|
 
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| REVIEW ARTICLE |
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| Year : 2019 | Volume
: 6
| Issue : 1 | Page : 1-6 |
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Dental stem cells – Sources and identification methods
Anjali Narwal1, Shruti Gupta2, Anita Hooda2
1 Department of Oral Pathology, Pt. B. D Sharma University of Health Sciences Post Graduate Institute of Dental Sciences, Rohtak, Haryana, India
2 Department of Oral Anatomy, Pt. B. D Sharma University of Health Sciences Post Graduate Institute of Dental Sciences, Rohtak, Haryana, India
| Date of Submission | 15-Jul-2018 |
| Date of Decision | 23-Aug-2018 |
| Date of Acceptance | 11-Nov-2018 |
| Date of Web Publication | 14-Feb-2019 |
Correspondence Address:
Shruti Gupta
H. No. 166, Old PLA Sector, Hisar - 125 001, Haryana
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/cjhr.cjhr_110_18
The banking of mesenchymal cells from the umbilical cord and harvesting them for future use is the current trend in medical science. Such sources are reservoirs of stem cells. Over the past decade, the field of dentistry has embossed its presence by taking major lead in the field of regenerative medicine and more precisely in the field of stem cells. These stem cells have the capacity for regeneration and repair by converting into any other cell type. However, these cells require signals for differentiation in a timely manner. Tooth and its associated structures have been discovered as the latest reservoirs of stem cells. In this review, a light has been thrown on such sources and their identification has been emphasized.
Keywords: Pluripotent, reservoir, stem cells
How to cite this article:
Narwal A, Gupta S, Hooda A. Dental stem cells – Sources and identification methods. CHRISMED J Health Res 2019;6:1-6 |
How to cite this URL:
Narwal A, Gupta S, Hooda A. Dental stem cells – Sources and identification methods. CHRISMED J Health Res [serial online] 2019 [cited 2023 Mar 28];6:1-6. Available from: https://www.cjhr.org/text.asp?2019/6/1/1/252282 |
| Introduction | |  |
Every year, billions of monies are spent for reconstruction of defects due to tissue loss or end-stage organ failure. Regeneration of tissues holds a promising alternative for the reconstruction of defects in the head-and-neck regions. Trauma, infectious diseases, inherited disorders, and neoplasms are the major etiological factor for the tissue loss in the craniofacial region. Various approaches have been considered in regenerative medicine, but currently, the most common is to use a “biodegradable scaffold in the shape of new tissue that is seeded with either stem cells or autologous cells from biopsies of damaged tissues.”[1] These seeded autologous or stem cells are pluripotent in nature, and under appropriate microenvironment, they differentiate into any cell type.
Due to developmental similarities with other organs such as the hair, kidney, and lungs, teeth are considered to be excellent models for studying organ regeneration and also they are clinically accessible and convenient for experimental research. Within the next 25 years, advances are going to take place in regenerative medicine, and dentist will have a pivotal role in providing stem cells from dental tissues which will not only generate a new tooth but also hold the potential for the regeneration of many other tissues also.
Stem cells are the unspecialized cells which have the potential of self-renewal and differentiation into many other cell types.[2] “Stemness is the ability of undifferentiated cells to undergo an indefinite number of replications and ability to give rise to any kind of specialized cells.” Differentiation can be appreciated microscopically by alteration in the morphology of cell as well as the presence of tissue-specific protein in its cytoplasm.[3] Stem cells may remain dormant or silent over long periods of time until there is a physiological need for more cells to maintain tissues or they are activated by disease or tissue injury. Such self-renewal or actively dividing and differentiating sites of tissue are known by the name “stem-cell niches.”[4] Such sites have been identified in the skin, adipose tissues,[5] peripheral blood,[5],[6] hair follicle, bone marrow, brain, intestine, pancreas, and teeth.[6],[7] Thus, the primary role of adult stem cells is to maintain and repair the tissue in which they are found.[4] The branch of health sciences in which stem cells are retrieved from their niches, cultured, and harvested at the required site is known as stem cell science. It has led to introduction and establishment of translational techniques such as artificial skin therapies, target cell-based therapies in diabetes, atherosclerosis, and neurodegenerative diseases in which stem cells are grown at the diseased site. Stem cells are present in different tissues, but stem cells from bone marrow have always been a surgeon's favorite choice because of their pluripotentiality. The need for an alternative to conventional mesenchymal stem cells (MSCs) to more accessible cells has propelled the research toward dental tissues, which are a rich source for stem cells.[8] The purpose of this article is to discuss the source, nature, and phenotype of dental stem cells.
| Basic Properties of Stem Cells | | |
- They are undifferentiated cells, that is, they have not developed into a specialized cell types
- They have the capability to undergo multiple cycles of cell division while maintaining their undifferentiated state
- They have the ability to differentiate into specialized cell types.[8]
| Types Of Stem Cells | | |
Stem cells are basically divided into three categories:
- Embryonic stem cells (ES cells) are derived from the blastocyst during embryonic development and are either totipotent or pluripotent in nature. They can give rise to all the three primary germ layers: ectoderm, endoderm, and mesoderm.[8] In contrast to adult stem cells, ES cells have the ability to divide actively for self-renewal without any differentiation for longer time period. ES cells attain epigenetic marks in their DNA on meeting a suitable environment, so they can differentiate into specialized cells of the eye, liver, muscle, nerve, and bone, for example[9] [Figure 1]
- Somatic or adult stem cells exist throughout the body in different tissues including the bone marrow, skin, peripheral blood, liver, retina, brain, blood vessels, pancreas, muscle, adipose tissue, and dental tissues. They can divide and give rise to another cell like itself but have a limited differentiation potential to other cell types.[8] Their detection can pose a difficulty as they reside in specific heterogeneous sites with other supporting cells. Slow cell division of stem cells prove to be a boon in their separation from the other neighboring cells[10] [Figure 2]
- “Induced pluripotent stem cell (iPS) is an evolving concept in which 3–4 genes found in the stem cells are transfected into the donor cells using appropriate vectors. The stem cells thus derived by culturing will have properties almost like ES cells.”[11] They are pluripotent in nature.[11] Yamanaka and Takahashi in 2006 cultivated first iPSs from adult mouse cells in their research laboratory. They succeeded in growing the iPS from human adult cells in 2007.[12] iPS cells have similar properties of ES cells, that is, they have a capacity to divide indefinitely without losing the potential of differentiation into any cells of three germ layers.[8],[11] [Figure 3].
Stem cell identification
The common techniques used for easy identification of stem cells are as follows:
- Flow cytometer with specific stem cell antibody marker (fluorescent antibody cell sorting) – In this process, stem cells are identified by staining the stem cells with specific antibody markers and using flow cytometry[13]
- Immunohistochemical staining[1]
- Physiological and histological criteria including phenotype, chemotaxis, mineralizing activity, proliferation, and differentiation[1],[13]
- Immunomagnetic bead selection – This method sort cells based on a highly expressed single surface marker using antibody-coated magnetic bead and magnetic field. This method have the combined advantage of high specificity of immunoassays and minimal invasiveness of magnetic force.[14]
Stem cells express different protein markers on their surface and hence cannot be identified by a single protein marker. CD34 protein is well expressed by stem cells in the peripheral blood and umbilical cord, and hence, it can be used for their identification.[15] Apart from CD34, hematopoietic stem cells express CD133, ABCG2, and Sca-1 which are used for identification. Markers which are helpful in identification of ES cells are Oct-3/4 and SSEMAs.[16] MSCs are identified by their positive expression of CD105, CD13, and CD 73 genes and are negative for the hematopoietic markers such as CD34 and CD45.[17]
| Stem Cells of Dental Origin | | |
The teeth act as an alternate source for stem cells as they have similar potency as that of bone marrow-derived mesenchymal cells. Potential sources of dental stem cells are as follows: dental pulp stem cells (DPSC),[18] dental follicle stem cells (DFSC),[19] stem cells from human exfoliated deciduous teeth (SHED),[20] stem cells from apical papilla (SCAP),[21] periodontal ligament stem cells (PDLSCs),[22] and gingival stem cells (GING SCs)[23] [Figure 4], [Figure 5], [Figure 6]. In spite of a common developmental pathway of dental tissues, it is still not fully understood whether these closely related tissues are programmed differently or not.[24]
Dental pulp stem cells
Cells derived from dental pulp consist of heterogeneous population of progenitor cells that are also called odontoblastoid cells as these cells synthesize and secrete dentin matrix like the odontoblast cells of dentin.[25],[26] The source of odontoblastoid cells that replace the odontoblasts and secrete reparative dentin bridges is controversial. It has been suggested that odontoblastoids differentiate from the zone of Hohl cells which is a subodontoblstic cell-rich zone.[27] A great deal of effort has been made in the past to isolate and identify the progenitor cells among them.[18] DPSCs are lineage restricted with limited self-renewal and multilineage differentiation capability and stem cell count is comparatively low. Hence, there is a great challenge for them to become a practical stem cell resource for clinical application.[28] They express positivity for CD9, CD10, CD13, CD29, CD44, CD49d, CD59, and CD73. Furthermore, they express CD90, CD105, CD106, CD146, CD166, STRO-1, Oct-4, Nanog, SSEA-4, and Vimentin.[18],[20],[21],[29],[30],[31],[32],[33],[34] They have the in vivo capacity to form dental tissues (dentin and pulp) and mesenchymal tissues such as adipose and muscle. In vitro, they can differentiate into odontoblast, osteoblast, chondrocyte, adipocyte, myocyte, and neuronal cells.[8],[35] It has also been recognized that DPSCs play an important role in balancing inflammation and repair during invasive carious lesions or pulp exposures.[36] This concept of balance has been investigated in vitro where it was seen that these cells migrate from perivasculature toward the dentin surface following injury to dentin matrix.[36] DPSCs also express toll-like receptors 2 (TLR2) and TLR4 and vascular endothelial growth factor in response to lipopolysaccharide which is a product of Gram-negative bacteria.[37]
Dental follicle stem cells
Dental follicle tissue acts as a source of DFSCs which have the ability to differentiate and form bone and cementum, and hence, they are used in periodontal and bone regeneration therapies.[38] Human third molar teeth serve as a vital niche for DFSCs, and they have higher proliferation rate than that of DPSCs.[38] They are easily available for cell culture and adhere well to the culture plates.[39]
Stem cell markers such as Nestin, Notch-1, and STRO-1 are positively expressed in DFSCs. They also express positivity for cementum attachment protein and cementum protein-23 (cementoblast marker) as well as for bone morphogenetic protein 1 (BMP-1) and BMP-7.[24] They express positivity for CD9, CD29, CD10, CD13, CD44, and CD49d. The positive expression for CD59, CD73, CD90, CD105, CD106, CD166, and HLA-Class I is definitely seen in DFSCs.[40],[41],[42],[43]
Stem cells from human exfoliated deciduous teeth
This type of stem cells can be isolated from exfoliated deciduous teeth and have high proliferation capacity. They can differentiate into various cell types such as osteoblasts, neural cells, adipocytes, odontoblasts, endothelial cells, myoblast and chondrocyte,[20],[35] and induce dentin and bone formation.[20],[44] They show positivity for CD13, CD44, CD73, CD90, CD105, CD146, Nanog, STRO-1, Oct-4, fibroblast growth factor 2 (FGF-2), Nestin, SSEA-3, SSEA-4, transforming growth factor-β (TGF-β), TGF-β2, collagen I (Col I), and Col III.[8],[24],[35] SHED cells have higher proliferative index than DPSCs highlighting more immature population of multipotent stem cells.[24] TGF-β1 and β2, FGF-2, and Col I and III are highly expressed in SHED as compared to DPSCs.[20]
Stem cells from apical papilla
The dental papilla differentiates and matures into dental pulp during the early stages of odontogenesis. During root development, apical part of the papilla gets separated from pulp by cell-rich zone.[31] This cell-rich zone constitutes SCAP cells. They are clonal cousins of fibroblast-like cells and have higher proliferation potential than DPSCs. SCAP cells express early mesenchymal surface markers, STRO-1, CD146, and CD24.[24]
Periodontal ligament stem cells
Around 20 years ago, Melcher first proposed the concept of PDLSCs.[45] These PDLSCs are the pool of progenitor cells such as fibroblasts, cementoblasts, odontoblasts, and osteoblasts. These cells exhibit 30% higher proliferative index as compared to bone marrow stem cells.[45] They exhibit markers such as STRO-1, scleraxis, and also positivity for CD9, CD10, CD13, CD29, CD44, and CD49d. They also exhibit expression for CD59, CD73, CD90, CD105, CD106, CD146, and CD166.[22],[46],[47] PDLSCs are the array of osteogenic markers such as bone sialoprotein, alkaline phosphatase, osteocalcin, and matrix extracellular phosphoglycoprotein and mesenchymal markers such as tendon marker scleraxis and STRO-1.[45]
Gingival stem cells
On extensive literature search, two different types of adult stem cells have been identified in the oral mucosa. One of them is oral epithelial progenitor cells and other type is derived from the lamina propria of gingiva.[35],[48],[49]
The cells derived from the lamina propria of gingiva are called gingival MSCs, gingival tissue-derived stem cells, gingival multipotent progenitor cells, and gingival margin-derived stem/proginetor cells, human oral mucosa stem cells, and oral mucosa lamina propria proginetor cells.[50],[51],[52],[53] They have retained the capacity for multilineage differentiation and its related gene expression. They also have the capacity to differentiate into osteoblasts, chrondoblasts, adipocyte, endothelial, and neural cells.[49] GING SCs proliferate faster than bone marrow-derived stem cells.[35] They exhibit positivity for STRO-1, Oct-4, Sox-2, SSEA-4, Nanog, HLA-ABC, Nestin, Tra2-49, and Tra2-54. They also exhibit markers such as CD29, CD44, CD73, CD90, CD105, CD106, CD146, and CD166.[35],[50],[54],[55],[56]
Aging of stem cell
After 120 days, MSCs start losing their proliferative potential in vitro expansion. Various changes occur in stem cells during culturing which including.
- Gradual decrease in proliferation index
- Shortening of telomere
- Functional impairment
- Typical Hayflick phenomenon of cellular aging.
“The Hayflick phenomenon is the number of times a normal human cell population will divide until cell division stops. Leonard Hayflick discovered 40 years ago that cultured normal human cells have limited capacity to divide, after which they become senescent, a phenomenon now known as the Hayflick limit.”[57],[58]
Storage of stem cells
Adult stem cells are ideal source of autologous transplants, and they can be obtained from individuals at any age in life. Hence, to carry out such procedures, there is a need to store these stem cells which can be done by cryopreservation in liquid nitrogen (−196°C). These cells will survive at such low temperatures only if they are suspended in cryopreservatives/cryoprotectants.[20] Cryopreservatives are necessary additives to stem cell concentrates, since they stop cell death by inhibiting the formation of intra- and extracellular crystals. Dimethyl sulfoxide is the standard cryoprotectant used in laboratories as it prevents freezing damage to living cells.[59] Rapid freezing of stem cells prevent the ice formation in or around the cells and also plays a role in prevention of dehydration of cells.[60]
| Conclusion | | |
In the recent years, the field of dentistry has embellished its presence by taking major hikes in research and bringing them into practice. The current focus of research in regenerative dentistry is on the isolation of stem cells from dental tissues, and these researches have provided a good deal of evidence that oral and maxillofacial regions are the good sources of stem cells. In the present time, stem cell banks have gain excessive popularity and stem cells from the umbilical cord are mainly preserved in these banks for future use. Thus, the dental professionals should recognize the importance of obtaining stem cells during routine procedures as they can be stored for regeneration therapies in the future.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
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