Nitric Oxide Induces the Expression of the Monocarboxylate Transporter MCT4 in Cultured Astrocytes by a cGMP-Independent Transcriptional Activation

The monocarboxylate transporter MCT4 is a proton-linked carrier particularly important for lactate release from highly glycolytic cells. In the central nervous system, MCT4 is exclusively expressed by astrocytes. Surprisingly, MCT4 expression in primary cultures of mouse cortical astrocytes is conspicuously low, suggesting that an external, nonastrocytic signal is necessary to obtain the observed pattern of expression in vivo. Here, we demonstrate that nitric oxide (NO), delivered by various NO donors, time- and dose-dependently induces MCT4 expression in cultured cortical astrocytes both at the mRNA and protein levels. In contrast, NO does not enhance the expression of MCT1, the other astrocytic monocarboxylate transporter. The transcriptional effect of NO is not mediated by a cGMP-dependent mechanism as shown by the absence of effect of a cGMP analog or of a selective guanylate cyclase inhibitor. NO causes an increase in astrocytic lactate transport capacity which requires the enhancement of MCT4 expression as both are prevented by the use of a specific siRNA against MCT4. In addition, cumulated lactate release by astrocytes over a period of 24 h was also enhanced by NO treatment. Our data suggest that NO represents a putative intercellular signal to control MCT4 expression in astrocytes and in doing so, to facilitate lactate transfer to other surrounding cell types in the central nervous system. (C) 2011 Wiley-Liss, Inc.

Phosphatidic acid mediates demyelination in Lpin1 mutant mice

Lipids play crucial roles in many aspects of glial cell biology, affecting processes ranging from myelin membrane biosynthesis to axo-glial interactions. In order to study the role of lipid metabolism in myelinating glial cells, we specifically deleted in Schwann cells the Lpin1 gene, which encodes the Mg2+-dependent phosphatidate phosphatase (PAP1) enzyme necessary for normal triacylglycerol biosynthesis. The affected animals developed pronounced peripheral neuropathy characterized by myelin degradation, Schwann cell dedifferentiation and proliferation, and a reduction in nerve conduction velocity. The observed demyelination is mediated by endoneurial accumulation of the substrate of the PAP1 enzyme, phosphatidic acid (PA). In addition, we show that PA is a potent activator of the MEK-Erk pathway in Schwann cells, and that this activation is required for PA-induced demyelination. Our results therefore reveal a surprising role for PA in Schwann cell fate determination and provide evidence of a direct link between diseases affecting lipid metabolism and abnormal Schwann cell function

Brain lactate kinetics: Modeling evidence for neuronal lactate uptake upon activation.

A critical issue in brain energy metabolism is whether lactate produced within the brain by astrocytes is taken up and metabolized by neurons upon activation. Although there is ample evidence that neurons can efficiently use lactate as an energy substrate, at least in vitro, few experimental data exist to indicate that it is indeed the case in vivo. To address this question, we used a modeling approach to determine which mechanisms are necessary to explain typical brain lactate kinetics observed upon activation. On the basis of a previously validated model that takes into account the compartmentalization of energy metabolism, we developed a mathematical model of brain lactate kinetics, which was applied to published data describing the changes in extracellular lactate levels upon activation. Results show that the initial dip in the extracellular lactate concentration observed at the onset of stimulation can only be satisfactorily explained by a rapid uptake within an intraparenchymal cellular compartment. In contrast, neither blood flow increase, nor extracellular pH variation can be major causes of the lactate initial dip, whereas tissue lactate diffusion only tends to reduce its amplitude. The kinetic properties of monocarboxylate transporter isoforms strongly suggest that neurons represent the most likely compartment for activation-induced lactate uptake and that neuronal lactate utilization occurring early after activation onset is responsible for the initial dip in brain lactate levels observed in both animals and humans.

Lipoxygenase 2 and the early steps of jasmonic acid biosynthesis in "Arabidopsis thaliana"

Résumé Les oxylipines, telles que l'acide jasmonique (AJ ou jasmonate), jouent un rôle central en réponse à la blessure et à la pathogenèse. De nombreuses études ont montré l'importance de la voie canonique du jasmonate lors de la défense des plantes. De plus, un précurseur cyclopentenone de l'AJ, l'acide oxo-phyto-dienoic (OPDA), a été impliqué comme jouant le rôle d'une molécule signal lors de la défense contre certains pathogènes. En utilisant des mutants bloqués dans la biosynthèse de l'acide jasmonique (aos) ou dans sa perception (coi1-1), nous avons cherché à définir dans quelle mesure l'OPDA joue un rôle de signal induisant l'expression génétique en réponse à la blessure chez Arabidopsis. A l'aide de puces à ADN (microarray), nous avons montré que les transcriptomes d'aos et de coi1-1 sont très semblables après blessure, ce qui suggère que les produits d'AOS sont tous perçus via COI1. Pourtant, lorsqu'on analyse les métabolites présents chez ces mutants, une différence est visible, puisque aos n'accumule pas d'AJ, alors que coi1-1 en accumule encore rapidement après blessure. Nous avons étudié la possibilité qu'un mécanisme de régulation post-traductionnelle sur la voie de biosynthèse du jasmonate explique l'accumulation d'AJ chez coi1-1 après blessure. La lipoxygenase 2 (LOX2) est la première enzyme impliquée dans la biosynthèse de l'AJ et est donc une cible potentielle d'un tel mécanisme. Un indice sur la manière dont l'activité LOX pourrait être régulée vient du mutant fou2 (pour fatty acid oxygenation upregcilated 2) dans lequel l'activité LOX ainsi que le niveau d'AJ sont constitutivement élevés. Cette mutation implique un flux de cation dans la régulation de la production de l'AJ. De plus, il a été montré que plusieurs LOXs, dans des organismes autres que des plantes, peuvent lier le calcium. Nous montrons que l'activité LOX requiert l'addition de cations divalents pour être maximale in vitro, et que non seulement le calcium mais aussi le magnésium joue ce rôle. De plus, nous caractérisons un mutant récessif de LOX2 chez Arabidopsis (lox2-1). Ces plantes sont fertiles, et une analyse quantitative montre qu'elles accumulent toujours un peu d'AJ après blessure. Ceci suggère que LOX2 n'est pas la seule LOX impliquée dans la synthèse d'AJ. Aussi les plantes lox2-1 ne sont pas plus sensibles que les plantes de type sauvage lorsqu'elles sont infectées par la moisissure Botrytis cinerea ou lorsqu'elles sont exposées à un détritivore, néanmoins elles sont plus sensibles lorsqu'elles sont offertes en nourriture à un insecte herbivore. Les insectes et les plantes ont co-évolué conjointement, ainsi une plante ne contenant qu'un niveau réduit d'AJ favorise l'insecte. La disponibilité d'un mutant avec un niveau intermédiaire d'AJ va permettre de mieux comprendre pourquoi les plantes produisent autant de jasmonate. Abstract Oxylipins such as jasmonic acid (JA) play central roles in the wound response and during pathogenesis and many studies have confirmed the important role of the canonical jasmonate pathway in plant defense. Moreover, the cyclopentenone precursor of JA, oxo-phytodienoic acid (OPDA), is also thought to function as a signaling molecule in defense towards some pathogens. Its action was reported to depend on a different signal pathway to JA. By using mutants blocked in the biosynthesis (aos) or perception (coil-1) of JA, we investigated to which extend OPDA works as signaling molecule to trigger gene expression in the wound response of Arabidopsis. Using microarrays, we showed that aos and coil-1 transcriptome are similar in response to wounding, suggesting that products of AOS are all perceived by COI1. However, we found a difference between the two mutants at the metobolomic level, since aos is devoid of JA, but coil-1 can still rapidly accumulate JA upon wounding. We investigated the possibility that the post-translational activation of JA biosynthesis could explain the fast accumulation of JA in coil-1 plants upon wounding. Lipoxygenase (LOX) 2 is the first enzyme implicated in JA synthesis and was thus chosen as a potential target for posttranslational regulation. A clue as to how LOX activity might be regulated came from the fatty acid oxygenation upregulated 2 (foul) mutant in which LOX activity and JA levels are elevated. The foul mutant implicates cations flux in the regulation of JA production, and several LOXs in organisms other than plants have been shown to bind calcium. We showed that Arabidopsis LOX requires divalent cations for full activity in vitro, and that not only calcium but also magnesium can play this role. Moreover, a single recessive mutant of AtLOX2 was characterized. These plants are fully fertile. Quantitative oxylipin analysis showed that lox2-1 can still accumulate some JA after wounding, which suggests that LOX2 is not the only LOX involved in JA biosynthesis. lox2-1 plants do not show altered susceptibility to the fungus Botrytis cinerea or to a detritivore, however, they are more susceptible to an insect herbivore. The insect and plants are closely co-evolved and a reduced ability to synthesize JA favors the insect. The availability of a lox2-1 mutant with intermediate JA levels will further help understanding why plants produce elevated JA levels.

A circuit-based gatekeeper for adult neural stem cell proliferation: Parvalbumin-expressing interneurons of the dentate gyrus control the activation and proliferation of quiescent adult neural stem cells.

Newborn neurons are generated in the adult hippocampus from a pool of self-renewing stem cells located in the subgranular zone (SGZ) of the dentate gyrus. Their activation, proliferation, and maturation depend on a host of environmental and cellular factors but, until recently, the contribution of local neuronal circuitry to this process was relatively unknown. In their recent publication, Song and colleagues have uncovered a novel circuit-based mechanism by which release of the neurotransmitter, γ-aminobutyric acid (GABA), from parvalbumin-expressing (PV) interneurons, can hold radial glia-like (RGL) stem cells of the adult SGZ in a quiescent state. This tonic GABAergic signal, dependent upon the activation of γ(2) subunit-containing GABA(A) receptors of RGL stem cells, can thus prevent their proliferation and subsequent maturation or return them to quiescence if previously activated. PV interneurons are thus capable of suppressing neurogenesis during periods of high network activity and facilitating neurogenesis when network activity is low.

Insulin and IGF-1 enhance the expression of the neuronal monocarboxylate transporter MCT2 by translational activation via stimulation of the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin pathway.

MCT2 is the main neuronal monocarboxylate transporter essential for facilitating lactate and ketone body utilization as energy substrates. Our study reveals that treatment of cultured cortical neurons with insulin and IGF-1 led to a striking enhancement of MCT2 immunoreactivity in a time- and concentration-dependent manner. Surprisingly, neither insulin nor IGF-1 affected MCT2 mRNA expression, suggesting that regulation of MCT2 protein expression occurs at the translational rather than the transcriptional level. Investigation of the putative signalling pathways leading to translation activation revealed that insulin and IGF-1 induced p44- and p42 MAPK, Akt and mTOR phosphorylation. S6 ribosomal protein, a component of the translational machinery, was also strongly activated by insulin and IGF-1. Phosphorylation of p44- and p42 MAPK was blocked by the MEK inhibitor PD98058, while Akt phosphorylation was abolished by the PI3K inhibitor LY294002. Phosphorylation of mTOR and S6 was blocked by the mTOR inhibitor rapamycin. In parallel, it was observed that LY294002 and rapamycin almost completely blocked the effects of insulin and IGF-1 on MCT2 protein expression, whereas PD98059 and SB202190 (a p38K inhibitor) had no effect on insulin-induced MCT2 expression and only a slight effect on IGF-1-induced MCT2 expression. At the subcellular level, a significant increase in MCT2 protein expression within an intracellular pool was observed while no change at the cell surface was apparent. As insulin and IGF-1 are involved in synaptic plasticity, their effect on MCT2 protein expression via an activation of the PI3K-Akt-mTOR-S6K pathway might contribute to the preparation of neurons for enhanced use of nonglucose energy substrates following altered synaptic efficacy.

An SH2 domain-containing 5' inositolphosphatase inhibits insulin-induced GLUT4 translocation and growth factor-induced actin filament rearrangement.

Tyrosine kinase receptors lead to rapid activation of phosphatidylinositol 3-kinase (PI3 kinase) and the subsequent formation of phosphatidylinositides (PtdIns) 3,4-P2 and PtdIns 3,4, 5-P3, which are thought to be involved in signaling for glucose transporter GLUT4 translocation, cytoskeletal rearrangement, and DNA synthesis. However, the specific role of each of these PtdIns in insulin and growth factor signaling is still mainly unknown. Therefore, we assessed, in the current study, the effect of SH2-containing inositol phosphatase (SHIP) expression on these biological effects. SHIP is a 5' phosphatase that decreases the intracellular levels of PtdIns 3,4,5-P3. Expression of SHIP after nuclear microinjection in 3T3-L1 adipocytes inhibited insulin-induced GLUT4 translocation by 100 +/- 21% (mean +/- the standard error) at submaximal (3 ng/ml) and 64 +/- 5% at maximal (10 ng/ml) insulin concentrations (P < 0.05 and P < 0.001, respectively). A catalytically inactive mutant of SHIP had no effect on insulin-induced GLUT4 translocation. Furthermore, SHIP also abolished GLUT4 translocation induced by a membrane-targeted catalytic subunit of PI3 kinase. In addition, insulin-, insulin-like growth factor I (IGF-I)-, and platelet-derived growth factor-induced cytoskeletal rearrangement, i.e., membrane ruffling, was significantly inhibited (78 +/- 10, 64 +/- 3, and 62 +/- 5%, respectively; P < 0.05 for all) in 3T3-L1 adipocytes. In a rat fibroblast cell line overexpressing the human insulin receptor (HIRc-B), SHIP inhibited membrane ruffling induced by insulin and IGF-I by 76 +/- 3% (P < 0.001) and 68 +/- 5% (P < 0.005), respectively. However, growth factor-induced stress fiber breakdown was not affected by SHIP expression. Finally, SHIP decreased significantly growth factor-induced mitogen-activated protein kinase activation and DNA synthesis. Expression of the catalytically inactive mutant had no effect on these cellular responses. In summary, our results show that expression of SHIP inhibits insulin-induced GLUT4 translocation, growth factor-induced membrane ruffling, and DNA synthesis, indicating that PtdIns 3,4,5-P3 is the key phospholipid product mediating these biological actions.

International union of basic and clinical pharmacology. XCI. structure, function, and pharmacology of acid-sensing ion channels and the epithelial Na+ channel.

The epithelial Na(+) channel (ENaC) and the acid-sensing ion channels (ASICs) form subfamilies within the ENaC/degenerin family of Na(+) channels. ENaC mediates transepithelial Na(+) transport, thereby contributing to Na(+) homeostasis and the maintenance of blood pressure and the airway surface liquid level. ASICs are H(+)-activated channels found in central and peripheral neurons, where their activation induces neuronal depolarization. ASICs are involved in pain sensation, the expression of fear, and neurodegeneration after ischemia, making them potentially interesting drug targets. This review summarizes the biophysical properties, cellular functions, and physiologic and pathologic roles of the ASIC and ENaC subfamilies. The analysis of the homologies between ENaC and ASICs and the relation between functional and structural information shows many parallels between these channels, suggesting that some mechanisms that control channel activity are shared between ASICs and ENaC. The available crystal structures and the discovery of animal toxins acting on ASICs provide a unique opportunity to address the molecular mechanisms of ENaC and ASIC function to identify novel strategies for the modulation of these channels by pharmacologic ligands.

The Th2 lymphoproliferation developing in LatY136F mutant mice triggers polyclonal B cell activation and systemic autoimmunity.

Lat(Y136F) knock-in mice harbor a point mutation in Tyr(136) of the linker for activation of T cells and show accumulation of Th2 effector cells and IgG1 and IgE hypergammaglobulinemia. B cell activation is not a direct effect of the mutation on B cells since in the absence of T cells, mutant B cells do not show an activated phenotype. After adoptive transfer of linker for activation of T cell mutant T cells into wild-type, T cell-deficient recipients, recipient B cells become activated. We show in vivo and in vitro that the Lat(Y136F) mutation promotes T cell-dependent B cell activation leading to germinal center, memory, and plasma cell formation even in an MHC class II-independent manner. All the plasma and memory B cell populations found in physiological T cell-dependent B cell responses are found. Characterization of the abundant plasmablasts found in secondary lymphoid organs of Lat(Y136F) mice revealed the presence of a previously uncharacterized CD93-expressing subpopulation, whose presence was confirmed in wild-type mice after immunization. In Lat(Y136F) mice, B cell activation was polyclonal and not Ag-driven because the increase in serum IgG1 and IgE concentrations involved Abs and autoantibodies with different specificities equally. Although the noncomplement-fixing IgG1 and IgE are the only isotypes significantly increased in Lat(Y136F) serum, we observed early-onset systemic autoimmunity with nephritis showing IgE autoantibody deposits and severe proteinuria. These results show that Th2 cells developing in Lat(Y136F) mice can trigger polyclonal B cell activation and thereby lead to systemic autoimmune disease.

The ArgR regulatory protein, a helper to the anaerobic regulator ANR during transcriptional activation of the arcD promoter in Pseudomonas aeruginosa.

Pseudomonas aeruginosa, when deprived of oxygen, generates ATP from arginine catabolism by enzymes of the arginine deiminase pathway, encoded by the arcDABC operon. Under conditions of low oxygen tension, the transcriptional activator ANR binds to a site centered 41.5 bp upstream of the arcD transcriptional start. ANR-mediated anaerobic induction was enhanced two- to threefold by extracellular arginine. This arginine effect depended, in trans, on the transcriptional regulator ArgR and, in cis, on an ArgR binding site centered at -73.5 bp in the arcD promoter. Binding of purified ArgR protein to this site was demonstrated by electrophoretic mobility shift assays and DNase I footprinting. This ArgR recognition site contained a sequence, 5'-TGACGC-3', which deviated in only 1 base from the common sequence motif 5'-TGTCGC-3' found in other ArgR binding sites of P. aeruginosa. Furthermore, an alignment of all known ArgR binding sites confirmed that they consist of two directly repeated half-sites. In the absence of ANR, arginine did not induce the arc operon, suggesting that ArgR alone does not activate the arcD promoter. According to a model proposed, ArgR makes physical contact with ANR and thereby facilitates initiation of arc transcription.

Activation of peroxisome proliferator-activated receptors (PPARs) by their ligands and protein kinase A activators.

The nuclear peroxisome proliferator-activated receptors (PPARs) alpha, beta, and gamma activate the transcription of multiple genes involved in lipid metabolism. Several natural and synthetic ligands have been identified for each PPAR isotype but little is known about the phosphorylation state of these receptors. We show here that activators of protein kinase A (PKA) can enhance mouse PPAR activity in the absence and the presence of exogenous ligands in transient transfection experiments. Activation function 1 (AF-1) of PPARs was dispensable for transcriptional enhancement, whereas activation function 2 (AF-2) was required for this effect. We also show that several domains of PPAR can be phosphorylated by PKA in vitro. Moreover, gel retardation experiments suggest that PKA stabilizes binding of the liganded PPAR to DNA. PKA inhibitors decreased not only the kinase-dependent induction of PPARs but also their ligand-dependent induction, suggesting an interaction between both pathways that leads to maximal transcriptional induction by PPARs. Moreover, comparing PPAR alpha knockout (KO) with PPAR alpha WT mice, we show that the expression of the acyl CoA oxidase (ACO) gene can be regulated by PKA-activated PPAR alpha in liver. These data demonstrate that the PKA pathway is an important modulator of PPAR activity, and we propose a model associating this pathway in the control of fatty acid beta-oxidation under conditions of fasting, stress, and exercise.

Functional interaction between peroxisome proliferator-activated receptors-alpha and Mef-2C on human carnitine palmitoyltransferase 1beta (CPT1beta) gene activation

Muscle-type carnitine palmitoyltransferase 1 (CPT1β) is considered to be the gene that controls fatty acid mitochondrial β-oxidation. A functional peroxisome proliferator-activated receptor (PPAR) responsive element (PPRE) and a myocite-specific (MEF2) site that binds MEF2A and MEF2C in the promoter of this gene had been previously identified. We investigated the roles of the PPRE and the MEF2 binding sites and the potential interaction between PPARα and MEF2C regulating the CPT1β gene promoter. Mutation analysis indicated that the MEF2 site contributed to the activation of the CPT1β promoter by PPAR in C2C12 cells. The reporter construct containing the PPRE and the MEF2C site was synergistically activated by co-expression of PPAR, retinoid X receptor (RXR) and MEF2C in non-muscle cells. Moreover, protein-binding assays demonstrated that MEF2C and PPAR specifically bound to one another in vitro. Also for the synergistic activation of the CPT1β gene promoter by MEF2C and PPARα-RXRα, a precise arrangement of its binding sites was essential.

Linking supply to demand: the neuronal monocarboxylate transporter MCT2 and the alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionic acid receptor GluR2/3 subunit are associated in a common trafficking process.

MCT2 is the major neuronal monocarboxylate transporter (MCT) that allows the supply of alternative energy substrates such as lactate to neurons. Recent evidence obtained by electron microscopy has demonstrated that MCT2, like alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionic acid (AMPA) receptors, is localized in dendritic spines of glutamatergic synapses. Using immunofluorescence, we show in this study that MCT2 colocalizes extensively with GluR2/3 subunits of AMPA receptors in neurons from various mouse brain regions as well as in cultured neurons. It also colocalizes with GluR2/3-interacting proteins, such as C-kinase-interacting protein 1, glutamate receptor-interacting protein 1 and clathrin adaptor protein. Coimmunoprecipitation of MCT2 with GluR2/3 and C-kinase-interacting protein 1 suggests their close interaction within spines. Parallel changes in the localization of both MCT2 and GluR2/3 subunits at and beneath the plasma membrane upon various stimulation paradigms were unraveled using an original immunocytochemical and transfection approach combined with three-dimensional image reconstruction. Cell culture incubation with AMPA or insulin triggered a marked intracellular accumulation of both MCT2 and GluR2/3, whereas both tumor necrosis factor alpha and glycine (with glutamate) increased their cell surface immunolabeling. Similar results were obtained using Western blots performed on membrane or cytoplasm-enriched cell fractions. Finally, an enhanced lactate flux into neurons was demonstrated after MCT2 translocation on the cell surface. These observations provide unequivocal evidence that MCT2 is linked to AMPA receptor GluR2/3 subunits and undergoes a similar translocation process in neurons upon activation. MCT2 emerges as a novel component of the synaptic machinery putatively linking neuroenergetics to synaptic transmission.

Activation/division of lymphocytes results in increased levels of cytoplasmic activation/proliferation-associated protein-1: prototype of a new family of proteins.

We purified from activated T lymphocytes a novel, highly conserved, 116-kDa, intracellular protein that occurred at high levels in the large, dividing cells of the thymus, was up-regulated when resting T or B lymphocytes or hemopoietic progenitors were activated, and was down-regulated when a monocytic leukemia, M1, was induced to differentiate. Expression of the protein was highest in the thymus and spleen and lowest in tissues with a low proportion of dividing cells such as kidney or muscle, although expression was high in the brain. The protein was localized to the cytosol and was phosphorylated, which is consistent with a previous report that the Xenopus laevis ortholog was phosphorylated by a mitotically activated kinase (1 ). The cDNA was previously mischaracterized as encoding p137, a 137-kDa GPI-linked membrane protein (2 ). We propose that the authentic protein encoded by this cDNA be called cytoplasmic activation/proliferation-associated protein-1 (caprin-1), and show that it is the prototype of a novel family of proteins characterized by two novel protein domains, termed homology regions-1 and -2 (HR-1, HR-2). Although we have found evidence for caprins only in urochordates and vertebrates, two insect proteins exhibit well-conserved HR-1 domains. The HR-1 and HR-2 domains have no known function, although the HR-1 of caprin-1 appeared necessary for formation of multimeric complexes of caprin-1. Overexpression of a fusion protein of enhanced green fluorescent protein and caprin-1 induced a specific, dose-dependent suppression of the proliferation of NIH-3T3 cells, consistent with the notion that caprin-1 plays a role in cellular activation or proliferation.

PPARbeta regulates vitamin A metabolism-related gene expression in hepatic stellate cells undergoing activation.

Activation of cultured hepatic stellate cells correlated with an enhanced expression of proteins involved in uptake and storage of fatty acids (FA translocase CD36, Acyl-CoA synthetase 2) and retinol (cellular retinol binding protein type I, CRBP-I; lecithin:retinol acyltransferases, LRAT). The increased expression of CRBP-I and LRAT during hepatic stellate cells activation, both involved in retinol esterification, was in contrast with the simultaneous depletion of their typical lipid-vitamin A (vitA) reserves. Since hepatic stellate cells express high levels of peroxisome proliferator activated receptor beta (PPARbeta), which become further induced during transition into the activated phenotype, we investigated the potential role of PPARbeta in the regulation of these changes. Administration of L165041, a PPARbeta-specific agonist, further induced the expression of CD36, B-FABP, CRBP-I, and LRAT, whereas their expression was inhibited by antisense PPARbeta mRNA. PPARbeta-RXR dimers bound to CRBP-I promoter sequences. Our observations suggest that PPARbeta regulates the expression of these genes, and thus could play an important role in vitA storage. In vivo, we observed a striking association between the enhanced expression of PPARbeta and CRBP-I in activated myofibroblast-like hepatic stellate cells and the manifestation of vitA autofluorescent droplets in the fibrotic septa after injury with CCl4 or CCl4 in combination with retinol.