Proliferation and mRNA expression of absorptive villous cell markers and mineral transporters in prolactin-exposed IEC-6 intestinal crypt cells

During pregnancy and lactation, prolactin (PRL) enhances intestinal absorption of calcium and other minerals for fetal development and milk production. Although an enhanced absorptive efficiency is believed to mainly result from the upregulation of mineral transporters in the absorptive villous cells, some other possibilities, such as PRL-enhanced crypt cell proliferation and differentiation to increase the absorptive area, have never been ruled out. Here, we investigated cell proliferation and mRNA expression of mineral absorption-related genes in the PRL-exposed IEC-6 crypt cells. As expected, the cell proliferation was not altered by PRL. Inasmuch as the mRNA expressions of villous cell markers, including dipeptidylpeptidase-4, lactase and glucose transporter-5, were not increased, PRL was not likely to enhance crypt cell differentiation into the absorptive villous cells. In contrast to the previous findings in villous cells, PRL was found to downregulate the expression of calbindin-D(9k), claudin-3 and occludin in IEC-6 crypt cells, while having no effect on transient receptor potential vanilloid family channels-5/6, plasma membrane Ca(2+)-ATPase (PMCA)-1b and Na(+)/Ca(2+) exchanger-1 expression. In conclusion, IEC-6 crypt cells did not respond to PRL by increasing proliferation or differentiation into villous cells. The present results thus supported the previous hypothesis that PRL enhanced mineral absorption predominantly by increasing transporter expression and activity in the absorptive villous cells.