Gap Junctions and Stem Cell Selection by Titanium Implant Substrates

Methods: Human mesenchymal stromal cells were cultured on plastic (TCP), smooth (SMO), rough (SLA) and rough hydrophilic (SLActive) Ti disks. The transcription of connexin genes GJA1 and GJC1 were quantified using real time PCR. Flow cytometry was used to estimate gap junction activity and the degree of apoptosis and necrosis after 24 hours of co-culture with Ti in growth medium and with a gap junction inhibitor present. This experiment was repeated using cells expanded after co-culture with Ti and mixed with untreated cells to determine whether an apoptotic signal was retained.

Results: After co-culture with Ti no significant differences between the expression of GJA1 and GJC1 was seen however flow cytometry showed that cells cultured on rough substrates had significantly lower (p<0.05) lower gap junction activity. The number of cells undergoing apoptosis on Ti in the presence of the gap junction inhibitor 18-α-GA was shown to be significantly reduced (p<0.05) in cells cultured on SLA. The presence of 18-α-GA was shown to reduce apoptosis in cells grown on SLA to a level comparable to cells grown on SLActive.

Conclusion: Cells cultured on rough Ti substrates have a lower gap junction activity. Both rough Ti substrates induce apoptosis, however SLA appears to induce an apoptotic signal that is gap junction permeable and retained within cells after they have been expanded in the absence of substrate.