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The role of corticosterone (Cort), the immune system's major stress hormone, in the regulation of hematopoietic stem and progenitor cells (HSPCs) and their dynamic bone marrow (BM) microenvironment is currently unknown. We report that corticotropin-releasing factor receptor 1 (CRFR1) mutant mice with chronically low Cort levels showed aberrant HSPC regulation, having higher HSPC numbers and upregulation of the chemokine CXCL12, phenotypes that were restored by Cort supplementation. Expanded stromal progenitors known to support HSPCs were also observed in these low-Cort-containing mice. A similar phenotype was induced in wild-type (WT) mice by Metyrapone, a Cort synthesis inhibitor. Conversely, high Cort exposure induced HSPC apoptosis, reduced long-term BM repopulation and decreased stromal progenitor cell numbers. We documented circadian oscillations of Cort in WT BM but not in CRFR1 mutant mice, leading to diminished circadian BM CXCL12 fluctuations and increased number of circulating HSPCs in these mice. Finally, low Cort induced expansion of stromal progenitors, CXCL12 expression, HSPC proliferation and BM repopulation capacity, involving Notch1 signaling. This was associated with upregulation of the Notch ligand, Jagged1, in BM myeloid cells. Our results suggest that daily physiologic Cort oscillations are critical for balanced HSPC proliferation and function involving Notch1 signaling and their supportive BM microenvironment.

Objective: To determine the role of bone marrow biopsy (BMBX), performed in association with comprehensive blood and imaging tests, in the evaluation of patients with fever of unknown origin (FUO)., Patients and Methods: We reviewed the medical records of 475 hospitalized patients who underwent BMBX in our medical center from January 1, 2005, to April 30, 2010. We identified 75 patients who fulfilled the accepted classic Petersdorf criteria for FUO. All patients underwent in-hospital investigation for fever, including chest and abdominal computed tomography., Results: In 20 patients (26.7%), BMBX established the final diagnosis. Sixteen patients had hematologic disorders, including 8 patients with non-Hodgkin lymphoma, 2 with acute leukemia, 1 with multiple myeloma, 1 with myelodysplastic syndrome, and 4 with myeloproliferative disorders. The remaining patients with diagnostic BMBX specimens had solid tumors (2 patients), granulomatous disease (1 patient), and hemophagocytic syndrome (1 patient). Multivariate analysis revealed the following as the significant positive predictive parameters for a diagnostic BMBX specimen: male sex (odds ratio [OR], 7.35; 95% confidence interval [CI], 1.19-45.45), clinical lymphadenopathy (OR, 21.98; 95% CI, 1.97-245.66), anemia (OR, 2.21; 95% CI, 1.28-3.80), and increased lactate dehydrogenase levels (OR, 1.003; 95% CI, 1.001-1.006)., Conclusion: Bone marrow biopsy is still a useful ancillary procedure for establishing the diagnosis of FUO, particularly if used in the appropriate clinical setting. Clinical and laboratory parameters associated with hematologic disease are predictive of a diagnostic BMBX specimen in patients with FUO., (Copyright © 2012 Mayo Foundation for Medical Education and Research. Published by Elsevier Inc. All rights reserved.)

Bone marrow niches are specialized microenvironments comprising a heterogeneous population of cells that support and regulate hematopoietic stem and progenitor cells. Considerable advances made in the field of hematopoiesis reveal a cross talk between cells, cytokines and neurotransmitters of the hematopoietic, immune and skeletal systems. Dynamic modulation and regulation of stem cells and their niches in response to internal and external stimuli are essential for homeostasis, host defense and repair. This review presents evidence to substantiate stem cell regulation via the "brain-bone-blood triad" beginning at the embryonic stage and continuing to adulthood.