Research Report - Nikolaus-Fiebiger-Zentrum für Molekulare Medizin

The mechanism of this transdifferentiation process remains to be elucidated. We
have preliminary evidence that after opening of the chondrocyte lacunae by
osteoclasts hypertrophic chondrocytes de-differentiate to bone marrow stem cells
which may then differentiate into osteoblasts precursor cells and other
mesenchymal cells. Studies to confirm this hypothesis are under investigation.
Fig.3 Fig. 4
Figure 3. YFP positive endosteal and bone marrow cells express osteoblast marker
gene mRNA. Adherent bone marrow and endosteal cells were isolated from long bones of
P21 BAC Col10 Cre;Rosa26-YFP reporter mice by bone flushing with collagenase P and
cultured for two weeks. (A) YFP positive cells were sorted by FACS. Gating for viable cells
(89.5% of total cells) is illustrated in the upper panel (pink circle). Lower panel: analysis of
viable cells for YFP fluorescence reveals a clearly defined population of positive cells
(12.4%). (B) RT-PCR analysis of RNA isolated from YFP + and YFP - cells after sorting and
reverse transcription. Expression of osteoblast markers was analyzed using specific primers
for the marker genes osterix, Runx2, osteocalcin, and Col1a1). Ppia (cyclophilin a) was used
as a housekeeping gene control. Gel electrophoresis of PCR products shows, that YFP
positive cells express high message levels of all four osteoblast marker genes (green box).
Cal.: calvarial cDNA.
Figure 4: Hypertrophic chondrocytes are an additional source of osteoblasts
Reporter gene expression is initiated in hypertrophic chondrocytes (HCs). The progeny of
HCs continues reporter gene expression and can be detected as YFP positive trabecular
osteoblasts (OBs). Some HCs are eliminated from the growth plate by apoptosis.
Additionally, osteoblast precursor cells (OBP) invade the cartilage template and give rise to
trabecular osteoblasts. Grey: cartilage matrix. Brown: bone trabeculae. Sand: bone marrow.
PCs: proliferating chondrocytes. RCs: resting chondrocytes
II: Synergistic control of mesenchymal stem cell differentiation by
nanoscale surface geometry and immobilized growth factors on TiO2
nanotubes ( P.I.: Dr. Jung Park)
Park J, Bauer S, Pittrof A, Killian MS, Schmuki P, von der Mark K.
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