Human umbilical cord mesenchymal stem cell-derived exosomes carrying miR-1827 downregulate SUCNR1 to inhibit macrophage M2 polarization and prevent colorectal liver metastasis

microRNA-1827 (miR-1827) is proposed to be enriched in exosomes from mesenchymal stem cells (MSCs-Exos). A recent study has addressed the suppressive effect of exosomes from human umbilical cord mesenchymal stem cells (hUC-MSCs-Exos) on colorectal cancer (CRC) metastasis. Hence, our study aims at investigating whether hUC-MSCs-Exos can modulate the liver metastasis in CRC by mediating miR-1827. Transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA) were used to identify hUC-MSCs-Exos. Using gain- and loss-of-function approaches, the expression of miR-1827 and succinate receptor 1 (SUCNR1) was altered. Consequently, the biological functions of CRC cells were assessed by CCK-8 and Transwell assays and macrophage M2 polarization was assayed by flow cytometry. Dual-luciferase reporter assay was applied to clarify interaction between miR-1827 and SUCNR1. CRC cells were incubated with hUC-MSCs-Exos and tumor-bearing mice were injected with hUC-MSCs-Exos to examine the effects on CRC cell growth and metastasis. SUCNR1, lowly expressed in CRC, could promote CRC cell growth and macrophage M2 polarization. miR-1827 could target SUCNR1 and hence suppress the progression and metastasis of CRC. hUC-MSCs-Exos carried miR-1827 to inhibit M2 macrophage polarization by downregulating SUCNR1 expression, and inhibited proliferating, migrating and invading properties of CRC cells. Furthermore, hUC-MSCs-Exos carrying miR-1827 blocked CRC liver metastasis in vivo. These findings indicate hUC-MSCs-Exos as an inhibitor of M2 macrophage polarization and liver metastasis in CRC through inducing miR-1827-targeted inhibition of SUCNR1. This provides a theoretical basis for understanding the mechanisms underlying Exos-based target therapy for CRC.