The interrelationships between neuronal viability, synaptic integrity, microglial responses, and amyloid-beta...

The interrelationships between neuronal viability, synaptic integrity, and microglial responses remain in infancy. In dealing with the question, we induced a stretch injury to evaluate the mechanical effects of trauma on rat primary cortical neurons and BV2 microglial cells in a transwell culture system. The viability of primary neurons and BV2 cells was determined by MTT. Synaptic integrity was evaluated by determining the expression of beta-secretase 1 (BACE1), amyloid-beta (Aβ), microtubule-associated protein 2 (MAP2), and synaptophysin (vehicle protein). Both CD16/32-positive (CD16/32⁺) and CD206-positive (CD206⁺) microglia cells were detected by immunofluorescence staining. The phagocytic ability of the BV2 cells was determined using pHrodo E. coli BioParticles conjugates and flow cytometry. We found that stretch injury BV2 cells caused reduced viability and synaptic abnormalities characterized by Aβ accumulation and reductions of BACE1, MAP2, and synaptophysin in primary neurons. Intact BV2 cells exhibited normal phagocytic ability and were predominantly CD206⁺ microglia cells, whereas the injured BV2 cells exhibited reduced phagocytic ability and were predominantly CD16/32⁺ microglial cells. Like a stretch injury, the injured BV2 cells can cause both reduced viability and synaptic abnormalities in primary neurons; intact BV2 cells, when cocultured with primary neurons, can protect against the stretch-injured-induced reduced viability and synaptic abnormalities in primary neurons. We conclude that CD206⁺ and CD16/32⁺ BV-2 cells can produce neuroprotective and cytotoxic effects on primary cortical neurons.