Ligands for the Peroxisome Proliferator-Activated Receptor-γ and the Retinoid X Receptor-α Exert Synergistic Antiproliferative Effects on Human Coronary Artery Smooth Muscle Cells

In human coronary artery vascular smooth muscle (hcaVSM) cells, the mechanisms that mediate the antiproliferative effects of ligands for the peroxisome proliferator-activated receptor-γ (PPARγ) and the retinoid X receptor-α (RXRα) are unclear. Dimerization of PPARγ with RXRα and occupancy by both ligands is required for maximal activation. Accordingly, we determined whether the antiproliferative activity of the PPARγ ligands, troglitazone or 15-deoxy-Δ-12,14-prostaglandin J2 (15d-PGJ2), was enhanced with the RXRα ligand, 9-cis-retinoic acid (9-cis-RA). Incubation of actively proliferating hcaVSM cells with either troglitazone or 15d-PGJ2 resulted in a dose-dependent inhibition of proliferation with half-maximal inhibitory concentrations (IC₅₀s) of 13 and 2 μM, respectively. Quiescent cells incubated with troglitazone or 15d-PGJ2 and subsequently stimulated with PDGF-BB showed a concentration-dependent decrease in the active form of MAP kinase, suggesting that inhibition of cell growth by troglitazone may involve the MAP kinase pathway, an important growth activation pathway in VSM cells. Incubation of cells with either 0.1 or 1.0 μM 9-cis-RA inhibited cell growth to a similar degree. Addition of troglitazone or 15d-PGJ2 to cells in combination with either concentration of 9-cis-RA resulted in a striking increase in growth inhibition, and was accompanied by an approximately 4-fold reduction in the IC₅₀s for both PPARγ ligands. These findings imply that RXRα activation by 9-cis-RA synergistically enhanced inhibition of hcaVSM cell growth. The precise nature of this cooperative interaction between PPARγ and RXRα remains to be determined.     

Effect of Peroxisome Proliferator-Activated Receptor-γ Coactivator-1 Alpha Variants on Spontaneous Clearance and Fibrosis Progression during Hepatitis C Virus Infection in Moroccan Patients

Virologica Sinica - Hepatitis C virus (HCV) is still one of the main causes of liver disease worldwide. Metabolic disorders, including non-alcoholic fatty liver disease (NAFLD), induced by HCV have...     

Advanced Glycation End Products Induce Peroxisome Proliferator-Activated Receptor γ Down-Regulation-Related Inflammatory Signals in Human Chondrocytes via Toll-Like Receptor-4 and Receptor for Advanced Glycation End Products

Accumulation of advanced glycation end products (AGEs) in joints is important in the development of cartilage destruction and damage in age-related osteoarthritis (OA). The aim of this study was to investigate the roles of peroxisome proliferator-activated receptor γ (PPARγ), toll-like receptor 4 (TLR4), and receptor for AGEs (RAGE) in AGEs-induced inflammatory signalings in human OA chondrocytes. Human articular chondrocytes were isolated and cultured. The productions of metalloproteinase-13 and interleukin-6 were quantified using the specific ELISA kits. The expressions of related signaling proteins were determined by Western blotting. Our results showed that AGEs enhanced the productions of interleukin-6 and metalloproteinase-13 and the expressions of cyclooxygenase-2 and high-mobility group protein B1 and resulted in the reduction of collagen II expression in human OA chondrocytes. AGEs could also activate nuclear factor (NF)-κB activation. Stimulation of human OA chondrocytes with AGEs significantly induced the up-regulation of TLR4 and RAGE expressions and the down-regulation of PPARγ expression in a time- and concentration-dependent manner. Neutralizing antibodies of TLR4 and RAGE effectively reversed the AGEs-induced inflammatory signalings and PPARγ down-regulation. PPARγ agonist pioglitazone could also reverse the AGEs-increased inflammatory signalings. Specific inhibitors for p38 mitogen-activated protein kinases, c-Jun N-terminal kinase and NF-κB suppressed AGEs-induced PPARγ down-regulation and reduction of collagen II expression. Taken together, these findings suggest that AGEs induce PPARγ down-regulation-mediated inflammatory signalings and reduction of collagen II expression in human OA chondrocytes via TLR4 and RAGE, which may play a crucial role in the development of osteoarthritis pathogenesis induced by AGEs accumulation.     

Modeling the Role of Peroxisome Proliferator-Activated Receptor γ and MicroRNA-146 in Mucosal Immune Responses to Clostridium difficile

Clostridium difficile is an anaerobic bacterium that has re-emerged as a facultative pathogen and can cause nosocomial diarrhea, colitis or even death. Peroxisome proliferator-activated receptor (PPAR) γ has been implicated in the prevention of inflammation in autoimmune and infectious diseases; however, its role in the immunoregulatory mechanisms modulating host responses to C. difficile and its toxins remains largely unknown. To characterize the role of PPARγ in C. difficile-associated disease (CDAD), immunity and gut pathology, we used a mouse model of C. difficile infection in wild-type and T cell-specific PPARγ null mice. The loss of PPARγ in T cells increased disease activity and colonic inflammatory lesions following C. difficile infection. Colonic expression of IL-17 was upregulated and IL-10 downregulated in colons of T cell-specific PPARγ null mice. Also, both the loss of PPARγ in T cells and C. difficile infection favored Th17 responses in spleen and colonic lamina propria of mice with CDAD. MicroRNA (miRNA)-sequencing analysis and RT-PCR validation indicated that miR-146b was significantly overexpressed and nuclear receptor co-activator 4 (NCOA4) suppressed in colons of C. difficile-infected mice. We next developed a computational model that predicts the upregulation of miR-146b, downregulation of the PPARγ co-activator NCOA4, and PPARγ, leading to upregulation of IL-17. Oral treatment of C. difficile-infected mice with the PPARγ agonist pioglitazone ameliorated colitis and suppressed pro-inflammatory gene expression. In conclusion, our data indicates that miRNA-146b and PPARγ activation may be implicated in the regulation of Th17 responses and colitis in C. difficile-infected mice.     

The Role of Peroxisome Proliferator-Activated Receptor and Effects of Its Agonist,Pioglitazone, on a Rat Model of Optic Nerve Crush: PPARγ in Retinal Neuroprotection

It has been shown that peroxisome proliferators-activated receptor gamma (PPARγ) is beneficial for central nervous system injury. However its role on optic nerve injury remains unknown. In the present study, we examined the change of PPARγ expression in rat retina following optic nerve injury and investigated the effect of pioglitazone (Pio), a PPARγ agonist, on retinal ganglion cells (RGCs) neuroprotection using a rat optic nerve crush (ONC) model. Our results showed that PPARγ mRNA and protein levels were increased after ONC, and most of PPARγ-immunoreactive cells colocalized with Müller cells. Pio treatment significantly enhanced the number of surviving RGCs and inhibited RGCs apoptosis induced by ONC. However, when PPARγ antagonist GW9662 was used, these neuroprotective effects were abolished. In addition, pio attenuated Müller cell activation after ONC. These results indicate that PPARγ appears to protect RGCs from ONC possibly via the reduction of Müller glial activation. It provides evidence that activation of PPARγ may be a potential alternative treatment for RGCs neuroprotection.     

The Synergistic Enhancement of Cloning Efficiency in Individualized Human Pluripotent Stem Cells by Peroxisome Proliferative-activated Receptor-γ (PPARγ) Activation and Rho-associated Kinase (ROCK) Inhibition

Although human pluripotent stem cells (hPSCs) provide valuable sources for regenerative medicine, their applicability is dependent on obtaining both suitable up-scaled and cost effective cultures. The Rho-associated kinase (ROCK) inhibitor Y-27632 permits hPSC survival upon dissociation; however, cloning efficiency is often still low. Here we have shown that pioglitazone, a selective peroxisome proliferative-activated receptor-γ agonist, along with Y-27632 synergistically diminished dissociation-induced apoptosis and increased cloning efficiency (2–3-fold versus Y-27632) without affecting pluripotency of hPSCs. Pioglitazone exerted its positive effect by inhibition of glycogen synthase kinase (GSK3) activity and enhancement of membranous β-catenin and E-cadherin proteins. These effects were reversed by GW-9662, an irreversible peroxisome proliferative-activated receptor-γ antagonist. This novel setting provided a step toward hPSC manipulation and its biomedical applications.     

Immune Response to Dengue Virus Infection in Pediatric Patients in New Delhi,India—Association of Viremia,Inflammatory Mediators and Monocytes with Disease Severity

Dengue virus, a mosquito-borne flavivirus, is a causative agent for dengue infection, which manifests with symptoms ranging from mild fever to fatal dengue shock syndrome. The presence of four serotypes, against which immune cross-protection is short-lived and serotype cross-reactive antibodies that might enhance infection, pose a challenge to further investigate the role of virus and immune response in pathogenesis. We evaluated the viral and immunological factors that correlate with severe dengue disease in a cohort of pediatric dengue patients in New Delhi. Severe dengue disease was observed in both primary and secondary infections. Viral load had no association with disease severity but high viral load correlated with prolonged thrombocytopenia and delayed recovery. Severe dengue cases had low Th1 cytokines and a concurrent increase in the inflammatory mediators such as IL-6, IL-8 and IL-10. A transient increase in CD14⁺CD16⁺ intermediate monocytes was observed early in infection. Sorting of monocytes from dengue patient peripheral blood mononuclear cells revealed that it is the CD14+ cells, but not the CD16+ or the T or B cells, that were infected with dengue virus and were major producers of IL-10. Using the Boruta algorithm, reduced interferon-α levels and enhanced aforementioned pro-inflammatory cytokines were identified as some of the distinctive markers of severe dengue. Furthermore, the reduction in the levels of IL-8 and IL-10 were identified as the most significant markers of recovery from severe disease. Our results provide further insights into the immune response of children to primary and secondary dengue infection and help us to understand the complex interplay between the intrinsic factors in dengue pathogenesis.     

Salmonella Induced IL-23 and IL-1β Allow for IL-12 Production by Monocytes and M?1 through Induction of IFN-γ in CD56+ NK/NK-Like T Cells

Background

The type-1 cytokine pathway plays a pivotal role in immunity against intracellular bacterial pathogens such as Salmonellae and Mycobacteria. Bacterial stimulation of pattern recognition receptors on monocytes, macrophages and dendritic cells initiates this pathway, and results in the production of cytokines that activate lymphocytes to produce interferon (IFN)-γ. Interleukin (IL)-12 and IL-23 are thought to be the key cytokines required for initiating a type-1 cytokine immune response to Mycobacteria and Salmonellae. The relative contribution of IL-23 and IL-12 to this process is uncertain.

Methodology/Principal Findings

We show that various TLR agonists induce the production of IL-23 but not IL-12 in freshly isolated human monocytes and cultured human macrophages. In addition, type 1 pro-inflammatory macrophages (Mϕ1) differentiated in the presence of GM-CSF and infected with live Salmonella produce IL-23, IL-1β and IL-18, but not IL-12. Supernatants of Salmonella-infected Mϕ1 contained more IL-18 and IL-1β as compared with supernatants of Mϕ1 stimulated with isolated TLR agonists, and induced IFN-γ production in human CD56⁺ cells in an IL-23 and IL-1β-dependent but IL-12-independent manner. In addition, IL-23 together with IL-18 or IL-1β led to the production of GM-CSF in CD56⁺ cells. Both IFN-γ and GM-CSF enhanced IL-23 production by monocytes in response to TLR agonists, as well as induced IL-12 production.

Conclusions/Significance

The findings implicate a positive feedback loop in which IL-23 can enhance its release via induction of IFN-γ and GM-CSF. The IL-23 induced cytokines allow for the subsequent production of IL-12 and amplify the IFN-γ production in the type-1 cytokine pathway.     

High Pulmonary Levels of IL-6 and IL-1β in Children with Chronic Suppurative Lung Disease Are Associated with Low Systemic IFN-γ Production in Response to Non-Typeable Haemophilus influenzae

Non-typeable Haemophilus influenzae (NTHi) is commonly associated with chronic suppurative lung disease in children. We have previously shown that children with chronic suppurative lung disease have a reduced capacity to produce IFN-γ in response to NTHi compared with healthy control children. The aim of this study was to determine if deficient NTHi-specific IFN-γ production is associated with heightened systemic or airway inflammation. We measured a panel of cytokines (IFN-γ, IL-1β, IL-6, IL-8, IL-12 p70), antimicrobial proteins (LL-37, IP-10) as well as cellular and clinical factors associated with airway and systemic inflammation in 70 children with chronic suppurative lung disease. IFN-γ was measured in peripheral blood mononuclear cells challenged in vitro with live NTHi. Regression analysis was used to assess the association between the systemic and airway inflammation and the capacity to produce IFN-γ. On multivariate regression, NTHi-specific IFN-γ production was significantly negatively associated with the BAL concentrations of the inflammatory cytokines IL-6 (β=-0.316; 95%CI -0.49, -0.14; p=0.001) and IL-1β (β=-0.023; 95%CI -0.04, -0.01; p=0.001). This association was independent of bacterial or viral infection, BAL cellularity and the severity of bronchiectasis (using modified Bhalla score on chest CT scans). We found limited evidence of systemic inflammation in children with chronic suppurative lung disease. In summary, increased local airway inflammation is associated with a poorer systemic cell-mediated immune response to NTHi in children with chronic suppurative lung disease. These data support the emerging body of evidence that impaired cell-mediated immune responses and dysregulated airway inflammation may be linked and contribute to the pathobiology of chronic suppurative lung disease.