Mesenchymal stem cells (MSCs) exist as an adult stem cell in major reservoirs primarily in the bone marrow and adipose tissue. Under normal physiologic conditions, MSCs serve mainly as the progenitor cell for adipocytes, chondrocytes, and osteocytes. The plasticity of MSCs has led researchers to investigate differentiation beyond their canonical lineages and since, in vitro studies have shown that MSCs can be induced to differentiate into renal cells, beta/islet cells, hepatocytes, cardiomyocytes, and even neurons. Differentiated MSCs exhibit changes in gene marker expression, morphology, and even gain functional characteristics. Previously, our lab has shown that neural-like characteristics can be induced in MSCs by exposure to the cyclic adenosine monophosphate (cAMP) elevating compounds, forskolin and isobutylmethylxanthine (IBMX). In addition to short-term neural-like morphology changes, MSCs gain expression of neural markers as well as sensitivity to dopamine. However, a molecular mechanism to explain why cAMP elevating compounds would have a proneural effect in MSCs is lacking. Differentiation of stem cells into a mature phenotype is strongly driven by transcription factors within a cell. Some transcription factors control regulation of so many genes required for the mature differentiated cell type that they are termed master transcriptional regulators. For example, during osteogenesis, the master transcriptional regulator Runx2 is essential for differentiation of MSCs to osteocytes. Yang et al. demonstrated that silencing the master transcriptional regulator, NRSF, in MSCs could induce several neural characteristics. Therefore, I hypothesized and went on to show that forskolin and IBMX could be driving neural-like differentiation of MSCs by regulating NRSF. Neural differentiation of MSCs has also been studied from a tissue engineering perspective. In particular, it has been demonstrated in several types of stem cells that culture on very soft substrates can promote neural differentiation. This phenomenon shows that stem cell differentiation can also be influenced by physical characteristics in its environment. However, the molecular mechanisms explaining how cells can sense and respond to soft surfaces to affect differentiation are still vaguely characterized. We hypothesized that since soft surfaces induce neural-like differentiation in stem cells that maybe soft surfaces were somehow affecting NRSF. We go on to show that soft PDMS somehow affects NRSF within MSCs and that this is the main driver of neural-like differentiation from soft surfaces. The aims of both projects show that neural differentiation in MSCs can be induced by both small molecules and the physical environment. Seemingly disparate stimuli are connected due to their ability to downregulate expression of NRSF. These studies highlight the role of transcription factors in determining stem cell fate and show that their modulation can even transdifferentiate cells across their germ line barriers.
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