Intercellular Tunneling Nanotube-mediated Mitochondrial Transport Induces Apoptosis Resistance In Acute Monocytic Leukemia Cells

Objective To observe the formation of tunneling nanotubes(TNTs)between human acute monocytic leukemia(AML-M5)cell line THP-1 and bone marrow mesenchymal stem cells(BM-MSCs);and investigate the effect of mitochondrial transport on apoptosis of THP-1 cells in TNTs,then to explore its molecular mechanism.Methods Specific fluorescent dyes were used to label mitochondria,cytoskeleton protein F-Actin and nucleus respectively.The formation of TNTs between BM-MSCs and THP-1 cells and the transmission of mitochondria in TNTs were observed by confocal microscope.After 5 days of co-culture of BM-MSCs and THP-1 cells,apoptosis of THP-1 cells was detected by flow cytometry.The co-culture system is divided into four groups: Direct co-culture(S),Transwell transmembrane co-culture(T),direct co-culture system with cytochalasin(TNTs inhibitor)Latrunculin B(L),no BM-MSCs but only culture medium(M);The expression of organelle transporter associated motor protein(KIF5B)was detected by Western blot.Results 1、TNTs formation was observed between BM-MSCs and THP-1 cells,Mitochondria in BM-MSCs cells were unidirectionally transmitted to THP-1 cells via TNTs,but no mitochondrial reverse transmission was observed.2、Annexin V-FITC/PI cell apoptosis assay results showed that the apoptosis rate of THP-1 cells in S、L groups were significantly lower compared with M group(P < 0.01),The apoptosis rate ofgroup L was higher than that of group S(P < 0.01),and that of group T was significantly higher than that of group S and group L(P < 0.01),there was no significant difference in apoptosis rate between group T and group M(P > 0.05).3、The expression level of KIF5 B in BM-MSCs was higher than that in THP-1 cells(P < 0.001).Rotenone significantly inhibited the expression of KIF5 B in BM-MSCs(P < 0.01).Conclusion Mitochondria of BM-MSCs are unidirectionally transmitted to THP-1 cells via TNTs,which may induces apoptosis resistance in THP-1 cells;Intercellular mitochondrial transport may be associated with motor protein KIF5 B.