Somatyczne komórki macierzyste/en

Definition

Somatic stem cells are undifferentiated cells that reside in many tissues of the adult body, where they play an important role in maintaining homeostasis and damaged tissues repair. They have a capacity for self-renewal and differentiation. Populations of somatic stem cells residing in a specific microenvironment of their cellular niche, are heterogenous and dynamic, and consisting of both active and quiescent cells. Somatic stem cells are an attractive tool for regenerative medicine, as compared to some types of immortalized or induced pluripotent cell lines, they do not carry a risk of tumor formation, do not come from embryos, and show low immunogenicity even in allogeneic systems .

Types of somatic stem cells

Mesenchymal, hematopoietic, neural, or epithelial stem cells are most commonly used.

• Epithelial stem cells are found e.g. in the small intestine, where they reside in crypts, migrate to villi and differentiate into enterocytes, goblet cells and enteroendocrine cells.
• Hematopoietic stem cells are most abundant in the bone marrow, but also present in umbilical cord blood, and in a smaller degree peripheral blood. They give rise to all types of blood and immune cells, and have been used successfully in transplantation procedures.
• Neural stem cells (NSC) reside in two main neurogenic niches of the adult mammalian brain: in the subventricular zone of lateral ventricles and the subgranular zone of the dentate gyrus. They differentiate into neurons, astrocytes and oligodendrocytes, although not all cells of the NSC population are capable of differentiation into all three types. They are considered for regenerative therapy of neurodegenerative diseases, although their primary function is contribute to brain plasticity, learning and memory rather than damage repair. Moreover, therapeutic use of NSCs is challenging as it requires either intracerebral or xenotransplantation, or otherwise is restricted to stimulation of existing cells; there are also concerns about the integration of transplanted NSCs with surrounding tissue, and the effects of such a procedure on brain function.
• Mesenchymal stem cells (MSC) are the most commonly used somatic stem cells, due to their high proliferation ability, multipotent differentiation potential (although they tend to favourably differentiate into the types of cells found in the tissue source), and immunomodulatory capacity. Originally characterised in bone marrow, MSCs were subsequently found in most vascularized tissues.

Sources of mesenchymal stem cells

• Bone marrow: abundant in MSCs capable of differentiation into many cell types, including osteoblasts, chondrocytes, hepatocytes etc. Bone marrow MSCs have been proven effective for therapeutic uses, even though their differentiation potential depends on donor characteristics such as age; however, the collection of those cells is one of the most invasive procedures of obtaining MSCs.
• Adipose tissue: rich in MSCs that are highly proliferative, easily obtainable through liposuction, and capable of differentiating into cells of adipogenic, osteogenic, chondrogenic and myogenic lineages.
• Skeletal muscle: distinct from the exclusively myogenic satellite cells, muscle-derived MSCs are capable of differentiation into cells of osteogenic and chondrogenic lineages , however, they are primarily used to repair skeletal and cardiac muscle tissue. They are characterised by high self-renewal properties, and can be obtained by biopsy from any muscle of the body.
• Skin: a source of highly proliferative cells, used especially for dermis reconstitution, e.g. in treatment of burns, but also capable of differentiation into myo-, adipo-, osteo- and chondrocytes, as well as neural and pancreatic cells. MSCs can be also isolated from hair follicles, which is probably the most easy and non-invasive way of obtaining stem cells; hair follicle MSCs can undergo adipogenesis and osteogenesis.
• Dental pulp: an easily accessible source of MSCs, as dental surgeries are common procedures. Dental pulp MSCs are usually used for bone and neural regeneration; their chondrogenic differentiation capacity is limited compared to other types of MSCs. They might also exhibit decreased proliferation over time.
• Placenta: abundant in MSCs characterised by high proliferation rates and strong immunosuppressive effects, capable of differentiation into e.g. hepatocytes or pancreatic cells.
• Amniotic fluid: MSCs sourced from amniotic fluid are mainly used alongside surgery as autologous material to aid organ repair in treatment of congenital birth anomalies such as spina bifida, diaphragmatic hernia or cardiac defects. Amniotic fluid is accessible by needle aspiration, and only small quantities are necessary to establish a cell culture, as they tend to proliferate rapidly.
• Peripheral blood: although easily obtained, peripheral blood is not abundant in MSCs. Their adipogenic potential is higher than that of bone marrow-derived MSCs, but the capacity to differentiate into cells of other lineages is relatively inferior.