Expression of cathepsin G-like and alpha 1-antichymotrypsin-like proteins in reactive astrocytes

Abstract

The central nervous system (CNS) of many different species responds to diverse neurologic injuries with an activation of astrocytes. Yet, the exact function of this reactive astrocytosis is unknown. In this report, mouse astrocytes were activated in vivo by focal penetrating brain injury. Reactive astrocytes were stained with antibodies raised against the serine protease cathepsin G (cat.G), the serine protease inhibitor alpha 1-antichymotrypsin (ACT), or the astrocytic marker glial fibrillary acidic protein (GFAP). Reactive astrocytes expressing both cat.G-like and ACT-like antigens were found around cerebral wound margins between 18 h and 13 days after neural lesions. The injury-induced immunostaining was unaltered by 900 rads of total body irradiation, suggesting that the astroglial reaction was relatively independent of bone marrow-derived cells. The in vivo immunostaining was complemented with biochemical assays on cultured primary astrocytes. A synthetic peptide was used as a substrate in combination with specific inhibitors to identify a proteolytic activity within astroglial lysates and culture supernatants that closely resembles cat.G. This activity increased substantially upon stimulation of astrocytes with dibutyryl cyclic AMP and was neutralized by antibodies raised against cat.G. In a separate report, it was shown that astrocytes also contain an ACT-like inhibitory activity. The production of ACT- and cat.G-like antigens and activities by activated astrocytes should allow these cells to participate in a number of important biologic processes. Many of these processes may benefit the CNS by assisting in early wound repair. However, astroglial proteases and their inhibitors could also contribute to the pathogenesis of certain neurologic diseases.