The Role of Intracellular Ca²⁺ and Mitochondrial ROS in Small A_1-42 Oligomer-Induced Microglial Death

Alzheimer's disease (AD) is the most common form of dementia worldwide, and it contributes up to 70% of cases. AD pathology involves abnormal amyloid beta (A beta) accumulation, and the link between the A beta(1-42) structure and toxicity is of major interest. NMDA receptors (NMDAR) are thought to be essential in A beta-affected neurons, but the role of this receptor in glial impairment is still unclear. In addition, there is insufficient knowledge about the role of A beta species regarding mitochondrial redox states in neurons and glial cells, which may be critical in developing A beta-caused neurotoxicity. In this study, we investigated whether different A beta(1-42) species-small oligomers, large oligomers, insoluble fibrils, and monomers-were capable of producing neurotoxic effects via microglial NMDAR activation and changes in mitochondrial redox states in primary rat brain cell cultures. Small A beta(1-42) oligomers induced a concentration- and time-dependent increase in intracellular Ca2+ and necrotic microglial death. These changes were partially prevented by the NMDAR inhibitors MK801, memantine, and D-2-amino-5-phosphopentanoic acid (DAP5). Neither microglial intracellular Ca2+ nor viability was significantly affected by larger A beta(1-42) species or monomers. In addition, the small A beta(1-42) oligomers caused mitochondrial reactive oxygen species (mtROS)-mediated mitochondrial depolarization, glutamate release, and neuronal cell death. In microglia, the A beta(1-42)-induced mtROS overproduction was mediated by intracellular calcium ions and A beta-binding alcohol dehydrogenase (ABAD). The data suggest that the pharmacological targeting of microglial NMDAR and mtROS may be a promising strategy for AD therapy.