Peroxisome Proliferator-Activated Receptor-γ and Retinoic Acid X Receptor α Represses theTGFβ1Gene via PTEN-Mediated p70 Ribosomal S6 Kinase-1 Inhibition: Role for Zf9 Dephosphorylation

Modulation of Krüppel-like factors (KLFs) interaction with their binding partners in cancers through acetylation and phosphorylation

Post-translational modifications (PTMs) of transcription factors regulate transcriptional activity and play a key role in essentially all biological processes and generate indispensable insight towards biological function including activity state, subcellular localization, protein solubility, protein folding, substrate trafficking, and protein-protein interactions. Amino acids modified chemically via PTMs, function as molecular switches and affect the protein function and characterization and increase the proteome complexity. Krüppel-like transcription factors (KLFs) control essential cellular processes including proliferation, differentiation, migration, programmed cell death and various cancer-relevant processes. We investigated the interactions of KLF group-2 members with their binding partners to assess the role of acetylation and phosphorylation in KLFs on their binding affinity. It was observed that acetylation and phosphorylation at different positions in KLFs have a variable effect on binding with specific partners. KLF2-EP300, KLF4-SP1, KLF6-ATF3, KLF6-JUN, and KLF7-JUN show stabilization upon acetylation or phosphorylation at variable positions. On the other hand, KLF4-CBP, KLF4-EP300, KLF5-CBP, KLF5-WWP1, KLF6-SP1, and KLF7-ATF3 show stabilization or destabilization due to acetylation or phosphorylation at variable positions in KLFs. This provides a molecular explanation of the experimentally observed dual role of KLF group-2 members as a suppressor or activator of cancers in a PTM-dependent manner.

Effect of isorhamnetin on carbonic anhydrase IX expression and tumorigenesis of bladder cancer by activating PPARγ/PTEN/AKT pathway

BACKGROUND

To clarify the research prospect and mechanism analysis of isorhamnetin as a therapeutic drug for bladder cancer.

METHODS

Firstly, the effects of different concentrations of isorhamnetin on the expression of PPARγ/PTEN/Akt pathway protein, CA9, PPARγ, PTEN and AKT protein were discussed by western blot. The effects of isorhamnetin on the growth of bladder cells were also analyzed. Secondly, we verified whether the effect of isorhamnetin on CA9 was related to PPARγ/PTEN/Akt pathway by western blot, and the mechanism of isorhamnetin on the growth of bladder cells is related to this pathway by CCK8, cell cycle and ball formation experiment. Further, nude mouse model of subcutaneous tumor transplantation was constructed to analyze the effects of isorhamnetin, PPAR and PTEN on 5637 cell tumorigenesis and the effects of isorhamnetin on tumorigenesis and CA9 expression through PPARγ/PTEN/Akt pathway.

RESULTS

Isorhamnetin inhibited the development of bladder cancer, and regulated the expression of PPAR, PTEN, AKT, CA9. Isorhamnetin inhibits cell proliferation and the transition of cells from G0/G1 phase to S phase, and tumor sphere formation. Carbonic anhydrase IX is a potential downstream molecule of PPARγ/PTEN/AKT pathway. Overexpression of PPARγ and PTEN inhibited expression of CA9 in bladder cancer cells and tumor tissues. Isorhamnetin reduced CA9 expression in bladder cancer via PPARγ/PTEN/AKT pathway, thereby inhibiting bladder cancer tumorigenicity.

CONCLUSION

Isorhamnetin has the potential to become a therapeutic drug for bladder cancer, whose antitumor mechanism is related to PPARγ/PTEN/AKT pathway. Isorhamnetin reduced CA9 expression in bladder cancer via PPARγ/PTEN/AKT pathway, thereby inhibiting bladder cancer tumorigenicity.

Modulatory Effects of Estradiol and Its Mixtures with Ligands of GPER and PPAR on MAPK and PI3K/Akt Signaling Pathways and Tumorigenic Factors in Mouse Testis Explants and Mouse Tumor Leydig Cells

The present study was designed to evaluate how estradiol alone or in combination with G protein-coupled estrogen receptor (GPER) agonists and GPER and peroxisome proliferator-activated receptor (PPAR) antagonists alter the expression of tumor growth factor β (TGF-β), cyclooxygenase-2 (COX-2), hypoxia inducible factor 1-alpha (HIF-1α), and vascular endothelial growth factor (VEGF) in mouse testis explants and MA-10 mouse tumor Leydig cells. In order to define the hormone-associated signaling pathway, the expression of MAPK and PI3K/Akt was also examined. Tissue explants and cells were treated with estradiol as well as GPER agonist (ICI 182,780), GPER antagonist (G-15), PPARα antagonist (GW6471), and PPARγ antagonist (T00709072) in various combinations. First, we showed that in testis explants GPER and PPARα expressions were activated by the GPER agonist and estradiol (either alone or in mixtures), whereas PPARγ expression was activated only by GPER agonist. Second, increased TGF-β expression and decreased COX-2 expression were found in all experimental groups of testicular explants and MA-10 cells, except for up-regulated COX-2 expression in estradiol-treated cells, compared to respective controls. Third, estradiol treatment led to elevated expression of HIF-1α and VEGF, while their lower levels versus control were noted in the remaining groups of explants. Finally, we demonstrated the up-regulation of MAPK and PI3Kp85/Akt expressions in estradiol-treated groups of both ex vivo and in vitro models, whereas estradiol in mixtures with compounds of agonistic or antagonistic properties either up-regulated or down-regulated signaling kinase expression levels. Our results suggest that a balanced estrogen level and its action together with proper GPER and PPAR signaling play a key role in the maintenance of testis homeostasis. Moreover, changes in TGF-β and COX-2 expressions (that disrupted estrogen pathway) as well as disturbed GPER-PPAR signaling observed after estradiol treatment may be involved in testicular tumorigenesis.

Downregulation of lncRNA Miat contributes to the protective effect of electroacupuncture against myocardial fibrosis

Background

Myocardial fibrosis changes the structure of myocardium, leads to cardiac dysfunction and induces arrhythmia and cardiac ischemia, threatening patients’ lives. Electroacupuncture at PC6 (Neiguan) was previously found to inhibit myocardial fibrosis. Long non-coding RNAs (lncRNAs) play a variety of regulatory functions in myocardial fibrosis, but whether electroacupuncture can inhibit myocardial fibrosis by regulating lncRNA has rarely been reported.

Methods

In this study, we constructed myocardial fibrosis rat models using isoproterenol (ISO) and treated rats with electroacupuncture at PC6 point and non-point as control. Hematoxylin–eosin, Masson and Sirius Red staining were performed to assess the pathological changes and collagen deposition. The expression of fibrosis-related markers in rat myocardial tissue were detected by RT-qPCR and Western blot. Miat, an important long non-coding RNA, was selected to study the regulation of myocardial fibrosis by electroacupuncture at the transcriptional and post-transcriptional levels. In post-transcriptional level, we explored the myocardial fibrosis regulation effect of Miat on the sponge effect of miR-133a-3p. At the transcriptional level, we studied the formation of heterodimer PPARG–RXRA complex and promotion of the TGF-β1 transcription.

Results

Miat was overexpressed by ISO injection in rats. We found that Miat can play a dual regulatory role in myocardial fibrosis. Miat can sponge miR-133a-3p in an Ago2-dependent manner, reduce the binding of miR-133a-3p target to the 3ʹUTR region of CTGF mRNA and improve the protein expression level of CTGF. In addition, it can also directly bind with PPARG protein, inhibit the formation of heterodimer PPARG–RXRA complex and then promote the transcription of TGF-β1. Electroacupuncture at PC6 point, but not at non-points, can reduce the expression of Miat, thus inhibiting the expression of CTGF and TGF-β1 and inhibiting myocardial fibrosis.

Conclusion

We revealed that electroacupuncture at PC6 point can inhibit the process of myocardial fibrosis by reducing the expression of lncRNA Miat, which is a potential therapeutic method for myocardial fibrosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-022-00615-6.

A novel minimally invasive OFM technique with orthotopic transplantation of hUC-MSCs and in vivo monitoring of liver metabolic microenvironment in liver fibrosis treatment

Background

Mesenchymal stromal cells (MSCs) transplantation showed promising therapeutic results in liver fibrosis. However, efficient cell delivery method is urgently needed and the therapeutic mechanism remains unclear. This study focused on developing a minimally invasive open-flow microperfusion (OFM) technique, which combined orthotopic transplantation of human umbilical cord-derived (hUC)-MSCs to liver and in vivo monitoring of liver microenvironment in mice with CCl₄-induced liver fibrosis.

Methods

The therapeutic potential of OFM route was evaluated by comparing OFM with intravenous (IV) injection route in terms of hUC-MSCs engraftment at the fibrosis liver, liver histopathological features, liver function and fibrotic markers expression after hUC-MSCs administration. OFM was also applied to sample liver interstitial fluid in vivo, and subsequent metabolomic analysis was performed to investigate metabolic changes in liver microenvironment.

Results

Compared with IV route, OFM route caused more hUC-MSCs accumulation in the liver and was more effective in improving the remodeling of liver structure and reducing collagen deposition in fibrotic liver. OFM transplantation of hUC-MSCs reduced blood ALT, AST, ALP and TBIL levels and increased ALB levels, to a greater extent than IV route. And OFM route appeared to have a more pronounced effect on ameliorating the CCl₄-induced up-regulation of the fibrotic markers, such as α-SMA, collagen I and TGF-β. In vivo monitoring of liver microenvironment demonstrated the metabolic perturbations induced by pathological condition and treatment intervention. Two metabolites and eight metabolic pathways, which were most likely to be associated with the liver fibrosis progression, were regulated by hUC-MSCs administration.

Conclusion

The results demonstrated that the novel OFM technique would be useful for hUC-MSCs transplantation in liver fibrosis treatment and for monitoring of the liver metabolic microenvironment to explore the underlying therapeutic mechanisms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02599-w.

The Importance of Being PI3K in the RAS Signaling Network

Ras proteins are essential mediators of a multitude of cellular processes, and its deregulation is frequently associated with cancer appearance, progression, and metastasis. Ras-driven cancers are usually aggressive and difficult to treat. Although the recent Food and Drug Administration (FDA) approval of the first Ras G12C inhibitor is an important milestone, only a small percentage of patients will benefit from it. A better understanding of the context in which Ras operates in different tumor types and the outcomes mediated by each effector pathway may help to identify additional strategies and targets to treat Ras-driven tumors. Evidence emerging in recent years suggests that both oncogenic Ras signaling in tumor cells and non-oncogenic Ras signaling in stromal cells play an essential role in cancer. PI3K is one of the main Ras effectors, regulating important cellular processes such as cell viability or resistance to therapy or angiogenesis upon oncogenic Ras activation. In this review, we will summarize recent advances in the understanding of Ras-dependent activation of PI3K both in physiological conditions and cancer, with a focus on how this signaling pathway contributes to the formation of a tumor stroma that promotes tumor cell proliferation, migration, and spread.

Cyclopentenone Prostaglandins: Biologically Active Lipid Mediators Targeting Inflammation

Cyclopentenone prostaglandins (cyPGs) are biologically active lipid mediators, including PGA2, PGA1, PGJ2, and its metabolites. cyPGs are essential regulators of inflammation, cell proliferation, apoptosis, angiogenesis, cell migration, and stem cell activity. cyPGs biologically act on multiple cellular targets, including transcription factors and signal transduction pathways. cyPGs regulate the inflammatory response by interfering with NF-κB, AP-1, MAPK, and JAK/STAT signaling pathways via both a group of nuclear receptor peroxisome proliferator-activated receptor-gamma (PPAR-γ) dependent and PPAR-γ independent mechanisms. cyPGs promote the resolution of chronic inflammation associated with cancers and pathogen (bacterial, viral, and parasitic) infection. cyPGs exhibit potent effects on viral infections by repressing viral protein synthesis, altering viral protein glycosylation, inhibiting virus transmission, and reducing virus-induced inflammation. We summarize their anti-proliferative, pro-apoptotic, cytoprotective, antioxidant, anti-angiogenic, anti-inflammatory, pro-resolution, and anti-metastatic potential. These properties render them unique therapeutic value, especially in resolving inflammation and could be used in adjunct with other existing therapies. We also discuss other α, β -unsaturated carbonyl lipids and cyPGs like isoprostanes (IsoPs) compounds.

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.

Two Sides of the Same Coin: The Roles of KLF6 in Physiology and Pathophysiology

The Krüppel-like factors (KLFs) family of proteins control several key biological processes that include proliferation, differentiation, metabolism, apoptosis and inflammation. Dysregulation of KLF functions have been shown to disrupt cellular homeostasis and contribute to disease development. KLF6 is a relevant example; a range of functional and expression assays suggested that the dysregulation of KLF6 contributes to the onset of cancer, inflammation-associated diseases as well as cardiovascular diseases. KLF6 expression is either suppressed or elevated depending on the disease, and this is largely due to alternative splicing events producing KLF6 isoforms with specialised functions. Hence, the aim of this review is to discuss the known aspects of KLF6 biology that covers the gene and protein architecture, gene regulation, post-translational modifications and functions of KLF6 in health and diseases. We put special emphasis on the equivocal roles of its full-length and spliced variants. We also deliberate on the therapeutic strategies of KLF6 and its associated signalling pathways. Finally, we provide compelling basic and clinical questions to enhance the knowledge and research on elucidating the roles of KLF6 in physiological and pathophysiological processes.

KLF6 Acetylation Promotes Sublytic C5b-9-Induced Production of MCP-1 and RANTES in Experimental Mesangial Proliferative Glomerulonephritis

Rat Thy-1 nephritis (Thy-1N) is an experimental mesangial proliferative glomerulonephritis (MsPGN) for studying human MsPGN. Although sublytic C5b-9 complex formation on glomerular mesangial cells (GMCs) and renal MCP-1 and RANTES production in rats with Thy-1N have been proved, the role and mechanism of MCP-1 or RANTES synthesis in GMCs induced by sublytic C5b-9 are poorly elucidated. In this study, we first found the expression of transcription factor (KLF6), co-activator (KAT7) and chemokines (MCP-1 and RANTES) was all up-regulated both in renal tissue of Thy-1N rats (in vivo) and in sublytic C5b-9-induced GMCs (in vitro). Further in vitro experiments revealed that KLF6 bound to MCP-1 promoter (-297 to -123 nt) and RANTES promoter (-343 to -191 nt), leading to MCP-1 and RANTES gene transcription. Meanwhile, KAT7 also bound to the same region of MCP-1 and RANTES promoter in a KLF6-dependent manner, and KLF6 was acetylated by KAT7 at lysine residue 100, which finally promoted MCP-1 and RANTES expression. Moreover, our in vivo experiments discovered that knockdown of renal KAT7 or KLF6 gene obviously reduced MCP-1 and RANTES production, GMCs proliferation, ECM accumulation, and proteinuria secretion in Thy-1N rats. Collectively, our study indicates that sublytic C5b-9-induced MCP-1 and RANTES synthesis is associated with KAT7-mediated KLF6 acetylation and elevated KLF6 transcriptional activity, which might provide a new insight into the pathogenesis of rat Thy-1N and human MsPGN.

Rosiglitazone attenuates paraquat-induced lung fibrosis in rats in a PPAR gamma-dependent manner

Rosiglitazone, a PPAR-γ agonist, possesses anti-fibritic effect; however, its inhibitory effect on paraquat (PQ)-induced pulmonary fibrosis is not completely understood. Here, we investigated the inhibitory effect of rosiglitazone on PQ-induced acute pulmonary fibrosis in rats and its underlying mechanism. Male Sprague-Dawly rats were administered a single intraperitoneal injection of 30 mg/kg PQ and euthanised 7, 14, 21, and 28 days after PQ poisoning. PQ-induced pulmonary fibrosis was most obvious on day 28. Male Sprague-Dawly rats were exposed either against distilled water as control groups or PQ (30 mg/kg, i.p.) as test groups. The control groups were nominated as NC group (without treatment), RSG group (only treatment with rosiglitazone, 10 mg/kg/d), and GW group (only treatment with GW9662, a PPAR-γ antagonist, 1 mg/kg/d). The test groups were nominated as PQ group (PQ exposed without treatment), PQ + RSG group (treatment with rosiglitazone), and PQ + RSG + GW group (treatment with rosiglitazone and GW9662). Rosiglitazone was able to recover the PQ-induced decrease in arterial oxygen partial pressure (PaO₂), increase in the wet-to-dry (W/D) lung tissue weight ratio and lung fibrosis score. Rosiglitazone inhibited the PQ-induced reduction in protein and mRNA levels of PPAR-γ and PTEN and elevation in protein and mRNA levels of TGF-β1 and α-SMA. GW9662 administration antagonized the effect of rosiglitazone. These data suggest that rosiglitazone attenuated PQ-induced pulmonary fibrosis by upregulateing PTEN and downregulating TGF-β1 expression in a PPAR-γ dependent manner.

Bexarotent Attenuated Chronic Constriction Injury-Induced Spinal Neuroinflammation and Neuropathic Pain by Targeting Mitogen-Activated Protein Kinase Phosphatase-1

It is widely accepted that neuroinflammation in the spinal cord contributes to the development of central sensitization in neuropathic pain. Mitogen-activated protein kinase (MAPK) activation plays a vital role in the development of neuroinflammation in the spinal cord. In this study, we investigated the effect of bexarotene (bex), a retinoid X receptor agonist, on MAPKs activation in chronic constriction injury (CCI)-induced neuropathic pain. The data showed that daily treatment with bex 50 mg/kg significantly alleviated CCI-induced nociceptive hypersensitivity in rats. Bex 50 mg/kg/day inhibited CCI-induced MAPKs (p38MAPK, ERK1/2, and JNK) activation and upregulation of proinflammatory factors (IL-1β, tumor necrosis factor-α and IL-6). Bex also reversed CCI-induced microglia activation in the ipsilateral spinal cord. Furthermore, bex treatment significantly upregulated MKP-1 in the spinal cord. These effects were completely abrogated by MKP-1 inhibitor BCI. These results indicated that bex relieved CCI-induced neuroinflammation and neuropathic pain by targeting MKP-1. Therefore, bex might be a potential agent for the treatment of neuropathic pain. PERSPECTIVE: Bex could relieve neuropathic pain behaviors in animals by reversing MKP-1 downregulation and MAPKs activation in the spinal cord. Therapeutic applications of bex may be extended beyond cutaneous T-cell lymphoma.

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.

Tumor suppressor RARRES1- A novel regulator of fatty acid metabolism in epithelial cells

Retinoic acid receptor responder 1 (RARRES1) is silenced in many cancers and is differentially expressed in metabolism associated diseases, such as hepatic steatosis, hyperinsulinemia and obesity. Here we report a novel function of RARRES1 in metabolic reprogramming of epithelial cells. Using non-targeted LC-MS, we discovered that RARRES1 depletion in epithelial cells caused a global increase in lipid synthesis. RARRES1-depleted cells rewire glucose metabolism by switching from aerobic glycolysis to glucose-dependent de novo lipogenesis (DNL). Treatment with fatty acid synthase (FASN) inhibitor, C75, reversed the effects of RARRES1 depletion. The increased DNL in RARRES1-depleted normal breast and prostate epithelial cells proved advantageous to the cells during starvation, as the increase in fatty acid availability lead to more oxidized fatty acids (FAO), which were used for mitochondrial respiration. Expression of RARRES1 in several common solid tumors is also contextually correlated with expression of fatty acid metabolism genes and fatty acid-regulated transcription factors. Pathway enrichment analysis led us to determine that RARRES1 is regulated by peroxisome proliferating activated receptor (PPAR) signaling. These findings open up a new avenue for metabolic reprogramming and identify RARRES1 as a potential target for cancers and other diseases with impaired fatty acid metabolism.

Oral vitamin-A-coupled valsartan nanomedicine: High hepatic stellate cell receptors accessibility and prolonged enterohepatic residence

So far, liver fibrosis still has no clinically-approved treatment. The loss of stored vitamin-A (V_A) in hepatic stellate cells (HSCs), the main regulators to hepatic fibrosis, can be applied as a mechanism for their targeting. Valsartan is a good candidate for this approach; it is a marketed oral-therapy with inverse- and partial-agonistic activity to the over-expressed angiotensin-II type1 receptor (AT1R) and depleted nuclear peroxisome proliferator-activated receptor-gamma (PPAR-γ), respectively, in activated HSCs. However, efficacy on AT1R and PPAR-γ necessitates high drug permeability which is lacking in valsartan. In the current study, liposomes were used as nanocarriers for valsartan to improve its permeability and hence efficacy. They were coupled to V_A and characterized for HSCs-targeting. Tracing of orally-administered fluorescently-labeled V_A-coupled liposomes in normal rats and their fluorescence intensity quantification in different organs convincingly demonstrated their intestinal entrapment. On the other hands, their administration to rats with induced fibrosis revealed preferential hepatic, and less intestinal, accumulation which lasted up to six days. This indicated their uptake by intestinal stellate cells that acted as a depot for their release over time. Confocal microscopical examination of immunofluorescently-stained HSCs in liver sections, with considerable formula accumulation, confirmed HSCs-targeting and nuclear uptake. Consequently, V_A-coupled valsartan-loaded liposomes (VLC)-therapy resulted in profound re-expression of hepatic Mas-receptor and PPAR-γ, potent reduction of fibrogenic mediators' level and nearly normal liver function tests. Therefore, VLC epitomizes a promising antifibrotic therapy with exceptional extended action and additional PPAR-γ agonistic activity.

Immunity and Fibrogenesis: The Role of Th17/IL-17 Axis in HBV and HCV-induced Chronic Hepatitis and Progression to Cirrhosis

Cirrhosis is a common final pathway for most chronic liver diseases; representing an increasing burden worldwide and is associated with increased morbidity and mortality. Current evidence has shown that, after an initial injury, the immune response has a significant participation in the ongoing damage, and progression from chronic viral hepatitis (CVH) to cirrhosis, driving the activation and maintenance of main fibrogenic pathways. Among immune deregulations, those related to the subtype 17 of T helper lymphocytes (Th17)/interleukin-17 (IL-17) axis have been recognized as key immunopathological and prognostic elements in patients with CVH. The Th17/IL-17 axis has been found involved in several points of fibrogenesis chain from the activation of stellate cells, increased expression of profibrotic factors as TGF-β, promotion of the myofibroblastic or epithelial–mesenchymal transition, stimulation of the synthesis of collagen, and induction of imbalance between matrix metalloproteinases and tissue inhibitors of metalloproteinases (TIMPs). It also promotes the recruitment of inflammatory cells and increases the expression of proinflammatory cytokines such as IL-6 and IL-23. So, the Th17/IL-17 axis is simultaneously the fuel and the flame of a sustained proinflammatory and profibrotic environment. This work aims to present the immunopathologic and prognostic role of the Th17/IL-17 axis and related pathways in fibrogenesis and progression to cirrhosis in patients with liver disease due to hepatitis B virus (HBV) and hepatitis C virus (HCV).

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.

The proto-oncogenic protein TAL1 controls TGF-β1 signaling through interaction with SMAD3

TGF-β1 is involved in many aspects of tissue development and homeostasis including hematopoiesis. The TAL1 transcription factor is also an important player of this latter process and is expressed very early in the myeloid and erythroid lineages. We previously established a link between TGF-β1 signaling and TAL1 by showing that the cytokine was able to induce its proteolytic degradation by the ubiquitin proteasome pathway. In this manuscript we show that TAL1 interacts with SMAD3 that acts in the pathway downstream of TGF-β1 association with its receptor. TAL1 expression strengthens the positive or negative effect of SMAD3 on various genes. Both transcription factors activate the inhibitory SMAD7 factor through the E box motif present in its transcriptional promoter. DNA precipitation assays showed that TAL1 present in Jurkat or K562 cells binds to this SMAD binding element in a SMAD3 dependent manner. SMAD3 and TAL1 also inhibit several genes including ID1, hTERT and TGF-β1 itself. In this latter case TAL1 and SMAD3 can impair the positive effect exerted by E47. Our results indicate that TAL1 expression can modulate TGF-β1 signaling by interacting with SMAD3 and by increasing its transcriptional properties. They also suggest the existence of a negative feedback loop between TAL1 expression and TGF-β1 signaling.

Combined treatment with bexarotene and rosuvastatin reduces angiotensin-II-induced abdominal aortic aneurysm in apoE(-/-) mice and angiogenesis

BACKGROUND AND PURPOSE

Abdominal aortic aneurysm (AAA) is a degenerative vascular disease associated with angiogenesis. Bexarotene is a retinoid X receptor (RXR) ligand with anti-angiogenic activity. Statins also exert anti-angiogenic activity and activate PPARs. Because RXR ligands form permissive heterodimers with PPARs and a single anti-angiogenic drug may not be sufficient to combat the wide array of angiogenic factors produced during AAA, we evaluated the effect of combined low doses of bexarotene and rosuvastatin in a mouse model of AAA.

EXPERIMENTAL APPROACH

The effect of the combined treatment was investigated in a murine model of angiotensin II-induced AAA in apoE(-/-) mice. This combination therapy was also evaluated in in vivo (Matrigel plug assay) and in vitro (endothelial cell differentiation assay) models of angiogenesis as well as the underlying mechanisms involved.

KEY RESULTS

Co-treatment with bexarotene plus rosuvastatin reduced aneurysm formation, inflammation and neovascularization compared with each single treatment. In HUVEC, the combination of suboptimal concentrations of bexarotene and rosuvastatin inhibited angiotensin II-induced morphogenesis, proliferation and migration. These effects were accompanied by diminished production of pro-angiogenic chemokines (CXCL1, CCL2 or CCL5) and VEGF, and seemed to be mediated by RXRα/PPARα and RXRα/PPARγ activation. This combined therapy reduced the activation of members of the downstream PI3K pathway (Akt/mTOR and p70S6K1) in vivo and in vitro.

CONCLUSIONS AND IMPLICATIONS

The combination of RXR agonists with statins at low doses synergistically interferes with the signalling pathways that modulate inflammation and angiogenesis and may constitute a new and safer therapeutic treatment for the control of AAA.

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.

Emerging role of the peroxisome proliferator-activated receptor-gamma in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the major leading cause of cancer death worldwide. Hepatitis B virus, hepatitis C virus, alcohol consumption, non-alcoholic fatty liver disease, and diabetes are the major risks for developing HCC. Until now, recurrence and metastasis are the major cause of death in HCC patients. Therefore, identification of new effective molecular targets is an urgent need for treatment of HCC. Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated nuclear receptor which could be activated by PPARγ agonists such as thiazolidinediones, and natural PPARγ ligand (such as 15-deoxy-Δ12,14-prostaglandin J₂, 15d-PGJ₂). Increasing in vitro and in vivo evidence has demonstrated that PPARγ agonists exhibit an inhibitory role on tumor cell growth, migration, and invasion, suggesting that PPARγ activation may play an important role in the regulation of growth of HCC. It has been reported that PPARγ activation by thiazolidinediones or overexpression of PPARγ by virus-mediated gene transfer has shown growth inhibitory effects in hepatoma cells, but the expression level of PPARγ in HCC tissues still remains conflicting. Notably, a novel PPARγ agonist, honokiol, has recently been found to activate the PPARγ/RXR heterodimer, and has also exhibited significant anti-cancer effects in hepatoma cells. In the present review, we summarized studies on the role and the molecular regulation of PPARγ in HCC development in vitro and in vivo. PPARγ has the potential to be a therapeutic target for future treatment of HCC.

Aspirin treatment improved mesenchymal stem cell immunomodulatory properties via the 15d-PGJ2/PPARγ/TGF-β1 pathway

Bone marrow mesenchymal stem cells (BMMSCs) have been used to treat a variety of autoimmune diseases in clinics. However, the therapeutic effects are largely dependent on the immunomodulatory capacity of culture-expanded BMMSCs. In the present study, we show that aspirin (acetylsalicylic acid, ASA)-treated BMMSCs have significantly improved immunomodulatory function, as indicated by upregulation of regulatory T cells (Tregs) and downregulation of Th17 cells via the 15d-PGJ2/PPARγ/TGF-β1 pathway. Furthermore, the therapeutic effect of ASA-pretreated BMMSCs was confirmed in a dextran sodium sulfate-induced experimental colitis mouse model, in which systemic infusion of ASA-pretreated BMMSCs significantly ameliorated disease activity index and colonic inflammation, along with an increased number of Tregs and decreased number of Th17 cells. Taken together, our results suggest that aspirin treatment is a feasible strategy to promote BMMSC-based immunomodulation.

Peroxisome proliferator-activated receptor γ agonist efatutazone impairs transforming growth factor β2-induced motility of epidermal growth factor receptor tyrosine kinase inhibitor-resistant lung cancer cells

Epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKI) are effective for non-small cell lung cancers (NSCLC) with EGFR-activating mutations. However, most responders develop resistance. Efatutazone, a novel peroxisome proliferator-activated receptor gamma (PPARγ) agonist, is currently under clinical evaluation; it has antiproliferative effects and induces cellular morphological changes and differentiation. The present study investigated the effects of efatutazone in EGFR-TKI-resistant NSCLC cells, while focusing on cell motility. The PC-9-derived NSCLC cell lines PC-9ER and PC-9ZD, resistant to EGFR-TKI due to v-crk avian sarcoma virus CT10 oncogene homolog-like (CRKL) amplification-induced phosphatidylinositol 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homolog (AKT) activation and an EGFR T790M mutation, respectively, were used. These cells exhibit enhanced cell motility due to transforming growth factor β (TGF-β)/Smad2 family member 2 (Smad2) pathway activation. Efatutazone had no growth-inhibitory effect on the tested cells but inhibited the motility of EGFR-TKI-resistant cells in wound closure and transwell assays. Efatutazone plus erlotinib treatment provided greater inhibition of PC-9ER cell migration than efatutazone or erlotinib alone. Efatutazone suppressed increased TGF-β2 secretion from both cell lines (shown by ELISA) and downregulation of TGF-β2 transcription (observed by quantitative RT-PCR). Immunoblot analysis and luciferase assays revealed that efatutazone suppressed Smad2 phosphorylation and its transcriptional activity. These results suggest that efatutazone inhibits cell motility by antagonizing the TGF-β/Smad2 pathway and effectively prevents metastasis in NSCLC patients with acquired resistance to EGFR-TKI regardless of the resistance mechanism.

Everolimus is a potent inhibitor of activated hepatic stellate cell functions in vitro and in vivo, while demonstrating anti-angiogenic activities

The present study demonstrates the therapeutic potential of everolimus for the treatment of hepatocellular carcinomas in the fibrotic liver by inhibiting hepatic stellate cell activation and angiogenesis.

Beneficial effects of pioglitazone on atrial structural and electrical remodeling in vitro cellular models

It has been demonstrated that atrial remodeling contributes toward atrial fibrillation (AF) maintenance and angiotensin II (AngII) is involved in the pathogenesis of atrial remodeling. Peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists have been shown to inhibit atrial remodeling. However, the underlying mechanisms are poorly understood. In the present study we investigated the regulating effects of PPAR-γ agonist on AngII-induced atrial structural and electrical remodeling in vitro cellular models. The effects of pioglitazone on AngII-induced connective tissue growth factor (CTGF) expression and cell proliferation were assessed in primary-cultured mouse atrial fibroblasts. The influences of pioglitazone on AngII-induced L-type calcium channel (ICa-L) α1c expression and current density were evaluated in atrial myocytes (HL-1). Pioglitazone attenuated AngII-induced CTGF expression and proliferation in atrial fibroblasts, and pioglitazone also inhibited the expression or phosphorylation of AngII-induced transforming growth factor-β1 (TGF-β1), tumor necrosis factor receptor associated factor 6 (TRAF6), TGF-β-associated kinase 1 (TAK1) and Smad2/3. In HL-1 cells, pioglitazone suppressed AngII-induced ICa-L α1c expression and current density as well as CAMP responsive element binding protein (CREB) phosphorylation. Besides, pioglitazone inhibited AngII-induced production of AngII type I receptor (AT1R) and downregulation of PPAR-γ in both atrial fibroblasts and HL-1 cells. In conclusion, Pioglitazone suppresses AngII-induced CTGF expression and proliferation in atrial fibroblasts, which might be at least in part related with its inhibitory effects on TGF-β1/Smad2/3 and TGF-β1/TRAF6/TAK1 signaling pathways. Moreover, pioglitazone also attenuates AngII-induced ICa-L remodeling in HL-1 cells, which might be at least in part associated with its inhibitory effect on CREB phosphorylation. It is suggested that PPAR-γ agonist may have potential applications in preventing atrial remodeling.

Amplified inhibition of stellate cell activation pathways by PPAR-γ, RAR and RXR agonists

Peroxisome proliferator activator receptors (PPAR) ligands such as 15-Δ12,13-prostaglandin L(2) [PJ] and all trans retinoic acid (ATRA) have been shown to inhibit the development of liver fibrosis. The role of ligands of retinoic X receptor (RXR) and its ligand, 9-cis, is less clear. The purpose of this study was to investigate the effects of combined treatment of the three ligends, PJ, ATRA and 9-cis, on key events during liver fibrosis in rat primary hepatic stellate cells (HSCs). We found that the anti-proliferative effect of the combined treatment of PJ, ATRA and 9-cis on HSCs was additive. Further experiments revealed that this inhibition was due to cell cycle arrest at the G0/G1 phase as demonstrated by FACS analysis. In addition, the combined treatment reduced cyclin D1 expression and increased p21 and p27 protein levels. Furthermore, we found that the three ligands down regulated the phosphorylation of mTOR and p70(S6K). The activation of HSCs was also inhibited by the three ligands as shown by inhibition of vitamin A lipid droplets depletion from HSCs. Studies using real time PCR and western blot analysis showed marked inhibition of collagen Iα1 and αSMA by the combination of the three ligands. These findings suggest that the combined use of PJ, ATRA and 9-cis causes inhibition of cell proliferation by cell cycle arrest and down-regulation of fibrotic markers to a greater extent compared to each of the ligands alone.

Peroxisome proliferator-activated receptor gamma and regulations by the ubiquitin-proteasome system in pancreatic cancer

Pancreatic cancer is one of the most lethal forms of human cancer. Although progress in oncology has improved outcomes in many forms of cancer, little progress has been made in pancreatic carcinoma and the prognosis of this malignancy remains grim. Several molecular abnormalities often present in pancreatic cancer have been defined and include mutations in K-ras, p53, p16, and DPC4 genes. Nuclear receptor Peroxisome Proliferator-Activated Receptor gamma (PPARγ) has a role in many carcinomas and has been found to be overexpressed in pancreatic cancer. It plays generally a tumor suppressor role antagonizing proteins promoting carcinogenesis such as NF-κB and TGFβ. Regulation of pathways involved in pancreatic carcinogenesis is effectuated by the Ubiquitin Proteasome System (UPS). This paper will examine PPARγ in pancreatic cancer, the regulation of this nuclear receptor by the UPS, and their relationship to other pathways important in pancreatic carcinogenesis.

Nuclear hormone receptors enable macrophages and dendritic cells to sense their lipid environment and shape their immune response

A key issue in the immune system is to generate specific cell types, often with opposing activities. The mechanisms of differentiation and subtype specification of immune cells such as macrophages and dendritic cells are critical to understand the regulatory principles and logic of the immune system. In addition to cytokines and pathogens, it is increasingly appreciated that lipid signaling also has a key role in differentiation and subtype specification. In this review we explore how intracellular lipid signaling via a set of transcription factors regulates cellular differentiation, subtype specification, and immune as well as metabolic homeostasis. We introduce macrophages and dendritic cells and then we focus on a group of transcription factors, nuclear receptors, which regulate gene expression upon receiving lipid signals. The receptors we cover are the ones with a recognized physiological function in these cell types and ones which heterodimerize with the retinoid X receptor. These are as follows: the receptor for a metabolite of vitamin A, retinoic acid: retinoic acid receptor (RAR), the vitamin D receptor (VDR), the fatty acid receptor: peroxisome proliferator-activated receptor γ (PPARγ), the oxysterol receptor liver X receptor (LXR), and their obligate heterodimeric partner, the retinoid X receptor (RXR). We discuss how they can get activated and how ligand is generated and eliminated in these cell types. We also explore how activation of a particular target gene contributes to biological functions and how the regulation of individual target genes adds up to the coordination of gene networks. It appears that RXR heterodimeric nuclear receptors provide these cells with a coordinated and interrelated network of transcriptional regulators for interpreting the lipid milieu and the metabolic changes to bring about gene expression changes leading to subtype and functional specification. We also show that these networks are implicated in various immune diseases and are amenable to therapeutic exploitation.

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

The intractable process of fibrosis underlies the pathogenesis of systemic sclerosis (SSc) and other diseases, and in aggregate contributes to 45% of deaths worldwide. Because currently there is no effective anti-fibrotic therapy, a better understanding of the pathways and cellular differentiation programs underlying fibrosis are needed. Emerging evidence points to a fundamental role of the nuclear hormone receptor peroxisome proliferator activated receptor-γ (PPAR-γ) in modulating fibrogenesis. While PPAR-γ has long been known to be important in lipid metabolism and in glucose homeostasis, its role in regulating mesenchymal cell biology and its association with pathological fibrosis had not been appreciated until recently. This article highlights recent studies revealing a consistent association of fibrosis with aberrant PPAR-γ expression and activity in various forms of human fibrosis and in rodent models, and reviews studies linking genetic manipulation of the PPAR-γ pathway in rodents and fibrosis. We survey the broad range of anti-fibrotic activities associated with PPAR-γ and the underlying mechanisms. We also summarize the emerging data linking PPAR-γ dysfunction and pulmonary arterial hypertension (PAH), which together with fibrosis is responsible for the mortality in patients in SSc. Finally, we consider current and potential future strategies for targeting PPAR-γ activity or expression as a therapy for controlling fibrosis.

PPAR gamma, bioactive lipids, and cancer progression

In this article we review the evolution of cancer research involving PPARgamma, including mechanisms, target genes, and clinical applications. For the last thirteen years, the effects of PPARgamma activity on tumor biology have been studied intensely. Most of this research has focused upon the potential for employing agonists of this nuclear receptor in cancer treatment. As a monotherapy such agonists have shown little success in clinical trials, while they have shown promise as components of combination treatments both in culture and in animal models. Other investigations have explored a possible role for PPARgamma as a tumor suppressor, and as an inducer of differentiation of cancer stem cells. Whereas early studies have yielded variable conclusions regarding the prevalence of PPARgamma mutations in cancer, the protein level of this receptor has been more recently identified as a significant prognostic marker. We predict that indicators of PPARgamma activity may also serve as predictive markers for tailoring treatments.

A phase I pharmacokinetic study of bexarotene with paclitaxel and carboplatin in patients with advanced non-small cell lung cancer (NSCLC)

PURPOSE

Preclinical data suggest that the synthetic retinoid bexarotene may be an effective chemopreventive agent and that it may act synergistically in combination with platinum-based chemotherapy. The primary objective of this study was to determine whether repeated doses of bexarotene capsules affect pharmacokinetic parameters of paclitaxel or carboplatin in patients with advanced non-small cell lung cancer.

METHODS

Patients received treatment with paclitaxel (200 mg/m(2)) and carboplatin to provide a target AUC of 6 mg min/mL (day 1) every 3 weeks. Continuous oral bexarotene therapy (400 mg/m(2)/day) was initiated on Day 4, and patients started lipid-lowering therapy prior to beginning chemotherapy. Blood sampling to characterize the pharmacokinetic profiles of the chemotherapeutic agents with or without bexarotene was performed during cycle 1 (without concomitant bexarotene) and during cycle 2 (with concomitant bexarotene).

RESULTS

An analysis of drug concentration data from 16 patients indicated that bexarotene did not affect the pharmacokinetics of paclitaxel, free carboplatin, or total carboplatin concentrations. However, both maximal plasma concentrations and total exposure of bexarotene increased by 80% in the presence of paclitaxel-carboplatin by an, as of yet, unexplained mechanism. The toxicities observed resembled those of either the chemotherapy regimen or bexarotene alone, and there was no evidence for an enhancement of any drug-related toxicity with the combined treatment.

CONCLUSIONS

The administration of bexarotene, paclitaxel, and carboplatin is feasible and safe; however, the increased bexarotene plasma concentrations and exposure warrant further investigation if this combination is to be utilized clinically.

The Role of PPARs in Lung Fibrosis

Pulmonary fibrosis is a group of disorders characterized by accumulation of scar tissue in the lung interstitium, resulting in loss of alveolar function, destruction of normal lung architecture, and respiratory distress. Some types of fibrosis respond to corticosteroids, but for many there are no effective treatments. Prognosis varies but can be poor. For example, patients with idiopathic pulmonary fibrosis (IPF) have a median survival of only 2.9 years. Prognosis may be better in patients with some other types of pulmonary fibrosis, and there is variability in survival even among individuals with biopsy-proven IPF. Evidence is accumulating that the peroxisome proliferator-activated receptors (PPARs) play important roles in regulating processes related to fibrogenesis, including cellular differentiation, inflammation, and wound healing. PPARα agonists, including the hypolidipemic fibrate drugs, inhibit the production of collagen by hepatic stellate cells and inhibit liver, kidney, and cardiac fibrosis in animal models. In the mouse model of lung fibrosis induced by bleomycin, a PPARα agonist significantly inhibited the fibrotic response, while PPARα knockout mice developed more serious fibrosis. PPARβ/δ appears to play a critical role in regulating the transition from inflammation to wound healing. PPARβ/δ agonists inhibit lung fibroblast proliferation and enhance the antifibrotic properties of PPARγ agonists. PPARγ ligands oppose the profibrotic effect of TGF-β, which induces differentiation of fibroblasts to myofibroblasts, a critical effector cell in fibrosis. PPARγ ligands, including the thiazolidinedione class of antidiabetic drugs, effectively inhibit lung fibrosis in vitro and in animal models. The clinical availability of potent and selective PPARα and PPARγ agonists should facilitate rapid development of successful treatment strategies based on current and ongoing research.

A Novel Mechanism of PPARgamma Regulation of TGFbeta1: Implication in Cancer Biology

Peroxisome proliferator-activated receptor-γ (PPARγ) and retinoic acid X-receptor (RXR) heterodimer, which regulates cell growth and differentiation, represses the TGFβ1 gene that encodes for the protein involved in cancer biology. This review will introduce the novel mechanism associated with the inhibition of the TGFβ1 gene by PPARγ activation, which regulates the dephosphorylation of Zf9 transcription factor. Pharmacological manipulation of TGFβ1 by PPARγ activators can be applied for treating TGFβ1-induced pathophysiologic disorders such as cancer metastasis and fibrosis. In this article, we will discuss the opposing effects of TGFβ on tumor growth and metastasis, and address the signaling pathways regulated by PPARγ for tumor progression and suppression.

The Fox and the Rabbits-Environmental Variables and Population Genetics (1) Replication Problems in Association Studies and the Untapped Power of GWAS (2) Vitamin A Deficiency, Herpes Simplex Reactivation and Other Causes of Alzheimer's Disease

Classical population genetics shows that varying permutations of genes and risk factors permit or disallow the effects of causative agents, depending on circumstance. For example, genes and environment determine whether a fox kills black or white rabbits on snow or black ash covered islands. Risk promoting effects are different on each island, but obscured by meta-analysis or GWAS data from both islands, unless partitioned by different contributory factors. In Alzheimer's disease, the foxes appear to be herpes, borrelia or chlamydial infection, hypercholesterolemia, hyperhomocysteinaemia, diabetes, cerebral hypoperfusion, oestrogen depletion, or vitamin A deficiency, all of which promote beta-amyloid deposition in animal models—without the aid of gene variants. All relate to risk factors and subsets of susceptibility genes, which condition their effects. All are less prevalent in convents, where nuns appear less susceptible to the ravages of ageing. Antagonism of the antimicrobial properties of beta-amyloid by Abeta autoantibodies in the ageing population, likely generated by antibodies raised to beta-amyloid/pathogen protein homologues, may play a role in this scenario. These agents are treatable by diet and drugs, vitamin supplementation, pathogen detection and elimination, and autoantibody removal, although again, the beneficial effects of individual treatments may be tempered by genes and environment.

Biology of Krüppel-like factor 6 transcriptional regulator in cell life and death

An essential role for the Krüppel-like transcription factor family has been determined in the regulation of remarkable processes including cell proliferation, differentiation, signal transduction, oncogenesis, and cell death. A member of this group, Krüppel-like factor 6 (KLF6), identified on the basis of its ability to regulate a group of genes belonging to the carcinoembryonic antigen gene family, has been involved in human carcinogenesis. Early studies proposed a tumor suppressor function for KLF6 because of its ability to reduce cell proliferation through several biochemical mechanisms including regulation of cell cycle components, oncogene products, and apoptosis. Mutations within the klf6 gene, decreased expression and/or loss-of-heterozygosity were associated with the development of different human malignancies, and, hence, further supporting the tumor suppressor function of KLF6. This view has been challenged by other studies in distinct types of human cancers describing infrequent genetic alterations of klf6 gene or even enhanced expression in some tumors. The scenario about KLF6 function became still more complex as the description of oncogenic KLF6 splice variant 1 (SV1) with dominant negative activity against the wild type KLF6 (wtKLF6) protein. Additionally, increased evidence is suggesting that KLF6 is a bonafide target of several signaling cascades, which ultimate regulatory effect on this protein could drive decisions of cell life and death, facing the dilemma about how wtKLF6 could be involved in both processes. These apparently conflicting situations, emerged by apparently opposite effects mediated by wtKLF6, may be related, at least in part, to the biological cross-talk with the c-Jun oncoprotein. Depending on the stimulus received by the cell, wtKLF6 interaction with c-Jun determines different cell outcomes such as proliferation control or apoptosis. Thus, KLF6 responsiveness represents a kind of cell warning signal on receiving different stimuli, including oncogenic activation and microbial infections, orchestrating the implementation of proliferation and apoptotic programs.

Effect of the regulation of retinoid X receptor-α gene expression on rat hepatic fibrosis

AIM

  To study the effect of retinoid X receptor-α (RXR-α) expression on rat hepatic fibrosis.

METHODS

  Rat hepatic fibrosis was induced by CCl(4) , and the rats were randomly divided into an early-phase hepatic fibrosis group (2 weeks) and a sustained hepatic fibrosis group (8 weeks). They were then divided into four groups (normal control, hepatic fibrosis, negative control and RXR-α groups). A recombinant lentiviral expression vector carrying the rat RXR-α gene was injected into the rats to induce RXR-α expression by intraportal infusion, hepatic tissue pathological examination was performed, and hydroxyproline content was detected. Hepatic stellate cells (HSC) were cultured in vitro, an RXR-α lentivirus vector was used to activate HSC, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) activation was assayed to detect HSC proliferation.

RESULTS

  In vivo experiments indicated that in the sustained hepatic fibrosis group, there were significant differences in the hydroxyproline content, and expression of RXR-α, α-smooth muscle actin (α-SMA) and type I collagen (P < 0.01). However, in the early-phase hepatic fibrosis group, hydroxyproline content and the protein level of RXR-α showed no significant difference compared with the normal control group (P > 0.05). In vitro studies revealed that expression of RXR-α significantly inhibited expression of α-SMA and type I collagen in activated HSC (P < 0.01), as well as HSC proliferation (P < 0.01).

CONCLUSION

  The increased RXR-α gene expression inhibited HSC activation and proliferation and the degree of hepatic fibrosis.

Protective effects of baicalin on carbon tetrachloride induced liver injury by activating PPARγ and inhibiting TGFβ1

CONTEXT

Traditional Chinese herbal medicines have attracted considerable attention in many countries with treatment of several end-stage liver diseases.

OBJECTIVE

The present study investigated the protective effects of baicalin on hepatotoxicity and hepatic fibrosis and explored the role of transforming growth factor β1 (TGFβ1) and peroxisome proliferator activated receptors γ (PPARγ) on the rat liver injury model.

MATERIALS AND METHODS

The rat liver injury model was introduced by subcutaneous injection of carbon tetrachloride (CCl(4)) for 8 weeks. At week 5, rats were treated with baicalin of different doses or silymarin. Detection of biochemical indicators, histological analysis, and enzyme-linked immunosorbent assays were employed to evaluate severity of liver inflammation, and western blotting and RT-PCR assay were performed to evaluate TGFβ1 and PPARγ pathway related proteins and gene expression.

RESULTS

The administration of baicalin could significantly improve histological changes of CCl(4) treated rat livers and return biochemical indicators for liver injury to nearly baseline level. In addition, the increased expression of TGFβ1 was markedly suppressed by baicalin, and decreased expression of PPARγ was also dramatically elevated by baicalin as well. The hepatoprotective effects of baicalin may be conferred by elevating the level of PPARγ contributing to down-regulation of TGFβ1 signaling pathway and suppression of hepatic stellate cell activation.

CONCLUSIONS

The studies demonstrated that baicalin is a potent and promising antifibrotic drug in the treatment of hepatic fibrosis.

PPAR-gamma agonist ameliorates kidney and liver disease in an orthologous rat model of human autosomal recessive polycystic kidney disease

In autosomal recessive polycystic kidney disease (ARPKD), progressive enlargement of fluid-filled cysts is due to aberrant proliferation of tubule epithelial cells and transepithelial fluid secretion leading to extensive nephron loss and interstitial fibrosis. Congenital hepatic fibrosis associated with biliary cysts/dilatations is the most common extrarenal manifestation in ARPKD and can lead to massive liver enlargement. Peroxisome proliferator-activated receptor γ (PPAR-γ), a member of the ligand-dependent nuclear receptor superfamily, is expressed in a variety of tissues, including the kidneys and liver, and plays important roles in cell proliferation, fibrosis, and inflammation. In the current study, we determined that pioglitazone (PIO), a PPAR-γ agonist, decreases polycystic kidney and liver disease progression in the polycystic kidney rat, an orthologous model of human ARPKD. Daily treatment with 10 mg/kg PIO for 16 wk decreased kidney weight (% of body weight), renal cystic area, serum urea nitrogen, and the number of Ki67-, pERK1/2-, and pS6-positive cells in the kidney. There was also a decrease in liver weight (% of body weight), liver cystic area, fibrotic index, and the number of Ki67-, pERK1/2-, pERK5-, and TGF-β-positive cells in the liver. Taken together, these data suggest that PIO inhibits the progression of polycystic kidney and liver disease in a model of human ARPKD by inhibiting cell proliferation and fibrosis. These findings suggest that PPAR-γ agonists may have therapeutic value in the treatment of the renal and hepatic manifestations of ARPKD.

Induction of thymidine kinase 1 after 5-fluorouracil as a mechanism for 3'-deoxy-3'-[18F]fluorothymidine flare

Imaging the pharmacodynamics of anti-cancer drugs may allow early assessment of anti-cancer effects. Increases in 3'-deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) uptake early after thymidylate synthase inhibition (TS) inhibition, the so-called flare response, is considered to be largely due to an increase in binding sites for type-1 equilibrative nucleoside transporter. We investigated the induction of thymidine kinase 1 (TK1) after 5-fluorouracil (5-FU) treatment as one of mechanisms for [(18)F]FLT flare. Exposure of nine cancer cell lines to 5-FU for 24h induced a 2.5- to 3.5-fold increase in [(18)F]FLT uptake, significantly higher than the 1.5-fold increase observed 2h after treatment. The increase of [(18)F]FLT uptake 24h after 5-FU exposure accompanied TK1 induction in most cell lines. In representative cell lines (A431 and HT29), 5-FU time-dependently increased [(18)F]FLT uptake, kinase activity and the levels of protein and mRNA for TK1, sequential cyclin E and A induction, and G(1)-S phase transition. Cycloheximide treatment and knockdown of TK1 completely inhibited 5-FU-induced [(18)F]FLT flare. On the other hand, HCT8 cells showed a biphasic [(18)F]FLT flare with lacked TK1 induction in response to the dosage of 5-FU. Cycloheximide did not inhibit 5-FU-induced [(18)F]FLT flare in this cells. In vivo dynamic [(18)F]FLT-PET and ex vivo analysis in HT29 tumor-bearing mice showed significantly increased [(18)F]FLT flux and TK1 activity of tumor tissue 24h after 5-FU administration (P<0.05). Conclusively, 5-FU induced TK1 and TK1-mediated high [(18)F]FLT flare in most of cell lines. [(18)F]FLT-PET may be used to assess pharmacodynamics of TS inhibitor by a mechanism involving TK1 induction.

The combination of sirolimus and rosiglitazone produces a renoprotective effect on diabetic kidney disease in rats

AIMS

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists and mammalian target of rapamycin (mTOR) inhibitors share mechanisms concerning cell growth and reduction of extracellular matrix accumulation. The purpose of this study was to evaluate the potential synergistic effect of this combination on diabetic kidney disease in rats.

MAIN METHODS

Diabetes was induced by streptozotocin in 42 male Sprague-Dawley rats. Sixteen weeks after diabetes induction, animals were divided into four groups: diabetic animals without intervention (D), diabetic animals with administration of sirolimus (D+SRL), diabetic animals with administration of rosiglitazone (D+RGT), and diabetic animals with administration of sirolimus and rosiglitazone (D+SRL+RGT).

KEY FINDINGS

At a 30-day follow up, diabetic rats showed higher kidney weight, mean glomerular volume, mesangial expansion and albuminuria compared with non-diabetic rats. mTOR downstream proteins, p-T389-S6K and p-T37/46-4EBP1, were higher in diabetic than non-diabetic kidneys, whereas p-S473-AKT was not, suggesting that hyperglycemia mainly activated the mTORC1 pathway in vivo. Moreover, the catalytic subunit of protein phosphatase 2A (PP2Ac) was down-regulated in the diabetic kidney. Sirolimus inhibited the mTORC1 pathway, while the PPAR-gamma agonist rosiglitazone enhanced PP2Ac and reduced p70S6K. Both drugs were associated with a reduction in albuminuria, renal enlargement and mesangial expansion, but without any improvement in glycemic control. Sirolimus and rosiglitazone in combination down-regulated the mTORC1 pathway and over-activated PP2Ac in diabetic kidney. This effect may account for the synergistic reduction of renal hypertrophy, albuminuria and renal TGF-beta1 observed in diabetic rats treated with SRL+RGT.

SIGNIFICANCE

The combination of sirolimus and rosiglitazone is renoprotective with respect to diabetic nephropathy.

Peroxisome proliferator activated receptor-γ and the ubiquitin-proteasome system in colorectal cancer

Peroxisome proliferator activated receptor-γ (PPARγ), a transcription factor of the nuclear receptor superfamily plays a significant role in colorectal cancer pathogenesis. In most experimental systems PPARγ activation has tumor suppressing effects in the colon. PPARγ is regulated at multiple levels by the ubiquitin-proteasome system (UPS). At a first level, UPS regulates PPARγ transcription. This regulation involves both PPARγ transcription specific factors and the general transcription machinery. At a second level UPS regulates PPARγ and its co-factors themselves, as PPARγ and many co-factors are proteasome substrates. At a third level of regulation, transduction pathways working in parallel but also having interrelations with PPARγ are regulated by the UPS, creating a network of regulation in the colorectal carcinogenesis-related pathways that are under UPS control. Activation of PPARγ transcription by direct pharmacologic activators and by stabilization of its molecule by proteasome inhibitors could be strategies to be exploited in colorectal cancer treatment.

PPARgamma1 and LXRalpha face a new regulator of macrophage cholesterol homeostasis and inflammatory responsiveness, AEBP1

Peroxisome proliferator-activated receptor γ1 (PPARγ1) and liver X receptor α (LXRα) are nuclear receptors that play pivotal roles in macrophage cholesterol homeostasis and inflammation; key biological processes in atherogenesis. The activation of PPARγ1 and LXRα by natural or synthetic ligands results in the transactivation of ABCA1, ABCG1, and ApoE; integral players in cholesterol efflux and reverse cholesterol transport. In this review, we describe the structure, isoforms, expression pattern, and functional specificity of PPARs and LXRs. Control of PPARs and LXRs transcriptional activity by coactivators and corepressors is also highlighted. The specific roles that PPARγ1 and LXRα play in inducing macrophage cholesterol efflux mediators and antagonizing macrophage inflammatory responsiveness are summarized. Finally, this review focuses on the recently reported regulatory functions that adipocyte enhancer-binding protein 1 (AEBP1) exerts on PPARγ1 and LXRα transcriptional activity in the context of macrophage cholesterol homeostasis and inflammation.

Rosiglitazone abrogates bleomycin-induced scleroderma and blocks profibrotic responses through peroxisome proliferator-activated receptor-gamma

The nuclear hormone receptor, peroxisome proliferator-activated receptor (PPAR)-gamma, originally identified as a key mediator of adipogenesis, is expressed widely and implicated in diverse biological responses. Both natural and synthetic agonists of PPAR-gamma abrogated the stimulation of collagen synthesis and myofibroblast differentiation induced by transforming growth factor (TGF)-beta in vitro. To characterize the role of PPAR-gamma in the fibrotic process in vivo, the synthetic agonist rosiglitazone was used in a mouse model of scleroderma. Rosiglitazone attenuated bleomycin-induced skin inflammation and dermal fibrosis as well as subcutaneous lipoatrophy and counteracted the up-regulation of collagen gene expression and myofibroblast accumulation in the lesioned skin. Rosiglitazone treatment reduced the induction of the early-immediate transcription factor Egr-1 in situ without also blocking the activation of Smad2/3. In both explanted fibroblasts and skin organ cultures, rosiglitazone prevented the stimulation of collagen gene transcription and cell migration elicited by TGF-beta. Rosiglitazone-driven adipogenic differentiation of both fibroblasts and preadipocytes was abrogated in the presence of TGF-beta; this effect was accompanied by the concomitant down-regulation of cellular PPAR-gamma mRNA expression. Collectively, these results indicate that rosiglitazone treatment attenuates inflammation, dermal fibrosis, and subcutaneous lipoatrophy via PPAR-gamma in a mouse model of scleroderma and suggest that pharmacological PPAR-gamma ligands, widely used as insulin sensitizers in the treatment of type-2 diabetes mellitus, may be potential therapies for scleroderma.

PARP-1 suppresses adiponectin expression through poly(ADP-ribosyl)ation of PPAR gamma in cardiac fibroblasts

AIMS

Our aim was to explore the mechanism underlying the transcriptional regulation of adiponectin and its receptors (AdipoR) in cultured rat cardiac fibroblasts.

METHODS AND RESULTS

Using western blot and real-time RT-PCR assays, the expression of adiponectin and its receptors was determined. Using Southwestern blot and electrophoretic mobility shift assays, the DNA binding activity of peroxisome proliferator activated receptor gamma (PPAR gamma) was determined. The results showed that adiponectin and AdipoR1 were highly expressed in cultured rat cardiac fibroblasts. Inhibition of poly(ADP-ribose) polymerase 1 (PARP-1) by 3-aminobenzamide, PJ34, or PARP-1 siRNA markedly increased the transcription of adiponectin and AdipoR1 in cultured fibroblasts, mature 3T3 L1 adipocytes, rat myocardium, and white adipose tissue. PPAR gamma was poly(ADP-ribosyl)ated by PARP-1 in cardiac fibroblasts under basal conditions. Poly(ADP-ribosyl)ation of PPAR gamma prevented its binding to DNA. Inhibition of PARP-1 enhanced the DNA binding and transactivation of PPAR gamma and increased the transcription of PPAR gamma-target genes including CD36, lipoprotein lipase, and leptin in cultured fibroblasts.

CONCLUSION

PARP-1 inhibits adiponectin and AdipoR1 expression as well as PPAR gamma transactivation through poly(ADP-ribosyl)ation of PPAR gamma in cultured rat cardiac fibroblasts.

Constitutive Smad signaling and Smad-dependent collagen gene expression in mouse embryonic fibroblasts lacking peroxisome proliferator-activated receptor-gamma

Transforming growth factor-beta (TGF-beta), a potent inducer of collagen synthesis, is implicated in pathological fibrosis. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a nuclear hormone receptor that regulates adipogenesis and numerous other biological processes. Here, we demonstrate that collagen gene expression was markedly elevated in mouse embryonic fibroblasts (MEFs) lacking PPAR-gamma compared to heterozygous control MEFs. Treatment with the PPAR-gamma ligand 15d-PGJ(2) failed to down-regulate collagen gene expression in PPAR-gamma null MEFs, whereas reconstitution of these cells with ectopic PPAR-gamma resulted in their normalization. Compared to control MEFs, PPAR-gamma null MEFs displayed elevated levels of the Type I TGF-beta receptor (TbetaRI), and secreted more TGF-beta1 into the media. Furthermore, PPAR-gamma null MEFs showed constitutive phosphorylation of cellular Smad2 and Smad3, even in the absence of exogenous TGF-beta, which was abrogated by the ALK5 inhibitor SB431542. Constitutive Smad2/3 phosphorylation in PPAR-gamma null MEFs was associated with Smad3 binding to its cognate DNA recognition sequences, and interaction with coactivator p300 previously implicated in TGF-beta responses. Taken together, these results indicate that loss of PPAR-gamma in MEFs is associated with upregulation of collagen synthesis, and activation of intracellular Smad signal transduction, due, at least in part, to autocrine TGF-beta stimulation.

The many faces of PPARgamma: anti-inflammatory by any means?

The peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear receptor superfamily, a group of transcription factors that regulate expression of their target genes upon ligand binding. As endogenous ligands, oxidized fatty acids and prostanoids can bind to and activate the receptor. Natural and synthetic PPARgamma activators have been studied extensively in many inflammatory settings and in most instances they have been shown to be anti-inflammatory. In this review we give an overview of the different molecular mechanisms how PPARgamma and its agonists exert their anti-inflammatory effects both at the cellular level and the level of the organism. The action of PPARgamma in acute and chronic inflammatory diseases and disease models will be presented.