108. FUNCTIONAL ROLE OF HTRA3 IN TROPHOBLAST CELL INVASION DURING HUMAN PLACENTAL DEVELOPMENT

Abstract

Controlled invasion of extravillous trophoblast (EVT) through the maternal decidua is important for placental development and function. Serine protease HtrA3 is highly expressed in the decidual cells in the late secretory phase of the menstrual cycle and throughout pregnancy. It is highly expressed in first trimester in most trophoblast cell types, but not in the invading interstitial trophoblast. HtrA3 and its family members are down-regulated in a number of cancers and are proposed as tumor-suppressors. We hypothesized that HtrA3 is an inhibitor of trophoblast invasion and is down-regulated in invading EVTs, while up-regulation of decidual HtrA3 controls the process. The current study investigated HtrA3 expression in human endometrial stromal cells (HESC) during decidualization in vitro and whether HtrA3 inhibits EVT cell invasion. Stromal cells isolated from human endometrium were decidualized in vitro with estrogen, progesterone and cAMP. Quantitative RT-PCR and western showed HtrA3 mRNA and protein expression was significantly increased in decidualized HESC compared to controls. Indirect immunofluorescence showed homogeneous pattern and increase in intensity of HtrA3 staining in decidualized HESC compared to non-decidualized cells. HTR-8 cells derived from first trimester of pregnancy EVT showed higher levels of HtrA3 mRNA expression compared to other human choriocarcinoma cell lines (AC-1M88, AC-1M32, JEG-3 and BeWo). Both intracellular and extracellular HtrA3 staining was observed in HTR8 cells. Functional role of HtrA3 in cell invasion was determined in HTR-8 cells using an in vitro invasion assay. Exogenous addition of mutant HtrA3 (inhibitor) resulted in a significant increase in HTR-8 cells invading through matrigel coated membrane compared with controls. TGFβ-1 (as positive control) completely inhibited invasion of HTR-8 cells. HtrA3 is tightly regulated during decidualization of HESC in vitro. Inhibition of HtrA3 activity in trophoblastic HTR-8 cells increased invasiveness supporting its functional role during placental development.