DONA® (crystalline GlcN sulfate) was obtained from Mylan Italia S.r.l., resuspended at 50 mg/ml and stored at 4°C. Histopaque®-1077, ascorbic acid-2-phosphate, β-glycerophosphate, dexamethasone, MTT, Alizarin Red S (ARS), paraformaldehyde, Triton X-100, tartrate-resistant acid phosphatase (TRAP) kit (cat. no. 386), fetal calf serum (FCS), L-glutamine and antibiotics (penicillin and streptomycin) were purchased from Sigma-Aldrich (Merck KGaA). A High Capacity cDNA Reverse Transcription kit, TaqMan Gene Expression assays, Universal Master Mix II and Alexa Fluor® 488 Phalloidin (cat. no. A12379) were purchased from Thermo Fisher Scientific, Inc. Antibodies for human runt-related transcription factor 2 (Runx2; cat. no. sc-10758), collagen type 1α (COL1a1; cat. no. sc-28657), nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1; cat. no. sc-13033) and cathepsin K (cat. no. sc-48353) were purchased from Santa Cruz Biotechnology, Inc., and osteopontin (OPN; clone LF-123) was a generous gift from Dr Larry Fisher (National Institutes of Health). High-glucose Dulbecco's modified Eagle's medium (DMEM), Ham's F12 and PBS were purchased from Euroclone SpA.