Mutations in the gene encoding gap junction protein beta-3 associated with autosomal dominant hearing impairment

Hearing impairment is the most commonly occurring condition that affects the ability of humans to communicate. More than 50% of the cases of profound early-onset deafness are caused by genetic factors. Over 40 loci for non-syndromic deafness have been genetically mapped, and mutations in several genes have been shown to cause hearing loss. Mutations in the gene encoding connexin 26 (GJB2) cause both autosomal recessive and dominant forms of hearing impairment. To study the possible involvement of other members of the connexin family in hereditary hearing impairment, we cloned the gene (GJB3) encoding human gap junction protein beta-3 using homologous EST searching and nested PCR. GJB3 was mapped to human chromosome 1p33-p35. Mutation analysis revealed that a missense mutation and a nonsense mutation of GJB3 were associated with high-frequency hearing loss in two families. Moreover, expression of Gjb3 was identified in rat inner ear tissue by RT-PCR. These findings suggest that mutations in GJB3 may be responsible for bilateral high-frequency hearing impairment.

Impairment of synaptic vesicle clustering and of synaptic transmission, and increased seizure propensity, in synapsin I-deficient mice

Synapsin I has been proposed to be involved in the modulation of neurotransmitter release by controlling the availability of synaptic vesicles for exocytosis. To further understand the role of synapsin I in the function of adult nerve terminals, we studied synapsin I-deficient mice generated by homologous recombination. The organization of synaptic vesicles at presynaptic terminals of synapsin I-deficient mice was markedly altered: densely packed vesicles were only present in a narrow rim at active zones, whereas the majority of vesicles were dispersed throughout the terminal area. This was in contrast to the organized vesicle clusters present in terminals of wild-type animals. Release of glutamate from nerve endings, induced by K+,4-aminopyridine, or a Ca2+ ionophore, was markedly decreased in synapsin I mutant mice. The recovery of synaptic transmission after depletion of neurotransmitter by high-frequency stimulation was greatly delayed. Finally, synapsin I-deficient mice exhibited a strikingly increased response to electrical stimulation, as measured by electrographic and behavioral seizures. These results provide strong support for the hypothesis that synapsin I plays a key role in the regulation of nerve terminal function in mature synapses.

T-complex polypeptide-1 is a subunit of a heteromeric particle in the eukaryotic cytosol

The murine t-complex encodes t-complex polypeptide-1 (TCP1), which is constitutively expressed in almost all cells, and upregulated during spermatogenesis. Mammalian sequences have greater than 96% identity with each other, and greater than 60% identity with Drosophila melanogaster and yeast orthologues. TCP1 is essential in yeast, and is postulated to be the cytosolic mammalian equivalent of groEL. We report here that, in the native state, murine and human TCP1 is distributed throughout the cytosol as an 800K-950K hetero-oligomeric particle in association with four to six unidentified proteins and two Hsp70 heat-shock proteins. Negative-stain electron microscopy indicates that the structure is two stacked rings, 12-16 nm in diameter. Therefore, despite similarities with the chaperonin 60 proteins, these data indicate that TCP1 is biochemically and structurally unique. We suggest that TCP1 may represent one of a family of molecules in the eukaryotic cytosol involved in protein folding and regulated in part by their heteromeric associations.

Characterization of universal small-subunit rRNA hybridization probes for quantitative molecular microbial ecology studies

Universal oligonucleotide hybridization probes targeting the small-subunit rRNA are commonly used to quantify total microbial representation in environmental samples. Universal probes also serve to normalize results obtained with probes targeting specific phylogenetic groups of microorganisms. In this study, six universal probes were evaluated for stability of probe-target duplexes by using rRNA from nine organisms representing the three domains of Bacteria, Archaea, and Eucarya. Domain-specific variations in dissociation temperatures were observed for all probes. This could lead to a significant bias when these probes are used to quantify microbial populations in environmental samples. We suggest lowering the posthybridization wash stringency for two of the universal probes (S-*-Univ-1390-a-A-18 and S-*-Univ-1392-a-A-15) examined. These two probes were evaluated with traditional and modified hybridization conditions to characterize defined mixtures of rRNAs extracted from pure cultures and rRNA samples obtained from anaerobic digester samples. Probe S-*-Univ-1390-a-A-18 provided excellent estimations of domain-level community composition of these samples and is recommended for future use in microbial ecology studies.

Changes in muscle strength, muscle fibre size and myofibrillar gene expression after immobilization and retraining in humans

1. Changes in muscle strength, vastus lateralis fibre characteristics and myosin heavy-chain (MyoHC) gene expression were examined in 48 men and women following 3 weeks of knee immobilization and after 12 weeks of retraining with 1866 eccentric, concentric or mixed contractions. 2. Immobilization reduced eccentric, concentric and isometric strength by 47 %. After 2 weeks of spontaneous recovery there still was an average strength deficit of 11 %. With eccentric and mixed compared with concentric retraining the rate of strength recovery was faster and the eccentric and isometric strength gains greater. 3. Immobilization reduced type I, IIa and IIx muscle fibre areas by 13, 10 and 10 %, respectively and after 2 weeks of spontaneous recovery from immobilization these fibres were 5 % smaller than at baseline. Hypertrophy of type I, IIa and IIx fibres relative to baseline was 10, 16 and 16 % after eccentric and 11, 9 and 10 % after mixed training (all P < 0.05), exceeding the 4, 5 and 5 % gains after concentric training. Type IIa and IIx fibre enlargements were greatest after eccentric training. 4. Total RNA/wet muscle weight and ty I, IIa and IIx MyoHC mRNA levels did not change differently after immobilization and retraining. Immobilization downregulated the expression of type I MyoHC mRNA to 0.72-fold of baseline and exercise training upregulated it to 0.95 of baseline. No changes occurred in type IIa MyoHC mRNA. Immobilization and exercise training upregulated type IIx MyoHC mRNA 2.9-fold and 1.2-fold, respectively. For the immobilization segment, type I, IIa and IIx fibre area and type I, IIa and IIx MyoHC mRNA correlated (r = 0.66, r = 0.07 and r = -0.71, respectively). 5. The present data underscore the role muscle lengthening plays in human neuromuscular function and adaptation.

Regulation of muscle GLUT-4 transcription by AMP-activated protein kinase

Skeletal muscle GLUT-4 transcription in response to treatment with 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR), a known activator of AMP-activated protein kinase (AMPK), was studied in rats and mice. The increase in GLUT-4 mRNA levels in response to a single subcutaneous injection of AICAR, peaked at 13 h in white and red quadriceps muscles but not in the soleus muscle. The mRNA level of chloramphenicol acyltransferase reporter gene which is driven by 1,154 or 895 bp of the human GLUT-4 proximal promoter was increased in AICAR-treated transgenic mice, demonstrating the transcriptional upregulation of the GLUT-4 gene by AICAR. However, this induction of transcription was not apparent with 730 bp of the promoter. In addition, nuclear extracts from AICAR-treated mice bound to the consensus sequence of myocyte enhancer factor-2 (from -473 to -464) to a greater extent than from saline-injected mice. Thus AMP-activated protein kinase activation by AICAR increases GLUT-4 transcription by a mechanism that requires response elements within 895 bp of human GLUT-4 proximal promoter and that may be cooperatively mediated by myocyte enhancer factor-2.

ATP induces large quaternary rearrangements in a cage-like chaperonin structure

BACKGROUND

The chaperonins, a family of molecular chaperones, are large oligomeric proteins that bind nonnative intermediates of protein folding. They couple the release and correct folding of their ligands to the binding and hydrolysis of ATP. Chaperonin 60 (cpn60) is a decatetramer (14-mer) of 60 kD subunits. Folding of some ligands also requires the cooperation of cpn10, a heptamer of 10 kD subunits.

RESULTS

We have determined the three-dimensional arrangements of subunits in Rhodobacter sphaeroides cpn60 in the nucleotide-free and ATP-bound forms. Negative stain electron microscopy and tilt reconstruction show the cylindrical structure of the decatetramer comprising two rings of seven subunits. The decatetramer consists of two cages joined base-to-base without a continuous central channel. These cages appear to contain bound polypeptide with an asymmetric distribution between the two rings. The two major domains of each subunit are connected on the exterior of the cylinder by a narrower bridge of density that could be a hinge region. Binding of ATP to cpn60 causes a major rearrangement of the protein density, which is reversed upon the hydrolysis of the ATP. Cpn10 binds to only one end of the cpn60 structure and is visible as an additional layer of density forming a cap on one end of the cpn60 cylinder.

CONCLUSIONS

The observed rearrangement is consistent with an inward 5-10 degrees rotation of subunits, pivoting about the subunit contacts between the two heptamers, and thus bringing cpn60 domains towards the position occupied by the bound polypeptide. This change could explain the stimulation of ATPase activity by ligands, and the effects of ATP on lowering the affinity of cpn60 for ligands and on triggering the release of folding polypeptides.

Protein NMR spectroscopy in structural genomics

Protein NMR spectroscopy provides an important complement to X-ray crystallography for structural genomics, both for determining three-dimensional protein structures and in characterizing their biochemical and biophysical functions.

Activation of mu opioid receptors inhibits transient high- and low-threshold Ca2+ currents, but spares a sustained current

Opioids and opiates decrease the duration of action potentials and the amount of neurotransmitter released from sensory neurons. The mu-type opioid receptor, the binding site for morphine, is thought to act exclusively on K+ channels. Here, we show that activation of the mu receptor inhibits Ca2+ channels in rat sensory neurons; the effect is blocked by a mu antagonist and is not mimicked by kappa or delta receptor agonists. Both low-threshold (T-type) and high-threshold Ca2+ currents are partially suppressed. omega-Conotoxin-sensitive and omega-conotoxin-insensitive, high-threshold Ca2+ currents are inhibited. The kinetic effect on high-threshold current is like that caused by diminished rest potential: the transient component is selectively lost, whereas the sustained component is spared.

Strong coupling of a spin ensemble to a superconducting resonator

We report the realization of a quantum circuit in which an ensemble of electronic spins is coupled to a frequency tunable superconducting resonator. The spins are nitrogen-vacancy centers in a diamond crystal. The achievement of strong coupling is manifested by the appearance of a vacuum Rabi splitting in the transmission spectrum of the resonator when its frequency is tuned through the nitrogen-vacancy center electron spin resonance.

The influence of aging on muscle strength and muscle fiber characteristics with special reference to eccentric strength

It is well established that aging seriously reduces isometric and concentric muscle strength due to atrophy, deterioration of mechanical properties, and motor unit loss. However, there is limited information on the impact of aging on eccentric strength despite the fact that such forces play an equally important role during daily activities. The purpose of this study was to examine the influence of aging on three expressions of muscle strength (isometric, concentric, and eccentric) in relation to muscle fiber characteristics, with special emphasis on eccentric force. Sedentary but healthy men (age range 18-80 years, n = 60) and women (20-74 years, n = 30) were tested for maximal effort isometric, concentric, and eccentric (1.05, 2.09, 3.14 rads.s-1) quadriceps strength, body composition, and muscle fiber characteristics of the vastus lateralis (men only). There was a significant (p < .05) approximately 30 N per decade decline in isometric and concentric forces, but only 9 N per decade reduction in eccentric strength. There was a significant reduction in Type II muscle fiber area with aging (p < .05). Isometric, eccentric, and concentric force correlated r = .33, r = .32 (p < .05), and r = .12 (p > .05) with Type II muscle fiber area, respectively. The correlation between age and fat-free mass/force ratio ranged from r = .39 to .43 in men and r = .27 to .50 in women. The data suggest a relative preservation of eccentric strength with aging in men and women that seems to be independent of muscle mass or muscle fiber type or size.

Major depression and all-cause mortality among white adults in the United States

PURPOSE

Depression is the most common psychiatric illness affecting adults. Despite the importance of a potential link between major depression and mortality, research has been surprisingly sparse.

METHODS

Information on 57,897 white adults aged 25 years and older who were included in the mental health supplement of the 1989 National Health Interview Survey was linked with the National Death Index to examine the relationship of major depression to mortality. Death status was obtained through December 1991. Sex-specific hazard rate ratios for mortality were calculated by Cox proportional hazards regression and Poisson regression to adjust for potential confounders (age, education, marital status, body mass index, and whether the target subject or a family member completed the survey about the subject).

RESULTS

Major depression was reported for 223 (0.8%) of 27,345 men and 392 (1.3%) of 30,552 women. During the 2.5-year follow-up, death certificate data were obtained for 848 (3.1%) men and 651 (2.1%) women. The adjusted hazard rate ratios for all-cause mortality associated with major depression were 3.1 (95% confidence interval; 2.0-4.9) for men and 1.7 (95% confidence interval; 0.9-3.1) for women.

CONCLUSIONS

These results suggest that major depression increases risk of all-cause mortality, particularly among men. Further research is needed to explain the mechanism.

A systematic review of antibiotics and antibiotic resistance genes in estuarine and coastal environments

Antibiotics and antibiotic resistance genes (ARGs) are prevalent in estuarine and coastal environments due to substantial terrestrial input, aquaculture effluent, and sewage discharge. In this article, based on peer-reviewed papers, the sources, spatial patterns, driving factors, and environmental implications of antibiotics and ARGs in global estuarine and coastal environments are discussed. Riverine runoff, WWTPs, sewage discharge, and aquaculture, are responsible for the prevalence of antibiotics and ARGs. Geographically, pollution due to antibiotics in low- and middle-income countries is higher than that in high-income countries, and ARGs show remarkable latitudinal variations. The distribution of antibiotics is driven by antibiotic usage and environmental variables (heavy metals, nutrients, organic pollutants, etc.), while ARGs are affected by antibiotics residues, environmental variables, microbial communities, and mobile genetic elements (MGEs). Antibiotics and ARGs alter microbial communities and biogeochemical cycles, as well as pose threats to marine organisms and human health. Our results provide comprehensive insights into the transport and environmental behaviors of antibiotics and ARGs in global estuarine and coastal environments.

Cardiolipin binds nonyl acridine orange by aggregating the dye at exposed hydrophobic domains on bilayer surfaces

10-N-Nonyl acridine orange (NAO) has been used at low concentrations as a fluorescent indicator for cardiolipin (CL) in membranes and bilayers. The mechanism of its selective fluorescence in the presence of CL, and not any other phospholipids, is not understood. The dye might recognize CL by its high pK (pK(2)>8.5). To investigate that, we established that NAO does not exhibit a pK in a pH range between 2.3 and 10.0. A second explanation is that the dye aggregates at hydrophobic domains on bilayers exposed by the CL. We found that a similar spectral shift occurs in the absence of CL in a concentrated solution of the dye in methanol and in the solid state. A model is proposed in which the nonyl group inserts in the bilayer at the hydrophobic surface generated by the presence of four chains on the phospholipid.

SPINE: an integrated tracking database and data mining approach for identifying feasible targets in high-throughput structural proteomics

High-throughput structural proteomics is expected to generate considerable amounts of data on the progress of structure determination for many proteins. For each protein this includes information about cloning, expression, purification, biophysical characterization and structure determination via NMR spectroscopy or X-ray crystallography. It will be essential to develop specifications and ontologies for standardizing this information to make it amenable to retrospective analysis. To this end we created the SPINE database and analysis system for the Northeast Structural Genomics Consortium. SPINE, which is available at bioinfo.mbb.yale.edu/nesg or nesg.org, is specifically designed to enable distributed scientific collaboration via the Internet. It was designed not just as an information repository but as an active vehicle to standardize proteomics data in a form that would enable systematic data mining. The system features an intuitive user interface for interactive retrieval and modification of expression construct data, query forms designed to track global project progress and external links to many other resources. Currently the database contains experimental data on 985 constructs, of which 740 are drawn from Methanobacterium thermoautotrophicum, 123 from Saccharomyces cerevisiae, 93 from Caenorhabditis elegans and the remainder from other organisms. We developed a comprehensive set of data mining features for each protein, including several related to experimental progress (e.g. expression level, solubility and crystallization) and 42 based on the underlying protein sequence (e.g. amino acid composition, secondary structure and occurrence of low complexity regions). We demonstrate in detail the application of a particular machine learning approach, decision trees, to the tasks of predicting a protein's solubility and propensity to crystallize based on sequence features. We are able to extract a number of key rules from our trees, in particular that soluble proteins tend to have significantly more acidic residues and fewer hydrophobic stretches than insoluble ones. One of the characteristics of proteomics data sets, currently and in the foreseeable future, is their intermediate size ( approximately 500-5000 data points). This creates a number of issues in relation to error estimation. Initially we estimate the overall error in our trees based on standard cross-validation. However, this leaves out a significant fraction of the data in model construction and does not give error estimates on individual rules. Therefore, we present alternative methods to estimate the error in particular rules.

Characterization of microbial communities in anaerobic bioreactors using molecular probes

The microbial community structure of twenty-one single-phase and one two-phase full-scale anaerobic sewage sludge digesters was evaluated using oligonucleotide probes complementary to conserved tracts of the 16S rRNAs of phylogenetically defined groups of methanogens and sulfate-reducing bacteria. These probe results were interpreted in combination with results from traditional chemical analyses and metabolic activity assays. It was determined that methanogens in "healthy" mesophilic, single-phase sewage sludge digesters accounted for approximately 8-12% of the total community and that Methanosarcinales and Methanomicrobiales constituted the majority of the total methanogen population. Methanobacteriales and Methanococcales played a relatively minor role in the digesters. Phylogenetic groups of mesophilic, Gram-negative sulfate-reducing bacteria were consistently present at significant levels: Desulfovibrio and Desulfobulbus spp. were the dominant sulfate-reducing populations, Desulfobacter and Desulfobacterium spp. were present at lower levels, and Desulfosarcina, Desulfococcus, and Desulfobotulus spp. were absent. Sulfate reduction by one or more of these populations played a significant role in all digesters evaluated in this study. In addition, sulfate-reducing bacteria played a role in favoring methanogenesis by providing their substrates. The analysis of the two-phase digester indicated that true phase separation was not accomplished: significant levels of active methanogens were present in the first phase. It was determined that the dominant populations in the second phase were different from those in the single-phase digesters.

Characterization of laboratory mutants of Venturia inaequalis resistant to the strobilurin-related fungicide kresoxim-methyl

Several agricultural fungicides related to the antifungal strobilurins act as inhibitors of respiration by binding to mitochondrial cytochrome b. Two types of laboratory mutants resisting higher doses of the strobilurin-related inhibitor kresoxim-methyl were characterized for Venturia inaequalis, the causal agent of apple scab. Selection of mutagenized conidia by kresoxim-methyl yielded mutants altered in the expression of alternative respiration during the stage of conidia germination. Cytochrome b sequences were not affected in the respective mutants. Selection of conidia on media containing the alternative oxidase inhibitor salicylhydroxamic acid in addition to kresoxim-methyl yielded a highly resistant mutant distinguished by a G143A exchange in cytochrome b. The status of mitochondrial cytochrome b genes remained heteroplasmic, and mitochondria containing wild-type cytochrome b returned to high frequencies during cultivation on inhibitor-free medium. However, continuation of the selection process led to a more pronounced replacement of sensitive by mutated mitochondria. The G143A mutation of cytochrome b causing resistance of V. inaequalis to a strobilurin-related inhibitor has been reported previously for mouse mitochondria; and a permanent G143A exchange rendering naturally resistant mitochondria has been reported for the strobilurin-producing basidiomycete Mycena galopoda and for the sea urchin Paracentrotus lividus. At the corresponding position, alanine was also present in chloroplast cytochrome b6 exhibiting low binding of strobilurin-related inhibitors. The mutation of cytochrome b reported here for V. inaequalis describes the first example of a mutation in filamentous ascomycetes and is part of an assessment of resistance risks inherent to strobilurin fungicides.

Takayasu arteritis in China: A report of 530 cases

A total of 530 patients with Takayasu arteritis were studied. Among 346 patients who were diagnosed by aortography, the female to male ratio was 2.9 to 1, and the age of onset ranged from 5 to 45 years. Three hundred and eighteen (60%) patients with secondary hypertension, including renovascular hypertension in 281, and 197 (37.2%) with pulseless extremities were found in the series. All the patients were treated with medical or surgical procedures. Surgical treatment is preferred if clinical status of the patient permits. The patients were followed for 1-29 years (average 7.8 years). There were 55 deaths (10.4%) in this series. Cerebral hemorrhage was found as a common cause of death. Five-year and ten-year survival rates were 93.1% and 91.1%, respectively.

Proatherogenic and proinflammatory properties of immune complexes prepared with purified human oxLDL antibodies and human oxLDL

Immune complexes (IC) prepared with human low density lipoprotein (LDL) and rabbit LDL antibodies induce foam cell transformation of human macrophages and activate the release of proinflammatory mediators by human macrophages and THP-1 cells. Because the affinity of human oxidized LDL (oxLDL) antibodies is lower than that of rabbit antibodies, IC formed with human antibodies could have limited pathogenic potential. Immune complexes prepared with human oxidized LDL (oxLDL) and purified human oxLDL antibodies (predominantly of the IgG1 and IgG3 isotypes) were presented to THP-1 cells using two protocols previously described in studies of the properties of LDL-IC prepared with rabbit antibodies. OxLDL/human oxLDL antibody IC immobilized by adsorption to red blood cells (RBC) induced the release of significantly higher levels of TNF from THP-1 cells (872-313 pg/ml) than oxLDL adsorbed to RBC (461-75.6 pg/ml) and caused a higher degree of cholesterol ester accumulation in the same cells (5.4-0.77 in cells incubated with IC-coated RBC vs 1.99-1.16 in oxLDL-coated RBC). Insoluble IC prepared with oxLDL/human oxLDL antibody were even more effective in promoting intracellular accumulation of cholesterol in THP-1 cells (total cholesterol = 53.8-13.5 and cholesterol esters = 24.0-7.2 mg/l in THP-1 cells incubated with insoluble IC (200 micrograms) vs total cholesterol = 32.4-8.2 and cholesterol esters = 7.7 +/- 2.8 micrograms/l in THP-1 cells incubated with an identical concentration of oxLDL) and also induced the release of TNF. Thus we have demonstrated that IC prepared with human oxLDL and human oxLDL antibodies have the same atherogenic and proinflammatory properties as IC prepared with human LDL and rabbit LDL antibodies. This strongly supports the concept that modified LDL-IC present in circulation and/or tissues play an important pathogenic role in arteriosclerosis.

Beta-adrenergic signaling promotes tumor angiogenesis and prostate cancer progression through HDAC2-mediated suppression of thrombospondin-1

Chronic behavioral stress and beta-adrenergic signaling have been shown to promote cancer progression, whose underlying mechanisms are largely unclear, especially the involvement of epigenetic regulation. Histone deacetylase-2 (HDAC2), an epigenetic regulator, is critical for stress-induced cardiac hypertrophy. It is unknown whether it is necessary for beta-adrenergic signaling-promoted cancer progression. Using xenograft models, we showed that chronic behavioral stress and beta-adrenergic signaling promote angiogenesis and prostate cancer progression. HDAC2 was induced by beta-adrenergic signaling in vitro and in mouse xenografts. We next uncovered that HDAC2 is a direct target of cAMP response element-binding protein (CREB) that is activated by beta-adrenergic signaling. Notably, HDAC2 is necessary for beta-adrenergic signaling to induce angiogenesis. We further demonstrated that, upon CREB activation, HDAC2 represses thrombospondin-1 (TSP1), a potent angiogenesis inhibitor, through epigenetic regulation. Together, these data establish a novel pathway that HDAC2 and TSP1 act downstream of CREB activation in beta-adrenergic signaling to promote cancer progression.

Global biogeography and projection of soil antibiotic resistance genes

Although edaphic antibiotic resistance genes (ARGs) pose serious threats to human well-being, their spatially explicit patterns and responses to environmental constraints at the global scale are not well understood. This knowledge gap is hindering the global action plan on antibiotic resistance launched by the World Health Organization. Here, a global analysis of 1088 soil metagenomic samples detected 558 ARGs in soils, where ARG abundance in agricultural habitats was higher than that in nonagricultural habitats. Soil ARGs were mostly carried by clinical pathogens and gut microbes that mediated the control of climatic and anthropogenic factors to ARGs. We generated a global map of soil ARG abundance, where the identified microbial hosts, agricultural activities, and anthropogenic factors explained ARG hot spots in India, East Asia, Western Europe, and the United States. Our results highlight health threats from soil clinical pathogens carrying ARGs and determine regions prioritized to control soil antibiotic resistance worldwide.

Differential expression of ob mRNA in rat adipose tissues in response to insulin

The recently cloned obese (ob) gene encodes a fat-specific mRNA and a protein which is believed to regulate satiety and metabolic rate so as to control fat storage. In the present study we investigated rat ob mRNA levels in different fat depots and the effects of insulin infusion on ob mRNA expression. Northern blot analysis showed the abdominal fat (epididymal and perirenal fat pads) had higher ob mRNA levels than subcutaneous fat. After a 2.5-hr infusion of insulin into fasted rats, ob mRNA levels were increased by 3.0 and 1.9-fold in epididymal and perirenal fat pads, respectively. However, no change of ob mRNA level was observed in the subcutaneous fat depot. These data demonstrate adipose depot site-specific expression of ob mRNA and support the hypothesis that insulin plays an important role in the expression of ob mRNA.

A high-fat diet elicits differential responses in genes coordinating oxidative metabolism in skeletal muscle of lean and obese individuals

CONTEXT

In lean individuals, increasing dietary lipid can elicit an increase in whole body lipid oxidation; however, with obesity the capacity to respond to changes in substrate availability appears to be compromised.

OBJECTIVE

To determine whether the responses of genes regulating lipid oxidation in skeletal muscle differed between lean and insulin resistant obese humans upon exposure to a high-fat diet (HFD).

DESIGN AND SETTING

A 5-d prospective study conducted in the research unit of an academic center.

PARTICIPANTS

Healthy, lean (n = 12; body mass index = 22.1 ± 0.6 kg/m(2)), and obese (n=10; body mass index = 39.6 ± 1.7 kg/m(2)) males and females, between ages 18 and 30.

INTERVENTION

Participants were studied before and after a 5-d HFD (65% fat).

MAIN OUTCOME MEASURES

Skeletal muscle biopsies (vastus lateralis) were obtained in the fasted and fed states before and after the HFD and mRNA content for genes involved with lipid oxidation determined. Skeletal muscle acylcarnitine content was determined in the fed states before and after the HFD.

RESULTS

Peroxisome proliferator activated receptor (PPAR) α mRNA content increased in lean, but not obese, subjects after a single high-fat meal. From Pre- to Post-HFD, mRNA content exhibited a body size × HFD interaction, where the lean individuals increased while the obese individuals decreased mRNA content for pyruvate dehydrogenase kinase 4, uncoupling protein 3, PPARα, and PPARγ coactivator-1α (P ≤ 0.05). In the obese subjects medium-chain acylcarnitine species tended to accumulate, whereas no change or a reduction was evident in the lean individuals.

CONCLUSIONS

These findings indicate a differential response to a lipid stimulus in the skeletal muscle of lean and insulin resistant obese humans.