Affiliations: Musculoskeletal Research Laboratory, Department of Orthopaedics and Rehabilitation, The Pennsylvania State University College of Medicine, Hershey, PA, 17033, USA
Note: [] Address for correspondence: Gwendolen Reilly, Tissue Engineering Laboratory Rm 237, Departments of Orthodontics and Bioengineering, MC 841, University of Illinois at Chicago, 801 South Paulina Street, Chicago, IL 60612‐7211, USA. Tel.: 312 996 2649; Fax: 312 996 7854; E‐mail: reilly1@uic.edu.
Note: [] Present address: Department of Anatomy Physiology and Cell Biology, School of Veterinary Medicine, University of California Davis, One Shields Avenue, 1321 Haring Hall, Davis, CA 95616, USA.
Note: [] Present address: Department of Veteran Affairs and Stanford University, Durand 211, BME, MC4038 Stanford, CA 94305‐4038, USA.
Abstract: It has been hypothesized that bone cells have a hyaluronic acid (HA) rich glycocalyx (cell coat or pericellular matrix) and that this contributes to bone cell mechanotransduction via fluid flow. The glycocalyx of bone cells of the MC3T3‐E1 osteoblastic cell line and the MLO‐Y4 osteocytic cell line were characterized. Alcian blue staining and lectin binding experiments suggested that these cells have a glycocalyx rich in HA. Sulphated proteoglycans were not detected. Staining with hyaluronic acid binding protein and degradation by hyaluronidase confirmed that HA was a major component of the glycocalyx. We subjected cells, with and without hyaluronidase treatment, to oscillating fluid flow under standardized in vitro conditions. There was no effect of glycocalyx degradation on the intracellular calcium signal, in either cell type, in terms of the percentage of cells responding (40–80%) or the magnitude of the response (2–5 times baseline). However, a 4‐fold fluid flow induced increase in PGE2 was eliminated by hyaluronidase pre‐treatment in MLO‐Y4 cells. We conclude that under these conditions the calcium and PGE2 responses occur via different pathways. An intact glycocalyx is not necessary in order to initiate a calcium signal in response to oscillating fluid flow. However, in osteocyte‐like cells the PGE2 pathway is more dependent on mechanical signals transmitted through the glycocalyx.
