Ovine corpus luteum proteins, with functions including oxidative stress and lipid metabolism, show complex alterations during implantation.

Progesterone (P(4)) secreted by the corpus luteum (CL) is critical for in utero embryo survival and development, although CL proteins are key regulatory factors during the luteal phase. We, therefore, characterised protein expression patterns in ovine CL of pregnancy (days 12, 16 and 20) compared with those of controls, CL of oestrous cycle (days 12 and 16), using two-dimensional gel electrophoresis (2DE) gel-based proteomics. Proteins in 24 significantly altered spots were identified by tandem mass spectroscopy. At the time of embryo implantation (day 16), 77 spots were up-regulated and 101 spots were down-regulated in CL of pregnancy compared with regressed CL. Vimentin, lamin A/C (LMNA), [Mn] superoxide dismutase (SOD2), isocitrate dehydrogenase 1, annexin A1 and elongation factor Tu, mitochondrial (TUFM) altered during CL regression, whereas glutathione S-transferase A1, apolipoprotein A-1, myxovirus resistance protein 1, ornithine aminotransferase and enoyl-CoA hydratase, mitochondrial (ECHS1) tended to be altered during CL maintenance. biliverdin reductase B (BLVRB), FDXR, guanine nucleotide-binding protein G(I)/G(S)/G(T) subunit beta-2 (GNB2) and cytochrome b-c1 complex subunit 1, mitochondrial (UQCRC1) showed divergent expression during CL regression and maintenance. The expression of two representative proteins, SOD2 and BLVRB, by western blot increased in CL of non-pregnant ewes on day 16 compared with that on day 12. SOD2 and BLVRB were localised in the large and small luteal cells and endothelial cells of CL over peri-implantation periods. 2DE gel and mass spectrometry have been used, for the first time, to study ovine CL function. We have identified proteins involved in key pathways, including oxidative stress, steroidogenesis, signal transduction and apoptosis, which have not previously been associated with changes occurring in the CL during the peri-implantation period. These proteins are most likely involved with mechanisms allowing the CL to produce P(4) during early pregnancy.