The control of UCP1 is dissociated from that of PGC-1alpha or of mitochondriogenesis as revealed by a study using beta-less mouse brown adipocytes in culture

TRPV1 Activation Antagonizes High-Fat Diet-Induced Obesity at Thermoneutrality and Enhances UCP-1 Transcription via PRDM-16

Body weight is a balance between energy intake and energy expenditure. Energy expenditure is mainly governed by physical activity and adaptive thermogenesis. Adaptive dietary thermogenesis in brown and beige adipose tissue occurs through mitochondrial uncoupling protein (UCP-1). Laboratory mice, when housed at an ambient temperature of 22-24 °C, maintain their body temperature by dietary thermogenesis, eating more food compared to thermoneutrality. Humans remain in the thermoneutral zone (TNZ) without expending extra energy to maintain normal body temperature. TRPV1 activation by capsaicin (CAP) inhibited weight gain in mice housed at ambient temperature by activating UCP-1-dependent adaptive thermogenesis. Hence, we evaluated the effect of CAP feeding on WT and UCP-1-/- mice maintained under thermoneutral conditions. Our research presents novel findings that TRPV1 activation by CAP at thermoneutrality counters obesity in WT mice and promotes PRDM-16-dependent UCP-1 transcription. CAP fails to inhibit weight gain in UCP-1-/- mice housed at thermoneutrality and in adipose tissue-specific PRDM-16-/- mice. In vitro, capsaicin treatment increases UCP-1 transcription in PRDM-16 overexpressing cells. Our data indicate for the first time that TRPV1 activation counters obesity at thermoneutrality permissive for UCP-1 and the enhancement of PRDM-16 is not beneficial in the absence of UCP-1.

Mitophagy Responds to the Environmental Temperature and Regulates Mitochondrial Mass in Adipose Tissues

There are at least two types of adipose tissues in the body, defined as brown adipose tissues (BATs) and white adipose tissues (WATs). These tissues comprise brown and white adipocytes, respectively. The adipocytes are commonly endowed with mitochondria, but they have diverse characteristics and roles. Brown adipocytes have abundant mitochondria that contribute to the β-oxidation of fatty acids to produce chemical energy and the production of heat via uncoupling of the mitochondrial membrane potential from ATP synthesis. Alternatively, white adipocytes have fewer mitochondria that contribute to the generation of free fatty acids via lipogenesis by providing key intermediates. Besides the described types of adipocytes, brown-like adipocytes, termed beige adipocytes, are developed in WAT depots during cold exposure. Beige adipocytes also contribute to thermogenesis. Notably, beige adipocytes may transform into white-like adipocytes after the withdrawal of cold exposure. This process is marked by the elimination of mitochondria through the activation of mitochondria autophagy (mitophagy). This review aims to describe the mitophagy that occurs during the beige-to-white transition and discuss recent insights into the molecular mechanisms of this transformation. Additionally, we describe the mitophagy monitoring strategy in adipose tissues using three independent reporter systems and discuss the availabilities and limitations of the method.

Topical application of the pharmacological cold mimetic menthol stimulates brown adipose tissue thermogenesis through a TRPM8, UCP1, and norepinephrine dependent mechanism in mice housed at thermoneutrality

Increasing whole-body energy expenditure via the pharmacological activation of uncoupling protein 1 (UCP1)-dependent brown adipose tissue (BAT) thermogenesis is a promising weight management strategy, yet most therapeutics studied in rodents to date either induce compensatory increases in energy intake, have thermogenic effects that are confounded by sub-thermoneutral housing temperatures or are not well tolerated in humans. Here, we sought to determine whether the non-invasive topical application of the pharmacological cold mimetic and transient receptor potential (TRP) cation channel subfamily M member 8 (TRPM8) agonist L-menthol (MNTH), could be used to stimulate BAT thermogenesis and attenuate weight gain in mice housed at thermoneutrality. Using three different strains of mice and multiple complimentary approaches to quantify thermogenesis in vivo, coupled with ex vivo models to quantify direct thermogenic effects, we were able to convincingly demonstrate the following: (1) acute topical MNTH application induces BAT thermogenesis in a TRPM8- and UCP1-dependent manner; (2) MNTH-induced BAT thermogenesis is sufficient to attenuate weight gain over time without affecting energy intake in lean and obese mice; (3) the ability of topical MNTH application to stimulate BAT thermogenesis is mediated, in part, by a central mechanism involving the release of norepinephrine. These data collectively suggest that topical application of MNTH may be a promising weight management strategy.

Flavonoids modulate AMPK/PGC-1α and interconnected pathways toward potential neuroprotective activities

As progressive, chronic, incurable and common reasons for disability and death, neurodegenerative diseases (NDDs) are significant threats to human health. Besides, the increasing prevalence of neuronal gradual degeneration and death during NDDs has made them a global concern. Since yet, no effective treatment has been developed to combat multiple dysregulated pathways/mediators and related complications in NDDs. Therefore, there is an urgent need to create influential and multi-target factors to combat neuronal damages. Accordingly, the plant kingdom has drawn a bright future. Among natural entities, flavonoids are considered a rich source of drug discovery and development with potential biological and medicinal activities. Growing studies have reported multiple dysregulated pathways in NDDs, which among those mediator AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) play critical roles. In this line, critical role of flavonoids in the upregulation of AMPK/PGC-1α pathway seems to pave the road in the treatment of Alzheimer's disease (AD), Parkinson's disease (PD), aging, central nervous system (brain/spinal cord) damages, stroke, and other NDDs. In the present study, the regulatory role of flavonoids in managing various NDDs has been shown to pass through AMPK/PGC-1α signaling pathway.

Brown Adipose Tissue Development and Metabolism

Brown adipose tissue is well known to be a thermoregulatory organ particularly important in small rodents and human infants, but it was only recently that its existence and significance to metabolic fitness in adult humans have been widely realized. The ability of active brown fat to expend high amounts of energy has raised interest in stimulating thermogenesis therapeutically to treat metabolic diseases related to obesity and type 2 diabetes. In parallel, there has been a surge of research aimed at understanding the biology of rodent and human brown fat development, its remarkable metabolic properties, and the phenomenon of white fat browning, in which white adipocytes can be converted into brown like adipocytes with similar thermogenic properties. Here, we review the current understanding of the developmental and metabolic pathways involved in forming thermogenic adipocytes, and highlight some of the many unknown functions of brown fat that make its study a rich and exciting area for future research.

Fndc5 loss-of-function attenuates exercise-induced browning of white adipose tissue in mice

Fibronectin type III domain containing 5 (Fndc5) is a transmembrane protein highly expressed in the skeletal muscle. It was reported that exercise promotes the shedding of the extracellular domain of Fndc5, generating a circulating peptide (irisin) that cross-talks to adipose tissues to convert lipid-storing white adipocytes to energy-catabolizing beige adipocytes. However, the requirement of Fndc5 in mediating the beneficial effect of exercise remains to be determined. Here, we created a mouse model of Fndc5 mutation through transcription activator-like effector nuclease-mediated DNA targeting. The Fndc5 mutant mice have normal skeletal muscle development, growth, regeneration, as well as glucose and lipid metabolism at resting state, even when fed a high-fat diet. In response to running exercise, however, the Fndc5 mutant mice exhibit reduced glucose tolerance and insulin sensitivity and have lower maximal oxygen consumption compared with the exercised wild-type mice. Mechanistically, Fndc5 mutation attenuates exercise-induced browning of white adipose tissue that is crucial for the metabolic benefits of physical activities. These data provide genetic evidence that Fndc5 is dispensable for muscle development and basal metabolism but essential for exercise-induced browning of white adipose tissues in mice.-Xiong, Y., Wu, Z., Zhang, B., Wang, C., Mao, F., Liu, X., Hu, K., Sun, X., Jin, W., Kuang, S. Fndc5 loss-of-function attenuates exercise-induced browning of white adipose tissue in mice.

Cold-sensing TRPM8 channel participates in circadian control of the brown adipose tissue

Transient receptor potential (TRP) channels are known to regulate energy metabolism, and TRPM8 has become an interesting player in this context. Here we demonstrate the role of the cold sensor TRPM8 in the regulation of clock gene and clock controlled genes in brown adipose tissue (BAT). We investigated TrpM8 temporal profile in the eyes, suprachiasmatic nucleus and BAT; only BAT showed temporal variation of TrpM8 transcripts. Eyes from mice lacking TRPM8 lost the temporal profile of Per1 in LD cycle. This alteration in the ocular circadian physiology may explain the delay in the onset of locomotor activity in response to light pulse, as compared to wild type animals (WT). Brown adipocytes from TrpM8 KO mice exhibited a larger multilocularity in comparison to WT or TrpV1 KO mice. In addition, Ucp1 and UCP1 expression was significantly reduced in TrpM8 KO mice in comparison to WT mice. Regarding circadian components, the expression of Per1, Per2, Bmal1, Pparα, and Pparβ oscillated in WT mice kept in LD, whereas in the absence of TRPM8 the expression of clock genes was reduced in amplitude and lack temporal oscillation. Thus, our results reveal new roles for TRPM8 channel: it participates in the regulation of clock and clock-controlled genes in the eyes and BAT, and in BAT thermogenesis. Since disruption of the clock machinery has been associated with many metabolic disorders, the pharmacological modulation of TRPM8 channel may become a promising therapeutic target to counterbalance weight gain, through increased thermogenesis, energy expenditure, and clock gene activation.

Haplotype-based interaction of the PPARGC1A and UCP1 genes is associated with impaired fasting glucose or type 2 diabetes mellitus

The aim of this study is to evaluate the effect of single-nucleotide polymorphisms (SNPs) of the PPARGC1A and UCP1 genes on impaired fasting glucose (IFG) or type 2 diabetes mellitus (T2DM) and the haplotype-based interaction between these genes.A cross-sectional study was conducted by cluster sampling in Henan province, China. Based on the level of fasting plasma glucose (FPG) and the history of T2DM, the participants were divided into 2 groups; 83 individuals were in the IFG+DM group (those with IFG or T2DM) and 445 individuals were in the NFPG group (those with normal FPG). Kernel canonical correlation analysis (KCCA), a haplotype-based gene-gene interaction method, which can increase the biological interpretability and extract nonlinear characteristics of SNPs, was used to analyze the correlation and interaction between PPARGC1A and UCP1 genes.The age, BMI, total cholesterol and triglycerides were statistically different between 2 groups (P ≤ .001). Haplotype analysis showed no significant difference in frequency distribution between the 2 groups when the PPARGC1A or UCP1 gene was tested (P > .05). KCCA analysis showed that the maximum kernel canonical correlation coefficient of the PPARGC1A and UCP1 genes was 0.9977 and 0.9995 in the IFG+DM and NPFG groups, respectively. A haplotype-based gene-gene interaction was observed significantly (U = -6.28, P < .001), indicating the possibility of an interaction between haplotype AAG of the PPARGC1A gene and haplotypes CTCG (odds ratio [OR] = 1.745, 95% confidence interval [95% CI] 1.069-2.847) and CTCA (OR = 0.239, 95% CI 0.060-0.958) of the UCP1 gene.Haplotype-based interaction between the PPARGC1A and UCP1 genes is associated with IFG or T2DM among residents in Henan, China.

Flow Cytometric Isolation and Differentiation of Adipogenic Progenitor Cells into Brown and Brite/Beige Adipocytes

Aside from mature adipocytes, adipose tissue harbors several distinct cell populations including immune cells, endothelial cells, and adipogenic progenitor cells (AdPCs). AdPCs represent the reservoir of regenerative cells that replenishes adipocytes during normal cellular turnover and during times of increased demand for triglyceride-storage capacity. The worldwide increase in pathologies associated with the metabolic syndrome, such as obesity and type-2 diabetes, has heightened public and scientific interest in adipose tissues and the cell biological processes of adipose tissue formation and function. Two distinct types of fat cells are known: White and brown adipocytes. Especially brown adipose tissue (BAT) has received considerable attention due to its unique capacity for thermogenic energy expenditure and potential role in the treatment of adiposity. Accordingly, the cold-induced conversion of white into brown-like adipocytes has become a feasible approach in humans and a study-subject in rodents to better understand the underlying molecular processes. Fluorescence-activated cell sorting (FACS) provides a method to isolate AdPCs and other cell populations from adipose tissue by using antibodies detecting unique surface markers. We here describe an approach to isolate cells committed to the adipogenic lineage and summarize established protocols to differentiate FACS-purified primary AdPCs into UCP1-expressing brown adipocytes under in vitro conditions.

Chronic l-menthol-induced browning of white adipose tissue hypothesis: A putative therapeutic regime for combating obesity and improving metabolic health

INTRODUCTION

Obesity constitutes a serious global health concern reaching pandemic prevalence rates. The existence of functional brown adipose tissue (BAT) in adult humans has provoked intense research interest in the role of this metabolically active tissue in whole-body energy balance and body weight regulation. A number of environmental, physiological, pathological, and pharmacological stimuli have been proposed to induce BAT-mediated thermogenesis and functional thermogenic BAT-like activity in white adipose tissue (WAT), opening new avenues for therapeutic strategies based on enhancing the number of beige adipocytes in WAT.

HYPOTHESIS

Recent evidence support a role of l-menthol cooling, mediated by TRPM8 receptor, on UCP1-dependent thermogenesis and BAT-like activity in classical WAT depots along with the recruitment of BAT at specific anatomical sites. l-Menthol-induced BAT thermogenesis has been suggested to occur by a β-adrenergic-independent mechanism, avoiding potential side-effects due to extensive β-adrenergic stimulation mediated by available beta receptor agonists. l-Menthol has been also linked to the activation of the cold-gated ion channel TRPA1. However, its role in l-menthol-induced UCP1-dependent thermogenic activity in BAT and WAT remains undetermined. White adipose tissue plasticity has important clinical implications for obesity prevention and/or treatment because higher levels of UCP1-dependent thermogenesis can lead to enhanced energy expenditure at a considerable extent. We hypothesize that chronic dietary l-menthol treatment could induce TRPM8- and TRPA1-dependent WAT adaptations, resembling BAT-like activity, and overall improve whole-body metabolic health in obese and overweight individuals.

CONCLUSIONS

The putative impact of chronic l-menthol dietary treatment on the stimulation of BAT-like activity in classical WAT depots in humans remains unknown. A detailed experimental design has been proposed to investigate the hypothesized l-menthol-induced browning of WAT. If our hypothesis was to be confirmed, TRPM8/TRPA1-induced metabolic adaptations of WAT to BAT-like activity could provide a promising novel therapeutic approach for increasing energy expenditure, regulating body weight, and preventing obesity and its related co-morbidities in humans.

Emerging Complexities in Adipocyte Origins and Identity

The global incidence of obesity and its comorbidities continues to rise along with a demand for novel therapeutic interventions. Brown adipose tissue (BAT) is attracting attention as a therapeutic target because of its presence in adult humans and high capacity to dissipate energy as heat, and thus burn excess calories, when stimulated. Another potential avenue for therapeutic intervention is to induce, within white adipose tissue (WAT), the formation of brown-like adipocytes called brite (brown-like-in-white) or beige adipocytes. However, understanding how to harness the potential of these thermogenic cells requires a deep understanding of their developmental origins and regulation. Recent cell-labeling and lineage-tracing experiments are beginning to shed light on this emerging area of adipocyte biology. We review here adipocyte development, giving particular attention to thermogenic adipocytes.

Synergism between cAMP and PPARγ Signalling in the Initiation of UCP1 Gene Expression in HIB1B Brown Adipocytes

Expression of the brown adipocyte-specific gene, uncoupling protein 1 (UCP1), is increased by both PPARγ stimulation and cAMP activation through their ability to stimulate the expression of the PPAR coactivator PGC1α. In HIB1B brown preadipocytes, combination of the PPARγ agonist, rosiglitazone, and the cAMP stimulator forskolin synergistically increased UCP1 mRNA expression, but PGC1α expression was only increased additively by the two drugs. The PPARγ antagonist, GW9662, and the PKA inhibitor, H89, both inhibited UCP1 expression stimulated by rosiglitazone and forskolin but PGC1α expression was not altered to the same extent. Reporter studies demonstrated that combined rosiglitazone and forskolin synergistically activated transcription from a full length 3.1 kbp UCP1 luciferase promoter construct, but the response was only additive and much reduced when a minimal 260 bp proximal UCP1 promoter was examined. Rosiglitazone and forskolin in combination were able to synergistically stimulate promoters comprising of tandem repeats of either PPREs or CREs. We conclude that rosiglitazone and forskolin act together to synergistically activate the UCP1 promoter directly rather than by increasing PGC1α expression and by a mechanism involving cross-talk between the signalling systems regulating the CRE and PPRE on the promoters.

Triiodothyronine induces UCP-1 expression and mitochondrial biogenesis in human adipocytes

Uncoupling protein (UCP)-1 expressed in brown adipose tissue plays an important role in thermogenesis. Recent data suggest that brown-like adipocytes in white adipose tissue (WAT) and skeletal muscle play a crucial role in the regulation of body weight. Understanding of the mechanism underlying the increase in UCP-1 expression level in these organs should, therefore, provide an approach to managing obesity. The thyroid hormone (TH) has profound effects on mitochondrial biogenesis and promotes the mRNA expression of UCP in skeletal muscle and brown adipose tissue. However, the action of TH on the induction of brown-like adipocytes in WAT has not been elucidated. Thus we investigate whether TH could regulate UCP-1 expression in WAT using multipotent cells isolated from human adipose tissue. In this study, triiodothyronine (T3) treatment induced UCP-1 expression and mitochondrial biogenesis, accompanied by the induction of the CCAAT/enhancer binding protein, peroxisome proliferator-activated receptor-γ coactivator-1α, and nuclear respiratory factor-1 in differentiated human multipotent adipose-derived stem cells. The effects of T3 on UCP-1 induction were dependent on TH receptor-β. Moreover, T3 treatment increased oxygen consumption rate. These findings indicate that T3 is an active modulator, which induces energy utilization in white adipocytes through the regulation of UCP-1 expression and mitochondrial biogenesis. Our findings provide evidence that T3 serves as a bipotential mediator of mitochondrial biogenesis.

Functional evolution of leptin of Ochotona curzoniae in adaptive thermogenesis driven by cold environmental stress

Background

Environmental stress can accelerate the directional selection and evolutionary rate of specific stress-response proteins to bring about new or altered functions, enhancing an organism's fitness to challenging environments. Plateau pika (Ochotona curzoniae), an endemic and keystone species on Qinghai-Tibetan Plateau, is a high hypoxia and low temperature tolerant mammal with high resting metabolic rate and non-shivering thermogenesis to cope in this harsh plateau environment. Leptin is a key hormone related to how these animals regulate energy homeostasis. Previous molecular evolutionary analysis helped to generate the hypothesis that adaptive evolution of plateau pika leptin may be driven by cold stress.

Methodology/Principal Findings

To test the hypothesis, recombinant pika leptin was first purified. The thermogenic characteristics of C57BL/6J mice injected with pika leptin under warm (23±1°C) and cold (5±1°C) acclimation is investigated. Expression levels of genes regulating adaptive thermogenesis in brown adipose tissue and the hypothalamus are compared between pika leptin and human leptin treatment, suggesting that pika leptin has adaptively and functionally evolved. Our results show that pika leptin regulates energy homeostasis via reduced food intake and increased energy expenditure under both warm and cold conditions. Compared with human leptin, pika leptin demonstrates a superior induced capacity for adaptive thermogenesis, which is reflected in a more enhanced β-oxidation, mitochondrial biogenesis and heat production. Moreover, leptin treatment combined with cold stimulation has a significant synergistic effect on adaptive thermogenesis, more so than is observed with a single cold exposure or single leptin treatment.

Conclusions/Significance

These findings support the hypothesis that cold stress has driven the functional evolution of plateau pika leptin as an ecological adaptation to the Qinghai-Tibetan Plateau.

A reservoir of brown adipocyte progenitors in human skeletal muscle

Brown adipose tissue uncoupling protein-1 (UCP1) plays a major role in the control of energy balance in rodents. It has long been thought, however, that there is no physiologically relevant UCP1 expression in adult humans. In this study we show, using an original approach consisting of sorting cells from various tissues and differentiating them in an adipogenic medium, that a stationary population of skeletal muscle cells expressing the CD34 surface protein can differentiate in vitro into genuine brown adipocytes with a high level of UCP1 expression and uncoupled respiration. These cells can be expanded in culture, and their UCP1 mRNA expression is strongly increased by cell-permeating cAMP derivatives and a peroxisome-proliferator-activated receptor-gamma (PPARgamma) agonist. Furthermore, UCP1 mRNA was detected in the skeletal muscle of adult humans, and its expression was increased in vivo by PPARgamma agonist treatment. All the studies concerning UCP1 expression in adult humans have until now been focused on the white adipose tissue. Here we show for the first time the existence in human skeletal muscle and the prospective isolation of progenitor cells with a high potential for UCP1 expression. The discovery of this reservoir generates a new hope of treating obesity by acting on energy dissipation.

Effects of leptin on energy metabolism in beta-less mice

OBJECTIVE

To investigate the impact of beta-adrenoceptor deficiency on the metabolic effects of leptin.

MEASUREMENTS

Leptin was infused subcutaneously through an osmotic minipump in wild-type (WT) and beta(1)/beta(2)/beta(3)-adrenoceptor knockout (beta-less) mice and its effects on food intake, energy expenditure, carbohydrate and lipid utilization as well as on the levels of expression of the brown adipose tissue (BAT), thermogenic marker uncoupling protein-1 (UCP1) and type II deiodinase (D2) mRNAs were compared.

RESULTS

Leptin treatment decreased food intake by 23% in both the WT and the beta-less mice. In pair-fed animals being used as controls, leptin treatment was found to increase energy expenditure in WT, but not in beta-less mice. No difference was observed in carbohydrate or fat utilization between leptin-treated WT and beta-less mice. Leptin increased UCP1 and D2 mRNA levels in WT mouse BAT 1.7- and 3-fold, respectively, but had no effect on the expression of these genes in beta-less mouse BAT.

CONCLUSION

The stimulatory effects of leptin on oxygen consumption, BAT UCP1 and D2 expression require functional beta-adrenoceptors, but its inhibitory effect on food intake and its stimulatory effect on fat utilization is independent of the beta-adrenoceptor signalling.

Metabolic remodeling in adipocytes promotes ciliary neurotrophic factor-mediated fat loss in obesity

Obesity is characterized by an expanded adipose tissue mass, and reversing obesity reduces the risk of insulin resistance and cardiovascular disease. Ciliary neurotrophic factor (CNTF) reverses obesity by promoting the preferential loss of white adipose tissue. We evaluated the cellular and molecular mechanisms by which CNTF regulates adiposity. Obese mice fed a high-fat diet were treated with saline or recombinant CNTF for 10 d, and adipose tissue was removed for analysis. Another group fed a high-fat diet was pair fed to CNTF mice. In separate experiments, 3T3-L1 adipocytes were treated with CNTF to examine metabolic responses and signaling. CNTF reduced adipose mass that resulted from reductions in adipocyte area and triglyceride content. CNTF treatment did not affect lipolysis but resulted in decreases in fat esterification and lipogenesis and enhanced fatty acid oxidation. The enhanced fat oxidation was associated with the expression of peroxisome proliferator-activated receptor coactivator-1alpha (PGC1alpha) and nuclear respiratory factor 1 and increases in oxidative phosphorylation subunits and mitochondrial biogenesis as determined by electron microscopy. Studies in cultured adipocytes revealed that CNTF activates p38 MAPK and AMP-activated protein kinase. Inhibiting p38 activation prevented the CNTF-induced increase in PGC1alpha but not AMP-activated protein kinase activation. Diminished food intake with pair feeding induced similar decreases in fat mass, but this was related to increased expression of uncoupling protein 1. We conclude that CNTF reprograms adipose tissue to promote mitochondrial biogenesis, enhancing oxidative capacity and reducing lipogenic capacity, thereby resulting in triglyceride loss.

Prolactin receptor signaling is essential for perinatal brown adipocyte function: a role for insulin-like growth factor-2

BACKGROUND

The lactogenic hormones prolactin (PRL) and placental lactogens (PL) play central roles in reproduction and mammary development. Their actions are mediated via binding to PRL receptor (PRLR), highly expressed in brown adipose tissue (BAT), yet their impact on adipocyte function and metabolism remains unclear.

METHODOLOGY/PRINCIPAL FINDINGS

PRLR knockout (KO) newborn mice were phenotypically characterized in terms of thermoregulation and their BAT differentiation assayed for gene expression studies. Derived brown preadipocyte cell lines were established to evaluate the molecular mechanisms involved in PRL signaling on BAT function. Here, we report that newborn mice lacking PRLR have hypotrophic BAT depots that express low levels of adipocyte nuclear receptor PPARgamma2, its coactivator PGC-1alpha, uncoupling protein 1 (UCP1) and the beta3 adrenoceptor, reducing mouse viability during cold challenge. Immortalized PRLR KO preadipocytes fail to undergo differentiation into mature adipocytes, a defect reversed by reintroduction of PRLR. That the effects of the lactogens in BAT are at least partly mediated by Insulin-like Growth Factor-2 (IGF-2) is supported by: i) a striking reduction in BAT IGF-2 expression in PRLR KO mice and in PRLR-deficient preadipocytes; ii) induction of cellular IGF-2 expression by PRL through JAK2/STAT5 pathway activation; and iii) reversal of defective differentiation in PRLR KO cells by exogenous IGF-2.

CONCLUSIONS

Our findings demonstrate that the lactogens act in concert with IGF-2 to control brown adipocyte differentiation and growth. Given the prominent role of brown adipose tissue during the perinatal period, our results identified prolactin receptor signaling as a major player and a potential therapeutic target in protecting newborn mammals against hypothermia.