Multinucleated fibroblastic cells in the periodontal ligaments of aged rats

Morphology of the non-sensory tissue components in rat aging vomeronasal organ

With 30 figures, 3 histograms and 3 tables

SUMMARY

The vomeronasal organ (VNO) is a chemosensory organ that detects environmental pheromones. The morphology of the 'non-sensory' epithelium (NSE) of the VNO and its lamina propria, as well as how it relates to ageing has received little attention. Histological, histochemical, morphometric and ultrastructural techniques were used to study the morphological structure of the rat NSE in five adult (3 months old) and five aged (2-2.5 years old) male albino rats. In adult rats, the NSE contained dark and light columnar cells with predominance of the latter. The surface of the epithelial cells was covered with microvilli and/or cilia. The lamina propria contained serous vomeronasal glands (VNGs), smooth muscles with numerous variable-sized mitochondria, vessels including lymphatic capillaries and nerve bundles. The following changes were detected in aged rats. The NSE exhibited an increase in number of dark columnar cells. Some cells revealed a prominent cell coat, dense aggregation of filaments in the luminal cytoplasm and appearance of multinucleated cells. Their surface revealed malformed configuration. Large mitochondria (2 μm), formed by fusion, were frequently observed in the smooth muscle cells of the lamina propria. Lipid droplets were frequently detected both in the VNGs acini and in the lymphatic endothelium. Ageing affected both the cells of the tissues and the extracellular matrix.

Apoptosis in the connective tissues of the periodontal ligament and gingivae of rat incisor and molar teeth at various stages of development

Apoptosis in the periodontal connective tissues was studied using the TUNEL technique, supported by electron microscopy. For 16 rats (aged 3, 8, or 104 weeks), nuclear fragmentation was assessed using the TUNEL technique (for 4 of the animals aged 8 weeks, incisor eruption was experimentally increased by trimming of teeth to the gingival margin--unimpeded eruption). A further 8 rats (aged 8 and 104 weeks) were employed for electron microscopy. For the incisor, prior to aging, and regardless of eruptive behavior (i.e., for both impeded and unimpeded incisors), there was little evidence of apoptosis in the periodontal ligament or gingival connective tissues. For the molar, apoptosis was also not usually detected when the teeth were erupting or in the mature, erupted state. In the aged animals, however, there was a marked increase in apoptosis (as assessed by the TUNEL technique) within the periodontal ligament and gingivae of both the molars and incisors (where eruption rates also increased). Nevertheless, electron microscopy indicated that significant numbers of apoptotic cells were only in the incisor periodontium. These findings are not consistent with the view that the periodontal fibroblasts provide a component of the force(s) responsible for eruption.

Cyclosporin A-induced gingival overgrowth in the rat: a histological, ultrastructural and histomorphometric evaluation

This investigation was undertaken to further study cyclosporin A (CsA)-induced gingival overgrowth. Thirty mg/kg/d of vehicle or CsA solutions were given orally to 6-wk-old male Sprague-Dawley rats. After 4, 9, 14 and 19 wk 2 control and 2 experimental rats were anaesthetized, tissues fixed by intracardiac perfusion of fixative solution and jaws processed for Epon inclusion. Histological and ultrastructural studies conducted in a gingival portion (free gingiva) revealed the presence of hyalinization areas and of multinucleated cells (MCs) containing collagen fibrils (connective tissue), of amorphous areas and disorders of keratinization (epithelia). Histomorphometric evaluation indicated that in the CsA rats the mean cross-sectional area of the free gingiva was 2.52-fold increased compared to the controls. The connective tissue comprised 41.43% of this area (instead of 31.49% in controls). Additional histomorphometric evaluation was performed in 3 groups of free gingival portions: control (C group), CsA-non-respondent (CsA-nR) and CsA-respondent (CsA-R). The cross-sectional gingival areas studied were slightly lower than the mean area of all the control sites previously defined (groups C and CsA-nR) or showed the higher degrees of enlargement (CsA-R). In the CsA-R group the mean cross-sectioned area of the vessel profiles was increased and the number of fibroblast profiles decreased. In the CsA-nR group the number of vessel profiles and that of MCs profiles were increased. In the epithelia of the CsA-R group were increased (a) keratinized epithelia: thickness; thickness of the inner and of the outer compartments; surface area of spinous cell profiles; (b) oral gingival epithelium: number of cell layers (inner compartment); (c) oral sulcular epithelium: surface area of granular cell profiles; (d) junctional epithelium: thickness; number of cell layers. These results indicate that (a) the CsA induced modifications are not limited to enlarged gingiva (b) the overgrowth of the GCT is the result of a vasodilatation and of an increase in the volume of the extracellular matrix and (c) the increase of the epithelial thickness is mainly the result of a cell hypertrophy in the keratinized epithelia and of a cell hyperplasia in the junctional epithelium.

Deregulation of collagen phagocytosis in aging human fibroblasts: effects of integrin expression and cell cycle

Intracellular degradation of collagen by phagocytosis in fibroblasts is essential for physiological remodeling of the extracellular matrix in a wide variety of connective tissues but imbalances between degradation and synthesis can lead to loss of tissue collagen. As aging is associated with loss of dermal and periodontal collagen and with increased lysomomal enzyme content in fibroblasts, we examined the regulation of collagen phagocytosis by integrin expression and the cell cycle in an in vitro fibroblast aging model. Two different fibroblast lines (CL1; CL2) at the fourth subculture were passaged up to replicative senescence to model aging processes in vitro. Cells were incubated with collagen-coated or BSA-coated green fluorescent beads for 3 h to assess alpha 2 beta 1-integrin-mediated or nonspecific phagocytosis, respectively. Single-cell suspensions were stained with DAPI and sulforhodamine 101 to separate cycling G1 and noncycling G0 cells. Staining for alpha 2-integrin, bead internalization, and bivariate analyses of DNA/protein content were measured by three-color flow cytometry. Serum deprivation was used to induce increases in the proportion of G0 cells. For G1 cells, the proportion of collagen phagocytic cells was > 50% for all passages and collagen beads were internalized > 5-fold more frequently than BSA beads. In contrast, G0 cells with diploid DNA content but low protein content exhibited greatly reduced phagocytic capacity (< 10% of cells internalized collagen or BSA beads), the number of beads per cells was 4-fold less, and alpha 2 integrin expression was very low compared to G1 cells. The proportion of collagen phagocytic cells and the proportion of alpha 2-integrin-positive cells increased with transit through the cell cycle. At higher passage numbers mean cell volume and cytoplasmic granularity were reduced approximately 30% but at replicative senescence cells with large surface area and subdiploid DNA predominated. The proportion of collagen and BSA phagocytic G1 cells increased 1.5- and 5-fold, respectively, and the number of beads per cell increased < 3-fold. However, surface alpha 2-integrin staining remained unchanged. These data indicate that the collagen and nonspecific internalization pathways were greatly unregulated, independent of cell cycle phase, and that cellular aging in vitro strongly influences the specificity and rate of phagocytic processes in fibroblasts. We suggest that age-related loss of collagen in connective tissues undergoing turnover may be a manifestation of a deregulated increase of collagen phagocytosis in which the net loss of degraded collagen exceeds new synthesis.

The effects of aging upon the connective tissues of the periodontal ligament

The ultrastructural features of the cells and of the oxytalan fibers within the periodontal ligaments of aged rats (2 year old) were quantified and compared with data for tissues obtained from younger animals (8 week old). Sections of the mid-root regions of the mandibular first molars were prepared for examination by TEM. The fibroblasts of the aged rats were found to differ in 3 respects: the areas occupied by endoplasmic reticulum were significantly less, the areas occupied by intracellular collagen profiles were also less, and both the numbers and sizes of intercellular contacts were significantly different (p < 0.05). For the oxytalan fibers, no differences were observed between the periodontal ligaments of the aged and control animals both in terms of numbers of fibers per 50 microns and in terms of area of tissue occupied. Thus, in contrast to the apparent lack of age changes so far determined for the extracellular matrix of the periodontal ligament (collagen fibrils and oxytalan), the periodontal fibroblasts exhibit some age changes as perceived at the ultrastructural level.

Phenotypic characterisation of stellate and giant cells in giant cell fibroma by immunocytochemistry

The origin of the stromal, stellate and multinucleate cells in oral giant cell fibroma is unclear. Sixteen giant cell fibromas were stained immunocytochemically for keratin (MNF 116), vimentin, S-100 protein, neurofilaments, glial fibrillary acidic protein, alpha-smooth muscle actin, desmin, CD31 (PECAM-1), CD68, Factor XIIIa and prolyl 4-hydroxylase (5B5). In all cases positive staining was found with vimentin and prolyl 4-hydroxylase, indicating a functional fibroblast phenotype. Reactivity for Factor XIIIa was seen in two cases and in only one was a small number of giant cells stained, suggesting that the majority of oral giant cell fibromas are unrelated to the histologically similar fibrous papule of the nose or facial angiofibroma.