Functional and molecular characterisation of mesenchymal stem cells derived from bone marrow and dental tissues.

Abstract

Mesenchymal stromal/stem cells (MSCs) are multipotent, progenitor cells with the ability to differentiate into cells of mesenchymal and non-mesenchymal tissues in vitro and in vivo. Characterisation of MSC-like cells residing in dental pulp (DPSC) and periodontal ligament (PDLSC) tissues has shown that these cells exhibit similar features to bone marrow stromal cells (BMSCs). The present project proposed that BMSCs, DPSCs and PDLSCs contain heterogeneous populations of progenitor cells including a minor subset of multipotential stem cells. Identification of the precise developmental stages and generation of gene expression profiles of these different cell populations will greatly improve our understanding of the fundamental cellular processes involved in MSC differentiation and proliferation pathways. Therefore, the aim of this PhD project was to assess the unique phenotype of BMSCs, DPSCs and PDLSCs and their differentiated progeny by studying their proliferative and differentiation potentials, and by assessing their gene expression profiles. Initial findings obtained from functional analyses of clonal populations present within BMSCs, DPSCs and PDLSCs support the hypothesis that within each of the populations, co-exist cells of varying levels of proliferation and differentiation potentials. Following on from these results, whole genome microarray analyses were used to determine gene expression patterns of clonal cell fractions exhibiting significant functional differences within each MSC population. The microarray data identified cohorts of differentially expressed genes in comparisons of cell clones of low proliferation potential and high/multi-differentiation potential within BMSC, DPSC and PDLSC populations. Further interrogation of the generated data identified 24 differentially up-regulated genes in long lived/multi-potential MSC clones, common to BMSC, DPSC and PDLSC populations. Specifically, E2F-2, LDB-2, PTTG-1 and TWIST-1, were identified as transcriptional regulators or co-regulators that may be involved in the proliferation and differentiation of these MSC populations. In light of the previously reported involvement of TWIST-1 in growth and development of BMSC, the effect of enforced TWIST-1 expression was investigated in DPSC and PDLSC populations. These findings demonstrated that TWIST-1 holds a stimulatory role in cell proliferation and is involved in the regulation of differentiation/commitment processes in MSCs. Overall, the identification of genes associated with MSCs of high growth and developmental potential lays the foundation for further definition of molecular mechanisms involved in MSC maintenance and survival. Elucidation of these fundamental processes is highly significant as it holds a critical role in the development of MSC-based tissue regeneration therapies.