Aberrant Level of Estrogen Correlates with Defective Thrombopoiesis during Pregnancy in Patients with Immune Thrombocytopenia

Abstract

Pregnancy seems to be a high-risk event in immune thrombocytopenia(ITP)because disease flares are frequently observed during gestation clinically, and the treatment with glucocorticoid is often ineffective. Sex hormones are changed dramatically during pregnancy to maintain a stable environment both for the mother and for the fetus. To determine the sex hormone levels during pregnancy in ITP, sex hormones were analyzed in patients with ITP and matched healthy women before, during, and after pregnancy. We demonstrated that there is a relationship between estrogen level and thrombopoiesis in ITP pregnancy. Moreover, we showed that estrogen plays a role in glucocorticoid resistance which is common in ITP patients who are pregnant.

Thirty consecutive successful pregnancies in 30 patients with ITP, 21 pregnancies in 21 healthy controls, twenty patients with primary ITP and 19 healthy subjects were studied. Serum samples for sex hormone testing, including estrogen, progesterone, testosterone, prolactin, LH and FSH, were collected and analyzed. We confirmed that serum levels of all sex hormones varied significantly during pregnancy and postpartum, both in the patients with ITP and in healthy controls, as expected. However, the concentration of estrogen was significantly lower in pregnant ITP patients, compared with healthy pregnant subjects, leading to a completely different profile.

To clarify whether the different estrogen concentration has a direct effect on megakaryocyte(MK) maturation and thrombopoiesis during pregnancy in ITP, BM-derived CD34+ cells from ITP patients and healthy controls in pregnancy, were treated with different doses of estrogen. We found that estrogen had the ability to promote MK polyploidization, maturation and proplatelet formation via estrogen receptor(ER) in healthy controls, but the concentration of estrogen, which was lower than that of the normal-pregnancy group, could not play the above role in CD34+ cells of pregnancy-ITP group. To determine the differences in MKs treated with estrogen of different doses in each group, we screened some essential transcription factors that may participate in the regulation of MK polyploidization and maturation. The expression levels of GATA1, FLI1, FOG-1, KLF-1, and NF-E2, were detected by RT-PCR and Western blot. We found that, in the pregnancy-ITP group treated with lower estrogen, the expression of GATA1 and NF-E2 was significantly reduced compared with the healthy control. We obtained similar results with the bone marrow samples, indicating that pregnant ITP patients showed more obvious detects in megakaryocyte maturation defect and lower expression of transcription factors. Further investigation is needed to evaluate the expression of ER and its nuclear translocation in MKs of the pregnancy-ITP group treated with the relatively lower level of estrogen.

We also explored if the relatively reduced estrogen level plays a role in glucocorticoid resistance which is commonly observed in ITP patients during pregnancy. We evaluated the inhibitory effects of dexamethasone, with or without different concentrations of estrogen, on the proliferation of PBMCs from the pregnancy-ITP group induced by a mitogen. We found that estrogen impaired the inhibitory effects of dexamethasone. Further study with immunofluorescence demonstrated that estrogen upregulated the expression of protein phosphatase, which affected the glucocorticoid receptor activation.

In conclusion, an unexpected lack of estrogen serum level increase occurs in patients with ITP during pregnancy. The relatively reduced level of estrogen cannot induce the expression of GATA1 and NF-E2 via ER in pregnant ITP patients, which is required for MK maturation and thrombopoiesis. Meanwhile, setrogen inhibits glucocorticoid action via protein phosphatase, which may account for the glucocorticoid resistance observed in pregnant ITP patients.