Prolactin Receptor Signaling Is Essential for Perinatal Brown Adipocyte Function: A Role for Insulin-like Growth Factor-2 Say Viengchareun1,2, Nathalie Servel3,4, Bruno Fe` ve1,2, Michael Freemark3,4,5, Marc Lombe` s1,2., Nadine Binart3,4.* 1 Inserm, U693, Le Kremlin-Bic eˆtre, France, 2 Faculte´ de Me´ decine Paris-Sud, Universite´ Paris-Sud, UMR-S693, Le Kremlin-Bic eˆtre, France, 3 Inserm, U845, Paris, France, 4 Facult e´ de Me´ decine Rene´ Descartes, Universite´ Paris-Descartes, Site Necker, UMR-S845, Paris, France, 5 Division of Pediatric Endocrinology and Diabetes, Duke University Medical Center, Durham, North Carolina, United States of America 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 PPARc2, its coactivator PGC-1a, uncoupling protein 1 (UCP1) and the b3 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. Citation: Viengchareun S, Servel N, Fe`ve B, Freemark M, Lombe` s M, et al (2008) Prolactin Receptor Signaling Is Essential for Perinatal Brown Adipocyte Function: A Role for Insulin-like Growth Factor-2. PLoS ONE 3(2): e1535. doi:10.1371/journal.pone.0001535 INTRODUCTION The lactogenic hormones of the placenta (placental lactogens, PL) and pituitary gland (prolactin, PRL) regulate a variety of physiological processes involved in gonadal function and reproduc- tion, mammary development and lactation, adrenal and pancreatic hormone secretion, and intermediary metabolism [1]. In humans and rodents, these actions are mediated via binding of lactogens to the prolactin receptor (PRLR), a class I cytokine receptor linked to activation of the JAK/STAT signaling pathway [2]. In postnatal rodents and ungulates, the PRLR and associated STAT5 activity are detected in most tissues at various stages of development [2,3]; in the fetus, on the other hand, PRLR emerge during mid-late gestation [4–6], when high expression levels are detected in the liver, lung, gastrointestinal tract, olfactory epithelium, renal tubules, pancreatic beta cells, and brown adipose tissue (BAT). The latter is of particular interest because BAT mediates adaptive (nonshivering) thermogenesis [7], the process of heat generation required for thermostabilization and survival during delivery and the transition from intrauterine to extrauterine life. The key effector of adaptive thermogenesis is uncoupling protein 1 (UCP1), whose expression is restricted to BAT mitochondria [8]. UCP1 dissipates the proton gradient at the inner mitochondrial membrane to prevent oxidative phosphory- lation, generating heat rather than ATP. A critical upstream regulator of adaptive thermogenesis is peroxisome proliferator gamma co-activator 1 alpha (PGC-1a), which promotes mito- chondrial biogenesis [9]. Recent studies have elucidated the molecular mechanisms controlling BAT development. The key transcriptional regulator of adipogenesis in brown, as in white, adipose tissue is PPARc [10]. Early in the course of adipocyte differentiation, C/EBPb and d are expressed transiently and contribute to induction of PPARc and C/EBPa, which is required to maintain PPARc expression. C/EBPa also functions synergistically with PPARc to promote the expression of genes found in both BAT and WAT [11] as well as PGC-1a and UCP1, which are preferentially or exclusively expressed in brown adipocytes. The expression of BAT genes is regulated by a number of hormones and growth factors including the thyroid hormones, catecholamines, leptin, insulin, and insulin-like growth factor-1 (IGF-1). However, cold adaptation can be maintained in the absence of thyroid hormones, and deletion of thyroid hormone receptor a and b [12] or of b1, b2 and b3 adrenergic receptor subtypes [13,14] has no effect on BAT PGC-1a mRNA or UCP1 protein levels under non-stressed conditions. Moreover, targeted Academic Editor: Patrick Callaerts, Katholieke Universiteit Leuven, Belgium Received September 20, 2007; Accepted December 25, 2007; Published February 6, 2008 Copyright: 2008 Viengchareun et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by grants from Inserm and Fondation de la Recherche Me´dicale, the National Institute of Child Health and Development (HD24192 to MF) and Pharmacia Corporation (to MF). Competing Interests: The authors have declared that no competing interests exist. * To whom correspondence should be addressed. E-mail: binart@necker.fr . These authors contributed equally to this work. PLoS ONE | www.plosone.org 1 February 2008 | Issue 2 | e1535