OBJECTIVETo study both the release of HMGB1 from irradiation-treated mesenchymal stem cells (MSCs) and the effects of HMGB1 on human cord blood CD34(+) hematopoietic progenitor cell proliferation and differentiation.

METHODSMSCs were obtained from human bone marrow. HMGB1 released by the MSCs after treatment with 12 Gy gamma-ray irradiation was determined by enzyme linked immunosorbent assay (ELISA). CD34(+) cells were positively selected with a MACS CD34 isolation kit. The freshly isolated CD34(+) cells were cultured in the presence of HMGB1 for 6 days. Phenotype of cultured cells surface molecules (CD13, CD14, CD11c, CD41 and CD71) were analyzed by flow cytometry. The proliferation and differentiation capacities of cord blood HSCs were assayed by colony forming cell assay. The receptors of HMGB1 (RAGE, TLR2 and TLR4) on cord blood CD34(+) cells were detected by flow cytometry.

RESULTSHMGB1 level in the supernatant \[(4.3 +/- 0.9) ng/ml\] of the irradiated MSC was significantly higher than that in control \[(0.4 +/- 0.2) ng/ml\] (P < 0.01). Human cord blood CD34(+) cells expressed the HMGB1 receptors RAGE, TLR2 and TLR4. The HMGB1-treated CD34(+) cells contained higher proportions of CD13(+) \[(32.6 +/- 5.9)% vs (18.4 +/- 3.8)%\], CD14(+)\[(25.4 +/- 4.4)% vs (12.6 +/- 2.7)%\], CD11c(+) \[(20.3 +/- 3.9)% vs (9.8 +/- 2.1)%\], CD71(+) \[(47.1 +/- 7.4)% vs (26.6 +/- 4.6)%\] cells compared with control group did. But HMGB1 did not induce the generation of CD41(+) cells \[(1.3 +/- 0.5)% vs (1.1 +/- 0.4)%\]. Furthermore, HMGB1 profoundly induced the growth of BFU-E, CFU-GM and total CFU in a dose-dependent manner, and this effect was partially inhibited by TLR2 and TLR4 antibodies.

CONCLUSIONHuman MSC treated with gamma-ray irradiation can release HMGB1, which can induce the proliferation and differentiation of human cord CD34(+) cells.