Oxidative stress-induced attenuation of thrombospondin-1 expression in primary rat Astrocytes

Astrocytes, the major glial population in the central nervous system (CNS), can secrete thrombospondin (TSP)-1 that plays the role in synaptogenesis and axonal sprouting during CNS development and tissue repair. However, little is known about the regulation of TSP-1 expression in astrocytes under oxidative stress condition. Here, a hypoxic mimetic reagent, cobalt chloride (CoCl ₂), was used to initiate hypoxia-induced oxidative stress in primary rat astrocytes. CoCl₂ at the concentration range of 0.1-0.5mM was found to cause no significant cell death in primary rat astrocytes. However, CoCl₂ at 0.2-0.5mM increased intracellular reactive oxygen species (ROS) levels and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene expression that is known as a hallmark for oxidative damage. We further found that TSP-1 mRNA expression in astrocytes was inhibited dose- and time-dependently by CoCl₂. TSP-1 mRNA levels were increased in CoCl₂- exposed astrocytes in the presence of the inhibitors (U0126 and PD98059) of mitogen-activated protein kinase/extracellular signal-regulated kinases (MAPK/ERK), when compared to that detected in the culture only exposed to CoCl₂. Moreover, the inhibition in TSP-1 mRNA expression by CoCl₂ was blocked by the addition of the potent antioxidant, N-acetylcysteine (NAC). Thus, we conclude that CoCl₂ inhibits TSP-1 mRNA expression in astrocytes via a ROS mechanism possibly involving MAPK/ERK. This inhibition may occur after CNS injury and impair the supportive function of astrocytes on neurite growth in the injured CNS tissues.