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

Difference in intracellular temperature rise between matured and precursor brown adipocytes in response to uncoupler and β-adrenergic agonist stimuli

Brown adipocytes function to maintain body temperature by heat production. However, direct measurement of heat production at a single cell level remains difficult. Here we developed a method to measure the temperature within primary cultured brown adipocytes using a cationic fluorescent polymeric thermometer. Placement of the thermometer within a matured brown adipocyte and a precursor cell enabled the detection of heat production following uncoupler treatment. The increase in the intracellular temperature due to stimulation with a mitochondrial uncoupler was higher in matured brown adipocytes than in precursor cells. Stimulation with a β-adrenergic receptor (β-AR) agonist, norepinephrine, raised the intracellular temperature of matured brown adipocytes to a level comparable to that observed after stimulation with a β3-AR-specific agonist, CL316.243. In contrast, neither β-AR agonist induced an intracellular temperature increase in precursor cells. Further, pretreatment of brown adipocytes with a β3-AR antagonist inhibited the norepinephrine-stimulated elevation of temperature. These results demonstrate that our novel method successfully determined the difference in intracellular temperature increase between matured brown adipocytes and precursor cells in response to stimulation by an uncoupler and β-AR agonists.

Proteomic differences between white and brown adipocytes

Although a series of protein levels from several protein pathways have been shown to differ between white (WA) and brown (BA) adipocytes, proteomic work on this subject with the exception of mitochondrial protein differences is limited. It was, therefore, the aim of the study to compare WA with BA soluble protein levels. Proteins were extracted from WA and BA and the soluble fraction was run on two-dimensional gel electrophoresis. Quantification of spot volume was carried out and protein spots, statistically different between groups (P < 0.01), were in-gel digested with trypsin and peptides were identified using nano-LC-ESI-MS/MS in the CID and ETD mode. Differences between selected proteins were evaluated by immunoblotting. A network was generated using the ingenuity pathway analysis. Five proteins, protein DJ-1, dihydrolipoyllysine-residue acetyltransferase component of pyruvate dehydrogenase complex, isocitrate dehydrogenase subunit alpha, electron transfer flavoprotein subunit alpha and immunoglobulin-binding protein 1, were increased in BA based on a gel-based proteomic method and differential expression was verified by immunoblotting. These individual proteins were represented by one spot each and sequence coverages were between 28 and 65%. A network generated based on these results indicated a link to ubiquitination. Differential protein levels between WA and BA allow interpretation of previous work on adipocyte biochemistry and form the basis for future studies with genetic or pharmacological inhibition of these proteins accompanied by work on phenotype and adipocyte function.

Weight loss and brown adipose tissue reduction in rat model of sleep apnea

Background -

Obesity is related to obstructive sleep apnea-hypopnea syndrome (OSAHS), but its roles in OSAHS as cause or consequence are not fully clarified. Isocapnic intermittent hypoxia (IIH) is a model of OSAHS. We verified the effect of IIH on body weight and brown adipose tissue (BAT) of Wistar rats.

Methods

Nine-month-old male breeders Wistar rats of two groups were studied: 8 rats submitted to IIH and 5 control rats submitted to sham IIH. The rats were weighed at the baseline and at the end of three weeks, after being placed in the IIH apparatus seven days per week, eight hours a day, in the lights on period, simulating an apnea index of 30/hour. After experimental period, the animals were weighed and measured as well as the BAT, abdominal, perirenal, and epididymal fat, the heart, and the gastrocnemius muscle.

Results

Body weight of the hypoxia group decreased 17 ± 7 grams, significantly different from the variation observed in the control group (p = 0,001). The BAT was 15% lighter in the hypoxia group and reached marginally the alpha error probability (p = 0.054).

Conclusion

Our preliminary results justify a larger study for a longer time in order to confirm the effect of isocapnic intermittent hypoxia on body weight and BAT.

Expression of a novel alternatively spliced UCP-2 transcript in osteogenic sarcoma

BACKGROUND

Development of chemoresistance is common in patients with osteogenic sarcoma (OGS); however, the underlying mechanism is largely unknown. Many anticancer drugs exert their therapeutic action by generating reactive oxygen radicals, which might be countered by the cancer cell through induction of uncoupling protein 2 (UCP-2). UCP-2 has been shown to be able to protect tumor cells from the cytotoxic actions of chemotherapeutic drugs. Because OGS is seldom completely cured by current chemotherapy regimens, we hypothesized that increased expression of UCP-2 underlies this phenomenon. The primary initial interest of our research was to evaluate the level of UCP-2 mRNA in OGS.

METHODS

The level of UCP-2 mRNA was determined by reverse transcriptase polymerase chain reaction (RT-PCR) comparing expression in normal-bone-derived specimens and OGS-derived specimens. Semiquantification of mRNA expression was achieved by radioactive RT-PCR. Nucleotide sequencing was performed using automated instruments.

RESULTS

Interestingly, we failed to observe induction of UCP-2 mRNA in OGS tumor specimens and OGS-derived primary cell lines compared to the expression level in normal bone. However, we found expression of a hitherto unknown UCP-2 transcript in eight of eight OGS-derived and one EWS-derived cell lines and in nine of ten OGS biopsy specimens but in only one of six normal bone-derived specimens. Thus, tumor samples express both types (normal and the novel one) of UCP-2 mRNAs, whereas normal bone expresses only the wild-type form. Further experiments identified the novel mRNA species as an alternatively spliced UCP-2 transcript (termed UCP-2as). UCP-2as has a 22-nucleotide insertion from the 3' end of intron 3 that introduces an early stop codon in exon 4, which theoretically can produce a protein 79 amino acids long.

CONCLUSIONS

We have identified a hitherto unknown UCP-2 transcript. Expression of the novel transcript appears to be OGS-specific, implying a function advantageous to the tumor.

Control and Regulatory Mechanisms Associated with Thermogenesis in Flying Insects and Birds

Most insects and birds are able to fly. The chitin made exoskeleton of insects poses them several constraints, and this is one the reasons they are in general small sized animals. On the other hand, because birds possess an endoskeleton made of bones they may grow much larger when compared to insects. The two taxa are quite different with regards to their general “design” platform, in particular with respect to their respiratory and circulatory systems. However, because they fly, they may share in common several traits, namely those associated with the control and regulatory mechanisms governing thermogenesis. High core temperatures are essential for animal flight irrespective of the taxa they belong to. Birds and insects have thus evolved mechanisms which allowed them to control and regulate high rates of heat fluxes. This article discusses possible convergent thermogenic control and regulatory mechanisms associated with flight in insects and birds.

[Identification of muscle-type carnitine palmitoyltransferase I and characterization of its gene structure]

To characterize energy metabolism in brown adipose tissue (BAT), differential screening of a cDNA library of rat BAT with a cDNA probe of rat white adipose tissue was carried out. We isolated one novel cDNA clone encoding a protein of 88.2 kDa consisting of 772 amino acids. The deduced amino acid sequence showed the highest homology (62.6%) with that of rat liver carnitine palmitoyltransferase I (CPTI). The transcript corresponding to this cDNA was abundantly expressed not only in BAT but also in the heart and skeletal muscle. CPTI is a protein necessary for the beta-oxidation of long-chain fatty acids in mammalian mitochondria, and it has been suggested that at least two isoforms, the liver type and muscle (M-CPTI) type, exist. Based on these observations, we concluded that the novel cDNA clone isolated from rat BAT encodes M-CPTI. Isolation and characterization of a genomic DNA clone revealed that the gene for human M-CPTI consists of two 5'-noncoding exons, 18 coding exons, and one 3'-noncoding exon spanning approximately 10 kbp, and a gene encoding choline/ethanolamine kinase-beta (CK/EK-beta) was located about 300 bp upstream from the M-CPTI gene with the same strand direction. Furthermore, we found atypical transcripts containing exons of both CK/EK-beta and M-CPTI genes in humans and rodents. The physiologic role(s) of these transcripts is still unknown. However, it is interesting that such transcripts are produced from two tightly arranged and functionally unrelated genes in mammalian tissues.

Identification of Muscle-Type Carnitine Palmitoyltransferase I and Characterization of Its Atypical Gene Structure

To characterize energy metabolism in rat brown adipose tissue (BAT), we carried out differential screening of a cDNA library of BAT with a cDNA probe of white adipose tissue and isolated one novel cDNA clone. It contained a single open-reading frame of 2316 bases, which encodes a protein of 88.2 kDa. The predicted amino acid sequence showed the highest homology (62.6%) with that of carnitine palmitoyltransferase I (CPTI) from rat liver. The transcript corresponding to this cDNA was found to be abundantly expressed not only in BAT but also in heart and skeletal muscle. CPTI is known to be a protein necessary for the beta-oxidation of long-chain fatty acids in mammalian mitochondria, and it has been suggested that at least two isoforms, the liver type and muscle type, exist. From these observations, a cDNA clone isolated from rat BAT was concluded to be encoding muscle-type CPTI (M-CPTI). Characterization of a genomic DNA clone revealed that the gene for human M-CPTI consists of two 5'-noncoding exons, 18 coding exons, and one 3'-noncoding exon spanning approximately 10 kbp, and a gene encoding choline/ethanolamine kinase-beta (CK/EK-beta) was located only about 300 bp upstream from the M-CPTI gene with the same strand direction. Furthermore, we found that unordinary transcripts containing exons of both CK/EK-beta and M-CPTI genes exist in human and rodent tissues. Although the physiologic role(s) of these transcripts is still unknown, it is interesting that such transcripts are produced from two tightly arranged and functionally unrelated genes.