Abstract: BACKGROUND: Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine, which is secreted in different types of stem cells and can regulate the proliferation, differentiation and migration of various types of stem cells. Our previous research has confirmed that human embryonic stem cells secrete MIF and that its concentration in the culture medium is relatively stable. However, whether MIF is involved in the survival, proliferation and differentiation of human embryonic stem cells remains unclear.
OBJECTIVE: To investigate the effects of MIF on survival, proliferation, and differentiation of human embryonic stem cells. 
METHODS: (1) Human embryonic stem cells H9 were cultured. The growth curve of cells was detected and plotted by CCK-8 assay. Enzyme-linked immunosorbent assay was used to determine the level of MIF in the medium. (2) To determine the effects of exogenous MIF on the survival and proliferation of human embryonic stem cells, different groups were established: the control group, which was cultured in stem cell medium without any modifications; the exogenous MIF group, which was treated with different concentrations (30, 100, 300 ng/mL) of MIF in the stem cell medium; the MIF inhibitor ISO-1 group, which was treated with different concentrations (2, 7, 21 μmol/L) of ISO-1 in the stem cell medium; and the MIF+ISO-1 group, which was treated with different concentrations of ISO-1 along with 100 ng/mL of MIF. Cell viability was assessed using the CCK-8 assay. (3) To further elucidate the effect of MIF gene on survival and proliferation of human embryonic stem cell, the MIF knockout H9 cell line was constructed by CRISPR-Cas 9 technology to observe the lineage establishment. (4) To determine the effect of high concentrations of MIF on human embryonic stem cell differentiation, 100 ng/mL MIF and 100 ng/mL of CXCR4 neutralizing antibody were separately added to the normal stem cell culture medium. The expression levels of self-renewal factors (KLF4, c-MYC, NANOG, OCT4, and SOX2) and differentiation transcription factors (FOXA2, OTX2) were measured using real-time quantitative polymerase chain reaction, immunofluorescence staining, and western blot analysis.
RESULTS AND CONCLUSION: (1) The logarithmic growth phase of H9 cells was between 3-6 days. Under normal growth conditions, human embryonic stem cells secreted MIF at a concentration of approximately 20 ng/mL, independent of cell quantity. (2) Compared to the control group, the addition of different concentrations of MIF had no effect on the proliferation of human embryonic stem cells (P > 0.05). ISO-1 significantly inhibited the proliferation of human embryonic stem cells, with a stronger inhibition observed at higher concentrations of ISO-1 (P < 0.05). The addition of MIF in the presence of ISO-1 reduced the inhibitory effect of ISO-1 (P < 0.05). (3) Real-time quantitative polymerase chain reaction showed that knocking out 50% of the MIF gene resulted in a significant decrease in the growth vitality of human embryonic stem cells and failure to establish cell lines. (4) Adding 100 ng/mL exogenous MIF to the culture medium resulted in a decrease in the mRNA, protein, and fluorescence expression levels of the self-renewal transcription factor KLF4, while the mRNA, protein, and fluorescence expression levels of the differentiation factor FOXA2 increased. (5) When 100 ng/mL CXCR4 neutralizing antibody was added to the culture medium, the mRNA and protein expression levels of KLF4 increased, while the mRNA and protein expression levels of FOXA2 decreased, contrary to the expression trend observed in the MIF group. In conclusion, the endogenous secretion of MIF by human embryonic stem cells is essential for their survival. The addition of MIF to the culture medium does not promote the proliferation of human embryonic stem cells. However, it can lead to a decrease in the expression of the self-renewal factor KLF4 and an increase in the expression of the transcription factor FOXA2. This provides a clue for further investigation into the effects and mechanisms of MIF on the differentiation of human embryonic stem cells. The MIF-CXCR4 axis plays a regulatory role in this process.

Key words: macrophage migration inhibitory factor, human embryonic stem cell, autocrine, survival, differentiation, CXCR4, KLF4, FOXA2