Reproduction Abstracts

Introduction: In the absence of pregnancy, the resumption of a new estrous cycle is assured by functional and structural regression of the corpus luteum (CL). We have recently characterized the involvement of Nodal, a morphogen from transforming growth factor beta superfamily, on functional luteolysis in the mare (Galvao et al, 2015 Endocrinology, 157:858–871). Also, tumor necrosis factor α (TNF) has been reported to mediate both functional and structural luteal regression. Herein, we demonstrate the dialogue between these two pathways towards luteolysis promotion in the mare.

Materials & methods: An in vitro study with enzymatically isolated luteal cells (n=6/group) from mid luteal stage (mid-CL), cultured in T25 culture flasks (5.0×10⁶ cells/mL), was performed. Cells were treated for 24 h with: (i) no factor (ii) Nodal (0.1–10 ng/mL) (iii) TNF (10 ng/mL) (iii) prostaglandin (PG) F2α (10⁻⁷M); or (iv) luteinizing hormone (LH) (10 ng/ml). TNF was quantified in culture media (ELISA). The mRNA transcription was evaluated by relative quantification real-time PCR (normalization with β-microglobulin- B2MG) and protein expression quantified by western blotting (normalization with β-actin).

Results & discussion: Nodal increased the TNF level in culture media (P<0.05), as well as mRNA and protein of TNF (P<0.05) and its receptor type I (P<0.05). Conversely, the TNF activation of Nodal signalling was supported by a consistent rise in mRNA and protein of Nodal (P<0.05) and its receptors Alk4 (P<0.01) and Alk7 (P<0.05). Ultimately, phosphorylation of Smad3 protein, an intracellular mediator of canonical Nodal signalling activation, by TNF testifies the cross talk between both pathways. The present results suggest the dialogue between TNF and Nodal signalling pathways for luteolytic signal amplification during CL regression in mares.

Work supported by MS&HE “Juwentus Plus” (IP2014011373) and NSC (2011/02/A/NZ5/00338).