Chondroblastic/Chondrocytic Phenotypes Emerging in Bone Marrow-Derived Osteoblastic Culture on Titanium

Abstract

Objective: This study characterizes chondrogenic phenotype possibly emerging or being altered while in an in vitro osteogenic environment with titanium and tests the hypotheses that(1) the process of osseointegration involves a novel cellular mechanism of chondroblastic/chondrocytic phenotype as well as osteoblastic phenotype and that (2) the chondroblastic/chondrocytic phenotype can be modulated by the surface topography of the titanium.
Materials and Methods: Two types of commercially pure titanium disks, a machined surface and a rough surface by acid-etching (AE), were prepared. Osteoblastic cells derived from rat bone marrow stromal cells were inoculated with an osteogenic medium onto polystyrene surfaces and machined titanium or AE titanium disks in 12-well culture plates. The cells were harvested, and total RNA was extracted at day 1, 3, 7, 14, 21 and 28 of culture. The mRNA expression of osteoblastic and chondroblastic/chondrocytic genes was examined using the reverse transcriptase polymerase chain reaction. The morphology was evaluated using a scanning electron microscope and the elements were quantified using an energy dispersive spectroscope in the day 28 mineralized cultures.
Result: Bone-related gene expressions, such as type I collagen, osteopontin and osteocalcin, were more upregulated in the titanium cultures than in the polystyrene culture. Chondroblastic/chondrocytic gene expressions, including type II, IX and X collagen, were exclusively expressed on the titanium surfaces. Biglycan and Sox9 genes tended to be more upregulated on both the titanium surfaces compared with the polystyrene surface. Such differential expression and upregulated expression of type II collagen genes were enhanced more on the AE titanium surface than on the machined titanium surface. The polystyrene culture seemed to be a fibrous structure and the machined titanium culture seemed to be a thicker structure compared with the polystyrene culture,while the AE titanium culture seemed to be a smooth surface structure. More sulfurelement was detected on the AE titanium surface than on the machined titanium or polystyrene surfaces.
Conclusion: Culturing osteoblastic cells derived from bone marrow stromal cells on titanium with the osteoblastic inducing media remarkably upregulates or induces chondrogenic gene expression, and the surface roughness of titanium boosts the unique transcriptional modulation.