Activation of CysLT receptors induces astrocyte proliferation and death after oxygen-glucose deprivation

We recently found that 5-lipoxygenase (5-LOX) is activated to produce cysteinyl leukotrienes (CysLTs), and CysLTs may cause neuronal injury and astrocytosis through activation of CysLT(1) and CysLT(2) receptors in the brain after focal cerebral ischemia. However, the property of astrocyte responses to in vitro ischemic injury is not clear; whether 5-LOX, CysLTs, and their receptors are also involved in the responses of ischemic astrocytes remains unknown. In the present study, we performed oxygen-glucose deprivation (OGD) followed by recovery to induce ischemic-like injury in the cultured rat astrocytes. We found that 1-h OGD did not injure astrocytes (sub-lethal OGD) but induced astrocyte proliferation 48 and 72 h after recovery; whereas 4-h OGD moderately injured the cells (moderate OGD) and led to death 24-72 h after recovery. Inhibition of phospholipase A(2) and 5-LOX attenuated both the proliferation and death. Sub-lethal and moderate OGD enhanced the production of CysLTs that was inhibited by 5-LOX inhibitors. Sub-lethal OGD increased the expressions of CysLT1 receptor mRNA and protein, while moderate OGD induced the expression of CysLT2 receptor mRNA. Exogenously applied leukotriene D-4 (LTD4) induced astrocyte proliferation at 1-10 nM and astrocyte death at 100-1,000 nM. The CysLT1 receptor antagonist montelukast attenuated astrocyte proliferation, the CysLT2 receptor antagonist BAY cysLT2 reversed astrocyte death, and the dual CysLT receptor antagonist BAY u9773 exhibited both effects. In addition, LTD4 (100 nM) increased the expression of CysLT2 receptor mRNA. Thus, in vitro ischemia activates astrocyte 5-LOX to produce CysLTs, and CysLTs result in CysLT1 receptor-mediated proliferation and CysLT2 receptor-mediated death. (c) 2007 Wiley-Liss, Inc.