15-Deoxy-12,14-prostaglandin J2 inhibits interferon gamma induced MHC class II but not class I expression on ARPE cells through a PPAR gamma independent mechanism

Emerging roles for nuclear receptors in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of vision loss in the elderly in the Western world. Over the last 30 years, our understanding of the pathogenesis of the disease has grown exponentially thanks to the results of countless epidemiology, genetic, histological, and biochemical studies. This information, in turn, has led to the identification of multiple biologic pathways potentially involved in development and progression of AMD, including but not limited to inflammation, lipid and extracellular matrix dysregulation, and angiogenesis. Nuclear receptors are a superfamily of transcription factors that have been shown to regulate many of the pathogenic pathways linked with AMD and as such they are emerging as promising targets for therapeutic intervention. In this review, we will present the fundamental phenotypic features of AMD and discuss our current understanding of the pathobiological disease mechanisms. We will introduce the nuclear receptor superfamily and discuss the current literature on their effects on AMD-related pathophysiology.

Transcriptional profiling reveals molecular signatures associated with HIV permissiveness in Th1Th17 cells and identifies peroxisome proliferator-activated receptor gamma as an intrinsic negative regulator of viral replication

BACKGROUND

We previously demonstrated that primary Th1Th17 cells are highly permissive to HIV-1, whereas Th1 cells are relatively resistant. Molecular mechanisms underlying these differences remain unknown.

RESULTS

Exposure to replication competent and single-round VSV-G pseudotyped HIV strains provide evidence that superior HIV replication in Th1Th17 vs. Th1 cells was regulated by mechanisms located at entry and post-entry levels. Genome-wide transcriptional profiling identified transcripts upregulated (n = 264) and downregulated (n = 235) in Th1Th17 vs. Th1 cells (p-value < 0.05; fold change cut-off 1.3). Gene Set Enrichment Analysis revealed pathways enriched in Th1Th17 (nuclear receptors, trafficking, p38/MAPK, NF-κB, p53/Ras, IL-23) vs. Th1 cells (proteasome, interferon α/β). Differentially expressed genes were classified into biological categories using Gene Ontology. Th1Th17 cells expressed typical Th17 markers (IL-17A/F, IL-22, CCL20, RORC, IL-26, IL-23R, CCR6) and transcripts functionally linked to regulating cell trafficking (CEACAM1, MCAM), activation (CD28, CD40LG, TNFSF13B, TNFSF25, PTPN13, MAP3K4, LTB, CTSH), transcription (PPARγ, RUNX1, ATF5, ARNTL), apoptosis (FASLG), and HIV infection (CXCR6, FURIN). Differential expression of CXCR6, PPARγ, ARNTL, PTPN13, MAP3K4, CTSH, SERPINB6, PTK2, and ISG20 was validated by RT-PCR, flow cytometry and/or confocal microscopy. The nuclear receptor PPARγ was preferentially expressed by Th1Th17 cells. PPARγ RNA interference significantly increased HIV replication at levels post-entry and prior HIV-DNA integration. Finally, the activation of PPARγ pathway via the agonist Rosiglitazone induced the nuclear translocation of PPARγ and a robust inhibition of viral replication.

CONCLUSIONS

Thus, transcriptional profiling in Th1Th17 vs. Th1 cells demonstrated that HIV permissiveness is associated with a superior state of cellular activation and limited antiviral properties and identified PPARγ as an intrinsic negative regulator of viral replication. Therefore, triggering PPARγ pathway via non-toxic agonists may contribute to limiting covert HIV replication and disease progression during antiretroviral treatment.

Inhibition of experimental auto-immune uveitis by the A3 adenosine receptor agonist CF101

Uveitis is an inflammation of the middle layer of the eye with a high risk of blindness. The Gi protein associated A3 adenosine receptor (A3AR) is highly expressed in inflammatory cells whereas low expression is found in normal cells. CF101 is a highly specific agonist at the A3AR known to induce a robust anti-inflammatory effect in different experimental animal models. The CF101 mechanism of action entails down-regulation of the NF-κB-TNF-α signaling pathway, resulting in inhibition of pro-inflammatory cytokine production and apoptosis of inflammatory cells. In this study the effect of CF101 on the development of retinal antigen interphotoreceptor retinoid-binding protein (IRBP)-induced experimental autoimmune uveitis (EAU) was assessed. Oral treatment with CF101 (10 µg/kg, twice daily), initiated upon disease onset, improved uveitis clinical score measured by fundoscopy and ameliorated the pathological manifestations of the disease. Shortly after treatment with CF101 A3AR expression levels were down-regulated in the lymph node and spleen cells pointing towards receptor activation. Downstream events included a decrease in PI3K and STAT-1 and proliferation inhibition of IRPB auto-reactive T cells ex vivo. Inhibition of interleukin-2, tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) production and up-regulation of interleukin-10 was found in cultured splenocytes derived from CF101-treated animals. Overall, the present study data point towards a marked anti-inflammatory effect of CF101 in EAU and support further exploration of this small molecule drug for the treatment of uveitis.

Omega-3 Fatty Acids and PPARgamma in Cancer

Omega-3 (or n-3) polyunsaturated fatty acids (PUFAs) and their metabolites are natural ligands for peroxisome proliferator receptor activator (PPAR)gamma and, due to the effects of PPARgamma on cell proliferation, survival, and differentiation, are potential anticancer agents. Dietary intake of omega-3 PUFAs has been associated with a reduced risk of certain cancers in human populations and in animal models. In vitro studies have shown that omega-3 PUFAs inhibit cell proliferation and induce apoptosis in cancer cells through various pathways but one of which involves PPARgamma activation. The differential activation of PPARgamma and PPARgamma-regulated genes by specific dietary fatty acids may be central to their distinct roles in cancer. This review summarizes studies relating PUFAs to PPARgamma and cancer and offers a new paradigm relating an n-3 PUFA through PPARgamma to the expression of the cell surface proteoglycan, syndecan-1, and to the death of cancer cells.

Research resource: nuclear receptor atlas of human retinal pigment epithelial cells: potential relevance to age-related macular degeneration

Retinal pigment epithelial (RPE) cells play a vital role in retinal physiology by forming the outer blood-retina barrier and supporting photoreceptor function. Retinopathies including age-related macular degeneration (AMD) involve physiological and pathological changes in the epithelium, severely impairing the retina and effecting vision. Nuclear receptors (NRs), including peroxisome proliferator-activated receptor and liver X receptor, have been identified as key regulators of physiological pathways such as lipid metabolic dysregulation and inflammation, pathways that may also be involved in development of AMD. However, the expression levels of NRs in RPE cells have yet to be systematically surveyed. Furthermore, cell culture lines are widely used to study the biology of RPE cells, without knowledge of the differences or similarities in NR expression and activity between these in vitro models and in vivo RPE. Using quantitative real-time PCR, we assessed the expression patterns of all 48 members of the NR family plus aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator in human RPE cells. We profiled freshly isolated cells from donor eyes (in vivo), a spontaneously arising human cell line (in vitro), and primary cell culture lines (in vitro) to determine the extent to which NR expression in the cultured cell lines reflects that of in vivo. To evaluate the validity of using cell culture models for investigating NR receptor biology, we determined transcriptional activity and target gene expression of several moderately and highly expressed NRs in vitro. Finally, we identified a subset of NRs that may play an important role in pathobiology of AMD.

Anticancer Role of PPARgamma Agonists in Hematological Malignancies Found in the Vasculature, Marrow, and Eyes

The use of targeted cancer therapies in combination with conventional chemotherapeutic agents and/or radiation treatment has increased overall survival of cancer patients. However, longer survival is accompanied by increased incidence of comorbidities due, in part, to drug side effects and toxicities. It is well accepted that inflammation and tumorigenesis are linked. Because peroxisome proliferator-activated receptor (PPAR)-gamma agonists are potent mediators of anti-inflammatory responses, it was a logical extension to examine the role of PPARgamma agonists in the treatment and prevention of cancer. This paper has two objectives: first to highlight the potential uses for PPARgamma agonists in anticancer therapy with special emphasis on their role when used as adjuvant or combined therapy in the treatment of hematological malignancies found in the vasculature, marrow, and eyes, and second, to review the potential role PPARgamma and/or its ligands may have in modulating cancer-associated angiogenesis and tumor-stromal microenvironment crosstalk in bone marrow.

PPARgamma enhances IFNgamma-mediated transcription and rescues the TGFbeta antagonism by stimulating CIITA in vascular smooth muscle cells

Chronic inflammatory response and active vascular remodeling are two featured pathophysiological events during atherogenesis. Gamma interferon (IFN-gamma) modulates these two processes through transcriptional control of major histocompatibility complex II (MHC II) and collagen type I (COL1A2) genes, mediated by class II transactivator (CIITA). Transforming growth factor (TGF-beta) antagonizes the effect of IFN-gamma in part by dampening the expression of CIITA. Here we report that peroxisome proliferator activated receptor gamma (PPARgamma) enhanced MHC II activation and COL1A2 repression by IFN-gamma while rescuing the antagonism by TGF-beta in a CIITA-dependent manner in human aortic smooth muscle cells judged by quantitative PCR and luciferase reporter assays. PPARgamma exerted its effect by augmenting the levels of CIITA and stimulating CIITA recruitment to target promoters as evidenced by chromatin immunoprecipitation assays. The up-regulation of CIITA levels was the result of PPARgamma-mediated transcriptional activation of CIITA through promoter IV, and increased CIITA protein stability. Thus, our data suggest that PPARgamma could be a key factor in fine-tuning inflammation as well as restructuring of vessel walls during atherogenesis by acting as a "balance tipper" of the differential effects exerted by cytokines.