Regulation of Matrix Remodeling by Peroxisome Proliferator-Activated Receptor-γ: A Novel Link Between Metabolism and Fibrogenesis

Interleukin-1α inhibits transforming growth factor-β1 and β2-induced extracellular matrix production, remodeling and signaling in human lung fibroblasts: Master regulator in lung mucosal repair

BACKGROUND

Lung fibroblasts play a central role in maintaining lung homeostasis and facilitating repair through the synthesis and organization of the extracellular matrix (ECM). This study investigated the cross-talk between interleukin-1 alpha (IL-1α) and transforming growth factor-β (TGF-β) signaling, two key regulators in tissue repair and fibrosis, in the context of lung fibroblast repair in the healthy lung.

RESULTS

Stimulation of lung fibroblasts with TGF-β1 and TGF-β2 induced collagen-I and fibronectin protein expression (p < 0.05), a response inhibited with co-treatment with IL-1α (p < 0.05). Additionally, TGF-β1 and TGF-β2 induced myofibroblast differentiation, and collagen-I gel contraction, which were both suppressed by IL-1α (p < 0.05). In contrast, interleukin (IL)-6, IL-8 and thymic stromal lymphopoietin induced by IL-1α, were unaffected by TGF-β1 or TGF-β2. Mechanistically, IL-1α administration led to the suppression of TGF-β1 and TGF-β2 signaling, through downregulation of mRNA and protein for TGF-β receptor II and the downstream adaptor protein TRAF6, but not through miR-146a that is known to be induced by IL-1α.

DISCUSSION

IL-1α acts as a master regulator, modulating TGF-β1 and TGF-β2-induced ECM production, remodeling, and myofibroblast differentiation in human lung fibroblasts, playing a vital role in balancing tissue repair versus fibrosis. Further research is required to understand the dysregulated cross-talk between IL-1α and TGF-β signaling in chronic lung diseases and the exploration of therapeutic opportunities.

METHODS

Primary human lung fibroblasts (PHLF) were treated with media control, or 1 ng/ml IL-1α with or without 50 ng/ml TGF-β1 or TGF-β2 for 1, 6 and 72 h. Cell lysates were assessed for the expression of ECM proteins and signaling molecules by western blot, miRNA by qPCR, mRNA by RNA sequencing and cell supernatants for cytokine production by ELISA. PHLFs were also seeded in non-tethered collagen-I gels to measure contraction, and myofibroblast differentiation using confocal microscopy.

PPARG-mediated autophagy activation alleviates inflammation in rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is a systemic inflammatory autoimmune disease characterized by joint inflammation and bone damage, that not only restricts patient activity but also tends to be accompanied by a series of complications, seriously affecting patient prognosis. Peroxisome proliferator-activated receptor gamma (PPARG), a receptor that controls cellular metabolism, regulates the function of immune cells and stromal cells. Previous studies have shown that PPARG is closely related to the regulation of inflammation. However, the role of PPARG in regulating the pathological processes of RA is poorly understood.

MATERIALS AND METHODS

PPARG expression was examined in the synovial tissues and peripheral blood mononuclear cells (PBMCs) from RA patients and the paw of collagen-induced arthritis (CIA) model rats. Molecular biology experiments were designed to examine the effect of PPARG and cannabidiol (CBD) on RAW264.7 cells and CIA rats.

RESULTS

The results reveal that PPARG accelerates reactive oxygen species (ROS) clearance by promoting autophagy, thereby inhibiting ROS-mediated macrophage polarization and NLRP3 inflammasome activation. Notably, CBD may be a promising candidate for understanding the mechanism by which PPARG regulates autophagy-mediated inflammation.

CONCLUSIONS

Taken together, these findings indicate that PPARG may have a role for distinguishing between RA patients and healthy control, and for distinguishing RA activity; moreover, PPARG could be a novel pharmacological target for alleviating RA through the mediation of autophagy. CBD can act as a PPARG agonist that alleviates the inflammatory progression of RA.

Eicosapentaenoic acid-rich oil supplementation activates PPAR-γ and delays skin wound healing in type 1 diabetic mice

Delayed wound healing is a devastating complication of diabetes and supplementation with fish oil, a source of anti-inflammatory omega-3 (ω-3) fatty acids including eicosapentaenoic acid (EPA), seems an appealing treatment strategy. However, some studies have shown that ω-3 fatty acids may have a deleterious effect on skin repair and the effects of oral administration of EPA on wound healing in diabetes are unclear. We used streptozotocin-induced diabetes as a mouse model to investigate the effects of oral administration of an EPA-rich oil on wound closure and quality of new tissue formed. Gas chromatography analysis of serum and skin showed that EPA-rich oil increased the incorporation of ω-3 and decreased ω-6 fatty acids, resulting in reduction of the ω-6/ω-3 ratio. On the tenth day after wounding, EPA increased production of IL-10 by neutrophils in the wound, reduced collagen deposition, and ultimately delayed wound closure and impaired quality of the healed tissue. This effect was PPAR-γ-dependent. EPA and IL-10 reduced collagen production by fibroblasts in vitro. In vivo, topical PPAR-γ-blockade reversed the deleterious effects of EPA on wound closure and on collagen organization in diabetic mice. We also observed a reduction in IL-10 production by neutrophils in diabetic mice treated topically with the PPAR-γ blocker. These results show that oral supplementation with EPA-rich oil impairs skin wound healing in diabetes, acting on inflammatory and non-inflammatory cells.

Efficacy of probiotic Streptococcus thermophilus in counteracting TGF-β1-induced fibrotic response in normal human dermal fibroblasts

BACKGROUND

Abnormal and deregulated skin wound healing associated with prolonged inflammation may result in dermal fibrosis. Since the current therapeutic strategies revealed unsatisfactory, the investigation of alternative approaches such as those based on the use of specific probiotic strains could provide promising therapeutic options. In this study, we aimed to evaluate whether the lysate from S. thermophilus could antagonize the fibrogenic effects of TGF-β1 in normal human dermal fibroblasts (NHDF).

METHODS

NHDF were exposed to TGF-β1 to establish a fibrotic phenotype. Proliferation rate and cell number were measured using the IncuCyte® Live Cell Imager system and the trypan blue dye exclusion test. Phenoconversion markers (α-SMA and fibronectin) and collagen I levels were assessed by western blot and immunofluorescence. The mRNA levels of TGF-β1 were evaluated by RT-PCR. The Smad2/3 phosphorylation level as well as β-catenin and PPARγ expression, were assessed by western blot. The cell contractility function and migration of NHDF were studied using collagen gel retraction assay, and scratch wound healing assay, respectively. The effects of S. thermophilus lysate, alone or combined with TGF-β1, were evaluated on all of the above-listed parameters and markers associated with TGF-β1-induced fibrotic phenotype.

RESULTS

Exposure to the S. thermophilus lysate significantly reduced the key mediators and events involved in the abnormal activation of myofibroblasts by TGF-β1 within the fibrotic profile. The S. thermophilus treatment significantly reduced cell proliferation, migration, and myo-differentiation. In addition, the treatment with probiotic lysate reduced the α-SMA, fibronectin, collagen-I expression levels, and affected the collagen contraction ability of activated dermal fibroblasts. Moreover, the probiotic targeted the TGF-β1 signaling, reducing Smad2/3 activation, TGF-β1 mRNA level, and β-catenin expression through the upregulation of PPARγ.

CONCLUSION

This is the first report showing that S. thermophilus lysate had a remarkable anti-fibrotic effect in TGF-β1-activated NHDF by inhibiting Smad signaling. Notably, the probiotic was able to reduce β-catenin and increase PPARγ levels. The findings support our point that S. thermophilus may help prevent or treat hypertrophic scarring and keloids.

Peroxisome proliferator-activated receptor gamma and its natural agonists in the treatment of kidney diseases

Kidney disease is one of the leading non-communicable diseases related to tremendous health and economic burden globally. Diabetes, hypertension, obesity and cardiovascular conditions are the major risk factors for kidney disease, followed by infections, toxicity and autoimmune causes. The peroxisome proliferator-activated receptor gamma (PPAR-γ) is a ligand-activated nuclear receptor that plays an essential role in kidney physiology and disease. The synthetic agonists of PPAR-γ shows a therapeutic effect in various kidney conditions; however, the associated side effect restricts their use. Therefore, there is an increasing interest in exploring natural products with PPARγ-activating potential, which can be a promising solution to developing effective and safe treatment of kidney diseases. In this review, we have discussed the role of PPAR-γ in the pathophysiology of kidney disease and the potential of natural PPAR-γ agonists in treating various kidney diseases, including acute kidney injury, diabetic kidney disease, obesity-induced nephropathy, hypertension nephropathy and IgA nephropathy. PPAR-γ is a potential target for the natural PPAR-γ agonists against kidney disease; however, more studies are required in this direction.

Serum microRNAs in Systemic Sclerosis, Associations with Digital Vasculopathy and Lung Involvement

Background and aims: Systemic sclerosis (SSc) is an autoimmune, rare multisystem chronic disease that is still not well-understood aetiologically and is challenging diagnostically. In the literature, there are ever-increasing assumptions regarding the epigenetic mechanisms involved in SSc development; one of them is circulating microRNAs. Many of them regulate TLR pathways and are significant in autoimmune balance. The aim of this study was to determine profile expression of selected microRNAs in SSc patients, including miR-126, -132, -143, -145, -155, -181a, -29a and -3148, in comparison to healthy controls. Methods: Serum microRNAs were isolated from 45 patients with SSc and 57 healthy donors (HC). Additionally, SSc patients were considered in the aspect of disease subtype, including diffuse systemic sclerosis (dcSSc) and limited systemic sclerosis (lcSSc). Results: miR-3148 was detected neither in the serum of HC nor in SSc patients. All of the rest of the analyzed microRNAs, excluding miR-126, miR-29a and miR-181a, were significantly upregulated in SSc patients in comparison to HC. However, miR-181a has been revealed only in the serum of patients with lcSSc but not dcSSc. Moderate positive correlations between the transfer factor of the lung for carbon monoxide (TLCO) and miR-126 and miR-145 were observed. A significant correlation has been found between serum miR-143 level and forced vital capacity (FVC). SSc patients with FVC ≤ 70% were characterized by significantly lower levels of miR-143 compared to patients with normal FVC. Additionally, the expression of miR-132 was significantly higher in dcSSc subgroup with detected active lung lesions compared to dcSSc patients with fibrotic lesions. Patients with an early scleroderma pattern of microangiopathy seen on nailfold video-capillaroscopy (NVC) revealed higher expression of miR-155 in serum than those with a late pattern. Conclusions: The expression profile of circulating cell-free miRNAs is significantly changed in the serum of SSc patients compared to healthy individuals. Downregulation of miRNA-181a and overexpression of miR-132, miR-143, miR-145 and miR-155 in serum may be significant in SSc in the context of biomarkers.

Novel insights in fibrotic pulmonary sarcoidosis

PURPOSE OF REVIEW

In chronic pulmonary sarcoidosis, the transition from the inflammatory to the fibrotic stage of the lungs occurs in about 10-20% of cases, eventually causing end-stage fibrotic disease. To date, pathogenetic mechanisms and clinical management remain challenging; thus, we highlight the recent evidence in pulmonary fibrotic processes, clinical signs for an early detection and the potential role of the current investigated antifibrotic agents and promising targeted therapies.

RECENT FINDINGS

Recent findings of relevant key cellular pathways can be considered as a glimmer of light in the complexity of sarcoidosis. In some patients, granulomas persist and serve as a nidus for fibrosis growth, sustained by several fibrosis-stimulating cytokines. Preclinical studies have detected profibrotic, antifibrotic and pleiotropic T cells as promoters of fibrosis. Epigenetics, genetics and transcriptomics research can lead to new target therapies. Antifibrotic drug nintedanib has shown a positive effect on non-idiopathic pulmonary fibrosis fibrotic lung diseases including fibrotic sarcoidosis; other antifibrotic drugs are under investigation.

SUMMARY

Pulmonary fibrosis strongly impacts the outcome of sarcoidosis, and a better understanding of the underlying pathogenic mechanisms can facilitate the development of novel treatments, improving clinical care and life expectancy of these patients. The greatest challenge is to investigate effective antifibrotic therapies once fibrosis develops. The role of these findings in fibrotic sarcoidosis can be translated into other interstitial lung diseases characterized by the coexistence of inflammatory and fibrotic processes.

Lobeglitazone attenuates fibrosis in corneal fibroblasts by interrupting TGF-beta-mediated Smad signaling

PURPOSE

Transforming growth factor beta 1 (TGF-β1) is an important cytokine released after ocular surface injury to promote wound healing. However, its persistence at the injury site triggers a fibrotic response that leads to corneal scarring and opacity. Thiazolidinediones (TZDs) are synthetic peroxisome proliferator-activated receptor gamma (PPAR-γ) ligands used to regulate glucose and lipid metabolism in the management of type 2 diabetes. Studies have also showed TZDs have antifibrotic effect. In this study, we investigated the antifibrotic effect of the TZD lobeglitazone on TGF-β1-induced fibrosis in corneal fibroblasts.

METHODS

Human primary corneal fibroblasts were cultivated and treated with TGF-β1 (5 ng/mL) to induce fibrosis, with or without pre-treatments with different concentrations of lobeglitazone. Myofibroblast differentiation and extracellular matrix (ECM) protein expression was evaluated by western blotting, immunofluorescence, real-time PCR, and collagen gel contraction assay. The effect of lobeglitazone on TGF-β1-induced reactive oxygen species (ROS) generation was evaluated by DCFDA-cellular ROS detection assay kit. Signaling proteins were evaluated by western blotting to determine the mechanism underlying the antifibrotic effect.

RESULTS

Our results showed lobeglitazone attenuated TGF-β1-induced ECM synthesis and myofibroblast differentiation of corneal fibroblasts. This antifibrotic effect appeared to be independent of PPAR signaling and rather due to the inhibition of the TGF-β1-induced Smad signaling. Lobeglitazone also blocked TGF-β1-induced ROS generation and nicotinamide adenine dinucleotide phosphate oxidase (Nox) 4 transcription.

CONCLUSION

These findings indicate that lobeglitazone may be a promising therapeutic agent for corneal scarring. KEY MESSAGES.

PPARγ agonists promote the resolution of myelofibrosis in preclinical models

Myelofibrosis (MF) is a non-BCR-ABL myeloproliferative neoplasm associated with poor outcomes. Current treatment has little effect on the natural history of the disease. MF results from complex interactions between (a) the malignant clone, (b) an inflammatory context, and (c) remodeling of the bone marrow (BM) microenvironment. Each of these points is a potential target of PPARγ activation. Here, we demonstrated the therapeutic potential of PPARγ agonists in resolving MF in 3 mouse models. We showed that PPARγ agonists reduce myeloproliferation, modulate inflammation, and protect the BM stroma in vitro and ex vivo. Activation of PPARγ constitutes a relevant therapeutic target in MF, and our data support the possibility of using PPARγ agonists in clinical practice.

An inflammatory triangle in Sarcoidosis: PPAR-γ, immune microenvironment, and inflammation

INTRODUCTION

Sarcoidosis is an inflammatory disorder characterized by granuloma formation in several organs. Sarcoidosis patients experience higher inflammatory responses resulting in pulmonary fibrosis. Although the precise mechanisms have not been well elucidated, the relationship between the immune system activation and inflammatory status is pivotal in the pathogenesis of sarcoidosis.

AREAS COVERED

Peroxisome proliferator-activated receptor (PPAR) includes the transcription factors involved in cell metabolism, proliferation, and immune response. In the alveolar macrophages of patients with sarcoidosis, the reduced activity and a decreased level of PPAR-γ have been shown. In this study, we discuss how reducing the level of PPAR-γ could lead to increased inflammation and immune responses in patients with sarcoidosis.

EXPERT OPINION

Lack of PPAR-γ may contribute to the development of a suitable milieu for the formation of immune-associated pulmonary granuloma. Reduced levels of PPAR-γ in sarcoidosis could result from over-activation of the immune system and elevated inflammatory responses, as well. Due to the anti-inflammatory function of PPAR-γ, identifying the relation between PPAR-γ, sarcoidosis development, and inflammatory state could be essential to identify the appropriate therapeutic targets. The synthesis of PPAR-γ agonists or PPAR-γ ligands may be an effective step toward the treatment of sarcoidosis patients in the future.

The effects of S-nitrosylation-induced PPARγ/SFRP5 pathway inhibition on the conversion of non-alcoholic fatty liver to non-alcoholic steatohepatitis

Background

Peroxisome proliferators-activated receptors γ (PPARγ) and secreted frizzled related protein 5 (SFRP5) are abnormally expressed in liver cells. But their role in the transformation of non-alcoholic fatty liver (NAFL) to non-alcoholic steatohepatitis (NASH) remains to be studied. We aimed to explore the role of S-nitrosylation (SNO) in the conversion of NAFL to NASH via the peroxisome PPARγ/SFRP5 pathway.

Methods

A normal diet and methionine-choline deficient diet were used to construct the NAFL and NASH mouse models, respectively. The differences between the SNO of PPARγ in both models were measured by irreversible biotinylation. Quantitative reverse transcription PCR (qRT-PCR) and Western blotting were used to detect the effect of SNO on the expression of PPARγ messageRNA (mRNA) and protein in L02 hepatocytes. Nubiscan software, luciferase reporter gene, and chromatin immunoprecipitation assay (CHIP) were used to verify the targeting relationship between PPAR and SFRP5. The expression of tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), and interleukin-6 (IL-6), which are indicators for the activation of Kupffer cells, were determined by enzyme linked immunosorbent assay (ELISA) after co-cultivation of L02 hepatocytes and Kupffer macrophages, as well as the exogenous regulation of SNO, PPARγ, and SFRP5 in hepatic L02 cells.

Results

The NAFL and NASH mouse models were successfully constructed, and the level of PPARγ SNO in the NAFL model was significantly lower than the NASH model (P<0.05). The level of PPARγ was significantly downregulated after increasing the SNO of L02 cells, respectively (P<0.05). Nubiscan software and CHIP confirmed that PPARγ could bind to the promoter region of SFRP5 (P<0.05). Overexpression of PPARγ and SFRP5 could significantly downregulate the expression of TNFα, IL-1β, and IL-6 (P<0.05) correspondingly, while increasing the SNO level of L02 cells could restore the expression levels of TNFα, IL-1β, and IL-6.

Conclusions

SNO promoted the activation of macrophage Kupffer cells by inhibiting the PPARγ/SFRP5 pathway in L02 hepatocytes, thereby promoting the conversion of NAFL into NASH.

Pathological changes of frozen shoulder in rat model and the therapeutic effect of PPAR-γ agonist

Frozen shoulder is a common shoulder disorder characterized by a gradual increase of pain and a limited range of motion. However, its pathophysiologic mechanisms remain unclear and there is no consensus as to the most effective treatment. The purpose of the study was to investigate the effect of transforming growth factor-β (TGF-β) on fibrosis and inflammatory response of the shoulder joint of rat models and to explore the therapeutic effect of the peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist. In the study, the effect of PPAR-γ agonist CDDO-IM treatment on cell proliferation, migration, and extracellular matrix proteins synthesis (vimentin, α-smooth muscle actin, collagen I, and collagen III) were tested by cell proliferation test, scratches test, real-time quantitative polymerase chain reaction, and Western blot analysis. The frozen shoulder was also established on the rat model by injecting adenovirus-TGF-β1 into rats' shoulder capsule. Pathological changes of the frozen shoulder tissue of the experimental group and PPAR-γ agonist treatment group were evaluated. The stiffness of joints of the three groups was tested. Inflammatory mediators' expression including cyclooxygenase-1, interleukin-1β, and tumor necrosis factor-α of the shoulder was tested by enzyme-linked immunosorbent assay, and the expression of extracellular matrix proteins was evaluated by hematoxylin and eosin staining and immunohistochemistry. The results showed that pathological changes of the frozen shoulder in the rat model include an abnormal proliferation of fibroblasts, infiltration of inflammatory cells, and disorder of fibrous structure, while rosiglitazone reduced the severity of the frozen shoulder in the treatment group. Clinically, PPAR-γ agonists may be a promising target for the treatment of the frozen shoulder.

Adipose-derived stem cells: Pathophysiologic implications vs therapeutic potential in systemic sclerosis

Adipose-derived stem cells (ADSCs) residing in the stromal vascular fraction (SVF) of white adipose tissue are recently emerging as an alternative tool for stem cell-based therapy in systemic sclerosis (SSc), a complex connective tissue disorder affecting the skin and internal organs with fibrotic and vascular lesions. Several preclinical and clinical studies have reported promising therapeutic effects of fat grafting and autologous SVF/ADSC-based local treatment for facial and hand cutaneous manifestations of SSc patients. However, currently available data indicate that ADSCs may represent a double-edged sword in SSc, as they may exhibit a pro-fibrotic and anti-adipogenic phenotype, possibly behaving as an additional pathogenic source of pro-fibrotic myofibroblasts through the adipocyte-to-myofibroblast transition process. Thus, in the perspective of a larger employ of SSc-ADSCs for further therapeutic applications, it is important to definitely unravel whether these cells present a comparable phenotype and similar immunosuppressive, anti-inflammatory, anti-fibrotic and pro-angiogenic properties in respect to healthy ADSCs. In light of the dual role that ADSCs seem to play in SSc, this review will provide a summary of the most recent insights into the preclinical and clinical studies employing SVF and ADSCs for the treatment of the disease and, at the same time, will focus on the main findings highlighting the possible involvement of these stem cells in SSc-related fibrosis pathogenesis.

The roles of PPARγ and its agonists in autoimmune diseases: A comprehensive review

Autoimmune diseases are common diseases of the immune system that are characterized by the loss of self-tolerance and the production of autoantibodies; the breakdown of immune tolerance and the prolonged inflammatory reaction are undisputedly core steps in the initiation and maintenance of autoimmunity. Peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors that belong to the nuclear hormone receptor family and act as ligand-activated transcription factors. There are three different isotypes of PPARs: PPARα, PPARγ, and PPARβ/δ. PPARγ is an established regulator of glucose homeostasis and lipid metabolism. Recent studies have demonstrated that PPARγ exhibits anti-inflammatory and anti-fibrotic effects in multiple disease models. PPARγ can also modulate the activation and polarization of macrophages, regulate the function of dendritic cells and mediate T cell survival, activation, and differentiation. In this review, we summarize the signaling pathways and biological functions of PPARγ and focus on how PPARγ and its agonists play protective roles in autoimmune diseases, including autoimmune thyroid diseases, multiple sclerosis, rheumatoid arthritis, systemic sclerosis, systemic lupus erythematosus, primary Sjogren syndrome and primary biliary cirrhosis.

Peroxisome Proliferator-Activated Receptor Gamma Agonist Attenuates Liver Fibrosis by Several Fibrogenic Pathways in an Animal Model of Cholestatic Fibrosis

PURPOSE

Peroxisome proliferator-activated receptor gamma (PPAR-γ) has a key role in hepatic fibrogenesis by virtue of its effect on the hepatic stellate cells (HSCs). Although many studies have shown that PPAR-γ agonists inhibit liver fibrosis, the mechanism remains largely unclear, especially regarding the cross-talk between PPAR-γ and other potent fibrogenic factors.

METHODS

This experimental study involved 25 male Wistar rats. Twenty rats were subjected to bile duct ligation (BDL) to induce liver fibrosis, further divided into an untreated group (BDL; n=10) and a group treated with the PPAR-γ agonist thiazolidinedione (TZD), at 14 days post-operation (BDL+TZD; n=10). The remaining 5 rats had a sham operation (sham; n=5). The effect of PPAR-γ agonist on liver fibrosis was evaluated by histopathology, protein immunohistochemistry, and mRNA expression quantitative polymerase chain reaction.

RESULTS

Histology and immunostaining showed markedly reduced collagen deposition, bile duct proliferation, and HSCs in the BDL+TZD group compared to those in the BDL group (p<0.001). Similarly, significantly lower mRNA expression of collagen α-1(I), matrix metalloproteinase-2, platelet-derived growth factor (PDGF)-B chain, and connective tissue growth factor (CTGF) were evident in the BDL+TZD group compared to those in the BDL group (p=0.0002, p<0.035, p<0.0001, and p=0.0123 respectively). Moreover, expression of the transforming growth factor beta1 (TGF-β1) was also downregulated in the BDL+TZD group (p=0.0087).

CONCLUSION

The PPAR-γ agonist inhibits HSC activation in vivo and attenuates liver fibrosis through several fibrogenic pathways. Potent fibrogenic factors such as PDGF, CTGF, and TGF-β1 were downregulated by the PPAR-γ agonist. Targeting PPAR-γ activity may be a potential strategy to control liver fibrosis.

TGF-β1 attenuates mitochondrial bioenergetics in pulmonary arterial endothelial cells via the disruption of carnitine homeostasis

Transforming growth factor beta-1 (TGF-β1) signaling is increased and mitochondrial function is decreased in multiple models of pulmonary hypertension (PH) including lambs with increased pulmonary blood flow (PBF) and pressure (Shunt). However, the potential link between TGF-β1 and the loss of mitochondrial function has not been investigated and was the focus of our investigations. Our data indicate that exposure of pulmonary arterial endothelial cells (PAEC) to TGF-β1 disrupted mitochondrial function as determined by enhanced mitochondrial ROS generation, decreased mitochondrial membrane potential, and disrupted mitochondrial bioenergetics. These events resulted in a decrease in cellular ATP levels, decreased hsp90/eNOS interactions and attenuated shear-mediated NO release. TGF-β1 induced mitochondrial dysfunction was linked to a nitration-mediated activation of Akt1 and the subsequent mitochondrial translocation of endothelial NO synthase (eNOS) resulting in the nitration of carnitine acetyl transferase (CrAT) and the disruption of carnitine homeostasis. The increase in Akt1 nitration correlated with increased NADPH oxidase activity associated with increased levels of p47^phox, p67^phox, and Rac1. The increase in NADPH oxidase was associated with a decrease in peroxisome proliferator-activated receptor type gamma (PPARγ) and the PPARγ antagonist, GW9662, was able to mimic the disruptive effect of TGF-β1 on mitochondrial bioenergetics. Together, our studies reveal for the first time, that TGF-β1 can disrupt mitochondrial function through the disruption of cellular carnitine homeostasis and suggest that stimulating carinitine homeostasis may be an avenue to treat pulmonary vascular disease.

TGF-β in fibrosis by acting as a conductor for contractile properties of myofibroblasts

Myofibroblasts are non-muscle contractile cells that play a key physiologically role in organs such as the stem villi of the human placenta during physiological pregnancy. They are able to contract and relax in response to changes in the volume of the intervillous chamber. Myofibroblasts have also been observed in several diseases and are involved in wound healing and the fibrotic processes affecting several organs, such as the liver, lungs, kidneys and heart. During the fibrotic process, tissue retraction rather than contraction is correlated with collagen synthesis in the extracellular matrix, leading to irreversible fibrosis and, finally, apoptosis of myofibroblasts. The molecular motor of myofibroblasts is the non-muscle type IIA and B myosin (NMMIIA and NMMIIB). Fibroblast differentiation into myofibroblasts is largely governed by the transforming growth factor-β1 (TGF-β1). This system controls the canonical WNT/β-catenin pathway in a positive manner, and PPARγ in a negative manner. The WNT/β-catenin pathway promotes fibrosis, while PPARγ prevents it. This review focuses on the contractile properties of myofibroblasts and the conductor, TGF-β1, which together control the opposing interplay between PPARγ and the canonical WNT/β-catenin pathway.

Rosiglitazone Suppresses Calcium Oxalate Crystal Binding and Oxalate-Induced Oxidative Stress in Renal Epithelial Cells by Promoting PPAR-γ Activation and Subsequent Regulation of TGF-β1 and HGF Expression

Peroxisome proliferator-activated receptor- (PPAR-) γ is a ligand-dependent transcription factor, and it has become evident that PPAR-γ agonists have renoprotective effects, but their influence and mechanism during the development of calcium oxalate (CaOx) nephrolithiasis remain unknown. Rosiglitazone (RSG) was used as a representative PPAR-γ agonist in our experiments. The expression of transforming growth factor-β1 (TGF-β1), hepatocyte growth factor (HGF), c-Met, p-Met, PPAR-γ, p-PPAR-γ (Ser112), Smad2, Smad3, pSmad2/3, and Smad7 was examined in oxalate-treated Madin-Darby canine kidney (MDCK) cells and a stone-forming rat model. A CCK-8 assay was used to evaluate the effects of RSG on cell viability. In addition, intracellular reactive oxygen species (ROS) levels were monitored, and lipid peroxidation in renal tissue was detected according to superoxide dismutase and malondialdehyde levels. Moreover, the location and extent of CaOx crystal deposition were evaluated by Pizzolato staining. Our results showed that, both in vitro and in vivo, oxalate impaired PPAR-γ expression and phosphorylation, and then accumulative ROS production was observed, accompanied by enhanced TGF-β1 and reduced HGF. These phenomena could be reversed by the addition of RSG. RSG also promoted cell viability and proliferation and decreased oxidative stress damage and CaOx crystal deposition. However, these protective effects of RSG were abrogated by the PPAR-γ-specific inhibitor GW9662. Our results revealed that the reduction of PPAR-γ activity played a critical role in oxalate-induced ROS damage and CaOx stone formation. RSG can regulate TGF-β1 and HGF/c-Met through PPAR-γ to exert antioxidant effects against hyperoxaluria and alleviate crystal deposition. Therefore, PPAR-γ agonists may be expected to be a novel therapy for nephrolithiasis, and this effect is related to PPAR-γ-dependent suppression of oxidative stress.

Molecular Understanding of the Cardiomodulation in Myocardial Infarction and the Mechanism of Vitamin E Protections

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Myocardial infarction is a major cause of deaths globally. Modulation of several molecular mechanisms occurs during the initial stages of myocardial ischemia prior to permanent cardiac tissue damage, which involves both pathogenic as well as survival pathways in the cardiomyocyte. Currently, there is increasing evidence regarding the cardioprotective role of vitamin E in alleviating the disease. This fat-soluble vitamin does not only act as a powerful antioxidant; but it also has the ability to regulate several intracellular signalling pathways including HIF-1, PPAR-γ, Nrf-2, and NF-κB that influence the expression of a number of genes and their protein products. Essentially, it inhibits the molecular progression of tissue damage and preserves myocardial tissue viability. This review aims to summarize the molecular understanding of the cardiomodulation in myocardial infarction as well as the mechanism of vitamin E protection.

Metabolic reprogramming in atherosclerosis: Opposed interplay between the canonical WNT/β-catenin pathway and PPARγ

Atherosclerosis, a chronic inflammatory and age-related disease, is a complex mechanism presenting a dysregulation of vessel structures. During this process, the canonical WNT/β-catenin pathway is increased whereas PPARγ is downregulated. The two systems act in an opposite manner. This paper reviews the opposing interplay of these systems and their metabolic-reprogramming pathway in atherosclerosis. Activation of the WNT/β-catenin pathway enhances the transcription of targets involved in inflammation, endothelial dysfunction, the proliferation of vascular smooth muscle cells, and vascular calcification. This complex mechanism, which is partly controlled by the WNT/β-catenin pathway, presents several metabolic dysfunctions. This phenomenon, called aerobic glycolysis (or the Warburg effect), consists of a shift in ATP production from mitochondrial oxidative phosphorylation to aerobic glycolysis, leading to the overproduction of intracellular lactate. This mechanism is partially due to the injury of mitochondrial respiration and an increase in the glycolytic pathway. In contrast, PPARγ agonists downregulate the WNT/β-catenin pathway. Therefore, the development of therapeutic targets, such as PPARγ agonists, for the treatment of atherosclerosis could be an interesting and innovative way of counteracting the canonical WNT pathway.

Bronchopulmonary Dysplasia: Crosstalk Between PPARγ, WNT/β-Catenin and TGF-β Pathways; The Potential Therapeutic Role of PPARγ Agonists

Bronchopulmonary dysplasia (BPD) is a serious pulmonary disease which occurs in preterm infants. Mortality remains high due to a lack of effective treatment, despite significant progress in neonatal resuscitation. In BPD, a persistently high level of canonical WNT/β-catenin pathway activity at the canalicular stage disturbs the pulmonary maturation at the saccular and alveolar stages. The excessive thickness of the alveolar wall impairs the normal diffusion of oxygen and carbon dioxide, leading to hypoxia. Transforming growth factor (TGF-β) up-regulates canonical WNT signaling and inhibits the peroxysome proliferator activated receptor gamma (PPARγ). This profile is observed in BPD, especially in animal models. Following a premature birth, hypoxia activates the canonical WNT/TGF-β axis at the expense of PPARγ. This gives rise to the differentiation of fibroblasts into myofibroblasts, which can lead to pulmonary fibrosis that impairs the respiratory function after birth, during childhood and even adulthood. Potential therapeutic treatment could target the inhibition of the canonical WNT/TGF-β pathway and the stimulation of PPARγ activity, in particular by the administration of nebulized PPARγ agonists.

Radiation-induced muscle fibrosis rat model: establishment and valuation

Background

Lack of animal model of radiation induced muscle fibrosis, this study aimed to establish such a model by using 90 Gy single dose irradiation to mimic clinical relevance and also to explore the potential post-irradiation regenerative mechanism.

Methods

SD rats were randomly divided into dose investigation groups and time gradient groups. Group1–6 were irradiated with a single dose of 65Gy, 70Gy, 75Gy, 80Gy, 85Gy and 90Gy respectively, and the degree of rectus femoris fibrosis in the irradiated area was detected at 4 weeks after irradiation. Group 7–9 were irradiated with a single dose of 90Gy, and the results were detected 1, 2, 4, and 8 weeks after irradiation. Then the general condition of rats was recorded. Masson staining was used to detect muscle fibrosis. The ultrastructure of muscles was observed by electron microscope, and the expression changes of satellite cell proliferation and differentiation related genes were detected by quantitative real-time-PCR.

Results

A single dose of 90Gy irradiation could cause muscle fibrosis in rats. As time goes on, the severity of muscle fibrosis and the expression of TGF- β1 increased. Significant swelling of mitochondria, myofilament disarrangement and dissolution, obvious endothelial cell swelling, increased vascular permeability, decrease of blood cell, deposition of fibrosis tissue around the vessel could be found compared with the control group. At around the 4th week, the expressions of Pax7, Myf5, MyoD, MyoG, Mrf4 increased.

Conclusion

Irradiation of 90Gy can successfully establish the rat model of radiation-induced muscle fibrosis. This model demonstrated that regenerative process was initiated by the irradiation only at an early stage, which can serve a suitable model for investigating regenerative therapy for post-radiation muscle fibrosis.

Thermodynamic Aspects and Reprogramming Cellular Energy Metabolism during the Fibrosis Process

Fibrosis is characterized by fibroblast proliferation and fibroblast differentiation into myofibroblasts, which generate a relaxation-free contraction mechanism associated with excessive collagen synthesis in the extracellular matrix, which promotes irreversible tissue retraction evolving towards fibrosis. From a thermodynamic point of view, the mechanisms leading to fibrosis are irreversible processes that can occur through changing the entropy production rate. The thermodynamic behaviors of metabolic enzymes involved in fibrosis are modified by the dysregulation of both transforming growth factor β (TGF-β) signaling and the canonical WNT/β-catenin pathway, leading to aerobic glycolysis, called the Warburg effect. Molecular signaling pathways leading to fibrosis are considered dissipative structures that exchange energy or matter with their environment far from the thermodynamic equilibrium. The myofibroblastic cells arise from exergonic processes by switching the core metabolism from oxidative phosphorylation to glycolysis, which generates energy and reprograms cellular energy metabolism to induce the process of myofibroblast differentiation. Circadian rhythms are far-from-equilibrium thermodynamic processes. They directly participate in regulating the TGF-β and WNT/β-catenin pathways involved in energetic dysregulation and enabling fibrosis. The present review focusses on the thermodynamic implications of the reprogramming of cellular energy metabolism, leading to fibroblast differentiation into myofibroblasts through the positive interplay between TGF-β and WNT/β-catenin pathways underlying in fibrosis.

Development and progression of immobilization-induced skin fibrosis through overexpression of transforming growth factor-ß1 and hypoxic conditions in a rat knee joint contracture model

PURPOSE

The purpose of this study was to investigate the pathology and mechanism of immobilization-induced skin fibrosis in a rat joint contracture model.

METHODS

Rats were randomly divided into control and immobilization groups. In the immobilization groups, knee joints of the rats were immobilized for 1, 2, and 4 weeks. After each immobilization, skin was dissected. To assess fibrosis in the skin, the thickness and area of adipocytes and connective tissue fibers were measured. Myofibroblasts were analyzed by immunohistochemistry by using anti-α-SMA as a marker. Gene expression levels of type I and III collagen, TGF-ß1, and HIF-1α were measured by using RT-PCR.

RESULTS

One week after immobilization, there was a marked increase in the area of connective tissue fibers in the immobilization group. Type I and type III collagen were significantly increased with prolonged immobilization. Higher numbers of α-SMA-positive cells were noted in the immobilized group at 2 and 4 weeks after immobilization. The expression level of TGF-β1 mRNA in the immobilization group increased after one week of immobilization. In contrast, the expression level of HIF1-α mRNA increased after 2 weeks of immobilization, and a greater increase was seen at 4 weeks after immobilization.

CONCLUSIONS

These results suggest that immobilization induces skin fibrosis with accumulation of types I and III collagen. These fibrotic changes may be evoked by upregulation of TGF-β1 after one week of immobilization. Additionally, upregulation of HIF-1α may relate to skin fibrosis by accelerating the differentiation of fibroblasts to myofibroblasts starting at 2 weeks after immobilization.

Interfacial Adipose Tissue in Systemic Sclerosis

Purpose of Review

This review provides a summary of recent insights into the role of the local white adipose tissue (WAT) in systemic sclerosis.

Recent Findings

Adipocytes located in an interfacial WAT area adjacent to fibrotic lesions have an intermediate phenotype and special properties implicated in fibrotic pathology in systemic sclerosis (SSc). The important role of these cells is recognized in different pathologies, such as wound healing, psoriasis, breast cancer, and prostate cancer. Additionally, both immature and mature adipocytes are involved in the appearance of fibroblast-like cells but exhibit different phenotypes and synthetic properties.

Summary

Adipocytes from interfacial WAT adjacent to the fibrotic area in SSc are phenotypically different from bulk adipocytes and are involved in pathogenesis of SSc. Immature and mature adipocytes from this WAT layer differentiate into various types of fibroblast-like cells, making the local ratio of immature to mature adipocytes in interfacial WAT of particular importance in SSc pathogenesis.

Impaired anti-inflammatory activity of PPARγ in the salivary epithelia of Sjögren's syndrome patients imposed by intrinsic NF-κB activation

Sjögren's syndrome (SS) patients manifest inflammation in the salivary glands (SG) and evidence of persistent intrinsic activation of ductal SG epithelial cells (SGEC), demonstrable in non-neoplastic SGEC lines derived from patients (SS-SGEC). The peroxisome-proliferator-activated receptor-γ (PPARγ) mediates important anti-inflammatory activities in epithelial cells. Herein, the comparative analysis of SG biopsies and SGEC lines obtained from SS patients and controls had revealed constitutively reduced PPARγ expression, transcriptional activity and anti-inflammatory function in the ductal epithelia of SS patients that were associated with cell-autonomously activated NF-κB and IL-1β pathways. Transcriptome profiling analysis revealed several differentially expressed proinflammatory and metabolism-related gene sets in SS-SGEC lines. These aberrations largely correlated with the severity of histopathologic lesions, the disease activity and the occurrence of adverse manifestations in SS patients studied, a fact which corroborates the key role of the persistently-activated epithelia in the pathogenesis of both local and systemic features of this disease. The treatment of control SGEC lines with PPARγ agonists was found to diminish the NF-κB activation and apoptosis induced by proinflammatory agents. In addition, the in-vitro application of PPARγ agonists and pharmacologic inhibitors of IL-1β and NF-κB had significant beneficial effects on SS-SGEC lines, such as the restoration of PPARγ functions and the reduction of their intrinsic activation, a fact which may advocate the future clinical study of the above agents as therapeutic modalities for SS.

Interactions between TGF-β1, canonical WNT/β-catenin pathway and PPAR γ in radiation-induced fibrosis

Radiation therapy induces DNA damage and inflammation leading to fibrosis. Fibrosis can occur 4 to 12 months after radiation therapy. This process worsens with time and years. Radiation-induced fibrosis is characterized by fibroblasts proliferation, myofibroblast differentiation, and synthesis of collagen, proteoglycans and extracellular matrix. Myofibroblasts are non-muscle cells that can contract and relax. Myofibroblasts evolve towards irreversible retraction during fibrosis process. In this review, we discussed the interplays between transforming growth factor-β1 (TGF-β1), canonical WNT/β-catenin pathway and peroxisome proliferator-activated receptor gamma (PPAR γ) in regulating the molecular mechanisms underlying the radiation-induced fibrosis, and the potential role of PPAR γ agonists. Overexpression of TGF-β and canonical WNT/β-catenin pathway stimulate fibroblasts accumulation and myofibroblast differentiation whereas PPAR γ expression decreases due to the opposite interplay of canonical WNT/β-catenin pathway. Both TGF-β1 and canonical WNT/β-catenin pathway stimulate each other through the Smad pathway and non-Smad pathways such as phosphatidylinositol 3-kinase/serine/threonine kinase (PI3K/Akt) signaling. WNT/β-catenin pathway and PPAR γ interact in an opposite manner. PPAR γ agonists decrease β-catenin levels through activation of inhibitors of the WNT pathway such as Smad7, glycogen synthase kinase-3 (GSK-3 β) and dickkopf-related protein 1 (DKK1). PPAR γ agonists also stimulate phosphatase and tensin homolog (PTEN) expression, which decreases both TGF-β1 and PI3K/Akt pathways. PPAR γ agonists by activating Smad7 decrease Smads pathway and then TGF-β signaling leading to decrease radiation-induced fibrosis. TGF-β1 and canonical WNT/β-catenin pathway promote radiation-induced fibrosis whereas PPAR γ agonists can prevent radiation-induced fibrosis.

Recent advances in the genetics of systemic sclerosis: toward biological and clinical significance

Significant advances have been made in understanding the genetic basis of systemic sclerosis (SSc) in recent years. Genomewide association and other large-scale genetic studies have identified 30 largely immunity-related genes which are significantly associated with SSc. We review these studies, along with genomewide expression studies, proteomic studies, genetic mouse models, and insights from rare sclerodermatous diseases. Collectively, these studies have begun to identify pathways that are relevant to SSc pathogenesis. The findings presented in this review illustrate how both genetic and genomic aberrations play important roles in the development of SSc. However, despite these recent discoveries, there remain major gaps between current knowledge of SSc, a unified understanding of pathogenesis, and effective treatment. To this aim, we address the important issue of SSc heterogeneity and discuss how future research needs to address this in order to develop a clearer understanding of this devastating and complex disease.

Matrix Remodeling Promotes Pulmonary Hypertension through Feedback Mechanoactivation of the YAP/TAZ-miR-130/301 Circuit

Pulmonary hypertension (PH) is a deadly vascular disease with enigmatic molecular origins. We found that vascular extracellular matrix (ECM) remodeling and stiffening are early and pervasive processes that promote PH. In multiple pulmonary vascular cell types, such ECM stiffening induced the microRNA-130/301 family via activation of the co-transcription factors YAP and TAZ. MicroRNA-130/301 controlled a PPAR?-APOE-LRP8 axis, promoting collagen deposition and LOX-dependent remodeling and further upregulating YAP/TAZ via a mechanoactive feedback loop. In turn, ECM remodeling controlled pulmonary vascular cell crosstalk via such mechanotransduction, modulation of secreted vasoactive effectors, and regulation of associated microRNA pathways. In vivo, pharmacologic inhibition of microRNA-130/301, APOE, or LOX activity ameliorated ECM remodeling and PH. Thus, ECM remodeling, as controlled by the YAP/TAZ-miR-130/301 feedback circuit, is an early PH trigger and offers combinatorial therapeutic targets for this devastating disease.

TGF-β/BMP proteins as therapeutic targets in renal fibrosis. Where have we arrived after 25 years of trials and tribulations?

The understanding of renal fibrosis in chronic kidney disease (CKD) remains as a challenge. More than 10% of the population of developed countries suffer from CKD. Proliferation and activation of myofibroblasts and accumulation of extracellular matrix proteins are the main features of kidney fibrosis, a process in which a large number of cytokines are involved. Targeting cytokines responsible for kidney fibrosis development might be an important strategy to face the problem of CKD. The increasing knowledge of the signaling pathway network of the transforming growth factor beta (TGF-β) superfamily members, such as the profibrotic cytokine TGF-β1 or the bone morphogenetic proteins (BMPs), and their involvement in the regulation of kidney fibrosis, has stimulated numerous research teams to look for potential strategies to inhibit profibrotic cytokines or to enhance the anti-fibrotic actions of other cytokines. The consequence of all these studies is a better understanding of all these canonical (Smad-mediated) and non-canonical signaling pathways. In addition, the different receptors involved for signaling of each cytokine, the different combinations of type I-type II receptors, and the presence and function of co-receptors that can influence the biological response have been also described. However, are these studies leading to suitable strategies to block the appearance and progression of kidney fibrosis? In this review, we offer a critical perspective analyzing the achievements using the most important strategies developed up till now: TGF-β antibodies, chemical inhibitors of TGF-β receptors, miRNAs and signaling pathways and BMP agonists with a potential role as therapeutic molecules against kidney fibrosis.

A candidate gene study reveals association between a variant of the Peroxisome Proliferator-Activated Receptor Gamma (PPAR-γ) gene and systemic sclerosis

Introduction

The multifunctional nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR-γ) has potent anti-fibrotic effects, and its expression and activity are impaired in patients with systemic sclerosis (SSc). We investigated PPAR-γ gene (PPARG) single nucleotide polymorphisms (SNPs) associated with SSc.

Methods

Tag SNPs spanning PPARG were genotyped in a European ancestry US discovery cohort comprising 152 SSc patients and 450 controls, with replication of our top signal in a European cohort (1031 SSc patients and 1014 controls from France). Clinical parameters and disease severity were analyzed to evaluate clinical associations with PPARG variants.

Results

In the discovery cohort, a single PPARG intronic SNP (rs10865710) was associated with SSc (p = 0.010; odds ratio = 1.52 per C allele, 95% confidence interval 1.10-2.08). This association was replicated in the French validation cohort (p = 0.052; odds ratio = 1.16 per C allele, 95% confidence interval 1.00-1.35). Meta-analysis of both cohorts indicated stronger evidence for association (p = 0.002; odds ratio = 1.22 per C allele, 95% confidence interval 1.07-1.40). The rs10865710 C allele was also associated with pulmonary arterial hypertension in the French SSc cohort (p = 0.002; odds ratio = 2.33 per C allele, 95% confidence interval 1.34-4.03).

Conclusions

A PPARG variant is associated with susceptibility to SSc, consistent with a role of PPAR-γ in the pathogenesis of SSc.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0641-2) contains supplementary material, which is available to authorized users.

The Role of PPAR Gamma in Systemic Sclerosis

Fibrosis is recognized as an important feature of many chronic diseases, such as systemic sclerosis (SSc), an autoimmune disease of unknown etiology, characterized by immune dysregulation and vascular injury, followed by progressive fibrosis affecting the skin and multiple internal organs. SSc has a poor prognosis because no therapy has been shown to reverse or arrest the progression of fibrosis, representing a major unmet medical need. Recently, antifibrotic effects of PPARγ ligands have been studied in vitro and in vivo and some theories have emerged leading to new insights. Aberrant PPARγ function seems to be implicated in pathological fibrosis in the skin and lungs. This antifibrotic effect is mainly related to the inhibition of TGF-β/Smad signal transduction but other pathways can be involved. This review focused on recent studies that identified PPARγ as an important novel pathway with critical roles in regulating connective tissue homeostasis, with emphasis on skin and lung fibrosis and its role on systemic sclerosis.

MicroRNA-130b regulates scleroderma fibrosis by targeting peroxisome proliferator-activated receptor γ

OBJECTIVES

To investigate the role of microRNA-130b (miR-130b) in systemic sclerosis (SSc) skin fibrosis and its regulatory effect on peroxisome proliferator-activated receptor γ (PPARγ).

METHODS

miR-130b was identified from microarray analyses in our previous studies. The expression of miR-130b, PPARγ, and fibrosis-related genes were determined by real-time PCR analysis. PPARγ protein levels were detected by immunohistochemistry and Western blot. Cells were transfected with microRNA mimics/inhibitor/scramble of miR-130b using Lipofectamine. Luciferase reporter gene assays were used to identify the direct target of miR-130b. Transforming growth factor β (TGF-β) was used for stimulation.

RESULTS

The expression of miR-130b was significantly upregulated and level of PPARγ was decreased in the dermis of the SSc skin biopsy samples and fibroblasts. Similar to human SSc, the same expression patterns of miR-130b, PPARγ, and fibrosis-related genes were observed in the bleomycin-induced skin fibrosis model; TGF-β induced the expression of miR-130b and fibrosis-related genes expression, but downregulated the expression of PPARγ. Overexpression of miR-130b in normal or SSc skin fibroblasts significantly decreased, and accordingly, knockdown of miR-130b increased the levels of PPARγ and fibrosis-related genes. In the reporter gene assay, cotransfection with miR-130b mimics significantly decreased the relative luciferase activity, which suggested a direct regulation of PPARγ by miR-130b.

CONCLUSIONS

These studies demonstrated that miR-130b played important profibrotic roles in SSc fibrosis, and enhanced TGF-β signaling through negative regulation of PPARγ expression. MiR-130b may be a potential therapeutic target in SSc fibrosis.

Effect of Persea americana (avocado) fruit extract on the level of expression of adiponectin and PPAR-γ in rats subjected to experimental hyperlipidemia and obesity

BACKGROUND

Persea americana, commonly known as avocado, is traditionally consumed fruit which possesses body fat lowering capacity. Adiponectin plays an important role in regulating obesity. In this study, the effect of hydro-alcoholic fruit extract of P. americana (HAEPA) on the level of blood lipids, glutathione, lipid peroxidation products, adiponectin and peroxisome proliferator activated receptor (PPAR)-γ expressions was investigated in rats fed a high-fat diet (HFD).

METHODS

Male Sprague Dawley rats were divided into four groups: groups 1 and 2 were fed normal rat chow (5% fat) and groups 3 and 4 were fed HFD (23% fat) for a period of 14 weeks. In addition, groups 2 and 4 rats were administered orally with 100 mg/kg body weight of HAEPA from third week. After 14 weeks, rats were sacrificed, and serum/plasma levels of total cholesterol, phospholipids, triglyceride, high-density lipoprotein (HDL), low-density lipoprotein (LDL) and adiponectin were determined. The mRNA expression of adiponectin, PPAR-γ and protein expression of PPAR-γ were also evaluated.

RESULTS

The body mass index (BMI), total fat pad mass and adiposity index were significantly decreased in HAEPA co-administered rats than in HFD-fed rats. The levels of LDL and lipid peroxides were significantly higher in HFD group than in HFD+HAEPA group. Levels of reduced glutathione, adiponectin, mRNA expression of adiponectin, PPAR-γ and protein expression of PPAR-γ were found to be increased in HFD+HAEPA group than in HFD group. The hypolipidemic effect of HAEPA is also evidenced by the histological observations in liver, heart and adipose tissue.

CONCLUSIONS

The results indicate that HAEPA exhibits hypolipidemic activity probably by increasing the mRNA expression of adiponectin and PPAR-γ, which reduce the risk of hyperlipidemia and obesity.

Protective effect of Satureja montana extract on cyclophosphamide-induced testicular injury in rats

The present study investigated the protective effect of Satureja montana extract against cyclophosphamide-induced testicular injury in rats. Total phenolic and flavonoid contents of the extract were 1.03% and 0.34%w/w of dry herb expressed as chlorogenic acid and quercetin, respectively. HPLC analysis identified caffeic, syringic and rosmarinic acids as the chief phenolic acids, and rutin as the major flavonoid in the extract. Oral daily administration of S.montana extract (50mg/kg/day) for 7days before and 7days after an intraperitoneal injection of cyclophosphamide (200mg/kg) restored the reduced relative testicular weight, serum testosterone level and testicular alkaline phosphatase activity, raised the lowered testicular sorbitol dehydrogenase and acid phosphatase activities, and decreased the elevated testicular hemoglobin absorbance. It also attenuated lipid peroxidation, restored the lowered glutathione content, glucose-6-phosphate dehydrogenase, glutathione peroxidase and glutathione reductase activities, and improved total antioxidant capacity. Moreover, S.montana extract mitigated testicular DNA fragmentation, decreased the elevated Fas and Bax gene expression, up-regulated the decreased Bcl-2 and peroxisome proliferator-activated receptor-gamma (PPAR-γ) gene expression and normalized Akt1 protein level. Histopathological investigation confirmed the protective effects of the extract. Conclusively, S.montana extract protects the rat testis against cyclophosphamide-induced damage via anti-oxidative and anti-apoptotic mechanisms that seem to be mediated, at least in part, by PPAR-γ and Akt1 up-regulation.

Bleomycin inhibits adipogenesis and accelerates fibrosis in the subcutaneous adipose layer through TGF-β1

Systemic sclerosis [scleroderma (SSc)]-associated skin fibrosis is characterized by increased fibrosis in the dermis and a reduction in the thickness of the subcutaneous adipose tissue layer. Although many studies have examined fibrosis in SSc, only a few studies have focused on the associated reduction in the thickness of the subcutaneous adipose tissue layer. In this study, we investigated the effects of SSc-induced fibrosis on adipose tissue. We found that bleomycin suppresses adipogenesis in adipose-derived stem cells (ASCs) and stimulates ASCs to express transforming growth factor β1 (TGF-β1), which suppresses adipogenesis and promotes fibrosis. Furthermore, we found that adipocyte-conditioned medium suppressed collagen synthesis by fibroblasts in fibrosis-like conditions. We concluded that in the skin affected by bleomycin-induced fibrosis, increased TGF-β1 expression suppresses adipogenesis and promotes adipocyte fibrosis. It was also suggested that adipocytes have an inhibitory effect on the progression of fibrosis.

Pulmonary hypertension and metabolic syndrome: Possible connection, PPARγ and Caveolin-1

A number of disparate diseases can lead to pulmonary hypertension (PH), a serious disorder with a high morbidity and mortality rate. Recent studies suggest that the associated metabolic dysregulation may be an important factor adversely impacting the prognosis of PH. Furthermore, metabolic syndrome is associated with vascular diseases including PH. Inflammation plays a significant role both in PH and metabolic syndrome. Adipose tissue modulates lipid and glucose metabolism, and also produces pro- and anti-inflammatory adipokines that modulate vascular function and angiogenesis, suggesting a close functional relationship between the adipose tissue and the vasculature. Both caveolin-1, a cell membrane scaffolding protein and peroxisome proliferator-activated receptor (PPAR) γ, a ligand-activated transcription factor are abundantly expressed in the endothelial cells and adipocytes. Both caveolin-1 and PPARγ modulate proliferative and anti-apoptotic pathways, cell migration, inflammation, vascular homeostasis, and participate in lipid transport, triacylglyceride synthesis and glucose metabolism. Caveolin-1 and PPARγ regulate the production of adipokines and in turn are modulated by them. This review article summarizes the roles and inter-relationships of caveolin-1, PPARγ and adipokines in PH and metabolic syndrome.

Fibroblasts in fibrosis: novel roles and mediators

Fibroblasts are the most common cell type of the connective tissues found throughout the body and the principal source of the extensive extracellular matrix (ECM) characteristic of these tissues. They are also the central mediators of the pathological fibrotic accumulation of ECM and the cellular proliferation and differentiation that occurs in response to prolonged tissue injury and chronic inflammation. The transformation of the fibroblast cell lineage involves classical developmental signaling programs and includes a surprisingly diverse range of precursor cell types—most notably, myofibroblasts that are the apex of the fibrotic phenotype. Myofibroblasts display exaggerated ECM production; constitutively secrete and are hypersensitive to chemical signals such as cytokines, chemokines, and growth factors; and are endowed with a contractile apparatus allowing them to manipulate the ECM fibers physically to close open wounds. In addition to ECM production, fibroblasts have multiple concomitant biological roles, such as in wound healing, inflammation, and angiogenesis, which are each interwoven with the process of fibrosis. We now recognize many common fibroblast-related features across various physiological and pathological protracted processes. Indeed, a new appreciation has emerged for the role of non-cancerous fibroblast interactions with tumors in cancer progression. Although the predominant current clinical treatments of fibrosis involve non-specific immunosuppressive and anti-proliferative drugs, a variety of potential therapies under investigation specifically target fibroblast biology.

A synthetic PPAR-γ agonist triterpenoid ameliorates experimental fibrosis: PPAR-γ-independent suppression of fibrotic responses

BACKGROUND

Persistent fibroblast activation initiated by transforming growth factor β (TGF-β) is a fundamental event in the pathogenesis of systemic sclerosis, and its pharmacological inhibition represents a potential therapeutic strategy. The nuclear receptor, peroxisome proliferator-activated receptor γ (PPAR-γ), exerts potent fibrotic activity. The synthetic oleanane triterpenoid, 2-cyano-3,12-dioxo-olean-1,9-dien-28-oic acid (CDDO), is a PPAR-γ agonist with potential effects on TGF-β signalling and dermal fibrosis.

OBJECTIVE

To examine the modulation of fibrogenesis by CDDO in explanted fibroblasts, skin organ cultures and murine models of scleroderma.

MATERIAL AND METHODS

The effects of CDDO on experimental fibrosis induced by bleomycin injection or by overexpression of constitutively active type I TGF-β receptor (TgfbR1ca) were evaluated. Modulation of fibrotic gene expression was examined in human skin organ cultures. To delineate the mechanisms underlying the antifibrotic effects of CDDO, explanted skin fibroblasts cultured in two-dimensional monolayers or in three-dimensional full-thickness human skin equivalents were studied.

RESULTS

CDDO significantly ameliorated dermal fibrosis in two complementary mouse models of scleroderma, as well as in human skin organ cultures and in three-dimensional human skin equivalents. In two-dimensional monolayer cultures of explanted normal fibroblasts, CDDO abrogated fibrogenic responses induced by TGF-β. These CDDO effects occurred via disruption of Smad-dependent transcription and were associated with inhibition of Akt activation. In scleroderma fibroblasts, CDDO attenuated the elevated synthesis of collagen. Remarkably, the in vitro antifibrotic effects of CDDO were independent of PPAR-γ.

CONCLUSIONS

The PPAR-γ agonist triterpenoid CDDO attenuates fibrogenesis by antagonistically targeting canonical TGF-β/Smad and Akt signalling in a PPAR-γ-independent manner. These findings identify this synthetic triterpenoid as a potential new therapy for the control of fibrosis.

Sonic advance: CCN1 regulates sonic hedgehog in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is the fifth leading cause of cancer internationally. As the precise molecular pathways that regulate pancreatic cancer are incompletely understood, appropriate targets for drug intervention remain elusive. It is being increasingly appreciated that the cellular microenvironment plays an important role in driving tumor growth and metastasis. CCN1, a member of the CCN family of secreted matricellular proteins, is overexpressed in pancreatic cancer, and may represent a novel target for therapy. Sonic hedgehog (SHh) is responsible for PDAC cell proliferation, epithelial-mesenchymal transition (EMT), maintenance of cancer stemness, migration, invasion, and metastatic growth; in a recent report, it was shown that CCN1 is a potent regulator of SHh expression via Notch-1. CCN1 activity was mediated, at least in part, through altering proteosome activity. These results suggest that CCN1 may be an ideal target for treating PDAC.