Regulation of gene expression by fatty acids: special reference to fatty acid-binding protein (FABP)

Effects of maternal protein supplementation and inclusion of rumen-protected fat in the finishing diet on nutrient digestibility and expression of intestinal genes in Nellore steers

The study aimed to evaluate nutrient digestibility and intestine gene expression in the progeny from cows supplemented during gestation and fed diets with or without rumen-protected fat (RPF) in the feedlot. Forty-eight Nellore steers, averaging 340 kg, were housed in individual pens and allotted in a completely randomized design using a 2 × 2 factorial arrangement (dams nutrition × RPF). Cows' supplementation started after 124 ± 21 days of gestation. The feedlot lasted 135 days and diets had the inclusion of zero or 6% of RPF. Digestibility was evaluated by total feces collection. Steers were slaughtered using the concussion technique and samples of pancreas and small intestine were collected immediately after the slaughter to analyze α-amylase activity, and the expression of SLC5A1, CD36, and CCK and villi morphometry. Feeding RPF increased nutrients digestibility (p < 0.01). There was no effect of maternal nutrition on digestibility and α-amylase activity in steers (p > 0.05). Duodenal expression of SLC5A1, CD36, and CCK increased in the progeny from restricted cows. In conclusion, protein restriction during mid to late gestation of dams has long-term effects on small-intestine length and on expression of membrane transporters genes in the duodenum of the progeny. However, maternal nutrition does not affect digestibility in the feedlot.

Modulatory effect of linoleic and oleic acid on cell proliferation and lipid metabolism gene expressions in primary bovine satellite cells

This study was performed to elucidate the effects of linoleic acid (LA), oleic acid (OA) and their combination (LA + OA) on cell proliferation, apoptosis, necrosis, and the lipid metabolism related gene expression in bovine satellite cells (BSCs), isolated from bovine muscles. Cell viability was significantly increased with the OA and LA treatment. Furthermore, LA + OA enhanced cell proliferation in a dose-dependent manner (10 to 100 µM), whereas it lowered at 250 µM. In addition, a cell-cycle analysis showed that 100 µM of LA and OA markedly decreased the G0/G1 phase proportion (62.58% and 61.33%, respectively), compared to controls (68.02%), whereas the S-phase cells' proportion was increased. The ratio of G2/M phase cells was not significantly different among the groups. Moreover, analyses with AO/EtBr staining showed that no apoptosis occurred. Necrosis were determined by flow cytometry using Annexin V-FITC/PI staining which revealed no early apoptosis in the cells pretreated with LA or OA, but occurred in the LA + OA group. We also analyzed the mRNA expression of lipid metabolizing genes such as peroxisome proliferator receptor alfa (PPARα), peroxisome proliferator receptor gamma (PPARγ), acyl-CoA oxidase (ACOX), lipoprotein lipase (LPL), carnitine palmitoyl transferase (CPT-1), and fatty-acid binding protein4 (FABP4), which were upregulated in LA or OA treated cells compared to the control group. In essence, LA and OA alone promote the cell proliferation without any apoptosis and necrosis, which might upregulate the lipid metabolism related gene expressions, and increase fatty-acid oxidation in the BSCs' lipid metabolism.

Effects of perilla extract on productive performance, serum values and hepatic expression of lipid-related genes in Shaoxing ducks

1. The aim of this study was to identify the effect of perilla extract, a source of polyunsaturated fatty acids, on lipid metabolism and expression of lipid-related genes in livers of Shaoxing ducks. 2. Two hundred and forty 28-week-old laying ducks received a commercial diet with perilla extract added at 0 (control) or 200 mg/kg of feed. 3. Ducks fed on a diet with perilla extract had increased laying rates compared with control ducks. 4. Serum concentrations of triglycerides were reduced by perilla extract, while high-density lipoprotein cholesterol and total serum cholesterol increased. 5. The expression of genes involved in hepatic lipogenesis, sterol regulatory element-binding protein-1, acetyl CoA carboxylase, stearoyl CoA desaturase, fatty acid synthase, apolipoprotein B, and apolipoprotein very low density lipoprotein, were decreased in the perilla group. 6. The mRNA expression of peroxisome proliferators-activated receptor alpha and acyl-coenzyme A oxidase was enhanced following treatment with perilla extract, and a similar tendency was observed in the expression of liver fatty acid-binding protein. 7. The results show that a diet with 200 mg/kg perilla extract regulated fat metabolism of Shaoxing ducks by improving egg laying, altering serum lipid profiles, stimulating lipid catabolic gene expression and inhibiting lipogenic gene expression in the liver.

Effects of linoleic acid and eicosapentaenoic acid on cell proliferation and lipid-metabolism gene expression in primary duck hepatocytes

Several studies have investigated that linoleic acid (LA) and eicosapentaenoic acid (EPA) affect cell proliferation and lipid catabolic gene expression in mammals. To determine if LA and EPA increase duck cell proliferation and lipid catabolic gene expression, the authors exposed duck primary hepatocyte cultures to LA or EPA. The results showed that both LA and EPA increased cell proliferation in a dose-dependent manner (100 μM). The effect on specific cell-cycle phases was also studied; LA and EPA (100 μM) deceased the proportion of cells in the G0/G1 phase from 83 to 80.8 and 80.3%, respectively, concomitant with an increase in the proportion of S-phase cells (11.5 and 10.5 vs. 8%, respectively). The expression of PPAR-α and PPAR-α target genes, such as acyl-CoA oxidase (ACOX), lipoprotein lipase (LPL), liver fatty acid-binding protein (L-FABP), was examined by quantitative real-time PCR. The results showed that the expression of the PPAR-α, ACOX, and LPL genes increased significantly following LA and EPA exposure, but that the expression of L-FABP remained unchanged. This study provides the first characterization of LA- and EPA-induced cell proliferation and PPAR-α and PPAR-α target gene transcriptional responses in duck primary hepatocyte cultures.

Dietary n-6 PUFA deprivation downregulates arachidonate but upregulates docosahexaenoate metabolizing enzymes in rat brain

BACKGROUND

Dietary n-3 polyunsaturated fatty acid (PUFA) deprivation increases expression of arachidonic acid (AA 20:4n-6)-selective cytosolic phospholipase A(2) (cPLA(2)) IVA and cyclooxygenase (COX)-2 in rat brain, while decreasing expression of docosahexaenoic acid (DHA 22:6n-3)-selective calcium-independent iPLA(2) VIA. Assuming that these enzyme changes represent brain homeostatic responses to deprivation, we hypothesized that dietary n-6 PUFA deprivation would produce changes in the opposite directions.

METHODS

Brain expression of PUFA-metabolizing enzymes and their transcription factors was quantified in male rats fed an n-6 PUFA adequate or deficient diet for 15weeks post-weaning.

RESULTS

The deficient compared with adequate diet increased brain mRNA, protein and activity of iPLA(2) VIA and 15-lipoxygenase (LOX), but decreased cPLA(2) IVA and COX-2 expression. The brain protein level of the iPLA(2) transcription factor SREBP-1 was elevated, while protein levels were decreased for AP-2α and NF-κB p65, cPLA(2) and COX-2 transcription factors, respectively.

CONCLUSIONS

With dietary n-6 PUFA deprivation, rat brain PUFA metabolizing enzymes and some of their transcription factors change in a way that would homeostatically dampen reductions in brain n-6 PUFA concentrations and metabolism, while n-3 PUFA metabolizing enzyme expression is increased. The changes correspond to reported in vitro enzyme selectivities for AA compared with DHA.

Effect of different oils in diets for finishing pigs: performance, carcass traits and fatty acid profile of the meat

An experiment was carried out in the Animal Science Department of Lavras University to determine the effects of different oils on the performance, carcass traits and fatty acid profile of meat from finishing pigs. In total, 80 Large White × Landrace animals, including 40 gilts and 40 barrows, with an average initial weight of 68.50 ± 1.45 kg, were used. Isoenergetic, isoprotein and isolysinic diets based on corn and soybean meal without the addition of oil or with 2% soybean oil, canola oil, linseed oil or PUFA commercial oil were tested. No significant (P > 0.05) effects were observed in the pigs’ performance. However, significant (P < 0.05) improvements were observed regarding the percentage of meat on the carcass and the loin area with the addition of linseed oil (2%) in the diets. The carcasses of the pigs fed diets containing linseed oil also had higher content of protein in the femoral biceps muscle compared with those from pigs fed soybean oil diets. The fatty acid composition of the intramuscular fat of the longissimus dorsi muscle reflected the composition of the oils added to the diets. In conclusion, linseed oil at 2.0% in the finishing pig diet improved lean tissue accretion (lean meat and loin area in the carcass). In addition, the fatty acid deposition in the muscles followed the dietary fatty acid profile.

Morphological, kinetic, membrane biochemical and genetic aspects of intestinal enteroplasticity

The process of intestinal adaptation (“enteroplasticity”) is complex and multifaceted. Although a number of trophic nutrients and non-nutritive factors have been identified in animal studies, successful, reproducible clinical trials in humans are awaited. Understanding mechanisms underlying this adaptive process may direct research toward strategies that maximize intestinal function and impart a true clinical benefit to patients with short bowel syndrome, or to persons in whom nutrient absorption needs to be maximized. In this review, we consider the morphological, kinetic and membrane biochemical aspects of enteroplasticity, focus on the importance of nutritional factors, provide an overview of the many hormones that may alter the adaptive process, and consider some of the possible molecular profiles. While most of the data is derived from rodent studies, wherever possible, the results of human studies of intestinal enteroplasticity are provided.

Lipids and lipid-based formulations: optimizing the oral delivery of lipophilic drugs

Highly potent, but poorly water-soluble, drug candidates are common outcomes of contemporary drug discovery programmes and present a number of challenges to drug development - most notably, the issue of reduced systemic exposure after oral administration. However, it is increasingly apparent that formulations containing natural and/or synthetic lipids present a viable means for enhancing the oral bioavailability of some poorly water-soluble, highly lipophilic drugs. This Review details the mechanisms by which lipids and lipidic excipients affect the oral absorption of lipophilic drugs and provides a perspective on the possible future applications of lipid-based delivery systems. Particular emphasis has been placed on the capacity of lipids to enhance drug solubilization in the intestinal milieu, recruit intestinal lymphatic drug transport (and thereby reduce first-pass drug metabolism) and alter enterocyte-based drug transport and disposition.

Heart fatty acid binding protein in the diagnosis of myocardial infarction: where do we stand today?

Heart fatty acid binding protein (hFABP) is a novel small cytosolic protein that is abundant in the heart. It is highly cardiac-specific (i.e. expressed primarily in cardiac tissue), but is also expressed at low concentrations in tissues outside the heart. After myocardial ischemic damage, hFABP can be detected in the blood as early as 1-3 h after onset of chest pain, with peak values reached at 6-8 h and plasma levels returning to normal within 24-30 h. hFABP's clinical diagnostic value is very limited in the presence of renal failure and skeletal muscle diseases as it is completely renally eliminated. In these conditions, the diagnosis of acute myocardial infarction (AMI) may be overestimated. The combination of initial hFABP release after symptom onset, rapid kidney clearance from the circulation and high cardiac specificity suggests great potential for clinical use. Serial measurements of hFABP in the first 24 h after onset of symptoms in AMI patients can: (a) identify patients who are susceptible to reperfusion strategies, (b) detect perioperative AMIs, (c) distinguish patients who reperfuse their infarct-related artery from those who do not, as early as 30 min after starting thrombolytic treatment, (d) detect re-infarction if it occurs within 10 h after symptom onset, and (e) permit an accurate estimation of myocardial infarct size providing important prognosis information.

Intestinal mucosal adaptation

Intestinal failure is a condition characterized by malnutrition and/or dehydration as a result of the inadequate digestion and absorption of nutrients. The most common cause of intestinal failure is short bowel syndrome, which occurs when the functional gut mass is reduced below the level necessary for adequate nutrient and water absorption. This condition may be congenital, or may be acquired as a result of a massive resection of the small bowel. Following resection, the intestine is capable of adaptation in response to enteral nutrients as well as other trophic stimuli. Identifying factors that may enhance the process of intestinal adaptation is an exciting area of research with important potential clinical applications.

POLYUNSATURATED FATTY ACID REGULATION OF GENES OF LIPID METABOLISM

Apart from being an important macronutrient, dietary fat has recently gained much prominence for its role in regulating gene expression. Polyunsaturated fatty acids (PUFAs) affect gene expression through various mechanisms including, but not limited to, changes in membrane composition, intracellular calcium levels, and eicosanoid production. Furthermore, PUFAs and their various metabolites can act at the level of the nucleus, in conjunction with nuclear receptors and transcription factors, to affect the transcription of a variety of genes. Several of these transcription mediators have been identified and include the nuclear receptors peroxisome proliferator-activated receptor (PPAR), hepatocyte nuclear factor (HNF)-4alpha, and liver X receptor (LXR) and the transcription factors sterol-regulatory element binding protein (SREBP) and nuclear factor-kappaB (NFkappaB). Their interaction with PUFAs has been shown to be critical to the regulation of several key genes of lipid metabolism. Working out the mechanisms by which these interactions and consequent effects occur is proving to be complicated but is invaluable to our understanding of the role that dietary fat can play in disease management and prevention.

Expression of PPAR, RXR isoforms and fatty acid transporting proteins in the rat and human gastrointestinal tracts

Dietary fatty acid (FA) absorption across the gastrointestinal (GI) tract is of critical importance for sustenance, however, excessive FA absorption has also been linked to metabolic syndrome and associated disorders. The expression of isoforms that regulate the dietary FA absorption are not as well characterized in the GI tract as they are elsewhere. Peroxisome proliferator-activated receptors (PPARalpha, beta, and gamma) and 9-cis-retinoic acid receptors (RXRalpha, beta, and gamma) are nuclear hormone transcription factors that control FA homeostasis, in part through the regulation of expression of membrane-bound FA transporting proteins. The present study was designed to elucidate the expression of PPAR and RXR isoforms and FA transporting proteins (FABPpm and FAT/CD36) in the rat and human GI tracts using reverse transcriptase-polymerase chain reaction (RT-PCR), immunoblotting, and immunohistochemical staining. The results revealed rat GI expression of all the PPAR and RXR isoforms, FABPpm and FAT/CD36. PPARalpha, PPARbeta, PPARgamma, RXRalpha, FABPpm, and FAT/CD36 isoforms exhibited ubiquitous expression in human GI tract, whereas RXRbeta was not detected. RXRgamma was observed in a majority of the human GI samples. These results provide a physiological foundation for rational drug design and drug delivery for the mitigation of metabolic syndrome and associated disorders to normalize intestinal FA absorption.

Cholesterol and cholesterol plus DHA diet-induced gene expression and fatty acid changes in mouse eye and brain

Both cholesterol and polyunsaturated fatty acid (PUFA) metabolism play an important role in retinal and brain development and function. Dietary intake of cholesterol is accompanied with higher risk of heart disease and was suggested to have a role in the pathogenesis of Alzheimer's disease, while dietary PUFAs were reported to act in an opposite way. The same phenomena could be seen in case of inflammation. These effects are mainly realized through gene expression changes. In the present study, the effects of dietary cholesterol and the combination of cholesterol and fish oil were analyzed on the modulation of fatty acid composition and gene expression in the brain and in the eye. At the transcription level, specific changes could be detected in both tissues among transcription factor genes coding for sterol regulatory element binding proteins, retinoid X receptors and peroxisome proliferator-activated receptors, and different fatty acid binding protein genes by using quantitative real-time PCR. In the eye, cholesterol diet attenuated the positive effects of fish oil on inflammatory gene expression as the combined diet resulted in increased RNAm level of phospholipase A-2, inducible nitric oxide synthase, TNF-alpha, COX-1, COX-2 and cytokine, ICAM-1. This induction was absent in the brain. Complex changes could be also recorded in the fatty acid composition of lipids extracted from eye and brain tissue due to the dietary intervention. One of the most interesting changes was the reduced level of docosahexaenoic acid by cholesterol in the eye. Our results on fatty acid composition and gene expression changes may open up new alleys in understanding the complex roles of cholesterol and PUFAs in normal and pathological visual and brain function.

Polyunsaturated Fatty Acid Regulation of Gene Expression

Polyunsaturated fatty acids (PUFAs), specifically the n-3 series, have been implicated in the prevention of various human diseases, including obesity, diabetes, coronary heart disease and stroke, and inflammatory and neurologic diseases. PUFAs function mainly by altering membrane lipid composition, cellular metabolism, signal transduction, and regulation of gene expression. PUFAs regulate the expression of genes in various tissues, including the liver, heart, adipose tissue, and brain. The role of transcription factors such as SREBP1c and nuclear receptors such as PPAR-alpha, HNF-4alpha, and LXRalpha in mediating the nuclear effects of PUFAs are addressed.

Effects of dietary omega-3 polyunsaturated fatty acids on brain gene expression

Polyunsaturated fatty acids (PUFA) are essential structural components of the central nervous system. Their role in controlling learning and memory has been well documented. A nutrigenomic approach with high-density microarrays was used to reveal brain gene-expression changes in response to different PUFA-enriched diets in rats. In aged rats fed throughout life with PUFA-enriched diets, genes with altered expressions included transthyretin, alpha-synuclein, and calmodulins, which play important roles in synaptic plasticity and learning. The effect of perinatal omega-3 PUFA supply on gene expression later in life also was studied. Several genes showed similar changes in expression in rats fed omega-3-deficient diets in the perinatal period, regardless of whether they or their mothers were fed omega-3 PUFA-sufficient diets after giving birth. In this experiment, among the down-regulated genes were a kainate glutamate receptor and a DEAD-box polypeptide. Among the up-regulated genes were a chemokine-like factor, a tumor necrosis factor receptor, and cytochrome c. The possible involvement of the genes with altered expression attributable to different diets in different brain regions in young and aged rats and the possible mode of regulatory action of PUFA also are discussed. We conclude that PUFA-enriched diets lead to significant changes in expression of several genes in the central nervous tissue, and these effects appear to be mainly independent of their effects on membrane composition. The direct effects of PUFA on transcriptional modulators, the downstream developmentally and tissue-specifically activated elements might be one of the clues to understanding the beneficial effects of the omega-3 PUFA on the nervous system.

Do we need additional markers of myocyte necrosis: the potential value of heart fatty-acid-binding protein

Heart fatty-acid-binding protein (FABP) is a small cytosolic protein that is abundant in the heart and has low concentrations in the blood and in tissues outside the heart. It appears in the blood as early as 1.5 h after onset of symptoms of infarction, peaks around 6 h and returns to baseline values in 24 h. These features of H-FABP make it an excellent potential candidate for the detection of acute myocardial infarction (AMI). We review the strengths and weaknesses of H-FABP as a clinically applicable marker of myocyte necrosis in the context of acute coronary syndromes.

Polyunsaturated fatty acids and gene expression in mammalian systems

Over the last 30 years it has become apparent that specific dietary fatty acids are capable of regulating, either directly or indirectly through various signal pathways, the expression of numerous genes, either positively or negatively. Such nutrient-gene interactions have important effects on cell metabolism, differentiation and growth, and ultimately on disease processes. The present review describes some of the more important fatty acid-gene interactions in relation to health and disease in mammalian species, and focuses on the underlying cell signal mechanisms, including various transcription factors, affected by fatty acids and some of their oxygenated derivatives, e.g. the eicosanoids. The review also attempts to clarify some of the complexities of the effects of fatty acids by suggesting a possible overriding regulation by the redox status of the cell. The latter will at least stimulate controversy in this exciting area of lipid research.

Intestinal resection- and steroid-associated alterations in gene expression were not accompanied by changes in lipid uptake

BACKGROUND/AIMS

Glucocorticosteroids alter the morphology and transport function of the intestine of adult rats. This study was undertaken to assess the possible effect on intestinal lipid uptake of the locally acting steroid budesonide, or the systemically active prednisone or dexamethasone.

METHODS

Sprague-Dawley rats underwent intestinal transection or 50% intestinal resection. Budesonide, prednisone, dexamethasone, or control vehicle was given for 2 weeks from the time of surgery. Uptake was measured using ring uptake technique.

RESULTS

Resection had no effect on the mRNA expression for the early response genes, for proglucagon, or for the ileal lipid binding protein (ILBP), but was associated with reduced jejunal ornithine decarboxylase (ODC) mRNA and with reduced jejunal mRNA for the liver fatty acid binding protein (L-FABP). All three steroids reduced jejunal mRNA for proglucagon and c-jun, and did not affect the mRNA for L-FABP or for ILBP. These resection- and steroid-associated changes in gene expression were not associated with alterations in the intestinal uptake of long chain fatty acids or cholesterol.

CONCLUSIONS

The resection-associated alterations in the RNA expression of ODC and L-FABP and the steroid-associated changes in mRNA expression of c-jun and proglucagon were not accompanied by variations in lipid uptake.

Is there a single mechanism for fatty acid regulation of gene transcription?

Besides their role as energetic molecules, fatty acids (FAs) also act as signals involved in regulating gene expression. This review focuses on a few examples of FA regulation. The hepatic lipogenic enzyme, fatty acid synthase (FAS) is negatively regulated by polyunsaturated FAs (PUFAs) which suppress sterol regulatory element-binding protein 1 (SREBP 1) gene expression and nuclear content in hepatocytes, thereby reducing FAS gene transcription. It was proposed recently that this reduction in SREBP 1 was the result of a PUFA-induced antagonism of ligand-dependent activation of the liver X nuclear receptor (LXR), known to be an inducer of the SREBP 1 gene. In contrast, several genes are turned on by long-chain (LCFAs) and nonmetabolized FAs in a physiologically relevant manner. These include the acyl-CoA oxidase (AOX), the liver carnitine palmitoyltransferase 1 (L-CPT 1) and the liver fatty acid binding protein (L-FABP). While induction of AOX gene transcription appears to be PPARalpha-dependent, that of the L-CPT 1 gene seems disconnected from PPAR activation. Results obtained in preadipocytes and in intestine cells are in support of a key role played by the beta/delta isoform of PPAR in LCFA induction of the FABP gene. Transcription of the phosphoenolpyruvate carboxykinase (PEPCK) gene is stimulated by unsaturated and nonmetabolized LCFAs specifically in adipocytes. Our results reported here support the notion that the mechanisms by which PPARgamma activators and FAs induce transcription of the PEPCK gene are distinct. Altogether these data argue that several FA effects are PPAR-independent. Evidences suggesting that other transcription factors might be involved are debated. It seems now clear that depending upon the cell-specific context and the target gene, FAs can take very different routes to alter transcription.

Expression of PPAR and RXR isoforms in the developing rat and human term placentas

Placental fatty acid transfer is critical to meet the foetal requirements necessary for the biosynthesis of biological membranes, myelin, and various signaling molecules. The primary objective of this research was to elucidate the placental expression patterns of genes that may potentially regulate placental fatty acid transfer and homeostasis. In this study, we have elucidated the temporal and spatial patterns of expression of peroxisome proliferator-activated receptor (PPAR) and 9-cis retinoic acid receptor (RXR) isoforms in the junctional and labyrinth zones of the developing rat chorioallantoic placenta and in human term placenta. PPAR (alpha, beta, and gamma) and RXR (alpha, beta, and gamma) isoforms are nuclear hormone receptors that are known to regulate gene transcription and protein expression levels of fatty acid transport and metabolism mediating proteins through the formation of a DNA binding heterodimer complex. In the present study, the expression patterns of PPAR and RXR isoforms were determined in developing rat placenta and human term placenta using RT-PCR and immunohistochemical analyses. PPARalpha, beta, gamma, RXRalpha, beta and gamma were expressed in both junctional (invasive/endocrine function) and labyrinth (transport barrier) zones of the rat placenta, from day 13 to day 21 of gestation. In the human term placenta, PPARalpha, beta, gamma, RXRalpha and gamma were observed, while RXRbeta was not detected. Immunocytochemistry staining results determined the presence of PPARalpha, beta, gamma, RXRalpha and gamma to be specific to the syncytial trophoblast layer of the human chorionic villi. The presence of PPAR and RXR isoforms in both the rat and human placentas suggest that PPAR and RXR isoforms are potential regulators of placental lipid transfer and homeostasis. Our work provides a framework for the further investigation of PPAR and RXR isoform specific regulation of placental fatty acid uptake, transport and metabolism.

Influence of peroxisome proliferator-activated receptor alpha agonists on the intracellular turnover and secretion of apolipoprotein (Apo) B-100 and ApoB-48

The peroxisome proliferator-activated receptor (PPAR) alpha agonist WY 14,643 increased the secretion of apolipoprotein (apo) B-100, but not that of apoB-48, and decreased triglyceride biosynthesis and secretion from primary rat hepatocytes. These effects resulted in decreased secretion of apoB-100-very low density lipoprotein (VLDL) and an increased secretion of apoB-100 on low density lipoproteins/intermediate density lipoproteins. ApoB-48-VLDL was also replaced by more dense particles. The proteasomal inhibitor lactacystin did not influence the recovery of apoB-100 or apoB-48 in primary rat hepatocytes, indicating that co-translational (proteasomal) degradation is of less importance in these cells. Treatment with WY 14,643 made the recovery of apoB-100 sensitive to lactacystin, most likely reflecting the decreased biosynthesis of triglycerides. The PPAR alpha agonist induced a significant increase in the accumulation of pulse-labeled apoB-100 even after a short pulse (2-5 min). There was also an increase in apoB-100 nascent polypeptides, indicating that the co-translational degradation of apoB-100 was inhibited. However, a minor influence on an early posttranslation degradation cannot be excluded. This decreased co-translational degradation of apoB-100 explained the increased secretion of the protein. The levels of apoB-48 remained unchanged during these pulse-chase experiments, and albumin production was not affected, indicating a specific effect of PPAR alpha agonists on the co-translational degradation of apoB-100. These findings explain the difference in the rate of secretion of the two apoB proteins seen after PPAR alpha activation. PPAR alpha agonists increased the expression and biosynthesis of liver fatty acid-binding protein (LFABP). Increased expression of LFABP by transfection of McA-RH7777 cells increased the secretion of apoB-100, decreased triglyceride biosynthesis and secretion, and increased PPAR alpha mRNA levels. These findings suggest that PPAR alpha and LFABP could interact to amplify the effect of endogenous PPAR alpha agonists on the assembly of VLDL.

PPAR gamma ligands, troglitazone and pioglitazone, up-regulate expression of HMG-CoA synthase and HMG-CoA reductase gene in THP-1 macrophages

Recently it has been reported that macrophages express a nuclear receptor, peroxisome proliferator-activated receptor gamma (PPAR gamma). Using a ligand of PPAR gamma, troglitazone or pioglitazone, we have shown that the expression of two genes involved in cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase and HMG-CoA reductase, were increased by activation of PPAR gamma through a PPAR response element (PPRE) in THP-1 macrophages. In addition, treatment with troglitazone significantly increased the activity of HMG-CoA reductase and the amount of intracellular cholesterol. Thus, we conclude that PPAR gamma and its agonists increase the cholesterol content of macrophages by the increased expression of genes involved in cholesterol biosynthesis. These findings suggest that PPAR gamma may play a role in cholesterol metabolism in macrophages.

Locally and systemically active glucocorticosteroids modify intestinal absorption of lipids in rats

Orally administered systemically active steroids enhance the digestive and absorptive functions of the intestine, but their effect on lipid uptake is unknown. The effect of the locally acting steroid budesonide on intestinal absorptive function also is unknown. Accordingly, this study was undertaken to assess the influence of 4 wk of treatment of weaning male rats with a daily oral gavage of budesonide (BUD), prednisone (PRED), or control vehicle on the jejunal and ileal uptake of fatty acids and cholesterol. BUD enhanced jejunal uptake of oleic acid and ileal uptake of linoleic acid. PRED increased jejunal uptake of cholesterol and ileal uptake of lauric, palmitic, linoleic, and linolenic acids. Higher doses of BUD (up to 1 mg/kg) given to adult rats for 2 wk further increased the uptake of some lipids. The changes in the uptake of lipids were not due to variations in the weight of the intestinal mucosa or in the animals' food intake. Ileal ornithine decarboxylase mRNA expression was increased with PRED, but there were no steroid-associated changes in the expression of the mRNA of the early response genes c-myc, c-jun, or c-fos or of proglucagon, the liver fatty acid-binding protein (FABP), the ileal lipid-binding protein, tumor necrosis factor alpha, interleukin 2 (IL-2), IL-6, or IL-10. In summary, treatment of weanling rats with BUD and PRED enhances the uptake of some lipids by a process that is independent of the effects of early response genes and genes encoding cytokines, proglucagon, and FABP.

Effects of fatty acids and growth hormone on liver fatty acid binding protein and PPARalpha in rat liver

The aim of this study was to investigate the interaction between long-chain fatty acids (LCFA) and growth hormone (GH) in the regulation of liver fatty acid binding protein (LFABP) and peroxisome proliferator-activated receptor-alpha (PPARalpha). Cultured rat hepatocytes were given oleic acid (OA; 500 microM) and GH (100 ng/ml) for 3 days. LFABP mRNA increased 3.6-fold by GH and 5.7-fold by OA, and combined incubation with GH and OA increased LFABP mRNA 17.6-fold. PPARalpha mRNA was decreased 50% by GH, but OA had no effect. Hypophysectomized (Hx) female rats were treated with L-thyroxine, cortisol, GH, and dietary fat for 7 days. PPARalpha mRNA levels were three- to fourfold higher in Hx than in normal female rats. GH decreased PPARalpha mRNA 50% in Hx rats. Dietary triglycerides (10% corn oil) increased LFABP mRNA and cytosolic LFABP about twofold but had no effect on PPARalpha mRNA in Hx rats. GH and dietary triglycerides had an additive effect on LFABP expression. Dietary triglycerides increased mitochondrial hydroxymethylglutaryl-CoA synthase mRNA only in the presence of GH. The diet increased serum triglycerides in Hx rats, and GH treatment prevented this increase. Addition of cholesterol to the diet did not influence LFABP levels but mitigated increased hepatic triglyceride content. In summary, these studies show that GH regulates LFABP expression independently of PPARalpha. Moreover, GH has different effects on PPARalpha-responsive genes and does not counteract the effect of LCFA on the expression of these gene products.

Adaptive increase in pyruvate dehydrogenase kinase 4 during starvation is mediated by peroxisome proliferator-activated receptor alpha

Pyruvate dehydrogenase kinase isoform 4 (PDK4) is upregulated by starvation in many tissues of the body during starvation. This causes inactivation of the pyruvate dehydrogenase complex which blocks pyruvate oxidation and conserves lactate and alanine for gluconeogenesis. Enhanced PDK4 expression may be caused by the increase in free fatty acids that occurs during starvation. Free fatty acids can activate peroxisome proliferator-activated receptor alpha (PPARalpha), and activation of PPARalpha can promote PDK4 expression. This model is supported by the findings reported here that WY-14,643, a synthetic PPARalpha activator, increases PDK4 expression in wild-type mice but not in PPARalpha-null mice. Starvation likewise increases the expression of PDK4 in tissues of wild-type mice but not in tissues of PPARalpha-null mice. These findings document the functional importance of PPARalpha for PDK4 expression during starvation and suggest an important role for elevated free fatty acids in the induction.

Differential involvement of peroxisome-proliferator-activated receptors alpha and delta in fibrate and fatty-acid-mediated inductions of the gene encoding liver fatty-acid-binding protein in the liver and the small intestine

Liver fatty-acid-binding protein (L-FABP) is a cytoplasmic polypeptide that binds with strong affinity especially to long-chain fatty acids (LCFAs). It is highly expressed in both the liver and small intestine, where it is thought to have an essential role in the control of the cellular fatty acid (FA) flux. Because expression of the gene encoding L-FABP is increased by both fibrate hypolipidaemic drugs and LCFAs, it seems to be under the control of transcription factors, termed peroxisome-proliferator-activated receptors (PPARs), activated by fibrate or FAs. However, the precise molecular mechanism by which these regulations take place remain to be fully substantiated. Using transfection assays, we found that the different PPAR subtypes (alpha, gamma and delta) are able to mediate the up-regulation by FAs of the gene encoding L-FABP in vitro. Through analysis of LCFA- and fibrate-mediated effects on L-FABP mRNA levels in wild-type and PPARalpha-null mice, we have found that PPARalpha in the intestine does not constitute a dominant regulator of L-FABP gene expression, in contrast with what is known in the liver. Only the PPARdelta/alpha agonist GW2433 is able to up-regulate the gene encoding L-FABP in the intestine of PPARalpha-null mice. These findings demonstrate that PPARdelta can act as a fibrate/FA-activated receptor in tissues in which it is highly expressed and that L-FABP is a PPARdelta target gene in the small intestine. We propose that PPARdelta contributes to metabolic adaptation of the small intestine to changes in the lipid content of the diet.

Regulation of Plasma fatty acid metabolism

Although adipose tissue serves a crucial function in energy storage, excess adipose tissue--that is, obesity--is often associated with diabetes and cardiovascular disease. A common thread in the weave of complications is increased plasma concentrations of fatty acids. In the present review, we have focused on two specific points that relate to obesity: (i) What are the metabolic consequences of increased free fatty acid concentrations? and (ii) What are the physiological factors that are involved in the regulation of fatty acid uptake or release from adipose tissue? We have tried to emphasize new factors that act as hormones on adipose tissue and in so doing regulate the net concentration of circulating free fatty acids.

Glutamine and regulation of gene expression in rat hepatocytes: the role of cell swelling

Glutamine is able to regulate the expression of various genes in rat hepatocytes. This includes genes coding for proteins involved in glutamine utilization, such as argininosuccinate synthetase (ureagenesis) or phosphoenolpyruvate carboxykinase (gluconeogenesis). Moreover, glutamine is also able to stimulate the expression of genes involved in the acute-phase response, such as the alpha 2-macroglobulin gene. The effect of glutamine on the regulation of gene expression may be explained, at least in part, by the cell swelling due to its sodium-dependent transport. The physiological significance of the effect of glutamine is discussed.

Regulation of gene expression by fatty acids

Long-chain fatty acids regulate the transcription of several genes encoding proteins involved in energetic metabolism. This review discusses the relative contribution of free fatty acids or their coenzyme A ester as metabolite signals and the possibility that the control of gene transcription could be independent of the activation of peroxisome proliferator-activated receptors.

Polyunsaturated fatty acid regulation of gene expression

For the past three decades, polyunsaturated fatty acids (PUFA) have been recognized as important energy sources and membrane components. PUFA also play key roles in many cellular events, such as gene regulation. Most recently, research has focused on identifying the mechanisms by which PUFA modulate gene transcription, mRNA stability and cellular differentiation. It is the purpose of this review to examine the effects of PUFA on gene expression in lipogenic as well as other tissues. Because the (n-3) and (n-6) series of PUFA are intimately involved in gene regulation, they will be the focus of review. The effects of other fatty acid families on gene expression are reviewed elsewhere.

9-cis-retinoic acid enhances fatty acid-induced expression of the liver fatty acid-binding protein gene

The role of retinoic acids (RA) on liver fatty acid-binding protein (L-FABP) expression was investigated in the well differentiated FAO rat hepatoma cell line. 9-cis-Retinoic acid (9-cis-RA) specifically enhanced L-FABP mRNA levels in a time- and dose-dependent manner. The higher induction was found 6 h after addition of 10(-6) M 9-cis-RA in the medium. RA also enhanced further both L-FABP mRNA levels and cytosolic L-FABP protein content induced by oleic acid. The retinoid X receptor (RXR) and the peroxisome proliferator-activated receptor (PPAR), which are known to be activated, respectively, by 9-cis-RA and long chain fatty acid (LCFA), co-operated to bind specifically the peroxisome proliferator-responsive element (PPRE) found upstream of the L-FABP gene. Our result suggest that the PPAR-RXR complex is the molecular target by which 9-cis-RA and LCFA regulate the L-FABP gene.