Transplantation of wild-type white adipose tissue normalizes metabolic, immune and inflammatory alterations in leptin-deficient ob/ob mice

Leptin-deficient ob/ob mice exhibit several metabolic and immune abnormalities, including thymus atrophy and markedly reduced inflammatory responses. We evaluated whether transplantation of wild-type (WT) white adipose tissue (WAT) into ob/ob mice could mimic the effect of recombinant leptin administration in normalizing metabolic, immune and inflammatory abnormalities. Female ob/ob mice received a subcutaneous transplantation of WAT obtained from WT littermates. A separate group of ob/ob mice was sham-operated. Despite raising leptin levels to only 15% of those observed in WT mice, WAT transplantation normalized metabolic abnormalities (glycemia, ALT, liver weight) in ob/ob mice and prevented further body weight gain. The transplanted group demonstrated normalization of thymus and spleen cellularity, thymocyte subpopulations and rates of thymocyte apoptosis. In the model of dextran sulfate sodium-induced colitis, WAT transplantation restored inflammation to levels equivalent to those of WT mice. Colonic production of IL-6 and MIP-2 was markedly reduced in the non-transplanted ob/ob group compared to transplanted ob/ob and WT mice. Our data indicate that WAT transplantation is an effective way to normalize metabolic as well as immune and inflammatory parameters in ob/ob mice. The threshold of leptin sufficient to normalize metabolic, immune and inflammatory function is significantly lower than levels present in lean WT mice. Finally, leptin derived exclusively from WAT is sufficient to normalize metabolic, immune and inflammatory parameters in ob/ob mice.     

Leptin selectively reduces white adipose tissue in mice via a UCP1-dependent mechanism in brown adipose tissue

We tested the hypothesis that leptin, in addition to reducing body fat by restraining food intake, reduces body fat through a peripheral mechanism requiring uncoupling protein 1 (UCP1). Leptin was administered to wild-type (WT) mice and mice with a targeted disruption of the UCP1 gene (UCP1 deficient), while vehicle-injected control animals of each genotype were pair-fed to each leptin-treated group. Leptin reduced the size of white adipose tissue (WAT) depots in WT mice but not in UCP1-deficient animals. This was accompanied by a threefold increase in the amount of UCP1 protein and mRNA in the brown adipose tissue (BAT) of WT mice. Leptin also increased UCP2 mRNA in WAT of both WT and UCP1-deficient mice but increased UCP2 and UCP3 mRNA only in BAT from UCP1-deficient mice. These results indicate that leptin reduces WAT through a peripheral mechanism requiring the presence of UCP1, with little or no involvement of UCP2 or UCP3.     

Overexpression of constitutively active PKG-I protects female, but not male mice from diet-induced obesity

Cyclic guanosine monophosphate (cGMP)-dependent protein kinase I (PKG-I) is a multifunctional protein. The direct effects of PKG-I activation on energy homeostasis and obesity development are not well understood. Herein, we generated transgenic mice with expression of the constitutively active PKG-I in adipose tissue as well as in other tissues. Male and female PKG-I overexpressing mice were fed a low-fat (LF) or high-fat (HF) diet for 16 weeks. HF-fed female PKG-I transgenic mice had decreased body weight gain, lower percentage of body fat, and improved glucose tolerance compared to HF-fed wild-type (WT) controls. In contrast, male transgenic PKG-I mice were not resistant to the development of HF-diet-induced obesity, and exhibited similar levels of adiposity and glucose intolerance as HF-fed WT controls. Furthermore, we found that HF-fed female transgenic PKG-I mice had increased energy expenditure and cold-induced adaptive thermogenesis compared to HF-fed WT controls, which was associated with increased expression of uncoupling protein-1 (UCP1) in brown adipose tissue (BAT). In addition, the rates of lipolysis in white adipose tissue (WAT) were also increased in female transgenic PKG-I mice compared to WT controls due to increased phosphorylation of hormone-sensitive lipase (HSL). However, in male mice, adaptive thermogenesis or WAT lipolysis was similar between transgenic PKG-I mice and WT controls. Together, these data demonstrate sex differences in effects of PKG-I activation on the regulation of adipose tissue function and its contribution to diet induced obesity.     

Cathepsin K null mice show reduced adiposity during the rapid accumulation of fat stores

Growing evidences indicate that proteases are implicated in adipogenesis and in the onset of obesity. We previously reported that the cysteine protease cathepsin K (ctsk) is overexpressed in the white adipose tissue (WAT) of obese individuals. We herein characterized the WAT and the metabolic phenotype of ctsk deficient animals (ctsk-/-). When the growth rate of ctsk-/- was compared to that of the wild type animals (WT), we could establish a time window (5-8 weeks of age) within which ctsk-/-display significantly lower body weight and WAT size as compared to WT. Such a difference was not observable in older mice. Upon treatment with high fat diet (HFD) for 12 weeks ctsk-/- gained significantly less weight than WT and showed reduced brown adipose tissue, liver mass and a lower percentage of body fat. Plasma triglycerides, cholesterol and leptin were significantly lower in HFD-fed-ctsk-/- as compared to HFD-fed WT animals. Adipocyte lipolysis rates were increased in both young and HFD-fed-ctsk-/-, as compared to WT. Carnitine palmitoyl transferase-1 activity, was higher in mitochondria isolated from the WAT of HFD treated ctsk-/- as compared to WT. Together, these data indicate that ctsk ablation in mice results in reduced body fat content under conditions requiring a rapid accumulation of fat stores. This observation could be partly explained by an increased release and/or utilization of FFA and by an augmented ratio of lipolysis/lipogenesis. These results also demonstrate that under a HFD, ctsk deficiency confers a partial resistance to the development of dyslipidemia.     

Relationship between FGF21 and UCP1 levels under time-restricted feeding and high-fat diet

Fibroblast growth factor 21 (FGF21) exhibits a circadian oscillation, and its induction is critical during fasting. When secreted by liver and skeletal muscle, FGF21 enhances thermogenic activity in brown adipose tissue (BAT) by utilizing uncoupling protein 1 (UCP1) to dissipate energy as heat. Recently, it has been reported that UCP1 is not required for FGF21-mediated reduction in body weight or improvements in glucose homeostasis. As the relationship between FGF21 and UCP1 induction in tissues other than BAT is less clear, we tested the effect of restricted feeding (RF) and high dietary fat on FGF21 circadian expression and its correlation with UCP1 expression in liver and white adipose tissue (WAT). High dietary fat disrupted Fgf21 mRNA circadian oscillation but increased its levels in WAT. RF led to increased liver FGF21 protein levels, whereas those of UCP1 decreased. In contrast, WAT FGF21 protein levels increased under high-fat diet, whereas those of UCP1 decreased under RF. In summary, FGF21 exhibits circadian oscillation, which is disrupted with increased dietary fat. The relationship between FGF21 and UCP1 levels depends on the tissue and the cellular energy status.     

Ketogenic Diet Impairs FGF21 Signaling and Promotes Differential Inflammatory Responses in the Liver and White Adipose Tissue

Background/HypothesisBeside its beneficial effects on weight loss, ketogenic diet (KD) causes dyslipidemia, a pro-inflammatory state involved in the development of hepatic steatosis, glucose intolerance and insulin resistance, although the latter is still being debated. Additionally, KD is known to increase fibroblast growth factor 21 (FGF21) plasma levels. However, FGF21 cannot initiate its beneficial actions on metabolism in these conditions. We therefore hypothesized and tested in the present study that KD may impair FGF21 signaling.Methods/ResultsUsing indirect calorimetry, we found that KD-fed mice exhibited higher energy expenditure than regular chow (RC)-fed mice associated with increased Ucp1 levels in white adipose tissue (WAT), along with increased plasma FGF21 levels. We then assessed the effect of KD on FGF21 signaling in both the liver and WAT. We found that Fgfr4 and Klb (β-klotho) were downregulated in the liver, while Fgfr1 was downregulated in WAT of KD-fed mice. Because inflammation could be one of the mechanisms linking KD to impaired FGF21 signaling, we measured the expression levels of inflammatory markers and macrophage accumulation in WAT and liver and found an increased inflammation and macrophage accumulation in the liver, but surprisingly, a reduction of inflammation in WAT.We also showed that KD enhances lipid accumulation in the liver, which may explain hepatic inflammation and impaired Fgfr4 and Klb expression. In contrast, import of lipids from the circulation was significantly reduced in WAT of KD-fed mice, as suggested by a downregulation of Lpl and Cd36. This was further associated with reduced inflammation in WAT.ConclusionAltogether, these results indicate that KD could be beneficial for a given tissue but deleterious for another.     

Delta-6 desaturase (Fads2) deficiency alters triacylglycerol/fatty acid cycling in murine white adipose tissue

The Δ-6 desaturase (D6D) enzyme is not only critical for the synthesis of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from α-linolenic acid (ALA), but recent evidence suggests that it also plays a role in adipocyte lipid metabolism and body weight; however, the mechanisms remain largely unexplored. The goal of this study was to investigate if a D6D deficiency would inhibit triacylglycerol storage and alter lipolytic and lipogenic pathways in mouse white adipose tissue (WAT) depots due to a disruption in EPA and DHA production. Male C57BL/6J D6D knockout (KO) and wild-type (WT) mice were fed either a 7% w/w lard or flax (ALA rich) diet for 21 weeks. Energy expenditure, physical activity, and substrate utilization were measured with metabolic caging. Inguinal and epididymal WAT depots were analyzed for changes in tissue weight, fatty acid composition, adipocyte size, and markers of lipogenesis, lipolysis, and insulin signaling. KO mice had lower body weight, higher serum nonesterified fatty acids, smaller WAT depots, and reduced adipocyte size compared to WT mice without altered food intake, energy expenditure, or physical activity, regardless of the diet. Markers of lipogenesis and lipolysis were more highly expressed in KO mice compared to WT mice in both depots, regardless of the diet. These changes were concomitant with lower basal insulin signaling in WAT. Collectively, a D6D deficiency alters triacylglycerol/fatty acid cycling in WAT by promoting lipolysis and reducing fatty acid re-esterification, which may be partially attributed to a reduction in WAT insulin signaling.     

Protein kinase Cβ deficiency attenuates obesity syndrome of ob/ob mice by promoting white adipose tissue remodeling

To explore the role of leptin in PKCβ action and to determine the protective potential of PKCβ deficiency on profound obesity, double knockout (DBKO) mice lacking PKCβ and ob genes were created, and key parameters of metabolism and body composition were studied. DBKO mice had similar caloric intake as ob/ob mice but showed significantly reduced body fat content, improved glucose metabolism, and elevated body temperature. DBKO mice were resistant to high-fat diet-induced obesity. Moreover, PKCβ deficiency increased β-adrenergic signaling by inducing expression of β1- and β3-adrenergic receptors (β-ARs) in white adipose tissue (WAT) of ob/ob mice. Accordingly, p38(MAPK) activation and expression of PGC-1α and UCP-1 were increased in WAT of DBKO mice. Consistent with results of in vivo studies, inhibition of PKCβ in WAT explants from ob/ob mice also increased expression of above β-ARs. In contrast, induction of PGC-1α and UCP-1 expression in brown adipose tissue of DBKO mice was not accompanied by changes in the expression of these β-ARs. Collectively, these findings suggest that PKCβ deficiency may prevent genetic obesity, in part, by remodeling the catabolic function of adipose tissues through β-ARs dependent and independent mechanisms.     

Regulation of Endogenous Glucose Production in Glucose Transporter 4 Over-Expressing Mice

Strategies to amplify whole-body glucose disposal are key therapies to treat type 2 diabetes. Mice that over-express glucose transporter 4 (Glut4) in skeletal muscle, heart, and adipose tissue (G4Tg) exhibit increased fasting glucose disposal and thus lowered blood glucose. Intriguingly, G4Tg mice also exhibit improved insulin-stimulated suppression of endogenous glucose production even though Glut4 is not present in the liver. It is unclear, however, if hepatic gluco-regulation is altered in G4Tg mice in the basal, non-insulin-stimulated state. The current studies were performed to examine fasting hepatic glucose metabolism in G4Tg mice and to determine whether gluco-regulatory adaptations exist in the non-insulin-stimulated condition. To test this question, phloridzin-glucose clamps were used to match blood glucose and pancreatic hormone levels while tracer dilution techniques were used to measure glucose flux. These techniques were performed in chronically-catheterized, conscious, and un-stressed 5h-fasted G4Tg and wild-type (WT) littermates. Results show reduced blood glucose, hepatic glycogen content, and hepatic glucokinase (GK) activity/expression as well as higher endogenous glucose production, glucose disposal, arterial glucagon, and hepatic glucose-6-phosphatase (G6Pase) activity/expression in G4Tg mice versus WT controls. Clamping blood glucose for 90 min at ∼115 mg/dLin G4Tg and WT mice normalized nearly all variables. Notably, however, net hepatic glycogen synthetic rates were disproportionately elevated compared to changes in blood glucose. In conclusion, these studies demonstrate that basal improvements in glucose tolerance due to increased uptake in extra-hepatic sites provoke important gluco-regulatory adaptations in the liver. Although changes in blood glucose underlie the majority of these adaptations, net hepatic glycogen synthesis is sensitized. These data emphasize that anti-diabetic therapies that target skeletal muscle, heart, and/or adipose tissue likely positively impact the liver.     

Loss of CD24 in Mice Leads to Metabolic Dysfunctions and a Reduction in White Adipocyte Tissue

CD24 is a glycophosphatidylinositol (GPI)-linked cell surface receptor that is involved in regulating the survival or differentiation of several different cell types. CD24 has been used to identify pre-adipocytes that are able to reconstitute white adipose tissue (WAT) in vivo. Moreover, we recently found that the dynamic upregulation of CD24 in vitro during early phases of adipogenesis is necessary for mature adipocyte development. To determine the role of CD24 in adipocyte development in vivo, we evaluated the development of the inguinal and interscapular subcutaneous WAT and the epididymal visceral WAT in mice with a homozygous deletion of CD24 (CD24KO). We observed a significant decrease in WAT mass of 40% to 74% in WAT mass from both visceral and subcutaneous depots in male mice, with no significant effect in female mice, compared to wild-type (WT) sex- and age-matched controls. We also found that CD24KO mice had increased fasting glucose and free fatty acids, decreased fasting insulin, and plasma leptin. No major differences were observed in the sensitivity to insulin or glucose, or in circulating triglycerides, total cholesterol, HDL-cholesterol, or LDL-cholesterol levels between WT and CD24KO mice. Challenging the CD24KO mice with either high sucrose (35%) or high fat (45%) diets that promote increased adiposity, increased WAT mass and fasting insulin, adiponectin and leptin levels, as well as reduced the sensitivity to insulin and glucose, to the levels of WT mice on the same diets. The CD24-mediated reduction in fat pad size was due to a reduction in adipocyte cell size in all depots with no significant reduction pre-adipocyte or adipocyte cell number. Thus, we have clearly demonstrated that the global absence of CD24 affects adipocyte cell size in vivo in a sex- and diet-dependent manner, as well as causing metabolic disturbances in glucose homeostasis and free fatty acid levels.     

Effects of interleukin-15 (IL-15) on adipose tissue mass in rodent obesity models: evidence for direct IL-15 action on adipose tissue

Interleukin-15 (IL-15) is a proinflammatory cytokine with multifunctional effects outside the immune system. Previous studies have indicated that treatment of normal rats with IL-15 reduces white adipose tissue (WAT) mass, but it was unclear if these effects were direct or indirect. In the present study, the effects of IL-15 on WAT mass and lipid metabolism were studied in two genetic models of obesity: the leptin receptor-negative fa/fa Zucker rat and the leptin-deficient ob/ob mouse. Lean Zucker rats, lean (+/+), and obese mice (ob/ob) responded to IL-15 with reductions in WAT mass and lipoprotein lipase activity (LPL), with no decreases in food intake. In contrast, fa/fa Zucker rats did not respond to IL-15 administration by any of the above measures of fat mass or lipid metabolism. In addition, ribonuclease protection assays (RPAs) were used to demonstrate that all three subunits (gamma(c), beta and alpha) of the IL-15 receptor complex are expressed by rat and mouse WAT, suggesting that the effects of IL-15 on adipose tissue metabolism could be direct. Additionally, the fa/fa rats expressed 84% lower levels of the gamma(c) signaling receptor subunit than lean Zucker rats, suggesting this decrease may play a role in the lack of adipose tissue response to IL-15 in the fa/fa genotype and lending further support for a direct action of IL-15 on adipose tissue.     

Diet‐induced Obese Mice Are Leptin Insufficient After Weight Reduction

Behavioral therapies aimed at reducing excess body fat result in limited fat loss after dieting. To understand the causes for maintenance of adiposity, high‐fat (HF) diet–induced obese (DIO) mice were switched to a low‐fat chow diet, and the effects of chow on histological and molecular alterations of adipose tissue and metabolic parameters were examined. DIO mice reduced and stabilized their body weights after being switched to chow (HF‐chow), but retained a greater amount of adiposity than chow‐fed mice. Reduction in adipocyte volume, not number, caused a decrease in fat mass. HF‐chow mice showed normalized circulating insulin and leptin levels, improved glucose tolerance, and reduced inflammatory status in white adipose tissue (WAT). Circulating leptin levels corrected for fat mass were lower in HF‐chow mice. Leptin administration was used to test whether reduced leptin level of HF‐chow mice inhibited further fat loss. Leptin treatment led to an additional reduction in adiposity. Finally, HF‐HF mice had lower mRNA levels of β₃ adrenergic receptor (β₃‐AR) in epididymal WAT (EWAT) compared to chow‐fed mice, and diet change led to an increase in the WAT β₃‐AR mRNA levels that were similar to the levels of chow‐fed mice, suggesting an elevation in sympathetic activation of WAT during diet switch relative to HF‐HF mice leading to the reduced leptin level and proinflammatory cytokine content. In summary, HF‐chow mice were resistant to further fat loss due to leptin insufficiency. Diet alteration from HF to low fat improved metabolic state of DIO mice, although their adiposity was defended at a higher level.     

Adipose Overexpression of Heme Oxygenase-1 Does Not Protect against High Fat Diet-Induced Insulin Resistance in Mice

Heme oxygenase-1 (HO-1) is a stress-responsive enzyme with potent anti-oxidant and anti-inflammatory activities. Previous studies have shown that systemic induction of HO-1 by chemical inducers reduces adiposity and improves insulin sensitivity. To dissect the specific function of HO-1 in adipose tissue, we generated transgenic mice with adipose HO-1 overexpression using the adipocyte-specific aP2 promoter. The transgenic (Tg) mice exhibit similar metabolic phenotype as wild type (WT) control under chow-fed condition. High fat diet (HFD) challenge significantly increased the body weights of WT and Tg mice to a similar extent. Likewise, HFD-induced glucose intolerance and insulin resistance were not much different between WT and Tg mice. Analysis of the adipose tissue gene expression revealed that the mRNA levels of adiponectin and interleukin-10 were significantly higher in chow diet-fed Tg mice as compared to WT counterparts, whereas HFD induced downregulation of adiponectin gene expression in both Tg and WT mice to a similar level. HFD-induced proinflammatory cytokine expression in adipose tissues were comparable between WT and transgenic mice. Nevertheless, immunohistochemistry and gene expression analysis showed that the number of infiltrating macrophages with preferential expression of M2 markers was significantly higher in the adipose tissue of obese Tg mice than WT mice. Further experiment demonstrated that myeloid cells from Tg mice expressed higher level of HO-1 and exhibited greater migration response toward chemoattractant in vitro. Collectively, these data indicate that HO-1 overexpression in adipocytes does not protect against HFD-induced obesity and the development of insulin resistance in mice.     

Adiponectin plays an important role in efficient energy usage under energy shortage

Adiponectin is an adipose tissue-specific secretory protein known to be an insulin-sensitizing protein. In this study, we generated adiponectin sense and antisense transgenic (Tg) mice to investigate whether adiponectin plays a role in the regulation of energy homeostasis during the growth stage. Spontaneous motor activity of antisense Tg mice were markedly reduced during fasting, particularly in young female mice, compared with wild type (Wt) and sense Tg mice. Furthermore, both body weight and adipose tissue mass of the antisense female Tg mice drastically reduced during fasting. To examine the relationship between the collapse of abdominal white adipose tissue (WAT) and serum adiponectin level, we measured the expression of genes related to energy expenditure, such as uncoupling protein (UCP). Notably, the mRNA of UCP1 in the WAT of antisense Tg female mice was markedly less than that of Wt mice and the UCP1 mRNA was strongly increased during fasting. These findings suggest that the serum adiponectin is important to maintaining energy homeostasis under energy shortage conditions, such as over female pubertal development.     

Differential regulation of fatty acid trapping in mouse adipose tissue and muscle by ASP

Acylation-stimulating protein (ASP) is a lipogenic hormone secreted by white adipose tissue (WAT). Male C3 knockout (KO; C3(-/-)) ASP-deficient mice have delayed postprandial triglyceride (TG) clearance and reduced WAT mass. The objective of this study was to examine the mechanism(s) by which ASP deficiency induces differences in postprandial TG clearance and body composition in male KO mice. Except for increased (3)H-labeled nonesterified fatty acid (NEFA) trapping in brown adipose tissue (BAT) of KO mice (P = 0.02), there were no intrinsic tissue differences between wild-type (WT) and KO mice in (3)H-NEFA or [(14)C]glucose oxidation, TG synthesis or lipolysis in WAT, muscle, or liver. There were no differences in WAT or skeletal muscle hydrolysis, uptake, and storage of [(3)H]triolein substrate [in situ lipoprotein lipase (LPL) activity]. ASP, however, increased in situ LPL activity in WAT (+64.8%, P = 0.02) but decreased it in muscle (-35.0%, P = 0.0002). In addition, after prelabeling WAT with [(3)H]oleate and [(14)C]glucose, ASP increased (3)H-lipid retention, [(3)H]TG synthesis, and [(3)H]TG-to-[(14)C]TG ratio, whereas it decreased (3)H-NEFA release, indicating increased NEFA trapping in WAT. Conversely, in muscle, ASP induced effects opposite to those in WAT and increased lipolysis, indicating reduced NEFA trapping within muscle by ASP (P < 0.05 for all parameters). In conclusion, novel data in this study suggest that 1) there is little intrinsic difference between KO and WT tissue in the parameters examined and 2) ASP differentially regulates in situ LPL activity and NEFA trapping in WAT and skeletal muscle, which may promote optimal insulin sensitivity in vivo.     

Interleukin-7 regulates adipose tissue mass and insulin sensitivity in high-fat diet-fed mice through lymphocyte-dependent and independent mechanisms

Although interleukin (IL)-7 is mostly known as a key regulator of lymphocyte homeostasis, we recently demonstrated that it also contributes to body weight regulation through a hypothalamic control. Previous studies have shown that IL-7 is produced by the human obese white adipose tissue (WAT) yet its potential role on WAT development and function in obesity remains unknown. Here, we first show that transgenic mice overexpressing IL-7 have reduced adipose tissue mass associated with glucose and insulin resistance. Moreover, in the high-fat diet (HFD)-induced obesity model, a single administration of IL-7 to C57BL/6 mice is sufficient to prevent HFD-induced WAT mass increase and glucose intolerance. This metabolic protective effect is accompanied by a significant decreased inflammation in WAT. In lymphocyte-deficient HFD-fed SCID mice, IL-7 injection still protects from WAT mass gain. However, IL-7-triggered resistance against WAT inflammation and glucose intolerance is lost in SCID mice. These results suggest that IL-7 regulates adipose tissue mass through a lymphocyte-independent mechanism while its protective role on glucose homeostasis would be relayed by immune cells that participate to WAT inflammation. Our observations establish a key role for IL-7 in the complex mechanisms by which immune mediators modulate metabolic functions.     

Central leptin regulates the UCP1 and ob genes in brown and white adipose tissue via different beta-adrenoceptor subtypes

The three known subtypes of beta-adrenoreceptors (beta(1)-AR, beta(2)-AR, and beta(3)-AR) are differentially expressed in brown and white adipose tissue and mediate peripheral responses to central modulation of sympathetic outflow by leptin. To assess the relative roles of the beta-AR subtypes in mediating leptin's effects on adipocyte gene expression, mice with a targeted disruption of the beta(3)-adrenoreceptor gene (beta(3)-AR KO) were treated with vehicle or the beta(1)/beta(2)-AR selective antagonist, propranolol (20 microgram/g body weight/day) prior to intracerebroventricular (ICV) injections of leptin (0.1 microgram/g body weight/day). Leptin produced a 3-fold increase in UCP1 mRNA in brown adipose tissue of wild type (FVB/NJ) and beta(3)-AR KO mice. The response was unaltered by propranolol in wild type mice, but was completely blocked by this antagonist in beta(3)-AR KO mice. In contrast, ICV leptin had no effect on leptin mRNA in either epididymal or retroperitoneal white adipose tissue (WAT) from beta(3)-AR KOs. Moreover, propranolol did not block the ability of exogenous leptin to reduce leptin mRNA in either WAT depot site of wild type mice. These results demonstrate that the beta(3)-AR is required for leptin-mediated regulation of ob mRNA expression in WAT, but is interchangeable with the beta(1)/beta(2)-ARs in mediating leptin's effect on UCP1 mRNA expression in brown adipose tissue.