Objectives: To investigate the mechanisms by which cytokines and 17beta-oestradiol (17beta-E2) modulate gene expression and activity of uridine diphosphoglucose dehydrogenase (UGDH), a key enzyme of GAG synthesis in articular chondrocytes.
Methods: Rabbit articular chondrocytes (RAC) from 3-week-old animals were incubated for 24 h with TGF-beta, insulin like growth factor-I (IGF-I), IL-1beta, IL-6 and 17beta-E2. GAG synthesis was measured by [35S]-sulphate labelling and the expression of the UGDH gene was estimated by both real-time polymerase chain reaction and western blotting, whereas the enzyme activity was assayed by a spectrophotometric procedure. In addition, the transcriptional activity of several UGDH gene promoter constructs was determined in RAC transiently transfected with wild-type or deleted human oestrogen receptor-alpha gene (hER alpha66 or hER alpha46, respectively).
Results: 17Beta-E2 and its receptor hER alpha66 enhanced GAG neosynthesis in rabbit articular chondrocytes, as did TGF-beta1 whereas IL-1beta decreased this synthesis. 17Beta-E2 was found to exert positive regulatory effects at mRNA, protein and UGDH activity levels. In addition, the receptor hER alpha66, but not hER alpha46, increased the transcriptional activity of the UGDH gene. In contrast, no clear correlation between transcription, translation and activity of the UGDH was found under the effects of the cytokines studied. However, TGF-beta enhanced the enzyme activity, whereas IL-1beta, IL-6 and IGF-I were without significant effect.
Conclusions: 17Beta-E2 enhanced GAG synthesis in chondrocytes via up-regulation of the UGDH gene expression and enzyme activity. These data provide insights into the molecular mechanisms involved in the regulation of the UGDH gene and offer new approaches to investigate its potential alteration in joint diseases.