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14MESENCHYMAL MARKERS AND NEEDED SCAFFOLDS FOR SUCCESSFUL REGENERATION
WITH DENTAL STEM CELLS
Godovanets O.
Doctor of Medicine, Professor, Head of the Department of Pediatric Dentistry, Bukovinian State Medical
University, Chernivtsi, Ukraine.
Sauka E.
student of the Dentistry Faculty, Bukovinian State Medical University, Chernivtsi, Ukraine.
Godovanets O.
PhD, Associate Professor of the Department of Pediatrics, neonatology and perinatal medicine, Bukovinian
State Medical University, Chernivtsi, Ukraine
Abstract
Objective: To analyze the literature in the direction of scientific-theoretical and clinical aspects of the possibilities of using mesenchymal stem cells obtained from different sources of the maxillofacial area.
Research methods: In the course of the research the bibliosemantic method and structural-logical analysis were used. A literature search was done using electronic databases PubMed, MEDLINE, Scopus, Web of Science and EMBASE by keywords «regenerative medicine», «regenerative dentistry», «stem cells», «dental mesenchymal stem cells», «stem cell therapy», «tissue engineering».
Conclusions: Based on the analysis of the literature, there is a great interest of scientists in dental stem cells and their use in regenerative practice, not only for dental purposes, but also for the treatment of somatic diseases of various origins. This is due to the non-invasive and simpler method of material collection, compared to human bone marrow or embryonic tissues. Stem cells differ in origin, differential activity and source, and have a significant potential for differentiation in the direction of different cell lines depending on the influence of growth factors and nutrient medium. After obtaining new pure cultures, it is possible to establish their origin by identifying the expression of distinctive markers of stem cells. However, despite the high expectations from the further development of regenerative therapy, scientists need to study deeper the possibilities of using these cells in the clinical trial, to investigate the immunological behavior of stem cells of odontogenic origin in varied environments.
Keywords: regenerative medicine, regenerative dentistry, stem cells, dental mesenchymal stem cells, tissue engineering.
Introduction. Regenerative medicine becomes an interesting field of research that solves the problem of the treatment of severe illnesses by replacing the affected structures with cell therapy or tissue engineering using autogenous stem cells [2]. Due to these researches over the past decade, scientists have been able to find new sources of stem cells in the adult body, improve treatment methods of various diseases, regenerate and replace tissues of many organs, and even correct some congenital defects [8]. The study of regenerative dentistry, which bases on the synergistic use of biomi-metic environments, growth factors and cells of odon-togenic origin in the framework of dental manipulations [28], also attracted attention. The findings of new sources of mesenchymal stem cells in adults had an crucial role in the development of further regenerative dentistry. Systematization of theoretical knowledge and clinical research in the field of regenerative dentistry is the basis for further selection of the right sources of stem cells and development of best methods of regeneration and their successful application in practical medicine.
The aim. To analyze the latest literature data on possible and available sources of stem cells, their mes-enchymal markers and the opportunity for further use of dental stem cells in practical medicine.
Material and methods. The bibliosemantic method was applied and the structural-logical analysis of the received data was carried out. Electronic databases such as PubMed, MEDLINE, Scopus, Web of Science and EMBASE were used for modern
scientific literature searching by keywords «regenerative medicine», «regenerative dentistry», «dental mesenchymal stem cells», «dental pulp», stem cells».
The sources of dental stem cells. Stem cells are characterized by two important features that ensure the implementation of regenerative process: first, they are able to self-repair by cell division, even after long periods of suspended division by genetic signals, and secondly, under certain physiological or experimental conditions they can form functional cells of different tissue or organ [19]. These cells can divide in unlimited quantities [23]. In the case of receiving a biological signal, stem cells acquire signs of more pronounced differentiation, which determines their subsequent specialization [29]. The primary role of stem cells is to maintain and repair the tissue in which they are found [22].
There are embryonic stem cells - pluripotent, derived from the cells of the embryo, and postnatal - stem cells of the adult body, which are present in the tissues in small quantities. Scientists have also been able to artificially synthesize induced pluripotent stem cells through genetic manipulation of somatic cells [26].
Regarding stem cells of odontogenic origin, such populations can be isolated from different tissues of the maxillofacial area: tooth pulp, exfoliated deciduous teeth, periodontal ligament, dental follicles, alveolar bones, apical papilla, teeth germs and gums [6; 9; 13; 27; 28; 30; 32]. Scientists (Gronthos S. et al., Erices et
al., Mitchell et al. 2003) were able to prove the affiliation of odontogenic origin cells to stem cells during a comparative study of the tooth pulp and bone marrow tissue. The study resulted in cell cultures with similar proliferative capacity, growth factors and components of the mineralized matrix. Based on the obtained results, odontoblast precursors were equated to mesen-chymal poorly differentiated bone marrow cells [9].
Stem cell markers. To determine the origin of cells, various research methods are used to identify specific proteins, which, depending on their location, can be extracellular or intracellular markers-identifiers. Stem cells extracted from tooth pulp tissue develop from the mesenchyme during odontogenesis, so the expression of markers specific for cells of mesenchymal origin is investigated in the identification of these cells.
Yalvac ME, Yilmaz Aysu, Mercan D et al. performed flow cytometry analysis of tooth germ progenitor cells (TGSCs) that were positive for CD73, CD90, CD105 and CD166, but negative for CD34, CD45 and CD133, indicating that these cells are mesenchymal stem cells (MSCs) [31]. Also, TGSCs are prone to expression of genes associated with the properties of plu-ripotent cells (nanog, Oct4, Sox2, Klf4 and c-Myc) [17; 31]. Immunohistochemical studies revealed dental pulp stem cells (DPSCs) around the blood vessels of the coronal pulp that are able to express STRO-1 and CD146, two early markers of MSCs. Stem cells from human exfoliated deciduous teeth (SHED) expressed osteogenic and angiogenic markers such as ALP, MEPE, bFGF, and endostatin. Miura M. Gronthos S, Zhao M et al. (2003) studied the potential for differentiation of SHED population cells into mineralized tissue. According to immunoblotting results, various bone markers, including CBFA1, ALP, MEPE, and bone sialoprotein, are expressed by cell populations during cultivation [18]. Populations of periodontal ligament stem cells (PDLSCs) and stem cells from apical papilla (SCAP) are also characterized by the expression of STRO-1 and CD146 [24]. In 2004 studies, PDLSCs demonstrated the expression of a specific marker of tendon transcription factor [7]. The CD24 marker distinguishes SCAP from dental mesenchymal stem cells from other sources. In addition, Jamal M. et al. (2015), Patil R. et al. (2014), Bakopoulou A. et al., Ruparel N. B. et al. (2013) found the expression of markers such as CD13, CD24, CD29, CD44, CD49, CD51, CD56, CD61, CD73, CD90, CD105, CD106, CD166, NOTCH3 and vimentin [3; 11; 14; 20]. At the same time, SCAPs do not express CD14, CD18, CD34, CD45, CD117 and CD150, which indicates that they do not have hemato-poietic origin [24]. The population of alveolar bone mesenchymal stem cells (ABMSCs) expresses surface markers of stem cells CD73, CD90, CD105 and STRO-1, and are negative in the expression of hematopoietic markers CD14, CD34 and CD45 [21]. Proper identification of stem cells is a basic step for their further successful cultivation and use in clinical practice with the predicted result.
Cell matrices (scaffolds) and growth factors are integral components of tissue engineering. Several criteria for ideal scaffolding have been described, includ-
ing chemical stability, mechanical strength, biocompat-ibility, controlled degradation, adhesion, and cell proliferation. Cell matrix materials that have the potential for regenerative dentistry include natural polymers (eg, collagen, chitosan, alginate, and hyaluronic acid); synthetic materials (eg polyglycolic acid, polylactic acid, polylactic polyglycolic acid) and bioactive ceramics (eg hydroxyapatite and bioglass) [1, 12, 15]. Although these matrices have shown efficacy in attempts to regenerate teeth, the potential problem of their use is associated with the risk of infection and inflammation, which encourages the study of new independent methods and protocols for regeneration [12].
In this context, a new approach was described, according to which three-dimensional cell constructions were created without scaffolds, but using thermosetting hydrogel and using dental pulp stem cells [5]. The result after 6 weeks of implantation indicated the formation of pulp-like tissues with rich blood vessels in the root canal of the previously depulped tooth.
A large number of growth factors are used to regulate the proliferation and induction of stem cell differentiation into the desired cells; these molecules bind to specific receptors associated with the cell membrane, thereby mobilizing a cascade of reactions and processes that lead to tissue formation [16, 25]. For example, bone morphogenetic protein (BMP) -2 mediates dentin-induced odontoblastic differentiation of dental pulp stem cells. On the other hand, transforming growth factor p (TGF-P) can stimulate odontoblast-like cell differentiation and DPSCs-mediated mineralization [16].
Epidermal growth factor (EGF) plays the role of an enhancer of osteogenic differentiation, as it is able to increase the mineralization of the extracellular matrix. EGF stimulates angiogenesis and vascularization. This growth factor is directly proportional to the activation of both the proliferation of DPSCs and their differentiation [10]. Another growth factor called insulinlike growth factors(IGF) is known to modulate key properties of dental pulp stem cells, such as their rate of proliferation, differentiation potential, and mineralization [4]. Therefore, the identification of appropriate growth factors or their combinations that will promote the regeneration of the dental complex or related structures is an important area of research.
Conclusions. Based on the analysis of the literature, there is a great interest of scientists in stem cells of odontogenic origin and their use in regenerative practice. These cells differ in origin, differential activity and source, and have a significant potential for differentiation into different cell lines depending on the influence of growth factors and nutrient medium. When obtaining new pure cultures, it is possible to establish their origin by identifying the expression of markers characteristic of stem cells. The result of the influence of growth factors is determined by the variety of activation processes and synthesis of plastic substances, which play an important role in the beginning of growth and subsequent differentiation of these cells.
However, despite the high expectations from the further development of regenerative therapy, scientists need to study more about the possibilities of using these cells at the stages of clinical trials, to investigate the
immunological behavior of stem cells of odontogenic origin in a given environment. Obtaining and using stem cells of odontogenic origin in further medical practice is a promising area of medicine, as they allow to invent more modern methods of treatment of diseases of various origins, including dental.
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