The effect of dexamethasone (DEX) on the expression of fibronectin (FN), proα1(I) collagen (Col1), integrin α2, α5and β1subunits mRNAs, were studied by quantitative in situ hybridization (ISH) with radiolabelled probes in relationship with the organization of the extracellular matrix (ECM) of FN in human skin fibroblasts. In particular, two fibroblast strains were analysed, one derived from a control donor, typically organizing a rich ECM of FN, and the other from a patient affected by Ehlers-Danlos syndrome (EDS), which did not assemble the FN-ECM.
Treatment of both fibroblast strains with 10−7mDEX slightly enhanced the level of FN mRNA (by about 1.5-fold), did not influence the level of α5subunit mRNA and reduced Col1, α2and β1integrin subunits mRNAs by 2–3-fold. These results show that, in these cells, DEX coordinately downregulates the expression of Col1 and its specific integrin α2β1. Moreover, DEX regulates in a different manner the α5and β1subunits forming the main FN receptor (FNR) in skin fibroblasts.
Immunofluorescence microscopy evidencing the FN-ECM and integrins containing α5and β1subunits showed that in control cells DEX induced a slight enhancement of the FN-ECM and of the α5β1receptors patches. Therefore, in these cells the decrease of β1FN receptor subunit mRNA, as well as the decrease of Col1 and its receptor mRNAs, did not influence the FN-ECM assembly. In EDS fibroblasts, DEX decreased the cytoplasmic accumulation of FN and induced the assembly of a rich FN-ECM through the formation of large FNR integrin patches, codistributing with the FN-ECM. We suggest that in EDS skin fibroblasts DEX corrects the defective FN-ECM favouring the sorting and the organization of FN and its α5β1integrin receptor.