Discordant Fetal Leptin Levels in Monochorionic Twins with Chronic Midtrimester Twin–Twin Transfusion Syndrome

The objective of this study was to determine the plasma leptin concentrations in monochorionic twin fetuses with and without twin-twin transfusion syndrome (TTTS). Paired maternal and fetal blood samples were obtained at birth from monochorionic twin pregnancies complicated with (n=12) or without TTTS (n=12). Amniotic fluid samples were also collected from twin pairs at amnioreduction and/or fetal blood sampling in utero. Plasma and amniotic fluid leptin concentrations were measured by radio-immunoassay. Fetal leptin levels in the growth-restricted donor were lower than the recipient twin of the TTTS group (Delta mean 3.7; CI 2.6 to 4.7 ng/ml; P< 0.001). Fetal leptin levels were comparable between non-TTTS twin pairs (Delta mean 0.9; CI 0.1 to 1.4 ng/ml; P=0.10) and recipient twins of TTTS (P=NS). Maternal plasma concentrations of leptin were comparable between the two groups and were higher than the fetal levels. There was a positive association between cord leptin levels and birthweight of twin pairs (y=0.002x-0.37; r=0.58; P< 0.01; n=48). A significant positive relation was also found between delta leptin levels and percentage discordance in birthweight in the TTTS group (y=0.25x-2.21; r=0.82; P< 0.001, n=12). In conclusion, leptin levels in the recipient twins were three times higher than their growth restricted donor twins. However further studies are warranted to elucidate the underlying mechanism.

The genetics and pathology of oxidative phosphorylation

The mitochondrial oxidative phosphorylation (OXPHOS) system is the final biochemical pathway in the production of ATP. The OXPHOS system consists of five multiprotein complexes, the individual subunits of which are encoded either by the mitochondrial or by the nuclear genome. Defects in the OXPHOS system result in devastating, mainly multisystem, diseases, and recent years have seen the description of the underlying genetic mutations in mitochondrial and nuclear genes. Advances in this arena have profited from progress in various genome projects, as well as improvements in our ability to create relevant animal models.

Up-regulation of uncoupling proteins by beta-adrenergic stimulation in L6 myotubes

Catecholamine-induced and beta-adrenergic receptor (beta-AR)-mediated thermogenesis in skeletal muscle is a significant component of whole-body energy expenditure. Skeletal muscle expresses uncoupling protein (UCP) 2 and UCP3, which can dissipate the transmitochondrial electrochemical gradient and thereby may be involved in regulation of energy metabolism. We investigated the effects of beta-AR stimulation on UCP2 and UCP3 expression in L6 myotubes. Stimulation of the cells with epinephrine increased the UCP3 mRNA level transiently at 6 h, and also the UCP2 mRNA level at 6-24 h. The stimulatory effects of epinephrine were also observed in the presence of carbacyclin and 9-cis retinoic acid, and mimicked by isoproterenol and salbutamol (beta2-AR agonists), but abolished by propranolol and ICI-118,551 (beta2-AR antagonists). Pharmacological and mRNA analyses revealed the existence of beta2-AR, but not beta1- and beta3-ARs, in L6 myotubes. These results suggested that catecholamines up-regulate UCP2 and UCP3 expression through direct action on the beta2-AR in skeletal muscle.

Morphological architecture and distribution of blood capillaries and elastic fibres in the human skin

This study was undertaken to clarify the morphological features in the blood capillary and elastic fibre distribution of the human skin in terms of susceptibility to pressure sore development. Skin tissues were obtained from bony areas: the sacrum and ischial tuberosity and non-bony area: the centre of the gluteus maximus of 5 aged subjects post mortem for examination using light and scanning electron microscopy. It was observed that the sacral skin had finger-like papillae and underneath the blood capillary loops were most numerous. In the ischial skin the dermal papillae consisted of a combination of finger-like and trapezoid shapes having moderate density of blood capillaries. In contrast, the dermal papillae in the gluteal skin were almost flat, so that the blood capillaries were scattered. The size of elastic bundles in the papillary layer of the sacral, ischial and gluteal skin ranged from 2 to 3 microns, 5 to 10 microns, and 3 to 5 microns, respectively. The elastic fibres were densely distributed in the ischial skin while less so in the sacral skin.

New developments in mechanisms of obesity-induced hypertension: role of adipose tissue

Hypertension develops in almost 60% of obese individuals. Apart from the recent observation of obesity-associated structural changes in kidney structure that may lead to enhanced tubular sodium reabsorbtion, reports of paracrine and hormonal factors derived from adipose tissue have prompted speculations about the role of adipose tissue in the pathophysiology of obesity-induced hypertension. We summarize recent data on leptin's sympathoexcitatory actions, the possible influence of adipose tissue on atrial natriuretic peptide levels, and the formation of vasoactive substances, such as angiotensin II and nonesterified fatty acids, by adipocytes. The mechanisms discussed herein may contribute to the typical findings in obesity-induced hypertension, including volume expansion, sodium retention, enhanced sympathetic nervous system activity, increased activity of the systemic renin-angiotensin system, low atrial natriuretic peptide levels, and disturbed glucose and insulin metabolism. Together, these data strengthen the hypothesis that adipose tissue is potentially a major regulator of cardiovascular-renal function.

What regulates mitochondrial DNA copy number in animal cells?

The study of the control of mitochondrial DNA copy number spans several decades and has identified many factors involved in the replication of the mitochondrial genome. However, the mechanisms involved in the regulation of this process are still obscure, particularly in animal cells. During the past decade, however, the identification of human diseases associated with drastically reduced levels of mtDNA caused renewed interest in this topic. Here, I will discuss recent work that sheds some light on how animal cells might maintain and control mtDNA levels.

Isoform-specific regulation of vascular endothelial growth factor (VEGF) family mRNA expression in cultured mouse brown adipocytes

We have shown that brown adipose tissue (BAT), a thermogenic organ in mammals, expresses high levels of vascular endothelial growth factor (VEGF) mRNA in response to exposure to cold, which may contribute to angiogenesis associated with cold-induced hyperplasia of this tissue. In the present study, we examined mRNA expression of not only VEGF, but also VEGF-B and VEGF-C, recently cloned VEGF isoforms, in vitro using immortal brown adipocytes (HB2) isolated from mouse BAT. HB2 preadipocytes expressed detectable levels of VEGF, VEGF-B and VEGF-C mRNA, but a low level of VEGF. After HB2 cells differentiated into adipocytes, the VEGF mRNA level increased without a noticeable change in the VEGF-B and VEGF-C mRNA levels. When HB2 cells were stimulated by norepinephrine, the VEGF mRNA level increased without a change in that of VEGF-B, while the VEGF-C mRNA level decreased. A marked reduction of VEGF-C mRNA expression was also found when HB2 cells were treated with agonists of peroxisome proliferator-activated receptor gamma (PPARgamma, troglitazone), retinoic acid receptor (RAR, all-trans retinoic acid) and retinoid X receptor (RXR, 9-cis retinoic acid). These results suggest a specific adrenergic mechanism for up-regulation of VEGF expression different from those for other VEGF isoforms, and thereby the major contribution of VEGF to the cold-induced angiogenesis in BAT. In addition, the agonists of PPARgamma, RAR and RXR are suggested to be inhibitory to angiogenesis through the reduction of VEGF-C production.

Restoration of insulin-sensitive glucose transporter (GLUT4) gene expression in muscle cells by the transcriptional coactivator PGC-1

Muscle tissue is the major site for insulin-stimulated glucose uptake in vivo, due primarily to the recruitment of the insulin-sensitive glucose transporter (GLUT4) to the plasma membrane. Surprisingly, virtually all cultured muscle cells express little or no GLUT4. We show here that adenovirus-mediated expression of the transcriptional coactivator PGC-1, which is expressed in muscle in vivo but is also deficient in cultured muscle cells, causes the total restoration of GLUT4 mRNA levels to those observed in vivo. This increased GLUT4 expression correlates with a 3-fold increase in glucose transport, although much of this protein is transported to the plasma membrane even in the absence of insulin. PGC-1 mediates this increased GLUT4 expression, in large part, by binding to and coactivating the muscle-selective transcription factor MEF2C. These data indicate that PGC-1 is a coactivator of MEF2C and can control the level of endogenous GLUT4 gene expression in muscle.

TNF-alpha inhibits UCP-1 expression in brown adipocytes via ERKs. Opposite effect of p38MAPK

Tumor necrosis factor-alpha (TNF-alpha) activates extracellular-regulated kinases (ERKs) and p38 mitogen-activated protein kinase (p38MAPK), and inhibits the expression of uncoupling protein-1 (UCP-1) and adipocyte-specific genes in rat fetal brown adipocytes. MEK inhibition with PD98059 abolished the inhibitory effect of TNF-alpha on UCP-1, but not on adipogenic genes. In contrast, inhibition of p38MAPK with SB203580 potentiated the negative effect of TNF-alpha on UCP-1 and adipogenic genes. The inhibitory action of TNF-alpha was partially correlated with changes in C/EBPalpha and beta protein levels and in their DNA binding activity, suggesting a role for these transcription factors. However, other transcription factors might explain the different regulation of UCP-1 and adipogenic genes by ERKs.

Molecular regulation of adipogenesis

Adipogenesis, or the development of fat cells from preadipocytes, has been one of the most intensely studied models of cellular differentiation. In part this has been because of the availability of in vitro models that faithfully recapitulate most of the critical aspects of fat cell formation in vivo. More recently, studies of adipogenesis have proceeded with the hope that manipulation of this process in humans might one day lead to a reduction in the burden of obesity and diabetes. This review explores some of the highlights of a large and burgeoning literature devoted to understanding adipogenesis at the molecular level. The hormonal and transcriptional control of adipogenesis is reviewed, as well as studies on a less well known type of fat cell, the brown adipocyte. Emphasis is placed, where possible, on in vivo studies with the hope that the results discussed may one day shed light on basic questions of cellular growth and differentiation in addition to possible benefits in human health.

Invited Review: contractile activity-induced mitochondrial biogenesis in skeletal muscle

Chronic contractile activity produces mitochondrial biogenesis in muscle. This adaptation results in a significant shift in adenine nucleotide metabolism, with attendant improvements in fatigue resistance. The vast majority of mitochondrial proteins are derived from the nuclear genome, necessitating the transcription of genes, the translation of mRNA into protein, the targeting of the protein to a mitochondrial compartment via the import machinery, and the assembly of multisubunit enzyme complexes in the respiratory chain or matrix. Putative signals involved in initiating this pathway of gene expression in response to contractile activity likely arise from combinations of accelerations in ATP turnover or imbalances between mitochondrial ATP synthesis and cellular ATP demand, and Ca(2+) fluxes. These rapid events are followed by the activation of exercise-responsive kinases, which phosphorylate proteins such as transcription factors, which subsequently bind to upstream regulatory regions in DNA, to alter transcription rates. Contractile activity increases the mRNA levels of nuclear-encoded proteins such as cytochrome c and mitochondrial transcription factor A (Tfam) and mRNA levels of upstream transcription factors like c-jun and nuclear respiratory factor-1 (NRF-1). mRNA level changes are often most evident during the postexercise recovery period, and they can occur as a result of contractile activity-induced increases in transcription or mRNA stability. Tfam is imported into mitochondria and controls the expression of mitochondrial DNA (mtDNA). mtDNA contributes only 13 protein products to the respiratory chain, but they are vital for electron transport and ATP synthesis. Contractile activity increases Tfam expression and accelerates its import into mitochondria, resulting in increased mtDNA transcription and replication. The result of this coordinated expression of the nuclear and the mitochondrial genomes, along with poorly understood changes in phospholipid synthesis, is an expansion of the muscle mitochondrial reticulum. Further understanding of 1) regulation of mtDNA expression, 2) upstream activators of NRF-1 and other transcription factors, 3) the identity of mRNA stabilizing proteins, and 4) potential of contractile activity-induced changes in apoptotic signals are warranted.

The regulation of skin proliferation and differentiation in the IR null mouse: implications for skin complications of diabetes

Impaired wound healing of skin is one of the most serious complications of diabetes. However, the pathogenesis of this process is not known, and it is unclear whether impaired insulin signaling could directly affect skin physiology. To elucidate the role of insulin in skin, we studied skin insulin receptor (IR) null mice. The morphology of the skin of newborn IR null mice was normal; however, these mice exhibited decreased proliferation of skin keratinocytes and changes in expression of skin differentiation markers. Due to the short life span of the IR null mice, further characterization was performed in cultured skin keratinocytes that can be induced to differentiate in vitro, closely following the maturation pattern of epidermis in vivo. It was found that despite a compensatory increase in the insulin-like growth factor I receptor autophosphorylation, differentiation of cultured IR null keratinocytes was markedly impaired. In vitro proliferation was not affected as much. Furthermore, although the basal glucose transport system of the null mice was not defective, the insulin-induced increase in glucose transport was abrogated. These results suggest that insulin regulates, via the IR, the differentiation and glucose transport of skin keratinocytes, whereas proliferation is affected by the diabetes milieu of IR knockout mice.

Uncoupling protein 3 transcription is regulated by peroxisome proliferator-activated receptor (alpha) in the adult rodent heart

Relatively little is known concerning the regulation of uncoupling proteins (UCPs) in the heart. We investigated in the adult rodent heart 1) whether changes in workload, substrate supply, or cytokine (TNF-alpha) administration affect UCP-2 and UCP-3 expression, and 2) whether peroxisome proliferator-activated receptor alpha (PPARalpha) regulates the expression of either UCP-2 or UCP-3. Direct comparisons were made between cardiac and skeletal muscle. UCP-2, UCP-3, and PPARalpha expression were reduced when cardiac workload was either increased (pressure overload by aortic constriction) or decreased (mechanical unloading by heterotopic transplantation). Similar results were observed during cytokine administration. Reduced dietary fatty acid availability resulted in decreased expression of both cardiac UCP-2 and UCP-3. However, when fatty acid (the natural ligand for PPARalpha) supply was increased (high-fat feeding, fasting, and STZ-induced diabetes), cardiac UCP-3 but not UCP-2 expression increased. Comparable results were observed in rats treated with the specific PPARalpha agonist WY-14,643. The level of cardiac UCP-3 but not UCP-2 expression was severely reduced (20-fold) in PPARalpha-/- mice compared to wild-type mice. These results suggest that in the adult rodent heart, UCP-3 expression is regulated by PPARalpha. In contrast, cardiac UCP-2 expression is regulated in part by a fatty acid-dependent, PPARalpha-independent mechanism.

Monoclonal antibody against brain natriuretic peptide and characterization of brain natriuretic peptide-transgenic mice

OBJECTIVE

Brain natriuretic peptide (BNP) is a ventricular hormone with natriuretic, diuretic and vasodilatory actions. Acute infusion of BNP reduces cardiac pre- and after-load in healthy and diseased subjects, but its long-term therapeutic usefulness remains unclear.

DESIGN

We prepared a monoclonal antibody specific to mouse BNP, and characterized transgenic mice overexpressing BNP in the liver (BNP-Tg mice) as a model of its chronic overproduction.

METHODS

Radioimmunoassay and neutralization experiments using the monoclonal antibody, KY-mBNP-I, were performed in BNP-Tg mice in conjunction with examinations of blood pressure (BP) and other markers for body fluid homeostasis.

RESULTS

We developed highly sensitive radioimmunoassay to mouse BNP. In BNP-Tg mice, the plasma BNP concentration increased more than 100-fold, while ventricular BNP concentration did not alter, suggesting that ventricular BNP production was not down-regulated in BNP-Tg mice. The BNP concentration in the kidneys was 10-fold higher than nontransgenic (nonTg) littermates, accompanied with marked reduction in the atrial natriuretic peptide (ANP) concentration, that may be due to binding of circulating BNP to the natriuretic peptide receptors. BNP-Tg mice showed significantly low arterial BP, and a bolus intraperitoneal administration of KYmBNP-I completely abolished enhanced cGMP excretion in the urine and significantly increased the systolic BP.

CONCLUSION

These results suggested that biological actions of BNP last and reduce cardiac overload in its longterm overproduction in the transgenic mouse model.

Transcriptional control of adipogenesis

The major transcriptional factors involved in the adipogenic process include proteins belonging to the CCAAT/enhancer binding protein family, peroxisome proliferator-activated receptor gamma, and adipocyte determination and differentiation dependent factor 1, also known as sterol regulatory element-binding protein 1. This process has been characterized with the aid of cell lines that represent various stages in the path of adipocyte commitment, ranging from pluripotent mesodermal fibroblasts to preadipocytes. Molecular analyses have led to a cascade model for adipogenesis based on timed expression of CCAAT/enhancer-binding proteins and peroxisome proliferator-activated receptor gamma. Gene targeting and transgenic-mouse technologies, which allow the manipulation of endogenous genes for these transcription factors, have also contributed to the understanding of adipogenesis. This review aims to integrate this information to gain an understanding of the transcriptional regulation of fat cell formation.

Regulation of metabolism and body fat mass by leptin

The relative stability of body weight over the long term and under a variety of environmental conditions that alter short-term energy intake and expenditure provides strong evidence for the regulation of body energy content. The lipostatic theory of energy balance regulation proposed 40 years ago that circulating factors, generated in proportion to body fat stores, acted as signals to the brain, eliciting changes in energy intake and expenditure. The discovery of leptin and its receptors has now provided a molecular basis for this theory. Leptin functions as much more than an adipocyte-derived signal of lipid stores, however. Although suppression of food intake is an important centrally mediated effect of leptin, considerable evidence indicates that leptin also functions both directly and indirectly, via the brain, to orchestrate complex metabolic changes in a number of organs and tissues, altering nutrient flux to favor energy expenditure over energy storage.

The role of hyperplasia in multiple parathyroid adenomas

BACKGROUND

Parathyroid adenoma is the most common cause of primary hyperparathyroidism (pHPT). Adenomas usually involve only a single gland, and the remaining glands are normal or suppressed. Multiple parathyroid adenomas have been reported to occur in as high as 11% of patients with pHPT. The significant incidence of multiple adenomas with histologic similarities to hyperplasia has raised the possibility that adenoma is a continuation of the hyperplasia state. To test this theory, we used molecular genetics to compare clonality and proliferative activity of parathyroid adenoma with its corresponding normal glandular tissue. Furthermore, we devised a scheme to definitively distinguish between the different parathyroid states on a molecular level, because histologic distinction is unreliable.

METHODS

The study included three patients with a diagnosis of singular parathyroid adenoma and three with double parathyroid adenomas. Paraffin-embedded surgical specimens of both adenomas and normal glands were retrieved from each patient. Clonal analysis of the phosphoglycerolkinase (PGK) gene has suggested that parathyroid adenomas are monoclonal. Clonality of parathyroid adenomas and normal parathyroid glands was studied by polymerase chain reaction-based restriction fragment length polymorphic analysis for the PGK gene. Proliferative activity of the specimens was also analyzed using the immunohistochemical markers PCNA and Ki-67.

RESULTS

All adenomas were monoclonal and all normal parathyroid glands were polyclonal for the PGK gene in both the single and double adenoma specimens. All adenomas stained positive for proliferative activity. In the three patients with singular adenoma, proliferative activity was not detected in the normal parathyroid tissue. However, in the double adenoma group, two of the three patients showed hyperproliferative activity in the normal glands.

CONCLUSION

Proliferative activity consistent with hyperplasia was present in some normal glands of multiple adenoma patients. Our observation supports the theory that multiple adenomas may be a continuation of the hyperplasia state.

Animal mitochondrial biogenesis and function: a regulatory cross-talk between two genomes

Mitochondria play a pivotal role in cell physiology, producing the cellular energy and other essential metabolites as well as controlling apoptosis by integrating numerous death signals. The biogenesis of the oxidative phosphorylation system (OXPHOS) depends on the coordinated expression of two genomes, nuclear and mitochondrial. As a consequence, the control of mitochondrial biogenesis and function depends on extremely complex processes that require a variety of well orchestrated regulatory mechanisms. It is now clear that in order to provide cells with the correct number of structural and functional differentiated mitochondria, a variety of intracellular and extracellular signals including hormones and environmental stimuli need to be integrated. During the last few years a considerable effort has been devoted to study the factors that regulate mtDNA replication and transcription as well as the expression of nuclear-encoded mitochondrial genes in physiological and pathological conditions. Although still in their infancy, these studies are starting to provide the molecular basis that will allow to understand the mechanisms involved in the nucleo-mitochondrial communication, a cross-talk essential for cell life and death.

Mechanisms for LEPR-mediated regulation of leptin expression in brown and white adipocytes in rat pups

To investigate the underlying mechanisms for leptin receptor (LEPR)-mediated regulation of leptin gene (Lep) expression in brown (BAT) and white (WAT) adipose tissue and resultant effects on plasma leptin concentrations (plasma-LEP), we examined effects of sympathetic nervous system (SNS) activity, caloric balance, and body fat content on leptin mRNA levels in BAT and WAT in 10-day-old rat pups segregating for Lepr(fa). In mother-reared pups, Lep mRNA levels were fa/fa > +/fa = +/+ in BAT and was fa/fa > +/fa > +/+ in WAT. The genotype effects on Lep expression in BAT and plasma-LEP were virtually eliminated when the differences in SNS activity between fa/fa and +/fa pups were equalized by artificial rearing of pups under thermoneutral conditions with or without oral norepinephrine (NE) administration. NE administration alone had little effect on the Lepr(fa)-dependent stratification of Lep expression in WAT. BAT-Lep mRNA was the main determinant of plasma-LEP. Metabolic rate, a surrogate indicator of SNS activity, explained 87% of the variation in BAT-Lep mRNA (R(2) = 0.93), whereas caloric balance (40%) and body fat mass (6%) accounted for most of the variation in WAT-Lep mRNA (R(2) = 0.53). We conclude that feedback regulation of Lep expression in BAT is primarily via central nervous system-mediated effects of leptin on SNS activity, whereas the control of leptin expression in WAT is more likely via mechanisms not directly dependent on SNS activity.

IGF-1 receptor as an alternative receptor for metabolic signaling in insulin receptor-deficient muscle cells

We have derived skeletal muscle cell lines from wild-type (wt) and insulin receptor (IR) knockout mice to unravel the metabolic potential of IGF-1 receptor (IGF-1R). Both wt and IR(-/-) myoblasts differentiated into myotubes with similar patterns of expression of muscle-specific genes such as MyoD, myogenin and MLC1A indicating that IR is not required for this process. Binding of 125I-IGF-1 on wt and IR(-/-) myotubes was similar showing that IGF-1R was not upregulated in the absence of IR. Stimulation of IR(-/-) myotubes with IGF-1 (10(-10) to 10(-7) M) increased glucose uptake and incorporation into glycogen, induced IRS-1 phosphorylation and activated PI 3-kinase and MAP kinase, two enzymes of major signaling pathways. These effects were comparable to those obtained with wt myotubes using insulin or IGF-1 or with IR(-/-) myotubes using insulin at higher concentrations. This study provides a direct evidence that IGF-1R can represent an alternative receptor for metabolic signaling in muscle cells.

Peroxisomal bifunctional enzyme binds and activates the activation function-1 region of the peroxisome proliferator-activated receptor alpha

The transcriptional activity of peroxisome proliferator-activated receptors (PPARs), and of nuclear hormone receptors in general, is subject to modulation by cofactors. However, most currently known co-activating proteins interact in a ligand-dependent manner with the C-terminal ligand-regulated activation function (AF)-2 domain of nuclear receptors. Since PPARalpha exhibits a strong constitutive transactivating function contained within an N-terminal AF-1 region, it can be speculated that a different set of cofactors might interact with this region of PPARs. An affinity purification approach was used to identify the peroxisomal enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase (bifunctional enzyme, BFE) as a protein which strongly and specifically interacted with the N-terminal 92 amino acids of PPARalpha. Protein-protein interaction assays with the cloned BFE confirmed this interaction, which could be mapped to amino acids 307-514 of the BFE and the N-terminal 70 amino acids of PPARalpha. Moreover, transient transfection experiments in hepatoma cells revealed a 2.2-fold increase in the basal and ligand-stimulated transcriptional activity of PPARalpha in the presence of BFE. This stimulatory effect is preferentially observed for the PPARalpha isoform and it is significantly stronger (4.8-fold) in non-hepatic cells, which presumably express lower levels of endogenous BFE. Hence, the BFE represents the first known cofactor capable of activating the AF-1 domain of PPAR without requiring additional regions of this receptor. These data are compatible with a model whereby the PPAR-regulated BFE is able to modulate its own expression through an enhancement of the activity of PPARalpha, representing a novel peroxisomal-nuclear feed-forward regulatory loop.

Peroxisome proliferator-activated receptor alpha activates transcription of the brown fat uncoupling protein-1 gene. A link between regulation of the thermogenic and lipid oxidation pathways in the brown fat cell

High expression of the peroxisome proliferator-activated receptor alpha (PPARalpha) differentiates brown fat from white, and is related to its high capacity of lipid oxidation. We analyzed the effects of PPARalpha activation on expression of the brown fat-specific uncoupling protein-1 (ucp-1) gene. Activators of PPARalpha increased UCP-1 mRNA levels severalfold both in primary brown adipocytes and in brown fat in vivo. Transient transfection assays indicated that the (-4551)UCP1-CAT construct, containing the 5'-regulatory region of the rat ucp-1 gene, was activated by PPARalpha co-transfection in a dose-dependent manner and this activation was potentiated by Wy 14,643 and retinoid X receptor alpha. The coactivators CBP and PPARgamma-coactivator-1 (PGC-1), which is highly expressed in brown fat, also enhanced the PPARalpha-dependent regulation of the ucp-1 gene. Deletion and point-mutation mapping analysis indicated that the PPARalpha-responsive element was located in the upstream enhancer region of the ucp-1 gene. This -2485/-2458 element bound PPARalpha and PPARgamma from brown fat nuclei. Moreover, this element behaved as a promiscuous responsive site to either PPARalpha or PPARgamma activation, and we propose that it mediates ucp-1 gene up-regulation associated with adipogenic differentiation (via PPARgamma) or in coordination with gene expression for the fatty acid oxidation machinery required for active thermogenesis (via PPARalpha).

CCAAT/enhancer-binding protein alpha is required for transcription of the beta 3-adrenergic receptor gene during adipogenesis

The beta(3)-adrenergic receptor (beta(3)AR) is expressed predominantly in adipocytes, and it plays a major role in regulating lipolysis and adaptive thermogenesis. Its expression in a variety of adipocyte cell models is preceded by the appearance of CCAAT/enhancer-binding protein alpha (C/EBP alpha), which has been shown to regulate a number of other adipocyte-specific genes. Importantly, it has been demonstrated that several adipocyte cell lines that fail to express C/EBP alpha exhibit reduced insulin sensitivity, despite an apparent adipogenic phenotype. Here we show that transcription and function of the beta(3)AR correlates with C/EBP alpha expression in these adipocyte models. A 5.13-kilobase pair fragment of the mouse beta(3)AR promoter was isolated and sequenced. This fragment conferred a 50-fold increase in luciferase reporter gene expression in adipocytes. Two putative C/EBP binding sites exist at -3306 to -3298 and at -1462 to -1454, but only the more distal site is functional. Oligonucleotides corresponding to both the wild-type and mutated -3306 element were inserted upstream of a thymidine kinase luciferase construct. When cotransfected in fibroblasts with a C/EBP alpha expression vector, reporter gene expression increased 3-fold only in the wild-type constructs. The same mutation, when placed into the intact 5.13-kilobase pair promoter, reduced promoter activity in adipocytes from 50-fold to <10-fold. Electrophoretic mobility shift analysis demonstrated that the site at -3306 generated a specific protein-oligonucleotide complex that was supershifted by C/EBP alpha antibody, while a probe corresponding to a putative site at -1462 did not. These results define C/EBP alpha as a key transcriptional regulator of the mouse beta(3)AR gene during adipogenesis.

Mitochondrial DNA instability and peri-implantation lethality associated with targeted disruption of nuclear respiratory factor 1 in mice

In vitro studies have implicated nuclear respiratory factor 1 (NRF-1) in the transcriptional expression of nuclear genes required for mitochondrial respiratory function, as well as for other fundamental cellular activities. We investigated here the in vivo function of NRF-1 in mammals by disrupting the gene in mice. A portion of the NRF-1 gene that encodes the nuclear localization signal and the DNA-binding and dimerization domains was replaced through homologous recombination by a beta-galactosidase-neomycin cassette. In the mutant allele, beta-galactosidase expression is under the control of the NRF-1 promoter. Embryos homozygous for NRF-1 disruption die between embryonic days 3.5 and 6.5. beta-Galactosidase staining was observed in growing oocytes and in 2. 5- and 3.5-day-old embryos, demonstrating that the NRF-1 gene is expressed during oogenesis and during early stages of embryogenesis. Moreover, the embryonic expression of NRF-1 did not result from maternal carryover. While most isolated wild-type and NRF-1(+/-) blastocysts can develop further in vitro, the NRF-1(-/-) blastocysts lack this ability despite their normal morphology. Interestingly, a fraction of the blastocysts from heterozygous matings had reduced staining intensity with rhodamine 123 and NRF-1(-/-) blastocysts had markedly reduced levels of mitochondrial DNA (mtDNA). The depletion of mtDNA did not coincide with nuclear DNA fragmentation, indicating that mtDNA loss was not associated with increased apoptosis. These results are consistent with a specific requirement for NRF-1 in the maintenance of mtDNA and respiratory chain function during early embryogenesis.

Coeliac- and enteropathy-associated autoantibodies in Spanish insulin-dependent diabetes mellitus patients and their relation to HLA antigens

The frequency of reticulin (ARA), endomysium (EmA), and gut epithelial cell (GECA) autoantibodies, and gliadin antibodies (AGA), was investigated in 86 Spanish diabetic patients by indirect immunofluorescence (IFI) and ELISA, along with their HLA phenotype. Four patients (5%) showed ARA-IgG (R1 pattern), eight (9%) showed AGA-IgG, and eight (9%) showed AGA-IgA. No EmA or GECA-positive patients were found. In diabetic patients, HLA-DR7 is increased in ARA-IgG+ vs. ARA-IgG- (though not significantly), and HLA-DR6 and HLA-DQ1 are significantly increased in the AGA-IgG+ group vs. the AGA-IgG- group. Comparison with a non-diabetic coeliac group showed that HLA-DR4 and HLA-DQ3 are significantly increased in the AGA-IgA+ group, whereas HLA-DQ2 shows a significant decrease in the AGA-IgG+ and AGA-IgA+ patients. Finally, when compared to the healthy group, HLA-DR7 frequency is decreased in the ARA-IgG- group, while HLA-DQ3 is significantly increased and HLA-DR6 and HLA-DQ1 significantly decreased in the AGA-IgG- group.Altogether, these data suggest that the genetic background leading to the appearance of coeliac-specific autoantibodies in Spanish diabetic patients differ depending on the autoantibody produced and is also different to the genetic background leading to diabetes in Spain.

Triiodothyronine-mediated up-regulation of UCP2 and UCP3 mRNA expression in human skeletal muscle without coordinated induction of mitochondrial respiratory chain genes

Triiodothyronine (T3) increases mitochondrial respiration and promotes the uncoupling between oxygen consumption and ATP synthesis. T3 effect is mediated partly through transcriptional control of genes encoding mitochondrial proteins. We determined the effect of T3 on mRNA levels of uncoupling proteins (UCP) and proteins involved in the biogenesis of the respiratory chain in human skeletal muscle and on UCP2 mRNA expression in adipose tissue. Ten young, healthy males received 75 to 100 5g of T3 per day for 14 days. The increase in plasma-free T3 levels was associated with an increase of resting metabolic rate and a decrease of respiratory quotient. In skeletal muscle, treatment with T3 induced a twofold increase of both UCP2 and UCP3 mRNA levels (p c oxidase subunits 2 and 4, nuclear respiratory factor 1, mitochondrial transcription factor A, and the co-activator PGC1 did not change during the treatment. In adipose tissue, UCP2 mRNA levels increased threefold. The direct effect of T3 on skeletal muscle an d adipose tissue UCP2 and UCP3 mRNA expression was demonstrated in vitro in human primary cultures. Our data show that T3 induces UCP2 and UCP3 mRNA expression in humans. In skeletal muscle, UCP regulation by T3 is not associated with the transcriptional regulation of respiratory chain proteins.

Effect of cold exposure on energy balance and liver respiratory capacity in post-weaning rats fed a high-fat diet

Variations in energy balance, body composition, and nutrient partitioning induced by high-fat feeding, cold exposure or by concomitant high-fat feeding and cold exposure were studied in young Wistar rats. Changes in hepatic metabolism as well as in serum free triiodothyronine and leptin levels were also evaluated. Rats were exposed to either 24 or 4 degrees C and fed either a low- or high-fat diet (10 % or 50 % energy respectively) for 2 weeks. Relative to low-fat feeding at 24 degrees C, both energy intake and expenditure were increased by high-fat feeding or by cold exposure, and these changes were accompanied by increased serum triiodothyronine levels. In response to concomitant high-fat feeding and cold exposure, serum triiodothyronine tended to be further elevated, but no further increases in energy intake or energy expenditure were observed. Independently of diet, the increased energy expenditure in cold-exposed rats was not completely balanced by adaptive hyperphagia, with consequential reductions in protein and fat gain, accompanied by marked decreases in serum leptin. Furthermore, unlike high-fat feeding at 24 degrees C, cold exposure enhanced hepatic mitochondrial oxidative capacity both in the low-fat- and high-fat-fed groups. It is concluded that in this strain of young Wistar rats, despite similarly marked stimulation of energy expenditure by high-fat feeding at 24 degrees C, by cold exposure and by concomitant high-fat feeding and cold exposure, an increased hepatic oxidative capacity occurred only in the presence of the cold stimulus.

The regulation of total body fat: lessons learned from lipectomy studies

Surgical removal of body fat (partial lipectomy) is a means of directly reducing fat such that metabolic and behavioral responses can be readily attributed to the lipid deficit. If total body fat is regulated, then lipectomy should trigger compensatory increases in nonexcised white adipose tissue (WAT) mass and/or regrowth at excision sites. Many species, including laboratory rats and mice, show lipectomy-induced compensatory recovery of body fat. Those animals exhibiting naturally occurring annual adiposity cycles, such as ground squirrels and hamsters, do so most impressively reaching seasonally appropriate body fat levels indistinguishable from controls. Reparation of the lipid deficit occurs without an increase in food intake, and generally through enlargement of non-excised WAT mass, rather than regrowth of excised WAT. A body fat regulatory system involving humoral and sensory neural inputs to the brain as well as sympathetic neural outputs from brain to adipose tissue is presented. Collectively, the lipectomy model appears useful for testing mechanisms controlling adiposity, or individual depot growth, and offers insight into how lipid stores fluctuate naturally.

Sonographic appearance of primary liver liposarcoma

Primary malignant mesenchymal tumors of the liver are extremely rare. We report a case of a primary liposarcoma in the right hepatic lobe of a 50-year-old man. Sonography showed a poorly defined, lobulated, infiltrating echogenic tumor with shadowing. Within the tumor were hyperechoic and hypoechoic foci thought to represent areas of hemorrhage and necrosis. Color Doppler sonography showed the mass to be avascular. A low-attenuation mass of fat density was confirmed on CT. The resected tumor was reasonably well circumscribed, with demonstrable infiltration of the liver parenchyma. Histologic analysis showed liposarcoma with high-grade sarcomatous features.

Expression and distribution of heme oxygenase-1 and -2 in rat brown adipose tissue: the modulatory role of the noradrenergic system

To investigate whether brown adipose tissue (BAT) expresses the inducible (HO-1) and the constitutive (HO-2) isoform of heme oxygenase, reverse transcriptase-polymerase chain reaction, Western blotting and immunohistochemistry were performed on interscapular BAT (IBAT) from rats acclimated at environmental temperature or exposed to cold. Both HO isoforms were detected in rat IBAT. They were immunolocalized in the cytoplasm and/or nuclei of brown adipocytes, in parenchymal capillaries, arteries and in some veins and nerves. Whereas cold exposure did not affect HO-2 expression, it significantly increased the expression of HO-1, both at mRNA (about 3-fold) and protein (about 2-fold) levels, reflecting the increased expression of HO-1 in the brown adipocytes and endothelial cells of parenchymal capillaries. Western blotting of cytosolic and nuclear protein extracts from cultured differentiated brown adipocytes showed that HO-1 and HO-2 are indeed localized in the cytosol and nuclei of brown adipocytes, and that noradrenaline stimulation significantly increased their amount in cytosol but not in the nuclear fraction.

Human genomics and obesity: finding appropriate drug targets

The increasing prevalence of obesity worldwide has prompted the World Health Organization (WHO) to classify it as a global epidemic. Around the globe, more than a half billion people are overweight, and the chronic disease of obesity represents a major threat to health care systems in developed and developing countries. The major health hazards associated with obesity are the risks of developing diabetes, cardiovascular disease, stroke, osteoarthritis and some forms of cancer. In this paper, we review the prevalence of obesity and its cost to health care systems and present the relative contribution of environmental conditions and genetic makeup to the development of obesity in people. We also discuss the concept of "essential" obesity in an "obesigenic" environment. Though weight gain results from a sustained imbalance between energy intake and energy expenditure, it is only recently that studies have identified important new mechanisms involved in the regulation of body weight. The etiology of the disease is presented as a feedback model in which afferent signals inform the central controllers in the brain as to the state of the external and internal environment and elicit responses related to the regulation of food intake and energy metabolism. Pharmaceutical agents may intervene at different levels of this feedback model, i.e., reinforce the afferent signals from the periphery, target the central pathways involved in the regulation of food intake and energy expenditure, and increase peripheral energy expenditure and fat oxidation directly. Since obesity results from genetic predisposition, combined with the proactive environmental situation, we discuss new potential targets for generation of drugs that may assist people in gaining control over appetite as well as increasing total energy expenditure and fat oxidation.

Genetic studies of brown adipocyte induction

We seek to discover an effective method for utilizing thermogenesis to reduce the caloric load in obese individuals. Experimental evidence indicates that nonshivering thermogenesis is the most effective cellular and biochemical mechanism known for reducing excessive adiposity. In this presentation, we describe our experiments aimed at understanding how nonshivering thermogenesis can be induced. In addition, these experiments have led to a genetic approach for the identification of variant genes that coordinate the expression of pathways of gene transcription that are associated with brown adipocyte induction.

Leptin and the adrenal gland

BACKGROUND

Leptin is involved in the maintenance of energy balance acting on food intake, thermogenesis and energy expenditure. Via its receptor in the hypothalamus, leptin modulates the functioning of the hypothalamic-pituitary-adrenal axis and the systemic sympathetic/adrenomedullary system, which are closely linked to the regulation of energy balance and body weight. In regard of potential interactions of leptin and adrenal hormones this study intended to characterize the role of leptin in the human adrenal gland.

MATERIALS AND METHODS

A novel technique of laser capture microdissection was used to separate cortical and chromaffin cells for mRNA expression studies of leptin receptor isoforms and leptin mRNA in adrenal tissue and cell line NCI-H295. Immunostaining was used to localize leptin receptor in human adrenal slices. The influence of leptin on basal and ACTH-stimulated steroid hormone secretion and enzyme expression was assessed. The effect of leptin on proliferation and viability of adrenal cells in primary culture and of the NCI-H295 cell line was studied by the WST-1 assay and by 3H-thymidine test.

RESULTS

Our data demonstrate that leptin can regulate the human adrenal function directly, via its receptors on adrenocortical cells. Leptin decreased the corticotropin-stimulated release of steroid hormones in vitro without any effect on cell proliferation. Leptin did not significantly affect the expression of cytochrome P450 scc m RNA in humans, but decreased the ACTH stimulated expression of the cytochrome P450 17alpha mRNA [corrected].

CONCLUSIONS

The adipo-adrenal interaction mediated by leptin further underscores the close link of metabolism and stress regulation in humans.

RGD-independent binding of integrin alpha9beta1 to the ADAM-12 and -15 disintegrin domains mediates cell-cell interaction

ADAMs (a disintegrin and metalloproteases) mediate several important processes (e.g. tumor necrosis factor-alpha release, fertilization, and myoblast fusion). The ADAM disintegrin domains generally lack RGD motifs, and their receptors are virtually unknown. Here we show that integrin alpha(9)beta(1) specifically interacts with the recombinant ADAMs-12 and -15 disintegrin domains in an RGD-independent manner. We also show that interaction between ADAM-12 or -15 and alpha(9)beta(1) supports cell-cell interaction. Interestingly, the cation requirement and integrin activation status required for alpha(9)beta(1)/ADAM-mediated cell adhesion and cell-cell interaction is similar to those required for known integrin-extracellular matrix interaction. These results are quite different from recent reports that ADAM-2/alpha(6)beta(1) interaction during sperm/egg fusion requires an integrin activation status distinct from that for extracellular matrix interaction. These results suggest that alpha(9)beta(1) may be a major receptor for ADAMs that lack RGD motifs, and that, considering a wide distribution of ADAMs and alpha(9)beta(1), this interaction may be of potential biological and pathological significance.

Expression of human alpha 2-adrenergic receptors in adipose tissue of beta 3-adrenergic receptor-deficient mice promotes diet-induced obesity

Catecholamines play an important role in controlling white adipose tissue function and development. beta- and alpha 2-adrenergic receptors (ARs) couple positively and negatively, respectively, to adenylyl cyclase and are co-expressed in human adipocytes. Previous studies have demonstrated increased adipocyte alpha 2/beta-AR balance in obesity, and it has been proposed that increased alpha 2-ARs in adipose tissue with or without decreased beta-ARs may contribute mechanistically to the development of increased fat mass. To critically test this hypothesis, adipocyte alpha 2/beta-AR balance was genetically manipulated in mice. Human alpha 2A-ARs were transgenically expressed in the adipose tissue of mice that were either homozygous (-/-) or heterozygous (+/-) for a disrupted beta 3-AR allele. Mice expressing alpha 2-ARs in fat, in the absence of beta 3-ARs (beta 3-AR -/- background), developed high fat diet-induced obesity. Strikingly, this effect was due entirely to adipocyte hyperplasia and required the presence of alpha2-ARs, the absence of beta 3-ARs, and a high fat diet. Of note, obese alpha 2-transgenic beta 3 -/- mice failed to develop insulin resistance, which may reflect the fact that expanded fat mass was due to adipocyte hyperplasia and not adipocyte hypertrophy. In summary, we have demonstrated that increased alpha 2/beta-AR balance in adipocytes promotes obesity by stimulating adipocyte hyperplasia. This study also demonstrates one way in which two genes (alpha 2 and beta 3-AR) and diet interact to influence fat mass.

Synergistic gene interactions control the induction of the mitochondrial uncoupling protein (Ucp1) gene in white fat tissue

Among a selected group of mouse strains susceptible to dietary obesity, those with an enhanced capacity for Ucp1 and brown adipocyte induction in white fat preferentially lost body weight following adrenergic stimulation. Based on the generality of this mechanism for reducing obesity, a genetic analysis was initiated to identify genes that control brown adipocyte induction in white fat depots in mice. Quantitative trait locus (QTL) analysis was performed using the variations of retroperitoneal fat Ucp1 mRNA expression in progeny of genetic crosses between the A/J and C57BL/6J parental strains and selected AXB recombinant inbred strains. Three A/J-derived loci on chromosomes 2, 3, and 8 and one C57BL/6J locus on chromosome 19 were linked to Ucp1 induction in retroperitoneal fat. Although A/J-derived alleles seemed to contribute to elevated Ucp1 expression, the C57BL/6J allele on chromosome 19 increased Ucp1 mRNA to levels higher than parental values. Thus, novel patterns of C57BL/6J and A/J recombinant genotypes among the four mapped loci resulted in a transgressive variation of Ucp1 phenotypes. Although the extent of the interchromosomal interactions have not been fully explored, strong synergistic interactions occur between a C57BL/6J allele on chromosome 19 and an A/J allele on chromosome 8. In addition to selective synergistic interactions between loci, variations in recessive and dominant effects also contribute to the final levels of Ucp1 expression.

Down-regulated STAT3 messenger ribonucleic acid and STAT3 protein in the hypothalamic arcuate nucleus of the obese leptin-deficient (ob/ob) mouse

Leptin is a weight-reducing hormone produced by adipose tissue, which reduces food intake via hypothalamic leptin receptors and the JAK-STAT signaling pathway. In vivo studies have shown that leptin activates specifically STAT3 in the hypothalamus. We have studied the cellular localization of STAT3 messenger RNA (mRNA) and STAT3 protein in the mouse mediobasal hypothalamus using, respectively, in situ hybridization and immunohistochemistry. Strong STAT3 mRNA and STAT3 immunoreactivity was demonstrated in neurons located in the ventral part of the mouse arcuate nucleus. Comparison of STAT3 mRNA levels in the arcuate nucleus of lean control mice and obese leptin-deficient ob/ob mice showed that the levels of STAT3 mRNA in the arcuate nucleus were significantly lower (31% less in ob/ob mice), compared with control mice. Hybridization with a probe specific for STAT3alpha mRNA showed that the down-regulated STAT3 expression in the arcuate nucleus of ob/ob mice is represented by STAT3alpha. There was a marked difference in numbers and intensity of STAT3-immunoreactive cell bodies, with virtually no STAT3-immunoreactive cell bodies in the mediobasal hypothalamus of ob/ob mice, compared with control mice. Direct double-labeling immunofluorescence histochemistry of sections from control mice, combining a goat antiserum raised against a peptide sequence present in all leptin receptor isoforms (Ob-R) or a guinea pig anti-serum generated to a peptide sequence specific for Ob-Rb with rabbit STAT3 antiserum, demonstrated colocalization of STAT3 and Ob-R as well as colocalization of STAT3 and Ob-Rb, in many cell bodies of the arcuate nucleus. The results suggest that circulating leptin acts via leptin receptor-/STAT3-containing neurons in the ventral arcuate nucleus and that congenital leptin deficiency, as seen in obese ob/ob mice, results in a down-regulation of STAT3 mRNA and protein levels.

Frataxin activates mitochondrial energy conversion and oxidative phosphorylation

Friedreich's ataxia (FA) is an autosomal recessive disease caused by decreased expression of the mitochondrial protein frataxin. The biological function of frataxin is unclear. The homologue of frataxin in yeast, YFH1, is required for cellular respiration and was suggested to regulate mitochondrial iron homeostasis. Patients suffering from FA exhibit decreased ATP production in skeletal muscle. We now demonstrate that overexpression of frataxin in mammalian cells causes a Ca(2+)-induced up-regulation of tricarboxylic acid cycle flux and respiration, which, in turn, leads to an increased mitochondrial membrane potential (delta psi(m)) and results in an elevated cellular ATP content. Thus, frataxin appears to be a key activator of mitochondrial energy conversion and oxidative phosphorylation.

Regulation of the expression of the sea urchin mitochondrial D-loop binding protein during early development

The Paracentrotus lividus mitochondrial D-loop binding protein (mtDBP) is a DNA-binding protein which is involved in the regulation of sea urchin mtDNA transcription. Immunoblots of Heparin Sepharose-bound proteins at selected early developmental stages, as well as electrophoretic mobility shift assay, show that mtDBP is present in the egg at a concentration of about 1 x 10(6) molecules/egg. Its level increases after fertilization of about twofold, remaining substantially unchanged between 16-h blastula stage and early pluteus stage and declines thereafter. The content of mtDBP mRNA, determined by RNase protection experiments, increases about sevenfold at the 16-h blastula stage compared to the egg. A considerable decrease occurs at the 40-h pluteus stage, which precedes that of the protein. These results suggest that the expression of mtDBP is regulated at transcriptional level up to blastula stage, while other factors, in addition to the level of the RNA, may control the content of this protein in the following stages of embryogenesis.

Differential regulation of the catalytic and accessory subunit genes of Drosophila mitochondrial DNA polymerase

The developmental pattern of expression of the genes encoding the catalytic (alpha) and accessory (beta) subunits of mitochondrial DNA polymerase (pol gamma) has been examined in Drosophila melanogaster. The steady-state level of pol gamma-beta mRNA increases during the first hours of development, reaching its maximum value at the start of mtDNA replication in Drosophila embryos. In contrast, the steady-state level of pol gamma-alpha mRNA decreases as development proceeds and is low in stages of active mtDNA replication. This difference in mRNA abundance results at least in part from differences in the rates of mRNA synthesis. The pol gamma genes are located in a compact cluster of five genes that contains three promoter regions (P1-P3). The P1 region directs divergent transcription of the pol gamma-beta gene and the adjacent rpII33 gene. P1 contains a DNA replication-related element (DRE) that is essential for pol gamma-beta promoter activity, but not for rpII33 promoter activity in Schneider's cells. A second divergent promoter region (P2) controls the expression of the orc5 and sop2 genes. The P2 region contains two DREs that are essential for orc5 promoter activity, but not for sop2 promoter activity. The expression of the pol gamma-alpha gene is directed by P3, a weak promoter that does not contain DREs. Electrophoretic mobility shift experiments demonstrate that the DRE-binding factor (DREF) regulatory protein binds to the DREs in P1 and P2. DREF regulates the expression of several genes encoding key factors involved in nuclear DNA replication. Its role in controlling the expression of the pol gamma-beta and orc5 genes establishes a common regulatory mechanism linking nuclear and mitochondrial DNA replication. Overall, our results suggest that the accessory subunit of mtDNA polymerase plays an important role in the control of mtDNA replication in Drosophila.

Dendritic cells in the rat pituitary gland evaluated by the use of monoclonal antibodies and electron microscopy

A detailed analysis of the difference in the localization and the immunoreactivity for various surface markers among folliculo-stellate cells, macrophages, and dendritic cells was performed using immunohistochemistry and electron microscopy of the rat pituitary gland. The folliculo-stellate cells were selectively labeled by an antiserum against S100 protein. The majority of dendritic cells were immunoreactive for the MHC class II (Ia) antigen (OX6) and/or the dendritic cell antibodies (OX62). The main population of macrophages was positive for the macrophage antibodies (ED1, ED2, and/or OX42). The cellular density of adenohypophyseal macrophages was significantly lower than that of folliculo-stellate cells and of dendritic cells. All the neurohypophyseal microglial cells were labeled with OX42, while the mAb OX6 labeled a small population of cells different from the cells identified by OX42 in the neurohypophysis. Double-immunoperoxidase staining for ED1 and OX6 revealed that positively stained cells could be classified into ED1+OX6-, ED1+OX6+, and ED1-OX6+ cells. Double staining with OX62 and OX6 mAbs showed that about 60% of the OX6+ cells were also immunolabeled with OX62 in the anterior lobe: OX62 detects a subpopulation of dendritic cells but does not recognize macrophage populations. Furthermore, double staining for S100 and OX6 resulted in no S100+ OX6+ cells. At the electron-microscopic level, reaction products for OX6 were confirmed in the cell membrane and labeled cells were distinguished from macrophages and folliculo-stellate cells by distinctive short, broad cytoplasmic processes and the rare presence of cytoplasmic organelles. Such cytological characteristics of the OX6-positive cells in the pituitary gland are similar to dendritic cells. Our results suggest that resident dendritic cells and folliculo-stellate cells are two different main components of interstitial cells in the pituitary gland.

The human uncoupling protein-1 gene (UCP1): present status and perspectives in obesity research

Energy expenditure through brown adipose tissue thermogenesis contributes either to maintenance of body temperature in a cold environment or to wasted food energy, i.e. cold-induced or diet-induced thermogenesis. Both mechanisms are due to a specific and unique protein: the uncoupling protein-1. Uncoupling protein-1 is exclusively expressed in mitochondria of brown adipocytes where it uncouples respiration from ATP synthesis, dissipating the proton gradient as heat. In humans, although uncoupling protein-1 can be detected, the inability to quantify brown adipose tissue makes it difficult to argue for a role for uncoupling protein-1 in thermogenesis and energy expenditure. This review summarizes data supporting the existence of brown adipocytes and the role of UCP1 in energy dissipation in adult humans. Understanding the mechanisms which regulate transcription and expression of the human UCP1 gene will facilitate the identification of molecules able to increase the levels of this protein in order to modulate energy expenditure in adult humans.

Peroxisome proliferator-activated receptor gamma coactivator-1 promotes cardiac mitochondrial biogenesis

Cardiac mitochondrial function is altered in a variety of inherited and acquired cardiovascular diseases. Recent studies have identified the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) as a regulator of mitochondrial function in tissues specialized for thermogenesis, such as brown adipose. We sought to determine whether PGC-1 controlled mitochondrial biogenesis and energy-producing capacity in the heart, a tissue specialized for high-capacity ATP production. We found that PGC-1 gene expression is induced in the mouse heart after birth and in response to short-term fasting, conditions known to increase cardiac mitochondrial energy production. Forced expression of PGC-1 in cardiac myocytes in culture induced the expression of nuclear and mitochondrial genes involved in multiple mitochondrial energy-transduction/energy-production pathways, increased cellular mitochondrial number, and stimulated coupled respiration. Cardiac-specific overexpression of PGC-1 in transgenic mice resulted in uncontrolled mitochondrial proliferation in cardiac myocytes leading to loss of sarcomeric structure and a dilated cardiomyopathy. These results identify PGC-1 as a critical regulatory molecule in the control of cardiac mitochondrial number and function in response to energy demands.