In mammalian cells, two cellular organelles, mitochondria and peroxisomes, share the ability to degrade fatty acid chains. Although each organelle harbors its own fatty acid β-oxidation pathway, a distinct mitochondrial system feeds the oxidative phosphorylation pathway for ATP synthesis. At the same time, the peroxisomal β-oxidation pathway participates in cellular thermogenesis. A scientific milestone in 1965 helped discover the hepatomegaly effect in rat liver by clofibrate, subsequently identified as a peroxisome proliferator in rodents and an activator of the peroxisomal fatty acid β-oxidation pathway. These peroxisome proliferators were later identified as activating ligands of Peroxisome Proliferator-Activated Receptor α (PPARα), cloned in 1990. The ligand-activated heterodimer PPARα/RXRα recognizes a DNA sequence, called PPRE (Peroxisome Proliferator Response Element), corresponding to two half-consensus hexanucleotide motifs, AGGTCA, separated by one nucleotide. Accordingly, the assembled complex containing PPRE/PPARα/RXRα/ligands/Coregulators controls the expression of the genes involved in liver peroxisomal fatty acid β-oxidation. This review mobilizes a considerable number of findings that discuss miscellaneous axes, covering the detailed expression pattern of PPARα in species and tissues, the lessons from several PPARα KO mouse models and the modulation of PPARα function by dietary micronutrients.

The peroxisome proliferator activated receptor gamma (PPARG) nuclear receptor regulates energy metabolism and insulin sensitivity. In this study, we present novel evidence for an essential role of PPARG in the regulation of osteocyte function, and support for the emerging concept of the conjunction between regulation of energy metabolism and bone mass. We report that PPARG is essential for sclerostin production, a recently approved target to treat osteoporosis. Our mouse model of osteocyte-specific PPARG deletion (Dmp1CrePparγflfl or γOTKO) is characterized with increased bone mass and reduced bone marrow adiposity, which is consistent with upregulation of WNT signaling and increased bone forming activity of endosteal osteoblasts. An analysis of osteocytes derived from γOTKO and control mice showed an excellent correlation between PPARG and SOST/sclerostin at the transcript and protein levels. The 8 kb sequence upstream of Sost gene transcription start site possesses multiple PPARG binding elements (PPREs) with at least two of them binding PPARG with dynamics reflecting its activation with full agonist rosiglitazone and correlating with increased levels of Sost transcript and sclerostin protein expression (Pearson\'s r = 0.991, p = 0.001). Older γOTKO female mice are largely protected from TZD-induced bone loss providing proof of concept that PPARG in osteocytes can be pharmacologically targeted. These findings demonstrate that transcriptional activities of PPARG are essential for sclerostin expression in osteocytes and support consideration of targeting PPARG activities with selective modulators to treat osteoporosis.

Human cytochrome P450 1B1 (CYP1B1)-mediated biotransformation of endobiotics and xenobiotics plays an important role in the progression of human breast cancer. In this study, we investigated the effects of WY-14643, a peroxisome proliferator-activated receptor α (PPARα) agonist, on CYP1B1 expression and the related mechanism in MCF7 breast cancer cells. We performed quantitative reverse transcription-polymerase chain reaction, transient transfection, and chromatin immunoprecipitation to evaluate the effects of PPARα on peroxisome proliferator response element (PPRE)-mediated transcription. WY-14643 increased the protein and mRNA levels of CYP1B1, as well as promoter activity, in MCF-7 cells. Moreover, WY-14643 plus GW6471, a PPARα antagonist, significantly inhibited the WY-14643-mediated increase in CYP1B1 expression. PPARα knockdown by a small interfering RNA markedly suppressed the induction of CYP1B1 expression by WY-14643, suggesting that WY-14643 induces CYP1B1 expression via a PPARα-dependent mechanism. Bioinformatics analysis identified putative PPREs (-833/-813) within the promoter region of the CYP1B1 gene. Inactivation of these putative PPREs by deletion mutagenesis suppressed the WY-14643-mediated induction of CYP1B1 promoter activation. Furthermore, WY-14643 induced PPARα to assume a form capable of binding specifically to the PPRE-binding site in the CYP1B1 promoter. Our findings suggest that WY-14643 induces the expression of CYP1B1 through activation of PPARα.

Tanshinone Ⅱ_A( Tan Ⅱ_A),the liposoluble constituents of Salvia miltiorrhiza,can not only ameliorate the lipidic metabolism and decrease the concentration of lipid peroxidation,but also resist oxidation damage,scavenge free radicals and control inflammation,with a protective effect on prognosis after liver function impairment. Therefore,the studies on the exact mechanism of Tan Ⅱ_A in protecting the liver can provide important theoretical and experimental basis for the prevention and treatment effect of Tan Ⅱ_A for liver injury. In the present study,the protective effects and mechanism of Tan Ⅱ_A on 4-hydroxynonenal( 4-HNE)-induced liver injury were investigated in vitro. Normal liver tissues NCTC 1469 cells were used to induce hepatocytes oxidative damages by 4-HNE treatment. The protective effect of Tan Ⅱ_A on hepatocytes oxidative damages was detected by release amount of lactate dehydrogenase( LDH) analysis and hoechst staining. The protein expression changes of peroxisome proliferator-activated receptor α( PPARα) and peroxisome proliferator response element( PPRE) were analyzed by Western blot analysis in NCTC 1469 cells before and after Tan Ⅱ_A treatment. The gene expression changes of fatty aldehyde dehydrogenase( FALDH) were analyzed by Real-time polymerase chain reaction( PCR) analysis. The results showed that 4-HNE increased the release amount of LDH,lowered the cell viability of NCTC 1469 cells,and Tan Ⅱ_A reversed 4-HNE-induced hepatocyte damage. Western blot analysis and RT-PCR analysis results showed that 4-HNE decreased the expression of PPARα and FALDH and increased the expression of 4-HNE. However,the expression of PPARα and FALDH were increased significantly and the expression of 4-HNE was decreased obviously after Tan Ⅱ_A treatment. This study confirmed that the curative effect of Tan Ⅱ_A was obvious on hepatocytes damage,and the mechanism may be associated with activating PPARα and FALDH expression as well as scavenging 4-HNE.

Obesity is a major public health problem in developed countries resulting from increased food intake and decreased energy consumption and usually associated with abnormal lipid metabolism. Here, we show that DEC1, a basic helix-loop-helix transcription factor, plays an important role in the regulation of lipid consumption in mouse brown adipose tissue (BAT), which is the major site of thermogenesis. Homozygous Dec1 deletion attenuated high-fat-diet-induced obesity, adipocyte hypertrophy, fat volume and hepatic steatosis. Furthermore, DEC1 deficiency increased body temperature during daytime and enhanced the expression of uncoupler protein 1, a key factor of thermogenesis, and various lipolysis-related genes in interscapular BAT. In vitro experiments suggested that DEC1 suppresses the expression of various lipolysis-related genes induced by the heterodimer of peroxisome proliferator-activated receptor γ and retinoid X receptor α (RXRα) through direct binding to RXRα. These observations suggest that enhanced lipolysis in BAT caused by DEC1 deficiency leads to an increase in lipid consumption, thereby decreasing lipid accumulation in adipose tissues and the liver. Thus, DEC1 may serve as an energy-saving factor that suppresses lipid consumption, which may be relevant to managing obesity.

Stromal Derived Factor-1α (SDF-1α) and its cognate receptor CXCR4 play a key role in mediating breast cancer cell invasion and metastasis. Therefore, drugs able to inhibit CXCR4 activation may add critical tools to reduce tumor progression, especially in the most aggressive form of the breast cancer disease. Peroxisome Proliferator-Activated Receptor (PPAR) γ, a member of the nuclear receptor superfamily, has been found to downregulate CXCR4 gene expression in different cancer cells, however the molecular mechanism underlying this effect is not fully understood. Here, we identified a novel PPARγ-mediated mechanism that negatively regulates CXCR4 expression in both epithelial and stromal breast cancer cells. We found that ligand-activated PPARγ downregulated CXCR4 transcriptional activity through the recruitment of the silencing mediator of retinoid and thyroid hormone receptor (SMRT) corepressor onto a newly identified PPAR response element (PPRE) within the CXCR4 promoter in breast cancer cell lines. As a consequence, the PPARγ agonist rosiglitazone (BRL) significantly inhibited cell migration and invasion and this effect was PPARγ-mediated, since it was reversed in the presence of the PPARγ antagonist GW9662. According to the ability of cancer-associated fibroblasts (CAFs), the most abundant component of breast cancer stroma, to secrete high levels of SDF-1α, BRL reduced migratory promoting activities induced by conditioned media (CM) derived from CAFs and affected CXCR4 downstream signaling pathways activated by CAF-CM. In addition, CAFs exposed to BRL showed a decreased expression of CXCR4, a reduced motility and invasion along with a phenotype characterized by an altered morphology. Collectively, our findings provide novel insights into the role of PPARγ in inhibiting breast cancer progression and further highlight the utility of PPARγ ligands for future therapies aimed at targeting both cancer and surrounding stromal cells in breast cancer patients.

Cachexia, the most severe paraneoplastic syndrome, occurs in about 80% of patients with advanced cancer; it cannot be reverted by conventional, enteral, or parenteral nutrition. For this reason, nutritional interventions must be based on the use of substances possessing, alongside nutritional and energetic properties, the ability to modulate production of the pro-inflammatory factors responsible for the metabolic changes characterising cancer cachexia. In light of their nutritional and anti-inflammatory properties, polyunsaturated fatty acids (PUFAs), and in particular n-3, have been investigated for treating cachexia; however, the results have been contradictory. Since both n-3 and n-6 PUFAs can affect cell functions in several ways, this research investigated the possibility that the effects of both n-3 and n-6 PUFAs could be mediated by their major aldehydic products of lipid peroxidation, 4-hydroxyhexenal (HHE) and 4-hydroxynonenal (HNE), and by their anti-inflammatory properties. An \"in vitro\" cancer cachexia model, consisting of human lung cancer cells (A427) and murine myoblasts (C2C12), was used. The results showed that: 1) both n-3 and n-6 PUFAs reduced the growth of lung cancer cells without causing cell death, increased lipid peroxidation and Peroxisome Proliferator-Activated Receptor (PPAR)α, and decreased TNFα; 2) culture medium conditioned by A427 cells grown in the absence of PUFAs blocked myosin production and the differentiation of C2C12 muscle cells; conversely, muscle cells grown in culture medium conditioned by the same cells in the presence of PUFAs showed myosin expression and formed myotubes; 3) adding HHE or HNE directly to C2C12 cells maintained in culture medium conditioned by A427 cells in the absence of PUFAs stimulated myosin production and myotube formation; 4) putative consensus sequences for (PPARs) have been found in genes encoding fast isoforms of myosin heavy chain, by a bioinformatics approach. The overall results show, first, the ability of both n-3 and n-6 PUFAs and their lipid peroxidation products to prevent the blocking of myosin expression and myotube formation caused in C2C12 cells by medium conditioned by human lung tumour cells. The C2C12 cell differentiation can be due to direct effect of lipid peroxidation products, as evidenced by treating C2C12 cells with HHE and HNE, and to the decrease of pro-inflammatory TNFα in A427 cell culture medium. The presence of consensus sequences for PPARs in genes encoding the fast isoforms of myosin heavy chain suggests that the effects of PUFAs, HHE, and HNE are PPAR-mediated.

In previous work, it is suggested that the excessive amount of fatty acids transported by FABP5 may facilitate the malignant progression of prostate cancer cells through a FABP5-PPARγ-VEGF signal transduction axis to increase angiogenesis. To further functionally characterise the FABP5-PPARγ-VEGF signal transduction pathway, we have, in this work, investigated the molecular mechanisms involved in its tumorigenicity promoting role in prostate cancer. Suppression of PPARγ in highly malignant prostate cancer cells produced a significant reduction (up to 53%) in their proliferation rate, invasiveness (up to 89%) and anchorage-independent growth (up to 94%) in vitro. Knockdown of PPARγ gene in PC3-M cells by siRNA significantly reduced the average size of tumours formed in nude mice by 99% and tumour incidence by 90%, and significantly prolonged the latent period by 3.5 fold. Results in this study combined with some previous results suggested that FABP5 promoted VEGF expression and angiogenesis through PPARγ which was activated by fatty acids transported by FABP5. Further investigations showed that PPARγ up-regulated VEGF expression through acting with the PPAR-responsive elements in the promoter region of VEGF gene in prostate cancer cells. Although androgen can modulate VEGF expression through Sp1/Sp3 binding site on VEGF promoter in androgen-dependent prostate cancer cells, this route, disappeared as the cells gradually lost their androgen dependency; was replaced by the FABP5-PPARγ-VEGF signalling pathway. These results suggested that the FABP5-PPARγ-VEGF signal transduction axis, rather than androgen modulated route, may be a more important novel therapeutic target for angiogenesis-suppression treatment of castration resistant prostate cancer.

OBJECTIVE: Adipose tissue is a highly versatile system in which mitochondria in adipocytes undergo significant changes during active tissue remodelling. BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3) is a mitochondrial protein and a known mitochondrial quality regulator. In this study, we investigated the role of BNIP3 in adipocytes, specifically under conditions of peroxisome proliferator-activated receptor-γ (PPARγ)-induced adipose tissue remodelling.
METHODS: The expression of BNIP3 was evaluated in 3T3-L1 adipocytes in vitro, C57BL/6 mice fed a high-fat diet and db/db mice in vivo. Mitochondrial bioenergetics was investigated in BNIP3-knockdown adipocytes after rosiglitazone treatment. A putative peroxisome proliferator hormone responsive element (PPRE) was characterised by promoter assay and electrophoretic mobility shift assay (EMSA).
RESULTS: The protein BNIP3 was more abundant in brown adipose tissue than white adipose tissue. Furthermore, BNIP3 expression was upregulated by 3T3-L1 pre-adipocyte differentiation, starvation and rosiglitazone treatment. Conversely, BNIP3 expression in adipocytes decreased under various conditions associated with insulin resistance. This downregulation of BNIP3 was restored by rosiglitazone treatment. Knockdown of BNIP3 in adipocytes inhibited rosiglitazone-induced mitochondrial biogenesis and function, partially mediated by the 5\' AMP-activated protein kinase (AMPK)-peroxisome proliferator-activated receptor γ, co-activator 1 α (PGC1α) signalling pathway. Rosiglitazone treatment increased the transcription level of Bnip3 in the reporter assay and the presence of the PPRE site in the Bnip3 promoter was demonstrated by EMSA.
CONCLUSIONS: The protein BNIP3 contributes to the improvement of mitochondrial bioenergetics that occurs on exposure to rosiglitazone. It may be a novel therapeutic target for restoring mitochondrial dysfunction under insulin-resistant conditions.

Peroxisome proliferator-activated receptors (PPARs) play major roles in the regulation of hepatic lipid metabolism through the control of numerous genes involved in processes such as lipid uptake and fatty acid oxidation. Here we identify hypoxia-inducible lipid droplet-associated (Hilpda/Hig2) as a novel PPAR target gene and demonstrate its involvement in hepatic lipid metabolism. Microarray analysis revealed that Hilpda is one of the most highly induced genes by the PPARα agonist Wy14643 in mouse precision cut liver slices. Induction of Hilpda mRNA by Wy14643 was confirmed in mouse and human hepatocytes. Oral dosing with Wy14643 similarly induced Hilpda mRNA levels in livers of wild-type mice but not Ppara(-/-) mice. Transactivation studies and chromatin immunoprecipitation showed that Hilpda is a direct PPARα target gene via a conserved PPAR response element located 1200 base pairs upstream of the transcription start site. Hepatic overexpression of HILPDA in mice via adeno-associated virus led to a 4-fold increase in liver triglyceride storage, without any changes in key genes involved in de novo lipogenesis, β-oxidation, or lipolysis. Moreover, intracellular lipase activity was not affected by HILPDA overexpression. Strikingly, HILPDA overexpression significantly impaired hepatic triglyceride secretion. Taken together, our data uncover HILPDA as a novel PPAR target that raises hepatic triglyceride storage via regulation of triglyceride secretion.