Enhanced Homing of HSPCs After Treatment with Prostaglandin E2 (PGE2) May Be An Effect of Transcriptional Regulation of CXC Chemokine Receptor 4 (CXCR4) Through Hypoxia Inducible Factor 1α (HIF1α)

Abstract 918 Hematopoietic stem cell (HSC) transplantation is widely used to treat a number of hematological malignancies. However, to be effective, transplanted HSCs must efficiently “home” to their supportive niches within the bone marrow. Limited HSC number and poor function are complications of transplant in some circumstances, and can lead to impaired immune function and bone marrow failure. Enhancing HSC homing is a strategy to improve stem cell transplantation outcomes. We have previously shown that treatment of mouse or human HSCs with 1μM 16–16 dimethyl PGE 2 (dmPGE 2 ) ex vivo increases their bone marrow homing efficiency and engraftment, coordinate with an increase in surface CXCR4 expression. The transcription factor Hypoxia Inducible Factor 1α (HIF1α) has been shown to up-regulate CXCR4 in certain cancer models. In addition, PGE 2 has been shown to stabilize HIF1α under normoxic conditions. We hypothesized that the effects of PGE 2 on CXCR4 expression and homing might result from stabilization of HIF1α and its subsequent transcriptional activity in the transplanted HSCs. Treatment of lineage neg bone marrow cells with 1μM dmPGE 2 resulted in a 33 ± 8.6% increase in HIF1α protein levels over vehicle (p neg Sca-1 pos c-kit pos (SKL) cells (11.3 ± 3.9% MFI over vehicle, p + umbilical cord blood cells (20.1 ± 3.6% MFI over vehicle), which was comparable to treatment with dmPGE 2 . This increase in CXCR4 expression translated to a functional increase in SKL migration to SDF-1 (46.7 ± 1.5% migration compared to 35 ± 3.1% migration in vehicle, p 2 on CXCR4 were due effects on HIF1 transcriptional activity, we employed two mouse hepatoma cell lines (ARNT- and ARNT+). These cells express detectable levels of CXCR4 as well as all four of the PGE 2 G-protein coupled receptors (EP1-4). However the ARNT- cell line lacks the HIF nuclear translocator, and thus lacks HIF1 transcriptional activity. While ARNT+ cells showed the characteristic increase in CXCR4 cell surface protein (91.3 ± 28.7%) and mRNA (5.69-fold increase) after treatment with 1μM dmPGE 2 , ARNT- cells failed to show a similar up-regulation of CXCR4 protein (15 ± 6.1% increase) and mRNA (0.44-fold increase) after PGE 2 treatment. These data suggest that HIF1 transcriptional activity is necessary for PGE 2 -mediated CXCR4 regulation. To determine whether HIF1α stabilization has similar effects on HSC function after transplant, in vivo homing studies were performed. Pulse-treatment of mouse SKL cells with 5μM DMOG ex vivo for 1 hour resulted in a 2.9-fold increase in homing (p 2 . Treatment of donor cells with the CXCR4 antagonist AMD3100 resulted in a statistically significant reduction in SKL homing (74.8 ± 9%, p 2 treatment. These data suggest the effects of PGE 2 on CXCR4 expression are at least partially due to the stabilization of HIF1α. Due to the importance of HIF1α and its involvement in HSC regulation, PGE 2 treatment could also have effects on other pathways associated with the hypoxic response mediated through HIF1α that could be targeted to modulate HSC function. Further studies could potentially identify more specific targets to improve the efficacy of HSCs after transplant. Disclosures: Hoggatt: Fate Therapeutics: Consultancy. Pelus: Fate Therapeutics: Consultancy.