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 (CoCl₂), was used to initiate hypoxia‐induced oxidative stress in primary rat astrocytes. CoCl₂ at the concentration range of 0.1–0.5 mM was found to cause no significant cell death in primary rat astrocytes. However, CoCl₂ at 0.2–0.5 mM 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. J. Cell. Biochem. 112: 59–70, 2011. © 2010 Wiley‐Liss, Inc.