Pig uterine luminal fluid contains the developmentally regulated neurotrophic factor, pleiotrophin

Abstract

The pig conceptus produces a non-invasive placenta which is probably dependent on uterine secretory products during both the pre- and post-attachment periods. Since some of these factors are also produced during the oestrous cycle, uterine luminal flushings (ULF) from adult nonpregnant pigs were analysed to identify potentially important maternally-secreted growth factors or cytokines. ULF contained several proteins that were detected on Western blots by an antibody raised against the N-terminal 14 amino acids of rat pleiotrophin (PTN). One of the proteins co-migrated on SDS-PAGE gels and co-eluted from heparin-affinity columns with 18 kDa recombinant human PTN, suggesting its identity as the intact native porcine PTN (pPTN) molecule. Additional immunoreactive forms of pPTN were identified that were of lower molecular mass (14-16 kDa), had lower heparin-affinities, were more hydrophobic, and were apparently C-terminally truncated. Native pPTN was isolated from ULF using cation-exchange chromatography, heparin-affinity fast protein liquid chromatography and C4 reverse-phase high performance liquid chromatography. Structural analysis of the purified protein resulted in definitive identification of 15 out of 17 N-terminal amino acids; these were 100% conserved with the corresponding residues of human, bovine and rat PTN. These results demonstrate various biochemical properties of pPTN and suggest that, in addition to the apparent involvement of PTN in differentiation during early neonatal life, it may be delivered in uterine secretory fluids to, as yet, undefined target cells in the reproductive tract of the adult female.