis by rat stellate cells, stimulates insulin-like growth factor binding protein-1 synthesis by hepatocytes

BACKGROUND/AIMS

Halofuginone, an inhibitor of collagen synthesis, prevented and caused resolution of established hepatic fibrosis. A genomic approach in vivo was used to search for additional genes responsible for halofuginone mode of action.

METHODS

Fibrosis was induced in rats by thioacetamide (TAA) and evaluated by collagen type I gene expression and the levels of collagen, tissue inhibitors of metalloproteinases-2 and smooth-muscle actin. Halofuginone was given in the diet. cDNA from liver biopsies was hybridized on Atlas arrays comprising of 588 genes. The results were confirmed by Northern blots and in situ hybridization.

RESULTS

Insulin-like growth factor binding protein-1 (IGFBP-1) was one of the 13 genes differentially expressed in the fibrotic liver after halofuginone treatment. After 2 and 4 weeks, halofuginone prevented the TAA-induced down-regulation of IGFBP-1 gene expression. Halofuginone also prevented the TAA-dependent changes in IGFBP-3 gene expression. Halofuginone affected IGFBP-1 synthesis in rat hepatocytes and cells of hepatocyte origin and caused time- and dose-dependent increases in the IGFBP-1 gene expression and synthesis by HepG2 cells. The IGFBP-1 secreted by HepG2-inhibited stellate cell motility.

CONCLUSIONS

Halofuginone is an anti-fibrotic drug that inhibits collagen synthesis by stellate cells and preventing alteration in the synthesis of IGFBPs by hepatic cells.

The Use of Halofuginone in Limiting Urethral Stricture Formation and Recurrence: An Experimental Study in Rabbits

PURPOSE

We developed a reproducible animal model for the induction of urethral stricture in the rabbit and evaluated the role of halofuginone in limiting stricture formation.

MATERIALS AND METHODS

A total of 20 New Zealand male rabbits were used in the first phase of the experiment. Bulbar urethral stricture was induced by electrocoagulation. The animals were then randomly assigned to 2 groups of 10 each, which received a diet containing halofuginone or a normal diet. In the second phase electrocoagulation induced stricture was treated with visual internal urethrotomy in 45 rabbits. These rabbits were randomly assigned to 2 groups, namely a halofuginone and a control group.

RESULTS

In the first phase stricture developed in 2 study rabbits (20%) vs 10 controls (100%). In the second phase 37 rabbits were evaluable (8 died). Recurrent stricture was observed in 5 of the 18 study rabbits (27%) vs 14 of the 19 controls (73%).

CONCLUSIONS

Halofuginone is effective in limiting the occurrence of de novo urethral stricture and recurrent stricture after visual internal urethrotomy. This antifibrotic molecule may become an important therapy to treat urethral stricture and/or recurrence following endoscopic manipulation of stricture in humans.

Identification of novel targets in scleroderma: update on population studies, cDNA arrays, SNP analysis, and mutations

PURPOSE OF REVIEW

Systemic sclerosis, or scleroderma, is an uncommon autoimmune connective tissue disease that results in systemic fibrosis. Its etiologic basis remains unclear. The pathogenesis of systemic sclerosis involves a proliferative and obliterative vasculopathy resulting from endothelial cell dysfunction, extensive fibrosis secondary to fibroblast activation, and autoimmunity as demonstrated by the presence of disease-specific autoantibodies. Although there is no clear and convincing evidence for an environmental trigger in most cases, accumulating data emphasize the role of genetic factors in systemic sclerosis. As in other complex human diseases, multiple genes likely contribute to disease susceptibility and the clinical manifestations of systemic sclerosis. This review will cover the application of genomics to the complex genetics of systemic sclerosis.

RECENT FINDINGS

The following review is an update on novel targets identified in scleroderma based on published reports (May 2000-May 2003) of mutation/polymorphism analysis (using SNP and haplotyping), the results from a recent genome-wide scan on a Native American population with systemic sclerosis, and gene expression studies (microarrays).

SUMMARY

The use of genomics has revealed novel targets and genetic associations that may contribute to the cause, the onset, and the subsequent pathologic changes that constitute systemic sclerosis. The identification of potential candidates for gene therapy or disease-specific targets amenable to pharmacologic intervention will benefit patients with systemic sclerosis who are currently being treated for their symptoms and not the disease process itself.

Molecular mechanisms of interleukin-4-induced up-regulation of type I collagen gene expression in murine fibroblasts

OBJECTIVE

There is evidence that interleukin-4 (IL-4) plays a major role in the induction of extracellular matrix protein synthesis in fibrotic disease. We therefore examined the effect of IL-4 on collagen synthesis in primary fibroblasts isolated from normal and TSK/+ mice, which spontaneously develop a scleroderma-like syndrome characterized by diffuse cutaneous hyperplasia.

METHODS

Expression of the IL-4 receptor was determined by flow cytometry and Western blotting. The IL-4 signal transduction cascade was analyzed by Western blotting. We assessed the role of signal transducer and activator of transcription 6 (STAT-6) in IL-4 induction of alpha2(I) collagen promoter activity and message levels via luciferase reporter assay and real-time polymerase chain reaction. The activation status of the transcription factors activator protein 1 (AP-1) and Sp-1 upon stimulation with IL-4 in normal and TSK/+ fibroblasts was examined by electrophoretic mobility shift assay.

RESULTS

Flow cytometry and Western blotting showed that IL-4 receptor alpha expression was elevated in TSK/+ fibroblasts compared with normal fibroblasts. After IL-4 stimulation, janus-activated kinase 1 (JAK-1) and JAK-2 were phosphorylated to a greater degree in TSK/+ fibroblasts than in C57BL/6 fibroblasts. TSK/+ fibroblasts appeared to be hyperresponsive to IL-4, displaying increased synthesis of alpha1(I) collagen messenger RNA (mRNA), collagen protein, and activity of a luciferase reporter construct containing the -300 to +54 murine alpha2(I) collagen promoter. Overexpression of STAT-6 enhanced this effect, whereas expression of a dominant-negative STAT-6 abrogated the ability of IL-4 to induce alpha1(I) collagen mRNA in TSK/+ fibroblasts. Moreover, IL-4 induced increased DNA binding activity of transcription factors that are important for collagen synthesis.

CONCLUSION

Our observations indicate that IL-4 has a profound effect on several factors that have been identified as playing major roles in the regulation of collagen synthesis and suggest that IL-4 increases the expression of type I collagen through a mechanism involving the activation of transcription factors that bind to and activate collagen promoter.