Expression of the G-CSF receptor on bone marrow monocytes is sufficient to trigger HSC mobilization in response to G-CSF, in part via effects on osteoblast lineage cells.

Recent studies demonstrate that inflammatory signals regulate hematopoietic stem cells (HSCs). Granulocyte-colony stimulating factor (G-CSF) is often induced with infection and plays a key role in the stress granulopoiesis response. However, its effects on HSCs are less clear. Herein, we show that treatment with G-CSF induces expansion and increased quiescence of phenotypic HSCs, but causes a marked, cell-autonomous HSC repopulating defect associated with induction of toll-like receptor (TLR) expression and signaling. The G-CSF-mediated expansion of HSCs is reduced in mice lacking TLR2, TLR4 or the TLR signaling adaptor MyD88. Induction of HSC quiescence is abrogated in mice lacking MyD88 or in mice treated with antibiotics to suppress intestinal flora. Finally, loss of TLR4 or germ free conditions mitigates the G-CSF-mediated HSC repopulating defect. These data suggest that low level TLR agonist production by commensal flora contributes to the regulation of HSC function and that G-CSF negatively regulates HSCs, in part, by enhancing TLR signaling.

Shwachman-Diamond Syndrome (SDS) is a rare multisystem disorder characterized by exocrine pancreatic insuffi-ciency, bone marrow dysfunction, and metaphyseal chondrodysplasia. Recent studies show that mutations of SBDS, a gene of unknown function, are present in the majority of patients with SDS. In the present study, we show that most, but not all, patients classified based on rigorous clinical criteria as having SDS had compound heterozygous mutations of SBDS. Full-length SBDS protein was not detected in leukocytes of SDS patients with the most common SBDS mutations, consistent with a loss-of-function mechanism. In contrast, SBDS protein was expressed at normal levels in SDS patients without SBDS mutations. These data confirm the absence of SBDS mutations in this subgroup of patients and suggest that SDS is a genetically heterogeneous disorder. The presence (or absence) of SBDS mutations may define subgroups of patients with SDS who share distinct clinical features or natural history. (Blood. 2004;104: 3588-3590) Introduction Shwachman-Diamond Syndrome (SDS) is a rare multisystem disorder characterized by exocrine pancreatic insufficiency, bone marrow dysfunction, and metaphyseal chondrodyspla-sia. 1-5 SDS is the second most common cause of congenital exocrine pancreatic insufficiency, after cystic fibrosis. Bone marrow dysfunction is present in nearly all patients with SDS. 3-6 In the largest published series (88 patients), chronic or intermittent neutropenia was present in 97%. 5 Anemia and thrombocyto-penia were present in more than a third of patients. Patients with SDS have a marked propensity to develop myelodysplasia or acute myeloid leukemia. 6-8 SDS is inherited in an autosomal recessive fashion. 9 Recently , Boocock et al 10 reported that compound heterozygous mutations of the SBDS (Shwachman-Bodian-Diamond syndrome) gene on chromosome 7 were present in the majority of patients with SDS. Most of these mutations resulted from gene conversion with a neighboring pseudogene (SBDSP). Similar data were reported in a smaller series of patients of Japanese ancestry. 11 Most of the SBDS mutations are predicted to truncate a substantial portion of the SBDS protein, suggesting that they act in a loss-of-function manner. Herein, we show that most, but not all, patients classified prospectively based on clinical criteria as having probable SDS had SBDS gene mutations. Moreover, a strong correlation between SBDS genotype and expression of full-length SBDS protein was observed. Study design Human subjects There were 33 families who attended the Second International Conference on Shwachman-Diamond Syndrome in St Louis in 1999 and who were invited to participate in a study to elucidate the genetic basis of SDS. After obtaining informed consent, a thorough history, physical examination, review of medical records, and selected laboratory testing were performed. In addition, genomic DNA was extracted from peripheral blood leukocytes using standard protocols. The diagnosis of SDS was based on the presence of the followin...

Vascular disrupting agents (VDA) cause acute shutdown of abnormal established tumor vasculature, followed by massive intratumoral hypoxia and necrosis. However, a viable rim of tumor tissue invariably remains from which tumor regrowth rapidly resumes. We have recently shown that an acute systemic mobilization and homing of bone marrow-derived circulating endothelial precursor (CEP) cells could promote tumor regrowth following treatment with either a VDA or certain chemotherapy drugs. The molecular mediators of this systemic reactive host process are unknown. Here, we show that following treatment of mice with OXi-4503, a second-generation potent prodrug derivative of combretastatin-A4 phosphate, rapid increases in circulating plasma vascular endothelial growth factor, stromal derived factor-1 (SDF-1), and granulocyte colonystimulating factor (G-CSF) levels are detected. With the aim of determining whether G-CSF is involved in VDA-induced CEP mobilization, mutant G-CSF-R À/À mice were treated with OXi-4503. We found that as opposed to wild-type controls, G-CSF-R À/À mice failed to mobilize CEPs or show induction of SDF-1 plasma levels. Furthermore, Lewis lung carcinomas grown in such mice treated with OXi-4503 showed greater levels of necrosis compared with tumors treated in wild-type mice. Evidence for rapid elevations in circulating plasma G-CSF, vascular endothelial growth factor, and SDF-1 were also observed in patients with VDA (combretastatin-A4 phosphate)-treated cancer. These results highlight the possible effect of druginduced G-CSF on tumor regrowth following certain cytotoxic drug therapies, in this case using a VDA, and hence G-CSF as a possible therapeutic target.

No abstract