Changes in Mitochondria Properties with the Transdifferentiation of Human Hematopoietic Stem Cells into Neuron-like Cells

Abstract

Recent progress in stem cell research has demonstrated the therapeutic potential for stem cells to repair the damage in humans that results from injury, degenerative disorders, and cellular abnormalities. Researchers frequently culture stem cells for prolonged periods of time and must verify that their stem cell properties are maintained during the extensive culturing. For optimal use of stem cell cultures in studies and therapies, laboratories would benefit from inexpensive, timely indicators of a cell line’s stemness. Using human adult stem cells, specifically human hematopoietic stem cells (hHSCs), this thesis examines two mitochondrial characteristics as possible biomarkers for stemness: perinuclear location of mitochondria within the cytoplasm and low ATP content per cell as compared to differentiated cells. We find that early passage hHSCs are characterized by a perinuclear arrangement of mitochondria. As opposed to 21% of transdifferentiated cells, 98% of the hHSCs (Passage 1 or 2) have perinuclear mitochondrial distribution. Further, we hypothesized that lower ATP content in stem cells could be a biomarker for stemness: however, contrary to this prediction, the transdifferentiated cells, instead, have lower ATP/cell content when compared to the stem cells (1.78 vs. 0.55 pmoles ATP/cell). Though this difference in ATP measures between undifferentiated and differentiated cells is found not to be statistically significant (P=0.07), these findings suggest that a lowering of ATP content could be related to differentiation into neuron-like cells. In this study, we also describe the morphological changes occurring with transdifferentiation of human hematopoietic-derived stem cells into neuron-like cells. In addition, we determine that appropriate cell markers for transdiffenentiation into neurons are the expression of polymerized neurofilaments and the loss of expression of the cell surface glycoprotein CD34, a purported marker of hematopoietic stem cells. This work represents a number of first studies on human adult stem cells, most importantly, 1) the first evaluation of two mitochondrial characteristics as possible biomarkers for stemness, 2) the first report of the ability of hematopoietic-derived stem cells to transdifferentiate into neuron-like cells, 3) the first study to determine that the presence of neurofilament protein alongside the polymerized form of neurofilaments is a biomarker for stemness, and 4) the first report examining whether mitochondrial morphology is related to the potential of stem cells to differentiate.