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. 2020 Sep 27;100(2):209–216. doi: 10.1177/0022034520960125

The Junctional Epithelium Is Maintained by a Stem Cell Population

X Yuan 1, J Chen 1,2, JA Grauer 1,3, Q Xu 1,4, LA Van Brunt 1, JA Helms 1,✉
PMCID: PMC8173348  PMID: 32985318

Abstract

The most fundamental function of an epithelial tissue is to act as a barrier, regulating interactions between the external environment and the body. This barrier function typically requires a contiguous cell layer but since teeth penetrate the oral epithelium, a modified barrier has evolved, called the junctional epithelium (JE). In health, the JE attaches to the tooth, sealing the inside of the body against oral micro-organisms. Breakdown of the JE barrier results in periodontal ligament (PDL) disintegration, alveolar bone resorption, and ultimately tooth loss. Using lineage tracing and DNA pulse-chase analyses, we identified an anatomical location in the JE that supported both fast- and slow-cycling Wnt-responsive stem cells that contributed to self-renewal of the tissue. Stem cells produced daughter cells with an extraordinarily high rate of turnover that maintained JE integrity for 1.4 y in mice. Blocking cell proliferation via a chemotherapeutic agent 5-fluorouracil (5-Fu) eliminated fast-cycling stem cells, which caused JE degeneration, PDL destruction, and bone resorption. Upon removal of 5-Fu, slow-cycling stem cells regenerated both the structure and barrier function of the JE. Taken together, our studies identified a stem cell population in the JE and have potential clinical implications for prevention and treatment of periodontitis.

Keywords: Wnt signaling pathway, epithelial cells, stem cell research, gingiva, periodontitis, cell proliferation

Introduction

When teeth erupt, the continuity of the oral epithelium (OE) is disrupted. To compensate for this breach, a specialized structure around erupting teeth provides OE integrity and protects underlying tissues from bacterial invasion (Wertz and Squier 1991; Gaengler and Metzler 1992). This specialized structure is known as the junctional epithelium (JE). Similar types of junctional epithelia exist in other parts of the body, including the intestine (Laukoetter et al. 2006). Both junctional epithelia are composed of adherens and tight junctions that simultaneously allow fluid movement while acting as a barrier to the ingression of microbes (Saito et al. 1981; Schroeder and Listgarten 1997; Shimono et al. 2003; Laukoetter et al. 2006).

Epithelia including the JE are designed to protect underlying tissues from physical and chemical trauma, and one mechanism by which it accomplished is via a high rate of cell proliferation (Hooper 1956; Creamer et al. 1961). In young, intact epidermis, the estimated rate of turnover is ~1 mo (Squier and Brogden 2011); in the cornea, the turnover rate is ~2 wk (Cenedella and Fleschner 1990; Douvaras et al. 2013), and in the intestine, the median turnover time is 4 d (Squier and Brogden 2011). The turnover rate of the JE rivals that of the intestine (Engler et al. 1966; Skougaard 1970), but how the JE is continuously self-renewed is not entirely clear. This is largely due to a paucity of information on whether the JE harbors a stem cell population.

Stem cells and their niches have been extensively studied in many epithelial tissues, including the intestine, skin, and cornea (Blanpain et al. 2007). Stem cells support epithelial tissue self-renewal throughout adult life, while the niche provides signals that maintain stem cell quiescence and self-renewal, as well as proliferation and differentiation (Blanpain et al. 2007; Trentesaux et al. 2020). Despite structural and functional differences among epithelia, their niches share common signaling pathways (e.g., Wnt/β-catenin signaling) (Blanpain et al. 2007). In the intestine, Wnt signals emanate from Paneth cells at the base of the villi and maintain a state of stemness in adjacent Lgr5-positive, crypt-based clonal cells (Beumer and Clevers 2016). In the lining epithelia of the lung, Wnt signals emanate from fibroblasts and maintain AT2 stem cells (Nabhan et al. 2018). In the corneal epithelium, Wnt signals from limbal cells also maintain stemness (Ouyang et al. 2014). Whether a Wnt-responsive stem cell population exists in the JE is not known.

Here, we began an investigation into the molecular mechanisms of cell dynamics in the JE. Using a label-retaining strategy, the mitotic activity and progression of cells through the JE were followed, along with their differentiation and ultimate fates. A chemotherapeutic agent, 5-fluorouracil (5-Fu), was then used to experimentally eliminate fast-cycling cells, and the consequences on JE integrity and barrier function were evaluated over time. Using a lineage-tracing strain of Wnt reporter mice, we then explored the contribution of Wnt-responsive cells and their progeny to the JE in health and after tissue damage.

Methods and Materials

Animals

All experimental protocols followed ARRIVE guidelines and were approved by the Stanford Committee on Animal Research (protocol #13146). Axin2LacZ/+, Axin2CreERT2/+ (#018867), and R26RmTmG/+ (#007576) mice were purchased from Jackson Laboratories. Mice were housed in a temperature-controlled environment with 12-h light/dark cycles.

Lineage Tracing

Tamoxifen (T5648; Sigma) was dissolved in ethanol and then diluted with sunflower seed oil to 10 mg/mL. A single dose of tamoxifen (5 mg/25 g body weight) was delivered intraperitoneally to Axin2CreERT2/+;R26RmTmG/+ mice to label Wnt-responsive cells.

EdU Injection

5-Ethynyl-2′-deoxyuridine (EdU), a thymidine analogue, is incorporated into replicating DNA (Salic and Mitchison 2008). EdU (BCK-IV-IM; Base Click) was dissolved in phosphate-buffered saline (PBS) at a concentration of 10 mg/mL. Mice were intraperitoneally injected with EdU (50 mg/kg) and sacrificed 2 h later to examine cell proliferation. To assess EdU+ve cell dynamics, 1.5-mo-old male and female littermates received intraperitoneal injections of EdU (50 mg/kg). Euthanasia followed 2 h, 8 h, 24 h, 72 h, and 17 d later.

Statistical Analyses

Results are presented as the mean ± standard deviation of independent replicates. Student’s t test was used to quantify the differences described in this article. P ≤ 0.05 was considered significant. GraphPad Prism (GraphPad Software) was used for statistical analyses.

Please see Appendix for details on 5-Fu treatment, sample preparation, histology, immunohistochemistry, EdU/BrdU (5-bromo-2′-deoxyuridine) injections and staining, tartrate-resistant acid phosphatase (TRAP)/alkaline phosphatase (ALP) staining, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick end-labeling (TUNEL) staining, Xgal staining, and quantification.

Results

Within Oral Epithelia, the JE Is Distinguished by Its High Turnover Rate

The JE is a nonkeratinized epithelial barrier juxtaposed to the tooth surface (Fig. 1A). The JE is contiguous with the adjacent sulcular epithelia and oral epithelia (SE and OE, respectively; Fig. 1B). All 3 regions of the oral epithelia have proliferating basal cells, shown by Ki67 and PCNA immunostaining (Fig. 1C, D). EdU/BrdU dual labeling revealed, however, that JE cells had a significantly shorter cell cycle than either SE or OE cells (Appendix Fig. 1).

Figure 1.

Figure 1.

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The junctional epithelium (JE) is a high-turnover tissue. (A) Pentachrome staining of the periodontium of the maxillary first molar. The gingiva is indicated by the black boxes. (B) Pentachrome staining of the JE, sulcular epithelia (SE), and oral epithelia (OE). Immunolocalization of (C) Ki67 and (D) PCNA. Following 5-ethynyl-2′-deoxyuridine (EdU) delivery, EdU+ve cells were examined in the samples that were sacrificed (E) 2 h, (F) 8 h, and (G) 24 h later. (H) Quantification of EdU+ve cells (n = 3). The data were expressed as mean ± SD. The doubling time (Td) was calculated by the data from 2-h and 24-h time points. Costaining of 72-h chase EdU with (I) involucrin, (J) laminin 5, and (K) terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL). (L) A 17-d chase of EdU. The arrow indicates the EdU label-retaining cell in the JE. Abbreviations: ab, alveolar bone; bm, buccal mucosa; den, dentin; e, enamel space; je, junctional epithelium; oe, oral epithelium; pdl, periodontal ligament; se, sulcular epithelium. Blue dashed lines indicate the edge of the enamel and white dotted lines indicate the boundary between the epithelium and connective tissue. Scale bars: 50 µm.

Cell proliferation within the JE is initiated at its base; cells are then thought to migrate coronally, where they eventually desquamate into the oral cavity (Yajima-Himuro et al. 2014). These events were followed by labeling cells with EdU, then following their distribution. Initially, EdU-positive cells were positioned at the base of the JE (Fig. 1E); 8 h after labeling, the EdU-positive population had expanded but still remained associated with the basal lamina (Fig. 1F; quantified in Fig. 1H). Twenty-four hours after labeling, the EdU-positive population had doubled, and at least some cells were displaced apically, toward the tip of the JE (Fig. 1G; quantified in Fig. 1H). The fates of the EdU-positive cells in the JE were explored by immunostaining. Seventy-two hours after labeling, a subset of EdU-positive cells coexpressed involucrin, an early marker of epithelial cell differentiation (Fig. 1I). EdU-positive cells located adjacent to the tooth coexpressed the hemidesmosomal marker laminin 5 (Fig. 1J). Another subset of EdU-positive cells was positive for TUNEL staining (Fig. 1K). Finally, a few cells retained the EdU label and remained associated with the basal lamina even after 17 d (arrow, Fig. 1L); these cells did not express differentiation markers such as involucrin, filaggrin, or loricrin (data not shown). Given that the calculated average doubling time for JE cells was 25.2 h (Fig. 1H) and the estimated life span of a JE cell was ~5 d (Appendix Fig. 2A, B), the persistence of EdU-positive cells suggested the JE was populated by both fast- and slow-cycling cells.

The Structure and Function of the JE Depend Upon Its High Turnover Rate

To better understand the contribution of proliferating cells to the structure/function of the JE, mice received daily injections of 5-Fu, which induces apoptosis in G1/S cells (Chung et al. 2018). After treating with 5-Fu for 7 d (Fig. 2A), EdU incorporation studies confirmed that mitotically active cells in the JE were largely eliminated (compare Fig. 2B, C; quantified in Fig. 2D). Coincident with the loss of proliferating cells was a disintegration of the entire epithelial architecture that affected the JE more than the OE (Fig. 2E, F). The JE’s attachment to the tooth was also lost (Fig. 2G, H).

Figure 2.

Figure 2.

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The structure and function of the junctional epithelium (JE) depend upon its high turnover rate. (A) Mice were treated with 5-fluorouracil (5-Fu) for 7 d and then examined 1 d after the last injection. The control groups received phosphate-buffered saline (PBS) instead of 5-Fu. (B,C) The cease of proliferation was confirmed by 5-ethynyl-2′-deoxyuridine (EdU) staining. (D) Quantification of EdU+ve cells in the JE (n = 6). The data were expressed as mean ± SD. *P < 0.0001. The tissues were also analyzed using staining of (E, F) Masson’s trichrome, (G, H) laminin 5, (I, J) myeloperoxidase, (K, L) CD45, and (M, N) picrosirius red and (O, P) TRAP activity. Abbreviations: as before and dgf, dentogingival fibers; 5-Fu, 5-fluorouracil; TRAP, tartrate-resistant acid phosphatase. Green dotted lines demarcate the periodontal ligament (PDL) from the tooth surface. Scale bars: 50 µm.

In the control group, myeloperoxidase-positive neutrophils were limited to the JE (Fig. 2I); in the 5-Fu treatment group, neutrophils had invaded the connective tissue and periodontal ligament (PDL) (Fig. 2J). CD45+ve lymphocyte invasion into the PDL was also observed (Fig. 2K, L). Dentogingival fibers in the PDL were disrupted (Fig. 2M, N), and directly underneath the JE, alveolar bone resorption by TRAP-positive osteoclasts was elevated (Fig. 2O, P). Lymphocyte invasion (Appendix Fig. 3A–D) and TRAP activity increase (Appendix Fig. 3E–H) were not observed in the connective tissue and bone underneath adjacent OE, demonstrating the periodontium destruction was due to the disintegration of the JE instead of the systemic toxic of 5-Fu. We drew 2 conclusions from these data: first, although 5-Fu was delivered systemically, its effects were more pronounced in the JE compared to the adjacent OE because cell proliferation was significantly higher in the JE. Second, cell proliferation was essential for the defensive properties of the JE since absent a proliferative population, the JE disintegrated, and as a direct consequence, there was a breakdown in the underlying periodontal tissues.

Wnt-Responsive Stem Cells Maintain JE Structure and Function

Having demonstrated that a proliferating population of cells was required to maintain the structure and function of the JE (Fig. 2), we next explored the source of the continuously produced cells. In multiple epithelial tissues, Wnt proteins function as stem cell niche signals; consequently, we focused on this pathway and used 2 strains of Wnt reporter mice. Using Axin2LacZ/+ mice and Xgal staining, Axin2+ve, Wnt-responsive cells were identified near the base of the JE (Appendix Fig. 4A). Immunostaining for the Wnt intracellular mediator, β-catenin showed that the immunohistochemistry signal colocalized with the nuclear marker DAPI (Appendix Fig. 4B). These 2 lines of evidence together demonstrated that cells at the base of the JE were Wnt responsive.

We then used the Axin2CreERT2/+;R26RmTmG/+ strain to follow the distribution of the Wnt-responsive cells and their progeny throughout the JE as a function of time. One day after tamoxifen was delivered, green fluorescent protein (GFP)–positive Wnt-responsive cells were identified at the base of the JE (Fig. 3A). Three days later, descendants of the Wnt-responsive population had formed a column within the JE (Fig. 3B), suggesting that they were clonal. Five days later, the JE was fully populated by descendants of the initial Wnt-responsive population (Fig. 3C).

Figure 3.

Figure 3.

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Wnt-responsive stem cells maintain junctional epithelium (JE) structure and function. (A) Distribution of Wnt-responsive after a 1-d chase. Distribution of the progeny of the Wnt-responsive population after a (B) 3-d, (C) 5-d, (D) 30-d, and (E) 480-d chase. (F) A schematic showing the lineage tracing experiment design and the green fluorescent protein–positive (GFP+ve) population size during the chase. Mice received 1 dose of tamoxifen to label Wnt-responsive cells. The progeny was examined 3, 5, 30, and 480 d later. (G) Wnt-responsive cells (1-d chase) were costained with Ki67. (H) Quantification (n = 4). The total GFP+ve JE cells and GFP+veKi67+ve JE cells were counted. The percentage of GFP+veKi67+ve JE cells was calculated by the ratio of GFP+veKi67+ve over the total GFP+ve. The progeny of the Wnt-responsive population on the 5-d chase was costained with (I) Laminin 5, (J) involucrin, and (K) caspase 3. Abbreviations: as before; TAM, tamoxifen. Scale bars: 50 µm.

Cells transit through the JE in ~5 d (Appendix Fig. 2), yet 30 d later, a GFP–positive population persisted in the JE (Fig. 3D). Even 480 d after a single tamoxifen injection, descendants of the initial population of Wnt-responsive cells persisted in the JE (Fig. 3E). Stem cells are defined in part by their ability to self-renew. Given the length of the JE cell cycle (Appendix Fig. 1), coupled with the persistence of GFP+ve cells for up to 1.4 y, these data support the conclusion that the JE harbored a population of self-renewing, Wnt-responsive stem cells (Fig. 3F). This JE stem cell population was distinct from GFP+ve descendants in the adjacent OE, which were largely eliminated by turnover in 30 d (Appendix Fig. 5).

Stem cells are also defined by their capacity to undergo transit amplification. Coimmunostaining with Ki67 and GFP demonstrated that most (~88%) of Wnt-responsive JE cells were undergoing active proliferation within 24 h of labeling (Fig. 3G, H). Stem cells are further defined by their capacity to differentiate into function-specific daughter cells. Five days after being labeled, cells coexpressed GFP and laminin 5, indicating that progeny of the Wnt-responsive stem cell pool had contributed to the JE attachment apparatus (Fig. 3I). Other progeny of the Wnt-responsive stem cell pool coexpressed involucrin (Fig. 3J), indicating their terminal epithelial differentiation. Still other progeny of the Wnt-responsive stem cell pool coexpressed caspase 3 (Fig. 3K), indicating that they were committed to undergoing programmed cell death and, ultimately, desquamation. Collectively, these data supported a model whereby a population of Wnt-responsive stem cells residing at the base of the JE generated progeny that rapidly expanded and then differentiated to form the tooth attachment apparatus and thus contributed to the integrity and function of the JE.

Slow-Cycling Stem Cells Are Responsible for JE Regeneration

Since not all the Wnt-responsive cells are proliferative (Fig. 3G), we reasoned whether slow-cycling Wnt-responsive cells existed. If so, they might escape the effects of the chemotherapeutic 5-Fu and be able to regenerate the JE after drug suspension. To test this possibility, Axin2CreERT2/+;R26RmTmG/+ mice received a single injection of tamoxifen to induce recombination, followed by 7 d of 5-Fu injection (Fig. 4A). After 5-Fu treatment was suspended, and tissues were harvested for analyses. As expected from our previous experimental results (Fig. 2), the structure of the JE had largely disintegrated in response to 5-Fu treatment (Fig. 4B), but significantly, a small population of GFP-positive cells nonetheless persisted in the base of the JE (arrow, Fig. 4C).

Figure 4.

Figure 4.

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Slow-cycling stem cells are responsible for junctional epithelium (JE) regeneration. (A) A schematic showing the experiment design. Mice were first injected with tamoxifen to label Wnt-responsive cells and then treated with 5-fluorouracil (5-Fu) for 7 d. (B) Morphology and (C) distribution of the progeny of Wnt-responsive cells were examined. Four days after the last 5-Fu injection, (D) morphology, (E) distribution of the progeny of Wnt-responsive cells, and (F) 5-ethynyl-2′-deoxyuridine–positive (EdU+ve) cells were examined. Seven days after the last 5-Fu injection, (G) morphology, (H) the progeny of Wnt-responsive cells, (I) laminin 5 expression, and (J) EdU+ve cells were examined. (K, L) Collagen fiber, (M, N) tartrate-resistant acid phosphatase (TRAP) activity, and (O, P) alkaline phosphatase (ALP) activity were compared between the 5-Fu group and intact group. (Q) Quantification of bone resorption and formation activity (n = 6). The bone resorption activity is expressed as the number of osteoclasts per bone surface. The bone formation activity is expressed as the pixels of ALP to the total pixels. The data were expressed as mean ± SD. Abbreviations: as before and ALP, alkaline phosphatase. Scale bars: 50 µm.

Over the next 4 d, the JE began to regain its structural integrity (Fig. 4D), accompanied by a significant expansion in the number of GFP+ve cells (Fig. 4E). EdU staining showed the proliferation was restricted in the epithelium and largely in the basal layer of the reforming JE (Fig. 4F). By recovery day 7, the structure of the JE was reestablished (Fig. 4G). The new JE was derived largely from GFP+ve cells (Fig. 4H), which included the regenerated laminin 5–mediated attachment apparatus (Fig. 4I). The number of proliferating cells in the JE had returned to baseline levels, although the number of EdU-positive cells in the OE remained higher than normal (Fig. 4J).

Not all periodontal tissues had fully recovered after 7 d, however. For example, the dentogingival fibers of the PDL remained disorganized compared to intact controls (Fig. 4K, L). TRAP and ALP activities in the adjacent alveolar bone also remained elevated relative to intact controls (Fig. 4M–P; quantified in Fig. 4Q). Collectively, these data demonstrate that a population of slow-cycling, Wnt-responsive stem cells escaped the effects of an antiproliferative drug, and following cessation of 5-Fu treatment, this stem cell population generated new cells that rebuilt the JE.

Discussion

Rapid Cell Turnover as a Defensive Function in the JE

In stratified squamous epithelial tissues, including the skin and masticatory oral mucosa, cells undergo terminal differentiation, creating an insoluble keratinized surface that protects underlying epithelial cells and connective tissues. When this process is disrupted, the result is oftentimes neonatal lethality (Shwayder 2004; Matsui and Amagai 2015), underscoring the importance of keratinization as a barrier function. The JE, however, does not employ keratinization as a barrier strategy; instead, the JE appears to use a high rate of cell turnover to form a dynamic barrier. In this regard, the cell dynamics of the gastrointestinal tract is a useful model for comparison. In the gastrointestinal tract, the continual production, migration, and shedding of cells constitute an efficient dynamic barrier to microbial invasion. Cells proliferate at the base of the villus and are shed from its tip into the gut lumen, and in doing so, homeostasis is maintained (Clevers 2013). Bacteria play an active role in regulating these processes: for example, in the colon of germ-free mice, the rate of cell proliferation is reduced, and stem cell niches contain fewer cells than in conventional mice (von Frieling et al. 2018). A similar situation exists in the JE. Our data demonstrate that the production of new cells takes place at the base of the JE and that these cells either migrate or are displaced apically as they differentiate (Fig. 1). This has also been demonstrated by 2-d BrdU staining (Yajima-Himuro et al. 2014). This proliferative characteristic is required for the dynamic barrier functions of the JE (Fig. 2). It has been reported that the JE of germ-free mice is smaller (Tsukamoto et al. 2012), raising the possibility that the Wnt-responsive stem cell population is also modified by the presence of bacteria. Examining the JE stem cell niche in germ-free mice may answer this question.

Stem Cell Niche in the JE

One function of tissue-specific stem cells is to replace cells that are lost during normal day-to-day living or as a result of an injury. Some tissue-specific stem cells persist in a slow-cycling state, but in response to an increased demand (e.g., injury), their cycling rate is increased; these cells are often identified by their label-retaining capacity (Cheung and Rando 2013; van Velthoven and Rando 2019). Here, we showed that in EdU label-retaining experiments, most EdU+ve cells either diluted the label by rapid dividing or were displaced by new cells (Fig. 1). Nonetheless, a few basal cells were labeled with EdU that remained undiluted even after 17 d (Fig. 1).

5-Fu is a chemotherapeutic agent that targets proliferating cells; consequently, tissues that are maintained by a high rate of cell turnover will be significantly affected by the drug. Indeed, in patients taking 5-Fu, oral mucositis and diarrhea are common side effects (Chang et al. 2015). Our data provide an explanation for an oral mucositis/periodontitis phenotype based on the fact that fast-cycling cells were eliminated from the JE, leading to its rapid degeneration (Fig. 2). Cells in G0 survive 5-Fu treatment, and at least some of these surviving cells were the progeny of a Wnt-responsive population (Fig. 4). Once 5-Fu treatment was suspended, GFP+ve cells expanded and repopulated the JE, thus demonstrating a direct role for slow-cycling cells in mediating JE regeneration (Fig. 4).

Collectively, our data support a model where quiescent and active adult stem cells coexist in the JE to meet both homeostatic and repair needs. A similar arrangement has been reported in the intestine, hair follicle, and bone marrow (Li and Clevers 2010).

Recovery versus Regeneration of the JE

After suspending 5-Fu treatment, we observed a rapid recovery of the JE structure and function (Fig. 4). Not all aspects of the tooth attachment apparatus, however, had returned to normal: cell proliferation remained elevated in the OE, and neither the PDL nor the adjacent bone had returned to their preinjury baseline state by recovery day 7 (Fig. 4). These results suggested that epithelia, versus the hard and soft connective tissues, might have different regenerative capacities. Alternatively, it could suggest that some tissues take much longer to repair/regenerate than others.

We considered other experimental methods that disrupt the JE, such as ligature-induced periodontitis models. Both hard and soft tissue breakdown occurs within days of placing ligatures (Viniegra et al. 2018). If ligatures are removed, then the JE appears to reform, but alveolar bone levels do not seem to recover to the same degree (Viniegra et al. 2018). These data suggest that the JE may regenerate, while PDL and bone may not. If the JE can regenerate, as has been stated in the historical literature (Listgarten 1972; Redd and Byers 1994; reviewed in Mackenzie 1987), then a clinically relevant question comes to mind: is a regenerated JE as efficient a barrier as an original JE? Thus far, clinical and preclinical studies have offered few insights. For example, following root planing and soft tissue curettage in patients, a “long junctional epithelium” forms at the tooth–connective tissue interface (Caton and Zander 1979). It has been stated that this long JE is distinguishable from a “new connective tissue attachment,” but the basis for this claim is its histological appearance and not its mechanical adhesivity (Caton and Zander 1979). Whether the barrier function of the long JE is less efficient than that of intact JE is also unresolved (Listgarten 1980; Magnusson et al. 1983; Beaumont et al. 1984; Noguchi et al. 2017). In future work, we intend to use mechanical testing to determine whether a “regenerated” JE is as adherent as an “original” JE.

Conclusion and Perspective

We provide evidence that Wnt-responsive stem cells support JE homeostasis. If JE stem cells are compromised, the result is the destruction of the PDL and alveolar bone. Does the soft tissue attachment to an implant also harbor an equivalent JE stem cell population? The literature describes a structure, histologically similar to a native JE, forms around dental implants (Atsuta et al. 2016), but the extent to which this peri-implant soft tissue attachment mimics a native JE is unknown. In future experiments, we intend to explore the similarities and differences in the stem cells and their niche around teeth versus implants.

Author Contributions

X. Yuan, contributed to conception, design, data acquisition, analysis, and interpretation, drafted and critically revised the manuscript; J. Chen, J.A. Grauer, Q. Xu, contributed to data acquisition, analysis, and interpretation, critically revised the manuscript; L.A. Van Brunt, contributed to data analysis and interpretation, critically revised the manuscript; J.A. Helms, contributed to conception, design, data analysis, and interpretation, drafted and critically revised the manuscript. All authors gave final approval and agree to be accountable for all aspects of the work.

Supplemental Material

DS_10.1177_0022034520960125 – Supplemental material for The Junctional Epithelium Is Maintained by a Stem Cell Population
Click here for additional data file. (6MB, pdf)

Supplemental material, DS_10.1177_0022034520960125 for The Junctional Epithelium Is Maintained by a Stem Cell Population by X. Yuan, J. Chen, J.A. Grauer, Q. Xu, L.A. Van Brunt and J.A. Helms in Journal of Dental Research

Acknowledgments

We thank Yunke Ren and Gladys Hernandez for their help in tissue processing and staining.

Footnotes

A supplemental appendix to this article is available online.

Declaration of Conflicting Interests: The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding: The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The study was funded by grants from the National Institute of Dental and Craniofacial Research R01DE024000-14 to J.A.H. and K99DE028585-02 to X.Y.

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DS_10.1177_0022034520960125 – Supplemental material for The Junctional Epithelium Is Maintained by a Stem Cell Population
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Supplemental material, DS_10.1177_0022034520960125 for The Junctional Epithelium Is Maintained by a Stem Cell Population by X. Yuan, J. Chen, J.A. Grauer, Q. Xu, L.A. Van Brunt and J.A. Helms in Journal of Dental Research

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