Tissue-Specific Molecular Signature May Explain Differentiative Bias of Human MSC from Different Tissues.

Regulatory factors integral to the differentiation of mesenchymal stem cells (MSC) and to their maintenance of pluripotency are not yet well defined. Characterizing the repertoire of such factors present within phenotypically similar MSC isolated from different tissues would provide pivotal insight into the developmental and regenerative capabilities of the MSC present within each of these tissues and could also reveal the ideal MSC sources to use for tissue-specific transdifferentiation in future stem cell therapies. In previous studies, we showed that Stro-1 + MSC isolated from various human tissues exhibit a predisposition to differentiate into cells of their tissue of origin following transplantation. Here, we examined these Stro-1 + human MSC from fetal brain, liver, lung, and adult bone marrow (BM) to identify genes common to MSC from all 4 tissues as well as differentially expressed genes to define the mechanism responsible for the in vivo differentiative bias of these MSC. We compared the transcriptomes of Stro-1 + MSC from each tissue with Affymetrix GeneChip microarrays, and analyzed the resultant data with GeneSifter software. Quantitative RT-PCR was used to confirm altered transcription levels of representative genes which the microarray indicated were differentially expressed. We identified 256 transcripts that were specifically upregulated in the BM-derived MSC relative to MSC from the other tissues, including Early B-cell factor 1, a Notch regulated transcription factor, and HoxA10 which is involved in hematopoietic lineage commitment. We also identified 145 transcripts that were downregulated in BM-derived MSC compared to MSC from the other tissues. In the liver-derived MSC, we identified 298 downregulated transcripts and 168 upregulated transcripts, including the putative lymphocyte G0/G1 switch gene 2 (G0S2), which is induced in the liver in response to fasting and plays a key role in adipogenesis. The lung-derived MSC displayed 316 downregulated transcripts and 173 upregulated transcripts, including secreted frizzled-related protein 1, a mediator between the WNT and hedgehog pathways, and SMAD-specific E3 ubiquitin protein ligase 2 (SMURF2), which plays a critical role in the regulation of TGF-b-Smad signaling. Brain-derived MSC exhibited 169 downregulated transcripts and 328 upregulated transcripts including Jagged 1, a Notch ligand involved in maintenance of an undifferentiated state; TAFA5, a brain-specific regulator of immune and nervous cells; and Growth-arrest specific 1, a potential tumor suppressor growth regulatory protein. Interestingly, MSC derived from liver and lung possessed similar gene expression profiles, exhibiting upregulation of similar genes when compared to MSC from brain and BM, perhaps due to their shared endodermal derivation. It is also of note that many of the Hox genes were found to be differentially regulated between the MSC from the four tissues, suggesting this gene family may play a role in the MSCs’ tissue identity. In conclusion, our studies show that MSC derived from 4 distinct tissues express many common genes, but also possess unique molecular signatures that tie them to their tissue of origin. These results provide a possible explanation for the propensity of MSC to give rise to cells of their native tissue upon transplantation and will also pave the way towards elucidating the precise genes that allow MSC to give rise to seemingly unrelated tissues in vivo.