title: Effects of ascorbic acid, calcitriol, and retinoic acid on the differentiation of preosteoblasts.
abstract: The responses of the immortalized rat preosteoblast UMR-201-10B to ascorbic acid (AA), 1,25(OH)2D3 (calcitriol), and retinoic acid (RA) were examined. UMR-201-10B cells have an undetectable basal alkaline phosphatase (ALP) activity that is induced after 24 h of treatment with 10(-6) M RA (4.64 +/- 0.06 mumol/h/mg of protein). The addition of 10(-8) M calcitriol resulted in a slight induction of ALP activity after 72 h (0.43 +/- 0.07 mumol/h/mg of protein). When calcitriol was added to RA, however, over the same period ALP activity was enhanced significantly compared with treatment with RA alone (RA and calcitriol, 12.29 +/- 0.86 mumol/h/mg of protein). Treatment with AA (50 micrograms/ml) alone had no effect on ALP activity but increased RA-induced ALP activity to 6.78 +/- 0.28 mumol/h/mg of protein at 24 h. In contrast, AA inhibited calcitriol-induced ALP activity after 7 days of combined treatment with calcitriol (calcitriol, 7.73 +/- 0.16 mumol/h/mg of protein; AA and calcitriol, 1.44 +/- 0.06 mumol/h/mg of protein). Individually, RA and calcitriol induced mRNA expression for ALP, matrix-gla protein (MGP), and osteopontin (OP). The steady state level of pro-alpha 1(I) collagen mRNA also was increased significantly by treatment with RA and AA individually. The combination of RA and calcitriol had a synergistic effect on ALP, OP, and especially MGP mRNA expression but significantly reduced the expression of pro-alpha 1(I) collagen mRNA. AA enhanced the effect of RA on the expression of pro-alpha 1(I) collagen, MGP, and ALP mRNAs as well as the effect of calcitriol on OP and MGP. The addition of AA to RA resulted in a decrease in the steady state level of OP, whereas its cotreatment with calcitriol caused a decrease in pro-alpha 1(I) collagen and ALP mRNA. In conclusion, these studies identify RA, calcitriol, and AA as regulators of differentiated osteoblast function.
authors.affiliation: Department of Orthopaedics, St. Vincent's Hospital, Melbourne, Australia.
authors.forename: P F
authors.initials: PF
authors.lastname: Choong
authors.forename: T J
authors.initials: TJ
authors.lastname: Martin
authors.forename: K W
authors.initials: KW
authors.lastname: Ng
mesh_terms: D000469:Alkaline Phosphatase / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D002117:Calcitriol / Q000494:pharmacology*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D003094:Collagen / Q000378:metabolism; D004357:Drug Synergism; D016326:Extracellular Matrix Proteins; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D053495:Osteopontin; D011506:Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D012795:Sialoglycoproteins / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology*; D000097568:Matrix Gla Protein
chemical_list: D000469:Alkaline Phosphatase; D001205:Ascorbic Acid; D002117:Calcitriol; D002135:Calcium-Binding Proteins; D003094:Collagen; D016326:Extracellular Matrix Proteins; D053495:Osteopontin; D011506:Proteins; D012333:RNA, Messenger; D012795:Sialoglycoproteins; D014212:Tretinoin; D000097568:Matrix Gla Protein; C506897:Spp1 protein, rat