Menstrual blood-derived mesenchymal stromal cell secretome modulates macrophage polarization in a preconditioning-dependent manner.

BACKGROUND: The effects of menstrual blood-derived mesenchymal stromal cell secretome (S-MenSC) on macrophage polarization remain unclear. This study studied the impact of secretomes from basal MenSCs (S-bMenSCs) and those preconditioned with IFNγ and TNFα (S-pMenSCs) on human monocytes and macrophages in vitro. METHODS: S-MenSCs were used to assess their effects on three stages of monocyte-derived cell maturation: i. monocyte differentiation; ii. polarization of monocyte-derived macrophages (MDMs) toward M1-like or M2-like phenotypes; and iii. reprogramming of pre-polarized M1 or M2 macrophages. Surface markers were analyzed by flow cytometry and cytokine gene expression by RT-qPCR. In addition, a proteomic profiling was performed to identify proteins involved in the observed effects. RESULTS: Our results confirmed the capacity of S-MenSCs of modulating innate immune response and in particular macrophage polarization. More concretely, the in vitro experiments showed that: i. both secretomes partly promoted monocyte differentiation into an M1-like phenotype; ii. during macrophage polarization, S-bMenSCs partially limited the shift to an M1 phenotype, whereas treatment with S-pMenSCs boosted it; and, iii. in the pre-polarized macrophages, S-bMenSCs reinforced M1 traits, whereas S-pMenSCs promote partial phenotype switching. Finally, proteomic analysis revealed significant differences in the composition of both secretomes, comprising key proteins associated with macrophage polarization. CONCLUSION: These findings extend the knowledge on the immunomodulatory capacity of the S-MenSC, supporting that MenSCs, particularly when preconditioned, may play a significant role in regulating macrophage polarization, and, thus, modulating the inflammatory response.