Expression of NAD(+)-dependent isocitrate dehydrogenase in brown adipose tissue

Effects of cold exposure on metabolites in brown adipose tissue of rats

Brown adipose tissue (BAT) plays an important role in regulation of energy expenditure while adapting to a cold environment. BAT thermogenesis depends on uncoupling protein 1 (UCP1), which is expressed in the inner mitochondrial membranes of BAT. Gene expression profiles induced by cold exposure in BAT have been studied, but the metabolomic biological pathway that contributes to the activation of thermogenesis in BAT remains unclear. In this study, we comprehensively compared the relative levels of metabolites between the BAT of rats kept at room temperature (22 °C) and of those exposed to a cold temperature (4 °C) for 48 h using capillary electrophoresis (CE) time-of-flight mass spectrometry (TOFMS) and liquid chromatography (LC)-TOFMS. We identified 218 metabolites (137 cations and 81 anions) by CE-TOFMS and detected 81 metabolites (47 positive and 34 negative) by LC-TOFMS in BAT. We found that cold exposure highly influenced the BAT metabolome. We showed that the cold environment lead to lower levels of glycolysis and gluconeogenesis intermediates and higher levels of the tricarboxylic acid (TCA) cycle metabolites, fatty acids, and acyl-carnitine metabolites than control conditions in the BAT of rats. These results indicate that glycolysis and β-oxidation of fatty acids in BAT are positive biological pathways that contribute to the activation of thermogenesis by cold exposure, thereby facilitating the generation of heat by UCP1. These data provide useful information for understanding the basal metabolic functions of BAT thermogenesis in rats in response to cold exposure.

Effects of aripiprazole and clozapine on the treatment of glycolytic carbon in PC12 cells

Aripiprazole is the only atypical antipsychotic drug known to cause the phosphorylation of AMP-activated protein kinase (AMPK) in PC12 cells. However, the molecular mechanisms underlying this phosphorylation in aripiprazole-treated PC12 cells have not yet been clarified. Here, using PC12 cells, we show that these cells incubated for 24 h with aripiprazole at 50 μM and 25 mM glucose underwent a decrease in their NAD⁺/NADH ratio. Aripiprazole suppressed cytochrome c oxidase (COX) activity but enhanced the activities of pyruvate dehydrogenase (PDH), citrate synthase and Complex I. The changes in enzyme activities coincided well with those in NADH, NAD⁺, and NAD⁺/NADH ratio. However, the bioenergetic peril judged by the lowered COX activity might not be accompanied by excessive occurrence of apoptotic cell death in aripiprazole-treated cells, because the mitochondrial membrane potential was not decreased, but rather increased. On the other hand, when PC12 cells were incubated for 24 h with clozapine at 50 μM and 25 mM glucose, the NAD⁺/NADH ratio did not change. Also, the COX activity was decreased; and the PDH activity was enhanced. These results suggest that aripiprazole-treated PC12 cells responded to the bioenergetic peril more effectively than the clozapine-treated ones to return the ATP biosynthesis back toward its ordinary level. This finding might be related to the fact that aripiprazole alone causes phosphorylation of AMPK in PC12 cells.

Differential expression of adipose tissue proteins between obesity-susceptible and -resistant rats fed a high-fat diet

One of the major questions in the field of obesity is why some humans become obese (obesity prone, OP) and others resist the development of obesity (obesity resistant, OR) when exposed to a high-calorie diet, which has not been completely studied. Therefore, in the present study, in order to gain insight into the molecular mechanisms underlying this propensity, we have performed a comparative analysis of protein expression profiles in white adipose tissue (WAT) and brown adipose tissue (BAT) of rats fed a high-fat diet by 2-DE and MALDI-TOF-MS. Protein mapping of homogenates revealed significant alterations to a number of proteins; 60 and 70 proteins were differentially regulated in BAT and WAT, respectively. For careful interpretation of proteomic results, we categorized the identified proteins into two groups by analysis of both average spot density of pooled six rat adipose tissues and individual spot density of each adipose tissue of six rats as a function of body weight. One of the most striking findings of this study was that significant changes of Ehd1 and laminin receptor in BAT as well as antiquitin, DJ-1 protein, and paraoxonase 2 in WAT were found for the first time in obese rats. In addition, we confirmed the increased expression of some thermogenic enzymes and decreased lipogenic enzymes in adipose tissues of OR rats by immunoblot analysis. To our knowledge, this is the first proteomic study of profiling of protein modulation in OP and OR rats, thereby providing the first global evidence for different propensities to obesity between OP and OR rats.

Synchronized changes in transcript levels of genes activating cold exposure-induced thermogenesis in brown adipose tissue of experimental animals

To identify genes whose expression in brown adipose tissue (BAT) is up- or down-regulated in cold-exposed rats, we performed microarray analysis of RNA samples prepared from the BAT of cold-exposed rats and of rats kept at room temperature. Previously reported elevations of transcript levels of uncoupling protein (UCP1), type II iodothyronine deiodinase (DIO2), and type III adenylate cyclase (AC3) in the BAT of cold-exposed rats over those in that of rats maintained at room temperature were confirmed. In addition to these changes, remarkable elevations of the transcript levels of several genes that seemed to be associated with the processes of cell-cycle regulation and DNA replication were detected in the BAT of cold-exposed rats, possibly reflecting the significant proliferation of brown adipocytes in response to cold exposure. Up-regulation of the gene encoding sarcomeric mitochondrial type creatine kinase in the BAT of cold-exposed rats was also detected by microarray analysis, but subsequent Northern analysis revealed that the expression of not only the sarcomeric mitochondrial type enzyme, but also that of 2 other subtypes, i.e., cytoplasmic brain type and cytoplasmic muscle type, was elevated in the BAT of cold-exposed rats. Microarray analysis also revealed a significant expression of myoglobin in BAT and its elevation in the BAT of cold-exposed rats, and this result was supported by calibrated Northern analysis. On the contrary, several genes such as regulator of G-protein signaling 2 and IMP dehydrogenase 1 were down-regulated in the BAT of cold-exposed rats. The physiological meaning of these changes accompanying cold exposure was discussed.

Identification of possible protein machinery involved in the thermogenic function of brown adipose tissue

Brown adipose tissue (BAT) is believed to function by dissipating excess energy in mammals. It is very important to understand the energy metabolism held in BAT since disorder of its energy-dissipating function may cause obesity or lifestyle-related diseases such as hypertension and diabetes. This function in BAT is mainly attributable to uncoupling protein (UCP), specifically expressed in its mitochondria. This protein consumes excess energy as heat by dissipating the H+ gradient across the inner mitochondrial membrane that is utilized as a driving force for ATP synthesis. In this review article, in addition to providing a brief introduction to the functional properties of BAT and UCP, we also describe and discuss properties of cultured brown adipocytes and the results of our exploratory studies on protein components involved in the energy-dissipating function in BAT.

Comparison of gene expression profiles between white and brown adipose tissues of rat by microarray analysis

To characterize the energy metabolism in brown adipose tissue (BAT), the differences in gene expression profiles between BAT and white adipose tissue (WAT) were analyzed using a high-density cDNA microarray. RNAs isolated from two adipose tissues were hybridized to an Agilent rat cDNA Microarray that contained about 14,500 cDNA probe sets. The expression levels of 499 cDNA/ESTs were found to be at least 5-fold higher or lower in BAT than in WAT. Consistent with our previous findings, high expression levels of genes encoding uncoupling protein 1, muscle-type carnitine palmitoyltransferase and some other proteins involved in energy metabolism in BAT were found. Most of the genes encoding mitochondrial proteins, such as subunits of ATP synthase, cytochrome c oxidase, and NADH dehydrogenase, were highly expressed, reflecting possible differences in the cellular content of mitochondria between BAT and WAT. However, the expression levels of several genes encoding mitochondrial protein, such as liver mitochondrial aldehyde dehydrogenase and dicarboxylate carrier, were remarkably lower in BAT. These results may give important clues to understand the unique energy metabolism in BAT.

Baicalin induces differential expression of cytochrome C oxidase in human lung H441 cell

In a previous study, we evaluated the effect of baicalin on the expression of SP-A (surfactant protein A), which was developmentally regulated in an alveolar type II cell, H441. SP-A is encoded by two similar genes, SP-A1 and SP-A2, in humans. The maximal induction of SP-A1 gene of H441 occurred at treating 150 nM of baicalin for 48 h. In the present study, cDNA subtraction analysis is performed to examine the differential expression in H441 cell upon baicalin treatment with a view to investigating the regulatory mechanism. The mRNA of H441 cell incubated with 150 nM baicalin for 48 h was compared to that of blank control. Two PCR products were obtained through subtractive cDNA amplification. A product encoding cytochrome c oxidase was demonstrated to be a differential signal by RT-PCR analysis, and the other was a false positive. The induction of cytochrome c oxidase might increase ATP level in cell, and consequently elevates cAMP, which upregulates surfactant synthesis and secretion.

PCR-select subtraction for characterization of messages differentially expressed in brown compared with white adipose tissue

To understand the energy metabolism occurring in brown adipose tissue (BAT), we subtracted the messages expressed in white adipose tissue (WAT) from those in BAT. Thereby we succeeded in identifying 37 cDNA clones as being significantly expressed in BAT but not in WAT. Of these, 24 clones were found to code for mitochondrial proteins. Since BAT is well known to have a higher mitochondrial content than WAT, these results would seem to reflect simply the differences in mitochondrial content between BAT and WAT. To examine this possibility, we next measured the amount of mitochondrial DNA (mtDNA) in various rat tissues. As a result, the mtDNA copy number per cell was found to be markedly different among the tissues analyzed, and the highest value of about 5.3x10(4) copies per cell was observed with the rat brain. BAT showed a value similar to that of brain, but this value was only about 3.5-fold higher than that for WAT. Since observed differences in mitochondrial content between BAT and WAT was smaller than those observed with transcript levels of proteins, we conclude that the observed differences in the transcript levels of certain proteins between BAT and WAT reflect the functional differences between BAT and WAT, and do not reflect the differences in mitochondrial content between BAT and WAT.