No abstract

Mitochondrial DNA haplotypes are associated with various phenotypes, such as altered susceptibility to disease, environmental adaptations, and aging. Accumulating evidence suggests that mitochondrial DNA is essential for cell differentiation and the cell phenotype. However, the effects of different mitochondrial DNA haplotypes on differentiation and development remain to be determined. Using embryonic stem cell lines possessing the same Mus musculus chromosomes but harboring one of Mus musculus, Mus spretus, or Mus terricolor mitochondrial DNA haplotypes, we have determined the effects of different mitochondrial DNA haplotypes on chromosomal gene expression, differentiation, and mitochondrial metabolism. In undifferentiated and differentiating embryonic stem cells, we observed mitochondrial DNA haplotype-specific expression of genes involved in pluripotency, differentiation, mitochondrial energy metabolism, and DNA methylation. These mitochondrial DNA haplotypes also influenced the potential of embryonic stem cells to produce spontaneously beating cardiomyocytes. The differences in gene expression patterns and cardiomyocyte production were independent of ATP content, oxygen consumption, and respiratory capacity, which until now have been considered to be the primary roles of mitochondrial DNA. Differentiation of embryonic stem cells harboring the different mitochondrial DNA haplotypes in a 3D environment significantly increased chromosomal gene expression for all haplotypes during differentiation. However, haplotype-specific differences in gene expression patterns were maintained in this environment. Taken together, these results provide significant insight into the phenotypic consequences of mitochondrial DNA haplotypes and demonstrate their influence on differentiation and development. We propose that mitochondrial DNA haplotypes play a pivotal role in the process of differentiation and mediate the fate of the cell. STEM CELLS 2013;31:703-716 Disclosure of potential conflicts of interest is found at the end of this article.

To develop neural tissue engineering strategies that are useful for repairing damaged neural pathways in the central nervous system, it is essential to control and optimise neurone and neurite interactions with functional scaffolds. In this study, the suitability of thermally gelling xyloglucan hydrogels, along with xyloglucan-graft-poly-D-lysine (PDL) hydrogels, was assessed through their implantation within the caudate putamen of adult rats. The ability of the hydrogel scaffolds to encourage the infiltration of axons in a controlled manner was investigated, as was the inflammatory response associated with the implantation. The microglia reaction was the same for unmodified xyloglucan and the xyloglucan-graft-PDL scaffolds, peaking after 3 days before decreasing back to homeostatic levels after approximately 28 days. Penetration of the microglia into the scaffold was not observed, with these cells accumulating at the scaffold-tissue interface. For astrocytes, the other type of glial cell with migratory capacity, the peak activation occurred between 14 and 21 days. This reaction subsided more rapidly for the unmodified scaffold compared to the xyloglucan-graft-PDL scaffolds, which remained elevated 21-28 days before returning to homeostatic levels within 60 days. Most noteworthy was the discovery of increased infiltration levels for astrocytes and neurites with higher concentrations of grafted PDL. The timing of the astrocyte migration coincided with neurite infiltration within the scaffolds, suggesting that astrocytes may have facilitated this infiltration, possibly due to the secretion of laminin.