Characterization of TNSALP expression, localization, and activity in ovine utero-placental tissues

Abstract

Tissue-nonspecific alkaline phosphatase (TNSALP; encoded by ALPL gene) has a critical role in the regulation of phosphate homeostasis postnatally. However, the utero-placental expression of TNSALP and the role in phosphate transport in pregnancy is poorly understood. Estrous cycles of ewes were synchronized, and ewes were euthanized and hysterectomized on Day 1, 9, or 14 of the estrous cycle or bred to fertile rams and euthanized and hysterectomized on Day 9, 12, 17, 30, 50, 70, 90, 110, or 125 of pregnancy. The expression of ALPL mRNA, immunolocalization of TNSALP protein, and quantification and localization of TNSALP enzymatic activity was performed on ovine endometria and placentomes. Day of the estrous cycle did not alter ALPL mRNA expression or enzymatic activity of TNSALP. TNSALP protein localized to uterine epithelial and stromal cells, blood vessels, myometrium, caruncular and cotyledonary stroma. TNSALP activity was localized to uterine epithelia, blood vessels, caruncular stroma (from Day 70 of gestation), and the apical surface of chorionic epithelia (from Day 50 of gestation). TNSALP protein and activity localized to the apical surface of uterine epithelia during the estrous cycle and in early pregnancy. Endometrial TNSALP enzymatic activity was downregulated on Day 17 and 30 of gestation (P < 0.05). Expression of ALPL mRNA decreased in late gestation in endometria and placentomes (P < 0.05). TNSALP activity peaked in placentomes on Days 70 and 90 of gestation. Collectively, these results suggest a potential role of TNSALP in the regulation of phosphate transport and homeostasis at the maternal-conceptus interface in ruminants.

Progesterone regulates tissue non-specific alkaline phosphatase (TNSALP) expression and activity in ovine utero-placental tissues

“…The relative expression of ALPL mRNA was quantified by qPCR as described previously [ 6 ]. RNA was extracted from snap-frozen endometria (Exp.…”

“…We recently characterized: 1) expression of ALPL mRNA; 2) localization of TNSALP protein; and 3) quantification and localization of TNSALP enzymatic activity in the endometria of cyclic ewes, and endometria and placentomes at multiple stages of gestation [ 6 ]. Interferon tau (IFNT), the maternal signal for pregnancy recognition in ruminants, and progesterone (P4), act both independently and synergistically to alter endometrial expression of mRNAs and proteins important for phosphate transport and utilization during the peri-implantation period of pregnancy in ruminants [ 7 , 8 ].…”

“…Interferon tau (IFNT), the maternal signal for pregnancy recognition in ruminants, and progesterone (P4), act both independently and synergistically to alter endometrial expression of mRNAs and proteins important for phosphate transport and utilization during the peri-implantation period of pregnancy in ruminants [ 7 , 8 ]. We recently demonstrated that the expression of ALPL mRNA tended to be lower in endometrium on Day 9 of the estrous cycle compared to Day 1, which could suggest that increasing concentrations of P4 in plasma is associated with decreased endometrial expression of ALPL mRNA [ 6 ]. Similarly, it has been reported that TNSALP protein is more abundant in ovine cervicovaginal mucus of ewes during estrus compared to diestrus [ 9 ].…”

“…Similarly, it has been reported that TNSALP protein is more abundant in ovine cervicovaginal mucus of ewes during estrus compared to diestrus [ 9 ]. Further, we recently demonstrated localization of TNSALP protein and enzymatic activity to the apical surface of uterine epithelia (luminal [LE], superficial glandular [sGE] and glandular [GE]) in cyclic and pregnant ewes [ 6 ]. As uterine epithelia have important roles in the synthesis and transport of nutrients, it is speculated that TNSALP may convert phosphocompound substrates into phosphate in uterine epithelial cells which could then be used by the epithelial cells or transported into the uterine lumen [ 6 ].…”

“…Further, we recently demonstrated localization of TNSALP protein and enzymatic activity to the apical surface of uterine epithelia (luminal [LE], superficial glandular [sGE] and glandular [GE]) in cyclic and pregnant ewes [ 6 ]. As uterine epithelia have important roles in the synthesis and transport of nutrients, it is speculated that TNSALP may convert phosphocompound substrates into phosphate in uterine epithelial cells which could then be used by the epithelial cells or transported into the uterine lumen [ 6 ]. Interestingly, in this study we demonstrated significant downregulation in the uterine sGE and deep GE, accompanied by complete absence of TNSALP activity in the uterine LE on Day 17 of pregnancy, which corresponds to the period of conceptus attachment in the sheep.…”