Ultrastructural localization of tartrate-resistant acid phosphatase (purple acid phosphatase) activity in chicken cartilage and bone

Reduced bone formation and increased bone resorption drive bone loss in Eimeria infected broilers

Coccidiosis is an economically significant disease in the global poultry industry, but little is known about the mechanisms of bone defects caused by coccidiosis; thus, the study focused on effects of coccidiosis on the bone homeostasis of young broiler chickens. A total of 480 male Cobb500 broilers were randomly allocated into four treatment groups, including an uninfected control consuming diet ad libitum, two infected groups were orally gavaged with two different concentrations of sporulated Eimeria oocysts, and an uninfected pair-fed group fed the same amount of feed as the high Eimeria-infected group consumed. Growth performance and feed intake were recorded, and samples were collected on 6 days post infection. Results indicated that coccidiosis increased systemic oxidative status and elevated immune response in bone marrow, suppressing bone growth rate (P < 0.05) and increasing bone resorption (P < 0.05) which led to lower bone mineral density (P < 0.05) and mineral content (P < 0.05) under Eimeria infection. With the same amount of feed intake, the uninfected pair-fed group showed a distinguished bone formation rate and bone resorption level compared with the Eimeria infected groups. In conclusion, inflammatory immune response and oxidative stress in broilers after Eimeria infection were closely associated with altered bone homeostasis, highlighting the role of inflammation and oxidative stress in broiler bone homeostasis during coccidiosis.

Multivalent Presentation of Peptide Targeting Groups Alters Polymer Biodistribution to Target Tissues

Drug delivery to bone is challenging, whereby drug distribution is commonly <1% of injected dose, despite development of several bone-targeted drug delivery systems specific to hydroxyapatite. These bone-targeted drug delivery systems still suffer from poor target cell localization within bone, as at any given time overall bone volume is far greater than acutely remodeling bone volume, which harbors relevant cell targets (osteoclasts or osteoblasts). Thus, there exists a need to target bone-acting drugs specifically to sites of bone remodeling. To address this need, this study synthesized oligo(ethylene glycol) copolymers based on a peptide with high affinity to tartrate-resistant acid phosphatase (TRAP), an enzyme deposited by osteoclasts during the bone resorption phase of bone remodeling, which provides greater specificity relevant for bone cell drugging. Gradient and random peptide orientations, as well as polymer molecular weights, were investigated. TRAP-targeted, high molecular weight (M_n) random copolymers exhibited superior accumulation in remodeling bone, where fracture accumulation was observed for at least 1 week and accounted for 14% of tissue distribution. Intermediate and low M_n random copolymer accumulation was lower, indicating residence time depends on M_n. High M_n gradient polymers were cleared, with only 2% persisting at fractures after 1 week, suggesting TRAP binding depends on peptide density. Peptide density and M_n are easily modified in this versatile targeting platform, which can be applied to a range of bone drug delivery applications.

Rab13 is upregulated during osteoclast differentiation and associates with small vesicles revealing polarized distribution in resorbing cells

Osteoclasts are bone-resorbing multinucleated cells that undergo drastic changes in their polarization due to heavy vesicular trafficking during the resorption cycle. These events require the precise orchestration of membrane traffic in order to maintain the unique characteristics of the different membrane domains in osteoclasts. Rab proteins are small GTPases involved in regulation of most, if not all, steps of vesicle trafficking. The investigators studied RAB genes in human osteoclasts and found that at least 26 RABs were expressed in osteoclasts. Out of these, RAB13 gene expression was highly upregulated during differentiation of human peripheral blood monocytic cells into osteoclasts. To study its possible function in osteoclasts, the investigators performed immunolocalization studies for Rab13 and various known markers of osteoclast vesicular trafficking. Rab13 localized to small vesicular structures at the superior parts of the osteoclast between the trans-Golgi network and basolateral membrane domain. Rab13 localization suggests that it is not involved in endocytosis or transcytosis of bone degradation products. In addition, Rab13 did not associate with early endosomes or recycling endosomes labeled with EEA1 or TRITC-conjugated transferrin, respectively. Its involvement in glucose transporter traffic was excluded as well. It is suggested that Rab13 is associated with a putative secretory function in osteoclasts.

Intracellular machinery for matrix degradation in bone-resorbing osteoclasts

In osteoclasts, TRACP co-localized with cathepsin K in transcytotic vesicles and was activated by cathepsin K in vitro, suggesting that TRACP may degrade organic matrix components in transcytotic vesicles in an event regulated by cathepsin K.

INTRODUCTION

TRACP is an enzyme with unknown biological function. In addition to its phosphatase activity, TRACP is capable of generating reactive oxygen species (ROS). Bone-resorbing osteoclasts contain large amounts of TRACP, and transgenic animal models suggest that TRACP has a role in bone resorption. Osteoclasts resorb bone by secreting acid and lysosomal enzymes such as cathepsin K into an extracellular resorption lacuna between the cell membrane and bone surface. Matrix degradation products are then endocytosed, transcytosed, and secreted through a functional secretory domain in the basolateral membrane facing bone marrow.

MATERIALS AND METHODS

We have studied intracellular localization of TRACP in osteoclasts with antibodies against various known endosomal and lysosomal proteins using confocal microscopy. We also studied co-localization of TRACP with cathepsin K and endocytosed bone matrix components and the effect of cathepsin K digestion on the ROS generating activity of TRACP in vitro.

RESULTS

Double-staining experiments of TRACP with endosomal and lysosomal markers showed that, although some endosomal staining was detected, TRACP was not present in lysosomes. However, TRACP was present in transcytotic vesicles, where it co-localized with cathepsin K. Cathepsin K digestion of TRACP in vitro increased the phosphatase activity by 5.6-fold and the ROS generating activity by 2.0-fold.

CONCLUSIONS

These results suggest that cathepsin K may activate the ROS-generating activity of TRACP in transcytotic vesicles of resorbing osteoclasts, the ROS being targeted to finalize degradation of organic bone matrix components during their transcytosis.

Acid phosphatases

Acid phosphatases (APs) are a family of enzymes that are widespread in nature, and can be found in many animal and plant species. Mystery surrounds the precise functional role of these molecular facilitators, despite much research. Yet, paradoxically, human APs have had considerable impact as tools of clinical investigation and intervention. One particular example is tartrate resistant acid phosphatase, which is detected in the serum in raised amounts accompanying pathological bone resorption. This article seeks to explore the identity and diversity of APs, and to demonstrate the relation between APs, human disease, and clinical diagnosis.

Alkaline fixation-resistant acid phosphatases in human tissues: histochemical evidence for a new type of acid phosphatase in endothelial, endometrial and neuronal sites

The effect of pH during formalin fixation on acid phosphatases in human tissues was studied. Lysosomal-type acid phosphatase was sensitive to alkaline fixation, being completely inactive after fixation at pH 9.0. Prostatic and tartrate-resistant osteoclastic/macrophagic types were alkaline fixation-resistant, as was an acid phosphatase localized in endothelium, endometrial stromal cells and intestinal nerves. The latter activity was further separable into fluoride- and tartrate-sensitive beta-glycerophosphatase and fluoride-sensitive, tartrate-resistant alpha-naphthyl phosphatase. The activities appeared to represent either different, tightly associated enzymes or separate activity centres of a single enzyme. Alkaline fixation-resistant alpha-naphthyl phosphatase at endothelial, endometrial and neuronal sites was also well demonstrated in unfixed or neutral formalin-fixed sections as tartrate-resistant activity similar to classical tartrate-resistant acid phosphatase, but these phosphatases appear to be antigenically different. Alkaline fixation-resistant acid phosphatase showed a restricted tissue distribution both in endothelium (mainly in vessels of abdominal organs) and at neuronal sites (only in intestinal nerves). Alkaline fixation-resistant acid phosphatase appears to represent a previously unknown or uncharacterized enzyme activity whose chemical properties could not be classified as any previously known type of acid or other phosphatases.

Development of a Kinetic Assay for Band 5b Tartrate-resistant Acid Phosphatase Activity in Serum

Background: Band 5 tartrate-resistant acid phosphatase (TrACP; EC 3.1.3.2) consists of two isoenzymes, bands 5a and 5b, of which band 5b TrACP is considered to be derived from bone. However, no kinetic method for the specific measurement of band 5b TrACP in serum is available. Our aim was to develop a kinetic assay method for the specific measurement of band 5b TrACP in serum.

Methods: Band 5b TrACP was measured kinetically in serum as tartrate-resistant fluoride-sensitive heparin-resistant ACP with 2,6-dichloro-4-acetylphenyl phosphate as substrate at pH 6.6.

Results: Heparin inhibited band 5a TrACP but had no effect on band 5b TrACP in serum or in bone extract. The presence of EDTA or ascorbic acid had no effect, but dithiothreitol inhibited enzyme activity. The within-run (n = 20) and between-run (n = 20) CVs of band 5b TrACP activity were 3.3–5.8% and 5.0–7.3%, respectively. The mean ± SD values of band 5b TrACP activity in males (n = 25) and females (n = 57) 20–29 years of age by this method were 8.0 ± 2.2 U/L and 6.4 ± 1.8 U/L, respectively. The band 5b TrACP value was significantly higher in females &gt;50 years of age compared with the younger subjects (20–29 years). The highest band 5b TrACP values were among children younger than 15 years.

Conclusions: This kinetic assay is a simple and specific method for the measurement of band 5b TrACP in serum samples and is useful in the evaluation of bone turnover activity.

Microscopic and histochemical study of odontoclasts in physiologic resorption of teeth of the polyphyodont lizard, Liolaemus gravenhorsti

Using tartrate-resistant acid phosphatase (TRAP), we examined the cytodifferentiation of odontoclast cells in resorbing areas of dental tissues during the replacement of teeth in a polyphyodont lizard, Liolaemus gravenhorsti. We also report, by means of Lectin-HRP histochemistry, the distribution pattern of some specific sugar residues of TRAPase-positive cells. For detection of TRAPase activity, the azo dye-coupling technique was used. Lectin binding sites were demonstrated by means of specific HRP-lectins. The process of tooth resorption was divided into four stages: 1) preresorption-the wall of the dental pulp is covered with an odontoblast layer, and no TRAP-positive cells are in the dental pulp; 2) early resorption-TRAP-positive multinucleate odontoclasts are present on the dental wall, but the rest of the pulp surface is still covered with an odontoblast layer; 3) later resorption-the entire surface of the pulp chamber is lined with multinucleate odontoclasts; and 4) final resorption-the tooth has been totally resorbed. Odontoclasts are usually detached from the resorbed surface, and show signs of degeneration. Of the six lectins used, PNA, ECA, and UEA-1 bind to multinucleated but not mononuclear cells. All the remaining lectins, BS-1, RCA(120), and LTA showed no binding to any cells of the teeth. The significance of saccharidic moieties such as acetyl-galactosamine, acetyl-glucosamine, and fucose sugar residues is difficult to ascertain. Perhaps these oligosaccharides might be borne on molecules associated with odontoclastic resorption or associated with multinucleation of odontoclasts after attachment to the dentine surface.

Is acid phosphatase activity present in bone matrix at sites of endochondral ossification in rabbit fracture callus?

It has been suggested that acid phosphatase activity is present in newly formed bone matrix at sites of endochondral ossification in rabbit fracture calluses. Because acid phosphatases are usually found intracellularly, it was decided to test this possibility more rigorously. Tissue from 10- and 14-day healing rabbit fractures was subjected to a series of critical tests for acid phosphatases with a pH optimum of 5.0. Fluoride, tartrate and molybdate were used as potential inhibitors of acid phosphatase activity. The effects of several counterstaining protocols were also investigated. A fluoride- and tartrate-resistant acid phosphatase is located in osteoclasts and mononuclear phagocytes. Diffuse staining of the bone matrix is seen, but it is dependent upon the length of incubation in the substrate medium and the distance from the acid phosphatase-reacting cells. It is concluded that the coloration of the bone matrix is probably caused by diffusion of the dye and reaction product and is, therefore, artifactual.

Cytodifferentiation of the odontoclast prior to the shedding of human deciduous teeth: an ultrastructural and cytochemical study

BACKGROUND

In human deciduous teeth, odontoclastic resorption takes place at the pulpal surface of the coronal dentine prior to shedding, and this resorption shows clear time-related histological changes (Sahara et al., 1992).

METHODS

Using this phenomenon as an observation system, we examined the cytodifferentiation of human odontoclasts by light and electron microscopy. For a histochemical marker of odontoclast differentiation and function, tartrate-resistant acid phosphatase (TRAP) activity was determined by light and electron microscopic enzyme histochemistry.

RESULTS

As root resorption neared completion, TRAP-positive mononuclear cells were initially detected in the pulp chamber. They had abundant mitochondria, small lysosomes, and moderately developed rough endoplasmic reticulum throughout their cytoplasm. In these mononuclear cells, TRAP activity was localized in compartments of the biosynthetic pathway, i.e., in cisternae of the endoplasmic reticulum and Golgi lamellae, as well as small lysosomes. The TRAP-positive mononuclear cells first made contact with the predentine surface by their elongated cellular processes. After attachment, they spread out along the predentine surface and developed specialized membrane structures, clear zones, and ruffled borders. Next, they fused with each other on the predentine surface and formed typical multinucleate odontoclasts. After termination of their resorption function, the odontoclasts lost their ruffled borders and became detached from the resorbed surface. Most of the detached odontoclasts had numerous large pale vacuoles and secondary lysosomes and appeared to be in the process of degeneration.

CONCLUSIONS

The present study demonstrates that: (1) odontoclasts differentiated from TRAP-positive mononuclear cells, which presumably originate from circulating progenitor cells, (2) membrane specialization of odontoclasts, i.e., development of a clear zone and ruffled border, is induced following their contact with the resorption surface, (3) multinucleation of odontoclasts takes place only after their attachment to the resorption surface, (4) mature multinucleate odontoclasts can resorb predentine as well as dentine in the same way as osteoclasts resorb bone, and (5) at the end of the resorption, odontoclasts gradually lose their ruffled borders and become detached from the resorbed surface.

Tartrate-resistant acid phosphatase accumulated in the matrix of developing medullary bone induced by estrogen treatment of male Japanese quail

Tartrate-resistant acid phosphatase (TRAP) in medullary bone matrix and bone cells was histochemically examined employing estrogen-induced medullary bone of male Japanese quail. Within 2 days after estrogen administration, medullary bone matrix was identified and the matrix and osteoblasts were negative for TRAP activity. Osteoclasts showing TRAP activity were occasionally seen. By 4 days, the projection of medullary bone trabeculae was seen and TRAP became positive in the deeper part of the bone matrix of trabeculae as well as the matrix located near cortical bone, but the surface areas and extending margins of medullary bone trabeculae were negative in activity. Osteoblasts were also negative for TRAP activity. By 7 days, TRAP-positive bone matrix conspicuously increased accompanying increment of bone volume, but TRAP-negative bone matrix was still seen at the surface areas or extending areas of the medullary bone trabeculae. Osteoblasts showed no reaction product. Osteoclasts showing TRAP activity increased in number. The results demonstrate that TRAP accumulates in medullary bone matrix with bone formation. Circumstantial evidence suggests that medullary bone osteoblasts may be involved in TRAP accumulation in the matrix despite their negative activity.

Conversion of skeletal tartrate-sensitive acid phosphatases into tartrate-resistant isoenzymes in vitro

1. Chicken skeletal tartrate-sensitive (TsACP) and -resistant (TrACP) acid phosphatase isoenzymes could be separated from each other by carboxylmethyl-sepharose ion exchange chromatography. 2. Chicken skeletal TsACP showed a gradual time-dependent loss of sensitivity to tartrate inhibition when incubated at room temperature, but not at 4 degrees C. 3. The loss of sensitivity to tartrate inhibition was associated with an activation of the enzyme activity. 4. These changes were accompanied with a shift in the electrophoretic mobility of the enzyme activity from a large molecular sized form to a smaller molecular sized form that resembled the freshly prepared TrACP on the native acidic polyacrylamide electrophoresis gels, and on molecular sieve Superose-12 Fast Protein Liquid Chromatography. 5. Kinetic evaluations of the biochemical properties of the "converted" TsACP activity resembled the TrACP. 6. The apparent "conversion" was not unique to chicken TsACP, since similar "conversion" was observed with partially purified preparations of bovine bone matrix TsACP and of human osteoblastic TsACP. 7. Addition of several serine protease inhibitors did not prevent the "conversion". 8. These findings are consistent with the possibility that skeletal TsACPs are precursors of skeletal TrACPs.

A histochemical study of acid phosphatases in medullary bone matrix and osteoclasts in laying Japanese quail

Acid phosphatase activity in medullary bone matrix and osteoclasts of laying Japanese quail was examined histochemically. To avoid nonspecific staining, the reactivity of the enzyme was evaluated using both the azo dye method and the lead salt method and nonembedded thick sections and resin-embedded thin sections. The pH of the incubation medium was also varied from the acid range (pH 5.0 and 6.5) to the alkaline range (pH 8.5). Medullary bone osteoclasts contain both tartrate-resistant acid phosphatase (TRAP) activity and fluoride-resistant acid phosphatase (FRAP) activity, and no significant difference in intensity was detected between active and inactive osteoclasts. The entire matrix of medullary bone was positive for tartrate-resistant, fluoride-sensitive acid phosphatase activity. No reaction product was observed in sections incubated in substrate-free and pH 8.5 media. The results demonstrate the existence of FRAP in medullary bone osteoclasts and suggest that medullary bone matrix includes TRAP throughout the matrix.