title: Tartrate-resistant acid phosphatase (TRAP) co-localizes with receptor activator of NF-KB ligand (RANKL) and osteoprotegerin (OPG) in lysosomal-associated membrane protein 1 (LAMP1)-positive vesicles in rat osteoblasts and osteocytes.
abstract: Tartrate-resistant acid phosphatase (TRAP) is well known as an osteoclast marker; however, a recent study from our group demonstrated enhanced number of TRAP + osteocytes as well as enhanced levels of TRAP located to intracellular vesicles in osteoblasts and osteocytes in experimental osteoporosis in rats. Such vesicles were especially abundant in osteoblasts and osteocytes in cancellous bone as well as close to bone surface and intracortical remodeling sites. To further investigate TRAP in osteoblasts and osteocytes, long bones from young, growing rats were examined. Immunofluorescence confocal microscopy displayed co-localization of TRAP with receptor activator of NF-KB ligand (RANKL) and osteoprotegerin (OPG) in hypertrophic chondrocytes and diaphyseal osteocytes with Pearson's correlation coefficient ≥0.8. Transmission electron microscopy showed co-localization of TRAP and RANKL in lysosomal-associated membrane protein 1 (LAMP1) + vesicles in osteoblasts and osteocytes supporting the results obtained by confocal microscopy. Recent in vitro data have demonstrated OPG as a traffic regulator for RANKL to LAMP1 + secretory lysosomes in osteoblasts and osteocytes, which seem to serve as temporary storage compartments for RANKL. Our in situ observations indicate that TRAP is located to RANKL-/OPG-positive secretory lysosomes in osteoblasts and osteocytes, which may have implications for osteocyte regulation of osteoclastogenesis.
authors.affiliation: Department of Pathology, The Core Facility for Advanced Electron Microscopy, Oslo University Hospital, Rikshospitalet, P.O. Box 4950, Nydalen, 0424, Oslo, Norway, l.b.solberg@gmail.com.
authors.forename: L B
authors.initials: LB
authors.lastname: Solberg
authors.forename: E
authors.initials: E
authors.lastname: Stang
authors.forename: S-H
authors.initials: SH
authors.lastname: Brorson
authors.forename: G
authors.initials: G
authors.lastname: Andersson
authors.forename: F P
authors.initials: FP
authors.lastname: Reinholt
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism*; D000818:Animals; D005455:Fluorescent Antibody Technique; D007527:Isoenzymes / Q000378:metabolism*; D052118:Lysosomal-Associated Membrane Protein 1 / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D010006:Osteoblasts / Q000201:enzymology / Q000382:microbiology; D010011:Osteocytes / Q000201:enzymology / Q000378:metabolism; D053244:Osteoprotegerin / Q000378:metabolism*; D021381:Protein Transport; D053245:RANK Ligand / Q000378:metabolism*; D051381:Rats; D000071681:Tartrate-Resistant Acid Phosphatase
chemical_list: D007527:Isoenzymes; D052118:Lysosomal-Associated Membrane Protein 1; D053244:Osteoprotegerin; D053245:RANK Ligand; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase