During the last fiscal year, the following advances were made: 1) Biological activity of stem cells The development of mouse genetic tools has made a significant contribution to the understanding of skeletal and hematopoietic stem cell niches in bone marrow. However, many experimental designs (e.g., selections of marker genes, target vector constructions, and choices of reporter murine strains) have unavoidable technological limitations and bias, which lead to experimental discrepancies, data reproducibility issues, and frequent data misinterpretation. Consequently, there are a number of conflicting views relating to fundamental biological questions, including origins and locations of skeletal and hematopoietic stem cells in the bone marrow. This year, we systematically reviewed complex data sets and provided comprehensive analyses of technological benefits, pitfalls, and challenges in frequently used mouse models, and discuss their translational relevance to human stem cell biology. In particular, we emphasized the important roles of using large human genomic data-informatics in facilitating genetic analyses of mouse models and resolving existing controversies in mouse and human bone marrow stromal (skeletal) stem cell biology (Stem Cell Reports, 14:1343-1368, 2017). As mentioned above, there is a great deal of controversy on the origins of various bone marrow stem-cell niches, cell identities, and their physiological roles in bone marrow. In order to resolve these issues, we have proposed a new concept of paralogous stem-cell niches; that is, progressively altered parallel niches within an individual species throughout the life span of the organism. Based on analysis of transcriptional signatures in two genes that encode Nestin-GFP and leptin receptors, which are frequently used to monitor SSC lineage development in murine bone marrow, a putative paralogous stem-cell niche code seems to be likely. A dynamic paralogous bone marrow niche model appears to explain the coupling and uncoupling mechanisms between bone marrow stem cell niches and their zones of active regeneration during different stages of development. Better characterization of these paralogous bone marrow niches should resolve the existing controversies such as where these niches are located, what their composition is, and how they are regulated (Stem Cells, 36:11-21, 2018). 2) Role in disease Bisphosphonates (BPs) are currently used in the treatment of diverse bone diseases including fibrous dysplasia of bone (FD). In pediatric patients, a radiographic consequence of cyclical administration of BPs is the development of sclerotic bands (bands of dense mineral), otherwise known as zebra lines, which result from the temporary inhibition of osteoclastic activity at the time of drug treatment. We had the opportunity to study a series of histological sections and x-rays take from a child with McCune-Albright syndrome (FD in addition to hyperfunctioning endocrinopathies and skin hyperpigmentation) treated with cyclical intravenous infusions of the bisphosphonate, pamidronate. Conventional radiography, contact microradiography, histology, and backscattered electron image analysis demonstrated that zebra lines formed only where bone was normal, were arrested at the boundary between FD-unaffected and FD-affected bone where bone is sclerotic, and were absent within the undermineralized FD bone. Moreover, in spite of the treatment, the FD lesions continued to expand. This case report is unique because no previously published studies correlated the radiographic and the histologic features of BP-induced zebra lines in the metaphysis of an FD-affected long bone of the limbs (Skeletal Radiol 46:1435-1439, 2017). 3) Stem cells in tissue engineering and regenerative medicine BMSCs have classically been cultured in media supplemented with fetal bovine serum (FBS). As an alternative to FBS, pooled solvent detergent apheresis platelets, HPGF-C18, was evaluated for BMSC culture in order to eliminate a xenogenic component of the growth medium. A comparison BMSCs at passage 2 revealed that 10% HPGF-C18 produced similar cell numbers as 20% FBS. Marrow aspirates from 5 healthy subjects were cultured for 4 passages in 10% HPGF-C18 or 20% FBS. Primary cultures of marrow aspirates in 10% HPGF-C18 and 20% FBS yielded similar numbers and colony forming efficiency. After 4 passages, 10% HPGF-C18 and 20% FBS yielded similar numbers of BMSCs, and surface marker expression patterns. However, gene and microRNA expression analysis revealed that BMSCs cultured under the two conditions had distinct expression profiles. Gene Set Enrichment Analysis (GSEA) revealed HPGF-C18-cultured BMSCs were enriched in metabolic processing and biosynthetic pathways, cell proliferation and cell cycle pathways, and immune response pathways. FBS-cultured BMSCs were enriched in MAPK signaling, TGF-beta signaling, cell adhesion and extracellular matrix pathways. Differently expressed microRNAs were related to the osteogenesis of BMSCs. The supernatant of HPGF-C18 BMSCs had higher levels of PEDF and TGFB1 and lower levels of IL6, VEGF, SDF1 and PLGF. Traditional measures, expansion, surface marker expression and inhibition of MLRs suggest that BMSC cultured in HPGF-C18 and FBS were similar, but analysis at the molecular level revealed many differences. BMSCs cultured in HPGF-C18 should be assessed in specific functional assays that reflect application-specific potency before substituting FBS with HPGF-C18 (J Transl Med 14:65, 2018).
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