Positive regulation of the peroxisomal beta-oxidation pathway by fatty acids through activation of peroxisome proliferator-activated receptors (PPAR).

Peroxisome proliferators regulate the transcription of genes by activating ligand-dependent transcription factors, which, due to their structure and function, can be assigned to the superfamily of nuclear hormone receptors. Three such peroxisome proliferator-activated receptors (PPAR alpha, beta, and gamma) have been cloned in Xenopus laevis. Their mRNAs are expressed differentially; xPPAR alpha and beta but not xPPAR gamma are expressed in oocytes and embryos. In the adult, expression of xPPAR alpha and beta appears to be ubiquitous, and xPPAR gamma is mainly observed in adipose tissue and kidney. Immunocytochemical analysis revealed that PPARs are nuclear proteins, and that their cytoplasmic-nuclear translocation is independent of exogenous activators. A target gene of PPARs is the gene encoding acyl-CoA oxidase (ACO), which catalyzes the rate-limiting step in the peroxisomal beta-oxidation of fatty acids. A peroxisome proliferator response element (PPRE), to which PPARs bind, has been identified within the promoter of the ACO gene. Besides the known xenobiotic activators of PPARs, such as hypolipidemic drugs, natural activators have been identified. Polyunsaturated fatty acids at physiological concentrations are efficient activators of PPARs, and 5,8,11,14-eicosatetraynoic acid (ETYA), which is the alkyne homolog of arachidonic acid, is the most potent activator of xPPAR alpha described to date. Taken together, our data suggest that PPARs have an important role in lipid metabolism.

Developing a Simple and Rapid Test for Monitoring the Heat Evolution of Concrete Mixtures for Both Laboratory and Field Applications, January 2006

Various test methods exist for measuring heat of cement hydration; however, most current methods require expensive equipment, complex testing procedures, and/or extensive time, thus not being suitable for field application. The objectives of this research are to identify, develop, and evaluate a standard test procedure for characterization and quality control of pavement concrete mixtures using a calorimetry technique. This research project has three phases. Phase I was designed to identify the user needs, including performance requirements and precision and bias limits, and to synthesize existing test methods for monitoring the heat of hydration, including device types, configurations, test procedures, measurements, advantages, disadvantages, applications, and accuracy. Phase II was designed to conduct experimental work to evaluate the calorimetry equipment recommended from the Phase I study and to develop a standard test procedure for using the equipment and interpreting the test results. Phase II also includes the development of models and computer programs for prediction of concrete pavement performance based on the characteristics of heat evolution curves. Phase III was designed to study for further development of a much simpler, inexpensive calorimeter for field concrete. In this report, the results from the Phase I study are presented, the plan for the Phase II study is described, and the recommendations for Phase III study are outlined. Phase I has been completed through three major activities: (1) collecting input and advice from the members of the project Technical Working Group (TWG), (2) conducting a literature survey, and (3) performing trials at the CP Tech Center’s research lab. The research results indicate that in addition to predicting maturity/strength, concrete heat evolution test results can also be used for (1) forecasting concrete setting time, (2) specifying curing period, (3) estimating risk of thermal cracking, (4) assessing pavement sawing/finishing time, (5) characterizing cement features, (6) identifying incompatibility of cementitious materials, (7) verifying concrete mix proportions, and (8) selecting materials and/or mix designs for given environmental conditions. Besides concrete materials and mix proportions, the configuration of the calorimeter device, sample size, mixing procedure, and testing environment (temperature) also have significant influences on features of concrete heat evolution process. The research team has found that although various calorimeter tests have been conducted for assorted purposes and the potential uses of calorimeter tests are clear, there is no consensus on how to utilize the heat evolution curves to characterize concrete materials and how to effectively relate the characteristics of heat evolution curves to concrete pavement performance. The goal of the Phase II study is to close these gaps.

ERK1/2 pathway is activated in degenerated Rpe65-deficient mice.

The MAPK family is composed of three majors kinases, JNK, p38 and ERK1/2, and is implicated in many degenerative processes, including retinal cell death. The purpose of our study was to evaluate the activation of ERK1/2 kinase, and its potential role in Müller cell gliosis, during photoreceptor cell death in Rpe65(-/-) mice. We assayed ERK1/2 mRNA and protein levels, and evaluated ERK1/2 phosphorylation involved in kinase activation, in 2, 4 and 6 month-old Rpe65(-/-) mice and in age-matched wild-type controls. No differences in ERK1/2 expression were detected between Rpe65(-/-) and wild-type mice, however, ERK1/2 phosphorylation was dramatically increased in the knock out mice at 4 and 6 months-of-age. Phosphorylated ERK1/2 co-localized with GFAP in the ganglion cell layer, and correlated with an increase in GFAP protein expression and retinal cell death. Accumulation of cFOS protein in the ganglion cell layer occurred concomitant with pERK1/2 activation. Müller cell proliferation was not observed. ERK1/2 activation did not occur in 2 month-old Rpe65(-/-) or in the Rpe65(-/-)/Gnat1(-/-) mice, in which no degeneration was evident. The observed activation ERK1/2 and GFAP, both markers of Müller cell gliosis, in the absence of Müller cell proliferation, is consistent with the activation of atypical gliosis occurring during the slow process of degeneration in Rpe65(-/-) mice. As Müller cell gliosis is activated in many neuronal and retinal degenerative diseases, further studies will be needed to determine whether atypical gliosis in Rpe65(-/-) mice contributes to, or protects against, the pathogenesis occurring in this model of Leber congenital amaurosis.

Angiotensin II-induced cardiac hypertrophy is associated with different mitogen-activated protein kinase activation in normotensive and hypertensive mice.

OBJECTIVE: In addition to its haemodynamic effects, angiotensin II (AngII) is thought to contribute to the development of cardiac hypertrophy via its growth factor properties. The activation of mitogen-activated protein kinases (MAPK) is crucial for stimulating cardiac growth. Therefore, the present study aimed to determine whether the trophic effects of AngII and the AngII-induced haemodynamic load were associated with specific cardiac MAPK pathways during the development of hypertrophy. Methods The activation of the extracellular-signal-regulated kinase (ERK), the c-jun N-terminal kinase (JNK) and the p38 kinase was followed in the heart of normotensive and hypertensive transgenic mice with AngII-mediated cardiac hypertrophy. Secondly, we used physiological models of AngII-dependent and AngII-independent renovascular hypertension to study the activation of cardiac MAPK pathways during the development of hypertrophy. RESULTS: In normotensive transgenic animals with AngII-induced cardiac hypertrophy, p38 activation is associated with the development of hypertrophy while ERK and JNK are modestly stimulated. In hypertensive transgenic mice, further activation of ERK and JNK is observed. Moreover, in the AngII-independent model of renovascular hypertension and cardiac hypertrophy, p38 is not activated while ERK and JNK are strongly stimulated. In contrast, in the AngII-dependent model, all three kinases are stimulated. CONCLUSIONS: These data suggest that p38 activation is preferentially associated with the direct effects of AngII on cardiac cells, whereas stimulation of ERK and JNK occurs in association with AngII-induced mechanical stress.

The Hippo Transducer YAP1 Transforms Activated Satellite Cells and Is a Potent Effector of Embryonal Rhabdomyosarcoma Formation.

The role of the Hippo pathway effector YAP1 in soft tissue sarcomas is poorly defined. Here we report that YAP1 activity is elevated in human embryonal rhabdomyosarcoma (ERMS). In mice, sustained YAP1 hyperactivity in activated, but not quiescent, satellite cells induces ERMS with high penetrance and short latency. Via its transcriptional program with TEAD1, YAP1 directly regulates several major hallmarks of ERMS. YAP1-TEAD1 upregulate pro-proliferative and oncogenic genes and maintain the ERMS differentiation block by interfering with MYOD1 and MEF2 pro-differentiation activities. Normalization of YAP1 expression reduces tumor burden in human ERMS xenografts and allows YAP1-driven ERMS to differentiate in situ. Collectively, our results identify YAP1 as a potent ERMS oncogenic driver and a promising target for differentiation therapy.

Peroxisome proliferator activated receptors: transcriptional regulators of adipogenesis, lipid metabolism and more....

The recent discovery of lipid-activatable transcription factors that regulate the genes controlling lipid metabolism and adipogenesis has provided insight into the way that organisms sense and respond to lipid levels. Identification of the signaling pathways in which these receptors are involved will help us to understand the control of energy balance and the molecular defects underlying its disorders.

Peroxisome-proliferator-activated receptors and cancers: complex stories.

Peroxisome-proliferator-activated receptors (PPARs) are nuclear hormone receptors that mediate the effects of fatty acids and their derivatives at the transcriptional level. Through these pathways, PPARs can regulate cell proliferation, differentiation and survival, so controlling carcinogenesis in various tissues. But what are the links between each PPAR isotype and carcinogenesis and what is the relevance of these findings to human pathology and therapy?

Functions of peroxisome proliferator-activated receptors (PPAR) in skin homeostasis.

The peroxisome proliferator-activated receptors (PPAR) are ligand-activated transcription factors that belong to the nuclear hormone receptor family. Three isotypes (PPAR alpha, PPAR beta or delta, and PPAR gamma) with distinct tissue distributions and cellular functions have been found in vertebrates. All three PPAR isotypes are expressed in rodent and human skin. They were initially investigated for a possible function in the establishment of the permeability barrier in skin because of their known function in lipid metabolism in other cell types. In vitro studies using specific PPAR agonists and in vivo gene disruption approaches in mice indeed suggest an important contribution of PPAR alpha in the formation of the epidermal barrier and in sebocyte differentiation. The PPAR gamma isotype plays a role in stimulating sebocyte development and lipogenesis, but does not appear to contribute to epidermal tissue differentiation. The third isotype, PPAR beta, regulates the late stages of sebaceous cell differentiation, and is the most effective isotype in stimulating lipid production in these cells, both in rodents and in humans. In addition, PPAR beta activation has pro-differentiating effects in keratinocytes under normal and inflammatory conditions. Finally, preliminary studies also point to a potential role of PPAR in hair follicle growth and in melanocyte differentiation. By their diverse biological effects on cell proliferation and differentiation in the skin, PPAR agonists or antagonists may offer interesting opportunities for the treatment of various skin disorders characterized by inflammation, cell hyperproliferation, and aberrant differentiation.

Peroxisome proliferator-activated receptor alpha mediates the adaptive response to fasting.

Prolonged deprivation of food induces dramatic changes in mammalian metabolism, including the release of large amounts of fatty acids from the adipose tissue, followed by their oxidation in the liver. The nuclear receptor known as peroxisome proliferator-activated receptor alpha (PPARalpha) was found to play a role in regulating mitochondrial and peroxisomal fatty acid oxidation, suggesting that PPARalpha may be involved in the transcriptional response to fasting. To investigate this possibility, PPARalpha-null mice were subjected to a high fat diet or to fasting, and their responses were compared with those of wild-type mice. PPARalpha-null mice chronically fed a high fat diet showed a massive accumulation of lipid in their livers. A similar phenotype was noted in PPARalpha-null mice fasted for 24 hours, who also displayed severe hypoglycemia, hypoketonemia, hypothermia, and elevated plasma free fatty acid levels, indicating a dramatic inhibition of fatty acid uptake and oxidation. It is shown that to accommodate the increased requirement for hepatic fatty acid oxidation, PPARalpha mRNA is induced during fasting in wild-type mice. The data indicate that PPARalpha plays a pivotal role in the management of energy stores during fasting. By modulating gene expression, PPARalpha stimulates hepatic fatty acid oxidation to supply substrates that can be metabolized by other tissues.

Activated group 3 innate lymphoid cells promote T-cell-mediated immune responses.

Group 3 innate lymphoid cells (ILC3s) have emerged as important cellular players in tissue repair and innate immunity. Whether these cells meaningfully regulate adaptive immune responses upon activation has yet to be explored. Here we show that upon IL-1β stimulation, peripheral ILC3s become activated, secrete cytokines, up-regulate surface MHC class II molecules, and express costimulatory molecules. ILC3s can take up latex beads, process protein antigen, and consequently prime CD4(+) T-cell responses in vitro. The cognate interaction of ILC3s and CD4(+) T cells leads to T-cell proliferation both in vitro and in vivo, whereas its disruption impairs specific T-cell and T-dependent B-cell responses in vivo. In addition, the ILC3-CD4(+) T-cell interaction is bidirectional and leads to the activation of ILC3s. Taken together, our data reveal a novel activation-dependent function of peripheral ILC3s in eliciting cognate CD4(+) T-cell immune responses.

Peroxisome proliferator-activated receptors: finding the orphan a home.

The peroxisome proliferator-activated receptor (PPAR) is a member of the steroid hormone receptor superfamily and is activated by a variety of fibrate hypolipidaemic drugs and non-genotoxic rodent hepatocarcinogens that are collectively termed peroxisome proliferators. A key marker of peroxisome proliferator action is the peroxisomal enzyme acyl CoA oxidase, which is elevated about ten fold in the livers of treated rodents. Additional peroxisome proliferator responsive genes include other peroxisomal beta-oxidation enzymes and members of the cytochrome P450 IVA family. A peroxisome proliferator response element (PPRE), consisting of an almost perfect direct repeat of the sequence TGACCT spaced by a single base pair, has been identified in the upstream regulatory sequences of each of these genes. The retinoid X receptor (RXR) forms a heterodimer with PPAR and binds to the PPRE. Furthermore, the RXR ligand, 9-cis retinoic acid, enhances PPAR action. Retinoids may therefore modulate the action of peroxisome proliferators and PPAR may interfere with retinoid action, perhaps providing one mechanism to explain the toxicity of peroxisome proliferators. Interestingly, a variety of fatty acids can activate PPAR supporting the suggestion that fatty acids, or their acyl CoA derivatives, may be the natural ligands of PPAR and that the physiological role of PPAR is to regulate fatty acid homeostasis. Taken together, the discovery of PPAR has opened up new opportunities in understanding how lipid homeostasis is regulated, how the fibrate hypolipidaemic drugs may act and should lead to improvements in the assessment of human risk from peroxisome proliferators based upon a better understanding of their mechanism of action.

Peroxisome proliferator-activated receptors and lipid metabolism.

PPARs are nuclear hormone receptors which, like the retinoid, thyroid hormone, vitamin D, and steroid hormone receptors, are ligand-activated transcription factors mediating the hormonal control of gene expression. Two lines of evidence indicate that PPARs have an important function in fatty acid metabolism. First, PPARs are activated by hypolipidemic drugs and physiological concentrations of fatty acids, and second, PPARs control the peroxisomal beta-oxidation pathway of fatty acids through transcriptional induction of the gene encoding the acyl-CoA oxidase (ACO), which is the rate-limiting enzyme of the pathway. Furthermore, the PPAR signaling pathway appears to converge with the 9-cis retinoic acid receptor (RXR) signaling pathway in the regulation of the ACO gene because heterodimerization between PPAR and RXR is essential for in vitro binding to the PPRE and because the strongest stimulation of this gene is observed when both receptors are exposed simultaneously to their activators. Thus, it appears that PPARs are involved in the 9-cis retinoic acid signaling pathway and that they play a pivotal role in the hormonal control of lipid metabolism.

Signaling cross-talk between peroxisome proliferator-activated receptor/retinoid X receptor and estrogen receptor through estrogen response elements.

Peroxisome proliferator-activated receptors (PPARs) and retinoid X receptors (RXRs) are nuclear hormone receptors that are activated by fatty acids and 9-cis-retinoic acid, respectively. PPARs and RXRs form heterodimers that activate transcription by binding to PPAR response elements (PPREs) in the promoter of target genes. The PPREs described thus far consist of a direct tandem repeat of the AGGTCA core element with one intervening nucleotide. We show here that the vitellogenin A2 estrogen response element (ERE) can also function as a PPRE and is bound by a PPAR/RXR heterodimer. Although this heterodimer can bind to several other ERE-related palindromic response elements containing AGGTCA half-sites, only the ERE is able to confer transactivation of test reporter plasmids, when the ERE is placed either close to or at a distance from the transcription initiation site. Examination of natural ERE-containing promoters, including the pS2, very-low-density apolipoprotein II and vitellogenin A2 genes, revealed considerable differences in the binding of PPAR/RXR heterodimers to these EREs. In their natural promoter context, these EREs did not allow transcriptional activation by PPARs/RXRs. Analysis of this lack of stimulation of the vitellogenin A2 promoter demonstrated that PPARs/RXRs bind to the ERE but cannot transactivate due to a nonpermissive promoter structure. As a consequence, PPARs/RXRs inhibit transactivation by the estrogen receptor through competition for ERE binding. This is the first example of signaling cross-talk between PPAR/RXR and estrogen receptor.