Biological Activities Encoded by the Murine Mesenchymal Stem Cell Transcriptome Provide a Basis for Their Developmental Potential and Broad Therapeutic Efficacy

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Abstract
We used serial analysis of gene expression to catalog the transcriptome of murine mesenchymal stem cells (MSCs) enriched from bone marrow by immunodepletion. Interrogation of this database, results of which are delineated in the appended databases, revealed that immunodepleted murine MSCs (IDmMSCs) highly express transcripts encoding connective tissue proteins and factors modulating T-cell proliferation, inflammation, and bone turnover. Categorizing the transcriptome based on gene ontologies revealed the cells also expressed mRNAs encoding proteins that regulate mesoderm development or that are characteristic of determined mesenchymal cell lineages, thereby reflecting both their stem cell nature and differentiation potential. Additionally, IDmMSCs also expressed transcripts encoding proteins regulating angiogenesis, cell motility and communication, hematopoiesis, immunity and defense as well as neural activities. Immunostaining and fluorescence-activated cell sorting analysis revealed that expression of various regulatory proteins was restricted to distinct subpopulations of IDmMSCs. Moreover, in some cases, these proteins were absent or expressed at reduced levels in other murine MSC preparations or cell lines. Lastly, by comparing their transcriptome to that of 17 other murine cell types, we also identified 43 IDmMSC-specific transcripts, the nature of which reflects their varied functions in bone and marrow. Collectively, these results demonstrate that IDmMSC express a diverse repertoire of regulatory proteins, which likely accounts for their demonstrated efficacy in treating a wide variety of diseases. The restricted expression pattern of these proteins within populations suggests that the cellular composition of marrow stroma and its associated functions are more complex than previously envisioned.