Neuronal apolipoprotein E is not synthesized in neuron after focal ischemia in rat brain

Apolipoprotein E (ApoE) is a major apolipoprotein in the central nervous system (CNS) that plays an important role in Alzheimer's disease. It may also be involved in other CNS disorders including ischemic injury. We investigated the changes of ApoE protein and mRNA expression in the brain with middle cerebral artery occlusion (MCAO) to clarify its origin after focal ischemia in rats. Increased ApoE immunoreactivity was recognized in astrocytes 3-14 days after MCAO in the affected side of cortex, and in neurons 4-14 days after MCAO in the same area. ApoE immunoreactivity was also detected in macrophages in the ischemic core 3-14 days after MCAO. In contrast, ApoE mRNA was expressed in astrocytes and macrophages, but not in neurons. These results suggested that neuronal ApoE was not synthesized in neurons, but derived from astrocytes.