Variation in collagen expression by cloned periodontal ligament cells

The role of cell surface markers and enamel matrix derivatives on human periodontal ligament mesenchymal progenitor responses in vitro

Periodontitis is a chronic-, infectious-disease of the human periodontium that is characterized by the loss of supporting tissues surrounding the tooth such as the periodontal ligament (PDL), cementum and alveolar bone. Regeneration of the periodontium is dependent on the participation of mesenchymal stem/stromal cells (MSC) resident in the PDL. Enamel matrix derivative (EMD), an extract from immature porcine enamel rich in amelogenin protein but that also contain bone morphogenetic protein (BMP), is used to treat periodontal defects. The effects of EMD on MSC cells of the PDL are not well characterized. In this in vitro study, we identify PDL progenitor cells from multiple individuals and demonstrate that EMD stimulates them. We show that the effect of EMD on cell proliferation and migration is mediated through the amelogenin it contains, while the differentiation of these progenitor cells to cell types of mineralized tissue is mainly due to BMP signaling.

Fibroblasts-a diverse population at the center of it all

The capacity of fibroblasts to produce and organize the extracellular matrix and to communicate with other cells makes them a central component of tissue biology. Even so, fibroblasts remain a somewhat enigmatic population. Our inability to fully comprehend these cells is in large part due to the paucity of unique cellular markers and to their pervasive diversity. Much of our understanding of fibroblast diversity has evolved from studies where subpopulations of these cells have been produced without resorting to cell surface markers. In this regard, cloning and mechanical separation of tissues prior to establishing cultures has provided multiple subpopulations. Nonetheless, in isolated situations, the expression or lack of expression of Thy-1/CD90 has been used to separate fibroblast subsets. The role of fibroblasts in intercellular communication is emerging through the implementation of organotypic studies in which three-dimensional fibroblast culture are combined with other populations of cells. Such studies have revealed critical paracrine loops that are essential for organ development and for wound repair. These studies also provide a backdrop for the emerging field of tissue engineering. The participation of fibroblasts in the regulation of tissue homeostasis and their contribution to the aging process are emerging issues that require better understanding. In short, fibroblasts represent a multifaceted, complex group of cells.

Stem cells and tooth tissue engineering

The notion that teeth contain stem cells is based on the well-known repairing ability of dentin after injury. Dental stem cells have been isolated according to their anatomical locations, colony-forming ability, expression of stem cell markers, and regeneration of pulp/dentin structures in vivo. These dental-derived stem cells are currently under increasing investigation as sources for tooth regeneration and repair. Further attempts with bone marrow mesenchymal stem cells and embryonic stem cells have demonstrated the possibility of creating teeth from non-dental stem cells by imitating embryonic development mechanisms. Although, as in tissue engineering of other organs, many challenges remain, stem-cell-based tissue engineering of teeth could be a choice for the replacement of missing teeth in the future.

Clonal characterization of fibroblasts in the superficial layer of the adult human dermis

The dermis of adult human skin contains a physiologically heterogeneous population of fibroblasts that interact to produce its unique architecture and that participate in inflammatory and wound repair functions in vivo. This heterogeneity has been well documented for fibroblasts located in the superficial papillary dermis and the deep reticular dermis. However, the existence of diverse fibroblast subpopulations within a given region of the dermis has not been explored. In this study, fibroblast cultures have been established from the superficial dermis following enzymatic dissociation of the tissue. These fibroblasts have been cloned by limiting dilution and initially selected on the basis of morphology and proliferation kinetics. Fibroblasts in some of the clones selected for study express alpha-smooth muscle actin, a myofibroblast characteristic. Significant differences for fibroblast clones obtained from the same piece of skin have been observed with regard to their rate of collagen lattice contraction, their ability to organize a fibronectin matrix, their release of specific growth factors/cytokines into culture medium, and their response to interleukin-1alpha. These differences in both morphological and physiological characteristics indicate that the superficial papillary dermis contains a heterogeneous population of fibroblasts. This heterogeneity might indicate that diverse subpopulations of fibroblasts are required to interact in both homeostatic and pathological situations in skin.

Stem cells in the periodontal ligament

The ability to identify and manipulate stem cells has been a significant advancement in regenerative medicine and has contributed to the development of tissue engineering-based clinical therapies. Difficulties associated with achieving predictable periodontal regeneration, means that novel techniques such as tissue engineering need to be developed in order to regenerate the extensive soft and hard tissue destruction that results from periodontitis. One of the critical requirements for a tissue engineering approach is the delivery of ex vivo expanded progenitor populations or the mobilization of endogenous progenitor cells capable of proliferating and differentiating into the required tissues. By definition, stem cells fulfill these requirements and the recent identification of stem cells within the periodontal ligament represents a significant development in the progress toward predictable periodontal regeneration. In order to explore the importance of stem cells in periodontal wound healing and regeneration, this review will examine contemporary concepts in stem cell biology, the role of periodontal ligament progenitor cells in the regenerative process, recent developments in identifying periodontal stem cells and the clinical implications of these findings.

Survival of human periodontal ligament cells in media proposed for transport of avulsed teeth

Many solutions have been examined as possible storage media for avulsed teeth. In this report, human periodontal ligament (PDL) cells were exposed for 1 h to culture medium, milk, Hanks Balanced Salt Solution (HBSS), Soft Wear, Opti Free, and Solo Care contact lens solutions, Gatorade, and tap water, at room temperature and on ice. The number of viable cells was counted using the trypan blue exclusion technique, immediately after exposure (0 h) and at 24 and 48 h, to test the proliferative capacity of the cells after treatment. The results indicated that a significantly higher number of cells survived and proliferated when the exposures were performed at 0 degrees C. Water had a detrimental effect on the cells, whereas culture medium and HBSS preserved significantly more viable cells than the other experimental solutions. Within the parameters of this study, it appears that HBSS is the optimal storage medium for avulsed teeth. Low-fat milk could serve as an alternative if ice is available. Contact lens solutions or Gatorade on ice could serve as short-term (1 h) storage media if the other solutions are not readily available.

Novel isolation of alkaline phosphatase-positive subpopulation from periodontal ligament fibroblasts

BACKGROUND

Periodontal ligament fibroblasts (PDLFs) are the cells essential for periodontal regeneration. PDLFs comprise a heterogeneous cell population and consist of several cell subsets that differ in their function. It is known that PDLFs produce osteoblast-related extracellular matrix proteins and show higher alkaline phosphatase (ALP) activity compared with gingival fibroblasts (GFs), implying that PDLFs have osteogenic characterisitics. The aim of the present study was to isolate the osteogenic population of PDLFs according to their expression of ALP.

METHODS

PDLFs and gingival fibroblasts were separated into two populations, ALP-positive and ALP-negative, with an immunomagnetic method using a monoclonal antibody against human bone type ALP and magnetic beads conjugated with a secondary antibody. Expression of basic fibroblast growth factor (bFGF) receptor and transforming growth factor (TGF)-beta receptor was investigated in these two populations. Osteoblast-related molecules, osteocalcin, and bone sialoprotein; ALP activity; and effect of bFGF on proliferation were also compared.

RESULTS

Effective separation was confirmed in both PDLFs and GFs by flow cytometry. The expression of FGF receptor (FGFR) and TGF-beta receptor was significantly higher in ALP-positive PDLFs than in ALP-negative PDLFs. ALP-positive PDLFs also expressed higher mRNA levels of osteocalcin and bone sialoprotein compared with ALP-negative PDLFs. The mitogenic effect of bFGF on ALP-positive PDLFs was greater than that of ALP-negative PDLFs.

CONCLUSIONS

These results indicate that osteoblastic and/or cementoblastic PDLF subsets could be isolated from the PDLF populations using an immunomagnetic method. Magnetic isolation of PDLFs may be a useful tool to obtain the cells which will potentially induce mineralization on the root surface.

Effect of cigarette smoking on human PDL fibroblasts attachment to periodontally involved root surfaces in vitro

BACKGROUND/AIM

Cigarette smoking is one of the most significant risk factors in the development and further advancement of inflammatory periodontal disease. However, no study has been performed to investigate the effect of smoking on the attachment of human periodontal ligament fibroblasts to either periodontally diseased or healthy roots. The present study was conducted to evaluate the attachment of fibroblasts derived from healthy human periodontal ligament (PDL) to periodontally diseased root surfaces of smokers.

METHOD

The subjects included 14 smokers and seven nonsmokers with at least a single periodontally involved anterior tooth planned for extraction. In addition, seven impacted third molars, which had been removed from nonsmoking adolescents, were used as a healthy control. The smoking status of each patient was determined by classifying the volunteers into four groups according to their level of cigarette consumption at the initial examination (seven patients each). Nonsmoking subjects who had never smoked cigarettes and had healthy periodontium were called healthy control (G1). In subjects with periodontal diseases, nonsmoking subjects who had never regularly smoked cigarettes (< 2 cigarettes/week) were called positive control (G2), smokers consuming <or=19 cigarettes/day were placed in group G3, and smokers consuming >or=20 cigarettes/day were located in group G4. To exclude the effects of all local irritants except for the adsorbed tobacco products, all teeth were subjected to thorough scaling and root planing 1 week before extraction. After 1 week of meticulous home care and continued smoking experience, teeth were extracted and the periodontally involved test areas were prepared for PDL culturing. PDL cells were cultured on root segments for 24 h. Samples were prepared for SEM viewing, photographing and counting at x750 in a standard area.

RESULTS

The results of this study indicated that smokers' data (G3, G4) revealed a significant reduction of attached PDL cells when compared to that of nonsmokers' healthy and positive controls (G1, G2). No significant difference in the mean number of attached cells was found between data derived from smokers' groups (G3 vs. G4). The attached cells in all groups varied in shape; they were flatter in the control groups, while they were round in smokers' groups, with no dose-dependent effect.

CONCLUSION

The present results suggest that cigarette smoking compromises PDL cell adhesion to root planed surfaces, which might affect periodontal regeneration following therapy.

Cyclic tension force activates nitric oxide production in cultured human periodontal ligament cells

BACKGROUND

Nitric oxide (NO) is involved in a number of physiological and pathophysiological processes. The aim of this study was to examine the ability of human periodontal ligament (PDL) cells to produce NO and whether mechanical forces could induce NO production in the PDL cells.

METHODS

Human PDL cells were seeded onto flexible bottoms of a culture plate and subjected to cyclic tension forces. NO production was evaluated by measuring concentration of NO2- and NO3- (NO2-/NO3-), the oxidized products of NO, in the culture medium. We employed reverse transcription polymerase chain reaction (RT-PCR) methods to detect NO synthase mRNA in the PDL cells. NO synthase immunoreactivity was also evaluated in both stimulated and unstimulated PDL cells.

RESULTS

In unstimulated PDL cell culture, NO2-/NO3- increased to 140% of the initial value in 12 hours. In contrast, NO2-/NO3- showed a 3-fold increase when the cells had been subjected to cyclic tension forces for 12 hours. The increase in NO production was blocked by NG-monomethyl-L-arginine (5 x 10(-4) M), an inhibitor of NO synthase. Endothelial NO synthase (ecNOS) mRNA was expressed in both stimulated and unstimulated PDL cells, whereas inducible NO synthase (iNOS) mRNA was detected in neither culturing condition. We found strong ecNOS but not iNOS immunoreactivity in the stimulated PDL cells.

CONCLUSIONS

These results suggest that human PDL cells produce NO by ecNOS and that the production is enhanced by stimulating the cells with cyclic tension forces. Mechanically stimulated PDL cells may modulate the function of periodontium by the upregulated NO production.

The response of periodontal ligament cells to fibronectin

Fibronectin (fn) is an extracellular matrix (ECM) molecule important in cell adhesion and migration and in wound healing. It is also likely important in periodontal ligament (PDL) cell-ECM interactions, and thus in regenerating periodontal tissues. In this study we characterized PDL cells and their interactions with FN, testing different PDL cell isolates taken from healthy and diseased conditions. PDL cells were characterized by their morphology, integrin profile, motility, and bone nodule formation. Cells were then assayed for adhesion, proliferation, and chemotaxis in response to FN or FN fragments. Cell isolates were morphologically heterogeneous and fibroblastic, had a normal-appearing actin cytoskeleton and a wide range of migration potentials, and formed bone-like nodules in vitro. They expressed alpha5, beta1, alpha v, and alpha4 integrin subunits, known receptors for FN, and in fact they bound FN preferentially at 5 and 10 microg/ml. Intact FN induced greater PDL cell proliferation and chemotaxis than did FN fragments (120-kDa cell-binding, 60-kDa heparin-binding, and 45-kDa collagen-binding). PDL cells harvested from diseased and healthy conditions were no different on the basis of these assays. These data demonstrate that PDL cells are a mixed population of fibroblastic cells, capable of forming a mineralized matrix. They also suggest that maximal proliferation and chemotaxis require specific FN domains that are present on the intact molecule but not its fragments.

Attachment formation following replantation of cultured cells into periodontal defects--a study in minipigs

Regeneration processes in the periodontium occur by the interaction of different cell populations. It is known that these cells are also capable of forming new periodontal tissue after culture in vitro. The present study investigated whether replanted cultured cells from the periodontium could contribute to attachment formation. Primary cell cultures from alveolar bone and periodontal ligament were obtained from 11 minipigs. Experimentally induced furaction and interdental defects (n = 168) were treated in groups: (a) flap surgery, replantation of alveolar bone cells, and covering of the defects with Teflon membranes (ABC group); (b) flap surgery, replantation of periodontal ligament cells and membranes (PLC group); (c) flap surgery, bone gelatin (carrier material) and membranes (BG group); (d) flap surgery and membranes (NBG group); (e) flap surgery (FS group); and (f) no treatment (NT group). The defects were clinically and histologically (polyfluorochrome labeling) assessed after 10, 30, and 90 days. In the ABC group, initial calcified tissue formation at the roots was apparent after only 8 days. Marked new formation of cementum and alveolar bone and the development of a new attachment were observed after 90 days. In the BG and the NBG groups, wound healing varied depending on membrane healing and the morphology of the defects, which led to significantly poorer and variable results. Similar results were found in the PLC group, although some defects showed extensive cementum and bone formation. Defects in the FS and the NT groups healed largely by epithelialization. The study shows that replantation of cultured alveolar bone cells leads to formation of new cementum and bone, which, in turn, leads to formation of a new attachment. It is likely that the cells stabilize the tissue formation in the defect or on the root surface in the early phase of wound healing and prevent epithelial downgrowth. Results also show that regeneration in the periodontium is determined by the availability of (precursor) cells capable of forming calcified tissues.

Is fibroblast heterogeneity relevant to the health, diseases, and treatments of periodontal tissues?

There are wide variations of gene expression and strikingly different responses to extracellular signals among different fibroblast populations. This has prompted a large number of in vitro studies which suggest that fibroblasts are not homogeneous but instead comprise multiple subpopulations with extensive site-to-site and intra-site variations. Conceivably, either fibroblasts are not all created equal, or, alternatively, discrete subpopulations may emerge in development, inflammatory lesions, or wound healing. While the heterogeneous nature of cultured fibroblasts has been known for some time, are these variations relevant to our understanding of the biology of oral tissues, their involvement in disease, and their response to therapy? Since fibroblasts are the predominant cell type in soft connective tissue matrices, the regulation of their proliferative, synthetic, and degradative behavior is likely to be important in tissue physiology and pathology. In this review, we use the current literature to assess whether fibroblast subpopulations really make a difference in the health and disease of periodontal tissues. We address the following questions: (1) Is fibroblast heterogeneity a real in vivo phenomenon? (2) How can we advance our knowledge of phenotypic variations and the regulation of fibroblast differentiation? (3) Could a knowledge of fibroblast heterogeneity have an impact on the development of new approaches to pathogenesis and the treatment of periodontal tissues?

Fibroblast heterogeneity in the periodontium and other tissues

Fibroblasts are the major resident cells which inhabit the periodontal tissues. As such, they are crucial for maintaining the connective tissues which support and anchor the tooth. Little is known of their origins, synthesis of regulatory cytokines and growth factors in health and disease, and importance in soft tissue regeneration. An emerging concept is that fibroblasts are not homogeneous, but instead consist of subsets of cells which can regulate bone marrow-derived cells such as T lymphocytes. Fibroblasts can be separated into subsets on the basis of morphology, size and expression of intermediate filaments as well as collagen subtypes. Differential surface marker expression has also been a key feature to distinguish fibroblast subsets from many tissues. Antigens such as Thy-1, class II MHC, and C1q are among those surface proteins which have been employed successfully to separate fibroblasts. Importantly, these fibroblast subsets are not only antigenically diverse, but also possess distinct functions. Thy 1+ pulmonary fibroblasts can display class II MHC antigens, synthesize IL-1 and can activate T lymphocytes, whereas the Thy 1+ subset is devoid of these functions. Recently, fibroblasts from the human orbit have also been shown to be separable on the basis of Thy 1 surface marker expression. Fibroblasts derived from human gingiva and periodontal ligament also appear to be composed of subsets with a heritable pattern of surface markers which will permit their separation into functional subpopulations. This paper will review findings of fibroblast heterogeneity in periodontal and other tissues. Evidence will be presented for the use of surface markers to delineate functional subsets. The ability to discriminate subsets of fibroblasts will aid in studies of periodontal disease pathogenesis and wound healing.

Albumin gene expression during mouse odontogenesis

Albumin protein is present in developing teeth of several species. Oligomer primers and cRNA probes specific for albumin were designed to perform RT-PCR, and for in situ hybridization, respectively. In situ hybridization failed to reveal albumin expression in any tooth cells, however, albumin PCR products were amplified from tissues adhering to the roots of developing teeth from four-week-old mice. It is concluded that this source is not the primary source of albumin protein found in developing enamel, because of the location and level of expression of albumin mRNA in periodontal tissue.

Subpopulations of fetal-like gingival fibroblasts: characterisation and potential significance for wound healing and the progression of periodontal disease

Wound healing in the adult is commonly compromised by excessive scar formation. In contrast, fetal wound healing is a regenerative process characterised by the conspicuous absence of scarring. Available evidence suggests that phenotypic differences between fetal and adult fibroblasts are important determinants of these distinct modes of tissue repair. In this context, a number of groups (including our own) have documented differences between fetal and adult fibroblasts with respect to such potentially relevant characteristics as migratory activity, motogenic response to cytokines and the synthesis of motility factors, cytokines and matrix macromolecules. The oral mucosa appears to be a privileged site in the adult in that it continues to display a fetal-like mode of wound healing. Data are presented in this review indicating that a subpopulation of gingival fibroblasts expresses several 'fetal-like' phenotypic characteristics. These observations are discussed in terms of both the continued expression of a fetal-like mode of wound healing in the oral mucosa and the possible differential involvement of distinct fibroblast subpopulations in the progression of periodontal disease.

Formation of differentiated tissues in vivo by periodontal cell populations cultured in vitro

The periodontium contains heterogeneous mesenchymal cell populations with various differentiation potentials. The capacity of these cells for tissue formation as well as the origin of their precursors are still not entirely defined. In this study, cells originating from different periodontal tissues were cultured in vitro, and tissue formation in vivo following orthotopic re-implantation was investigated. Cells were recovered from the alveolar bone and periodontal ligament tissue of six minipigs, and cultured cells were then grown on extracted dental roots from the homologous animals by means of co-culture in vitro. Each minipig received 2 roots covered with alveolar bone cells, 2 roots covered with periodontal ligament cells, and 2 control roots (without cells) implanted into palatal bone defects. Intravital fluorochrome labeling was performed, and two minipigs were histologically examined after 2, 4, and 12 weeks in each case. Controls showed widespread resorption and ankylosis, whereas roots covered with cultured periodontal cells exhibited tissue formation in vivo. Alveolar bone cells synthesized a calcified cellular tissue resembling cellular cementum, suggesting that cells within this population might differentiate into cementoblasts when reimplanted with a dental substrate in vivo. Periodontal ligament cells exhibited no calcified tissue formation in vivo, but cells synthesized a connective tissue with orientated fiber bundles attached to both host bone and root, resembling periodontal ligament.

DNA content and alkaline phosphatase expression in cells of different gingival overgrowths

The present study compared the alkaline phosphatase (ALPase) expression and DNA content at specific periods in cultured cells derived from non-inflamed enlarged gingivae of idiopathic gingivofibromatosis (IGF) and phenytoin-induced hyperplasia (PHG). Cultured cells from healthy gingiva or periodontal ligament (PDL) were used as controls. The DNA assay, ALPase assay and cytochemical staining for ALPase in cultured cells were performed at four, seven, and nine days. The presence of intense ALPase activity was a prominent feature in cultured IGF cells, whereas very low ALPase activity was detected in PHG cells. The cell lines tested showed no significant differences in DNA content. The expression of ALPase in these cells was population density-dependent. The observation that cells isolated from both types of gingival overgrowth exhibited a different ALPase profile at variance with normal gingival fibroblasts suggested that a distinct pathogenic mechanism may be involved in each type of gingival overgrowth.

A comparison of the effect of epidermal growth factor, platelet-derived growth factor, and fibroblast growth factor on rat periodontal ligament fibroblast-like cells' DNA synthesis and morphology

An enhanced formation of bone, dentin, and collagen fibers in periodontal wounds after application of polypeptide growth factors has recently been reported. However, the complex environment in vivo makes it impossible to determine the specific effects of growth factors on various cells involved in the wound-healing process. We have therefore investigated the mitogenic and morphogenic effects of recombinant epidermal growth factor (rEGF), natural platelet-derived growth factor (nPDGF), and natural fibroblast growth factor (nFGF) on periodontal ligament fibroblast-like cells. A cell line was established from rat PDL tissue. The cell line was characterized according to morphology, growth pattern, cytoskeletal proteins, and growth kinetics. The mitogenic effect of growth factors was assessed by incorporation of [3H]thymidine in the cellular DNA for 4 hours. Differences between groups of observations were assessed by the Student t-test. The morphogenic effects of growth factors were described with respect to growth pattern, cell orientation, and cell and nucleus form after a random photographic recording. The fibroblast-like cell type and the non-transformed phenotype of the cell line have been identified by the presence of parameters considered to be characteristic of a normal fibroblast-like cell line. The morphogenic analysis of both experimental and control cultures showed a monolayer of adherent cells with spindle or stellate morphology, a random alignment and round or elongated nuclei. Incorporation of [3H]-thymidine was increased in a dose-dependent manner by all growth factors. Maximal effect on the DNA synthesis was: rEGF, 131%; nPDGF, 274%; and nFGF, 182%.(ABSTRACT TRUNCATED AT 250 WORDS)

Inter- and intra-site heterogeneity in the expression of fetal-like phenotypic characteristics by gingival fibroblasts: potential significance for wound healing

We have previously reported that fetal and adult skin fibroblasts display distinctive migratory phenotypes on 3-D collagen substrata and that these behavioural characteristics may be quantified by a function defined as the cell density migration index (CDMI). Subsequent work indicated that this difference in migratory phenotype was due to the production by fetal fibroblasts of a migration stimulating factor (MSF) that is not produced by normal adult skin fibroblasts. We now present data indicating that: (a) unselected fibroblasts obtained from 14/14 (100%) of adult gingival explants expressed fetal-like CDMI values compared to only 1/10 (10%) of similarly explanted paired skin cells; (b) 12/12 (100%) of these gingival fibroblast lines also produced detectable quantities of MSF compared to 0/9 (0%) of the tested skin cells; (c) by microdissection studies, gingival fibroblasts obtained from different anatomical microdomains consisted of behaviourally distinct subpopulations, with cells derived from the papillary tips (PAP fibroblasts) displaying fetal-like CDMI values and persistent MSF production, whilst cells obtained from the deeper reticular tissue (RET fibroblasts) were adult-like with respect to these two criteria; (d) PAP fibroblasts were also smaller and achieved higher saturation cell densities compared to paired RET cells; (e) PAP fibroblasts passaged in vitro underwent a fetal-to-adult phenotypic transition characterized by the adoption of various RET cell characteristics, including the acquisition of CDMI values falling within the adult range and cessation in MSF production; and (f) early passage PAP fibroblasts incubated in the presence of an affinity-purified anti-MSF rabbit polyclonal antibody were induced to alter their migratory phenotype and exhibited CDMI values falling within the adult range. Statistical analysis indicated a highly significant correlation between the expression of a fetal-like CDMI and production of MSF (P &lt; 0.00001, using the Fisher exact contingency test). Taken together, these observations suggest that the production of MSF by PAP fibroblasts is responsible for their characteristically fetal-like migratory behaviour. The existence of such inter- and intra-site phenotypic heterogeneity in populations of skin and gingival fibroblasts is discussed in the context of fibroblast lineage relationships and the possible contribution of persistently fetal-like fibroblast subpopulations to connective tissue function in wound healing.

Cloning and characterization of human gingival and periodontal ligament fibroblasts

Fibroblast heterogeneity in human periodontal tissues was characterized by cloning and immuno-histochemical techniques. Cell suspensions from primary cultures gingival (GF) and PDL fibroblasts (PF) were cloned. The relative intensity of double-labeled immunofluorescence, using specific antibodies to the extracellular matrix (ECM) molecules collagen type I (CI), type III (CIII), and fibronectin (Fn), was measured by photometry. Most clones derived from either GF or PF showed positive intracellular staining for both CI and Fn, and CIII and Fn. However, there were variations in fluorescence intensity for CI and Fn, ranging from relatively weak to strongly positive. The fluorescence for CI and CIII was relatively weak in most isolated GF clones in contrast to their PF clones. These observations coupled with studies of growth and cellular morphology in individual clones suggest that: 1) GF and PF contain functionally heterogeneous subpopulations; and 2) the synthesis and expression of extracellular matrix molecules of GF may be essentially different from that of PF.

Bone-like nodules formed in vitro by rat periodontal ligament cells

The periodontal ligament has been shown to possess the ability to regenerate both new cementum and alveolar bone as well as a self-regenerative capacity; however, the source of cementoblasts and osteoblasts is not still clear. We investigated the development of bone-like tissue in vitro by periodontal ligament cells, in order to determine whether the periodontal ligament contains osteoprogenitor cells. Periodontal ligament cells were obtained from periodontal ligament tissue attached to the maxillary incisors of 6-week-old WKA rats by means of the explant technique. Cells at passage #3 were cultured for long term in alpha-minimum essential medium containing 10% fetal bovine serum, antibiotics, and 50 micrograms/ml ascorbic acid, and were then examined using phase-contrast microscopy, histochemistry, transmission electron microscopy, X-ray microanalysis, and electron diffraction. Nodules were formed in the cultures, and when 10 mM Na-beta-glycerophosphate was added, these nodules became mineralized. The mineralized nodules were identified as bone-like elements in view of the presence of osteoblast-like and osteocyte-like cells, collagenous matrix, a mineral composed of hydroxyapatite, and intense alkaline phosphatase activity. The results show that the periodontal ligament contains osteoprogenitor cells, which differentiate into osteoblasts and produce bone-like tissue.

Characterization of fibroblast clones from periodontal granulation tissue in vitro

Connective tissues are known to be composed of heterogeneous fibroblast subpopulations. The significance of this heterogeneity in different physiological and pathological conditions is poorly understood. Granulation tissue is formed in connective tissue during wound healing, chronic inflammation, and certain pathological conditions. In this study, heterogeneity of fibroblasts from granulation tissue was investigated by cell-cloning techniques. Granulation-tissue fibroblasts (GTFs) from both chronically inflamed periodontal lesions and healing wound granulation tissue behaved similarly. GTFs showed a more pronounced decrease in proliferative capacity with increasing cumulative population doubling levels (CPDLs) and 30-40% lower cloning efficiency compared with normal gingival fibroblasts (HGFs). Morphologically, cells in GTF cultures were mainly large, whereas HGFs were mainly small in size. Both cell-line types showed heterogeneity in cell morphology. Clones composed of large stellate-like cells predominated in GTF cultures, whereas clones composed of small spindle-shaped or epithelioid cells predominated in HGF cultures. In both cell-line type the proportion of clones composed of large cells increased without increasing CPDL. These findings show that the properties of the fibroblasts changed during their in vitro life spans. The finding that normal connective tissue and granulation tissues contain morphologically distinct fibroblast clones in different proportions suggests that local factors could stimulate local fibroblasts to differentiate into GTFs. Alternatively, local factors could select some fibroblast subpopulations to overgrow the others to form granulation tissue.

Odontogenic tumors in mice carrying albumin-myc and albumin-rats transgenes

Odontogenic tumors that produce abnormal tooth-like structures are repeatedly observed in mandibles of mice that carry both albumin-myc and albumin-ras transgenes. The earliest lesions appear among the periodontal ligament mesenchymal cells, but later lesions include an epithelial component. Subsequent tumor development recapitulates the process of normal tooth formation, which requires multiple sequential cell signals, and results in cell differentiation, matrix secretion, and mineralization. Tumor cells with epithelial morphology produce ras oncoprotein, consistent with an epithelial origin of these tumors. As albumin regulatory sequences direct oncogene expression in these mice, our findings also suggest that some of the albumin present in normal teeth may be locally produced and have a role in tooth mineral formation. The reproducibility of this phenotype makes these mice an excellent model for studies of both normal and neoplastic odontogenesis.

Alpha-smooth muscle actin is expressed in a subpopulation of cultured and cloned fibroblasts and is modulated by gamma-interferon

Clinical and experimental investigations have shown that, during wound healing and fibrocontractive diseases, fibroblasts acquire, more or less permanently according to the situation, morphological and biochemical features of smooth muscle (SM) cells including the expression of alpha-SM actin. Primary and passaged cultures of rat and human fibroblasts contain a subpopulation of cells expressing alpha-SM actin. These cells could derive from SM cells and/or pericytes present in the tissue from which cultures have been produced or represent bona fide fibroblasts. We have investigated the presence of alpha-SM actin in fibroblast cultures, clones, and subclones. In all cases the fibroblastic populations studied showed a proportion of alpha-SM actin expressing cells. Even after cloning, we never obtained populations negative for alpha-SM actin. We conclude that alpha-SM actin expression in fibroblastic cultures is not due to contaminant cells but is a feature of fibroblasts themselves. Our results support the view that fibroblastic cells are a heterogeneous population. It has been previously shown that gamma-interferon (gamma-IFN) decreases alpha-SM actin expression in SM cells. In rat and human fibroblasts, gamma-IFN decreases alpha-SM actin protein and mRNA expression as well as proliferation. The properties of this cytokine make it a good candidate for exerting an anti-fibrotic activity in vivo.

Role of fibroblast subpopulations in periodontal physiology and pathology

Fibroblasts are the principal cell type in the soft connective tissues of the periodontium; they perform important functions in development, physiology, and disease. A growing number of reports have indicated site-specific phenotypic variation of fibroblasts. Heterogeneity of metabolic traits has been demonstrated in cells from healthy and diseased tissues. The tissue distribution and relative proportions of fibroblast subpopulations have a significant impact on the regulation of connective tissue function in health and disease.

Discrimination of two fibroblast progenitor populations in early explant cultures of hamster gingiva

Numerous metabolic studies have demonstrated heterogeneity of fibroblast populations in culture, yet little is known about the structure of fibroblast populations in adult tissues in vivo. To determine if populations of both cycling and non-cycling cells are present in gingiva, hamsters were labelled with [3H]-thymidine to label cycling cells in vivo, and explanted biopsies were subsequently incubated with bromodeoxyuridine to label cycling cells in vitro. Cycling cells were identified by combined immunohistochemistry and radioautography. Fibroblasts were recognized by the presence of vimentin and the absence of keratin as determined by immunofluorescence. The largest proportion of cells were double-labelled with [3H]-thymidine and bromodeoxyuridine (43.8%) indicating the presence of actively cycling populations that maintained their proliferative status upon explanation. Cultures also exhibited a second population of cells labelled only with bromodeoxyuridine (38.7%) that did not cycle in vivo, but retained the capacity for proliferation in vitro. However, limiting dilution analysis of single-cell suspensions revealed only a single class of progenitors capable of forming large colonies in vitro. Approximately 1 in 190 plated cells was capable of colony-formation, indicating that, upon explanation, a subset of the cycling cells in vitro exhibits extensive proliferative capacity. There was also a small population of cells unlabeled with either [3H]-thymidine or bromodeoxyuridine (9.4%) that appeared to be terminally differentiated. Different substrates, including glass and thin films of gelatin and collagen, did not significantly alter the fraction of cells labelled with [3H]-thymidine. These data demonstrate the existence of 2 separate progenitor-cell populations with different capacities for proliferation in vivo and in vitro.

Characterization of fibroblasts derived from human periodontal ligament and gingiva

Growth characteristics and macromolecular synthesis of fibroblasts derived from human periodontal ligament (PDLF) and gingiva (GF) have been compared in cell culture. Cells were isolated from explants and plated at 500,000 cells/100 mm culture dish (day 0) with daily changes of culture medium. DNA histograms were obtained by flow microfluorimetric analysis to confirm the growth state of the cell cultures. Human PDLF cultures became confluent at day 6 as determined by cell number and cell cycle analysis while GF were confluent by day 4. Initially, DNA content of logarithmically growing cells was significantly greater in GF cultures; however, when confluent, DNA content and cell number was greater in PDLF cultures. Total protein content in GF was slightly greater than PDLF until day 7 but this difference was not significant. Analysis of collagen and noncollagen protein synthesis revealed a greater trend in noncollagen protein synthesis in the GF cultures compared to PDLF cultures. Analysis of glycosaminoglycans in the culture medium of GF and PDLF revealed similar distributions of components. In the cellular fraction, GF had greater amounts of hyaluronic acid and heparin and lesser amounts of chondroitin sulfates A and C than PDLF cultures. The results indicate that the growth characteristics of PDLF and GF, although similar in many respects, do exhibit specific differences in proliferative rates and macromolecular synthesis. The differences observed in these parameters may be important during in vivo events, such as guided tissue regeneration, where significant functional differences are observed between gingival connective tissue and periodontal ligament connective tissue.

Histological characteristics associated with suppurating periodontal pockets

The purpose of this study was to characterize histologically the gingival lesion associated with suppuration in advanced periodontitis. Thirty-three bleeding, suppurating (S) and 23 bleeding, nonsuppurating (NS) interproximal biopsies were obtained from nine patients and processed for light microscopy. Pocket depths (mean +/- SD) were 6.7 +/- 1.6 mm (S) and 5.4 +/- 2.2 mm (NS). Six-micron serial sections were stained with (1) hematoxylin/eosin and (2) van Gieson. Quantitative cell types were determined by a grid intersection counting technique at x 1000. Volumetric analysis of collagen-poor (inflammation) areas was conducted using a computer biometric system that revealed three histologic patterns: Type I sites showed mild to moderate inflammation (less than 50% infiltrate, S = 15, NS = 20); Type II sites showed intense inflammation (greater than 50% infiltrate, S = 17, NS = 3); and only one (S) site had a large connective tissue abscess (Type III). The mean percentage of collagen-poor area was significantly larger in suppurating (42.1 +/- 25.5%) versus nonsuppurating (27.7 +/- 20.4%) sites (P = 0.02). In both S and NS sites, plasma cells (means = 66%) and lymphocytes (means = 27%) predominated in the inflammatory infiltrates. Histologically, suppuration appeared to be associated with increased gingival inflammation and a slight increase in connective tissue neutrophils.

A comparative study of human periodontal ligament cells and gingival fibroblasts in vitro

Both periodontal ligament and gingival tissue are thought to harbor cells with the ability to stimulate periodontal regeneration, i.e., formation of new bone, cementum, and connective tissue attachment. To understand further the role of these cells in the regenerative process, we compared human periodontal ligament cells and gingival fibroblasts, both derived from the same patient, same passage, in vitro. Protein and collagen production was significantly greater in periodontal ligament cells when compared with that of gingival fibroblasts. In addition, periodontal ligament cells had higher alkaline phosphatase levels when compared with those of gingival fibroblasts.

Cellular and soluble mediator components of the local immune response to dental plaque

The host immune response to dental plaque products leads to altered levels of activity by several types of cells involved in host defence. Cells of the periodontium which contribute to the supporting tissues of the teeth may be directly damaged by cellular attack, or their activity may be modulated by a range of soluble mediators released by host immune cells. These changes contribute to the modification of the tooth-supporting tissue which is seen in chronic inflammatory periodontal disease.

Estrogen receptors and growth response in cultured human periodontal ligament cells

The periodontal ligament (PDL) is a connective tissue involved in the remodeling process associated with tooth development and positioning. PDL cells grown in culture were analyzed for the capacity to specifically bind steroid hormones and for growth response to estradiol-17 beta. Using [3H]estradiol-17 beta as the ligand, PDL cells in first passage cultures exhibited a specific estrogen binding capacity of 881 fmol/mg cell protein. With [3H]dexamethasone as a ligand, the binding capacity of the glucocorticoid receptor was 143 fmol/mg protein. With [3H]R5020 as a ligand, the progestin receptor exhibited a binding capacity of 5 pmol/mg protein. Scatchard analysis of estradiol binding at 37 degrees revealed a dissociation constant of 2.7 X 10(-9) M, representative of the estrogen receptor. The addition of estradiol-17 beta at concentrations of 10(-9) and 10(-8) M to culture media induced a dose-dependent decrease in growth (DNA content) to 62% and 38% control values, respectively. The addition of the antiestrogens tamoxifen and 4-hydroxytamoxifen at concentrations of 10(-7) and 10(-6) M similarly depressed cell growth. These results show that PDL cells contain high affinity receptors for several steroid hormones and further that these cells are targets for the action of estrogens.

Synthetic activities of mass cultures and clones of human gingival fibroblasts

The percentage of synthesis dedicated to collagen is elevated in low-density cultures of human gingival fibroblasts, as is per-cell total protein synthetic activity and glycosaminoglycan accumulation. These observations can be explained, in part, by a decrease in membrane transport of precursor substance in high-density cultures. Synthetic activity by human fibroblasts can be reliably assayed in vitro using as few as 500 cells sparsely seeded. Such low-cell number assay is essential for study of single-cell clones, where replicative life span is limited.

Fibronectin-independent attachment of human gingival fibroblasts to interstitial and basement membrane collagens

We have studied the ability of human gingival fibroblasts (HGF) to attach to different interstitial (types I, II and III) and basement membrane (types IV and V) collagens. HGF cells were plated onto collagen-coated Petri dishes under various conditions and the percentage of cells attaching to the collagen was determined. HGF were found to attach to all the different types of native collagens, but attached poorly to the corresponding denatured collagens. When plated in the presence of 15% fetal bovine serum (FBS) or fibronectin-depleted FBS, similar percentages (approximately 85%) of cells attached to both interstitial and basement membrane collagens, demonstrating an attachment mechanism that is independent of plasma fibronectin. That the attachment in the presence of serum was also independent of cellular fibronectin was shown by the inability of fibronectin antibodies to block attachment to any of the collagen types. HGF were also capable of attaching to all of the collagen types in the complete absence of serum. In previous studies, investigators using cell lines have suggested that cell attachment in the absence of serum is non-physiological. However, the serum-free attachment of HGF to collagen was found to be dependent on cellular protein synthesis indicating that this attachment mechanism has biological significance.