Recombinant humanized type III collagen attenuates recurrent spontaneous abortion by regulating stromal cell decidualization and reinforcing protective immune microenvironment at the maternal–fetal interface

Recurrent spontaneous abortion (RSA), the common early pregnancy complication, remains elusive in its pathogenesis and treatment. Recombinant humanized type III collagen (rhCOLIII), a novel biomaterial, has demonstrated efficacy in treating various diseases. However, the role of rhCOLIII in RSA is unclear. This study aimed to explore the therapeutic potential and underlying mechanisms of rhCOLIII in RSA at single-cell resolution. Human endometrium/decidua samples derived from healthy donors/normal pregnant and RSA patients were obtained to detect type III collagen (COLIII) expression via immunohistochemistry (IHC) and Western blot. A murine RSA model (CBA/J ♀ × DBA/2 ♂) was established, followed by intrauterine perfusion of rhCOLIII to evaluate its therapeutic efficacy. Uterine tissues from RSA and rhCOLIII-treated mice were collected on gestation day 8 for single-cell RNA sequencing, with findings validated by IHC, multiplex IHC (mIHC), and flow cytometry (FCM). COLIII expression was significantly reduced in RSA endometrial/decidual tissues. Intrauterine rhCOLIII treatment in a murine RSA model significantly decreased the embryo resorption rate from 31.62% to 3.82% ( P < 0.001). Single-cell analysis identified 19 cell clusters, with stromal cells as the predominant population, further classified into seven functional subtypes and their differential composition between the RSA and rhCOLIII groups was confirmed by mIHC. Furthermore, rhCOLIII reprogrammed stromal cell function by activating oxidative-stress response pathways and regulating decidualization. Concurrently, our results showed that rhCOLIII could enhance anti-inflammatory macrophage activity and increase CD16 + NK cell abundance. Cell–cell communication analysis uncovered that APOE–TREM2 signaling between decidual stromal cells and macrophages, as well as BSG–PPIA signaling in decidual stromal cell–NK cell interactions, was augmented following rhCOLIII treatment. FCM analysis demonstrated that rhCOLIII increased TREM2 + macrophages associated with M2 polarization. Our study demonstrates that rhCOLIII exerts therapeutic effects in RSA mice potentially by modulating stromal cell decidualization and promoting a protective immune microenvironment, highlighting a promising therapeutic strategy for RSA. • Low expression of type III collagen (COLIII) in the decidua is associated with recurrent spontaneous abortion (RSA). • Intrauterine administration of recombinant human COLIII (rhCOLIII) decreases the embryo resorption rate in RSA mice. • rhCOLIII exerts antioxidant effects in decidual stromal cells (DSCs) and regulates uterine decidualization in RSA mice. • rhCOLIII increases CD16 + NK cells and enhances the anti-inflammatory activity of macrophages in uterine tissues of RSA mice. • rhCOLIII reprograms DSC crosstalk with C1q + Mφ and trNK cells, promoting immune homeostasis at the maternal-fetal interface.