In vivo investigations on anti-fibrotic potential of proteasome inhibition in lung and skin fibrosis

Tree shrews as a new animal model for systemic sclerosis research

Objective

Systemic sclerosis (SSc) is a chronic systemic disease characterized by immune dysregulation and fibrosis for which there is no effective treatment. Animal models are crucial for advancing SSc research. Tree shrews are genetically, anatomically, and immunologically closer to humans than rodents. Thus, the tree shrew model provides a unique opportunity for translational research in SSc.

Methods

In this study, a SSc tree shrew model was constructed by subcutaneous injection of different doses of bleomycin (BLM) for 21 days. We assessed the degree of inflammation and fibrosis in the skin and internal organs, and antibodies in serum. Furthermore, RNA sequencing and a series of bioinformatics analyses were performed to analyze the transcriptome changes, hub genes and immune infiltration in the skin tissues of BLM induced SSc tree shrew models. Multiple sequence alignment was utilized to analyze the conservation of selected target genes across multiple species.

Results

Subcutaneous injection of BLM successfully induced a SSc model in tree shrew. This model exhibited inflammation and fibrosis in skin and lung, and some developed esophageal fibrosis and secrum autoantibodies including antinuclear antibodies and anti-scleroderma-70 antibody. Using RNA sequencing, we compiled skin transcriptome profiles in SSc tree shrew models. 90 differentially expressed genes (DEGs) were identified, which were mainly enriched in the PPAR signaling pathway, tyrosine metabolic pathway, p53 signaling pathway, ECM receptor interaction and glutathione metabolism, all of which are closely associated with SSc. Immune infiltration analysis identified 20 different types of immune cells infiltrating the skin of the BLM-induced SSc tree shrew models and correlations between those immune cells. By constructing a protein-protein interaction (PPI) network, we identified 10 hub genes that were significantly highly expressed in the skin of the SSc models compared to controls. Furthermore, these genes were confirmed to be highly conserved in tree shrews, humans and mice.

Conclusion

This study for the first time comfirmed that tree shrew model of SSc can be used as a novel and promising experimental animal model to study the pathogenesis and translational research in SSc.

Non-peptidic immunoproteasome β5i-selective inhibitor as potential treatment for idiopathic pulmonary fibrosis: Virtual screening, hit evolution and lead identification

The immunoproteasome has emerged as a potential therapeutic target for idiopathic pulmonary fibrosis (IPF). We report herein our efforts to discover novel non-peptidic immunoproteasome inhibitors as potential treatment for IPF. A structure-based virtual screening was initially performed and the hit compound VS-7 with an IC50 of 9.437 μM against β5i was identified. Hit evolution based on the interaction mode of VS-7 proceeded, and a potent β5i inhibitor 54 (IC50 = 8.463 nM) with favorable subunit-selective profiles was obtained. Compound 54 also imposed significant effects on the release of TNF-α and IL-6, the transcriptional activity of NF-κB, as well as TGF-β1 induced fibroblast proliferation, activation and collagen synthesis. Notably, when administered at 30 mg/kg in a bleomycin-induced IPF mouse model, compound 54 showed anti-fibrotic effects comparable to the clinical drug nintedanib. The results suggest that selective inhibition of immunoproteasome could be an effective approach to treat IPF.

Novel Therapeutic Strategies in the Treatment of Systemic Sclerosis

Systemic sclerosis is a connective tissue disease of unknown origin and with an unpredictable course, with both cutaneous and internal organ manifestations. Despite the enormous progress in rheumatology and clinical immunology, the background of this disease is largely unknown, and no specific therapy exists. The therapeutic approach aims to treat and preserve the function of internal organs, and this approach is commonly referred to as organ-based treatment. However, in modern times, data from other branches of medicine may offer insight into how to treat disease-related complications, making it possible to find new drugs to treat this disease. In this review, we present therapeutic options aiming to stop the progression of fibrotic processes, restore the aberrant immune response, stop improper signalling from proinflammatory cytokines, and halt the production of disease-related autoantibodies.

Disruption of proteostasis causes IRE1 mediated reprogramming of alveolar epithelial cells

Disruption of alveolar type 2 cell (AEC2) protein quality control has been implicated in chronic lung diseases, including pulmonary fibrosis (PF). We previously reported the in vivo modeling of a clinical surfactant protein C (SP-C) mutation that led to AEC2 endoplasmic reticulum (ER) stress and spontaneous lung fibrosis, providing proof of concept for disruption to proteostasis as a proximal driver of PF. Using two clinical SP-C mutation models, we have now discovered that AEC2s experiencing significant ER stress lose quintessential AEC2 features and develop a reprogrammed cell state that heretofore has been seen only as a response to lung injury. Using single-cell RNA sequencing in vivo and organoid-based modeling, we show that this state arises de novo from intrinsic AEC2 dysfunction. The cell-autonomous AEC2 reprogramming can be attenuated through inhibition of inositol-requiring enzyme 1 (IRE1α) signaling as the use of an IRE1α inhibitor reduced the development of the reprogrammed cell state and also diminished AEC2-driven recruitment of granulocytes, alveolitis, and lung injury. These findings identify AEC2 proteostasis, and specifically IRE1α signaling through its major product XBP-1, as a driver of a key AEC2 phenotypic change that has been identified in lung fibrosis.

Autoantibodies as Biomarker and Therapeutic Target in Systemic Sclerosis

Systemic sclerosis (SSc) is a rare connective tissue disorder characterized by immune dysregulation evoking the pathophysiological triad of inflammation, fibrosis and vasculopathy. In SSc, several alterations in the B-cell compartment have been described, leading to polyclonal B-cell hyperreactivity, hypergammaglobulinemia and autoantibody production. Autoreactive B cells and autoantibodies promote and maintain pathologic mechanisms. In addition, autoantibodies in SSc are important biomarkers for predicting clinical phenotype and disease progression. Autoreactive B cells and autoantibodies represent potentially promising targets for therapeutic approaches including B-cell-targeting therapies, as well as strategies for unselective and selective removal of autoantibodies. In this review, we present mechanisms of the innate immune system leading to the generation of autoantibodies, alterations of the B-cell compartment in SSc, autoantibodies as biomarkers and autoantibody-mediated pathologies in SSc as well as potential therapeutic approaches to target these.

Evaluation of Proteasome Inhibitors in the Treatment of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most common form of idiopathic interstitial pneumonia, and it has a worse prognosis than non-small cell lung cancer. The pathomechanism of IPF is not fully understood, but it has been suggested that repeated microinjuries of epithelial cells induce a wound healing response, during which fibroblasts differentiate into myofibroblasts. These activated myofibroblasts express α smooth muscle actin and release extracellular matrix to promote matrix deposition and tissue remodeling. Under physiological conditions, the remodeling process stops once wound healing is complete. However, in the lungs of IPF patients, myofibroblasts re-main active and deposit excess extracellular matrix. This leads to the destruction of alveolar tissue, the loss of lung elastic recoil, and a rapid decrease in lung function. Some evidence has indicated that proteasomal inhibition combats fibrosis by inhibiting the expressions of extracellular matrix proteins and metalloproteinases. However, the mechanisms by which proteasome inhibitors may protect against fibrosis are not known. This review summarizes the current research on proteasome inhibitors for pulmonary fibrosis, and provides a reference for whether proteasome inhibitors have the potential to become new drugs for the treatment of pulmonary fibrosis.

Bortezomib Inhibits Lung Fibrosis and Fibroblast Activation Without Proteasome Inhibition

The FDA-approved proteasomal inhibitor bortezomib (BTZ) has attracted interest for its potential anti-fibrotic actions. However, neither its in vivo efficacy in lung fibrosis nor its dependence on proteasome inhibition has been conclusively defined. In this study, we assessed the therapeutic efficacy of BTZ in a mouse model of pulmonary fibrosis, developed an in vitro protocol to define its actions on diverse fibroblast activation parameters, determined its reliance on proteasome inhibition for these actions in vivo and in vitro and explored alternative mechanisms of action. The therapeutic administration of BTZ diminished the severity of pulmonary fibrosis without reducing proteasome activity in the lung. In experiments designed to mimic this lack of proteasome inhibition in vitro, BTZ reduced fibroblast proliferation, differentiation into myofibroblasts, and collagen synthesis. It promoted de-differentiation of myofibroblasts and overcame their characteristic resistance to apoptosis. Mechanistically, BTZ inhibited kinases important for fibroblast activation while inducing expression of dual-specificity phosphatase 1 or DUSP1, and knockdown of DUSP1 abolished its anti-fibrotic actions in fibroblasts. Collectively, these findings suggest that BTZ exhibits a multidimensional profile of robust inhibitory actions on lung fibroblasts as well as anti-fibrotic actions in vivo. Unexpectedly, these actions appear to be independent of proteasome inhibition, and instead attributable to induction of DUSP1.

PolyG mitigates silica-induced pulmonary fibrosis by inhibiting nucleolin and regulating DNA damage repair pathway

Polyguanylic acid potassium salt (PolyG) has an anti-fibrotic G-quadruplex (G4) structure. It could inhibit the expression of nucleolin, a protein involved in cell proliferation and apoptosis. However, its role in regulating nucleolin in silicosis is still unknown. After instillation of 50 μl of crystalline silica suspension (50 mg/ml) into the trachea of C57BL/6 mice, we show that nucleolin expression is upregulated in mouse pulmonary tissue following the treatment with silica and that PolyG, which were injected 2.5 mg/kg body weight into mice by abdomen, could alleviate pulmonary fibrosis through inhibiting the expression of nucleolin. Further, we demonstrated that the expression of the DNA double-strand break (DSB) marker, γ-H2AX, increased in response to silica treatment. PolyG could efficiently reduce the protein expression of γ-H2AX and decreased the level of fibrosis-related genes, such as Col1a1 and Col3a1, as well as the levels of fibrosis-associated proteins α-SMA and vimentin in the lungs of silica-treated mice. These findings show that PolyG could regulate nucleolin and DNA damage repair to control fibrotic response in experimental silicosis and provide a new target for preventive intervention.

Is biological therapy in systemic sclerosis the answer?

Systemic sclerosis is a systemic fibrosing disorder associated with significant morbidity and mortality, with no universally accepted disease-modifying therapy. Significant advances in the understanding of systemic sclerosis in recent years have guided the exploration of biological drugs in systemic sclerosis. In this narrative review, we summarize the published literature on biologic therapies in systemic sclerosis. A double-blind randomized trial, and an open label trial of tocilizumab (which antagonizes the interleukin 6 receptor), identified potential benefits in skin and lung fibrosis in systemic sclerosis; however, these differences failed to attain statistical significance. Two open-label trials compared rituximab (which depletes B lymphocytes) to conventional treatment/ cyclophosphamide in systemic sclerosis-associated interstitial lung disease (ILD), and revealed significant improvements in lung functions and skin disease with rituximab. Significant observational data also support the use of rituximab in skin, lung, muscle and joint manifestations of systemic sclerosis. Abatacept (which blocks T lymphocyte activation) has demonstrated utility for skin and joint disease in systemic sclerosis; a recent clinical trial failed to demonstrate benefits in improving skin thickness compared to placebo. Agents targeting type I interferons, interleukin 17 pathway, CD19 and plasma cells hold promise in systemic sclerosis; however, high-quality evidence is lacking. The results of different ongoing clinical trials targeting B lymphocytes, T lymphocytes, various cytokines (interleukins 6, 17, 4, 13, IL-1α), platelet-derived growth factor receptor, proteasome, integrins or oncostatin M may help guide future therapeutic regimens with biological agents in systemic sclerosis.

Effects of thalidomide on Th17, Treg cells and TGF-β1/Smad3 pathway in a mouse model of systemic sclerosis

OBJECTIVE

To evaluate the immune regulatory and anti-fibrosis function of thalidomide (Thal) in systemic sclerosis (SSc), we investigated the effects of Thal on: (a) Th17 and Treg cell production; (b) related factors expression; and (c) transforming growth factor (TGF)-β1/Smad3 pathway, using a mouse model of SSc.

METHODS

Forty female BALB/c mice were randomly divided into a normal control (NC) group, SSc group (bleomycin [BLM]-induced experimental SSc), BLM + Thal (10 mg/kg/day) group, BLM + Thal (20) group, and BLM + Thal (30) group. Thal was administered a day after BLM. At the end of the animal experiments, mouse tissues were collected for detection of pathological changes and hydroxyproline content. Flow cytometry, real-time polymerase chain reaction, enzyme-linked immunosorbent assay, immunohistochemistry, Western blot and other methods were used to measure Th17, Treg cell population and their related factors, as well as TGF-β1/Smad3 pathway expression.

RESULTS

Thal treatment: (a) reduced skin, and pulmonary tissue fibrosis, inflammation score, and hydroxyproline content (P < .001) in BLM-induced SSc mice; (b) reduced the percentages of Th17 cells and associated interleukin (IL)-17A expression (both P < .05) but increased the percentages of Treg cells and its transcription factor Foxp3 expression (both P < .05); (c) correlation analysis found positive correlations between Th17/Treg ratio, the inflammatory score of the skin and pulmonary tissues, hydroxyproline content, and type I collagen messenger RNA expression (r = .8546, .8656, .6902, .6807, .8118, and .8424, respectively, P < .01); (d) Thal inhibited TGF-β1 expression and Smad3 phosphorylation (both P < .05); (e) TGF-β1 was positively correlated with the IL-17A and Th17/Treg ratio (r = .5856, P = .005; r = .6684, P = .0107, respectively).

CONCLUSION

Thal can effectively prevent skin and pulmonary tissue fibrosis in a mouse model of SSc through the TGF-β1/Smad3 signaling pathway and can rectify the distortion of the Th17/Treg balance in SSc by potentially regulating Th17 and Treg cell production, as well as their related factors expression.

Proteasome dysfunction in alveolar type 2 epithelial cells is associated with acute respiratory distress syndrome

Proteasomes are a critical component of quality control that regulate turnover of short-lived, unfolded, and misfolded proteins. Proteasome activity has been therapeutically targeted and considered as a treatment option for several chronic lung disorders including pulmonary fibrosis. Although pharmacologic inhibition of proteasome activity effectively prevents the transformation of fibroblasts to myofibroblasts, the effect on alveolar type 2 (AT2) epithelial cells is not clear. To address this knowledge gap, we generated a genetic model in which a proteasome subunit, RPT3, which promotes assembly of active 26S proteasome, was conditionally deleted in AT2 cells of mice. Partial deletion of RPT3 resulted in 26S proteasome dysfunction, leading to augmented cell stress and cell death. Acute loss of AT2 cells resulted in depletion of alveolar surfactant, disruption of the alveolar epithelial barrier and, ultimately, lethal acute respiratory distress syndrome (ARDS). This study underscores importance of proteasome function in maintenance of AT2 cell homeostasis and supports the need to further investigate the role of proteasome dysfunction in ARDS pathogenesis.

Bortezomib attenuates renal interstitial fibrosis in kidney transplantation via regulating the EMT induced by TNF-α-Smurf1-Akt-mTOR-P70S6K pathway

Allograft interstitial fibrosis was characterized by massive extracellular matrix deposition caused by activated fibroblasts and myofibroblasts. Epithelial‐mesenchymal transition (EMT) is recognized as an important source of myofibroblasts contributing to the pathogenesis of allograft interstitial fibrosis. Smad ubiquitination regulatory factor 1 (Smurf1) has been recently reported to be involved in the progression of EMT. Our study was to detect the effect of Bortezomib and Smurf1 in the EMT and allograft interstitial fibrosis. Biomarkers of EMT, as well as Smurf1, were examined in human proximal tubular epithelial cells (HK‐2) treated with tumour necrosis factor‐alpha (TNF‐α) in various doses or at various time points by Western Blotting or qRT‐PCR. We knockdown or overexpressed Smurf1 in HK‐2 cells. Furthermore, rat renal transplant model was established and intervened by Bortezomib. Allograft tissues from human and rats were also collected and prepared for HE, Masson's trichrome, immunohistochemical staining and western blotting assays. As a result, we found that TNF‐α significantly promoted the development of EMT in a time‐dependent and dose‐dependent manner through Smurf1/Akt/mTOR/P70S6K signalling pathway. More importantly, Bortezomib alleviated the progression of EMT and allograft interstitial fibrosis in vivo and in vitro by inhibiting the production of TNF‐α and expression of Smurf1. In conclusion, Smurf1 plays a critical role in the development of EMT induced by TNF‐α. Bortezomib can attenuate the Sumrf1‐mediated progression of EMT and renal allograft interstitial fibrosis, which could be suggested as a novel choice for the prevention and treatment of renal allograft interstitial fibrosis.

Myofibroblast transdifferentiation: The dark force in ocular wound healing and fibrosis

Wound healing is one of the most complex biological processes to occur in life. Repair of tissue following injury involves dynamic interactions between multiple cell types, growth factors, inflammatory mediators and components of the extracellular matrix (ECM). Aberrant and uncontrolled wound healing leads to a non-functional mass of fibrotic tissue. In the eye, fibrotic disease disrupts the normally transparent ocular tissues resulting in irreversible loss of vision. A common feature in fibrotic eye disease is the transdifferentiation of cells into myofibroblasts that can occur through a process known as epithelial-mesenchymal transition (EMT). Myofibroblasts rapidly produce excessive amounts of ECM and exert tractional forces across the ECM, resulting in the distortion of tissue architecture. Transforming growth factor-beta (TGFβ) plays a major role in myofibroblast transdifferentiation and has been implicated in numerous fibrotic eye diseases including corneal opacification, pterygium, anterior subcapsular cataract, posterior capsular opacification, proliferative vitreoretinopathy, fibrovascular membrane formation associated with proliferative diabetic retinopathy, submacular fibrosis, glaucoma and orbital fibrosis. This review serves to introduce the pathological functions of the myofibroblast in fibrotic eye disease. We also highlight recent developments in elucidating the multiple signaling pathways involved in fibrogenesis that may be exploited in the development of novel anti-fibrotic therapies to reduce ocular morbidity due to scarring.

Tristetraprolin Down-Regulation Contributes to Persistent TNF-Alpha Expression Induced by Cigarette Smoke Extract through a Post-Transcriptional Mechanism

Rationale

Tumor necrosis factor-alpha (TNF-α) is a potent pro-inflammatory mediator and its expression is up-regulated in chronic obstructive pulmonary disease (COPD). Tristetraprolin (TTP) is implicated in regulation of TNF-α expression; however, whether TTP is involved in cigarette smoke-induced TNF-α expression has not been determined.

Methods

TTP expression was examined by western blot analysis in murine alveolar macrophages and alveolar epithelial cells challenged without or with cigarette smoke extract (CSE). TNF-α mRNA stability, and the decay of TNF-α mRNA, were determined by real-time quantitative RT-PCR. TNF-α protein levels were examined at the same time in these cells. To identify the molecular mechanism involved, a construct expressing the human beta-globin reporter mRNA containing the TNF-α 3’-untranslated region was generated to characterize the TTP targeted site within TNF-α mRNA.

Results

CSE induced TTP down-regulation in alveolar macrophages and alveolar epithelial cells. Reduced TTP expression resulted in significantly increased TNF-α mRNA stability. Importantly, increased TNF-α mRNA stability due to impaired TTP function resulted in significantly increased TNF-α levels in these cells. Forced TTP expression abrogated the increased TNF-α mRNA stability and expression induced by CSE. By using the globin reporter construct containing TNF-α mRNA 3’-untranslated region, the data indicate that TTP directly targets the adenine- and uridine-rich region (ARE) of TNF-α mRNA and negatively regulates TNF-α expression at the post-transcriptional level.

Conclusion

The data demonstrate that cigarette smoke exposure reduces TTP expression and impairs TTP function, resulting in significantly increased TNF-α mRNA stability and excessive TNF-α expression in alveolar macrophages and epithelial cells. The data suggest that TTP is a novel post-transcriptional regulator and limits excessive TNF-α expression and inflammatory response induced by cigarette smoke.

B cell abnormalities and therapeutic strategies in systemic sclerosis

One of the major roles of B cells is to generate antibodies to specific antigens. Secreted antibodies are the principal molecules involved in humoral immunity, with the capacity not only to neutralize pathogens, but also to enhance their elimination by activating phagocytosis or complement proteins. Recently, it has been highlighted that B cells exert important regulatory roles independent of their antibody producing function. These roles include efficiently presenting antigens to the T cells, secreting cytokines, and inducing immune cell differentiation. Thus, B cells have emerged as cells that play crucial roles in immune systems in addition to producing antibodies. Systemic sclerosis (SSc) is characterized by autoimmunity and tissue fibrosis of several organs. Although the pathogenic relationship between systemic autoimmunity and the clinical manifestations of SSc remains unknown, SSc patients display a variety of abnormal immune activation including the production of disease-specific autoantibodies. Previous studies have demonstrated that immune cells, mainly including B cells, play a critical role in systemic autoimmunity and disease expression, though the role of autoimmunity in generating the clinical and pathologic phenotype in SSc remains uncertain. SSc patients have B cell abnormalities characterized by chronic hyper-reactivity of memory B cells. Although distinct subsets of autoantibodies do not have a proven pathogenic role, they are selectively associated with unique disease manifestations. To date, the treatment of SSc has largely relied on cytotoxic immunosuppressants and corticosteroids. Although this has resulted in improved disease survival, these patients may still suffer severe adverse events and refractory disease to conventional immunosuppressive therapies. Recently, clinical trials involving the chimeric monoclonal antibody rituximab have raised high expectations. B cell depleting therapy with rituximab offers a promising treatment for the rheumatic autoimmune diseases including SSc. This article reviews the current knowledge of B cell biology and pathogenesis in SSc as well as the therapeutic approaches focusing on the targeting of B cell specific surface molecules and on the blocking of B cell activation and survival.

Regulation of 26S Proteasome Activity in Pulmonary Fibrosis

RATIONALE

The ubiquitin-proteasome system is critical for maintenance of protein homeostasis by degrading polyubiquitinated proteins in a spatially and temporally controlled manner. Cell and protein homeostasis are altered upon pathological tissue remodeling. Dysregulation of the proteasome has been reported for several chronic diseases of the heart, brain, and lung. We hypothesized that proteasome function is altered upon fibrotic lung remodeling, thereby contributing to the pathogenesis of idiopathic pulmonary fibrosis (IPF).

OBJECTIVES

To investigate proteasome function during myofibroblast differentiation.

METHODS

We treated lung fibroblasts with transforming growth factor (TGF)-β and examined proteasome composition and activity. For in vivo analysis, we used mouse models of lung fibrosis and fibrotic human lung tissue.

MEASUREMENTS AND MAIN RESULTS

We demonstrate that induction of myofibroblast differentiation by TGF-β involves activation of the 26S proteasome, which is critically dependent on the regulatory subunit Rpn6. Silencing of Rpn6 in primary human lung fibroblasts counteracted TGF-β-induced myofibroblast differentiation. Activation of the 26S proteasome and increased expression of Rpn6 were detected during bleomycin-induced lung remodeling and fibrosis. Importantly, Rpn6 is overexpressed in myofibroblasts and basal cells of the bronchiolar epithelium in lungs of patients with IPF, which is accompanied by enhanced protein polyubiquitination.

CONCLUSIONS

We identified Rpn6-dependent 26S proteasome activation as an essential feature of myofibroblast differentiation in vitro and in vivo, and our results suggest it has an important role in IPF pathogenesis.

Validation of the 2nd Generation Proteasome Inhibitor Oprozomib for Local Therapy of Pulmonary Fibrosis

Proteasome inhibition has been shown to prevent development of fibrosis in several organs including the lung. However, effects of proteasome inhibitors on lung fibrosis are controversial and cytotoxic side effects of the overall inhibition of proteasomal protein degradation cannot be excluded. Therefore, we hypothesized that local lung-specific application of a novel, selective proteasome inhibitor, oprozomib (OZ), provides antifibrotic effects without systemic toxicity in a mouse model of lung fibrosis. Oprozomib was first tested on the human alveolar epithelial cancer cell line A549 and in primary mouse alveolar epithelial type II cells regarding its cytotoxic effects on alveolar epithelial cells and compared to the FDA approved proteasome inhibitor bortezomib (BZ). OZ was less toxic than BZ and provided high selectivity for the chymotrypsin-like active site of the proteasome. In primary mouse lung fibroblasts, OZ showed significant anti-fibrotic effects, i.e. reduction of collagen I and α smooth muscle actin expression, in the absence of cytotoxicity. When applied locally into the lungs of healthy mice via instillation, OZ was well tolerated and effectively reduced proteasome activity in the lungs. In bleomycin challenged mice, however, locally applied OZ resulted in accelerated weight loss and increased mortality of treated mice. Further, OZ failed to reduce fibrosis in these mice. While upon systemic application OZ was well tolerated in healthy mice, it rather augmented instead of attenuated fibrotic remodelling of the lung in bleomycin challenged mice. To conclude, low toxicity and antifibrotic effects of OZ in pulmonary fibroblasts could not be confirmed for pulmonary fibrosis of bleomycin-treated mice. In light of these data, the use of proteasome inhibitors as therapeutic agents for the treatment of fibrotic lung diseases should thus be considered with caution.

IL-21 induction of CD4+ T cell differentiation into Th17 cells contributes to bleomycin-induced fibrosis in mice

Systemic sclerosis (SSc) is a connective tissue disease characterized by fibrosis of the skin and internal organs. Th17 cells and interleukin-17 (also called IL-17A) have been found to be increased in peripheral blood and skin in patients with SSc. IL-21 is a potent inducer of Th17 differentiation that is produced by activated T cells, and whose relationship with Th17 cells in SSc is unclear. Here, using a bleomycin (BLM)-induced mouse model of skin fibrosis, we detected the frequency of CD4+/IL-17+ (Th17) cells, CD4+/IL-21+ T cells and IL-21+ Th17 cells in peripheral blood, skin and lungs, as well as the serum content of IL-17A and IL-21. In addition, we assessed the differentiation of CD4+ T cells cultured from these mice into Th17 cells in response to treatment with IL-21. Compared with the control mice, Th17 cell counts and IL-17A levels were significantly increased and correlated with inflammatory and fibrotic indices in the skin and lungs of the BLM-induced fibrosis mice. Moreover, serum levels of CD4+/IL-21+ T cells, IL-21+ Th17 cells, and IL-21 were significantly increased in these mice, and correlated positively with serum levels of Th17 cells. In vitro experiments showed that IL-21 treated CD4+ T cells derived from BLM-induced mice differentiated into Th17 cells. Our results indicate that Th17 cells and IL-17A contributes to inflammatory and fibrotic processes in the skin and lungs in a BLM-induced mouse model of SSc. Moreover, the expansion of the Th17 cell population may be subsequent to IL-21 promotion of the differentiation of CD4+ T cells in these mice.

Regulation of the proteasome: evaluating the lung proteasome as a new therapeutic target

SIGNIFICANCE

Lung diseases are on the second rank worldwide with respect to morbidity and mortality. For most respiratory diseases, no effective therapies exist. Whereas the proteasome has been successfully evaluated as a novel target for therapeutic interventions in cancer, neurodegenerative, and cardiac disorders, there is a profound lack of knowledge on the regulation of proteasome activity in chronic and acute lung diseases.

RECENT ADVANCES

There are various means of how the amount of active proteasome complexes in the cell can be regulated such as transcriptional regulation of proteasomal subunit expression, association with different regulators, assembly and half-life of proteasomes and regulatory complexes, as well as post-translational modifications. It also becomes increasingly evident that proteasome activity is fine-tuned and depends on the state of the cell. We propose here that 20S proteasomes and their regulators can be regarded as dynamic building blocks, which assemble or disassemble in response to cellular needs. The composition of proteasome complexes in a cell may vary depending on tissue, cell type and compartment, stage of development, or pathological context.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Dissecting the expression and regulation of the various catalytic forms of 20S proteasomes, such as constitutive, immuno-, and mixed proteasomes, together with their associated regulatory complexes will not only greatly enhance our understanding of proteasome function in lung pathogenesis but will also pave the way to develop new classes of drugs that inhibit or activate proteasome function in a defined setting for treatment of lung diseases.

Novel investigational agents for the treatment of scleroderma

INTRODUCTION

The purpose of this article is to highlight novel therapies that are being used in scleroderma (SSc). Therapeutic interventions in SSc generally target at least one of three ongoing biological processes characteristic of the disease: vasculopathy, autoimmunity and tissue fibrosis. Treatment decisions in SSc are determined by the level of disease activity and the degree of specific organ involvement. Traditional therapy has primarily focused on organ-specific management without clear evidence of overall disease modification.

AREAS COVERED

The authors provide a review of a variety of agents, which are already used for other autoimmune diseases, that are now being used to treat active SSc skin or lung disease, including rituximab, tocilizumab and IVIG. Several agents studied in vitro and in animal models of fibrosis have shown promise, including bortezomib, LPA-1 antagonists, anti-CCN2 therapy, anti-IL-13 and thrombin antagonists. The authors also provide details on targeting intracellular molecular pathways and matricellular proteins, which is another novel area of investigation.

EXPERT OPINION

Combination therapy may be necessary to control the complex biological network active in SSc. Most of the current evidence that suggest benefit of these agents is based on small population studies. Ultimately well-designed clinical trials are required to define the role of these agents in treating SSc.

MicroRNA-21 in scleroderma fibrosis and its function in TGF-β-regulated fibrosis-related genes expression

Uncontrolled fibrosis in multiple organs is the main cause of death in systemic sclerosis (SSc), and transforming growth factor-β (TGF-β) activation plays a fundamental role in the process. Our previous study demonstrated that miR-21 was significantly up-regulated in SSc fibroblasts. Here, we found that TGF-β regulated the expression of miR-21 and fibrosis-related genes, and decreased Smad7 expression. Over-expression of miR-21 in fibroblasts decreased the levels of Smad7, whereas knockdown of miR-21 increased its expression. Further study using a reporter gene assay demonstrated Smad7 was a direct target of miR-21. Similar to human SSc, the expression of miR-21 increased in the bleomycin induced skin fibrosis. Inhibition of fibrosis by treatment with anti-fibrosis drug bortezomib restored the levels of miR-21 and Smad7. MiR-21 may function in an amplifying circuit to enhance TGF-β signaling events in SSc fibrosis, and suggesting that miR-21 may act as a potential therapeutic target.

HDAC inhibitor L-carnitine and proteasome inhibitor bortezomib synergistically exert anti-tumor activity in vitro and in vivo

Combinations of proteasome inhibitors and histone deacetylases (HDAC) inhibitors appear to be the most potent to produce synergistic cytotoxicity in preclinical trials. We have recently confirmed that L-carnitine (LC) is an endogenous HDAC inhibitor. In the current study, the anti-tumor effect of LC plus proteasome inhibitor bortezomib (velcade, Vel) was investigated both in cultured hepatoma cancer cells and in Balb/c mice bearing HepG2 tumor. Cell death and cell viability were assayed by flow cytometry and MTS, respectively. Gene, mRNA expression and protein levels were detected by gene microarray, quantitative real-time PCR and Western blot, respectively. The effect of Vel on the acetylation of histone H3 associated with the p21(cip1) gene promoter was examined by using ChIP assay and proteasome peptidase activity was detected by cell-based chymotrypsin-like (CT-like) activity assay. Here we report that (i) the combination of LC and Vel synergistically induces cytotoxicity in vitro; (ii) the combination also synergistically inhibits tumor growth in vivo; (iii) two major pathways are involved in the synergistical effects of the combinational treatment: increased p21(cip1) expression and histone acetylation in vitro and in vivo and enhanced Vel-induced proteasome inhibition by LC. The synergistic effect of LC and Vel in cancer therapy should have great potential in the future clinical trials.

Protein damage, repair and proteolysis

Proteins are continuously affected by various intrinsic and extrinsic factors. Damaged proteins influence several intracellular pathways and result in different disorders and diseases. Aggregation of damaged proteins depends on the balance between their generation and their reversal or elimination by protein repair systems and degradation, respectively. With regard to protein repair, only few repair mechanisms have been evidenced including the reduction of methionine sulfoxide residues by the methionine sulfoxide reductases, the conversion of isoaspartyl residues to L-aspartate by L-isoaspartate methyl transferase and deglycation by phosphorylation of protein-bound fructosamine by fructosamine-3-kinase. Protein degradation is orchestrated by two major proteolytic systems, namely the lysosome and the proteasome. Alteration of the function for both systems has been involved in all aspects of cellular metabolic networks linked to either normal or pathological processes. Given the importance of protein repair and degradation, great effort has recently been made regarding the modulation of these systems in various physiological conditions such as aging, as well as in diseases. Genetic modulation has produced promising results in the area of protein repair enzymes but there are not yet any identified potent inhibitors, and, to our knowledge, only one activating compound has been reported so far. In contrast, different drugs as well as natural compounds that interfere with proteolysis have been identified and/or developed resulting in homeostatic maintenance and/or the delay of disease progression.

Proteasome inhibition prevents development of experimental dermal fibrosis

Scleroderma is a chronic fibrotic disorder. Bortezomib, a proteasome inhibitor, is reported to attenuate experimentally induced renal and cardiac fibrosis. This study aimed to evaluate the preventive and therapeutic efficacies of bortezomib on a bleomycin (BLM)-induced scleroderma model. Dermal fibrosis was induced in Balb/c mice by subcutaneous BLM (100 μg/day) injections. Bortezomib (1.6 mg/kg twice/week) was applied intraperitoneally to BLM-injected mice during the first 3 weeks for preventive interventions and in the second 3 weeks for therapeutic interventions. IL-4 and TGF-β1 serum levels, dermal thicknesses, dermal inflammatory cell counts, and α-SMA-positive fibroblastic cell counts were determined, and type-I collagen, NF-κBp65, I-κBα, and JNK1 expressions were assessed. BLM applications increased serum IL-4 level, dermal inflammatory cell counts, α-SMA-positive cell counts, expression of type-I collagen, NF-κB, and JNK1, and dermal thickness in early stage of fibrosis, but serum IL-4 level and dermal inflammatory cell counts showed no increases in later stages. As a preventive intervention, bortezomib decreased dermal thickness, inflammatory cell infiltrations, fibroblastic activity, and expression of type-I collagen, NF-κB, and JNK1, but did not decrease fibroblastic activity and dermal thickness at later stages of fibrosis. Inflammatory status is prominent in the early stage of dermal fibrosis, but declines at later stages. In BLM-induced dermal fibrosis, bortezomib has a preventive anti-fibrotic and anti-inflammatory efficacy, but has no therapeutic anti-fibrotic efficacy in preexisting tissue fibrosis. These findings suggest that the effect of proteasome inhibition in early stages of dermal fibrosis may be related to its anti-inflammatory effects.

Bortezomib alleviates experimental pulmonary arterial hypertension

Vascular remodeling and endothelial dysfunction are important pathogenic features of pulmonary arterial hypertension (PAH). There is a growing body of evidence that proteasome inhibitors may be beneficial in vascular diseases by inhibiting proliferation of vascular smooth muscle cells (VSMCs) and ameliorating endothelial dysfunction. Here, we evaluated whether bortezomib (BTZ) could alleviate hypoxia- and monocrotaline (MCT)-induced PAH. BTZ (at doses from 1 to 100 μg/kg, or a dose of 100 μg/kg) was administered to mice every other day for the last 2 weeks of a 5-week hypoxia (10% O(2)) period, or to rats once daily from Day 22 to Day 34 after MCT challenge, respectively. BTZ treatment substantially suppressed elevation of right ventricular (RV) systolic pressure, RV hypertrophy, and pulmonary vascular remodeling in hypoxia-exposed mice. Similarly, BTZ treatment inhibited RV hypertrophy and vascular remodeling in MCT-injected rats. Strikingly, BTZ rescued 70% of MCT-injected rats up to Day 60, along with a considerable reduction in RV systolic pressure and suppression of vascular remodeling, whereas, among MCT-injected rats not administered BTZ, there were no survivors by Day 41. BTZ significantly suppressed proliferation of pulmonary VSMCs in vivo and in vitro. Furthermore, BTZ increased not only endothelial nitric oxide (NO) synthase (eNOS), phosphorylated eNOS, and NO production in vitro, but also eNOS and p-eNOS in hypoxia-exposed mice and MCT-injected rats, respectively. In contrast to the beneficial effects, BTZ increased active caspase-3 in cardiac ventricles of MCT-injected rats. Taken together, with caution for cardiotoxicity, BTZ could be a potential therapeutic strategy in PAH, possibly acting by inhibition of VSMC proliferation and amelioration of endothelial dysfunction.

Proteasome inhibition reduces proliferation, collagen expression, and inflammatory cytokine production in nasal mucosa and polyp fibroblasts

Proteasome inhibitors, used in cancer treatment for their proapoptotic effects, have anti-inflammatory and antifibrotic effects on animal models of various inflammatory and fibrotic diseases. Their effects in cells from patients affected by either inflammatory or fibrotic diseases have been poorly investigated. Nasal polyposis is a chronic inflammatory disease of the sinus mucosa characterized by tissue inflammation and remodeling. We tested the hypothesis that proteasome inhibition of nasal polyp fibroblasts might reduce their proliferation and inflammatory and fibrotic response. Accordingly, we investigated the effect of the proteasome inhibitor Z-Leu-Leu-Leu-B(OH)(2) (MG262) on cell viability and proliferation and on the production of collagen and inflammatory cytokines in nasal polyp and nasal mucosa fibroblasts obtained from surgery specimens. MG262 reduced the viability of nasal mucosa and polyp fibroblasts concentration- and time-dependently, with marked effects after 48 h of treatment. The proteasome inhibitor bortezomib provoked a similar effect. MG262-induced cell death involved loss of mitochondrial membrane potential, caspase-3 and poly(ADP-ribose) polymerase activation, induction of c-Jun phosphorylation, and mitogen-activated protein kinase phosphatase-1 expression. Low concentrations of MG262 provoked growth arrest, inhibited DNA replication and retinoblastoma phosphorylation, and increased expression of the cell cycle inhibitors p21 and p27. MG262 concentration-dependently inhibited basal and transforming growth factor-β-induced collagen mRNA expression and interleukin (IL)-1β-induced production of IL-6, IL-8, monocyte chemoattractant protein-1, regulated on activation normal T cell expressed and secreted, and granulocyte/macrophage colony-stimulating factor in both fibroblast types. MG262 inhibited IL-1β/tumor necrosis factor-α-induced activation of nuclear factor-κB. We conclude that noncytotoxic treatment with MG262 reduces the proliferative, fibrotic, and inflammatory response of nasal fibroblasts, whereas high MG262 concentrations induce apoptosis.

Mechanisms of fibrosis: therapeutic translation for fibrotic disease

Fibrosis is a pathological feature of most chronic inflammatory diseases. Fibrosis, or scarring, is defined by the accumulation of excess extracellular matrix components. If highly progressive, the fibrotic process eventually leads to organ malfunction and death. Fibrosis affects nearly every tissue in the body. Here we discuss how key components of the innate and adaptive immune response contribute to the pathogenesis of fibrosis. We also describe how cell-intrinsic changes in important structural cells can perpetuate the fibrotic response by regulating the differentiation, recruitment, proliferation and activation of extracellular matrix-producing myofibroblasts. Finally, we highlight some of the key mechanisms and pathways of fibrosis that are being targeted as potential therapies for a variety of important human diseases.

Mechanisms of fibrosis: therapeutic translation for fibrotic disease

Fibrosis is a pathological feature of most chronic inflammatory diseases. Fibrosis, or scarring, is defined by the accumulation of excess extracellular matrix components. If highly progressive, the fibrotic process eventually leads to organ malfunction and death. Fibrosis affects nearly every tissue in the body. Here we discuss how key components of the innate and adaptive immune response contribute to the pathogenesis of fibrosis. We also describe how cell-intrinsic changes in important structural cells can perpetuate the fibrotic response by regulating the differentiation, recruitment, proliferation and activation of extracellular matrix-producing myofibroblasts. Finally, we highlight some of the key mechanisms and pathways of fibrosis that are being targeted as potential therapies for a variety of important human diseases.

Evaluation of the antifibrotic effect of fenofibrate and rosiglitazone on bleomycin-induced pulmonary fibrosis in rats

Idiopathic pulmonary fibrosis is the most prevalent chronic fibrosing lung disease. Peroxisome proliferator-activated receptors-gamma agonists provide potential therapy for fibrotic diseases of the lung. Peroxisome proliferator-activated receptors-alpha agonists may be helpful in the treatment of lung inflammatory diseases, however their therapeutic potential on the "fibro-proliferative" process and extracellular matrix accumulation in idiopathic pulmonary fibrosis has been less well studied. So, the present study was conducted to evaluate the anti-fibrotic effects of fenofibrate (peroxisome proliferator-activated receptors-alpha agonist) alone and in combination with rosiglitazone (peroxisome proliferator-activated receptors-gamma agonist) on lung injury induced by bleomycin administration. Oral administration of either rosiglitazone (5 mg/kg/d) or fenofibrate (100 mg/kg/d) for 14 days, attenuated the severity of bleomycin-induced lung injury and fibrosis through decreasing lung water contents, lung fibrotic grading, lung hydroxyproline contents and lung transforming growth factor-beta1 levels; with no significant difference between them. Combined low doses of rosiglitazone (1 mg/kg/d) and fenofibrate (30 mg/kg/d) provided more benefits than full separate doses of each on the deleterious effects accompanied bleomycin administration. These findings suggested the potential use of peroxisome proliferator-activated receptors-alpha ligands as anti-fibrotic agents in lung fibrosis. Additionally, the concurrent administration of fenofibrate and rosiglitazone in low doses has synergistic effect and enhanced the beneficial effects afforded by either fenofibrate or rosiglitazone.

Inhibition of VCAM-1 expression in endothelial cells by CORM-3: the role of the ubiquitin-proteasome system, p38, and mitochondrial respiration

Carbon monoxide (CO) abrogates TNF-α-mediated inflammatory responses in endothelial cells, yet the underlying mechanism thereof is still elusive. We have previously shown that the anti-inflammatory effect of CO-releasing molecule-3 (CORM-3) is not completely mediated via deactivation of the NF-κB pathway. In this study, we sought to explore other potential mechanisms by which CORM-3 downregulates VCAM-1 expression on TNF-α-stimulated HUVECs. By genome-wide gene expression profiling and pathway analysis we studied the relevance of particular pathways for the anti-inflammatory effect of CORM-3. In CORM-3-stimulated HUVECs significant changes in expression were found for genes implicated in the proteasome and porphyrin pathways. Although proteasome activities were increased by CORM-3, proteasome inhibitors did not abolish the effect of CORM-3. Likewise, heme oxygenase-1 inhibitors did not abrogate the ability of CORM-3 to downregulate VCAM-1 expression. Interestingly, CORM-3 inhibited MAPK p38, and the p38 inhibitor SB203580 downregulated VCAM-1 expression. However, downregulation of VCAM-1 by CORM-3 occurred only at concentrations that partly inhibit ATP production and sodium azide and oligomycin paralleled the effect of CORM-3 in this regard. Our results indicate that CORM-3-induced downregulation of VCAM-1 is mediated via p38 inhibition and mitochondrial respiration, whereas the ubiquitin-proteasome system seems not to be involved.

Proteasomal inhibition after injury prevents fibrosis by modulating TGF-β(1) signalling

BACKGROUND

The development of organ fibrosis after injury requires activation of transforming growth factor β(1) which regulates the transcription of profibrotic genes. The systemic administration of a proteasomal inhibitor has been reported to prevent the development of fibrosis in the liver, kidney and bone marrow. It is hypothesised that proteasomal inhibition would prevent lung and skin fibrosis after injury by inhibiting TGF-β(1)-mediated transcription.

METHODS

Bortezomib, a small molecule proteasome inhibitor in widespread clinical use, was administered to mice beginning 7 days after the intratracheal or intradermal administration of bleomycin and lung and skin fibrosis was measured after 21 or 40 days, respectively. To examine the mechanism of this protection, bortezomib was administered to primary normal lung fibroblasts and primary lung and skin fibroblasts obtained from patients with idiopathic pulmonary fibrosis and scleroderma, respectively.

RESULTS

Bortezomib promoted normal repair and prevented lung and skin fibrosis when administered beginning 7 days after the initiation of bleomycin. In primary human lung fibroblasts from normal individuals and patients with idiopathic pulmonary fibrosis and in skin fibroblasts from a patient with scleroderma, bortezomib inhibited TGF-β(1)-mediated target gene expression by inhibiting transcription induced by activated Smads. An increase in the abundance and activity of the nuclear hormone receptor PPARγ, a repressor of Smad-mediated transcription, contributed to this response.

CONCLUSIONS

Proteasomal inhibition prevents lung and skin fibrosis after injury in part by increasing the abundance and activity of PPARγ. Proteasomal inhibition may offer a novel therapeutic alternative in patients with dysregulated tissue repair and fibrosis.

Tenascin-C deficiency attenuates TGF-ß-mediated fibrosis following murine lung injury

Tenascin-C (TNC) is an extracellular matrix glycoprotein of unknown function that is highly expressed in adult lung parenchyma following acute lung injury (ALI). Here we report that mice lacking TNC are protected from interstitial fibrosis in the bleomycin model of ALI. Three weeks after exposure to bleomycin, TNC-null mice had accumulated 85% less lung collagen than wild-type mice. The lung interstitium of TNC-null mice also appeared to contain fewer myofibroblasts and fewer cells with intranuclear Smad-2/3 staining, suggesting impaired TGF-β activation or signaling. In vitro, TNC-null lung fibroblasts exposed to constitutively active TGF-β expressed less α-smooth muscle actin and deposited less collagen I into the matrix than wild-type cells. Impaired TGF-β responsiveness was correlated with dramatically reduced Smad-3 protein levels and diminished nuclear translocation of Smad-2 and Smad-3 in TGF-β-exposed TNC-null cells. Reduced Smad-3 in TNC-null cells reflects both decreased transcript abundance and enhanced ubiquitin-proteasome-mediated protein degradation. Together, these studies suggest that TNC is essential for maximal TGF-β action after ALI. The clearance of TNC that normally follows ALI may restrain TGF-β action during lung healing, whereas prolonged or exaggerated TNC expression may facilitate TGF-β action and fibrosis after ALI.

Neurophysiological and neuropathological characterization of new murine models of chemotherapy-induced chronic peripheral neuropathies

Cisplatin, paclitaxel and bortezomib belong to some of the most effective families of chemotherapy drugs for solid and haematological cancers. Epothilones represent a new family of very promising antitubulin agents. The clinical use of all these drugs is limited by their severe peripheral neurotoxicity. Several in vivo rat models have reproduced the characteristics of the peripheral neurotoxicity of these drugs. However, since only a very limited number of cancer types can be studied in immunocompetent rats, these animal models do not represent an effective way to evaluate, at the same time, the antineoplastic activity and the neurotoxic effects of the anticancer compounds. In this study, we characterized the neurophysiological impairment induced by chronic chemotherapy treatment in BALB/c mice, a strain suitable for assessing the activity of anticancer treatments. At the end of a 4-week period of treatment with cisplatin, paclitaxel, epothilone-B or bortezomib, sensory and sensory/motor nerve conduction velocities (NCV) were determined in the caudal and digital nerves and dorsal root ganglia (DRG) and sciatic nerves were collected for histopathological analysis. The electrophysiological studies revealed that all the compounds caused a statistically significant reduction in the caudal NCV, while impairment of the digital NCV was less severe. This functional damage was confirmed by the histopathological observations evidencing axonal degeneration in the sciatic nerve induced by all the drugs associated with pathological changes in DRG induced only by cisplatin and bortezomib. These results confirm the possibility to use our models to combine the study of the antineoplastic activity of anticancer drugs and of their toxic effects on the peripheral nervous system in the BALB/c mouse strain.

Proteasomal regulation of pulmonary fibrosis

It is estimated that, combined, 400,000 people are diagnosed with idiopathic pulmonary fibrosis (IPF) or acute lung injury/acute respiratory distress syndrome annually in the United States, and both diseases are associated with an unacceptably high mortality rate. Although these disorders are distinct clinical entities, they share pathogenic mechanisms that may provide overlapping therapeutic targets. One example is fibroblast activation, which occurs concomitant with acute lung injury as well as in the progressive fibrosis of IPF. Both clinical entities are characterized by elevations of the profibrotic cytokine, transforming growth factor (TGF)-beta1. Protein degradation by the ubiquitin-proteasomal system modulates TGF-beta1 expression and signaling. In this review, we highlight the effects of proteasomal inhibition in various animal models of tissue fibrosis and mechanisms by which it may regulate TGF-beta1 expression and signaling. At present, there are no effective therapies for fibroproliferative acute respiratory distress syndrome or IPF, and proteasomal inhibition may provide a novel, attractive target in these devastating diseases.

Transcriptional regulation of matrix metalloproteinase-1 and collagen 1A2 explains the anti-fibrotic effect exerted by proteasome inhibition in human dermal fibroblasts

Introduction

Extracellular matrix (ECM) turnover is controlled by the synthetic rate of matrix proteins, including type I collagen, and their enzymatic degradation by matrix metalloproteinases (MMPs). Fibrosis is characterized by an unbalanced accumulation of ECM leading to organ dysfunction as observed in systemic sclerosis. We previously reported that proteasome inhibition (PI) in vitro decreases type I collagen and enhances MMP-1 production by human fibroblasts, thus favoring an antifibrotic fibroblast phenotype. These effects were dominant over the pro-fibrotic phenotype induced by transforming growth factor (TGF)-β. Here we investigate the molecular events responsible for the anti-fibrotic phenotype induced in fibroblasts by the proteasome inhibitor bortezomib.

Methods

The steady-state mRNA levels of COL1A1, COL1A2, TIMP-1, MMP-1, and MMP-2 were assessed by quantitative PCR in human dermal fibroblasts cultured in the presence of TGF-β, bortezomib, or both. Transient fibroblast transfection was performed with wild-type and mutated COL1A1 and MMP-1 promoters. Chromatin immunoprecipitation, electrophoretic mobility shift assay (EMSA), and DNA pull-down assays were used to assess the binding of c-Jun, SP1, AP2, and Smad2 transcription factors. Immunoblotting and immunofluorescent microscopy were performed for identifying phosphorylated transcription factors and their cellular localization.

Results

Bortezomib decreased the steady-state mRNA levels of COL1A1 and COL1A2, and abrogated SP1 binding to the promoter of COL1A2 in both untreated and TGF-β-activated fibroblasts. Reduced COL1A2 expression was not due to altered TGF-β-induced Smad2 phosphorylation, nuclear translocation, or binding to the COL1A2 promoter. In contrast to collagen, bortezomib specifically increased the steady-state mRNA levels of MMP-1 and enhanced the binding of c-Jun to the promoter of MMP-1. Furthermore, disruption of the proximal AP-1-binding site in the promoter of MMP-1 severely impaired MMP-1 transcription in response to bortezomib.

Conclusions

By altering the binding of at least two transcription factors, c-Jun and SP1, proteasome inhibition results in increased production of MMP-1 and decreased synthesis of type I collagen in human dermal fibroblasts. Thus, the antifibrotic phenotype observed in fibroblasts submitted to proteasome inhibition results from profound modifications in the binding of key transcription factors. This provides a novel rationale for assessing the potential of drugs targeting the proteasome for their anti-fibrotic properties.

Proteasome inhibition modulates kinase activation in neural cells: relevance to ubiquitination, ribosomes, and survival

In this study we examined whether established signal transduction cascades, p44/42 mitogen-activated protein kinase (ERK1/2) and Jun N-terminal kinases (JNK) pathways, are altered in N2a neural cells in response to proteasome inhibition. Additionally, we sought to elucidate the relative contribution of these signal transduction pathways to the multiple downstream effects of proteasome inhibition. Our data indicate that ERK1/2 and JNK are activated in response to proteasome inhibition. Washout of proteasome inhibitor (MG132) results in an enhancement of ERK1/2 activation and amelioration of JNK activation. Treatment with an established MAPK inhibitor resulted in an increase in proteasome inhibitor toxicity, and incubation with JNK inhibitor was observed to attenuate proteasome inhibitor toxicity significantly. Subsequent studies demonstrated that inhibition of ERK1/2 and JNK activity does not alter the gross increase in ubiquitinated protein following proteasome inhibitor administration. Similarly, ERK1/2 and JNK activity do not appear to play a role in the disruption of polysomes following proteasome inhibitor administration in neural cells. Together these data indicate that ERK1/2 and JNK activation may play differential roles in modulating neurochemical disturbances and neurotoxicity induced by proteasome inhibition.