Two small leucine-rich proteoglycans (SLRP), decorin and biglycan, play important roles in structural-functional integrity of the placenta and fetal membranes, and their alterations can result in several pregnancy-associated diseases. In this review, we briefly discuss normal placental structure and functions, define and classify SLRPs, and then focus on two SLRPs, decorin (DCN) and biglycan (BGN). We discuss the consequences of deletions/mutations of DCN and BGN. We then summarize DCN and BGN expression in the pregnant uterus, myometrium, decidua, placenta, and fetal membranes. Actions of these SLRPs as ligands are then discussed in the context of multiple binding partners in the extracellular matrix and cell surface (receptors), as well as their alterations in pathological pregnancies, such as preeclampsia, fetal growth restriction, and preterm premature rupture of membranes. Lastly, we raise some unanswered questions as food for thought.
Keywords: Ehlers–Danlos syndrome (EDS); biglycan; decidua; decorin; fetal growth restriction; leucine-rich proteoglycans; placenta; preeclampsia; pregnancy; premature labor; premature preterm rupture of membranes (PPROM); trophoblast; trophoblast invasion.