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#Mitochondrial stress increases in stem cell during aging
#Mitochondrial dysfunction and aging produces similar defects in stem cells
#Stem cells do not age at the same rate; about one third od chronologically aged HSCs exhibit regeberative function similar to healthy young HSCs, coinciding with the health of mitochondria. === Stem cell === In [https://en.wikipedia.org/wiki/Multicellular_organisms multicellular organisms], '''stem cells''' are [https://en.wikipedia.org/wiki/Cellular_differentiation undifferentiated] or partially differentiated [https://en.wikipedia.org/wiki/Cell_(biology) cells] that can change into various [https://en.wikipedia.org/wiki/Types_of_cells types of cells] and [https://en.wikipedia.org/wiki/Cell_proliferation proliferate] indefinitely to produce more of the same stem cell. They are the earliest type of cell in a [https://en.wikipedia.org/wiki/Cell_lineage cell lineage].<sup id="cite_ref-:7_1-0">[https://en.wikipedia.org/wiki/Stem_cell#cite_note-:7-1 [1]]</sup> They are found in both [https://en.wikipedia.org/wiki/Embryo embryonic] and adult organisms, but they have slightly different properties in each. They are usually distinguished from [https://en.wikipedia.org/wiki/Progenitor_cells progenitor cells], which cannot divide indefinitely, and [https://en.wikipedia.org/wiki/Precursor_cell precursor] or blast cells, which are usually committed to differentiating into one cell type. In [https://en.wikipedia.org/wiki/Mammals mammals], roughly 50 to 150 cells make up the [https://en.wikipedia.org/wiki/Inner_cell_mass inner cell mass] during the [https://en.wikipedia.org/wiki/Blastocyst blastocyst] stage of [https://en.wikipedia.org/wiki/Embryonic_development embryonic development], around days 5–14. These have stem-cell capability. ''[https://en.wikipedia.org/wiki/In_vivo In vivo]'', they eventually differentiate into all of the body's cell types (making them [https://en.wikipedia.org/wiki/Pluripotent pluripotent]). This process starts with the differentiation into the three [https://en.wikipedia.org/wiki/Germ_layers germ layers] – the [https://en.wikipedia.org/wiki/Ectoderm ectoderm], [https://en.wikipedia.org/wiki/Mesoderm mesoderm] and [https://en.wikipedia.org/wiki/Endoderm endoderm] – at the [https://en.wikipedia.org/wiki/Gastrulation gastrulation] stage. However, when they are isolated and [https://en.wikipedia.org/wiki/Cell_culture cultured] ''[https://en.wikipedia.org/wiki/In_vitro in vitro]'', they can be kept in the stem-cell stage and are known as [https://en.wikipedia.org/wiki/Embryonic_stem_cells embryonic stem cells] (ESCs). [https://en.wikipedia.org/wiki/Adult_stem_cells Adult stem cells] are found in a few select locations in the body, known as [https://en.wikipedia.org/wiki/Stem-cell_niche niches], such as those in the [https://en.wikipedia.org/wiki/Bone_marrow bone marrow] or [https://en.wikipedia.org/wiki/Gonads gonads]. They exist to replenish rapidly lost cell types and are [https://en.wikipedia.org/wiki/Multipotent multipotent] or unipotent, meaning they only differentiate into a few cell types or one type of cell. In mammals, they include, among others, [https://en.wikipedia.org/wiki/Hematopoietic_stem_cells hematopoietic stem cells], which replenish blood and immune cells, [https://en.wikipedia.org/wiki/Stratum_basale basal cells], which maintain the skin [https://en.wikipedia.org/wiki/Epithelium epithelium], and [https://en.wikipedia.org/wiki/Mesenchymal_stem_cells mesenchymal stem cells], which maintain bone, [https://en.wikipedia.org/wiki/Cartilage cartilage], muscle and fat cells. Adult stem cells are a small minority of cells; they are vastly outnumbered by the progenitor cells and terminally differentiated cells that they differentiate into.<sup id="cite_ref-:7_1-1">[https://en.wikipedia.org/wiki/Stem_cell#cite_note-:7-1 [1]]</sup> Research into stem cells grew out of findings by Canadian biologists [https://en.wikipedia.org/wiki/Ernest_McCulloch Ernest McCulloch], [https://en.wikipedia.org/wiki/James_Till James Till] and Andrew J. Becker at the [https://en.wikipedia.org/wiki/University_of_Toronto University of Toronto] and the Ontario Cancer Institute in the 1960s.<sup id="cite_ref-2">[https://en.wikipedia.org/wiki/Stem_cell#cite_note-2 [2]]</sup><sup id="cite_ref-3">[https://en.wikipedia.org/wiki/Stem_cell#cite_note-3 [3]]</sup> As of 2016, the only established [https://en.wikipedia.org/wiki/Stem-cell_therapy medical therapy using stem cells] is [https://en.wikipedia.org/wiki/Hematopoietic_stem_cell_transplantation hematopoietic stem cell transplantation],<sup id="cite_ref-4">[https://en.wikipedia.org/wiki/Stem_cell#cite_note-4 [4]]</sup> first performed in 1958 by French oncologist [https://en.wikipedia.org/wiki/Georges_Mathé Georges Mathé]. Since 1998 however, it has been possible to culture and differentiate human embryonic stem cells (in [https://en.wikipedia.org/wiki/Stem-cell_lines stem-cell lines]). The process of isolating these cells has been [https://en.wikipedia.org/wiki/Stem_cell_controversy controversial], because it typically results in the destruction of the embryo. Sources for isolating ESCs have been [https://en.wikipedia.org/wiki/Stem_cell_laws restricted] in some European countries and Canada, but others such as the UK and China have promoted the research.<sup id="cite_ref-Pew_Intl_5-0">[https://en.wikipedia.org/wiki/Stem_cell#cite_note-Pew_Intl-5 [5]]</sup> [https://en.wikipedia.org/wiki/Somatic_cell_nuclear_transfer Somatic cell nuclear transfer] is a [https://en.wikipedia.org/wiki/Cloning cloning] method that can be used to create a cloned embryo for the use of its embryonic stem cells in stem cell therapy.<sup id="cite_ref-6">[https://en.wikipedia.org/wiki/Stem_cell#cite_note-6 [6]]</sup> In 2006, a Japanese team led by [https://en.wikipedia.org/wiki/Shinya_Yamanaka Shinya Yamanaka] discovered a method to convert mature body cells back into stem cells. These were termed [https://en.wikipedia.org/wiki/Induced_pluripotent_stem_cells induced pluripotent stem cells] (iPSCs).<sup id="cite_ref-:6_7-0">[https://en.wikipedia.org/wiki/Stem_cell#cite_note-:6-7 [7]]</sup><br/> <br/> full txt link : [https://en.wikipedia.org/wiki/Stem_cell https://en.wikipedia.org/wiki/Stem_cell]
