Uncoupling Protein mRNA In Adipose Tissue Research Articles

Effect of naltrexone on feeding, neuropeptide Y and uncoupling protein gene expression during lactation.

Neuropeptide Y increases feeding and decreases measures of brown adipose tissue thermogenesis. In lactating rats, increased feeding, increased hypothalamic neuropeptide Y neuroactivity and decreased thermogenesis occur. Naltrexone is an opioid receptor antagonist which decreases neuropeptide Y-induced feeding and reverse neuropeptide Y-induced decreases in brown adipose tissue thermogenesis. We hypothesized that opioid receptors are involved in neuropeptide Y neuroactivity during lactation. To see if naltrexone would alter feeding neuropeptide Y gene expression in the arcuate nucleus, neuropeptide Y levels in the paraventricular nucleus, and uncoupling protein gene expression in brown adipose tissue of lactating rats, osmotic minipumps pre-filled with either 0.9% saline or naltrexone (70 micrograms/h) were implanted subcutaneously in 47 female Sprague-Dawley rats weighing 309 +/- 5 g. Half these rats were studied on days 10-16 of lactation, and the other half were studied 7 days after lactation. After 48 h, neuropeptide Y mRNA levels and uncoupling protein mRNA levels were determined using specific cDNA probes. Neuropeptide Y peptide levels in the paraventricular nucleus were measured by radioimmunoassay. Naltrexone decreased food intake by 26% in the postlactating rats, but had no effect on feeding in the lactating animals. Lactation resulted in significantly increased arcuate neuropeptide Y mRNA, decreased neuropeptide Y levels in the paraventricular nucleus and decreased brown adipose tissue uncoupling protein mRNA levels. Naltrexone did not influence any of these parameters. Thus, the alterations in neuropeptide Y neuroactivity and brown fat thermogenesis which occur in lactation is not altered by generalized opioid receptor blockade.

The beta 3-adrenoceptor agonist ICI-D7114 is not as efficient on reinduction of uncoupling protein mRNA in sheep as it is in dogs and smaller species.

Adipose tissue in newborn lambs is brown, but within a few days it is transformed into white adipose tissue. In the same way, preadipocytes cultured in serum-free chemically defined medium achieve full differentiation and express uncoupling protein (UCP), a marker of brown adipose tissue, when isolated from perirenal adipose tissue of the newborn, whereas they no longer express UCP when isolated from older lambs. The effects of a chronic stimulation of adipose tissue by novel beta 3-adrenoceptor agonist (ICI D7114) on the maintenance after birth and on the reinduction in older lambs of UCP mRNA in adipose tissue were studied. Treatment of newborn lambs with this agonist for 25 d maintained a slight level of UCP mRNA in perirenal and pericardiac, but not in omental and inguinal, adipose tissue depots. Preadipocytes isolated from perirenal adipose tissue of treated animals differentiated, in vitro, into adipocytes, but no UCP mRNA could be detected either in the absence or in the presence of the beta 3-adrenoceptor agonist in the culture medium. Treatment of 1-mo-old lambs with ICI D7114 for 12 d restored UCP mRNA in perirenal and pericardiac adipose tissues of two of four treated lambs, but at a much lower level than in the same tissues at birth. In both experiments, the final BW and the ADG of lambs treated with ICI D7114 were not statistically different from controls. These results are quite different from those obtained with the same beta 3-adrenoceptor agonist in dogs and rodents.

Rabbit brown adipose tissue uncoupling protein MRNA: Use of only one of two polyadenylation signals in its processing

A cDNA containing the complete coding sequence of rabbit brown adipose tissue uncoupling protein was isolated and sequenced. The coding region is 80.6% identical to rat UCP cDNA and the protein is about 86% identical to the rat and hamster proteins. Despite the presence of 2 AATAAA polyadenylation consensus sequences in rabbit UCP cDNA, only one rabbit UCP mRNA was detected indicating that only the 3′-downstream signal is used in contrast to rat and mouse where both are used.

Effects of exposure temperature on brown adipose tissue uncoupling protein mRNA levels.

The effect of temperature on the amount of uncoupling protein mRNA in rat brown adipose tissue was examined after 1 and 14 days of exposure to cold. The relative amounts after 1 day, compared with rats kept at a thermoneutral temperature of 28 degrees C, were 3.2 at 19 degrees C, 3.3 at 11 degrees C, and 2.1 at 3 degrees C. This suggests that in warm-acclimated rats, a maximal response to a cold stimulus in brown adipose tissue is reached by 19 degrees C. In contrast to these results, the relative amounts of uncoupling protein mRNA after 14 days of cold exposure, compared with rats left at 28 degrees C, were 1.2 at 19 degrees C, 1.9 at 11 degrees C, and 2.1 at 3 degrees C. Since it is known that the amount of uncoupling protein in cold-acclimated rats increases continuously with decrease in temperature, the amount of protein reflects the mRNA levels during later times but not the initial time of exposure to cold.

Detection of brown adipose tissue uncoupling protein mRNA in adult patients by a human genomic probe

1. Studies on human brown adipose tissue require specific molecular probes. A human genomic library has been screened with a complementary DNA corresponding to the uncoupling protein (UCP) of rat brown adipose tissue mitochondria. 2. Two recombinant phages were isolated, carrying genomic sequences of human UCP. From them we have subcloned a 0.5 kilobase fragment. This fragment, H-Ucp-0.5, contained two intronic regions and two exonic regions. Exonic regions encoded a sequence of 84 amino acids which exhibited a strong homology with central domain at rat UCP. The organization of H-Ucp-0.5 was confirmed by SI mapping analysis. 3. A Southern analysis suggested that the gene is single type in the human, as it is in rodents. 4. In Northern analysis experiments, H-Ucp-0.5 detected a specific 1.8 kb mRNA in human brown adipose tissue obtained from six patients with phaeochromocytoma and from one patient with a hibernoma. This molecular probe is a new, sensitive and reliable tool with which to study human brown adipocytes.

Loss of brown adipose tissue uncoupling protein mRNA on deacclimation of cold-exposed rats

The effect of environmental temperature on the level of uncoupling protein mRNA from rat brown adipose tissue was examined using a cDNA probe. A 4.4 fold increase in the mRNA level was observed after 1 day exposure of rats to 6 °C, which was followed by a slow loss with longer times of exposure. When rats were returned to a thermoneutral environment, there was a dramatic loss of uncoupling protein mRNA within 1 day. Comparison with poly(A) + RNA levels suggest that the response to temperature is specific for uncoupling protein mRNA.