Nitric oxide synthase induction in astroglial cell cultures: Effect on heat shock protein 70 synthesis and oxidant/antioxidant balance

Glial cells in the nervous system can produce nitric oxide in response to c ytokines, This production is mediated by the inducible isoform of nitric ox ide synthase, Radical oxygen species (ROS) and nitric oxide (NO) derivative s have been claimed to play a crucial role in many different processes, bot h physiological such as neuromodulation, synaptic plasticity, response to g lutamate, and pathological such as ischemia and various neurodegenerative d isorders, In the present study we investigated the effects of NO synthase ( iNOS) induction in astrocyte cultures on the synthesis of heat shock protei ns, the activity of respiratory chain complexes and the oxidant/antioxidant balance. Treatment of astrocyte cultures for 18 hr with LPS and INF gamma produced a dose dependent increase of iNOS associated with an increased syn thesis of hsp70 stress proteins, This effect was abolished by the NO syntha se inhibitor L-NMMA and significantly decreased by addition of SOD/CAT in t he medium. Time course experiments showed that iNOS induced protein express ion increased significantly by 2 hr after treatment with LPS and INF gamma and reached a plateau at 18 hr; hsp70 protein synthesis peaked around 18 an d 36 hr after the same treatment, Addition to astrocytes of the NO donor so dium nitroprusside resulted in a dose dependent increase in hsp70 protein t hat was comparable to that found after a mild heat shock. Additionally, a d ecrease in cytochrome oxidase activity, a marked decrease in ATP and protei n sulfhydryl contents, an increase in the activity of the antioxidant enzym es mt-SOD and catalase were found which were abolished by L-NMMA, These fin dings suggest the importance of mitochondrial energy impairment as a critic al determinant of the susceptibility of astrocytes to neurotoxic processes and point to a possible pivotal role of hsp70 in the signalling pathways of stress tolerance. (C) 2000 Wiley-Liss, Inc.