TGF-β1 reduces the heterogeneity of astrocytic cyclooxygenase-2 and nitric oxide synthase-2 gene expression in a stimulus-independent manner

Transforming growth factor-β1 (TGF-β1) is upregulated by inflammatory mediators in several neurological diseases/disorders where it either participates in the pathology or provides protection. Often, the biological outcome of TGF-β1 is dependent upon changes in gene expression. Recently, we demonstrated that TGF-β1 enhances astrocytic nitric oxide production induced by lipopolysaccharide (LPS) plus interferon-γ (IFNγ) by increasing the number of astrocytes in a population that express NOS-2. The purpose of this study was twofold: (1) to determine whether this effect occurs more generally by assessing the effect of TGF-β1 on another pro-inflammatory gene, cyclooxygenase-2 (COX-2); and (2) to assess stimulus specificity. We found that TGF-β1 augmented LPS plus IFNγ-induced COX-2 mRNA and protein expression, by nearly tripling the number of astrocytes that express COX-2. The effect was not stimulus-specific as TGF-β1 enhanced the number of astrocytes that expressed both COX-2 and NOS-2 protein when either IL-1β or TNFα was used in lieu of LPS. Collectively, these results suggest that TGF-β1 augments overall protein expression levels of select pro-inflammatory genes in astrocytes in a promiscuous manner by reducing the magnitude of noise in the cellular population.