Oct4 Expression and Mesenchymal Stromal Cell Plasticity

Mesenchymal stromal cells (MSCs) have the capacity to differentiate along multiple lineages and are now in cell therapy clinical trials, especially for injured myocardium. Mechanisms mediating tissue regeneration remain unclear and are likely multifactorial. We recently showed that bone marrow-derived murine MSCs can acquire cardiac markers but retain MSCs properties when co-cultured with rat embryonic cardiomyocytes (RECs) (Rose et. al., Stem Cells. Aug7, 2008). The aim of our study was to determine whether expression of the embryonic transcription factor, Oct4 was modulated in this model of MSC plasticity. Wild-type Fvb mouse MSCs (passage 4) were co-cultured with RECs for 5 days and expression of Oct4, Nanog and Sox2, was analyzed by qRT-PCR with mouse-specific primers. Oct4 protein was assessed by immunocytochemistry (ICC) and flow cytometry (FC). The MSCs expressed Oct4, Nanog, and Sox2 transcripts. After co-culture, mRNA levels for Oct4 and Sox2 were upregulated 2.6±1.2-fold (p<0.05) and 2.4±0.4-fold (p<0.05), respectively, compared with MSCs controls, in contrast to Nanog gene expression which remained unchanged (1.2±0.3-fold; p=ns). 83±9% of MSCs nuclei were positive for Oct4 by ICC. To distinguish mouse from rat cells in co-culture, cells were stained with an anti-mouse CD44 antibody which does not cross react with rat CD44. CD44 is expressed on all MSCs and absent on RECs. Flow cytometry showed that Oct4 was over-expressed in CD44+ cells after co-culture. Our data demonstrate that these embryonic transcription factors are constitutively expressed in murine MSCs and that Oct4 and Sox2 transcript levels are increased after co-culture with RECs. Oct4, Nanog and Sox2 are known to maintain pluripotency of embryonic stem cells. Moreover, induced pluripotent stem cells can be generated from mouse fibroblasts by the introduction of Oct4 and Sox2 without the need for Nanog (