Endocrine Abstracts

The active form of vitamin D, 1,25-dihydroxyvitamin D₃ (1,25D₃) is a potent antiproliferative/immunomodulatory steroid hormone with many applications outside calcium homeostasis. This is particularly true in the placenta which can generate 1,25D₃ locally via the enzyme 1alpha-hydroxylase (CYP27b) in both trophoblast and decidua. We have investigated the potential function of 1,25D₃ across gestation using human tissue obtained after local ethical approval. Using real-time RT-PCR we showed that mRNA for CYP27b was greatest in 1^st trimester with a 75-fold increase in placenta (P<0.001) and 564-fold increase in decidua (P<0.001) compared to 3^rd trimester placenta. The vitamin D receptor (VDR) followed a similar pattern with a 30-fold increase in 1^st trimester decidua compared to 3^rd trimester placenta (P<0.001). CYP24, encoding the inactivating enzyme 24-hydroxylase was ubiquitous throughout gestation, indicating increased 1,25D₃ signalling in early gestation. Using positive immunomagnetic selection we purified stromal (CD10positive) and immune-enriched (CD10negative) decidual cells and demonstrated expression of CYP27b, VDR and CYP24 mRNA in both fractions. In 1^st trimester CD10postitive cells CYP27b was 326 times higher than similar 3^rd trimester cells (P<0.001). CYP27b was also expressed 158 times higher in 1^st trimester compared to 3^rd trimester CD10negative cells (P<0.001). This, in conjunction with our finding that CYP27b expression only correlated with the macrophage marker CD14 in CD10negative cells (not stromal cells), highlights a potential immunomodulatory role for 1,25D₃ in early gestation. To investigate this further we cultured whole decidual cell suspensions in the presence of 1,25D₃ (100nM) for 12-18 hours and then used immunomagnetic selection to isolate CD56postitive natural killer (NK) cells from 1^st trimester decidua. Cells cultured in 1,25D₃ showed reduction of NK activity as measured by lysis of K562 cells in a standard chromium release assay. These data provide evidence for an immunomodulatory role for vitamin D in early gestation via localised synthesis of active 1,25D₃.