Deficiency in fibroblast PPARß/δ reduces nonmelanoma skin cancers in mice.

The incidence of nonmelanoma skin cancer (NMSC) has been increasing worldwide. Most studies have highlighted the importance of cancer-associated fibroblasts (CAFs) in NMSC progression. However much less is known about the communication between normal fibroblasts and epithelia; disruption of this communication affects tumor initiation and the latency period in the emergence of tumors. Delineating the mechanism that mediates this epithelial-mesenchymal communication in NMSC could identify more effective targeted therapies. The nuclear receptor PPARß/δ in fibroblasts has been shown to modulate adjacent epithelial cell behavior, however, its role in skin tumorigenesis remains unknown. Using chemically induced skin carcinogenesis, we showed that FSPCre-Pparb/dex4 mice, whose Pparb/d gene was selectively deleted in fibroblasts, had delayed emergence and reduced tumor burden compared with control mice (Pparb/dfl/fl). However, FSPCre-Pparb/dex4-derived tumors showed increased proliferation, with no difference in differentiation, suggesting delayed tumor initiation. Network analysis revealed a link between dermal Pparb/d and TGF-ß1 with epidermal NRF2 and Nox4. In vitro investigations showed that PPARß/δ deficiency in fibroblasts increased epidermal Nox4-derived H2O2 production, which triggered an NRF2-mediated antioxidant response. We further showed that H2O2 upregulated NRF2 mRNA via the B-Raf-MEK1/2 pathway. The enhanced NRF2 response altered the activities of PTEN, Src, and AKT. In vivo, we detected the differential phosphorylation profiles of B-Raf, MEK1/2, PTEN, Src, and AKT in the vehicle-treated and chemically treated epidermis of FSPCre-Pparb/dex4 mice compared with that in Pparb/dfl/fl mice, prior to the first appearance of tumors in Pparb/dfl/fl. Our study revealed a role for fibroblast PPARß/δ in the epithelial-mesenchymal communication involved in cellular redox homeostasis.

Collaborative Regulation of LRG1 by TGF-ß1 and PPAR-ß/δ Modulates Chronic Pressure Overload-Induced Cardiac Fibrosis.

BACKGROUND: Despite its established significance in fibrotic cardiac remodeling, clinical benefits of global inhibition of TGF (transforming growth factor)-ß1 signaling remain controversial. LRG1 (leucine-rich-α2 glycoprotein 1) is known to regulate endothelial TGFß signaling. This study evaluated the role of LRG1 in cardiac fibrosis and its transcriptional regulatory network in cardiac fibroblasts. METHODS: Pressure overload-induced heart failure was established by transverse aortic constriction. Western blot, quantitative reverse transcription polymerase chain reaction, immunofluorescence, and immunohistochemistry were used to evaluate the expression level and pattern of interested targets or pathology during fibrotic cardiac remodeling. Cardiac function was assessed by pressure-volume loop analysis. RESULTS: LRG1 expression was significantly suppressed in left ventricle of mice with transverse aortic constriction-induced fibrotic cardiac remodeling (mean difference, -0.00085 [95% CI, -0.0013 to -0.00043]; P=0.005) and of patients with end-stage ischemic-dilated cardiomyopathy (mean difference, 0.13 [95% CI, 0.012-0.25]; P=0.032). More profound cardiac fibrosis (mean difference, -0.014% [95% CI, -0.029% to -0.00012%]; P=0.048 for interstitial fibrosis; mean difference, -1.3 [95% CI, -2.5 to -0.2]; P=0.016 for perivascular fibrosis), worse cardiac dysfunction (mean difference, -2.5 ms [95% CI, -4.5 to -0.4 ms]; P=0.016 for Tau-g; mean difference, 13% [95% CI, 2%-24%]; P=0.016 for ejection fraction), and hyperactive TGFß signaling in transverse aortic constriction-operated Lrg1-deficient mice (mean difference, -0.27 [95% CI, -0.47 to -0.07]; P<0.001), which could be reversed by cardiac-specific Lrg1 delivery mediated by adeno-associated virus 9. Mechanistically, LRG1 inhibits cardiac fibroblast activation by competing with TGFß1 for receptor binding, while PPAR (peroxisome proliferator-activated receptor)-ß/δ and TGFß1 collaboratively regulate LRG1 expression via SMRT (silencing mediator for retinoid and thyroid hormone receptor). We further demonstrated functional interactions between LRG1 and PPARß/δ in cardiac fibroblast activation. CONCLUSIONS: Our results established a highly complex molecular network involving LRG1, TGFß1, PPARß/δ, and SMRT in regulating cardiac fibroblast activation and cardiac fibrosis. Targeting LRG1 or PPARß/δ represents a promising strategy to control pathological cardiac remodeling in response to chronic pressure overload.

Heme-Regulated eIF2α Kinase Modulates Hepatic FGF21 and Is Activated by PPARß/δ Deficiency.

Fibroblast growth factor 21 (FGF21), a peptide hormone with pleiotropic effects on carbohydrate and lipid metabolism, is considered a target for the treatment of diabetes. We investigated the role of peroxisome proliferator-activated receptor (PPAR) ß/δ deficiency in hepatic FGF21 regulation. Increased Fgf21 expression was observed in the livers of PPARß/δ-null mice and in mouse primary hepatocytes when this receptor was knocked down by small interfering RNA (siRNA). Increased Fgf21 was associated with enhanced protein levels in the heme-regulated eukaryotic translation initiation factor 2α (eIF2α) kinase (HRI). This increase caused enhanced levels of phosphorylated eIF2α and activating transcription factor (ATF) 4, which is essential for Fgf21-induced expression. siRNA analysis demonstrated that HRI regulates Fgf21 expression in primary hepatocytes. Enhanced Fgf21 expression attenuated tunicamycin-induced endoplasmic reticulum stress, as demonstrated by using a neutralizing antibody against FGF21. Of note, increased Fgf21 expression in mice fed a high-fat diet or hepatocytes exposed to palmitate was accompanied by reduced PPARß/δ and activation of the HRI-eIF2α-ATF4 pathway. Moreover, pharmacological activation of HRI increased Fgf21 expression and reduced lipid-induced hepatic steatosis and glucose intolerance, but these effects were not observed in Fgf21-null mice. Overall, these findings suggest that HRI is a potential target for regulating hepatic FGF21 levels.

Endothelial, but not smooth muscle, peroxisome proliferator-activated receptor ß/δ regulates vascular permeability and anaphylaxis.

BACKGROUND: Remodeling of quiescent vessels with increases in permeability, vasodilatation, and edema are hallmarks of inflammatory disorders. Factors involved in this type of remodeling represent potential therapeutic targets. OBJECTIVES: We investigated whether the nuclear hormone receptor peroxisome proliferator-activated receptor (PPAR) ß/δ, a regulator of metabolism, fibrosis, and skin homeostasis, is involved in regulation of this type of remodeling. METHODS: Wild-type and various Pparb/d mutant mice were used to monitor dermal acute vascular hyperpermeability (AVH) and passive systemic anaphylaxis-induced hypothermia and edema. PPARß/δ-dependent kinase activation and remodeling of endothelial cell-cell junctions were addressed by using human endothelial cells. RESULTS: AVH and dilatation of dermal microvessels stimulated by vascular endothelial growth factor A, histamine, and thrombin are severely compromised in PPARß/δ-deficient mice. Selective deletion of the Pparb/d-encoding gene in endothelial cells in vivo similarly limits dermal AVH and vasodilatation, providing evidence that endothelial PPARß/δ is the major player in regulating acute dermal microvessel remodeling. Furthermore, endothelial PPARß/δ regulatory functions are not restricted to the skin vasculature because its deletion in the endothelium, but not in smooth muscle cells, also leads to reduced systemic anaphylaxis, the most severe form of allergic reaction, in which an acute vascular response plays a key role. PPARß/δ-dependent AVH activation likely involves the activation of mitogen-activated protein kinase and Akt pathways and leads to downstream destabilization of endothelial cell-cell junctions. CONCLUSION: These results unveil not only a novel function of PPARß/δ as a direct regulator of acute vessel permeability and dilatation but also provide evidence that antagonizing PPARß/δ represents an important strategy to consider for moderating diseases with altered endothelial integrity, such as acute inflammatory and allergic disorders.

PPARß/δ prevents endoplasmic reticulum stress-associated inflammation and insulin resistance in skeletal muscle cells through an AMPK-dependent mechanism.

AIM/HYPOTHESIS: Endoplasmic reticulum (ER) stress, which is involved in the link between inflammation and insulin resistance, contributes to the development of type 2 diabetes mellitus. In this study, we assessed whether peroxisome proliferator-activated receptor (PPAR)ß/δ prevented ER stress-associated inflammation and insulin resistance in skeletal muscle cells. METHODS: Studies were conducted in mouse C2C12 myotubes, in the human myogenic cell line LHCN-M2 and in skeletal muscle from wild-type and PPARß/δ-deficient mice and mice exposed to a high-fat diet. RESULTS: The PPARß/δ agonist GW501516 prevented lipid-induced ER stress in mouse and human myotubes and in skeletal muscle of mice fed a high-fat diet. PPARß/δ activation also prevented thapsigargin- and tunicamycin-induced ER stress in human and murine skeletal muscle cells. In agreement with this, PPARß/δ activation prevented ER stress-associated inflammation and insulin resistance, and glucose-intolerant PPARß/δ-deficient mice showed increased phosphorylated levels of inositol-requiring 1 transmembrane kinase/endonuclease-1α in skeletal muscle. Our findings demonstrate that PPARß/δ activation prevents ER stress through the activation of AMP-activated protein kinase (AMPK), and the subsequent inhibition of extracellular-signal-regulated kinase (ERK)1/2 due to the inhibitory crosstalk between AMPK and ERK1/2, since overexpression of a dominant negative AMPK construct (K45R) reversed the effects attained by PPARß/δ activation. CONCLUSIONS/INTERPRETATION: Overall, these findings indicate that PPARß/δ prevents ER stress, inflammation and insulin resistance in skeletal muscle cells by activating AMPK.

The nuclear receptor peroxisome proliferator-activated receptor-ß/δ (PPARß/δ) promotes oncogene-induced cellular senescence through repression of endoplasmic reticulum stress.

Endoplasmic reticulum (ER) stress and ER stress-associated unfolded protein response (UPR) can promote cancer cell survival, but it remains unclear whether they can influence oncogene-induced senescence. The present study examined the role of ER stress in senescence using oncogene-dependent models. Increased ER stress attenuated senescence in part by up-regulating phosphorylated protein kinase B (p-AKT) and decreasing phosphorylated extracellular signal-regulated kinase (p-ERK). A positive feed forward loop between p-AKT, ER stress, and UPR was discovered whereby a transient increase of ER stress caused reduced senescence and promotion of tumorigenesis. Decreased ER stress was further correlated with increased senescence in both mouse and human tumors. Interestingly, H-RAS-expressing Pparß/δ null cells and tumors having increased cell proliferation exhibited enhanced ER stress, decreased cellular senescence, and/or enhanced tumorigenicity. Collectively, these results demonstrate a new role for ER stress and UPR that attenuates H-RAS-induced senescence and suggest that PPARß/δ can repress this oncogene-induced ER stress to promote senescence in accordance with its role as a tumor modifier that suppresses carcinogenesis.

PPARß interprets a chromatin signature of pluripotency to promote embryonic differentiation at gastrulation.

Epigenetic post-transcriptional modifications of histone tails are thought to help in coordinating gene expression during development. An epigenetic signature is set in pluripotent cells and interpreted later at the onset of differentiation. In pluripotent cells, epigenetic marks normally associated with active genes (H3K4me3) and with silent genes (H3K27me3) atypically co-occupy chromatin regions surrounding the promoters of important developmental genes. However, it is unclear how these epigenetic marks are recognized when cell differentiation starts and what precise role they play. Here, we report the essential role of the nuclear receptor peroxisome proliferator-activated receptor ß (PPARß, NR1C2) in Xenopus laevis early development. By combining loss-of-function approaches, large throughput transcript expression analysis by the mean of RNA-seq and intensive chromatin immunoprecipitation experiments, we unveil an important cooperation between epigenetic marks and PPARß. During Xenopus laevis gastrulation PPARß recognizes H3K27me3 marks that have been deposited earlier at the pluripotent stage to activate early differentiation genes. Thus, PPARßis the first identified transcription factor that interprets an epigenetic signature of pluripotency, in vivo, during embryonic development. This work paves the way for a better mechanistic understanding of how the activation of hundreds of genes is coordinated during early development.

Tau hyperphosphorylation and increased BACE1 and RAGE levels in the cortex of PPARß/δ-null mice.

The role of peroxisome proliferator activator receptor (PPAR)ß/δ in the pathogenesis of Alzheimer's disease has only recently been explored through the use of PPARß/δ agonists. Here we evaluated the effects of PPARß/δ deficiency on the amyloidogenic pathway and tau hyperphosphorylation. PPARß/δ-null mice showed cognitive impairment in the object recognition task, accompanied by enhanced DNA-binding activity of NF-κB in the cortex and increased expression of IL-6. In addition, two NF-κB-target genes involved in ß-amyloid (Aß) synthesis and deposition, the ß site APP cleaving enzyme 1 (Bace1) and the receptor for advanced glycation endproducts (Rage), respectively, increased in PPARß/δ-null mice compared to wild type animals. The protein levels of glial fibrillary acidic protein (GFAP) increased in the cortex of PPARß/δ-null mice, which would suggest the presence of astrogliosis. Finally, tau hyperphosphorylation at Ser199 and enhanced levels of PHF-tau were associated with increased levels of the tau kinases CDK5 and phospho-ERK1/2 in the cortex of PPARß/δ(-/-) mice. Collectively, our findings indicate that PPARß/δ deficiency results in cognitive impairment associated with enhanced inflammation, astrogliosis and tau hyperphosphorylation in the cortex.

Role of PPARbeta in fibroblast response to heat injury.

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear hormone receptor family of ligand-inducible transcription factors. Our previous study has shown that in human umbilical vein endothelial cells PPARbeta initiates a protective mechanism that limits the extent of damage due to H2O2-induced injury. Although fibroblasts are one of the main cell types involved in wound repair, the role of PPARbeta in the fibroblast response to heat injury has not been investigated. Thus, in this study, we examined possible protective role of PPARbeta in fibroblasts from heat injury. We developed a novel dermal fibroblast heat injury model to characterize the mechanisms of the heat injury healing response that involved PPARbeta. The specific PPARbeta ligand GW0742, a PPARbeta activator and a short hairpin RNA (shRNA) plasmid against PPARbeta were used to reveal the action mechanism of PPARbeta in heat injury-induced fibroblast changes in morphology and increased proliferation. In response to heat injury (52 degrees C for 30 s), fibroblast activation of PPARbeta increased 1.56-fold. Administration of GW0742 significantly induced a protective effect on heat injury-induced fibroblasts by minimizing the structural damage and increasing the cell proliferation response. Likewise, inhibition of PPARbeta using shRNA exacerbated the damage by inhibiting the de novo synthesis of PPARbeta. These results indicated that heat injury enhanced PPARbeta expression and PPARbeta protected fibroblast structure and proliferation.

Induction of cardiac Angptl4 by dietary fatty acids is mediated by peroxisome proliferator-activated receptor beta/delta and protects against fatty acid-induced oxidative stress.

RATIONALE: Although dietary fatty acids are a major fuel for the heart, little is known about the direct effects of dietary fatty acids on gene regulation in the intact heart. OBJECTIVE: To study the effect of dietary fatty acids on cardiac gene expression and explore the functional consequences. METHODS AND RESULTS: Oral administration of synthetic triglycerides composed of one single fatty acid altered cardiac expression of numerous genes, many of which are involved in the oxidative stress response. The gene most significantly and consistently upregulated by dietary fatty acids encoded Angiopoietin-like protein (Angptl)4, a circulating inhibitor of lipoprotein lipase expressed by cardiomyocytes. Induction of Angptl4 by the fatty acid linolenic acid was specifically abolished in peroxisome proliferator-activated receptor (PPAR)beta/delta(-/-) and not PPARalpha(-/-) mice and was blunted on siRNA-mediated PPARbeta/delta knockdown in cultured cardiomyocytes. Consistent with these data, linolenic acid stimulated binding of PPARbeta/delta but not PPARalpha to the Angptl4 gene. Upregulation of Angptl4 resulted in decreased cardiac uptake of plasma triglyceride-derived fatty acids and decreased fatty acid-induced oxidative stress and lipid peroxidation. In contrast, Angptl4 deletion led to enhanced oxidative stress in the heart, both after an acute oral fat load and after prolonged high fat feeding. CONCLUSIONS: Stimulation of cardiac Angptl4 gene expression by dietary fatty acids and via PPARbeta/delta is part of a feedback mechanism aimed at protecting the heart against lipid overload and consequently fatty acid-induced oxidative stress.

Transcriptional profiling reveals divergent roles of PPARalpha and PPARbeta/delta in regulation of gene expression in mouse liver.

Little is known about the role of the transcription factor peroxisome proliferator-activated receptor (PPAR) beta/delta in liver. Here we set out to better elucidate the function of PPARbeta/delta in liver by comparing the effect of PPARalpha and PPARbeta/delta deletion using whole genome transcriptional profiling and analysis of plasma and liver metabolites. In fed state, the number of genes altered by PPARalpha and PPARbeta/delta deletion was similar, whereas in fasted state the effect of PPARalpha deletion was much more pronounced, consistent with the pattern of gene expression of PPARalpha and PPARbeta/delta. Minor overlap was found between PPARalpha- and PPARbeta/delta-dependent gene regulation in liver. Pathways upregulated by PPARbeta/delta deletion were connected to innate immunity and inflammation. Pathways downregulated by PPARbeta/delta deletion included lipoprotein metabolism and various pathways related to glucose utilization, which correlated with elevated plasma glucose and triglycerides and reduced plasma cholesterol in PPARbeta/delta-/- mice. Downregulated genes that may underlie these metabolic alterations included Pklr, Fbp1, Apoa4, Vldlr, Lipg, and Pcsk9, which may represent novel PPARbeta/delta target genes. In contrast to PPARalpha-/- mice, no changes in plasma free fatty acid, plasma beta-hydroxybutyrate, liver triglycerides, and liver glycogen were observed in PPARbeta/delta-/- mice. Our data indicate that PPARbeta/delta governs glucose utilization and lipoprotein metabolism and has an important anti-inflammatory role in liver. Overall, our analysis reveals divergent roles of PPARalpha and PPARbeta/delta in regulation of gene expression in mouse liver.

Ligand activation of peroxisome proliferator-activated receptor-beta/delta and inhibition of cyclooxygenase-2 enhances inhibition of skin tumorigenesis.

Ligand activation of peroxisome proliferator-activated receptor (PPAR)-beta/delta and inhibition of cyclooxygenase-2 (COX-2) activity by nonsteroidal anti-inflammatory drugs can attenuate skin tumorigenesis. There is also evidence that attenuation of skin tumorigenesis by inhibition of COX-2 activity occurs through PPARbeta/delta-independent mechanisms. The present study examined the hypothesis that combining ligand activation of PPARbeta/delta with inhibition of COX-2 activity will cooperatively inhibit chemically induced skin tumor progression using both in vivo and ex vivo models. A two-stage chemical carcinogenesis bioassay was performed in wild-type and Pparbeta/delta-null mice. After 22 weeks, cohorts of both mouse lines were divided into four experimental groups: (1) control, (2) topical application of the PPARbeta/delta ligand GW0742, (3) dietary administration of the COX-2 inhibitor nimesulide, or (4) both GW0742 and nimesulide. Ligand activation of PPARbeta/delta did not influence skin tumor progression, while a modest decrease in skin tumor multiplicity was observed with dietary nimesulide. Interestingly, the combined treatment of GW0742 and nimesulide increased the efficacy of the decrease in papilloma multiplicity for 6 weeks in wild-type mice, but this effect was not found at later time points and was not found in similarly treated Pparbeta/delta-null mice. Neoplastic keratinocyte lines cultured with GW0742 and nimesulide also exhibited enhanced inhibition of cell proliferation coincident with increased expression of Keratin messenger RNAs. Results from these studies support the hypothesis that combining ligand activation of PPARbeta/delta with inhibition of COX-2 activity can inhibit chemically induced skin tumor progression by modulating differentiation.

Regulation of epithelial-mesenchymal IL-1 signaling by PPARbeta/delta is essential for skin homeostasis and wound healing.

Skin morphogenesis, maintenance, and healing after wounding require complex epithelial-mesenchymal interactions. In this study, we show that for skin homeostasis, interleukin-1 (IL-1) produced by keratinocytes activates peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) expression in underlying fibroblasts, which in turn inhibits the mitotic activity of keratinocytes via inhibition of the IL-1 signaling pathway. In fact, PPARbeta/delta stimulates production of the secreted IL-1 receptor antagonist, which leads to an autocrine decrease in IL-1 signaling pathways and consequently decreases production of secreted mitogenic factors by the fibroblasts. This fibroblast PPARbeta/delta regulation of the IL-1 signaling is required for proper wound healing and can regulate tumor as well as normal human keratinocyte cell proliferation. Together, these findings provide evidence for a novel homeostatic control of keratinocyte proliferation and differentiation mediated via PPARbeta/delta regulation in dermal fibroblasts of IL-1 signaling. Given the ubiquitous expression of PPARbeta/delta, other epithelial-mesenchymal interactions may also be regulated in a similar manner.

Peroxisome proliferator-activated receptor-beta/delta protects against chemically induced liver toxicity in mice.

UNLABELLED: Potential functional roles for the peroxisome proliferator-activated receptor-beta/delta (PPARbeta/delta) in skeletal muscle fatty acid catabolism and epithelial carcinogenesis have recently been described. Whereas PPARbeta/delta is expressed in liver, its function in this tissue is less clear. To determine the role of PPARbeta/delta in chemically induced liver toxicity, wild-type and PPARbeta/delta-null mice were treated with azoxymethane (AOM) and markers of liver toxicity examined. Bile duct hyperplasia, regenerative hyperplasia, and increased serum alanine aminotransferase (ALT) were found in AOM-treated PPARbeta/delta-null mice, and these effects were not observed in similarly treated wild-type mice. Exacerbated carbon tetrachloride (CCl(4)) hepatoxicity was also observed in PPARbeta/delta-null as compared with wild-type mice. No differences in messenger RNAs (mRNAs) encoding cytochrome2E1 required for the metabolic activation of AOM and CCl(4) were observed between wild-type or PPARbeta/delta-null mice in response to CCl(4). Significant differences in the expression of genes reflecting enhanced nuclear factor kappa B (NF-kappaB) activity were noted in PPARbeta/delta-null mice. CONCLUSION: Results from these studies show that PPARbeta/delta is protective against liver toxicity induced by AOM and CCl(4), suggesting that this receptor is hepatoprotective against environmental chemicals that are metabolized in this tissue.

MRI monitoring of focal cerebral ischemia in peroxisome proliferator-activated receptor (PPAR)-deficient mice.

Peroxisome proliferator-activated receptors (PPARs) are a potential target for neuroprotection in focal ischemic stroke. These nuclear receptors have major effects in lipid metabolism, but they are also involved in inflammatory processes. Three PPAR isotypes have been identified: alpha, beta (or delta) and gamma. The development of PPAR transgenic mice offers a promising tool for prospective therapeutic studies. This study used MRI to assess the role of PPARalpha and PPARbeta in the development of stroke. Permanent middle cerebral artery occlusion induced focal ischemia in wild-type, PPARalpha-null mice and PPARbeta-null mice. T(2)-weighted MRI was performed with a 7 T MRI scan on day 0, 1, 3, 7 and 14 to monitor lesion growth in the various genotypes. General Linear Model statistical analysis found a significant difference in lesion volume between wild-type and PPAR-null mice for both alpha and beta isotypes. These data validate high-resolution MRI for monitoring cerebral ischemic lesions, and confirm the neuroprotective role of PPARalpha and PPARbeta in the brain.

Ligand activation of peroxisome proliferator-activated receptor beta inhibits colon carcinogenesis.

There is considerable debate whether peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) ligands potentiate or suppress colon carcinogenesis. Whereas administration of a PPARbeta ligand causes increased small intestinal tumorigenesis in Apc(min/+) mice, PPARbeta-null (Pparb-/-) mice exhibit increased colon polyp multiplicity in colon cancer bioassays, suggesting that ligand activation of this receptor will inhibit colon carcinogenesis. This hypothesis was examined by treating wild-type (Pparb+/+) and Pparb-/- with azoxymethane, coupled with a highly specific PPARbeta ligand, GW0742. Ligand activation of PPARbeta in Pparb+/+ mice caused an increase in the expression of mRNA encoding adipocyte differentiation-related protein, fatty acid-binding protein, and cathepsin E. These findings are indicative of colonocyte differentiation, which was confirmed by immunohistochemical analysis. No PPARbeta-dependent differences in replicative DNA synthesis or expression of phosphatase and tensin homologue, phosphoinositide-dependent kinase, integrin-linked kinase, or phospho-Akt were detected in ligand-treated mouse colonic epithelial cells although increased apoptosis was found in GW0742-treated Pparb+/+ mice. Consistent with increased colonocyte differentiation and apoptosis, inhibition of colon polyp multiplicity was also found in ligand-treated Pparb+/+ mice, and all of these effects were not found in Pparb-/- mice. In contrast to previous reports suggesting that activation of PPARbeta potentiates intestinal tumorigenesis, here we show that ligand activation of PPARbeta attenuates chemically induced colon carcinogenesis and that PPARbeta-dependent induction of cathepsin E could explain the reported disparity in the literature about the effect of ligand activation of PPARbeta in the intestine.

PPARbeta/delta selectively induces differentiation and inhibits cell proliferation.

Peroxisome proliferator-activated receptor (PPAR) beta-null mice exhibit exacerbated epithelial cell proliferation and enhanced sensitivity to skin carcinogenesis, suggesting that ligand activation of PPARbeta will inhibit keratinocyte proliferation. By using of a highly specific ligand (GW0742) and the PPARbeta-null mouse model, activation of PPARbeta was found to selectively induce keratinocyte terminal differentiation and inhibit keratinocyte proliferation. Additionally, GW0742 was found to be anti-inflammatory due to inhibition of myeloperoxidase activity, independent of PPARbeta. These data suggest that ligand activation of PPARbeta could be a novel approach to selectively induce differentiation and inhibit cell proliferation, thus representing a new molecular target for the treatment of skin disorders resulting from altered cell proliferation such as psoriasis and cancer.

Increased infarct size and lack of hyperphagic response after focal cerebral ischemia in peroxisome proliferator-activated receptor beta-deficient mice.

Peroxisome proliferator-activated receptors (PPARs) are involved in energy expenditure, regulation of inflammatory processes, and cellular protection in peripheral tissues. Among the different types of PPARs, PPARbeta is the only one to be widely expressed in cortical neurons. Using PPARbeta knockout (KO) mice, we report here a detailed investigation of the role of PPARbeta in cerebral ischemic damage, associated inflammatory and antioxidant processes as well as food intake regulation after middle cerebral artery occlusion (MCAO). The PPARbeta KO mice had a two-fold increase in infarct size compared with wild-type (WT) mice. Brain oxidative stress was dramatically enhanced in these KO mice, as documented by an increased content of malondialdehyde, decreased levels of glutathione and manganese superoxide dismutase, and no induction of uncoupling protein 2 (UCP2) mRNA. Unlike WT mice, PPARbeta KO mice showed a marked increase of prooxidant interferon-gamma but no induction of nerve growth factor and tumor necrosis factor alpha after MCAO. In WT mice, MCAO resulted in inflammation-specific transient hyperphagia from day 3 to day 5 after ischemia, which was associated with an increase in neuropeptide Y (NPY) mRNA. This hyperphagic phase and NPY mRNA induction were not observed in PPARbeta KO mice. Furthermore, our study also suggests for the first time that UCP2 is involved in MCAO food intake response. These data indicate that PPARbeta plays an important role in integrating and regulating central inflammation, antioxidant mechanisms, and food intake after MCAO, and suggest that the use of PPARbeta agonists may be of interest for the prevention of central ischemic damage.

Genetic- or transforming growth factor-beta 1-induced changes in epidermal peroxisome proliferator-activated receptor beta/delta expression dictate wound repair kinetics.

Advances in wound care are of great importance in clinical injury management. In this respect, the nuclear receptor peroxisome proliferator-activated receptor (PPAR)beta/delta occupies a unique position at the intersection of diverse inflammatory or anti-inflammatory signals that influence wound repair. This study shows how changes in PPARbeta/delta expression have a profound effect on wound healing. Using two different in vivo models based on topical application of recombinant transforming growth factor (TGF)-beta1 and ablation of the Smad3 gene, we show that prolonged expression and activity of PPARbeta/delta accelerate wound closure. The results reveal a dual role of TGF-beta1 as a chemoattractant of inflammatory cells and repressor of inflammation-induced PPARbeta/delta expression. Also, they provide insight into the so far reported paradoxical effects of the application of exogenous TGF-beta1 at wound sites.

Peroxisome proliferator-activated receptor-beta/delta inhibits epidermal cell proliferation by down-regulation of kinase activity.

Recent work has shown that peroxisome proliferator-activated receptor beta (PPARbeta) attenuates cell proliferation and skin carcinogenesis, and this is due in part to regulation of ubiquitin C expression. In these studies, the role of PPARbeta in modulating ubiquitin-dependent protein kinase Calpha (PKCalpha) levels and phosphorylation signaling pathways was evaluated. Intracellular phosphorylation analysis showed that phosphorylated PKCalpha and other kinases were lower in wild-type mouse skin treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) as compared with PPARbeta-null mouse skin. No differences in expression levels of other PKC isoforms present in skin were observed. Lower ubiquitination of PKCalpha was found in TPA-treated PPARbeta-null skin as compared with wild-type, and inhibition of ubiquitin-dependent proteasome degradation prevented TPA-induced down-regulation of PKCalpha. The activity of PKCalpha and downstream signaling kinases is enhanced, and expression of cyclooxygenase-2 (COX-2) is significantly greater, in PPARbeta-null mouse skin in response to TPA compared with wild-type mouse skin. Inhibition of PKCalpha or COX-2 reduced cell proliferation in TPA-treated PPARbeta-null keratinocytes in a dose-dependent manner, whereas it only slightly influenced cell proliferation in wild-type keratinocytes. Combined, these studies provide strong evidence that PPARbeta attenuates cell proliferation by modulating PKCalpha/Raf1/MEK/ERK activity that may be due in part to reduced ubiquitin-dependent turnover of PKCalpha.