1 HES1, a new target for interleukin-1β in chondrocytes

2 Objectives: To investigate the effects of interleukin 1β (IL-1β) treatment on the Notch1/Hes1 pathway in chondrocytes in vitro. Methods: Mouse articular chondrocytes in primary culture were challenged with IL-1β, alone or combined with Notch1 and IL-β pathways inhibitors. Notch1 and Hes1 expressions were investigated by immunocytochemistry, western blot and real-time qPCR. IL-β-responsive genes were assessed by real-time qPCR and a specific siRNA against Hes1 was used to identify Hes1 target genes. Results: Notch1 labeling remained nuclear and stable in intensity irrespective of treatment, suggesting a steady-state activation of this pathway in our model. IL-1β transiently increased Hes1 mRNA (2.5-fold) and protein expression in treated versus naive chondrocytes. Hes1 mRNA level then decreased below control and its cyclic pattern of expression was lost. This was associated with nuclear translocation of the cytoplasmic Hes1 protein. IL-1β induced increase in Hes1 mRNA was transcriptional, occurred through NF-κB activation and appeared to b