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E.-M. Demmerath et al.
sions in PGE2-treated cells (Figure 3E and Online Supplementary Figure S3B). Considering this, the reduced susceptibility of PGE2-treated HSPCs to taxol and etopo- side might be rather due to the proliferation repression than to deregulated apoptosis signaling since both drugs primarily target proliferating cells. We hypothesized that PGE2-mediated inhibition of cell proliferation 24 h prior cytotoxic stress would further reduce susceptibility to apoptosis but noted no additional benefit (Online Supplementary Figure S2C).
To test whether the protective in vitro effect of PGE2 can be translated to an in vivo situation, we irradiated recipient mice sublethally four weeks after xenotrans- plantation. A second group of xenograft mice was sub- jected once daily to etoposide for one week to better mimic a chemotherapy cycle. Animals from both groups were treated daily with dmPGE2 at a dose that had been shown earlier to protect murine HSPCs from apoptosis induced by sublethal irradiation in vivo.9 Seven days after treatment, animals were sacrificed and analyzed.
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Figure 4. Prostaglandin E2 (PGE2) does not promote human hematopoietic regeneration. (A and B) Human CD34+ cells were transplanted into sublethally irradiated Rag2−/−γc−/− mice. Four weeks later, mice were irradiated with 3 Gy or left untreated. Mice that were irradiated received daily injections of dmPGE2. Eight days after irradiation, mice were sacrificed and % human CD45+ cells were determined in bone marrow (BM) (A) and spleen (B). Bars represent means±Standard Error of Mean (SEM) of n=4-7 animals from 5 independent experiments. Mann-Whitney test, *P≤0.05; **P≤0.01; ***P≤0.001. (C-F) Human CD34+ cells were transplanted into sublethally irradiated Rag2−/−γc−/− mice. Four weeks later, mice were treated daily with etoposide alone, or together with dmPGE2. Eight days after treatment start, mice were sacrificed and % human CD45+ cells was determined in BM (C) and spleen (E). Cell counts of human CD45+ cells were determined in BM (D) and spleen (F). Bars represent means±SEM of 2-7 animals from at least 2 independent experiments.
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haematologica | 2019; 104(4)