An electron microscopic radioautographic study of collagen secretion in periodontal ligament fibroblasts of the mouse: II. Colchicine-treated fibroblasts

Effects of colchicine on gingival inflammation, apoptosis, and alveolar bone loss in experimental periodontitis

BACKGROUND

The aim of the study was to investigate the effects of colchicine on cytokine production, apoptosis, alveolar bone loss, and oxidative stress in an experimental model of periodontitis in rats.

METHODS

Forty-eight rats were divided equally into four groups: healthy (H); periodontitis (P); periodontitis+colchicine low dose (CL, 30 μg/kg/day), and periodontitis+colchicine high dose (CH, 100 μg/kg/day). After 11 days, interleukin (IL) -1β, IL-8, and IL-10 were analyzed in gingival samples using Enzyme-Linked ImmunoSorbent Assay. Receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegerin (OPG), total oxidative stress (TOS), total antioxidant status (TAS), and oxidative stress index (OSI) were measured in gingiva and serum. Alveolar bone volume was evaluated via micro-CT. Apoptotic cells were detected by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay in histological sections.

RESULTS

Colchicine treatment significantly reduced IL-1β, IL-8, RANKL, RANKL/OPG, TOS, OSI, and bone volume ratio levels, and increased TAS levels compared to group P (p < 0.05). High dose colchicine treatment (CH) significantly decreased TUNEL+ cell counts compared to group P (p < 0.05).

CONCLUSIONS

These finding suggest that colchicine has a prophylactic potential for the prevention of periodontal tissue destruction through anti-inflammatory, anti-oxidative, anti-apoptotic, and bone-protective effects.

Actin Filaments Are Required for Fibripositor-mediated Collagen Fibril Alignment in Tendon

Cells in tendon deposit parallel arrays of collagen fibrils to form a functional tissue, but how this is achieved is unknown. The cellular mechanism is thought to involve the formation of intracellular collagen fibrils within Golgi to plasma membrane carriers. This is facilitated by the intracellular processing of procollagen to collagen by members of the tolloid and ADAMTS families of enzymes. The carriers subsequently connect to the extracellular matrix via finger-like projections of the plasma membrane, known as fibripositors. In this study we have shown, using three-dimensional electron microscopy, the alignment of fibripositors with intracellular fibrils as well as an orientated cable of actin filaments lining the cytosolic face of a fibripositor. To demonstrate a specific role for the cytoskeleton in coordinating extracellular matrix assembly, cytochalasin was used to disassemble actin filaments and nocodazole or colchicine were used to disrupt microtubules. Microtubule disruption delayed procollagen transport through the secretory pathway, but fibripositor numbers were unaffected. Actin filament disassembly resulted in rapid loss of fibripositors and a subsequent disappearance of intracellular fibrils. Procollagen secretion or processing was not affected by cytochalasin treatment, but the parallelism of extracellular collagen fibrils was altered. In this case a significant proportion of collagen fibrils were found to no longer be orientated with the long axis of the tendon. The results suggest an important role for the actin cytoskeleton in the alignment and organization of the collagenous extracellular matrix in embryonic tendon.

Effects of mebendazole on protein biosynthesis and secretion in human-derived fibroblast cultures

Previous results of our group revealed that mebendazole, a broad spectrum anthelmintic drug with antimicrotubular properties, used for the treatment of liver cirrhosis, decreased total collagen content and biosynthesis in liver upon treatment. In the present study, we have evaluated the effects of mebendazole (5-50 micrograms/mL) on protein synthesis, secretion, and deposition in human-derived fibroblast cultures. The results showed a decrease in cell viability (18.5 +/- 0.9%) at 50 micrograms/mL. [3H]Thymidine incorporation diminished gradually with increasing mebendazole concentrations, reaching a plateau (53.67%) between 30 and 50 micrograms/mL. In late logarithmic phase cultures, the drug caused a decrease of [3H]proline incorporation (43.10%) and collagen biosynthesis (58.61%) in the extracellular matrix. This correlated with an increase in radioactivity in total proteins (51.28%) of the intracellular fraction. Similar results were obtained when mebendazole was assayed in post-confluent fibroblast cultures. The electrophoretic patterns of the extracellular matrix showed a decrease of radioactive collagenous components (alpha chains and beta dimers). By contrast, in the intracellular fraction an increase of radioactive collagen precursors (pro alpha chains) was observed. Immunofluorescence studies and immunotransfer analysis, using polyclonal anti-type I collagen antibodies, revealed an accumulation of intracellular collagen which included: collagen pro alpha chains, alpha chains, and low molecular weight peptides. The results obtained suggest that mebendazole interferes with the transcellular mobilization of proteins, resulting in a decrease of secretion and deposition of extracellular matrix proteins, and an accumulation of intracellular collagenous components. The intracellular accumulation of newly synthesized proteins could cause a feedback regulation in fibroblast cultures.

The effect of vinblastine on the incorporation of [3H]-glycine into proteins of the periodontal ligament of impeded and unimpeded mouse incisors

The effect of vinblastine on the protein metabolism of the periodontal ligament of impeded and unimpeded mouse incisors was studied by [3H]-glycine labelling and radioautography. The silver-grain concentration was determined in areas adjacent to the tooth, areas adjacent to bone and, as an internal control, in the dentine matrix. From 1 to 12 h there was no difference between treated and control animals; thus the drug did not alter protein biosynthesis. Later, the silver-grain concentration was significantly higher in areas adjacent to both bone and tooth in vinblastine-treated animals, suggesting a longer half-life of the labelled proteins. No significant differences between normal or unimpeded erupting incisors of both groups were detected. Dentine matrix showed a possibly higher re-utilization of the labelled amino acid in vinblastine-treated animals. The amount of labelled protein removed by collagenase was similar in both groups, while the concentration of grains due to collagenase-resistant proteins was significantly higher in treated animals, particularly at 96 h after the injection of labelled glycine. The relation between the increased amount of non-collagenous proteins in the periodontal ligament and the decrease in the rate of eruption caused by vinblastine was not established. However, among these proteins, fibronectin and proteoglycans are thought to be important factors in tooth eruption.

Ultrastructural morphometry of membrane-bound intracytoplasmic collagen fibrils in tendon fibroblasts exposed to He:Ne laser beam

Collagen fibrils are not found in fibroblast cytoplasm except in certain pathological conditions or in the presence of drugs and other agents that accelerate collagen turnover. Because low energy laser photostimulation is both a non-pathogenic and non-chemical accelerator of collagen synthesis, its effects were studied on four groups of calcaneal tendons from 18 rabbits (1) to test the hypothesis that vacuolar fibrils are not produced exclusively by diseases and chemical agents, and (2) to compare the morphometry of matrical and vacuolar fibrils. The right calcaneal tendons of nine rabbits were surgically tenotomized and repaired; six of these were transcutaneously irradiated with He:Ne laser everyday. The right calcaneal tendon of six of the remaining nine rabbits were similarly irradiated with laser, but without prior tenotomy and repair. 21 days later, all tendons were fixed in situ and processed for electron microscopy. Fibril-bearing vacuoles were found only in fibroblasts of tenotomized laser-irradiated tendons. Similar vacuoles were not seen in non-tenotomized laser-irradiated tendons nor in non-irradiated tendons whether tenotomized or not. Mann-Whitney U tests revealed no statistically significant differences in the cross-sectional areas or diameters of matrical and vacuolar fibrils. These findings suggest (a) that matrical and vacuolar fibrils have a common origin, and (b) that vacuolar fibrils can be induced by a non-pathologic, non-chemical accelerator of collagen synthesis.

Traffic through the Golgi apparatus as studied by radioautography

The ability to radiolabel biological molecules, in conjunction with radioautographic or cell fractionation techniques, has brought about a revolution in our knowledge of dynamic cellular processes. This has been particularly true since the 1940's, when isotopes such as 35S and 14C became available, since these isotopes could be incorporated into a great variety of biologically important compounds. The first dynamic evidence for Golgi apparatus involvement in biosynthesis came from light microscope radioautographic studies by Jennings and Florey in the 1950's, in which label was localized to the supranuclear Golgi region of goblet cells soon after injection of 35S-sulfate. When the low energy isotope tritium became available, and when radioautography could be extended to the electron microscope level, a great improvement in spatial resolution was achieved. Studies using 3H-amino acids revealed that proteins were synthesized in the rough endoplasmic reticulum, migrated to the Golgi apparatus, and thence to secretion granules, lysosomes, or the plasma membrane. The work of Neutra and Leblond in the 1960's using 3H-glucose provided dramatic evidence that the Golgi apparatus was involved in glycosylation. Work with 3H-mannose (a core sugar in N-linked side chains), showed that this sugar was incorporated into glycoproteins in the rough endoplasmic reticulum, providing the first radioautographic evidence that glycosylation of proteins did not occur solely in the Golgi apparatus. Studies with the tritiated precursors of fucose, galactose, and sialic acid, on the other hand, showed that these terminal sugars are mainly added in the Golgi apparatus. With its limited spatial resolution, radioautography cannot discriminate between label in adjacent Golgi saccules. Nonetheless, in some cell types, radioautographic evidence (along with cytochemical and cell fractionation data) has indicated that the Golgi is subcompartmentalized in terms of glycosylation, with galactose and sialic acid being added to glycoproteins only within the trans-Golgi compartment. In the last ten years, radioautographic tracing of radioiodinated plasma membrane molecules has indicated a substantial recycling of such molecules to the Golgi apparatus.

Membrane-bound intracellular collagen fibrils in fibroblasts and myofibroblasts of regenerating rabbit calcaneal tendons

The ultrastructures of 33 rabbit calcaneal tendons were studied to determine (1) whether vacuolar fibrils are present in three regions of tendons undergoing normal healing after tenotomy and repair, and (2) to stimulate collagen synthesis via functional loading, and hence determine the effect of loading on the presence of vacuolar fibrils in healing tendons. In all the loaded tendons, electron microscopy revealed membrane-bound collagen fibril equivalents in sections of neotendon obtained from the site of tenotomy, and in sections of tendon segments proximal and distal to the site of surgery. Similar vacuolar fibrils were visualized in sections of the proximal and distal segments of the non-loaded regenerating tendons, and also in sections of neotendons formed at the site of tenotomy after 12 and 15 days of healing without functional loading. No such fibrils were visualized in the non-tenotomized normal control tendons. These findings indicate that chemical agents and disease are not necessary to induce the appearance of intracytoplasmic fibrils in vivo and that functional loading augments the presence of fibril-bearing vacuoles in regenerating tendons.

Radioautographic study of [3H]mannose utilization during cementoblast differentiation, formation of acellular cementum, and development of periodontal ligament principal fibers

The formation of acellular cementum and the deposition of [3H]mannose-labeled extracellular matrix were studied in 14-day-old Sprague-Dawley rats. The sequential events of cementogenesis and periodontal ligament formation observed by light and electron microscopy were described from the stage of an intact root sheath to postcementogenesis. Ultrastructural examination of cementoblasts and periodontal ligament fibroblasts revealed [3H]mannose labeling of the Golgi apparatus at 10 minutes, collagen secretion granules at 30 minutes, and the extracellular matrix beginning at 30 minutes. The extracellular matrix between cementoblasts and dentin was heavily labeled at 1 and 4 hours. Newly formed principal fibers of the periodontal ligament were also heavily labeled at 4 hours. Fully differentiated cementoblasts exhibited the largest sectional profiles and the highest number of silver grains per unit area of cytoplasm. The morphologic and radioautographic data suggest that during the formation of acellular cementum, the cementoblast phenotype is expressed for a short period of time, after which cementoblasts appear to mix with the fibroblasts of the periodontal ligament.

Budding of small vesicles from the rough-surfaced endoplasmic reticulum in secretory ameloblasts of rat molar tooth germs

The budding of small vesicles from the rough-surfaced endoplasmic reticulum (rER) was examined in the secretory ameloblast of rat molar tooth germs by ordinary fixation or prolonged osmium fixation. The budding of small vesicles from the rER was observed not only at the special region (transitional region) of the rER system, which abutted on the cis-face of the Golgi apparatus, but also at other regions of the rER in the secretory ameloblast. Small vesicles (presumed to be transitional vesicles) were adjacent to the rER, which also showed budding of vesicles. After prolonged osmium treatment, osmium deposits appeared in small vesicles, as well as in the cisternae of the cis saccule of the Golgi apparatus. Small vesicles containing osmium deposits were located at various regions of the cell, including the cis-face of the Golgi apparatus. These findings indicate that the budding of small vesicles from the rER is not restricted to the transitional region of the rER system of the secretory ameloblast, but is found at various regions of the cell. This indicates that newly synthesized proteins may be transferred from the rER cisternae to the transitional vesicles not only in the transitional region of the rER system adjacent to the Golgi apparatus, but also in other regions of the secretory ameloblast.

Effect of colchicine on collagen synthesis by liver fibroblasts in murine schistosomiasis

Colchicine, an antimicrotubular agent, was shown to block the transcellular movement of certain structural macromolecules such as collagen. In the present study, the effect of colchicine on collagen synthesis and secretion by monolayer cultures of fibroblasts from livers of mice infected with Schistosoma mansoni was investigated. The effect of colchicine on proliferation of these fibroblasts was studied as well. Collagen and non-collagen protein synthesis was measured by incubating cultures with [14C]proline and measuring the incorporation of radioactivity into these protein fractions in both culture media and cell layers. Proliferation was measured by [3H]thymidine uptake. The isolated fibroblasts actively formed collagen and secreted most of it into the culture medium; 10-20% of the collagenase-sensitive radioactive protein remained in the cell layer. The addition of colchicine to culture medium led to selective inhibition of collagen formation with negligible effects on non-collagen protein synthesis. Fibroblast proliferation was also reduced by colchicine treatment. Both inhibition of collagen synthesis and inhibition of fibroblast proliferation were dose-dependent. Comparison of medium and cell layer collagen radioactivity confirmed inhibition of synthesis rather than only inhibition of secretion. These data suggest that colchicine has a specific effect on synthesis of collagen and proliferative activity by fibroblasts from S. mansoni-infected liver and may, therefore, be useful in modulating schistosomal hepatic fibrosis.

Effect of colchicine on the transport of precursor enamel protein in secretory ameloblasts studied by 3H-proline radioautography in vitro

The incorporation of 3H-proline into the secretory ameloblasts of rat molar tooth germs cultured with or without colchicine was studied by light and electron microscope radioautography to determine the function of microtubules in the transport of precursor enamel protein from the rough-surfaced endoplasmic reticulum (rER) to the Golgi cisternae. The grain counts over the transitional vesicles, which accumulated in various cellular regions with colchicine treatment, continued to increase with chase time, unlike in controls. At 30 and 90 min chase, these counts were significantly higher than in controls. Moreover, the total grain count over the organelles (rER, pale granules, and transitional vesicles), which are positioned before the Golgi cisternae in the synthetic pathway, maintained a significantly higher level at 90 min chase in colchicine-treated tooth germs than in controls. The transport of synthesized protein to the Golgi cisternae via transitional vesicles was suppressed in colchicine-treated tooth germs. Some grains appeared with time over pale granular materials that appeared in the intercellular spaces of secretory ameloblasts with colchicine treatment. However, at each chase period, the grain count over pale granular materials was not so high as the count over the enamel in control. The present results indicate that colchicine affects the transport of newly synthesized protein from the rER to the Golgi cisterna via transitional vesicles, probably by interfering with the oriented transport related to microtubular function. It is suggested that the microtubular system may be concerned with the movement of the transitional vesicles.

3H-mannose utilization by fibroblasts of the periodontal ligament

The synthesis, intracellular translocation, and secretion of mannose-containing glycoproteins(s) by periodontal ligament fibroblasts have been investigated by means of electron microscopic radioautography. Tritiated mannose was administered to young mice via jugular vein, and radioautographs were prepared at 5, 10, 20, and 35 minutes, 4 and 8 hours after injection. Analysis of electron microscopic radioautographs revealed a maximum labeling (94%) with 3H-mannose of the rough endoplasmic reticulum at 5 minutes. Labeling of the Golgi components started to increase from 10 minutes (14%) and reached a maximum level at 20 minutes (31.2%). At 35 minutes, secretion granules, dense bodies, profiles of intracellular collagen, and the cell surface were labeled. At 8 hours, most labelling (79.2%) was extracellular, and associated either with the collagenous matrix (43.7%) or the cell surface (35.5%). Cytoplasmic vesicles containing dense materials around collagen fibrils were also labeled at 8 hours. It is concluded that mannose is directly incorporated into the rough endoplasmic reticulum (RER), and that mannose-containing glycoprotein(s) are packaged in the Golgi apparatus into secretory granules. Mannose-containing glycoprotein(s) become distributed on the periodontal ligament (PDL) fibroblast cell surface, cytoplasmic dense bodies, and the extracellular matrix.

The role of microtubules in the phagocytosis of collagen by fibroblasts

The effects of the anti-microtubular agents, colchicine and vinblastine, on the phagocytosis of collagen by fibroblasts were assessed quantitatively in cultured mouse bone explants. It was found that in the absence of the microtubular system the volume density of lysosomal vacuoles containing cross-banded collagen fibrils in periosteal cells did not differ from that seen in controls. In contrast, cytochalasin B which interferes with the microfilament system prevented the accumulation of collagen-containing vacuoles in the cytoplasm. The data indicate that the phagocytosis of collagen fibrils by fibroblasts does not depend on the integrity of the microtubular apparatus, but seems to require an intact microfilament system.

Microtubules and the organization of the Golgi complex

Electron microscopic and cytochemical studies indicate that microtubules play an important role in the organization of the Golgi complex in mammalian cells. During interphase microtubules form a radiating pattern in the cytoplasm, originating from the pericentriolar region (microtubule-organizing centre). The stacks of Golgi cisternae and the associated secretory vesicles and lysosomes are arranged in a circumscribed juxtanuclear area, usually centered around the centrioles, and show a defined orientation in relation to the rough endoplasmic reticulum. Exposure of cells to drugs such as colchicine, vinblastine and nocodazole leads to disassembly of microtubules and disorganization of the Golgi complex, most typically a dispersion of its stacks of cisternae throughout the cytoplasm. These alterations are accompanied by disturbances in the intracellular transport, processing and release of secretory products as well as inhibition of endocytosis. The observations suggest that microtubules are partly responsible for the maintenance and functioning of the Golgi complex, possibly by arranging its stacks of cisternae three-dimensionally within the cell and in relation to other organelles and ensuring a normal flow of material into and away from them. During mitosis, microtubules disassemble (prophase) and a mitotic spindle is built up (metaphase) to take care of the subsequent separation of the chromosomes (anaphase). The breaking up of the microtubular cytoskeleton is followed by vesiculation of the rough endoplasmic reticulum and partial atrophy, as well as dispersion of the stacks of Golgi cisternae. After completion of the nuclear division (telophase), the radiating microtubule pattern is re-established and the rough endoplasmic reticulum and the Golgi complex resume their normal interphase structure. This sequence of events is believed to fulfil the double function to provide tubulin units and space for construction of the mitotic spindle and to guarantee an approximately equal distribution of the rough endoplasmic reticulum and the Golgi complex on the two daughter cells.

Influence of colchicine and vinblastine on the intracellular migration of secretory and membrane glycoproteins: I. Inhibition of glycoprotein migration in various rat cell types as shown by light microscope radioautography after injection of 3H-fucose

Previous studies have shown that colchicine and vinblastine inhibit secretion in many cell types by interrupting the normal intracellular migration of secretory products. In the present work, radioautography has been used to study the effects of these drugs on migration of membrane and secretory glycoproteins in a variety of cell types. Young (40 gm) rats were given a single intravenous injection of colchicine (4.0 mg) or vinblastine (2.0 mg). At 10 min after colchicine and 30 min after vinblastine administration, the rats were injected with 3H-fucose. Control rats received 3H-fucose only. All rats were sacrificed 90 min after 3H-fucose injection and their tissues processed for light microscope radioautography. Examination of secretory cell types such as ameloblasts and thyroid follicular cells in control animals revealed reactions of approximately equal intensity over the Golgi region and over extracellular secretion products, while in drug-treated rats most of the reaction was confined to the Golgi region. In a variety of other cell types, including endocrine cells (e.g., hepatocytes) and cells generally considered as nonsecretory (e.g., intestinal columnar cells), reaction in control animals occurred both over the Golgi region and over various portions of the cell surface. In drug-treated animals, a strong Golgi reaction was present, but reaction over the cell surface was weak or absent. These results indicate that in many cell types, colchicine and vinblastine inhibit migration out of the Golgi region not only of secretory glycoproteins, but also of membrane glycoproteins destined for the plasma membrane.

The effect of beta-aminoproprionitrile on the periodontal ligament: II. Radioautographic study of collagen secretion from fibroblasts

Fibroblasts are distributed evenly throughout the periodontal ligament (PDL) of normal mice. In mice fed beta-aminoproprionitrile (beta-APN) the fibroblasts undergo aggregation to form palisades of closely juxtaposed cells abutting pools of acellular collagenous matrix. Individual fibroblasts within these aggregates retain their polarized cytoplasmic organization and continue to synthesize and secrete collagen. However, unlike normal PDL fibroblasts, the beta-APN-treated cells appear immobilized by well-developed cell-to-cell adherens-type junctions along their lateral surfaces. We studied collagen secretion from beta-APN-treated fibroblasts by light and electron microscopic radioautography after injection of 3H-proline. Newly synthesized collagen was secreted from the distal ends of the beta-APN-aggregated fibroblasts as a distinct band of labeled material, resembling the pattern of matrix deposition seen in osteogenesis and dentinogenesis. The radioactive band of collagenous matrix was displaced further away from the fibroblasts at 2 and 4 days after 3H-proline injection as more collagen was secreted. This pattern of radiolabeled collagen secretion confirmed previous observations that PDL fibroblasts are highly polarized and that collagen secretory granules are extruded from the distal or secretory pole of the cell. In normal PDL the even distribution of fibroblasts and the complex interrelationship of their distal cell processes leads to a diffuse pattern of silver grain deposition, masking the oriented flow of new collagen from the distal ends of individual fibroblasts. Analysis of electron microscopic radioautographs revealed that newly synthesized collagen was packaged and secreted from beta-APN-treated fibroblasts via the normal cytoplasmic pathways but at a slower rate.

Formation of multinucleated fibroblasts in the periodontal ligaments of old mice

Multinucleated cells were observed to account for more than 17% of all cells in the periodontal ligament (PDL) of 20-month-old mice. The number of nuclei contained in sections of these cells ranged from 2 to 17, with over 50% of the multinucleated cells containing four or more nuclei within the plane of section. The multinucleated cells contained several cytoplasmic features resembling those previously described by the authors as characteristic of PDL fibroblasts. The multinucleated cells did not resemble osteoclasts or foreign body giant cells. It is suggested that fibroblasts develop a tendency to fuse and form multinucleated cells in the aged PDL. Similar cells were not observed in the PDL of young (5-week-old) mice or in the tail tendon at any age.

An electron microscopic radioautographic study of collagen secretion in periodontal ligament fibroblasts of the mouse: I. Normal fibroblasts

Analysis of electron microscopic radioautographs revealed a maximum labeling with 3H-proline of rough endoplasmic reticulum (RER) at 3 minutes, Golgi saccules 1 and 2 at 10 minutes, Golgi saccules type 3 at 20 minutes, and presecretory and secretory granules at 30 minutes. Labeling of the extra-cellular collagen matrix occurred at 30 minutes and increased with time. These observations suggest that pro-a-chains of collagen in periodontal ligament fibroblasts are synthesized in the RER and transported to the Golgi apparatus within 10 minutes. These chains then undergo parallel alignment in Golgi saccules type 2 and form segment-long-spacing-like crystallites in Golgi saccules type 3 between 10 and 20 minutes. The peak labeling of presecretory granules and mature secretory granules in small amounts at 30 minutes and the rapid increase in labeling of extracellular collagen matrix which begins at 30 minutes, indicates that the formation of secretory granules requires approximately 30 minutes and that a rapid system of secretory granule translocation exists in periodontal ligament fibroblasts. This evidence further supports the previously published morphologic evidence for a microtubule-dependent system of collagen secretion in periodontal ligament fibroblasts (Cho and Garant, 1981b).