CONTRASTING EFFECTS OF INFLAMMATROY CYTOKINES AND GLUCOCORTICOIDS ON THE PRODUCTION OF ACTIVIN A IN HUMAN MARROW STROMAL CELLS AND THEIR IMPLICATIONS

Human marrow stromal cells were analysed with immunocytochemical staining, Northern blot, and functional bioassay for production of activin A. Although Northern blot and immunocytochemical staining did not detect the α subunit of inhibin in human marrow stromal cells, RT-PCR analyses confirmed its presence, along with the expected activin βAPCR products. Present studies showed that human marrow fibroblastoid cells were reactive with anti-activin A antibodies and that the production of βARNA was upregulated by pro-inflammatory cytokines/regulators like interleukin 1α (IL-1α), tumour necrosis factor-α (TNF-α), lipopolysaccharide (LPS) or 12-O-tetradecanoylphorbol 13-acetate (TPA). IL-1α or TNF-α stimulated-marrow stromal cells accumulated βARNA after 2 h of incubation, reaching a peak stimulation at approximately 8 h. Biologically active activin A molecules were detected in the conditioned media by a bioassay, and their activity was specifically inhibited by a blocking antibody or an activin-binding protein, follistatin. Accumulation of bioactive activin A in conditioned medium of human marrow stromal cells increased after incubation with IL-1α or TNF-α. Nuclear run-off assays with TNF-α stimulated marrow stromal cells showed that the enhanced expression of activin A was related to an increase in its rate of transcription. In contrast to the stimulatory effect of pro-inflammatory cytokines, hydrocortisone and dexamethasone at 1×10−7to 1×10−6M inhibited both the constitutive and the cytokine-stimulated expression of activin βARNA, and also the production of bioactive activin A protein. The upregulation of activin A production by cytokines and its suppression by glucocorticoids imply that activin A may also act as a moderator in diverse functions including host defences.