Is FAS/Fas Ligand System Involved in Equine Corpus Luteum Functional Regression?1

Abstract

Proapoptotic factor Fas ligand (FASL) and its cell surface receptor FAS are tumor necrosis factor superfamily members that trigger apoptosis in different cell types. However, their influence on luteal steroidogenesis is not clearly understood. The aim of the present work was to determine (i) the presence of the cytokine FASL and its receptor FAS in the mare's corpus luteum (CL) throughout the luteal phase, as well as (ii) the influence of FASL alone, or together with the cytokines tumor necrosis factor alpha (TNF) and interferon gamma (IFNG), on equine luteal cell production of luteotrophic and luteolytic factors, cell viability, and apoptosis. FASL and FAS protein expression and mRNA transcription were evaluated in different luteal stages of the equine CL by Western blotting and real-time PCR assays, respectively. Protein expression and FASL mRNA transcription increased in the late CL. Also, FAS and FASL proteins were present in large steroidogenic and endothelial CL cells throughout the luteal phase, as demonstrated by immunohistochemistry. Equine luteal cells isolated from midluteal phase CL were stimulated without (control) or with exogenous cytokines: FASL (10 ng/ml); TNF+IFNG (10 ng/ml each; positive control) or FASL+TNF+IFNG (10 ng/ml each). FASL clearly inhibited in vitro progesterone and prostaglandin E(2) (PGE(2)) production by equine luteal cells but increased prostaglandin F(2alpha) (PGF(2alpha)). Furthermore, FASL effect on equine luteal cell viability depended on the presence of cytokines TNF and IFNG. In conclusion, this study shows the presence of FASL and FAS in the equine CL and suggests their importance in functional luteolysis.

Role of the cell cycle in regression of the corpus luteum

“…Luteal blood flow and plasma progesterone declined at luteolysis in cows (Acosta et al 2002, Nishimura et al 2008 and hypoxia reduced progesterone synthesis (Nishimura et al 2006) and caused apoptosis of bovine luteal cells (Nishimura et al 2008). Pro-apoptotic proteins such as the cytokines tumor necrosis factor a and FASL increase during luteolysis and are believed to contribute to structural regression (Shaw & Britt 1995, Friedman et al 2000, Quirk et al 2000b, Petroff et al 2001, Taniguchi et al 2002, Carambula et al 2003, Okuda & Sakumoto 2003, Skarzynski et al 2003, Galvao et al 2010, Atli et al 2012. The results of the current study suggest that luteal cells reenter the cell cycle and become susceptible to apoptosis during the same time period when cytotoxic pathways are activated in vivo.…”

“…It is well established that FASL triggers apoptosis in sensitive cells upon binding to its cell surface receptor, FAS (TNF receptor superfamily member 6). The FAS pathway is present in most cells including luteal cells (Roughton et al 1999, Quirk et al 2000b, Taniguchi et al 2002, Galvao et al 2010, Atli et al 2012, granulosa cells, and theca cells .…”

Seasonal Changes in Luteal Progesterone Concentration and mRNA Expressions of Progesterone Synthesis-related Proteins in the Corpus Luteum of Mares

“…In mares, administration of GnRH, eLH or hCG increased circulating P 4 concentrations in vivo [23][24][25][26]. In addition, in vitro studies demonstrated that either eLH or hCG increased the P 4 production by equine luteal cells [14,24]. Moreover, treatment of mares with an antiserum against equine gonadotropins during diestrous decreased the luteal size [27,28], and treatment of mares with a GnRH antagonist during diestrous decreased the circulating P 4 concentrations [29,30].…”

“…Luteinizing hormone (LH) secreted by the anterior pituitary is the main regulator of luteal function. LH acts through its specific cell surface receptor (LHCGR) and stimulates P 4 production by the CL in ewes [11], rats, sows [12], cows [13] and mares [14]. Steroidogenic acute regulatory protein (StAR) transfers cholesterol from the outer to inner mitochondrial membrane, allowing enzymatic cleavage of the side chain of cholesterol to pregnenolone by P450 cholesterol side-chain cleavage (P450scc).…”

Cytokines and neutrophil extracellular traps in the equine endometrium: friends or foes?

“…Even though cytokines in the endometrium of mares were first addressed in pathologic conditions, such as endometritis (Fumuso et al 2003), lately their role on the physiologic regulation of endometrial secretory and angiogenic function has been studied (Roberto da Costa et al 2008). Specifically in the mare reproductive tract, cytokines tumor necrosis factor alpha (TNFa), interferon gamma (IFNg), Fas ligand (FASL), transforming growth factor beta (TGFa), and interleukins (IL) have been related to luteal secretory capacity (Galvão et al 2010); endometrial and/or trophoblast growth and differentiation during placentation (Lennard et al 1995) and endometrial response to semen (Palm et al 2008). Nevertheless, the specific manner concerning cytokines interaction in the equine endometrium for the establishment of different events during the estrous cycle, is not well known.…”