ObjectiveControversy surrounds the identity and functionality of rare bone marrow–derived multipotential stromal cells (BM‐MSCs), including their differentiation capabilities, their relationship to pericytes and hematopoiesis‐supporting stromal cells, and the relevance of their culture‐expanded progeny in studies of skeletal biology and development of cell‐based therapies. The aim of this study was to clarify the nature of candidate BM‐MSCs by profiling transcripts that reflect different aspects of their putative functions in vivo.MethodsRare, sorted BM‐derived CD45−/low CD271bright (CD271) cells were analyzed using 96‐gene expression arrays focused on transcripts relevant to mesenchymal‐lineage differentiation (toward bone, cartilage, fat, or muscle), hematopoietic and stromal support, and molecules critical to skeletal homeostasis. These cells were compared to matched CD45+ CD271− hematopoietic‐lineage cells, culture‐expanded MSCs, and skin fibroblasts. When feasible, transcription was validated using flow cytometry.ResultsCD271 cells had a transcriptional profile consistent with the multiple fates of in vivo MSCs, evident from the observed simultaneous expression of osteogenic, adipogenic, pericytic, and hematopoiesis‐supporting genes (e.g., SP7 [osterix], FABP4 [fatty acid binding protein 4], ANGPT1 [angiopoietin 1], and CXCL12 [stromal cell–derived factor 1], respectively). Compared to culture‐expanded MSCs and fibroblasts, CD271 cells exhibited greater transcriptional activity, particularly with respect to Wnt‐related genes (>1,000‐fold increased expression of FRZB [secreted frizzled‐related protein 3] and WIF1 [Wnt inhibitory factor 1]). A number of transcripts were identified as novel markers of MSCs.ConclusionThe native, BM‐derived in vivo MSC population is endowed with a gene signature that is compatible with multiple functions, reflecting the topographic bone niche of these cells, and their signature is significantly different from that of culture‐expanded MSCs. This indicates that studies of the biologic functions of MSCs in musculoskeletal diseases, including osteoporosis and osteoarthritis, should focus on in vivo MSCs, rather than their culture‐adapted progeny.

Aspiration of iliac crest bone marrow (ICBM) remains the most frequent technique used in harvesting multipotential stromal cells (MSCs) for bone regeneration. Although this tissue type is easily accessed by a surgeon, it has a low frequency of MSCs, which is significant given the high cell numbers required for bone regeneration strategies. Lipoaspirates possess higher MSC frequencies, albeit cells with a differentiation profile less suited to orthopaedic interventions. Intra-medullary cavities of long bones have previously been shown to harbour MSCs in animals, however evaluation of their frequency, differentiation capacity and phenotype in humans had not previously been performed.Long bone fatty bone marrow (LBFBM) was collected prior to harvesting bone graft. Basic cellular compositions of donor-matched LBFBM and ICBM aspirates, including the numbers of CD34+ hematopoietic stem cells and CD31+ endothelial cells, were similar. MSCs were enumerated using colony-forming-unit-fibroblast assays and flow cytometry for the presence of a resident LBFBM CD45−/low CD271+ MSC population and revealed a trend for higher MSC numbers (average 5 fold, n = 6) per millilitre of LBFBM compared to donor-matched ICBM. Functional characteristics of resident MSCs, including their growth rates, differentiation potentials and surface phenotypes (CD73+CD105+CD90+) before and after culture-amplification, were similar. Enhanced numbers of MSCs could be recovered following brief enzymatic treatment of solid fragments of LBFBM.Our findings therefore reveal that the intramedullary cavity of the human femur is a depot of MSCs, which, although closely associated with fat, have a differentiation profile equivalent to ICBM. This anatomical site is frequently accessed by the orthopaedic/trauma surgeon and aspiration of the intramedullary cavity represents a ‘low-tech’ method of harvesting potentially large numbers of MSCs for regenerative therapies and research.This article is part of a Special Issue entitled: Interactions Between Bone, Adipose Tissue and Metabolism.

Bone reconstruction requires the use of autografts from patients' iliac crest (IC); for large-volume defects bone void fillers and autologous mesenchymal stem cells (MSCs) are often added. The Reamer/Irrigator/Aspirator (RIA) device provides the means of harvesting large amounts of autograft and additionally yields a waste bag containing MSCs, which is currently discarded. The aim of this study was to enumerate and characterise native MSCs from RIA waste bag and compare them to 'gold-standard' donormatched MSCs from IC bone marrow (BM). IC-BM from age matched trauma patients was used as control.In RIA waste bags the median MSC yield established using a colony-forming fibroblast assay was 314333 (range 5 x 10 4 -1.4 x 10 6 ), equivalent to approximately one litre of IC-BM aspirate. CD271+ cells were present at high levels in RIA waste bags, had MSC surface phenotype (CD90 + CD73 + CD105 + CD34 -CD61 -CD19 -CD31 -CD33 -) and expressed genes associated with multipotentiality, osteogenesis, adipogenesis and angiogenic support. RIA-CD271 + MSCs were transcriptionally similar to donormatched IC-CD271 + MSCs (76 % transcripts); with the majority of bone-related and Wnt pathway molecules being expressed at comparable levels. Lower-level expression of MCAM/CD146 and 5/13 hypoxia-related molecules was found in RIA-CD271 + MSCs, potentially reflecting their native residence in a more hypoxic environment of the endosteum and bone cortex.These data suggest that long bones contain very large numbers of MSCs, transcriptionally-similar to IC-BM MSCs; they can be procured by reaming using the RIA device and used, following concentration, as autologous and potentially allogeneic bone repair therapy.

Objective: To compare the difference in diameter of the medullary cavity of the humerus in Arab and South Asian patients in Kuwait. Subjects and Methods: In 46 patients (29 Arab, 17 South Asian) treated at Al-Razi Hospital, Kuwait, for diaphyseal fracture of the humerus, the medullary cavity of the humerus on the radiographs of the uninjured (contralateral side) was examined. Bone density was also measured. Statistical significance was calculated by parametric and nonparametric test using SPSS package. Results: South Asians had a significantly narrower medullary cavity (p < 0.05) and higher cortical indices (p < 0.05) than Arabs, and also a narrower external diameter of the humerus at levels 5 and 6 (p < 0.05). Conclusion: In cases of fracture of the humerus, radiographic measurements of the diameter of the medullary cavity of the uninjured side were essential in selecting the appropriate fixation device.