Abstract: Different model systems using osteoblastic cell
lines have been developed to help understand the process of
bone formation. Here, we report the establishment of two
human osteoblastic cell lines obtained from primary cultures
upon transduction of immortalizing genes. The resulting
cell lines had no major differences to their parental lines
in their gene expression profiles. Similar to primary osteoblastic
cells, osteocalcin transcription increased following
1,25-dihydroxyvitamin D3 treatment and the immortalized
cells formed a mineralized matrix, as detected by Alizarin
Red staining. Moreover, these human cell lines responded
by upregulating ALPL gene expression after treatment with
the demethylating agent 5-aza-2Œ-deoxycytidine (AzadC),
as shown before for primary osteoblasts. We further demonstrate
that these cell lines can differentiate in vivo,
using a hydroxyapatite/tricalcium phosphate composite as
a scaffold, to produce bone matrix. More importantly, we
show that these cells respond to demethylating treatment, as shown by the increase in SOST mRNA levels, the gene
encoding sclerostin, upon treatment of the recipient mice
with AzadC. This also confirms, in vivo, the role of DNA
methylation in the regulation of SOST expression previously
shown in vitro. Altogether our results show that these
immortalized cell lines constitute a particularly useful
model system to obtain further insight into bone homeostasis,
and particularly into the epigenetic mechanisms regulating
sclerostin production.