PPARδ Agonist GW501516 Suppresses the TGF-β-Induced Profibrotic Response of Human Bronchial Fibroblasts from Asthmatic Patients

The airway wall remodeling observed in asthma is associated with subepithelial fibrosis and enhanced activation of human bronchial fibroblasts (HBFs) in the fibroblast to myofibroblast transition (FMT), induced mainly by transforming growth factor-β (TGF-β). The relationships between asthma severity, obesity, and hyperlipidemia suggest the involvement of peroxisome proliferator-activated receptors (PPARs) in the remodeling of asthmatic bronchi. In this study, we investigated the effect of PPARδ ligands (GW501516 as an agonist, and GSK0660 as an antagonist) on the FMT potential of HBFs derived from asthmatic patients cultured in vitro. This report shows, for the first time, the inhibitory effect of a PPARδ agonist on the number of myofibroblasts and the expression of myofibroblast-related markers-α-smooth muscle actin, collagen 1, tenascin C, and connexin 43-in asthma-related TGF-β-treated HBF populations. We suggest that actin cytoskeleton reorganization and Smad2 transcriptional activity altered by GW501516 lead to the attenuation of the FMT in HBF populations derived from asthmatics. In conclusion, our data demonstrate that a PPARδ agonist stimulates antifibrotic effects in an in vitro model of bronchial subepithelial fibrosis. This suggests its potential role in the development of a possible novel therapeutic approach for the treatment of subepithelial fibrosis during asthma.

Hepatogenesis and hepatocarcinogenesis: Alignment of the main signaling pathways

Development is a symphony of cells differentiation in which different signaling pathways are orchestrated at specific times and periods to form mature and functional cells from undifferentiated cells. The similarity of the gene expression profile in malignant and undifferentiated cells is an interesting topic that has been proposed for many years and gave rise to the differentiation-therapy concept, which appears a rational insight and should be reconsidered. Hepatocellular carcinoma (HCC), as the sixth common cancer and the third leading cause of cancer death worldwide, is one of the health-threatening complications in communities where hepatotropic viruses are endemic. Sedentary lifestyle and high intake of calories are other risk factors. HCC is a complex condition in which various dimensions must be addressed, including heterogeneity of cells in the tumor mass, high invasiveness, and underlying diseases that limit the treatment options. Under these restrictions, recognizing, and targeting common signaling pathways during liver development and HCC could expedite to a rational therapeutic approach, reprograming malignant cells to well-differentiated ones in a functional state. Accordingly, in this review, we highlighted the commonalities of signaling pathways in hepatogenesis and hepatocarcinogenesis, and comprised an update on the current status of targeting these pathways in laboratory studies and clinical trials.

Mechanical and Thermodynamic Properties of Non-Muscle Contractile Tissues: The Myofibroblast and the Molecular Motor Non-Muscle Myosin Type IIA

Myofibroblasts are contractile cells found in multiple tissues. They are physiological cells as in the human placenta and can be obtained from bone marrow mesenchymal stem cells after differentiation by transforming growth factor-β (TGF-β). They are also found in the stroma of cancerous tissues and can be located in non-muscle contractile tissues. When stimulated by an electric current or after exposure to KCl, these tissues contract. They relax either by lowering the intracellular Ca2+ concentration (by means of isosorbide dinitrate or sildenafil) or by inhibiting actin-myosin interactions (by means of 2,3-butanedione monoxime or blebbistatin). Their shortening velocity and their developed tension are dramatically low compared to those of muscles. Like sarcomeric and smooth muscles, they obey Frank-Starling's law and exhibit the Hill hyperbolic tension-velocity relationship. The molecular motor of the myofibroblast is the non-muscle myosin type IIA (NMIIA). Its essential characteristic is the extreme slowness of its molecular kinetics. In contrast, NMIIA develops a unitary force similar to that of muscle myosins. From a thermodynamic point of view, non-muscle contractile tissues containing NMIIA operate extremely close to equilibrium in a linear stationary mode.

Necrotizing Enterocolitis: LPS/TLR4-Induced Crosstalk Between Canonical TGF-β/Wnt/β-Catenin Pathways and PPARγ

Necrotizing enterocolitis (NEC) represents one of the major causes of morbidity and mortality in premature infants. Several recent studies, however, have contributed to a better understanding of the pathophysiology of this dreadful disease. Numerous intracellular pathways play a key role in NEC, namely: bacterial lipopolysaccharide (LPS), LPS toll-like receptor 4 (TLR4), canonical Wnt/β-catenin signaling and PPARγ. In a large number of pathologies, canonical Wnt/β-catenin signaling and PPARγ operate in opposition to one another, so that when one of the two pathways is overexpressed the other is downregulated and vice-versa. In NEC, activation of TLR4 by LPS leads to downregulation of the canonical Wnt/β-catenin signaling and upregulation of PPARγ. This review aims to shed light on the complex intracellular mechanisms involved in this pathophysiological profile by examining additional pathways such as the GSK-3β, NF-κB, TGF-β/Smads, and PI3K-Akt pathways.

Statistical Mechanics of Non-Muscle Myosin IIA in Human Bone Marrow-Derived Mesenchymal Stromal Cells Seeded in a Collagen Scaffold: A Thermodynamic Near-Equilibrium Linear System Modified by the Tripeptide Arg-Gly-Asp (RGD)

Mesenchymal stromal cells (MSCs) were obtained from human bone marrow and amplified in cultures supplemented with human platelet lysate. Once semi-confluent, cells were seeded in solid collagen scaffolds that were rapidly colonized by the cells generating a 3D cell scaffold. Here, they acquired a myofibroblast phenotype and when exposed to appropriate chemical stimulus, developed tension and cell shortening, similar to those of striated and smooth muscle cells. Myofibroblasts contained a molecular motor-the non-muscle myosin type IIA (NMMIIA) whose crossbridge (CB) kinetics are dramatically slow compared with striated and smooth muscle myosins. Huxley's equations were used to determine the molecular mechanical properties of NMMIIA. Thank to the great number of NMMIIA molecules, we determined the statistical mechanics (SM) of MSCs, using the grand canonical ensemble which made it possible to calculate various thermodynamic entities such as the chemical affinity, statistical entropy, internal energy, thermodynamic flow, thermodynamic force, and entropy production rate. The linear relationship observed between the thermodynamic force and the thermodynamic flow allowed to establish that MSC-laden in collagen scaffolds were in a near-equilibrium stationary state (affinity ≪ RT), MSCs were also seeded in solid collagen scaffolds functionalized with the tripeptide Arg-Gly-Asp (RGD). This induced major changes in NMMIIA SM particularly by increasing the rate of entropy production. In conclusion, collagen scaffolds laden with MSCs can be viewed as a non-muscle contractile bioengineered tissue operating in a near-equilibrium linear regime, whose SM could be substantially modified by the RGD peptide.

Multiple Targets of the Canonical WNT/β-Catenin Signaling in Cancers

Canonical WNT/β-catenin signaling is involved in most of the mechanisms that lead to the formation and development of cancer cells. It plays a central role in three cyclic processes, which are the cell division cycle, the immune cycle, and circadian rhythms. When the canonical WNT pathway is upregulated as in cancers, the increase in β-catenin in the nucleus leads to activation of the expression of numerous genes, in particular CYCLIN D1 and cMYC, where the former influences the G1 phase of the cell division cycle, and the latter, the S phase. Every stage of the immune cycle is disrupted by the canonical WNT signaling. In numerous cancers, the dysfunction of the canonical WNT pathway is accompanied by alterations of the circadian genes (CLOCK, BMAL1, PER). Induction of these cyclic phenomena leads to the genesis of thermodynamic mechanisms that operate far from equilibrium, and that have been called “dissipative structures.” Moreover, upregulation of the canonical WNT/β-catenin signaling is important in the myofibroblasts of the cancer stroma. Their differentiation is controlled by the canonical WNT /TGF-β1 signaling. Myofibroblasts present ultraslow contractile properties due to the presence of the non-muscle myosin IIA. Myofibroblats also play a role in the inflammatory processes, often found in cancers and fibrosis processes. Finally, upregulated canonical WNT deviates mitochondrial oxidative phosphorylation toward the Warburg glycolysis metabolism, which is characteristic of cancers. Among all these cancer-generating mechanisms, the upregulated canonical WNT pathway would appear to offer the best hope as a therapeutic target, particularly in the field of immunotherapy.

Insights into myofibroblasts and their activation in scleroderma: opportunities for therapy?

PURPOSE OF REVIEW

The persistence of myofibroblasts is a key feature of fibrosis and in fibrotic diseases including scleroderma. This review evaluates the emerging concepts of the origins and cell populations that contribute to myofibroblasts and the molecular mechanisms that govern phenotypic conversion and that highlight opportunities for new interventional treatments in scleroderma.

RECENT FINDINGS

Studies have defined heterogeneity in fibroblast-like cells that can develop into myofibroblast in normal wound healing, scarring and fibrosis. Characterizing these distinct cell populations and their behaviour has been a key focus. In addition, the overarching impact of epigenetic regulation of genes associated with inflammatory responses, cell signalling and cell communication and the extracellular matrix (ECM) has provided important insights into the formation of myofibroblast and their function. Important new studies include investigations into the relationship between inflammation and myofibroblast production and further evidence has been gathered that reveal the importance of ECM microenvironment, biomechanical sensing and mechanotransduction.

SUMMARY

This review highlights our current understanding and outlines the increasing complexity of the biological processes that leads to the appearance of the myofibroblast in normal functions and in diseased tissues. We also focus on areas of special interest in particular, studies that have therapeutic potential in fibrosis and scleroderma.

Tripeptide Arg-Gly-Asp (RGD) modifies the molecular mechanical properties of the non-muscle myosin IIA in human bone marrow-derived myofibroblasts seeded in a collagen scaffold

Mesenchymal stem cells (MSCs) were obtained from human bone marrow and amplified in cultures supplemented with human platelet lysate in order to generate myofibroblasts. When MSCs were seeded in solid collagen scaffolds, they differentiated into myofibroblasts that were observed to strongly bind to the substrate, forming a 3D cell scaffold network that developed tension and shortening after KCl stimulation. Moreover, MSC-laden scaffolds recapitulated the Frank-Starling mechanism so that active tension increased in response to increases in the initial length of the contractile system. This constituted a bioengineering tissue that exhibited the contractile properties observed in both striated and smooth muscles. By using the A. F. Huxley formalism, we determined the myosin crossbridge (CB) kinetics of attachment (f1) and detachment (g1 and g2), maximum myosin ATPase activity, molar myosin concentration, unitary CB force and maximum CB efficiency. CB kinetics were dramatically slow, characterizing the non-muscle myosin type IIA (NMMIIA) present in myofibroblasts. When MSCs were seeded in solid collagen scaffolds functionalized with Arg-Gly-Asp (RGD), contractility increased and CB kinetics were modified, whereas the unitary NMMIIA-CB force and maximum CB efficiency did not change. In conclusion, we provided a non-muscle bioengineering tissue whose molecular mechanical characteristics of NMMIIA were very close to those of a non-muscle contractile tissue such as the human placenta.

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.

Interplay between the renin-angiotensin system, the canonical WNT/β-catenin pathway and PPARγ in hypertension

PURPOSE OF REVIEW

Heterogeneous causes can determinate hypertension.

RECENT FINDINGS

The renin-angiotensin system (RAS) has a major role in the pathophysiology of blood pressure. Angiotensin II and aldosterone are overexpressed during hypertension and lead to hypertension development and its cardiovascular complications. In several tissues, the overactivation of the canonical WNT/β-catenin pathway leads to inactivation of peroxisome proliferator-activated receptor gamma (PPARγ), while PPARγ stimulation induces a decrease of the canonical WNT/β-catenin pathway. In hypertension, the WNT/β-catenin pathway is upregulated, whereas PPARγ is decreased. The WNT/β-catenin pathway and RAS regulate positively each other during hypertension, whereas PPARγ agonists can decrease the expression of both the WNT/β-catenin pathway and RAS. We focus this review on the hypothesis of an opposite interplay between PPARγ and both the canonical WNT/β-catenin pathway and RAS in regulating the molecular mechanism underlying hypertension. The interactions between PPARγ and the canonical WNT/β-catenin pathway through the regulation of the renin-angiotensin system in hypertension may be an interesting way to better understand the actions and the effects of PPARγ agonists as antihypertensive drugs.

Opposite Interplay Between the Canonical WNT/β-Catenin Pathway and PPAR Gamma: A Potential Therapeutic Target in Gliomas

In gliomas, the canonical Wingless/Int (WNT)/β-catenin pathway is increased while peroxisome proliferator-activated receptor gamma (PPAR-γ) is downregulated. The two systems act in an opposite manner. This review focuses on the interplay between WNT/β-catenin signaling and PPAR-γ and their metabolic implications as potential therapeutic target in gliomas. Activation of the WNT/β-catenin pathway stimulates the transcription of genes involved in proliferation, invasion, nucleotide synthesis, tumor growth, and angiogenesis. Activation of PPAR-γ agonists inhibits various signaling pathways such as the JAK/STAT, WNT/β-catenin, and PI3K/Akt pathways, which reduces tumor growth, cell proliferation, cell invasiveness, and angiogenesis. Nonsteroidal anti-inflammatory drugs, curcumin, antipsychotic drugs, adiponectin, and sulforaphane downregulate the WNT/β-catenin pathway through the upregulation of PPAR-γ and thus appear to provide an interesting therapeutic approach for gliomas. Temozolomide (TMZ) is an antiangiogenic agent. The downstream action of this opposite interplay may explain the TMZ-resistance often reported in gliomas.

Demyelination in Multiple Sclerosis: Reprogramming Energy Metabolism and Potential PPARγ Agonist Treatment Approaches

Demyelination in multiple sclerosis (MS) cells is the site of several energy metabolic abnormalities driven by dysregulation between the opposed interplay of peroxisome proliferator-activated receptor γ (PPARγ) and WNT/β-catenin pathways. We focus our review on the opposing interactions observed in demyelinating processes in MS between the canonical WNT/β-catenin pathway and PPARγ and their reprogramming energy metabolism implications. Demyelination in MS is associated with chronic inflammation, which is itself associated with the release of cytokines by CD4⁺ Th17 cells, and downregulation of PPARγ expression leading to the upregulation of the WNT/β-catenin pathway. Upregulation of WNT/β-catenin signaling induces activation of glycolytic enzymes that modify their energy metabolic behavior. Then, in MS cells, a large portion of cytosolic pyruvate is converted into lactate. This phenomenon is called the Warburg effect, despite the availability of oxygen. The Warburg effect is the shift of an energy transfer production from mitochondrial oxidative phosphorylation to aerobic glycolysis. Lactate production is correlated with increased WNT/β-catenin signaling and demyelinating processes by inducing dysfunction of CD4⁺ T cells leading to axonal and neuronal damage. In MS, downregulation of PPARγ decreases insulin sensitivity and increases neuroinflammation. PPARγ agonists inhibit Th17 differentiation in CD4⁺ T cells and then diminish release of cytokines. In MS, abnormalities in the regulation of circadian rhythms stimulate the WNT pathway to initiate the demyelination process. Moreover, PPARγ contributes to the regulation of some key circadian genes. Thus, PPARγ agonists interfere with reprogramming energy metabolism by directly inhibiting the WNT/β-catenin pathway and circadian rhythms and could appear as promising treatments in MS due to these interactions.

Crosstalk Between Peroxisome Proliferator-Activated Receptor Gamma and the Canonical WNT/β-Catenin Pathway in Chronic Inflammation and Oxidative Stress During Carcinogenesis

Inflammation and oxidative stress are common and co-substantial pathological processes accompanying, promoting, and even initiating numerous cancers. The canonical WNT/β-catenin pathway and peroxisome proliferator-activated receptor gamma (PPARγ) generally work in opposition. If one of them is upregulated, the other one is downregulated and vice versa. WNT/β-catenin signaling is upregulated in inflammatory processes and oxidative stress and in many cancers, although there are some exceptions for cancers. The opposite is observed with PPARγ, which is generally downregulated during inflammation and oxidative stress and in many cancers. This helps to explain in part the opposite and unidirectional profile of the canonical WNT/β-catenin signaling and PPARγ in these three frequent and morbid processes that potentiate each other and create a vicious circle. Many intracellular pathways commonly involved downstream will help maintain and amplify inflammation, oxidative stress, and cancer. Thus, many WNT/β-catenin target genes such as c-Myc, cyclin D1, and HIF-1α are involved in the development of cancers. Nuclear factor-kappaB (NFκB) can activate many inflammatory factors such as TNF-α, TGF-β, interleukin-6 (IL-6), IL-8, MMP, vascular endothelial growth factor, COX2, Bcl2, and inducible nitric oxide synthase. These factors are often associated with cancerous processes and may even promote them. Reactive oxygen species (ROS), generated by cellular alterations, stimulate the production of inflammatory factors such as NFκB, signal transducer and activator transcription, activator protein-1, and HIF-α. NFκB inhibits glycogen synthase kinase-3β (GSK-3β) and therefore activates the canonical WNT pathway. ROS activates the phosphatidylinositol 3 kinase/protein kinase B (PI3K/Akt) signaling in many cancers. PI3K/Akt also inhibits GSK-3β. Many gene mutations of the canonical WNT/β-catenin pathway giving rise to cancers have been reported (CTNNB1, AXIN, APC). Conversely, a significant reduction in the expression of PPARγ has been observed in many cancers. Moreover, PPARγ agonists promote cell cycle arrest, cell differentiation, and apoptosis and reduce inflammation, angiogenesis, oxidative stress, cell proliferation, invasion, and cell migration. All these complex and opposing interactions between the canonical WNT/β-catenin pathway and PPARγ appear to be fairly common in inflammation, oxidative stress, and cancers.

Warburg effect hypothesis in autism Spectrum disorders

Autism spectrum disorder (ASD) is a neurodevelopmental disease which is characterized by a deficit in social interactions and communication with repetitive and restrictive behavior. In altered cells, metabolic enzymes are modified by the dysregulation of the canonical WNT/β-catenin pathway. In ASD, the canonical WNT/β-catenin pathway is upregulated. We focus this review on the hypothesis of Warburg effect stimulated by the overexpression of the canonical WNT/β-catenin pathway in ASD. Upregulation of WNT/β-catenin pathway induces aerobic glycolysis, named Warburg effect, through activation of glucose transporter (Glut), pyruvate kinase M2 (PKM2), pyruvate dehydrogenase kinase 1(PDK1), monocarboxylate lactate transporter 1 (MCT-1), lactate dehydrogenase kinase-A (LDH-A) and inactivation of pyruvate dehydrogenase complex (PDH). The aerobic glycolysis consists to a supply of a large part of glucose into lactate regardless of oxygen. Aerobic glycolysis is less efficient in terms of ATP production than oxidative phosphorylation because of the shunt of the TCA cycle. Dysregulation of energetic metabolism might promote cell deregulation and progression of ASD. Warburg effect regulation could be an attractive target for developing therapeutic interventions in ASD.

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.