623: Decreased myometrial expression of matrix-Gla protein (MGP) is associated with preterm and term laboring state

Abstract

Uterine contractions are driven by complex calcium mediated mechanisms. Matrix Gla-protein (MGP) is an emerging vitamin K2-dependent protein with key roles in calcium homeostasis and inhibition of smooth muscle calcification. We sought to study MGP expression to provide new insight into the physiology of term and preterm contracting human myometrium. Myometrial expression of MGP was investigated in the following groups: 1) term labor (TL, n=5, GA: 39); 2) term non-labor (TNL, n=5, GA: 39); 3) preterm labor (PTL, n=5, GA: 28); 4) preterm non-labor (PTNL, n=13, GA: 29). Serum levels of MGP were measured by ELISA. Myometrial expression was assessed using immunohistochemistry and RNAseq with qRT-PCR validation. MGP and calcium-related proteins were localized with immunofluorescence in pregnant (PHM1) and non-pregnant (hTERT) human myometrial cell lines. 1) Pregnant myometrial cell lines had greater expression of MGP compared to non-pregnant state (Figure A). 2) At term, maternal serum MGP levels were unaffected by labor. 3) Cytoplasm of human myocytes display MGP immunostaining constitutively. 4) By qRT-PCR, we identified significantly higher levels of MGP gene expression in non-laboring myometrium compared to laboring preterm (p=0.002) and term (p=0.0004) tissues (Figure B). 5) This expression pattern was paralleled in mRNAseq of term (p=0.003) and preterm (p=0.002) uterus. 6) Immunocytochemistry showed that MGP colocalized with smooth-muscle actin monofilaments, but not calcium exchangers (SERCA, PMCA1) and Golgi marker. Our study presents the novel findings that MGP is present in human myometrium, and its tissue withdrawal is associated with a laboring state.