Mitochondrial Rejuvenation After Induced Pluripotency

Abstract

BackgroundAs stem cells of the early embryo mature and differentiate into all tissues, the mitochondrial complement undergoes dramatic functional improvement. Mitochondrial activity is low to minimize generation of DNA-damaging reactive oxygen species during pre-implantation development and increases following implantation and differentiation to meet higher metabolic demands. It has recently been reported that when the stem cell type known as induced pluripotent stem cells (IPSCs) are re-differentiated for several weeks in vitro, the mitochondrial complement progressively re-acquires properties approximating input fibroblasts, suggesting that despite the observation that IPSC conversion “resets” some parameters of cellular aging such as telomere length, it may have little impact on other age-affected cellular systems such as mitochondria in IPSC-derived cells.Methodology/Principal FindingsWe have examined the properties of mitochondria in two fibroblast lines, corresponding IPSCs, and fibroblasts re-derived from IPSCs using biochemical methods and electron microscopy, and found a dramatic improvement in the quality and function of the mitochondrial complement of the re-derived fibroblasts compared to input fibroblasts. This observation likely stems from two aspects of our experimental design: 1) that the input cell lines used were of advanced cellular age and contained an inefficient mitochondrial complement, and 2) the re-derived fibroblasts were produced using an extensive differentiation regimen that may more closely mimic the degree of growth and maturation found in a developing mammal.Conclusions/SignificanceThese results — coupled with earlier data from our laboratory — suggest that IPSC conversion not only resets the “biological clock”, but can also rejuvenate the energetic capacity of derived cells.

Human Induced Pluripotent Stem Cells Harbor Homoplasmic and Heteroplasmic Mitochondrial DNA Mutations While Maintaining Human Embryonic Stem Cell–like Metabolic Reprogramming

“…These mitochondrial changes also impacted the cellular bioenergetic profile, which shifted from OXPHOS to glycolysis upon reprogramming and returned to OXPHOS during subsequent differentiation [18,19]. Other groups confirmed these results and showed that mitochondria within human iPSCs exhibits low oxidative stress [20] and energetic rejuvenation [21]. Moreover, small molecules inducing metabolic switch toward glycolytic metabolism enhanced reprogramming efficiency [22].…”

Reprogramming and Carcinogenesis—Parallels and Distinctions

“…Interestingly, iPS cells not only express stem cell markers, but also stem cell characteristics including anaerobic metabolism, low reactive oxygen species generation and decrease in mitochondrial mass and number (Armstrong et al, 2010;Prigione et al, 2010;Suhr et al, 2010). It has been suggested that the decrease in mitochondrial numbers contributes to lower generation of superoxide ions in iPS cells as compared to their progenitors (Vessoni et al, 2012).…”

Strategies for Oral Mucosal Repair by Engineering 3D Tissues with Pluripotent Stem Cells

“…Recent studies have shown that iPSC-derived cells may also display functional improvements when compared to the parental cells from which these iPSC were originally reprogrammed, indicating that they can be a preferred source for autologous cell-based therapies. For example, fibroblasts differentiated from iPSC displayed improved functional features, such as extended replicative potential, increased mitochondrial function, 1,2 and wound reparative potential. 3 Acquisition of these features suggests that iPSC are rapidly becoming a renewable source for regenerative therapies of the oral mucosa.…”

“…4 There is intriguing evidence that iPSC reprogramming may improve cellular function upon iPSC differentiation to a fibroblast lineage. 1,3,5 In this light, the use of iPSC-derived fibroblasts may circumvent the limitations of existing sources of fibroblasts that are currently used for tissue repair. This suggests that it may soon be possible to leverage the biological potential of iPSC-derived cells to improve current strategies for oral mucosal wound healing.…”

“…For example, it has been shown that iPSC reprogrammed from senescent fibroblasts showed an improvement on a spectrum of functions upon their subsequent differentiation to a fibroblast lineage, that included evasion of cell senescence, elongation of telomeres, and improved mitochondrial function. 1 Additional evidence that an improved repair potential can be acquired after reprogramming and subsequent differentiation were seen in iPSC-derived mesenchymal stem cells (MSC), which showed improved vascular rescue of limb ischemia when compared to adult-derived MSC. 5 Fibroblasts derived from iPSC also have been shown to produce greater amounts of ECM proteins than the parental cells from which they were derived.…”