Characteristics and properties of osteocytes in culture

Abstract

Although the osteocyte is the most abundant among the highly differentiated cells of mature bone (osteocytes, lining cells, osteoblasts, and osteoclasts), its properties and functions are the least known and understood. Here we isolated osteocytes from mixed populations of bone cells liberated from fetal chick calvariae by alternate treatments with collagenase and EDTA. The osteocytes were removed from the bone cell populations by binding them via an osteocyte-specific antibody (MAb OB 7.3) to magnetic beads and removing the beads together with the coupled osteocytes from the population using a magnet. Isolated osteocytes were found to be highly differentiated, postmitotic cells that required their typical stellate morphology in culture. Osteocyte populations had alkaline phosphatase (ALP) activity somewhat lower than that of the osteoblast-like cell populations from which they were separated by the immunodissection procedure. On the single-cell level, the ALP activity was highly variable. Parathyroid hormone (PTH) receptors were found to be present on osteocytes as well as on osteoblast-like cells, but not on fibroblast-like cells of the outer periosteum. In response to PTH, osteocytes increased their intracellular levels of cAMP, as did the osteoblast-like cells. Osteocytes appeared to be somewhat more sensitive to PTH than osteoblasts. When seeded onto dentin slices, osteocytes did not corrode the dentin surface to any appraisable degree. We therefore found no evidence to support the notion that osteocytes play a role in the calcium homeostasis through osteocytic osteolysis. Whether osteocytes play an important role in perceiving and transducing hormonal and/or mechanical stimuli remains open for future research.

Osteocyte Remodeling of the Perilacunar and Pericanalicular Matrix

“…In addition, van der Plas and co-workers assumed that osteocytes would form resorption lacunae or pits similar to those formed by osteoclasts. When isolated avian osteocytes did not form resorption lacunae when cultured on sperm whale dentin, the concept of osteocyte resorption was discredited (van der Plas et al, 1994). The irregular morphology, variability in spacing, and lack of consistent orientation especially in trabecular bone of osteocyte lacunae created technical challenges when using two dimensional measurements.…”

Transcriptional Regulatory Cascades in Runx2-Dependent Bone Development

“…The osteocytes are the most numerous cells in mature bone, which reside in a mineralized extracellular matrix. 1 So far, the process of osteocytogenesis is largely unknown. A cartilage intermediate is not involved during intramembranous ossification.…”

Acute and Stress-related Injuries of Bone and Cartilage: Pertinent Anatomy, Basic Biomechanics, and Imaging Perspective

“…They are trapped within the osteoid material in small lacunar spaces, interconnected by numerous dendritic cytoplasmic processes, and they do not directly secrete matrix or resorb bone (7,8). Osteocytes interact with osteoblasts by releasing molecules that inhibit osteoblast function and bone formation (9).…”