Linolamide in Apoptotic Bodies: A Key Factor in Mesenchymal Stem Cell Immunotherapy for Two Abortion Models

Background: Unexplained recurrent spontaneous abortion (URSA) is a distressing pregnancy disorder with no effective medical intervention. As a potential treatment for URSA, human umbilical cord mesenchymal stem cells (hucMSCs) undergo apoptosis and release apoptotic bodies (ABs) shortly after transplantation. However, the medical effects and the exact doses of ABs in the therapy for URSA remain unclear. Methods: Staurosporine (STS) and ultraviolet (UV) induced apoptosis in hucMSCs. Differential centrifugation, transmission electron microscopy, immunofluorescent staining, and flow cytometry were used to isolate and characterize hucMSC-derived ABs (hucMSC-ABs), respectively. Two mouse abortion models (LPS-induced and CBA/J×DBA/2 immune-mediated) mimicked URSA. Flow cytometry, real-time quantitative PCR, immunofluorescence staining, and western blotting were used to analyze macrophage polarization and inflammatory pathways. Untargeted metabolomic analysis was used to detect the metabolic composition of hucMSC-ABs. RNA sequencing analysis was used to detect the transcriptome of macrophages (Macs). Dorsomorphin was used to inhibit the AMPK signaling pathway. Small interfering RNA (siRNA) was used to knock down Gys1 in raw246.7 macrophages. Results: STS- and UV- induced hucMSC-ABs effectively alleviated abortion in both models, depended on Macs. However, excessive dosage of hucMSC-ABs induced pro-inflammatory Macs (pro-inflam Macs), worsening fetal loss. Appropriate doses suppressed the NF-κB pathway in Macs, while high doses activated it. Neither RNase nor trypsin fully abolished hucMSC-ABs' regulatory effects on macrophage polarization. Metabolomics identified linoleamide and palmitic acid (PA) as the dominant hucMSC-AB metabolites (~1:1 ratio). RNA-seq revealed hucMSC-ABs modulated Nfkb1 and Gys1 in Macs, linked to linoleamide. Appropriate doses of the 1:1 mixture of linoleamide and PA induced anti-inflam Macs, while high dosages of the mixture induced pro-inflam Macs. Linoleamide alone activated AMPK, suppressed NF-κB via Gys1, and protected pregnancy, whereas PA induced pro-inflam Macs and promoted abortion. Conclusion: Appropriate doses of hucMSC-ABs induce anti-inflam Macs in the uterus and prevent fetal loss, while high doses promote the polarization of pro-inflam Macs and lead to fetal loss. The effects of hucMSC-ABs in regulating Macs and treating URSA are related to different doses of linoleamide and PA on Macs. Linoleamide activates AMPK and suppresses NF-κB via Gys1. This study revealed the effect and mechanism of hucMSC-ABs intervention in fetal loss and provided a new idea for the treatment of URSA.