Table 1 The table summarizes the main evidence regarding the involvement of ECM components in the various processes occurring in the early phases of pregnancy

Collagen I

Rapidly thickens and rearranges around the decidual cells and is necessary for a correct decidualization [29, 30, 37,38,39]

Functions as an adhesive substrate for trophoblasts, if excessively expressed suppresses the proliferation and invasion of trophoblasts through the inhibition of the ERK and WNT/β-catenin signaling [99,100,101]

Provides the villous structural scaffold [140]

Promotes Treg differentiation [52]

Collagen III

Rapidly thickens and rearranges around the decidual cells [29]

Promotes trophoblast migration [102]

Collagen IV

Selectively up-regulated during decidualization [29, 30, 45]

Increases around the spiral arteries; participates in decidual vascular remodeling [45]

Expressed in the mesenchyme of placental villi, participates in glycocalyx formation [144]

Collagen V

Rapidly thickens and rearranges around the decidual cells [29]

Collagen XVIII

Widely expressed in the decidua during the first and third trimesters of pregnancy [44]

Degraded by MMPs releases endostatin, that inhibits trophoblasts invasion by binding to integrin α5β1 [105]

Fibronectin

Supports the structural organization of the evolving ECM by interacting with other stromal proteins [50, 51]

Present on the luminal endometrial epithelium, interacts with α5β1 integrin expressed by the trophectoderm [60]

Binds to αIIbβ3 on trophoblasts [76, 77]; regulates trophoblast adhesion and migration into maternal tissue through the activation of Erk and Akt signaling pathways [107, 108, 110]

Promotes the differentiation of endovascular trophoblasts [130]

Acts as a ‘glue’ between fetal and maternal tissues by mediating the anchoring of syncytiotrophoblast columns to the decidua [134]

Laminins

Different isoforms are expressed in the endometrium, changing along with the process of decidualization [93, 94]

Expressed by the trophectoderm, interact with integrins present on endometrial luminal cells [56]

Laminin isoforms influence the direction and quality of invasion of trophoblast cells [95,96,97]

Biglycan

Promotes a regular ECM fibrillar organization [31, 32, 36]

Localizes within endothelial and subendothelial cells of the perivascular region of fetal capillaries [24, 147]

Decorin

Contributes to the differentiation of endometrial stromal fibroblasts into secretory decidual cells [22, 24]

Limits trophoblast invasion through modulation of the availability of TGF-β and the activity of MMPs [8, 24, 111, 116,117,118]

Interferes with the differentiation into endovascular trophoblasts through VEGFR2 [116]

Is produced by mesenchymal stromal cells of the chorionic villi [24, 145]

Promotes the polarization of decidual macrophages towards a pro-inflammatory M1 phenotype [54]

Perlecan

Expressed by both the trophectoderm and endometrial basal lamina [85]

Facilitates trophoblast invasion and differentiation by modulating the activity of MMPs [62, 86, 87]

Forms a supportive scaffold that maintains the structural integrity of placental tissues [89, 90]

Syndecans

SDC1 promotes endometrial stromal decidualization by binding to osteoprotegerin [152]; SDC1 serves as storage molecule for many chemokines and angiogenic factors [152, 153]

Expressed by the trophectoderm, interact with integrins present on endometrial luminal cells [56]

SDC1 promotes EVT migration into the maternal decidua by interacting with ADAM12 [87, 154]

SDC1 protects the syncytiotrophoblast from oxidative stress and inflammation [87]; interaction of syndecans with PSG1 promotes endothelial tube formation [162]

Versican

Interacts with other ECM components facilitating the structural remodeling of maternal tissues [124,125,126,127,128,129]

Promotes trophoblast proliferation and differentiation [124]

Promotes uNK cell proliferation and facilitates the remodeling and dilation of spiral arteries [124]

Supports the formation of syncytiotrophoblast [123, 133]

Hyaluronan

Peaks of HA deposition are observed during the mid-proliferative and the mid-secretory phase [64,65,66]

Acts as a linker by binding to CD44 receptors present on both embryo’s trophectoderm and endometrial epithelial cells [67]

Trophoblasts secrete large amounts of HA that function in an autocrine manner enhancing their proliferation and migration [70]

Serves as substrate for mesenchymal cell migration; promotes the sprouting of blood vessels [141]

Instructs decidual macrophages to polarize towards an M2 immunosuppressive phenotype [71]