Age-Dependent Cytokine Responses: Trimethyltin Hippocampal Injury in Wild-Type, APOE Knockout, and APOE4 Mice

Abstract

In this study, the hippocampal neurotoxicant trimethyltin (TMT) was used to examine possible differential susceptibility associated with the apolipoprotein E genotype. Mice—wild type (C57BL6J), APOE knockout, and APOE4 transgenic—received either saline or TMT (2 mg/kg, ip) at either 21 days or 8 months of age. At both ages, similar mRNA levels were seen in the hippocampus across genotypes for ICAM-1, A20, and MAC-1. GFAP mRNA was higher in the APOE knockouts and APOE4 as compared to wild-type mice. Within 24 h, TMT produced cell death of hippocampal dentate granule neurons and mild astrogliosis in all animals. In 21-day-old mice, TMT exposure significantly increased mRNA levels for ICAM-1 and MIP-1α in all genotypes. EB-22, GFAP, TNFα, and TGF-β1 levels were significantly elevated in both wild-type and APOE knockout mice following TMT. At 8 months of age, genotype specific differences were observed. mRNA levels for GFAP, TNFβ, TNFα, and MIP-1α were increased in both APOE knockout and APOE4 mice compared to wild-type mice. TMT exposure significantly increased mRNA levels for GFAP and MIP-1α in all animals. TNFα mRNA levels were increased in wild-type and APOE4 mice while EB22 mRNA levels were increased in both the APOE knockout and APOE4 mice but not wild-type mice. These data suggest an age-dependent effect on both microglia early inflammatory responses to injury associated with the APOE genotype.