Accidental or deliberate ionizing radiation exposure can be fatal due to widespread hematopoietic destruction. However, little is known about either the course of injury or the molecular pathways that regulate the subsequent regenerative response. Here we show that the Wnt signaling pathway is critically important for regeneration after radiation-induced injury. Using Wnt reporter mice, we show that radiation triggers activation of Wnt signaling in hematopoietic stem and progenitor cells. b-Catenin-deficient mice, which lack the ability to activate canonical Wnt signaling, exhibited impaired hematopoietic stem cell regeneration and bone marrow recovery after radiation. We found that, as part of the mechanism, hematopoietic stem cells lacking b-catenin fail to suppress the generation of reactive oxygen species and cannot resolve DNA double-strand breaks after radiation. Consistent with the impaired response to radiation, b-catenin-deficient mice are also unable to recover effectively after chemotherapy. Collectively, these data indicate that regenerative responses to distinct hematopoietic injuries share a genetic dependence on b-catenin and raise the possibility that modulation of Wnt signaling may be a path to improving bone marrow recovery after damage.

Purpose: Myelodysplastic syndrome (MDS) is associated with a dysregulated innate immune system. The purpose of this study was to determine whether modulation of the innate immune system via high mobility group box-1 (HMGB1) could reduce cell viability in MDS.Experimental Design: We quantified HMGB1 in an MDS cell line MDS-L and in primary MDS cells compared with nonmalignant hematopoietic cells. We performed loss-offunction studies of HMGB1 using pooled siRNAs and a small-molecule inhibitor sivelestat compared with standard chemotherapy. We measured levels of engraftment of MDS-L cells in NOD-scidIL2Rg null (NSG) mice following treatment with sivelestat. Mechanistically, we interrogated cell survival pathways and 45 targets within the NFkB pathway using both protein analysis and a proteome profiler array.Results: We discovered that HMGB1 had increased expression in both MDS-L cells and in primary CD34 þ MDS cells compared with healthy CD34 þ hematopoietic cells. Sivelestat impaired MDS cell expansion, increased cellular death, and spared healthy hematopoietic cells. MDS-L marrow engraftment is reduced significantly at 17 weeks following treatment with sivelestat compared with control mice. Treatment of CD34 þ MDS cells with sivelestat and azacitidine or decitabine was additive to increase apoptotic cell death compared with chemotherapy alone. Sivelestat promoted apoptosis with increased expression of PUMA, activated caspase 3, and increased DNA double-strand breaks. Inhibition of HMGB1 reduced levels of Toll-like receptors (TLR) and suppressed activation of NFkB in MDS-L cells.Conclusions: Inhibition of HMGB1 could promote MDS cell death and alter innate immune responses via suppression of NFkB pathways.

Hematopoietic stem and progenitor cells (HSPCs) depend on regulatory cytokines from the marrow microenvironment. From an unbiased cytokine screen of murine marrow supernatants, we identified CC motif chemokine ligand 5 (CCL5) as an endothelial cell-secreted hematopoietic growth factor. Following treatment with CCL5, hematopoietic regeneration is accelerated and survival is prolonged after radiation. In mice with deletion of Ccr5, hematopoietic regeneration is delayed compared to control mice. Deletion of Ccr5 specifically in hematopoietic cells was sufficient to delay regeneration, while the deletion of Ccr5 in stromal/endothelial cells was not. Mechanistically, CCL5 promotes hematopoietic cell cycling and cell survival. Like murine hematopoietic cells, human hematopoietic cells (cord blood, healthy marrow, and peripheral blood) increase CCR5 expression after radiation exposure to promote cell survival. These data establish that CCL5 and CCR5 signaling play critical roles in hematopoietic regeneration and could serve as therapeutic targets to shorten the duration of myelosuppression.

Background Graft-versus-host disease (GVHD) complicates half of hematopoietic stem cell transplants (HCT), and the gastrointestinal tract is commonly affected. Endoscopic biopsies have a key role in the diagnosis. The optimal procedure(s) to perform and site(s) to biopsy remain unclear. Methods We retrospectively analyzed the charts of all adult patients who underwent allogeneic HCT at Duke University Medical Center between 1/1/05 and 1/1/11 and extracted data from those who underwent endoscopic biopsy for suspected GVHD. All histology was re-evaluated by blinded pathologists using 2006 NIH diagnostic criteria and then compared to the original clinical diagnosis of GVHD. Results A total of 169 adult patients underwent 250 endoscopic procedures to evaluate GVHD. The sensitivity of biopsies for clinical GVHD was 76 and 72 % for upper and lower tract sites, respectively. In the presence of nausea, upper tract biopsies were positive for GVHD in 65 %, 70 % while lower tract biopsies were positive in 61–70 %. In the presence of diarrhea, lower tract biopsies were positive in 65 %, while upper tract sites were positive in 64–69 %. Twenty six (40 %) of the sixty-five endoscopies that simultaneously sampled upper and lower tract sites had discordant results. All were histologically positive for GVHD, yet 15 % of upper tract biopsies and 25 % of lower tract biopsies were negative. Conclusions In this large review, the overall sensitivity of biopsies taken during EGD and Flex-Sig was 76 and 72 %, respectively. A symptom-driven biopsy approach was not clearly supported as upper tract and lower tract biopsies were similarly diagnostic for GVHD regardless of symptoms.

Hematopoietic regeneration following chemotherapy may be distinct from regeneration following radiation. While we have shown that epidermal growth factor (EGF) accelerates regeneration following radiation, its role following chemotherapy is currently unknown. We sought to identify EGF as a hematopoietic growth factor for chemotherapy-induced myelosuppression. Following 5-fluorouracil (5-FU), EGF accelerated hematopoietic stem cell regeneration and prolonged survival compared with saline-treated mice. To mitigate chemotherapy-induced injury to endothelial cells in vivo, we deleted Bax in VEcadherin cells (VEcadherinCre;Bax mice). Following 5-FU, VEcadherinCre;Bax mice displayed preserved hematopoietic stem/progenitor content compared with littermate controls. 5-FU and EGF treatment resulted in increased cellular proliferation, decreased apoptosis, and increased DNA double-strand break repair by non-homologous end-joining recombination compared with saline-treated control mice. When granulocyte colony stimulating factor (G-CSF) is given with EGF, this combination was synergistic for regeneration compared with either G-CSF or EGF alone. EGF increased G-CSF receptor (G-CSFR) expression following 5-FU. Conversely, G-CSF treatment increased both EGF receptor (EGFR) and phosphorylation of EGFR in hematopoietic stem/progenitor cells. In humans, the expression of EGFR is increased in patients with colorectal cancer treated with 5-FU compared with cancer patients not on 5-FU. Similarly, EGFR signaling is responsive to G-CSF in humans in vivo with both increased EGFR and phospho-EGFR in healthy human donors following G-CSF treatment compared with donors who did not receive G-CSF. These data identify EGF as a hematopoietic growth factor following myelosuppressive chemotherapy and that dual therapy with EGF and G-CSF may be an effective method to accelerate hematopoietic regeneration. Stem Cells 2018;36:252-264.