Structural Elements Directing G Proteins and ß-Arrestin Interactions with the Human Melatonin Type 2 Receptor Revealed by Natural Variants.

G protein-coupled receptors (GPCRs) can engage distinct subsets of signaling pathways, but the structural determinants of this functional selectivity remain elusive. The naturally occurring genetic variants of GPCRs, selectively affecting different pathways, offer an opportunity to explore this phenomenon. We previously identified 40 coding variants of the MTNR1B gene encoding the melatonin MT2 receptor (MT2). These mutations differently impact the ß-arrestin 2 recruitment, ERK activation, cAMP production, and Gαi1 and Gαz activation. In this study, we combined functional clustering and structural modeling to delineate the molecular features controlling the MT2 functional selectivity. Using non-negative matrix factorization, we analyzed the signaling signatures of the 40 MT2 variants yielding eight clusters defined by unique signaling features and localized in distinct domains of MT2. Using computational homology modeling, we describe how specific mutations can selectively affect the subsets of signaling pathways and offer a proof of principle that natural variants can be used to explore and understand the GPCR functional selectivity.

Circadian, Sleep and Caloric Intake Phenotyping in Type 2 Diabetes Patients With Rare Melatonin Receptor 2 Mutations and Controls: A Pilot Study.

BACKGROUND: Melatonin modulates circadian rhythms in physiology and sleep initiation. Genetic variants of the MTNR1B locus, encoding the melatonin MT2 receptor, have been associated with increased type 2 diabetes (T2D) risk. Carriers of the common intronic MTNR1B rs10830963 T2D risk variant have modified sleep and circadian traits such as changes of the melatonin profile. However, it is currently unknown whether rare variants in the MT2 coding region are also associated with altered sleep and circadian phenotypes, including meal timing. MATERIALS AND METHODS: In this pilot study, 28 individuals [50% male; 46-82 years old; 50% with rare MT2 mutations (T2D MT2)] wore actigraphy devices and filled out daily food logs for 4 weeks. We computed circadian, sleep, and caloric intake phenotypes, including sleep duration, timing, and regularity [assessed by the Sleep Regularity Index (SRI)]; composite phase deviations (CPD) as well a sleep timing-based proxy for circadian misalignment; and caloric intake patterns throughout the day. Using regression analyses, we estimated age- and sex-adjusted mean differences (MD) and 95% confidence intervals (95%CI) between the two patient groups. Secondary analyses also compare T2D MT2 to 15 healthy controls. RESULTS: Patients with rare MT2 mutations had a later sleep onset (MD = 1.23, 95%CI = 0.42;2.04), and midsleep time (MD = 0.91, 95%CI = 0.12;1.70), slept more irregularly (MD in SRI = -8.98, 95%CI = -16.36;-1.60), had higher levels of behavioral circadian misalignment (MD in CPD = 1.21, 95%CI = 0.51;1.92), were more variable in regard to duration between first caloric intake and average sleep offset (MD = 1.08, 95%CI = 0.07;2.08), and had more caloric episodes in a 24 h day (MD = 1.08, 95%CI = 0.26;1.90), in comparison to T2D controls. Secondary analyses showed similar patterns between T2D MT2 and non-diabetic controls. CONCLUSION: This pilot study suggests that compared to diabetic controls, T2D MT2 patients display a number of adverse sleep, circadian, and caloric intake phenotypes, including more irregular behavioral timing. A prospective study is needed to determine the role of these behavioral phenotypes in T2D onset and severity, especially in view of rare MT2 mutations.

Melatonin MT1 and MT2 receptor ERK signaling is differentially dependent on Gi/o and Gq/11 proteins.

G protein-coupled receptors (GPCRs) transmit extracellular signals into cells by activating G protein- and ß-arrestin-dependent pathways. Extracellular signal-regulated kinases (ERKs) play a central role in integrating these different linear inputs coming from a variety of GPCRs to regulate cellular functions. Here, we investigated human melatonin MT1 and MT2 receptors signaling through the ERK1/2 cascade by employing different biochemical techniques together with pharmacological inhibitors and siRNA molecules. We show that ERK1/2 activation by both receptors is exclusively G protein-dependent, without any participation of ß-arrestin1/2 in HEK293 cells. ERK1/2 activation by MT1 is only mediated though Gi/o proteins, while MT2 is dependent on the cooperative activation of Gi/o and Gq/11 proteins. In the absence of Gq/11 proteins, however, MT2 -induced ERK1/2 activation switches to a ß-arrestin1/2-dependent mode. The signaling cascade downstream of G proteins is the same for both receptors and involves activation of the PI3K/PKCζ/c-Raf/MEK/ERK cascade. The differential G protein dependency of MT1 - and MT2 -mediated ERK activation was confirmed at the level of EGR1 and FOS gene expression, two ERK1/2 target genes. Gi/o /Gq/11 cooperativity was also observed in Neuroscreen-1 cells expressing endogenous MT2 , whereas in the mouse retina, where MT2 is engaged into MT1 /MT2 heterodimers, ERK1/2 signaling is exclusively Gi/o -dependent. Collectively, our data reveal differential signaling modes of MT1 and MT2 in terms of ERK1/2 activation, with an unexpected Gi/o /Gq/11 cooperativity exclusively for MT2 . The plasticity of ERK activation by MT2 is highlighted by the switch to a ß-arrestin1/2-dependent mode in the absence of Gq/11 proteins and by the switch to a Gi/o mode when engaged into MT1 /MT2 heterodimers, revealing a new mechanism underlying tissue-specific responses to melatonin.

O-linked melatonin dimers as bivalent ligands targeting dimeric melatonin receptors.

A series of dimeric melatonin analogues 3a-e obtained by connecting two melatonin molecules through the methoxy oxygen atoms with spacers spanning 16-24 atoms and the agomelatine dimer 7 were synthesized and characterized in 2-[125-I]-iodomelatonin binding assays, bioluminescence resonance energy transfer (BRET) experiments, and in functional cAMP and ß-arrestin recruitment assays at MT1 and MT2 receptors. The binding affinity of 3a-e generally increased with increasing linker length. Bivalent ligands 3a-e increased BRET signals of MT1 dimers up to 3-fold compared to the monomeric control ligand indicating the simultaneous binding of the two pharmacophores to dimeric receptors. Bivalent ligands 3c and 7 exhibited important changes in functional properties on the Gi/cAMP pathway but not on the ß-arrestin pathway compared to their monomeric counterparts. Interestingly, 3c (20 atoms spacer) shows inverse agonistic properties at MT2 on the Gi/cAMP pathway. In conclusion, these findings indicate that O-linked melatonin dimers are promising tools to develop signaling pathway-based bivalent melatonin receptor ligands.

Melatonin in type 2 diabetes mellitus and obesity.

Despite considerable advances in the past few years, obesity and type 2 diabetes mellitus (T2DM) remain two major challenges for public health systems globally. In the past 9 years, genome-wide association studies (GWAS) have established a major role for genetic variation within the MTNR1B locus in regulating fasting plasma levels of glucose and in affecting the risk of T2DM. This discovery generated a major interest in the melatonergic system, in particular the melatonin MT2 receptor (which is encoded by MTNR1B). In this Review, we discuss the effect of melatonin and its receptors on glucose homeostasis, obesity and T2DM. Preclinical and clinical post-GWAS evidence of frequent and rare variants of the MTNR1B locus confirmed its importance in regulating glucose homeostasis and T2DM risk with minor effects on obesity. However, these studies did not solve the question of whether melatonin is beneficial or detrimental, an issue that will be discussed in the context of the peculiarities of the melatonergic system. Melatonin receptors might have therapeutic potential as they belong to the highly druggable G protein-coupled receptor superfamily. Clarifying the precise role of melatonin and its receptors on glucose homeostasis is urgent, as melatonin is widely used for other indications, either as a prescribed medication or as a supplement without medical prescription, in many countries in Europe and in the USA.

Type 2 diabetes-associated variants of the MT2 melatonin receptor affect distinct modes of signaling.

Melatonin is produced during the night and regulates sleep and circadian rhythms. Loss-of-function variants in MTNR1B, which encodes the melatonin receptor MT2, a G protein-coupled receptor (GPCR), are associated with an increased risk of type 2 diabetes (T2D). To identify specific T2D-associated signaling pathway(s), we profiled the signaling output of 40 MT2 variants by monitoring spontaneous (ligand-independent) and melatonin-induced activation of multiple signaling effectors. Genetic association analysis showed that defects in the melatonin-induced activation of Gαi1 and Gαz proteins and in spontaneous ß-arrestin2 recruitment to MT2 were the most statistically significantly associated with an increased T2D risk. Computational variant impact prediction by in silico evolutionary lineage analysis strongly correlated with the measured phenotypic effect of each variant, providing a predictive tool for future studies on GPCR variants. Together, this large-scale functional study provides an operational framework for the postgenomic analysis of the multiple GPCR variants present in the human population. The association of T2D risk with signaling pathway-specific defects opens avenues for pathway-specific personalized therapeutic intervention and reveals the potential relevance of MT2 function during the day, when melatonin is undetectable, but spontaneous activity of the receptor occurs.

Melatonin receptors limit dopamine reuptake by regulating dopamine transporter cell-surface exposure.

Melatonin, a neuro-hormone released by the pineal gland, has multiple effects in the central nervous system including the regulation of dopamine (DA) levels, but how melatonin accomplishes this task is not clear. Here, we show that melatonin MT1 and MT2 receptors co-immunoprecipitate with the DA transporter (DAT) in mouse striatal synaptosomes. Increased DA re-uptake and decreased amphetamine-induced locomotor activity were observed in the striatum of mice with targeted deletion of MT1 or MT2 receptors. In vitro experiments confirmed the interactions and recapitulated the inhibitory effect of melatonin receptors on DA re-uptake. Melatonin receptors retained DAT in the endoplasmic reticulum in its immature non-glycosylated form. In conclusion, we reveal one of the first molecular complexes between G protein-coupled receptors (MT1 and MT2) and transporters (DAT) in which melatonin receptors regulate the availability of DAT at the plasma membrane, thus limiting the striatal DA re-uptake capacity in mice.

The orphan GPR50 receptor promotes constitutive TGFß receptor signaling and protects against cancer development.

Transforming growth factor-ß (TGFß) signaling is initiated by the type I, II TGFß receptor (TßRI/TßRII) complex. Here we report the formation of an alternative complex between TßRI and the orphan GPR50, belonging to the G protein-coupled receptor super-family. The interaction of GPR50 with TßRI induces spontaneous TßRI-dependent Smad and non-Smad signaling by stabilizing the active TßRI conformation and competing for the binding of the negative regulator FKBP12 to TßRI. GPR50 overexpression in MDA-MB-231 cells mimics the anti-proliferative effect of TßRI and decreases tumor growth in a xenograft mouse model. Inversely, targeted deletion of GPR50 in the MMTV/Neu spontaneous mammary cancer model shows decreased survival after tumor onset and increased tumor growth. Low GPR50 expression is associated with poor survival prognosis in human breast cancer irrespective of the breast cancer subtype. This describes a previously unappreciated spontaneous TGFß-independent activation mode of TßRI and identifies GPR50 as a TßRI co-receptor with potential impact on cancer development.

Nocturnal activation of melatonin receptor type 1 signaling modulates diurnal insulin sensitivity via regulation of PI3K activity.

Recent genetic studies have highlighted the potential involvement of melatonin receptor 1 (MT1 ) and melatonin receptor 2 (MT2 ) in the pathogenesis of type 2 diabetes. Here, we report that mice lacking MT1 (MT1 KO) tend to accumulate more fat mass than WT mice and exhibit marked systemic insulin resistance. Additional experiments revealed that the main insulin signaling pathway affected by the loss of MT1 was the activation of phosphatidylinositol-3-kinase (PI3K). Transcripts of both catalytic and regulatory subunits of PI3K were strongly downregulated within MT1 KO mice. Moreover, the suppression of nocturnal melatonin levels within WT mice, by exposing mice to constant light, resulted in impaired PI3K activity and insulin resistance during the day, similar to what was observed in MT1 KO mice. Inversely, administration of melatonin to WT mice exposed to constant light was sufficient and necessary to restore insulin-mediated PI3K activity and insulin sensitivity. Hence, our data demonstrate that the activation of MT1 signaling at night modulates insulin sensitivity during the day via the regulation of the PI3K transcription and activity. Lastly, we provide evidence that decreased expression of MTNR1A (MT1 ) in the liver of diabetic individuals is associated with poorly controlled diabetes.

Orphan GPR61, GPR62 and GPR135 receptors and the melatonin MT2 receptor reciprocally modulate their signaling functions.

Understanding the function of orphan G protein-coupled receptors (GPCRs), whose cognate ligand is unknown, is of major importance as GPCRs are privileged drug targets for many diseases. Recent phylogenetic studies classified three orphan receptors, GPR61, GPR62 and GPR135 among the melatonin receptor subfamily, but their capacity to bind melatonin and their biochemical functions are not well characterized yet. We show here that GPR61, GPR62 and GPR135 do not bind [3H]-melatonin nor 2-[125I]iodomelatonin and do not respond to melatonin in several signaling assays. In contrast, the three receptors show extensive spontaneous ligand-independent activities on the cAMP, inositol phosphate and ß-arrestin pathways with distinct pathway-specific profiles. Spontaneous ß-arrestin recruitment internalizes all three GPRs in the endosomal compartment. Co-expression of the melatonin binding MT2 receptor with GPR61, GPR62 or GPR135 has several consequences such as (i) the formation of receptor heteromers, (ii) the inhibition of melatonin-induced ß-arrestin2 recruitment to MT2 and (iii) the decrease of elevated cAMP levels upon melatonin stimulation in cells expressing spontaneously active GPR61 and GPR62. Collectively, these data show that GPR61, GPR62 and GPR135 are unable to bind melatonin, but show a reciprocal regulatory interaction with MT2 receptors.

Design and validation of the first cell-impermeant melatonin receptor agonist.

BACKGROUND AND PURPOSE: The paradigm that GPCRs are able to prolong or initiate cellular signalling through intracellular receptors recently emerged. Melatonin binds to G protein-coupled MT1 and MT2 receptors. In contrast to most other hormones targeting GPCRs, melatonin and its synthetic analogues are amphiphilic molecules easily penetrating into cells, but the existence of intracellular receptors is still unclear mainly due to a lack of appropriate tools. EXPERIMENTAL APPROACH: We therefore designed and synthesized a series of hydrophilic melatonin receptor ligands coupled to the Cy3 cyanin fluorophore to reliably monitor its inability to penetrate cells. Two compounds, one lipophilic and one hydrophilic, were then functionally characterized in terms of their affinity for human and murine melatonin receptors expressed in HEK293 cells and their signalling efficacy. KEY RESULTS: Among the different ligands, ICOA-13 showed the desired properties as it was cell-impermeant and bound to human and mouse MT1 and MT2 receptors. ICOA-13 showed differential activities on melatonin receptors ranging from partial to full agonistic properties for the Gi /cAMP and ERK pathway and ß-arrestin 2 recruitment. Notably, ICOA-13 enabled us to discriminate between Gi /cAMP signalling of the MT1 receptor initiated at the cell surface and neuronal mitochondria. CONCLUSIONS AND IMPLICATIONS: We report here the first cell-impermeant melatonin receptor agonist, ICOA-13, which allows us to discriminate between signalling events initiated at the cell surface and intracellular compartments. Detection of mitochondrial MT1 receptors may have an important impact on the development of novel melatonin receptor ligands relevant for neurodegenerative diseases, such as Huntington disease.

Extracellular acidification stimulates GPR68 mediated IL-8 production in human pancreatic ß cells.

Acute or chronic metabolic complications such as diabetic ketoacidosis are often associated with extracellular acidification and pancreatic ß-cell dysfunction. However, the mechanisms by which human ß-cells sense and respond to acidic pH remain elusive. In this study, using the recently developed human ß-cell line EndoC-ßH2, we demonstrate that ß-cells respond to extracellular acidification through GPR68, which is the predominant proton sensing receptor of human ß-cells. Using gain- and loss-of-function studies, we provide evidence that the ß-cell enriched transcription factor RFX6 is a major regulator of GPR68. Further, we show that acidic pH stimulates the production and secretion of the chemokine IL-8 by ß-cells through NF-кB activation. Blocking of GPR68 or NF-кB activity severely attenuated acidification induced IL-8 production. Thus, we provide mechanistic insights into GPR68 mediated ß-cell response to acidic microenvironment, which could be a new target to protect ß-cell against acidosis induced inflammation.

[Involvement of melatonin MT2 receptor mutants in type 2 diabetes development]. / Implication des mutations du récepteur de la mélatonine MT2 dans la survenue du diabète de type 2.

Genetic and environmental factors participate in the development of type 2 diabetes (T2D). Genome-wide association studies have revealed new genetic variants associated with T2D, including the rs10830963 variant located in the intron of the MTNR1B gene. This gene encodes the melatonin MT2 receptor, a member of the family of G protein-coupled receptors involved in the regulation of circadian and seasonal rhythms. This surprising result stimulated new investigations in the field of T2D to better understand the role of MT2 receptors and circadian rhythms in this emerging disease. The current article intends to cover this issue starting from the discovery of the first MTNR1B gene variants until the establishment of a functional link between MTNR1B variants and the risk of developing T2D and finishes by proposing some hypotheses that might potentially explain the importance of impaired MT2 function in T2D development.

Cold-induced changes in gene expression in brown adipose tissue, white adipose tissue and liver.

Cold exposure imposes a metabolic challenge to mammals that is met by a coordinated response in different tissues to prevent hypothermia. This study reports a transcriptomic analysis in brown adipose tissue (BAT), white adipose (WAT) and liver of mice in response to 24 h cold exposure at 8°C. Expression of 1895 genes were significantly (P<0.05) up- or down-regulated more than two fold by cold exposure in all tissues but only 5 of these genes were shared by all three tissues, and only 19, 14 and 134 genes were common between WAT and BAT, WAT and liver, and BAT and liver, respectively. We confirmed using qRT-PCR, the increased expression of a number of characteristic BAT genes during cold exposure. In both BAT and the liver, the most common direction of change in gene expression was suppression (496 genes in BAT and 590 genes in liver). Gene ontology analysis revealed for the first time significant (P<0.05) down regulation in response to cold, of genes involved in oxidoreductase activity, lipid metabolic processes and protease inhibitor activity, in both BAT and liver, but not WAT. The results reveal an unexpected importance of down regulation of cytochrome P450 gene expression and apolipoprotein, in both BAT and liver, but not WAT, in response to cold exposure. Pathway analysis suggests a model in which down regulation of the nuclear transcription factors HNF4α and PPARα in both BAT and liver may orchestrate the down regulation of genes involved in lipoprotein and steroid metabolism as well as Phase I enzymes belonging to the cytochrome P450 group in response to cold stress in mice. We propose that the response to cold stress involves decreased gene expression in a range of cellular processes in order to maximise pathways involved in heat production.

Minireview: Toward the establishment of a link between melatonin and glucose homeostasis: association of melatonin MT2 receptor variants with type 2 diabetes.

The existence of interindividual variations in G protein-coupled receptor sequences has been recognized early on. Recent advances in large-scale exon sequencing techniques are expected to dramatically increase the number of variants identified in G protein-coupled receptors, giving rise to new challenges regarding their functional characterization. The current minireview will illustrate these challenges based on the MTNR1B gene, which encodes the melatonin MT2 receptor, for which exon sequencing revealed 40 rare nonsynonymous variants in the general population and in type 2 diabetes (T2D) cohorts. Functional characterization of these MT2 mutants revealed 14 mutants with loss of Gi protein activation that associate with increased risk of T2D development. This repertoire of disease-associated mutants is a rich source for structure-activity studies and will help to define the still poorly understood role of melatonin in glucose homeostasis and T2D development in humans. Defining the functional defects in carriers of rare MT2 mutations will help to provide personalized therapies to these patients in the future.

Ascertainment and critical assessment of the views of the general public and healthcare professionals on nutrigenomics in Greece.

AIM: The aim of this study was to understand the general public's and healthcare professionals' views on nutrigenomics. PATIENTS & METHODS: We designed a cross-sectional survey of healthcare professionals (n = 87) and the general public (n = 1504) in the three largest cities in Greece (Athens, Thessaloniki and Patras). RESULTS: Our data revealed that only 11.5% of respondents from the general public had been advised to take a genetic test in order to explore the relationship between their genes and their nutritional status. Although 80.5% of healthcare professionals would have been willing to recommend their patients/clients to undergo nutrigenomic analysis to correlate their genetic profile with their diet, only 17.2% of respondents had actually done so. In general, the general public was opposed to direct-access nutrigenomics testing. CONCLUSION: The application of genomic information in the context of nutritional choice requires the continuing education of healthcare professionals and the dissemination of accurate and reliable information to the general public.

Combinatorial transcription factor regulation of the cyclic AMP-response element on the Pgc-1alpha promoter in white 3T3-L1 and brown HIB-1B preadipocytes.

Cold stress in rodents increases the expression of UCP1 and PGC-1alpha in brown and white adipose tissue. We have previously reported that C/EBPbeta specifically binds to the CRE on the proximal Pgc-1alpha promoter and increases forskolin-sensitive Pgc-1alpha and Ucp1 expression in white 3T3-L1 preadipocytes. Here we show that in mice exposed to a cold environment for 24 h, Pgc-1alpha, Ucp1, and C/ebpbeta but not C/ebpalpha or C/ebpdelta expression were increased in BAT. Conversely, expression of the C/EBP dominant negative Chop10 was increased in WAT but not BAT during cold exposure. Reacclimatization of cold-exposed mice to a warm environment for 24 h completely reversed these changes in gene expression. In HIB-1B, brown preadipocytes, forskolin increased expression of Pgc-1alpha, Ucp1, and C/ebpbeta early in differentiation and inhibited Chop10 expression. Employing chromatin immunoprecipitation, we demonstrate that C/EBPbeta, CREB, ATF-2, and CHOP10 are bound to the Pgc-1alpha proximal CRE, but CHOP10 does not bind in HIB-1B cell lysates. Forskolin stimulation and C/EBPbeta overexpression in 3T3-L1 cells increased C/EBPbeta and CREB but displaced ATF-2 and CHOP10 binding to the Pgc-1alpha proximal CRE. Overexpression of ATF-2 and CHOP10 in 3T3-L1 cells decreased Pgc-1alpha transcription. Knockdown of Chop10 in 3T3-L1 cells using siRNA increased Pgc-1alpha transcription, whereas siRNA against C/ebpbeta in HIB-1B cells decreased Pgc-1alpha and Ucp1 expression. We conclude that the increased cAMP stimulation of Pgc-1alpha expression is regulated by the combinatorial effect of transcription factors acting at the CRE on the proximal Pgc-1alpha promoter.

C/EBPbeta reprograms white 3T3-L1 preadipocytes to a Brown adipocyte pattern of gene expression.

cAMP-dependent protein kinase induction of PPARgamma coactivator-1alpha (PGC-1alpha) and uncoupling protein 1 (UCP1) expression is an essential step in the commitment of preadipocytes to the brown adipose tissue (BAT) lineage. We studied the molecular mechanisms responsible for differential expression of PGC-1alpha in HIB1B (BAT) and 3T3-L1 white adipose tissue (WAT) precursor cell lines. In HIB1B cells PGC-1alpha and UCP1 expression is cAMP-inducible, but in 3T3-L1 cells, expression is reduced and is cAMP-insensitive. A proximal 264-bp PGC-1alpha reporter construct was cAMP-inducible only in HIB1B cells and was suppressed by site-directed mutagenesis of the proximal cAMP response element (CRE). In electrophoretic mobility shift assays, the transcription factors CREB and C/EBPbeta, but not C/EBPalpha and C/EBPdelta, bound to the CRE on the PGC-1alpha promoter region in HIB1B and 3T3-L1 cells. Chromatin immunoprecipitation studies demonstrated that C/EBPbeta and CREB bound to the CRE region in HIB1B and 3T3-L1 cell lysates. C/EBPbeta expression was induced by cAMP only in HIB1B cells, and overexpression of C/EBPbeta rescued cAMP-inducible PGC-1alpha and UCP1 expression in 3T3-L1 cells. These data demonstrate that differentiation of preadipocytes toward the BAT rather than the WAT phenotype is controlled in part by the action of C/EBPbeta on the CRE in PGC-1alpha proximal promoter.

Ontogenic loss of brown adipose tissue sensitivity to beta-adrenergic stimulation in the ovine.

In ruminants and other large animals, expression of uncoupling protein-1 (UCP1) in brown adipose tissue (BAT) is confined to the perinatal period when it plays a key role in nonshivering thermogenesis. This study determined whether loss of expression of the BAT phenotype was due to reduced response to a beta-agonist, isoprenaline, and expression of the peroxisome proliferator-activated receptor (PPAR) family [PPARalpha, PPARgamma, PPAR coactivator 1alpha (PGC-1alpha)], which regulates UCP1 gene expression. Perirenal adipose tissue (PAT) was sampled from ovine fetuses, newborn lambs, and lambs on d 1, 5, 7, and 21 of life. UCP1 mRNA and protein in PAT increased from d 123 of fetal life to reach a maximum at birth followed by a rapid decrease over the first 5 d of life. Expression of the coactivator, PGC-1alpha and PPAR alpha, peaked between fetal day 123 and birth, and then declined to undetectable levels in the first days of life. In vivo administration of isoprenaline was able to induce expression of UCP1, PGC-1alpha, and PPARalpha in BAT up to 5 d of age but thereafter was ineffective. In vitro addition of beta-receptor, PPARalpha, and PPARgamma agonists were unable to overcome the suppression of UCP1, PPARalpha, and PPARgamma expression observed in differentiated adipocytes prepared from 30-d-old compared with 1-d-old lambs. These data are consistent with a model in which postnatal loss of UCP1 expression and beta-adrenergic induction of the brown adipocyte phenotype is due to loss of expression of PGC-1alpha and PPARalpha.