Npas4-mediated dopaminergic regulation of safety memory consolidation.

Amygdala circuitry encodes associations between conditioned stimuli and aversive unconditioned stimuli and also controls fear expression. However, whether and how non-threatening information for unpaired conditioned stimuli (CS-) is discretely processed remains unknown. The fear expression toward CS- is robust immediately after fear conditioning but then becomes negligible after memory consolidation. The synaptic plasticity of the neural pathway from the lateral to the anterior basal amygdala gates the fear expression of CS-, depending upon neuronal PAS domain protein 4 (Npas4)-mediated dopamine receptor D4 (Drd4) synthesis, which is precluded by stress exposure or corticosterone injection. Herein, we show cellular and molecular mechanisms that regulate the non-threatening (safety) memory consolidation, supporting the fear discrimination.

Hydrocarboxylic acid receptor 1 in BAT regulates glucose uptake in mice fed a high-fat diet.

Interscapular brown adipose tissue (BAT) has the capability to take up glucose from the circulation. Despite the important role of BAT in the control of glucose homeostasis, the metabolic fate and function of glucose in BAT remain elusive as there is clear dissociation between glucose uptake and BAT thermogenesis. Interestingly, intracellular glycolysis and lactate production appear to be required for glucose uptake by BAT. Here, we specifically examine whether activation of lactate receptors in BAT plays a key role in regulating glucose homeostasis in mice fed a high-fat diet (HFD). When C57BL/6J mice are given HFD for 5 weeks at 28°C, male, but not female, mice gain body weight and develop hyperglycemia. Importantly, high-fat feeding upregulates expression of the lactate receptor hydroxycarboxylic acid receptor 1 (HCAR1) in female C57BL/6J mice, whereas male C57BL/6J mice show reduced HCAR1 expression in BAT. Treatment with the HCAR1 agonist lowers systemic glucose levels in male DIO mice. This reduction is associated with increased glucose uptake in BAT. Therefore, our results suggest that HCAR1 in BAT may contribute to the development of hyperglycemia in male C57BL/6J DIO mice.

Ligand-activated interaction of PPARδ with c-Myc governs the tumorigenicity of breast cancer.

Peroxisome proliferator-activated receptor (PPAR) δ is a promising therapeutic target in metabolic and inflammatory disorders. However, its role in oncogenesis is controversial, and its therapeutic potential remains to be determined. In our study, we show that ligand-activated PPARδ forms a complex with the proto-oncogene product c-Myc. The interaction of PPARδ with c-Myc affected the transcriptional activity of c-Myc and the expression of its target genes. The PPARδ-dependent regulation of c-Myc activity was associated with decreased tumorigenicity in breast cancer cells. Administration of the PPARδ ligand GW501516 inhibited tumor growth in xenograft model mice bearing MDA-MB-231 cells stably expressing wild-type PPARδ, but not those expressing dominant-negative PPARδ, by interfering with c-Myc function through protein-protein interaction. Our results indicating that PPARδ forms an antitumorigenic complex with c-Myc in the presence of ligand suggest a potential role of PPARδ in breast cancer development.

Activation of PPARδ attenuates neurotoxicity by inhibiting lipopolysaccharide-triggered glutamate release in BV-2 microglial cells.

Neuroinflammation-associated release of glutamate from activated microglia has been implicated in the progression of neurodegenerative diseases. However, the regulatory mechanisms underlying this glutamate release are poorly understood. Here, we show that peroxisome proliferator-activated receptor delta (PPARδ) modulates neurotoxicity by inhibiting glutamate release in lipopolysaccharide (LPS)-activated BV-2 microglial cells. Activation of PPARδ by GW501516, a specific PPARδ agonist, inhibited glutamate release in BV-2 cells. This effect of GW501516 was significantly blocked by shRNA-mediated knockdown of PPARδ and by treatment with GSK0660, a specific PPARδ antagonist, indicating that PPARδ is associated with blockade of glutamate release. Additionally, GW501516-activated PPARδ suppressed generation of reactive oxygen species and expression of gp91phox, a functional subunit of NADPH oxidase 2, in BV-2 cells stimulated with LPS. The inhibitory effect of GW501516 on gp91phox expression and glutamate release was further potentiated in the presence of AG490, a specific inhibitor of janus kinase 2 (JAK2), leading to the inhibition of signal transducer and activator of transcription 1 (STAT1). By contrast, GW501516 upregulated the expression of suppressor of cytokine signaling 1 (SOCS1), an endogenous inhibitor of JAK2. Furthermore, neurotoxicity induced by conditioned media from LPS-stimulated BV-2 cells was significantly reduced when conditioned media from BV-2 cells treated with both LPS and GW501516 were used. These results indicate that PPARδ attenuates LPS-triggered neuroinflammation by enhancing SOCS1-mediated inhibition of JAK2/STAT1 signaling, thereby inhibiting neurotoxicity associated with glutamate release.

Ligand-Activated Peroxisome Proliferator-Activated Receptor δ Attenuates Vascular Oxidative Stress by Inhibiting Thrombospondin-1 Expression.

Thrombospondin-1 (TSP-1) is implicated in vascular diseases associated with oxidative stress, such as abdominal aortic aneurysms, ischemia-reperfusion injury, and atherosclerosis. However, the regulatory mechanisms underlying TSP-1 expression are not fully elucidated. In this study, we found that peroxisome proliferator-activated receptor δ (PPARδ) inhibited oxidative stress-induced TSP-1 expression and migration in vascular smooth muscle cells (VSMCs). Activation of PPARδ by GW501516, a specific ligand for PPARδ, significantly attenuated hydrogen peroxide (H2O2)-induced expression of TSP-1 in VSMCs. Small interfering RNA-mediated knockdown of PPARδ and treatment with GSK0660, a selective PPARδ antagonist, reversed the effect of GW501516 on H2O2-induced expression of TSP-1, suggesting that PPARδ is associated with GW501516 activity. Furthermore, JNK (c-Jun N-terminal kinase), but not p38 and ERK (extracellular signal-regulated kinase), mediated PPARδ-dependent inhibition of TSP-1 expression in VSMCs exposed to H2O2. GW501516- activated PPARδ also reduced the H2O2-induced generation of reactive oxygen species, concomitant with inhibition of VSMC migration. In particular, TSP-1 contributed to the action of PPARδ in the regulation of H2O2-induced interleukin-1ß expression. These results suggest that PPARδ-modulated downregulation of TSP-1 is associated with reduced cellular oxidative stress, thereby inhibiting H2O2-induced pheno-typic changes in vascular cells.

Ligand-Dependent Interaction of PPARδ With T-Cell Protein Tyrosine Phosphatase 45 Enhances Insulin Signaling.

Peroxisome proliferator-activated receptor (PPAR) δ plays a pivotal role in metabolic homeostasis through its effect on insulin signaling. Although diverse genomic actions of PPARδ are postulated, the specific molecular mechanisms whereby PPARδ controls insulin signaling have not been fully elucidated. We demonstrate here that short-term activation of PPARδ results in the formation of a stable complex with nuclear T-cell protein tyrosine phosphatase 45 (TCPTP45) isoform. This interaction of PPARδ with TCPTP45 blocked translocation of TCPTP45 into the cytoplasm, thereby preventing its interaction with the insulin receptor, which inhibits insulin signaling. Interaction of PPARδ with TCPTP45 blunted interleukin 6-induced insulin resistance, leading to retention of TCPTP45 in the nucleus, thereby facilitating deactivation of the signal transducer and activator of transcription 3 (STAT3)-suppressor of cytokine signaling 3 (SOCS3) signal. Finally, GW501516-activated PPARδ improved insulin signaling and glucose intolerance in mice fed a high-fat diet through its interaction with TCPTP45. This novel interaction of PPARδ constitutes the most upstream component identified of the mechanism downregulating insulin signaling.

ADAMTS1-mediated targeting of TSP-1 by PPARδ suppresses migration and invasion of breast cancer cells.

Migration and invasion of cancer cells into surrounding tissue is a key stage of cancer metastasis. Here, we show that peroxisome proliferator-activated receptor (PPAR) δ regulates migration and invasion of human breast cancer cells via thrombospondin-1 (TSP-1) and its degrading protease, a disintegrin and metalloprotease domains with thrombospondin motifs 1 (ADAMTS1). Activation of PPARδ by GW501516, a specific ligand for PPARδ, led to marked inhibition in the cell migration and TSP-1 expression of breast cancer. These effects were suppressed by small interfering RNA-mediated knock-down of ADAMTS1, indicating that ADAMTS1 is involved in PPARδ-mediated inhibition of migration and TSP-1 expression in breast cancer cells. In addition, ligand-activated PPARδ upregulated expression of ADAMTS1 at the transcriptional level via binding of PPARδ to a direct repeat-1 site within the ADAMTS1 gene promoter. Furthermore, ligand-activated PPARδ suppressed invasion of breast cancer cells in an ADAMTS1-dependent manner. Taken together, these results demonstrate that PPARδ suppresses migration and invasion of breast cancer cells by downregulating TSP-1 in a process mediated by upregulation of ADAMTS1.

A Dalbergia odorifera extract improves the survival of endotoxemia model mice by inhibiting HMGB1 release.

BACKGROUND: Dalbergia odorifera T. Chen (Leguminosae) is an indigenous medicinal herb that is widely used as a popular remedy in northern and eastern Asia. However, the cellular mechanisms underlying the biological activity of D. odorifera are not fully elucidated. METHODS: Anti-inflammatory effect of D. odorifera extract (DOE) was determined through intraperitoneal injection in a mouse model of endotoxemia induced by lipopolysaccharide (LPS). RAW 264.7 cells, a murine macrophage, were also treated with LPS to generate a cellular model of inflammation, and investigated the anti-inflammatory activity and underlying mechanisms of DOE and its constituent isoliquiritigenin. RESULTS: DOE dose-dependently inhibited LPS-induced release of high mobility group box 1 (HMGB1), a late proinflammatory cytokine, and decreased cytosolic translocation of HMGB1 in RAW264.7 cells. This inhibitory effect of DOE on HMGB1 release was observed in cells treated with DOE before or after LPS treatment, suggesting that DOE is effective for both treatment and prevention. In addition, DOE significantly inhibited LPS-induced formation of nitric oxide (NO) and expression of inducible NO synthase (iNOS) in a dose-dependent manner. These effects of DOE were accompanied by suppression of HMGB1 release triggered by LPS, suggesting a possible mechanism by which DOE modulates HMGB1 release through NO signaling. Isoriquiritigenin, a constituent of DOE, also attenuated LPS-triggered NO formation and HMGB1 release in RAW264.7 cells, indicating that isoriquiritigenin is an indexing molecule for the anti-inflammatory properties of DOE. Furthermore, c-Jun N-terminal kinase, but not extracellular signal-regulated kinase and p38, mediated DOE-dependent inhibition of HMGB1 release and NO/iNOS induction in RAW 264.7 cells exposed to LPS. Notably, administration of DOE ameliorated survival rates in a mouse model of endotoxemia induced by LPS, where decreased level of circulating HMGB1 was observed. CONCLUSION: These results suggest that DOE confers resistance to LPS-triggered inflammation through NO-mediated inhibitory effects on HMGB1 release.

Upregulation of MKP-7 in response to rosiglitazone treatment ameliorates lipopolysaccharide-induced destabilization of SIRT1 by inactivating JNK.

Silent mating type information regulation 2 homolog 1 (SIRT1), a NAD-dependent deacetylase, mediates cellular processes involved in gene silencing and aging. The regulation of lifespan by SIRT1 has been extensively investigated, but less is known about the mechanisms associated with its cellular turnover during inflammatory responses. In this study, we found that peroxisome proliferator-activated receptor (PPAR) γ is associated with SIRT1 stability in murine macrophage RAW 264.7 cells exposed to lipopolysaccharide (LPS). Activation of PPARγ by rosiglitazone, a specific ligand of PPARγ, rescues LPS-induced destabilization of SIRT1, with a concomitant decrease in phosphorylation of residue Ser-46, which is targeted by JNK-1 to promote proteasome-mediated degradation of SIRT1. The rosiglitazone-mediated increase in SIRT1 stability is accompanied by upregulation of mitogen-activated protein kinase phosphatase (MKP)-7, a JNK-specific phosphatase. These effects are significantly influenced by ablation or ectopic expression of PPARγ, indicating that PPARγ is directly involved in the regulation of SIRT1 stability. Furthermore, gain of MKP-7 function mimicked the effect of rosiglitazone on LPS-induced destabilization and ubiquitination of SIRT1. These results indicate that PPARγ-dependent upregulation of MKP-7 improves the stability of SIRT1 by inactivating JNK during inflammatory responses of LPS-activated macrophages.

Sirtuin 1 Mediates the Actions of Peroxisome Proliferator-Activated Receptor δ on the Oxidized Low-Density Lipoprotein-Triggered Migration and Proliferation of Vascular Smooth Muscle Cells.

Peroxisome proliferator-activated receptor δ (PPARδ) has been implicated in vascular pathophysiology. However, its functions in atherogenic changes of the vascular wall have not been fully elucidated. PPARδ activated by GW501516 (2-[2-methyl-4-[[4-methyl-2-[4-(trifluoromethyl)phenyl]-1,3-thiazol-5-yl]methylsulfanyl]phenoxy]acetic acid) significantly inhibited the migration and proliferation of vascular smooth muscle cells (VSMCs) triggered by oxidized low-density lipoprotein (oxLDL). These GW501516-mediated effects were significantly reversed by PPARδ-targeting small-interfering RNA (siRNA), indicating that PPARδ is involved in the action of GW501516. The antiproliferative effect of GW501516 was directly linked to cell cycle arrest at the G0/G1 to S phase transition, which was followed by the down-regulation of cyclin-dependent kinase 4 along with increased levels of p21 and p53. In VSMCs treated with GW501516, the expression of sirtuin 1 (SIRT1) mRNA and protein was time-dependently increased. This GW501516-mediated up-regulation of SIRT1 expression was also demonstrated even in the presence of oxLDL. In addition, GW501516-dependent inhibition of oxLDL-triggered migration and proliferation of VSMCs was almost completely abolished in the presence of SIRT1-targeting siRNA. These effects of GW501516 on oxLDL-triggered phenotypic changes of VSMCs were also demonstrated via activation or inhibition of SIRT1 activity by resveratrol or sirtinol, respectively. Finally, gain or loss of SIRT1 function imitated the action of PPARδ on oxLDL-triggered migration and proliferation of VSMCs. Taken together, these observations indicate that PPARδ-dependent up-regulation of SIRT1 contributes to the antiatherogenic activities of PPARδ by suppressing the migration and proliferation of VSMCs linked to vascular diseases such as restenosis and atherosclerosis.

Deacetylation-mediated interaction of SIRT1-HMGB1 improves survival in a mouse model of endotoxemia.

Inflammatory signal-mediated release of high-mobility group box 1 (HMGB1) is a damage-associated molecular pattern or alarmin. The inflammatory functions of HMGB1 have been extensively investigated; however, less is known about the mechanisms controlling HMGB1 release. We show that SIRT1, the human homolog of the Saccharomyces cerevisiae protein silent information regulator 2, which is involved in cellular senescence and possibly the response to inflammation, forms a stable complex with HMGB1 in murine macrophage RAW264.7 cells. SIRT1 directly interacted with HMGB1 via its N-terminal lysine residues (28-30), and thereby inhibited HMGB1 release to improve survival in an experimental model of sepsis. By contrast, inflammatory stimuli such as lipopolysaccharide (LPS) and tumor necrosis factor-α promoted HMGB1 release by provoking its dissociation from SIRT1 dependent on acetylation, thereby increasing the association between HMGB1 and chromosome region maintenance 1, leading to HMGB1 translocation. In vivo infection with wild-type SIRT1 and HMGB1(K282930R), a hypo-acetylation mutant, improved survival (85.7%) during endotoxemia more than infection with wild-type SIRT1 and HMGB1-expressing adenovirus, indicating that the acetylation-dependent interaction between HMGB1 and SIRT1 is critical for LPS-induced lethality. Taken together, we propose that SIRT1 forms an anti-inflammatory complex with HMGB1, allowing cells to bypass the response to inflammation.

Ligand-activated PPARδ upregulates α-smooth muscle actin expression in human dermal fibroblasts: A potential role for PPARδ in wound healing.

BACKGROUND: The phenotypic changes that accompany differentiation of resident fibroblasts into myofibroblasts are important aspects of the wound healing process. Recent studies showed that peroxisome proliferator-activated receptor (PPAR) δ plays a critical role in wound healing. OBJECTIVE: To determine whether the nuclear receptor PPARδ can modulate the differentiation of human dermal fibroblasts (HDFs) into myofibroblasts. METHODS: These studies were undertaken in primary HDFs using Western blot analyses, small interfering (si)RNA-mediated gene silencing, reporter gene assays, chromatin immunoprecipitation (ChIP), migration assays, collagen gel contraction assays, and real-time PCR. RESULTS: Activation of PPARδ by GW501516, a specific ligand of PPARδ, specifically upregulated the myofibroblast marker α-smooth muscle actin (α-SMA) in a time- and concentration-dependent manner. This induction was significantly inhibited by the presence of siRNA against PPARδ, indicating that PPARδ is involved in myofibroblast transdifferentiation of HDFs. Ligand-activated PPARδ increased α-SMA promoter activity in a dual mode by directly binding a direct repeat-1 (DR1) site in the α-SMA promoter, and by inducing expression of transforming growth factor (TGF)-ß, whose downstream effector Smad3 interacts with a Smad-binding element (SBE) in another region of the promoter. Mutations in these cis-elements totally abrogated transcriptional activation of the α-SMA gene by the PPARδ ligand; thus both sites represent novel types of PPARδ response elements. GW501516-activated PPARδ also increased the migration and contractile properties of HDFs, as demonstrated by Transwell and collagen lattice contraction assays, respectively. In addition, PPARδ-mediated upregulation of α-SMA was correlated with elevated expression of myofibroblast markers such as collagen I and fibronectin, with a concomitant reduction in expression of the epithelial marker E-cadherin. CONCLUSION: PPARδ plays pivotal roles in wound healing by promoting fibroblast-to-myofibroblast differentiation via TGF-ß/Smad3 signaling.

PPARδ modulates oxLDL-induced apoptosis of vascular smooth muscle cells through a TGF-ß/FAK signaling axis.

The peroxisome proliferator-activated receptor delta (PPARδ) has been implicated in the modulation of vascular homeostasis. However, its roles in the apoptotic cell death of vascular smooth muscle cells (VSMCs) are poorly understood. Here, we demonstrate that PPARδ modulates oxidized low-density lipoprotein (oxLDL)-induced apoptosis of VSMCs through the transforming growth factor-ß (TGF-ß) and focal adhesion kinase (FAK) signaling pathways. Activation of PPARδ by GW501516, which is a specific ligand, significantly inhibited oxLDL-induced cell death and generation of reactive oxygen species in VSMCs. These inhibitory effects were significantly reversed in the presence of small interfering (si)RNA against PPARδ, or by blockade of the TGF-ß or FAK signaling pathways. Furthermore, PPARδ-mediated recovery of FAK phosphorylation suppressed by oxLDL was reversed by SB431542, a specific ALK5 receptor inhibitor, indicating that a TGF-ß/FAK signaling axis is involved in the action of PPARδ. Among the protein kinases activated by oxLDL, p38 mitogen-activated protein kinase was suppressed by ligand-activated PPARδ. In addition, oxLDL-induced expression and translocation of pro-apoptotic or anti-apoptotic factors were markedly affected in the presence of GW501516. Those effects were reversed by PPARδ siRNA, or inhibitors of TGF-ß or FAK, which also suggests that PPARδ exerts its anti-apoptotic effect via a TGF-ß/FAK signaling axis. Taken together, these findings indicate that PPARδ plays an important role in the pathophysiology of disease associated with apoptosis of VSMC, such as atherosclerosis and restanosis.

Ethanol extract of Dalbergia odorifera protects skin keratinocytes against ultraviolet B-induced photoaging by suppressing production of reactive oxygen species.

Dalbergia odorifera T. Chen (Leguminosae), an indigenous medicinal herb, has been widely used in northern and eastern Asia to treat diverse diseases. Here, we investigated the anti-senescent effects of ethanolic extracts of Dalbergia odorifera (EEDO) in ultraviolet (UV) B-irradiated skin cells. EEDO significantly inhibited UVB-induced senescence of human keratinocytes in a concentration-dependent manner, concomitant with inhibition of reactive oxygen species (ROS) generation. UVB-induced increases in the levels of p53 and p21, biomarkers of cellular senescence, were almost completely abolished in the presence of EEDO. Sativanone, a major constituent of EEDO, also attenuated UVB-induced senescence and ROS generation in keratinocytes, indicating that sativanone is an indexing (marker) molecule for the anti-senescence properties of EEDO. Finally, treatment of EEDO to mice exposed to UVB significantly reduced ROS levels and the number of senescent cells in the skin. Thus, EEDO confers resistance to UVB-induced cellular senescence by inhibiting ROS generation in skin cells.

Dalbergia odorifera Extract Ameliorates UVB-Induced Wrinkle Formation by Modulating Expression of Extracellular Matrix Proteins.

Preclinical Research Emerging evidence suggests that Dalbergia odorifera T. Chen (Leguminosae), an indigenous medicinal herb, has therapeutic potential. This study examined the antiwrinkle effects of ethanol extracts of D. odorifera in UVB-irradiated human skin cells. Ethanol extracts of D. odorifera and thier constituents, dalbergin and sativanone, induced expression of collagen type I and transforming growth factor (TGF)-ß1 in human dermal fibroblasts. In HR-1 hairless mice exposed to UVB, the ethanol extract reduced wrinkle formation and skin thickness. This inhibitory effect of ethanol extract was associated with the restoration of collagen type I, TGF-ß1, and elastin to levels approaching those in skin tissues not exposed to UVB, which was accompanied by the reduction of matrix metalloproteinase-2 and upregulation of tissue inhibitors of metalloproteinase (TIMP)-2 and TIMP-3 in skin tissue exposed to UVB. These results suggest that the ethanol extracts prevent some effects of photoaging and maintain skin integrity by regulating the degradation of the extracellular matrix proteins. © 2015 Wiley Periodicals, Inc.

Ligand-activated PPARδ modulates the migration and invasion of melanoma cells by regulating Snail expression.

Peroxisome proliferator-activated receptor (PPAR) δ is implicated in the carcinogenesis of several types of cancer. However, the therapeutic efficacy of PPARδ ligands against cancer progression is unclear. Here, we showed that PPARδ modulates the migration and invasion of melanoma cells by up-regulating Snail expression. Activation of PPARδ by GW501516, a specific ligand for PPARδ, significantly increased the migration and invasion of highly metastatic A375SM cells, but not that of low metastatic A375P cells. The migration- and invasion-promoting effects of PPARδ on A375SM cells was associated with increased Snail expression, which was accompanied by a decrease in E-cadherin expression. Furthermore, a significant concentration- and time-dependent increase in the levels of Snail mRNA and protein was observed in A375SM cells (but not A375P cells) treated with GW501516. The effects of GW501516 were almost completely abrogated by a small interfering RNA against PPARδ, suggesting that PPARδ mediates the effects of GW501516. Activation of PPARδ in SK-MEL-2 and SK-MEL-5 (but not SK-MEL-3) melanoma cell lines also led to significant increases in the expression of Snail mRNA and protein, which mirrored the invasive and migratory potential of these cell lines. These results suggest that PPARδ promotes the aggressive phenotype observed in highly metastatic melanoma cells by up-regulating Snail.

Activation of peroxisome proliferator-activated receptor δ inhibits angiotensin II-induced activation of matrix metalloproteinase-2 in vascular smooth muscle cells.

We investigated the role of peroxisome proliferator-activated receptor (PPAR) δ on angiotensin (Ang) II-induced activation of matrix metalloproteinase (MMP)-2 in vascular smooth muscle cells (VSMCs). Activation of PPARδ by GW501516, a specific ligand for PPARδ, attenuated Ang II-induced activation of MMP-2 in a concentration-dependent manner. GW501516 also inhibited the generation of reactive oxygen species in VSMCs treated with Ang II. A marked increase in the mRNA levels of tissue inhibitor of metalloproteinase (TIMP)-2 and -3, endogenous antagonists of MMPs, was also observed in GW501516-treated VSMCs. These effects were markedly reduced in the presence of siRNAs against PPARδ, indicating that the effects of GW501516 are PPARδ dependent. Among the protein kinases inhibited by GW501516, suppression of phosphatidylinositol 3-kinase/Akt signaling was shown to have the greatest effect on activation of MMP-2 in VSMCs treated with Ang II. Concomitantly, GW501516-mediated inhibition of MMP-2 activation in VSMCs treated with Ang II was associated with the suppression of cell migration to levels approaching those in cells not exposed to Ang II. Thus, activation of PPARδ confers resistance to Ang II-induced degradation of the extracellular matrix by upregulating expression of its endogenous inhibitor TIMP and thereby modulating cellular responses to Ang II in vascular cells.

Peroxisome proliferator-activated receptor δ modulates MMP-2 secretion and elastin expression in human dermal fibroblasts exposed to ultraviolet B radiation.

BACKGROUND: Changes in skin connective tissues mediated by ultraviolet (UV) radiation have been suggested to cause the skin wrinkling normally associated with premature aging of the skin. Recent investigations have shown that peroxisome proliferator-activated receptor (PPAR) δ plays multiple biological roles in skin homeostasis. OBJECTIVE: We attempted to investigate whether PPARδ modulates elastin protein levels and secretion of matrix metalloproteinase (MMP)-2 in UVB-irradiated human dermal fibroblasts (HDFs) and mouse skin. METHODS: These studies were undertaken in primary HDFs or HR-1 hairless mice using Western blot analyses, small interfering (si)RNA-mediated gene silencing, and Fluorescence microscopy. RESULTS: In HDFs, UVB irradiation induced increased secretion of MMP-2 and reduced levels of elastin. Activation of PPARδ by GW501516, a ligand specific for PPARδ, markedly attenuated UVB-induced MMP-2 secretion with a concomitant increase in the level of elastin. These effects were reduced by the presence of siRNAs against PPARδ or treatment with GSK0660, a specific inhibitor of PPARδ. Furthermore, GW501516 elicited a dose- and time-dependent increase in the expression of elastin. Modulation of MMP-2 secretion and elastin levels by GW501516 was associated with a reduction in reactive oxygen species (ROS) production in HDFs exposed to UVB. Finally, in HR-1 hairless mice, administration of GW501516 significantly reduced UVB-induced MMP-2 expression with a concomitant increase in elastin levels, and these effects were significantly reduced by the presence of GSK0660. CONCLUSION: Our results suggest that PPARδ-mediated modulation of MMP-2 secretion and elastin expression may contribute to the maintenance of skin integrity by inhibiting ROS generation.

PPARδ reduces abdominal aortic aneurysm formation in angiotensin II-infused apolipoprotein E-deficient mice by regulating extracellular matrix homeostasis and inflammatory responses.

BACKGROUND: Abdominal aortic aneurysm (AAA) is an inflammatory disorder characterized by a localized degradation of connective tissue and apoptosis of vascular smooth muscle cells. This study examined whether the ligand-activated peroxisome proliferator-activated receptor (PPAR) δ can directly antagonize angiotensin II (Ang II)-induced AAA formation in apoE-deficient mice. METHODS AND RESULTS: Six-month-old male apoE-deficient mice were infused with Ang II and/or GW501516 (1.44 and 3.3mg/kg/day, respectively) via osmotic mini-pumps. At day 28, aortic size was measured and tissues were collected for analyses. Co-infusion of GW501516, an activator of PPARδ, attenuated both the incidence and the severity of Ang II-induced AAA in apoE-deficient mice. Ligand-activated PPARδ also reduced infiltration of macrophages, resulting in significant decreases in chemotactic proteins such as monocyte chemoattractant protein-1, macrophage inflammatory protein-1ß, and inducible nitric oxide synthase. The anti-inflammatory effect of GW501516 was associated with the suppression of apoptotic cell death, along with the inhibition of medial smooth muscle cell loss and focal elastin destruction, which leads to a medial dissection and aortic rupture. These ameliorative effects of GW501516 on Ang II-induced aneurysm were correlated with increased expression of extracellular matrix (ECM) proteins, such as types I and III collagen, fibronectin, and elastin, along with the up-regulation of transforming growth factor-ß1. In addition, ligand-activated PPARδ also increased the expression of tissue inhibitor of metalloproteinase (TIMP)-2 and TIMP-3, while it strongly suppressed that of matrix metalloproteinase-2. CONCLUSIONS: PPARδ attenuates Ang II-induced AAA formation by regulating ECM homeostasis and inflammatory responses, suggesting a novel strategy for the treatment of AAA.

PPARδ inhibits UVB-induced secretion of MMP-1 through MKP-7-mediated suppression of JNK signaling.

In the present study, we investigated the role of peroxisome proliferator-activated receptor (PPAR) δ in modulating matrix-degrading metalloproteinases and other mechanisms underlying photoaging processes in the skin. In human dermal fibroblasts (HDFs), activation of PPARδ by its specific ligand GW501516 markedly attenuated UVB-induced secretion of matrix metalloproteinase (MMP)-1, concomitant with decreased generation of reactive oxygen species. These effects were significantly reduced in the presence of PPARδ small interfering RNA and GSK0660. Furthermore, c-Jun N-terminal kinase (JNK), but not p38 or extracellular signal-regulated kinase, mediated PPARδ-dependent inhibition of MMP-1 secretion in HDFs exposed to UVB. PPARδ-mediated messenger RNA stabilization of mitogen-activated protein kinase phosphatase (MKP)-7 was responsible for the GW501516-mediated inhibition of JNK signaling. Inhibition of UVB-induced secretion of MMP-1 by PPARδ was associated with the restoration of types I and III collagen to levels approaching those in cells not exposed to UVB. Finally, in HR-1 hairless mice exposed to UVB, administration of GW501516 significantly reduced wrinkle formation and skin thickness, downregulated MMP-1 and JNK phosphorylation, and restored the levels of MKP-7, types I and III collagen. These results suggest that PPARδ-mediated inhibition of MMP-1 secretion prevents some effects of photoaging and maintains the integrity of skin by inhibiting the degradation of the collagenous extracellular matrix.