The effect of oxygen partial pressure on protein synthesis and collagen hydroxylation by mature periodontal tissues maintained in organ cultures

Abstract

Mature periodontal tissues from adult-mouse first mandibular molars were cultured in a continuous-flow organ-culture system which allowed the regulation of both ascorbic acid concentration and pO₂ (oxygen partial pressure). Protein synthesis was measured by analysing the incorporation of [³H]proline into collagenous and non-collagenous proteins during the last 24h of a 2-day culture. At low pO₂ [16.0kPa (approx. 120mmHg)] approx. 60% of protein-incorporated [³H]proline was found in collagenous proteins. However, it was evident that this collagen was considerably underhydroxylated. At high pO₂ [56.0kPa (approx. 420mmHg)], both the amount of collagen deposited in the tissues and the degree of hydroxylation were increased considerably. In contrast, no significant effect on non-collagenous protein was observed. Tissues cultured at low pO₂ for the first 48h were unable to respond to a subsequent increase in pO₂ during the last 24h. Analysis of pepsin-solubilized collagen α-chains labelled with [¹⁴C]glycine demonstrated the synthesis of both type-I and type-III collagens by explants cultured for 48h at high pO₂. Type-III collagen comprised 20–30% of the radioactivity in α-chains in both the periodontal ligament and the tissues of the alveolar process. The pattern of protein synthesis in the alveolar tissues at high pO₂ was similar to that observed in these tissues in vivo. However, in the cultured periodontal ligament the proportions of non-collagenous proteins and type-III collagens were increased in comparison with the tissue in vivo.