Camptothecin regulates microglia polarization and exerts neuroprotective effects via the AKT/Nrf2/HO-1-NF-κB signal axis in vivo and in vitro

Abstract Background Parkinson's disease (PD), the second largest neurodegenerative disease seriously affects human health. Microglia, the main immune cells in the brain participate in the innate immune response in the central nervous system (CNS). Studies have shown that microglia can be polarized into pro-inflammatory M1 and anti-inflammatory M2 phenotypes. Accumulated evidences suggest that over-activated M1 microglia release pro-inflammatory mediators that damage neurons and lead to Parkinson's disease (PD). In contrast, M2 microglia release neuroprotective factors and exert the effects of neuroprotection. Camptothecin (CPT), an extract of the plant Camptotheca acuminate, has been reported to have anti-inflammation and antitumor effects. However the effect of CPT on microglia polarization and microglia-mediated inflammation responses has not been reported. Therefore, we aim to explore the effect of CPT on microglia polarization and its underlying mechanism on neuroinflammation. Methods C57BL/6 mice (25–30 g) were injected LPS or PBS into the substantia nigra (SN). Open-Field Test and Immunohistochemistry were performed to test the dyskinesia of mice and the loss of neurons in the substantia nigra (SN). Microglia cell line BV-2, the neuroblastoma SH-SY5Y and dopaminergic neuron MN9D cell were cultured. Cytotoxicity assay, reverse transcription quantitative real-time polymerase chain reaction (RT-PCR), Western blot, ELISA and Immunofluorescence staining were performed. All results were presented with mean ± SD. Results In vivo, CPT improved dyskinesia of mice, reduced the loss of neurons in the substantia nigra (SN) and inhibited neuro-inflammatory responses in LPS-injected mice. In vitro, CPT inhibited M1 polarization of microglia and promotes M2 polarization via the AKT/Nrf2/HO-1-NF-κB signal axis. Furthermore, CPT protected the neuroblastoma cell line SH-SY5Y and dopaminergic neuron cell line MN9D from neurotoxicity of mediated by microglia activation. Conclusion CPT regulates the microglia polarization phenotype via the AKT/Nrf2/HO-1-NF-κB signal axis, inhibits neuro-inflammatory responses and exerts neuroprotective effects in vivo and in vitro.