Transforming growth factor-beta 1 (TGF-beta 1) expression and regulation in rat cortical astrocytes.

Transforming growth factor-beta 1 (TGF-beta 1) is a potent modulator of immune and glial cells' functions and thus, could play an important role in neuro-immune interaction. However, published reports disagree on whether or not TGF-beta 1 is expressed in normal brain. We demonstrate here the constitutive expression of TGF-beta 1 mRNA but not protein in both cerebral cortex and primary rat cortical astrocytes. Steady-state TGF-beta 1 mRNA level increased 2-fold in adult compared to neonatal cortex and during proliferation and differentiation of astrocytes in primary culture. This response was not accompanied by the appearance of detectable TGF-beta protein either in vivo or in vitro. However, both intracellular immunoreactive TGF-beta and extracellular TGF-beta 1 activity were detected upon in vitro stimulation of astrocytes with interleukin-1 (IL-1). The extracellular TGF-beta 1 increased with time of exposure to and concentration of IL-1. In contrast, the amount of TGF-beta 1 mRNA remained unchanged during stimulation of astrocytes with IL-1. These results suggest that the production of TGF-beta 1 in astrocytes is regulated at both mRNA and protein levels. The former may occur during astrocytic development, and the latter during astrocytic response to injury in association with elevation of IL-1.