PPARdelta is a type 1 IFN target gene and inhibits apoptosis in T cells

New Insights into the Role of PPARγ in Skin Physiopathology

Peroxisome proliferator-activated receptor gamma (PPARγ) is a transcription factor expressed in many tissues, including skin, where it is essential for maintaining skin barrier permeability, regulating cell proliferation/differentiation, and modulating antioxidant and inflammatory responses upon ligand binding. Therefore, PPARγ activation has important implications for skin homeostasis. Over the past 20 years, with increasing interest in the role of PPARs in skin physiopathology, considerable effort has been devoted to the development of PPARγ ligands as a therapeutic option for skin inflammatory disorders. In addition, PPARγ also regulates sebocyte differentiation and lipid production, making it a potential target for inflammatory sebaceous disorders such as acne. A large number of studies suggest that PPARγ also acts as a skin tumor suppressor in both melanoma and non-melanoma skin cancers, but its role in tumorigenesis remains controversial. In this review, we have summarized the current state of research into the role of PPARγ in skin health and disease and how this may provide a starting point for the development of more potent and selective PPARγ ligands with a low toxicity profile, thereby reducing unwanted side effects.

Peroxisome Proliferator-Activated Receptors and the Hallmarks of Cancer

Peroxisome proliferator-activated receptors (PPARs) function as nuclear transcription factors upon the binding of physiological or pharmacological ligands and heterodimerization with retinoic X receptors. Physiological ligands include fatty acids and fatty-acid-derived compounds with low specificity for the different PPAR subtypes (alpha, beta/delta, and gamma). For each of the PPAR subtypes, specific pharmacological agonists and antagonists, as well as pan-agonists, are available. In agreement with their natural ligands, PPARs are mainly focused on as targets for the treatment of metabolic syndrome and its associated complications. Nevertheless, many publications are available that implicate PPARs in malignancies. In several instances, they are controversial for very similar models. Thus, to better predict the potential use of PPAR modulators for personalized medicine in therapies against malignancies, it seems necessary and timely to review the three PPARs in relation to the didactic concept of cancer hallmark capabilities. We previously described the functions of PPAR beta/delta with respect to the cancer hallmarks and reviewed the implications of all PPARs in angiogenesis. Thus, the current review updates our knowledge on PPAR beta and the hallmarks of cancer and extends the concept to PPAR alpha and PPAR gamma.

Accelerated Barrier Repair in Human Skin Explants Induced with a Plant-Derived PPAR-α Activating Complex via Cooperative Interactions

Background

Peroxisome proliferator-activated receptors (PPARs) govern epidermal lipid synthesis and metabolism. In skin, PPAR activation has been shown to regulate genes responsible for permeability barrier homeostasis, epidermal differentiation, lipid biosynthesis, and inflammation.

Objective

Given the known dermatologic benefits of PPARs, we set out to discover a naturally derived, multi-molecule complex that would be superior to the more commonly formulated conjugated linoleic acids (CLAs). We hypothesized that a complex may be capable of modulating PPAR-α by cooperative or multi-ligand binding interactions to accelerate skin barrier repair.

Methods

To achieve this, we assembled a novel PPAR-α agonist complex, referred to as RFV3, from a combination of small molecules routinely used in Ayurvedic medicine and accepted in cosmetic and topical over-the-counter dermatologic products. We tested RFV3’s potential as a PPAR-α agonist by evaluating its transcriptional response, ligand binding affinity to PPAR-α, gene expression profiles and barrier repair properties in human skin explant models.

Results

We assembled RFV3 by solubilizing two standardized plant extracts in a suitable solvent and induced a significant transcriptional response in PPAR-α luciferase reporter assay. Furthermore, transcriptome profiling of RFV3-treated epidermal substitutes revealed expressed genes consistent with known targets of PPAR-α, including those involved in epidermal barrier repair. In addition, in silico modeling demonstrated differential co-binding affinities of RFV3 to PPAR-α compared with those of the endogenous ligands (CLAs) and a synthetic PPAR-α agonist. Lastly, delipidated skin explant models confirmed accelerated barrier repair activity with significant increases in ceramides, filaggrin and transglutaminase-1 after treatment.

Conclusion

These findings suggest that the RFV3 complex successfully mimics a PPAR-α agonist and induces synthesis of skin barrier lipids and proteins consistent with known PPAR pathways.

PPAR Beta/Delta and the Hallmarks of Cancer

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear hormone receptor family. Three different isoforms, PPAR alpha, PPAR beta/delta and PPAR gamma have been identified. They all form heterodimers with retinoic X receptors to activate or repress downstream target genes dependent on the presence/absence of ligands and coactivators or corepressors. PPARs differ in their tissue expression profile, ligands and specific agonists and antagonists. PPARs attract attention as potential therapeutic targets for a variety of diseases. PPAR alpha and gamma agonists are in clinical use for the treatment of dyslipidemias and diabetes. For both receptors, several clinical trials as potential therapeutic targets for cancer are ongoing. In contrast, PPAR beta/delta has been suggested as a therapeutic target for metabolic syndrome. However, potential risks in the settings of cancer are less clear. A variety of studies have investigated PPAR beta/delta expression or activation/inhibition in different cancer cell models in vitro, but the relevance for cancer growth in vivo is less well documented and controversial. In this review, we summarize critically the knowledge of PPAR beta/delta functions for the different hallmarks of cancer biological capabilities, which interplay to determine cancer growth.

Transcriptional Regulation of T-Cell Lipid Metabolism: Implications for Plasma Membrane Lipid Rafts and T-Cell Function

It is well established that cholesterol and glycosphingolipids are enriched in the plasma membrane (PM) and form signaling platforms called lipid rafts, essential for T-cell activation and function. Moreover, changes in PM lipid composition affect the biophysical properties of lipid rafts and have a role in defining functional T-cell phenotypes. Here, we review the role of transcriptional regulators of lipid metabolism including liver X receptors α/β, peroxisome proliferator-activated receptor γ, estrogen receptors α/β (ERα/β), and sterol regulatory element-binding proteins in T-cells. These receptors lie at the interface between lipid metabolism and immune cell function and are endogenously activated by lipids and/or hormones. Importantly, they regulate cellular cholesterol, fatty acid, glycosphingolipid, and phospholipid levels but are also known to modulate a broad spectrum of immune responses. The current evidence supporting a role for lipid metabolism pathways in controlling immune cell activation by influencing PM lipid raft composition in health and disease, and the potential for targeting lipid biosynthesis pathways to control unwanted T-cell activation in autoimmunity is reviewed.

PPAR-delta promotes survival of chronic lymphocytic leukemia cells in energetically unfavorable conditions

Targeting the mechanisms that allow chronic lymphocytic leukemia (CLL) cells to survive in harsh cancer microenvironments should improve patient outcomes. The nuclear receptor peroxisome proliferator activated receptor delta (PPARδ) sustains other cancers, and in silico analysis showed higher PPARD expression in CLL cells than normal lymphocytes and other hematologic cancers. A direct association was found between PPARδ protein levels in CLL cells and clinical score. Transgenic expression of PPARδ increased the growth and survival of CD5⁺ Daudi cells and primary CLL cells in stressful conditions including exhausted tissue culture media, low extracellular glucose, hypoxia and exposure to cytotoxic drugs. Glucocorticoids and synthetic PPARδ agonists up-regulated PPARD expression and also protected Daudi and primary CLL cells from metabolic stressors. Survival in low glucose was related to increased antioxidant expression, substrate utilization and mitochondrial performance, and was reversed by genetic deletion and synthetic PPARδ antagonists. These findings suggest PPARδ conditions CLL cells to survive in harsh microenvironmental conditions by reducing oxidative stress and increasing metabolic efficiency. Targeting PPARδ may be beneficial in the treatment of CLL.

A role for Peroxisome Proliferator-Activated Receptor Beta in T cell development

Metabolism plays an important role in T cell biology and changes in metabolism drive T cell differentiation and fate. Most research on the role of metabolism in T lymphocytes focuses on mature T cells while only few studies have investigated the role of metabolism in T cell development. In this study, we report that activation or overexpression of the transcription factor Peroxisome Proliferator-Activated Receptor β (PPARβ) increases fatty acid oxidation in T cells. Furthermore, using both in vivo and in vitro models, we demonstrate that PPARβ activation/overexpression inhibits thymic T cell development by decreasing proliferation of CD4⁻CD8⁻ double-negative stage 4 (DN4) thymocytes. These results support a model where PPARβ activation/overexpression favours fatty acid- instead of glucose-oxidation in developing T cells, thereby hampering the proliferative burst normally occurring at the DN4 stage of T cell development. As a consequence, the αβ T cells that are derived from DN4 thymocytes are dramatically decreased in peripheral lymphoid tissues, while the γδ T cell population remains untouched. This is the first report of a direct role for a member of the PPAR family of nuclear receptors in the development of T cells.

Identification of a novel PPARβ/δ/miR-21-3p axis in UV-induced skin inflammation

Although excessive exposure to UV is widely recognized as a major factor leading to skin perturbations and cancer, the complex mechanisms underlying inflammatory skin disorders resulting from UV exposure remain incompletely characterized. The nuclear hormone receptor PPARβ/δ is known to control mouse cutaneous repair and UV-induced skin cancer development. Here, we describe a novel PPARβ/δ-dependent molecular cascade involving TGFβ1 and miR-21-3p, which is activated in the epidermis in response to UV exposure. We establish that the passenger miRNA miR-21-3p, that we identify as a novel UV-induced miRNA in the epidermis, plays a pro-inflammatory function in keratinocytes and that its high level of expression in human skin is associated with psoriasis and squamous cell carcinomas. Finally, we provide evidence that inhibition of miR-21-3p reduces UV-induced cutaneous inflammation in ex vivo human skin biopsies, thereby underlining the clinical relevance of miRNA-based topical therapies for cutaneous disorders.

PPAR-delta promotes survival of breast cancer cells in harsh metabolic conditions

Expression of the nuclear receptor peroxisome proliferator activated receptor delta (PPARδ) in breast cancer cells is negatively associated with patient survival, but the underlying mechanisms are not clear. High PPARδ protein levels in rat breast adenocarcinomas were found to be associated with increased growth in soft agar and mice. Transgenic expression of PPARδ increased the ability of human breast cancer cell lines to migrate in vitro and form lung metastases in mice. PPARδ also conferred the ability to grow in exhausted tissue culture media and survive in low-glucose and other endoplasmic reticulum stress conditions such as hypoxia. Upregulation of PPARδ by glucocorticoids or synthetic agonists also protected human breast cancer cells from low glucose. Survival in low glucose was related to increased antioxidant defenses mediated in part by catalase and also to late AKT phosphorylation, which is associated with the prolonged glucose-deprivation response. Synthetic antagonists reversed the survival benefits conferred by PPARδ in vitro. These findings suggest that PPARδ conditions breast cancer cells to survive in harsh microenvironmental conditions by reducing oxidative stress and enhancing survival signaling responses. Drugs that target PPARδ may have a role in the treatment of breast cancer.

Reduced expression of peroxisome proliferator-activated receptor alpha in BAL and blood T cells of non-löfgren's sarcoidosis patients

BACKGROUND

Sarcoidosis is a granulomatous disease affecting in particular the lungs. The peroxisome proliferator-activated receptors (PPARs) play important regulatory roles in inflammation. The aim of this study was to gain more insight about the expression of all three PPARs (α, β/δ and γ) in sarcoidosis.

METHODS

Bronchoalveolar lavage (BAL) cells and peripheral blood cells were obtained from healthy controls (HC) and sarcoidosis patients with Löfgren's syndrome (LS) and without Löfgren's syndrome (non-LS). PPARs mRNA expression was analyzed in total BAL cells and in FACS (Fluorescence-activated cell sorting) sorted alveolar macrophages (AM) and CD4(+) T cells respectively by comparative RT-PCR. PPARs protein expression was analyzed in AM, and in BAL and blood CD4(+) and CD8(+) T cells by flow cytometry.

RESULTS

In BAL CD4(+) T cells, we noticed a significantly lower PPARα mRNA expression in sarcoidosis patients compared with HC. In non-LS patients, a significantly lower PPARα protein expression in BAL CD4(+) T cells was detected as compared with LS patients. In peripheral blood CD4(+) T cells, non-LS patients had a significantly lower expression of PPARα and PPARγ compared with LS patients.

CONCLUSION

The lower protein expression of PPARα and PPARγ could contribute to the persistent T-cell driven inflammation noted especially in non-resolving sarcoidosis, common in non-LS patients.

Physiological functions of peroxisome proliferator-activated receptor β

The peroxisome proliferator-activated receptors, PPARα, PPARβ, and PPARγ, are a family of transcription factors activated by a diversity of molecules including fatty acids and fatty acid metabolites. PPARs regulate the transcription of a large variety of genes implicated in metabolism, inflammation, proliferation, and differentiation in different cell types. These transcriptional regulations involve both direct transactivation and interaction with other transcriptional regulatory pathways. The functions of PPARα and PPARγ have been extensively documented mainly because these isoforms are activated by molecules clinically used as hypolipidemic and antidiabetic compounds. The physiological functions of PPARβ remained for a while less investigated, but the finding that specific synthetic agonists exert beneficial actions in obese subjects uplifted the studies aimed to elucidate the roles of this PPAR isoform. Intensive work based on pharmacological and genetic approaches and on the use of both in vitro and in vivo models has considerably improved our knowledge on the physiological roles of PPARβ in various cell types. This review will summarize the accumulated evidence for the implication of PPARβ in the regulation of development, metabolism, and inflammation in several tissues, including skeletal muscle, heart, skin, and intestine. Some of these findings indicate that pharmacological activation of PPARβ could be envisioned as a therapeutic option for the correction of metabolic disorders and a variety of inflammatory conditions. However, other experimental data suggesting that activation of PPARβ could result in serious adverse effects, such as carcinogenesis and psoriasis, raise concerns about the clinical use of potent PPARβ agonists.

Limited Applicability of GW9662 to Elucidate PPARγ-Mediated Fatty Acid Effects in Primary Human T-Helper Cells

Synthetic antagonists of the nuclear receptor PPARγ such as GW9662 are widely used to elucidate receptor-mediated ligand effects. In addition and complementary to recent work, we examined whether GW9662 is suitable to serve for mechanistic investigation in T-helper cells. Human peripheral blood mononuclear cells (PBMC) were preincubated with increasing concentrations of GW9662 (0, 0.4, 2, and 10 μmol/L) 30 min before adding the c9,t11-isomer of conjugated linoleic acid (c9,t11-CLA) as representative of PPARγ-activating fatty acids with immunomodulatory properties. Corresponding cultures were incubated with GW9662 in the absence of the fatty acid. After 19 h, cells were mitogen stimulated for further 5 h. Subsequently, intracellular IL-2 was measured in CD3⁺CD4⁺ lymphocytes by means of flow cytometry. 100 μmol/L c9,t11-CLA reduced the number of T-helper cells expressing IL-2 by 68%. GW9662 failed to abrogate this fatty acid effect, likely due to the fact that the compound exerted an own inhibitory effect on IL-2 production. Moreover, GW9662 dose-dependently induced cell death in human leukocytes. These results suggest that application of GW9662 is not conducive in this experimental setting.

Role of PPAR, LXR, and PXR in epidermal homeostasis and inflammation

Epidermal lipid synthesis and metabolism are regulated by nuclear hormone receptors (NHR) and in turn epidermal lipid metabolites can serve as ligands to NHR. NHR form a large superfamily of receptors modulating gene transcription through DNA binding. A subgroup of these receptors is ligand-activated and heterodimerizes with the retinoid X receptor including peroxisome proliferator-activated receptor (PPAR), liver X receptor (LXR) and pregnane X receptor (PXR). Several isotypes of these receptors exist, all of which are expressed in skin. In keratinocytes, ligand activation of PPARs and LXRs stimulates differentiation, induces lipid accumulation, and accelerates epidermal barrier regeneration. In the cutaneous immune system, ligand activation of all three receptors, PPAR, LXR, and PXR, has inhibitory properties, partially mediated by downregulation of the NF-kappaB pathway. PXR also has antifibrotic effects in the skin correlating with TGF-beta inhibition. In summary, ligands of PPAR, LXR and PXR exert beneficial therapeutic effects in skin disease and represent promising targets for future therapeutic approaches in dermatology. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

A cutting edge overview: psoriatic disease

Psoriasis is a lifelong skin disease, affecting about 2% of the global population. Generalized involvement of the body (erythroderma), extensive pustular lesions, and an associated arthritis known as psoriatic arthritis (PsA) are severe complications of psoriasis. Genetic, immunologic, and environmental factors contribute to its pathogenesis. A complete understanding of the pathogenesis of psoriasis and psoriatic arthritis is lacking. Cytokines, chemokines, adhesion molecules, growth factors like NGF, neuropeptides, and T cell receptors all act in an integrated way to evolve into unique inflammatory and proliferative processes typical of psoriasis and PsA. Management of psoriasis requires exemplary skin care along with careful monitoring of arrays of comorbidities which includes arthritis and coronary artery disease. In many ways, psoriasis can be considered a model autoimmune disease. This statement itself is ironic considering that it was not recognized as immune mediated until relatively recently. Fortunately, the immunobiology has made enormous strides and there are now excellent therapeutic options for patients. In this thematic review, we have attempted to provide summaries of not only basic science and clinical research, but also an overview of future research directions.

Peroxisome proliferator-activated receptor delta and cardiovascular disease

Recent reports have shown that peroxisome proliferator-activated receptor delta (PPARD) plays an important role in different vascular processes suggesting that PPARD is a significant modulator of cardiovascular disease. This review will focus on PPARD in relation to cardiovascular risk factors based on cell, animal and human data. Mouse studies suggest that Ppard is an important metabolic modulator that may have implications for cardiovascular disease (CVD). Specific human PPARD gene variants show no clear association with CVD but interactions between variants and lifestyle factors might influence disease risk. During recent years, development of specific and potent PPARD agonists has also made it possible to study the effects of PPARD activation in humans. PPARD agonists seem to exert beneficial effects on dyslipidemia and insulin-resistant syndromes but safety issues have been raised due to the role that PPARD plays in cell proliferation. Thus, large long term outcome as well as detailed safety and tolerability studies are needed to evaluate whether PPARD agonists could be used to treat CVD in humans.

A peroxisome proliferator-activated receptor-δ agonist provides neuroprotection in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinson's disease

Peroxisome proliferator-activated receptor (PPAR)-γ and PPARα have shown neuroprotective effects in models of Parkinson's disease (PD). The role of the third, more ubiquitous isoform PPARδ has not been fully explored. This study investigated the role of PPARδ in PD using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to model the dopaminergic neurodegeneration of PD. In vitro administration of the PPARδ antagonist GSK0660 (1 μM) increased the detrimental effect of 1-methyl-4-phenylpyridinium iodide (MPP⁺) on cell viability, which was reversed by co-treatment with agonist GW0742 (1 μM). GW0742 alone did not affect MPP⁺ toxicity. PPARδ was expressed in the nucleus of dopaminergic neurons and in astrocytes. Striatal PPARδ levels were increased (over two-fold) immediately after MPTP treatment (30 mg/kg for 5 consecutive days) compared to saline-treated mice. PPARδ heterozygous mice were not protected against MPTP toxicity. Intra-striatal infusion of GW0742 (84 μg/day) reduced the MPTP-induced loss of dopaminergic neurons (5036±195) when compared to vehicle-infused mice (3953±460). These results indicate that agonism of PPARδ provides protection against MPTP toxicity, in agreement with the effects of other PPAR agonists.

Nonsteroidal anti-inflammatory drugs induce apoptosis in cutaneous T-cell lymphoma cells and enhance their sensitivity for TNF-related apoptosis-inducing ligand

Cutaneous T-cell lymphomas (CTCL) form a heterogeneous group of non-Hodgkin's lymphomas of the skin. In previous studies, we had characterized CTCL cells as resistant to the death ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which correlated to pronounced expression of the caspase-8/-10 inhibitor c-FLIP. For identification of proapoptotic strategies in CTCL cells and for overcoming their death ligand resistance, we investigated the effects of nonsteroidal anti-inflammatory drugs (NSAIDs) such as acetylsalicylic acid, sodium salicylate, and diclofenac (DF). These drugs strongly enhanced apoptosis, as well as decreased CTCL cell proliferation and vitality, and DF furthermore sensitized for TRAIL-induced apoptosis. Full activation of the caspase cascade (caspase-3, -8, -9) and decreased mitochondrial membrane potential were characteristic for NSAID treatment, whereas cytochrome c release was seen only for DF. Downregulation of Mcl-1 and enhanced surface expression of TRAIL were seen in response to NSAIDs. Most characteristic for apoptosis induction was the downregulation of c-FLIP. In agreement with the critical role of c-FLIP for apoptosis deficiency of CTCL cells, its overexpression decreased NSAID-mediated apoptosis and its downregulation by small hairpin RNA-enhanced apoptosis. The study provides a rationale for the use of NSAIDs as a new therapeutic option for CTCL patients. Supporting this concept, ex vivo lymphoma cells of CTCL patients also revealed significant sensitivity for NSAID treatment.

Research resource: Comparative nuclear receptor atlas: basal and activated peritoneal B-1 and B-2 cells

Naïve murine B cells are typically divided into three subsets based on functional and phenotypic characteristics: innate-like B-1 and marginal zone B cells vs. adaptive B-2 cells, also known as follicular or conventional B cells. B-1 cells, the innate-immune-like component of the B cell lineage are the primary source of natural antibodies and have been shown to modulate autoimmune diseases, human B-cell leukemias, and inflammatory disorders such as atherosclerosis. On the other hand, B-2 cells are the principal mediators of the adaptive humoral immune response and represent an important pharmacological target for various conditions including rheumatoid arthritis, lupus erythematosus, and lymphomas. Using the resources of the Nuclear Receptor Signaling Atlas program, we used quantitative real-time PCR to assess the complement of the 49 murine nuclear receptor superfamily expressed in quiescent and toll-like receptor (TLR)-stimulated peritoneal B-1 and B-2 cells. We report the expression of 24 nuclear receptors in basal B-1 cells and 25 nuclear receptors in basal B-2 cells, with, in some cases, dramatic changes in response to TLR 4 or TLR 2/1 stimulation. Comparative nuclear receptor profiling between B-1 and peritoneal B-2 cells reveals a highly concordant expression pattern, albeit at quantitatively dissimilar levels. We also found that splenic B cells express 23 nuclear receptors. This catalog of nuclear receptor expression in B-1 and B-2 cells provides data to be used to better understand the specific roles of nuclear receptors in B cell function, chronic inflammation, and autoimmune disease.

Peroxisome proliferator activating receptor (PPAR) in cerebral malaria (CM): a novel target for an additional therapy

Cerebral malaria (CM) is a global life-threatening complication of Plasmodium infection and represents a major cause of morbidity and mortality among severe forms of malaria. Despite developing knowledge in understanding mechanisms of pathogenesis, the current anti-malarial agents are not sufficient due to drug resistance and various adverse effects. Therefore, there is an urgent need for the novel target and additional therapy. Recently, peroxisome proliferator-activated receptor (PPAR) a nuclear receptors (NR) and agonists of its isoforms (PPARγ, PPARα and PPARβ/δ) have been demonstrated to exhibit anti-inflammatory and immunomodulatory properties, which are driven to a new approach of research on inflammatory diseases. Although many studies on PPARs have confirmed their diverse biological role, there is a lack of knowledge of its therapeutic use in CM. The major objective of this review is to explore the possible experimental studies to link these two areas of research. We focus on the data describing the beneficial effects of this receptor in inflammation, which is observed as a basic pathology in CM. In conclusion, PPARs could be a novel target in treating inflammatory diseases, and continued work with the available and additional agonists screened from various sources may result in a potential new treatment for CM.

Resistance of cutaneous anaplastic large-cell lymphoma cells to apoptosis by death ligands is enhanced by CD30-mediated overexpression of c-FLIP

Death ligands, including TNF-alpha, CD95L/FasL, and TRAIL, mediate safeguard mechanisms against tumor growth and critically contribute to lymphocyte homeostasis. We investigated death receptor-mediated apoptosis and CD30/CD95 crosstalk in four CD30-positive cell lines of cutaneous anaplastic large-cell lymphoma (cALCL). Whereas CD95 stimulation strongly induced apoptosis in cALCL cells, the pro-apoptotic pathways of TNF-alpha and TRAIL were completely blocked at an early step. Expression of TNF receptor 1 was lost in three of four cell lines, providing an explanation for TNF-alpha unresponsiveness. TRAIL resistance may be explained by the consistent overexpression of cellular flice inhibitory protein (c-FLIP) (four of four cell lines) and frequent loss of the pro-apoptotic Bcl-2 protein Bid (three of four cell lines). Changes at the receptor-expression level were largely ruled out. CD30/CD95 crosstalk experiments showed that CD30 ligation leads to NF-kappaB-mediated c-FLIP upregulation in cALCL cells, which in turn conferred enhanced resistance to CD95-mediated apoptosis. Knockdown of c-FLIP by a lentiviral approach enhanced basic apoptosis rates in cALCL cells and diminished the CD30-mediated suppression of apoptosis, thus proving the significance of c-FLIP in this context. These in vitro findings may be indicative of the clinical situation of cALCL. Further clarifying the defects in apoptosis pathways in cutaneous lymphomas may lead to improved therapies for these disorders.

Emerging roles of peroxisome proliferator-activated receptor-beta/delta in inflammation

Peroxisome proliferator-activated receptor (PPAR)-beta/delta is a member of the PPAR nuclear hormone receptor family. The PPARs are a family of 3 ligand-activated transcription factors: PPARalpha (NR1C1), PPARbeta/delta (NR1C2), and PPARgamma (NR1C3). All the PPARs play important roles in the regulation of metabolic pathways, including those of lipid of biosynthesis and glucose metabolism, as well as in a variety of cell differentiation, proliferation, and apoptosis pathways. Recently, there has been a great deal of interest in the involvement of PPARs in the inflammatory processes. In particular, PPARalpha and PPARgamma inhibit the activation of inflammatory gene expression and can negatively interfere with pro-inflammatory transcription factor signalling pathways in vascular and inflammatory cells. In contrast, the roles of PPARbeta/delta regulating inflammation and immunity are only just emerging. This review will focus on these emerging roles of PPARbeta/delta in regulating inflammatory processes.