Komórki macierzyste/en

=Definiton=

Stem cells are primary, unspecialized cells, which are characterized with unlimited self-renewal capacity and differentiation into specialized descendant progenitor cells forming tissues and organs. The proper function of the body depends on tissue homeostasis, and the maintenance of homeostasis is related with stem cell pool , that balances the number of somatic cells in the body. In each organ of the body thoroughly appears new cells, which maturate and differentiate into organ-specific cells, and after fulfilling their specific biological function they undergo into programmed cell death called apoptosis. Stem cells which reside in a cellular niche of a given organ, receive signals from the environment of the damaged tissue, and starts repair process leading for tissue regeneration.

Stem Cell Types

1. Totipotent stem cells – – they are the most primordial cells – the only type of cells capable to differentiate into all types of embryonic somatic cells and form entire human body. They arise as a result of fertilization forming zygote and then in further developmental process they create the blastomers. They are capable to give rise placenta connecting the embryo with the body of the mother.
2. Pluripotent stem cells – these cells are descendants of totipotent stem cells and can give rise to cells of the three germ layers: endoderm, mesoderm, and ectoderm. The cells are capable to organize and form any tissue (except placenta) in the process of embryogenesis. Along with fetal development and formation of individual tissue structures, the cells lose their pluripotent character in favor of tissue-specific character. The pluripotent cells can be found only during embryonic development and they are unable to go back into totipotent cells.
3. Multipotent stem cells– the cells are characterized with ability to differentiate and form tissue from one out of three germ layers
   • The first germ layer (ectoderm) – nerve tissue, epithelium, skin appendages,
   • The second germ layer (endoderm) – digestive system, respiratory system, endocrine system, urinary tract, sensory organs,
   • The third germ layer (mesoderm) – bones, cartilage, skeletal muscle, smooth muscles, heart muscle, tendons, ligaments, adipose tissue. The example of multipotent cells of third germ layer are Mesenchymal Stem/Stromal Cells (MSC).Multipotent cells reside in cellular niches and their number usually decreases with age and with the body's ability to renew itself.
4. Unipotent stem cells– specialized cells capable to division (unlike mature cells), dedicated to differentiate into the cells of given definite tissue. The example of unipotent stem cells are myoblasts capable to differentiate and form myocytes and then myofibers of skeletal muscle. Another example are osteoblasts capable to differentiate into osteocytes and form bone tissue. The tissue resident unipotent cells respond to damage signals from local environment by their activation and starting the process of tissue regeneration.

Classification of stem cell types by source of origin

1. Embrionalne (zarodkowe) komórki macierzyste – pochodzą z komórek zarodka (komórki totipotencjalne) lub z węzła zarodkowego blastocysty (komórki pluripotencjalne), mogą przekształcić się we wszystkie rodzaje komórek organizmu. Jednakże, użycie embrionalnych komórek macierzystych w celach terapeutycznych budzi wątpliwości natury etycznej, zatem ich zastosowanie nie powinno mieć miejsca w medycynie regeneracyjnej.
2. Płodowe komórki macierzyste – mogą być pozyskane z krwi pępowinowej i z tkanek popłodu takich jak pępowina czy łożysko, tkanki te stanowią naturalne źródło ich pozyskania gdyż niewykorzystane poddawane są utylizacji medycznej.
3. Somatyczne komórki macierzyste – dojrzałe, znajdują się w tkankach dorosłego organizmu i są odpowiedzialne za ich regenerację. Są to zarówno komórki multipotencjalne (m. in. komórki krwiotwórcze) jak i komórki unipotencjalne (np. komórki satelitowe mięśni szkieletowych). Pozyskanie somatycznych komórek macierzystych jest dobrze udokumentowane i wiele z nich znalazło zastosowanie w terapiach komórkowych np. przeszczepianie komórek krwiotwórczych w schorzeniach układu hematologicznego.