Characterization of the stromal osteogenic cell line MN7: mRNA steady-state level of selected osteogenic markers depends on cell density and is influenced by 17β-estradiol

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Abstract
The steady-state mRNA levels of different osteogenic markers and their modulation by 17β-estradiol in the murine osteogenic cell line MN7 during proliferation and differentiation in vitro were examined. mRNA of collagen type I, osteopontin, bone morphogenetic protein 2, plasminogen activator inhibitor 1, alkaline phosphatase, and osteocalcin were isolated from MN7 cultures grown for 7, 11, 14, and 17 days. Northern blot analysis revealed steady-state transcript levels depending on MN7 cell density. The order of appearance of Col I, OP, ALP, and OC resembled the pattern of gene expression observed during osteoblast maturation in vitro. Furthermore, PAI-1 steady-state transcript levels peaked during subconfluence (day 11) but BMP-2 RNA levels reached their maximum after the culture had become confluent. 17β-Estradiol showed a dose-dependent stimulation of the different osteoblast-related transcripts present in a subconfluent MN7 culture at the time of analysis. Furthermore, the effects of 17β-estradiol (17βE2) at different time points of MN7 growth varied according to cell density. 17βE2 added to subconfluent MN7 cultures modulated the transcript level in a negative way, but RNA levels of the investigated osteogenic markers in confluent cultures were stimulated with 100 nM 17β-estradiol. No effect of 17β-estradiol on proliferation was detected. The present studies have revealed differential osteoblast gene expression related to MN7 cell proliferation and differentiation in vitro and emphasize the importance of 17βE2 in the regulation of growth of this preosteoblastic cell line in vitro.
Funding Information
  • Vlaams Aktie-programma Biotechnologie ((VLAB-ETC 009))

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