Changes in osteocalcin response to 1,25-dihydroxyvitamin D-3 stimulation and basal vitamin D receptor expression in human osteoblastic cells according to donor age and skeletal origin

Age-related osteopenia is known to occur differently throughout the skeleto n. In the present study, we examine the influence of donor age (< 50 and > 50 years), and bone structure (cortical vs. trabecular) on osteocalcin and vitamin D receptor (VDR) expression in primary cultures of human osteoblast ic cells (hOB) cells. Cells were isolated from trabecular bone samples obta ined from donors undergoing either knee (mainly trabecular) (n = 22; 4 < 50 years, 18 > 50 years) or hip (mainly cortical) (n = 16; 6 < 50 years, 10 > 50 years) arthroplasty. Pooling the results from knee and hip hOB cell cul tures, we found that secreted osteocalcin was higher in hOB cells from the younger donors, compared with that in older donors, and peaked after stimul ation with 10(-6)-10(-8) mol/L 1,25-dihydroxyvitamin D-3 [1,25(OH)(2)D-3]. In cells from the latter donors, this secretion was maximal after 10(-6) mo l/L 1,25(OH),D3 treatment. On the other hand, using reverse transcription f ollowed by polymerase chain reaction, baseline osteocalcin mRNA was found t o be lower in hOB cells from the older donors than in those from younger do nors. After treatment with 10(-6)-10(-8) mol/L 1,25(OH)(2)D-3, osteocalcin mRNA increased over baseline in all groups of hOB cells studied. In age-mat ched cultures, both basal and 10(-6)-10(-8) mol/L 1,25(OH)(2)D-3-stimulated osteocalcin mRNA showed similar values in hOB cells from both skeletal sit es in younger donors. However, in the older donors, baseline as well as 10( -8) mol/L 1,25(OH)(2)D-3-stimulated osteocalcin mRNA were higher in knee hO B cells than in hip hOB cells. Furthermore, baseline VDR mRNA expression wa s also higher in the former cells than in the latter cells in the older gro up. Considering the influence of donor age at each skeletal site of origin, we found lower baseline osteocalcin and VDR mRNA levels in hip hOB cells i n the older group than in the younger group. Our findings indicate that the response of osteocalcin secretion and its mRNA to physiological doses of 1 ,25(OH),D, decreases with aging and is associated with decreased VDR mRNA e xpression in hOB cells from mainly cortical bone. (C) 2001 by Elsevier Scie nce Inc. All rights reserved.