TLR4 in POMC neurons regulates thermogenesis in a sex-dependent manner

The rising prevalence of obesity has become a worldwide health concern. Obesity usually occurs when there is an imbalance between energy intake and energy expenditure. However, energy expenditure consists of several components, including metabolism, physical activity, and thermogenesis. Toll-like receptor 4 (TLR4) is a transmembrane pattern recognition receptor, and it is abundantly expressed in the brain. Here, we showed that pro-opiomelanocortin (POMC)-specific deficiency of TLR4 directly modulates brown adipose tissue thermogenesis and lipid homeostasis in a sex-dependent manner. Deleting TLR4 in POMC neurons is sufficient to increase energy expenditure and thermogenesis resulting in reduced body weight in male mice. POMC neuron is a subpopulation of tyrosine hydroxylase neurons and projects into brown adipose tissue, which regulates the activity of sympathetic nervous system and contributes to thermogenesis in POMC-TLR4-KO male mice. By contrast, deleting TLR4 in POMC neurons decreases energy expenditure and increases body weight in female mice, which affects lipolysis of white adipose tissue (WAT). Mechanistically, TLR4 KO decreases the expression of the adipose triglyceride lipase and lipolytic enzyme hormone-sensitive lipase in WAT in female mice. Furthermore, the function of immune-related signaling pathway in WAT is inhibited because of obesity, which exacerbates the development of obesity reversely. Together, these results demonstrate that TLR4 in POMC neurons regulates thermogenesis and lipid balance in a sex-dependent manner.     

Pollination ecology of Arum italicum (Araceae)

The pollination ecology of Arum italicum was studied in south-western France. This plant attracts olfactory dung-breeding flies through deceit. These insects are principally represented by Diptera, all belonging to saprophyte families. The volatilization of the odouriferous compounds, responsible for their attraction, is achieved through the production of heat by the appendix. The insects are trapped for 24 h in order to participate in both sexual phases of the protogynous inflorescence. The male flowers produce three heat events during flowering. These peaks of heat seem to be involved in the spathe movements, since they occur during the opening of the inflorescence and the liberation of the insects. The last male heat event may be linked with the liberation of pollen and its dispersion by stimulating trapped flies. According to their frequency and pollen-load, two Psychoda species appear to be the most efficient pollinators ( P. crassipenis and P. pusilla ). Nevertheless, each of the other attracted species could play a significant role under different spatio-temporal conditions. Experiments on self-pollination have shown that obligate cross-pollination is necessary for A. italicum to set seeds. Moreover, hand- and natural-pollinated plants showed similarly high abortion frequencies suggesting that seed set may be more constrained by resources rather than by pollination limitation.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 205–214.     

Non-shivering thermogenesis in winter-acclimatized and in long-scotophase and cold-acclimated Apodemus mystacinus (Rodentia)

1. 1.|Resistance to cold through non-shivering thermogenesis (the absolute increase in O₂ consumption caused by noradrenaline injection) was increased 3-fold in individuals of the broad-toothed mouse A. mystacinus, kept for 3 weeks under a short photoperiod (long scotophase 8L:16D) at an ambient temperature of 28°C, compared to control conditions (12L:12D; 28°C), and did not differ significantly from the winter-acclimatized group.

2. 2.|Acclimation of the same individuals to long scotophase and cold (8L:16d; 7°C) caused a significant (P < 0.01) increase in absolute O₂ consumption and maximal body temperature, as a response to noradrenaline injectin, when compared to long-scotophase individuals (8L:16D; 28°C).

3. 3.|The results of this study support the idea that winter acclimatization of heat-production mechanisims may be induced by the extension of scotophase, which cycles very regulary in nature and in the Mediterranean region occurs before the beginning of the cold season.

Rnf20 deficiency in adipocyte impairs adipose tissue development and thermogenesis

RNF20,an E3 ligase critical for monoubiquitination of histone H2B at lysine 120 (H2Bub),has been implicated in the regulation of various cellar processes;however,its physiological roles in adipocytes remain poorly characterized.Here,we report that the adipocyte-speci-fic knockout of Rnf20 (ASKO) in mice led to progressive fat loss,organomegaly and hyperinsulinemia.Despite signs of hyperinsulinemia,normal insulin sensitivity and improved glucose tolerance were observed in the young and aged CD-fed ASKO mice.In addition,high-fat diet-fed ASKO mice developed severe liver steatosis.More-over,we observed that the ASKO mice were extremely sensitive to a cold environment due to decreased expression levels of brown adipose tissue (BAT) selec-tive genes,including uncoupling protein 1 (Ucp1),and impaired mitochondrial functions.Significantly decreased levels of peroxisome proliferator-activated receptor gamma (Ppary) were observed in the gonadal white adipose tissues (gWAT) from the ASKO mice,suggesting that Rnf20 regulates adipogenesis,at least in part,through Ppary.Rosiglitazone-treated ASKO mice exhibited increased fat mass compared to that of the non-treated ASKO mice.Collectively,our results illus-trate the critical role of RNF20 in control of white and brown adipose tissue development and physiological function.     

The phytochemical hyperforin triggers thermogenesis in adipose tissue via a Dlat-AMPK signaling axis to curb obesity

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Role of gut microbiota in the postnatal thermoregulation of Brandt’s voles

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A torch in the rain forest: thermogenesis of the Titan arum (Amorphophallus titanum)

An outstanding flagship species in the plant kingdom is the Titan arum ( Amorphophallus titanum ), which produces a fountain-like bloom up to 3 m high. The unique appearance of three simultaneous inflorescences in May 2006 was a chance to analyse the flowering behaviour and thermogenesis of this giant. For the first time, the heating of the central column (spadix) could be documented using a high-performance thermographic camera. Time series analyses of the infrared image sequences revealed that the 3-m high spadix surface heats up in pulses emanating from the base of the inflorescence. The surface temperature reaches over 36 °C, compared to the ambient temperature of 27 °C. Waves of the carrion-like odour are synchronised with these heat pulses. The combination of heat pulses, the fountain-like shape plus the enormous size lead to a unique type of 'convection flower'. On the basis of our observations, we assume that Amorphophallus titanum is able to overcome thermodynamic decoupling by a self-produced convective process.     

Daily rhythms of nonshivering thermogenesis in common spiny mice Acomys cahirinus under short and long photoperiods

Daily rhythms of nonshivering thermogenesis NST were studied in common spiny mice Acomys cahirinus, acclimated to different photoperiod regimes (16L:8D and 8L:16D) at a constant ambient temperature of 26°C. Noradrenaline NA (1.5 mg/kg subcutaneous) was injected at: 06:00, 12:00, 18:00 and 24:00 h (±15 min). NST was measured as the ratio between the maximal oxygen consumption (VO₂) as response to NA — VO₂NA and VO₂ measured at 26°C — VO_{2 min}. Rectal temperatures T_bNA and T_{b min} respectively were recorded at the end of VO₂ measurements. Significant variations in T_{b min}, T_bNA, and NST were revealed, under the two different photoperiod regimes. Significant differences in VO_{2 min}, NST, T_{b min} and T_bNA were also recorded within each photoperiod acclimation group. These results suggest that daily and photoperiod depended variations in the brown adipose tissue activity, presumably emerge from amount of unoccupied receptors or changes in the receptors affinity to NA.     

Dehydroepiandrosterone and Body Fat

Dehydroepiandrosterone sulfate (DHEA-S) is the most abundant circulating adrenal steroid in man, yet its physiologic role and that of its parent compound DHEA are unknown. Age-related decreases in DHEA in association with increases in obesity, insulin resistance, and atherosclerosis are well known. Recent investigations in lower mammals (which do not secrete DHEA) have suggested that DHEA (or its metabolites) may function as an antiobesity agent in these models of obesity independent of food intake. Proposed mechanisms for the decrease in fat mass and lower weight gain when DHEA is given orally include increases in futile cycling and peroxisomal β-oxidation and decreases in de novo lipogenesis. Alterations in the availability of reducing equivalents for lipid synthesis do not appear to explain this decrease. Changes in pancreatic insulin secretion or insulin sensitivity may also be responsible for some of these effects. Studies in humans have failed to demonstrate a beneficial effect of DHEA on body composition or energy expenditure at either pharmacologic or physiologic replacement doses for 1–3 months. Administration of DHEA to men or women has also not been shown to alter insulin sensitivity as measured by the minimal model or the euglycemic clamp technique. The effect of DHEA on peroxisomal β-oxidation and de novo lipogenesis is not known. We conclude that a significant role for DHEA in the pharmacologic treatment of human obesity is unlikely.