Intervertebral disc cells exhibit differences in gene expression in alginate and monolayer culture

Study Design. The mRNA levels of aggrecan and collagen were quantified in i ntervertebral disc cells cultured under three conditions primary alginate c ulture, monolayer culture, and re-encapsulation in alginate after monolayer culture. Objectives. To compare the phenotype of intervertebral disc cells under dif ferent culture conditions and to investigate the reversibility of cell phen otype after re-encapsulation in alginate after monolayer culture. Summary of Background Data. The intervertebral disc contains heterogeneous populations of cells that vary with anatomic region. These cells possess si gnificant differences in phenotype that can be preserved in vitro, although the effect of culture conditions on the phenotype of these cells is poorly understood. Methods. The intervertebral disc cells of 4-5-month-old pigs were isolated enzymatically from three anatomic zones: anulus fibrosus (AF), transition z one (TZ), and nucleus pulposus (NP). Gene expression levels of aggrecan and collagen Types I and II were measured using a quantitative reverse transcr iptase-polymerase chain reaction. Results. Gene expression levels of anulus fibrosus and transition zone cell s were shifted in monolayer compared with alginate, although the shift was partially reversed when re-encapsulated in alginate. However, NP cells appe ared to be insensitive to culture conditions. Furthermore, characteristic p atterns of gene expression among AF, TZ, and NP cells in primary alginate c ulture did not exist in monolayer culture, but they were also observed afte r re-encapsulation in alginate. Conclusion. The findings of this study suggest that anulus fibrosus and tra nsition zone cells undergo a reversible shift in phenotype when cultured in monolayer compared with alginate. These differences suggest that the cultu re system exerts a strong influence on cell phenotype and may play a role i n the response of these cells to biophysical and biochemical stimuli in vit ro.