A comparative study of the biological and molecular properties of mesenchymal stem cells isolated from bone marrow and the olfactory system

Neurodegenerative conditions such as Multiple Sclerosis (MS) and spinal cord injury (SCI) affect hundreds of thousands of people each year worldwide, and numerous cell transplant-based therapeutic strategies are being investigated to aid in the repair and regeneration of the central nervous system. Of particular interest are mesenchymal stem cells (MSCs), due to their differentiation potential, their immunomodulatory effects, and their ability to stimulate various biological properties due to the substantial variety of growth factors, chemokines, and other signalling molecules secreted by these cells. MSCs taken from the bone marrow (BM-MSCs) have demonstrated significant reparative potential in animal models of both MS and SCI. The question I address throughout this thesis however, is whether MSCs from another niche; the olfactory mucosa (OM-MSCs), are a preferable or at least alternative candidate for such therapies, compared to BM-MSCs, and if they are, why are they? Previous studies have shown that OM-MSCs can be purified and grown from human olfactory mucosa and when incubated with rat glial/neuronal co-cultures are capable of increasing axonal myelination, an effect not elicited by BM-MSCs. This potentially has great therapeutic benefit for a range of neurodegenerative conditions, as a significant part of the regenerative process involves replacing the protective myelin membrane which ensheaths axons. A comparative study of the two types of MSCs shows a number of similarities, including the expression of the same panel of MSC markers, a 64% homology in miRNA expression, an ability to differentiate towards bone and fat, and a propensity for bone formation when cultured on osteogenic nanotographies. This thesis also outlines a number of differences between each phenotype which suggest that OM-MSCs could even be a preferred alternative, especially in neuroregenerative therapies. OM-MSCs were shown to express significantly more Nestin than BM-MSCs, and to proliferate at a significantly higher rate, two observations which may be related. This increased proliferation would have enormous benefit for their use, as BM-MSCs are mitotically quite slow, and any MSC-based therapies would require very large numbers of cells. Twenty six different miRNA were shown to be differentially expressed between BM-MSCs and OM-MSCs. Three of these; miR-140-5p, miR-146a-5p, and miR-335-5p were linked to three important biological functions; myelination, cell survival, and cell proliferation respectively. These three biological functions, importantly, are ones which were observed as being behavioural differences between OM-MSCs and BM-MSCs. OM-MSCs were also shown to secrete significantly more of the pro-myelinating chemokine, CXCL12, which was confirmed as being regulated by the microRNA, miR-140-5p. This offered a potential mechanism for the pro-myelinating effect of OM-MSCs, and also opens up new research potential for investigating therapeutic targets to regulate myelination. The data presented in this thesis shows many similarities between BM-MSCs and OM-MSCs, but it also highlights some profound differences which suggest that either they originate from a different lineage entirely, or that the cellular niche that they reside in does indeed affect the differentiation and behaviour of mesenchymal stem cells.