Abstract
Podoplanin, a reliable marker of lymphatic endothelium, is a mucin-type transmembrane protein. Although the human placenta is devoid of a lymphatic system, chorionic villous stromal (CVS) cells express podoplanin. In this study, the pattern of podoplanin expression in normal and pathological placental tissues and the biological role of podoplanin were investigated. In total, 198 placental tissues belonging to 184 patients, seen at the Department of Pathology of Bulent Ecevit University Education and Research Hospital, Zonguldak, Turkey, were evaluated histopathologically and determined to meet the study criteria. The tissues were assigned to control, cisternal placental disorders, inflammation and hypoxic-ischemic pathology groups. Podoplanin expression in CVS cells was graded from 0 to 3 depending on the staining intensity, as determined by an immunohistochemical evaluation of chorionic villi in the most intensively stained tissue region. Podoplanin levels in control CVS cells increased in parallel with placental maturation, whereas in molar pregnancies podoplanin expression was lower than in control tissues. In the acute placental inflammation group, podoplanin immunoreactivity was similar to that in the control group, whereas in the preeclampsia group, podoplanin expression was higher than in all other groups. Our study showed an increase in podoplanin expression in CVS cells during pregnancy. In preeclamptic patients, the increase in podoplanin expression may be a response to hypoxic-ischemic conditions, whereas in molar pregnancies the decrease in podoplanin levels may cause villous swelling by disrupting intercellular fluid homeostasis.
Highlights
Podoplanin is a mucin-type transmembrane protein composed of 162 amino acid residues
In the study of Volchek et al.[11], non-decidualized gestational endometrium was shown to be rich in lymphatic vascular structures, which regressed with increasing decidualization
31.4% were in the hydropic placental pathologies group; 7.6% in the acute placental inflammation group; and 19.1% were in the hypoxic-ischemic pathologies groups (Table 1)
Summary
Podoplanin is a mucin-type transmembrane protein composed of 162 amino acid residues. The few studies that investigated podoplanin expression in normal and pathological placental tissues, and the role of the protein in placental pathologies, yielded contradictory results. A PUBMED search using the keywords placenta-podoplanin-D2-40 identified 12 articles, the first of which was published in 20086–17 Most of these studies investigated the presence of a mature lymphatic system in the placenta; their findings are summarized below. Bellini et al.[6] found no evidence of mature lymphatic vessels in chorionic villi, but noted that stromal cells were positive for podoplanin. The authors argued that podoplanin-expressing stromal cells function as primitive lymphatic channels. Lundell et al.[17] showed that CVS and maternal decidual stromal cells are the major sources of podoplanin in the human placenta, and that podoplanin-secreting cells in placental tissue play a role in feto-maternal immunological tolerance
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