Dynamics and precision of thermoregulatory responses of eastern skunk cabbage Symplocarpus foetidus

Inflorescences of the arum lily Symplocarpus foetidus are thermogenic and thermoregulatory. The spadix increases respiratory heat production rate as ambient temperature decreases. This study examined the relationships between spadix temperature (T_s), respiration rate () and ambient temperature (T_a) at equilibrium and during transient responses to step changes in T_a. Intact inflorescences inside a miniature constant temperature cabinet in the field showed the most precise temperature regulation yet recorded; over a 37.4 °C range in T_a (?10.3 to 27.1 °C), T_s changed only 3.5 °C (22.7 to 26.2 °C). Regulated temperatures were not related to spadix size (1.9–7.3 g) or circadian cycle. Dynamic responses to step changes in T_a involved a phasic change in T_s, first in the same direction as T_a, then reversing at 38.3 min, and finally approaching equilibrium at 87.6 min, on average. Meanwhile changed in a monotonic curve toward equilibrium. Models revealed that the dynamics of temperature change were inconsistent with simply a physical lag in the system, but involved some form of biochemical regulation, possibly by changes in activity of a rate‐limiting functional protein.     

Binding of fatty acids to the uncoupling protein from brown adipose tissue mitochondria

The uncoupling protein 1 (UCP1) is a H(+) carrier which plays a key role in heat generation in brown adipose tissue. The H(+) transport activity of UCP1 is activated by long-chain fatty acids and inhibited by purine nucleotides. While nucleotide binding has been well characterized, the interaction of fatty acid with UCP1 remains unknown. Here I demonstrate the binding of fatty acids by competition with a fluorescent nucleotide probe 2(')-O-dansyl guanosine 5(')-triphosphate (GTP), which has been shown previously to bind at the nucleotide binding site in UCP1. Fatty acids but not their esters competitively inhibit the binding of 2(')-O-dansyl GTP to UCP1. The fatty acid effect was enhanced at higher pH, suggesting the binding of fatty acid anion to UCP1. The inhibition constants K(i) were determined by fluorescence titrations for various fatty acids. Short-chain (C<8) fatty acids display no affinity, whereas medium-chain (C10-14) and unsaturated C18 fatty acids exhibit stronger affinity (K(i)=65 microM, for elaidic acid). This specificity profile agrees with previous functional data obtained in both proteoliposomes and mitochondria, suggesting a possible physiological role of this fatty acid binding site.     

Increased uncoupling protein-2 and -3 gene expressions in skeletal muscle of STZ-induced diabetic rats

Streptozotocin (STZ)-induced diabetic animals are vulnerable to cold stress. Uncoupling proteins (UCPs) play an important role in regulating thermogenesis. We investigated the gene expressions of UCPs in brown adipose tissue (BAT), white adipose tissue (WAT), liver and gastrocnemius muscle of STZ-diabetic rats using Northern blot. UCP-1, -2 and -3 mRNA expressions in BAT were all remarkably lower in STZ-diabetic rats than those in control rats. Both UCP-2 and -3 gene expressions in gastrocnemius muscle were substantially elevated in STZ-diabetic rats and insulin treatment restored UCP gene expressions to normal levels. These results suggest that in STZ-diabetic rats, the overexpression of UCP-2 and UCP-3 in skeletal muscle provides a defense against hypothermogenesis caused by decreased UCPs in BAT.     

Nitric oxide reduces the thermogenic changes induced by lateral hypothalamic lesion

The experiment described here tests the effect of intracerebroventricular (icv) injection of nitric oxide (NO) precursors, such as L-arginine (L-arg) and nitroprusside (NP), on the thermogenic changes induced by lesion of the lateral hypothalamus (LH). The firing rate of the nerves innervating interscapular brown adipose tissue (IBAT), along with IBAT and colonic temperatures (T_IBAT and T_C) were monitored in urethane-anesthetized male Sprague-Dowley rats lesioned in the LH. These variables were measured before and after and icv injection of 4 μmol L-arg or 400 nmol NP. The same variables were also monitored in: a) lesioned rats with icv administration of saline; b) sham-lesioned animals with icv injection of L-arg or NP; c) sham-lesioned rats with icv injection of saline. The results show that L-arg or NP injection reduces the increases in firing rate, T_IBAT, and T_C induced by LH lesion. These findings suggest that NO plays a key role in the thermogenic changes following LH lesion.     

Determination of tissue contributions to the circulating lipid pool in cold exposure via systematic assessment of lipid profiles

Plasma lipid levels are altered in chronic conditions such as type 2 diabetes and cardiovascular disease as well as during acute stresses such as fasting and cold exposure. Advances in MS-based lipidomics have uncovered a complex plasma lipidome of more than 500 lipids that serve functional roles, including as energy substrates and signaling molecules. This plasma lipid pool is maintained through regulation of tissue production, secretion, and uptake. A major challenge in understanding the lipidome complexity is establishing the tissues of origin and uptake for various plasma lipids, which is valuable for determining lipid functions. Using cold exposure as an acute stress, we performed global lipidomics on plasma and in nine tissues that may contribute to the circulating lipid pool. We found that numerous species of plasma acylcarnitines (ACars) and ceramides (Cers) were significantly altered upon cold exposure. Through computational assessment, we identified the liver and brown adipose tissue as major contributors and consumers of circulating ACars, in agreement with our previous work. We further identified the kidney and intestine as novel contributors to the circulating ACar pool and validated these findings with gene expression analysis. Regression analysis also identified that the brown adipose tissue and kidney are interactors with the plasma Cer pool. Taken together, these studies provide an adaptable computational tool to assess tissue contribution to the plasma lipid pool. Our findings have further implications in understanding the function of plasma ACars and Cers, which are elevated in metabolic diseases.     

The effect of short-term fasting on shivering thermogenesis in Japanese quail chicks (Coturnix coturnix japonica): indications for a significant role of diet-induced/growth related thermogenesis

(1) The effect of short-term fasting on metabolism and shivering thermogenesis was studied in 9-day-old Japanese quail. (2) After 31 h of fasting, heat production decreased 39% and body temperature over 2°C in the thermoneutral zone. The difference in heat production between control and fasting groups decreased with decreasing ambient temperature. (3) Despite the lower metabolic rate, the amplitudes of shivering EMGs were higher in fasted chicks, especially in pectoralis. This indicates that fasted quails used shivering to compensate the decrease in diet-induced/growth related thermogenesis. (4) In cold, conductance of control birds decreased simultaneously with increasing heat production while in fasted chicks, conductance decreased to its minimum before heat production was activated. (5) Japanese quail chicks adapt quickly to short-term fasting by decreasing metabolism but they maintain their ability to thermoregulate in cold. Diet-induced/growth related thermogenesis has a significant role in thermoregulation since it reduces the need of shivering thermogenesis.     

Thermoregulation: What Role for UCPs in Mammals and Birds?

Mammals and birds are endotherms and respond to cold exposure by the means of regulatory thermogenesis, either shivering or non-shivering. In this latter case, waste of cell energy as heat can be achieved by uncoupling of mitochondrial respiration. Uncoupling proteins, which belong to the mitochondrial carrier family, are able to transport protons and thus may assume a thermogenic function. The mammalian UCP1 physiological function is now well understood and gives to the brown adipose tissue the capacity for heat generation. But is it really the case for its more recently discovered isoforms UCP2 and UCP3? Additionally, whereas more and more evidence suggests that non-shivering also exists in birds, is the avian UCP also involved in response to cold exposure? In this review, we consider the latest advances in the field of UCP biology and present putative functions for UCP1 homologues.     

Does non-exercise activity thermogenesis contribute to non-shivering thermogenesis?

We wanted to examine if spontaneous physical activity contributes to non-shivering thermogenesis. Ten lean, healthy male subjects wore a physical activity, micro-measurement system while the room temperature was randomly altered at two hourly intervals between thermoneutral (72 °F), cool (62 °F) and warm (82 °F) temperatures. Physical activity measured during the thermoneutral, cooling and warming periods was not significantly different. Cooling increased energy expenditure above basal and thermoneutral values 2061±344 kcal/day (p<0.01). Thus, the increase in energy expenditure associated with short-term environmental cooling in lean, healthy males does not appear to be due to increased spontaneous physical activity or fidgeting.     

MiR-92a regulates brown adipocytes differentiation,mitochondrial oxidative respiration,and heat generation by targeting SMAD7

Brown adipocytes are rich in mitochondria and linked to the body's blood fat levels and obesity. MiR-92a is negatively correlated with the activity of brown adipocytes. This study aimed to explore the mechanism of miR-92a on brown adipocytes. The expression of miR-92a in C2C12 cell was detected by a quantitative real-time-polymerase chain reaction (qRT-PCR). C2C12 cells were induced to brown adipocytes. The direct target gene of miR-92a was determined using the dual-luciferase reporter assay. Brown adipocytes were treated with isoprenaline (Iso) and transfected by miR-92a inhibitor and siSMAD7. The expression of heat-producing genes and adipose differentiation genes related to brown adipocytes were detected by qRT-PCR and Western blot analysis. The expression of SMAD7, p-SMAD2, and p-SMAD3 were detected using Western blot analysis. The mitochondrial content was measured by mitotracker fluorescent staining. MiR-92a inhibitor significantly decreased the expression of miR-92a in C2C12 cells. MiR-92a inhibitor could upregulate the expression of Ucp1, Cox7a1, Elovl3, Ppargc1α, PPARγ, and FABP4, and its effect on Ucp1 was increased after the treatment of isoprenaline. Moreover, miR-92a inhibitor increased mitochondrial content, oxygen consumption rate (OCR) and the expression of SMAD7 and suppressed the expressions of p-SMAD2 and p-SMAD3, whereas miR-92a directly targeted SMAD7 to exert its inhibitory effects. SiSMAD7 reversed the effects of the inhibitor on heat-producing genes, mitochondrial content, OCR and the expressions of SMAD7, p-SMAD2, and p-SMAD3 in brown adipocytes. Blocking miR-92a might promote brown adipocytes differentiation, mitochondrial oxidative respiration, and thermogenesis by targeting SMAD7 to inhibit the expressions of p-SMAD2 and p-SMAD3.     

Encapsulation Thermogenic Preadipocytes for Transplantation into Adipose Tissue Depots

Cell encapsulation was developed to entrap viable cells within semi-permeable membranes. The engrafted encapsulated cells can exchange low molecular weight metabolites in tissues of the treated host to achieve long-term survival. The semipermeable membrane allows engrafted encapsulated cells to avoid rejection by the immune system. The encapsulation procedure was designed to enable a controlled release of bioactive compounds, such as insulin, other hormones, and cytokines. Here we describe a method for encapsulation of catabolic cells, which consume lipids for heat production and energy dissipation (thermogenesis) in the intra-abdominal adipose tissue of obese mice. Encapsulation of thermogenic catabolic cells may be potentially applicable to the prevention and treatment of obesity and type 2 diabetes. Another potential application of catabolic cells may include detoxification from alcohols or other toxic metabolites and environmental pollutants.