EFFECT OF OXYGEN LEVELS ON PROTEOGLYCAN SYNTHESIS BY IVD CELLS

Abstract

Purpose: In vivo, intertervertebral disc cells exist in a low oxygen environment ranging from 5% O2 for the annulus fibrosus (AF) cells to 1% O2 for the nucleus pulpous (NP) cells. Various conditions have been used for in vitro cell culture and seem that AF and NP cells can respond differently in the different systems, which may differ from the in vivo environment in terms of nutrient supply, O2 levels and biomechanical loading. The aim of this study was to determine how AF and NP cells respond to different O2 concentrations when cultured in a 3 dimensional system consisting of an alginate scaffold.

Methods: Bovine AF and NP cells were embedded in alginate beads and incubated in airtight polypropylene containers at different O2 concentration of 1%, 5% or 21%. Culture medium was changed every third day and the culture was carried out for 21 days. The pro-teoglycan content of the medium was analyzed using the DMMB assay. Cells were recovered from the alginate beads at two time points, day 8 and day 21 and RT-PCR was performed to amplify gene expression of GAPDH and aggrecan.

Results: In both cell types, the cumulative production of GAG increased with time in culture up to day 9, and then tended to plateau in the AF cells but continue to increase in the NP cells. At all time points, the level of GAG synthesis by NP cells was greater than by AF cells. All GAG synthesis trends were the similar at all O2 levels (1%, 5% and 21%).

Conclusions: In the alginate scaffold NP cells continue to exhibit their in situ behaviour by producing more proteoglycan than AF cells. Perhaps surprisingly, both cell types showed little change in GAG production with variations of O2 levels from 1–21%. This contrasts with other studies where GAG production is dependent on O2 concentrations. In the culture system used in this work, both cell types metabolize easily well at low oxygen as they do in normal conditions. Funding: Other Education Grant