Early embryonic and endometrial regulation of tumor necrosis factor and tumor necrosis factor receptor 2 in the cattle uterus E. Correia-Álvarez a , E. Gómez a , D. Martín a , S. Carrocera a , S. Pérez b , N. Peynot c , C. Giraud-Delville c , J.N. Caamaño a , A. Balseiro a , O. Sandra c , V. Duranthon c , M. Muñoz a, * a Centro de Biotecnología Animal-SERIDA, Gijón, Asturias, Spain b Unidad de Coordinación de Trasplantes y Terapia Celular, Hospital Universitario Central de Asturias, Oviedo, Spain c INRA, UMR1198 Biologie du Développement et Reproduction, Jouy-en-Josas, France article info Article history: Received 14 August 2014 Received in revised form 26 November 2014 Accepted 2 December 2014 Keywords: Bovine Blastocyst In vivo Leukocyte Cytokine abstract Tumor necrosis factor (TNF) alpha likely mediates embryomaternal communication in mammals. In bovine, we have previously found that the uterine fluid of heifers that carried early embryos shows downregulation in the TNF and nuclear factor kB system. In this work, we assessed the expression of TNF and its receptor TNFR2 in the bovine endome- trium and embryos during blastocyst development. Moreover, to explore the endometrial immune response to early embryos, we analyzed the number of CD45 leukocytes in the bovine endometrium. Day 8 endometrium and blastocyst recovered from animals after transfer of Day 5 embryos showed TNF and TNFR2 mRNA transcription and protein colocalization. The presence of embryos increased endometrial TNF and TNFR2 protein, whereas endometrial leukocytes decreased. Blastocysts exposed to the uterine tract had undetectable levels of TNF and lower levels of TNFR2 mRNA. These results suggest that the endometrium might lower the TNF concentration in the blastocyst by (1) regulating TNF secretion into the uterine fluid and (2) inducing decreased TNF and TNFR2 mRNA tran- scription in the embryo. Thus, TNF and TNFR2 might participate in early embryomaternal communication. Ó 2015 Elsevier Inc. All rights reserved. 1. Introduction Embryomaternal communication is essential for embryo implantation and successful pregnancy to term [1]. Failure to replicate the maternal environment surrounding the embryo hampers the in vitro reproduction procedures [2], making research in this field a priority for reproductive biology. In natural conditions, communication is governed by growth factors produced and secreted by the embryo and the endo- metrium [3]. One of such factors might be tumor necrosis factor (TNF), a proinflammatory cytokine that mediates cell differentiation, survival, renewal, and tissue homeostasis [4]. Tumor necrosis factor activates several intracellular path- ways through its binding to two distinct receptors, TNFR1 and TNFR2 [5]. Receptor TNFR1 associates with apoptosis and TNFR2 is more versatile leading to apoptotic or proliferation processes depending on the stimulus. Some evidence supports the participation of TNF and TNFR2 in normal reproduction. Thus, TNF and TNFR2 endo- metrial expression vary throughout the estrous cycle in humans and domestic animals [6–9], and both seem to exert a role during pregnancy in humans, mice, and dogs [8,10–12]. In bovine, TNF and TNFR2 mRNA and protein have been detected in the cyclic and pregnant endometrium [7,13]. Expression of * Corresponding author. Tel.: þ34 984502010; fax: þ34 984502012. E-mail address: mmunoz@serida.org (M. Muñoz). Contents lists available at ScienceDirect Theriogenology journal homepage: www.theriojournal.com 0093-691X/$ – see front matter Ó 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.theriogenology.2014.12.007 Theriogenology 83 (2015) 1028–1037