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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 evidence suggests 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. In our study we found that CPT improved motor performance of mice and reduced the loss of neurons in the substantia nigra (SN) of the midbrain in LPS-injected mice. In the mechanism study, we found that CPT inhibited M1 polarization of microglia and promotes M2 polarization via the AKT/Nrf2/HO-1 and NF-κB signals. Furthermore, CPT protected the neuroblastoma cell line SH-SY5Y and dopaminergic neuron cell line MN9D from damage mediated by microglia activation. In conclusion, our results demonstrate that CPT regulates the microglia polarization phenotype via activating AKT/Nrf2/HO-1 and inhibiting NF-κB pathways, inhibits neuro-inflammatory responses, and exerts neuroprotective effects in vivo and in vitro.

Microglia are the brain's immune cells and play an important role in regulating the microenvironment in the central nervous system. Activated microglia are capable of acquiring the pro-inflammatory (M1) phenotype and anti-inflammatory (M2) phenotype. Overactivation of microglia is neurotoxic and may lead to neuroinflammatory brain disorders. Neuroinflammation in the brain plays a crucial role part in the pathophysiology of many psychiatric and neurological diseases. The inhibition of M1 microglia and promotion of M2 microglia was demonstrated to treat and prevent these diseases through reduced neuroinflammation. Isovitexin (IVX) has anti-inflammatory properties and passes through the blood-brain barrier; however, the molecular mechanism that modulates IVX-mediated microglial polarization remains unclear. In BV-2 cells and mouse primary microglia, IVX suppressed the expression of M1 microglial markers, enhanced the expression of M2 microglial markers, and enhanced the release of interleukin 10 (IL-10). IVX promoted the expression of peroxisome proliferator-activated receptor-γ (PPARγ) and PPARγ coactivator-1α (PGC-1α) in LPS-induced microglial activation. The inhibition of PPARγ and PGC-1α attenuated the regulatory effect of IVX in LPS-induced microglial polarization. IVX increased the expression of p-CaMKKβ, p-AMPK, and PGC-1α in BV-2 cells. Inhibition of CaMKKβ with STO-609 or knockdown of CaMKKβ with CaMKKβ siRNA attenuated IVX-mediated M2 microglial polarization in LPS-treated cells. In LPS-treated mice, the inhibition of CaMKKβ and PGC-1α attenuated the IVX-mediated prevention of sickness behavior and enhanction of IVX-mediated M2 microglial polarization. IVX promoted M2 microglial polarization which exerted anti-inflammatory effects on LPS-induced neuroinflammation via the activation of the CaMKKβ/AMPK-PGC-1α signaling axis.

Parkinson's disease (PD) is a common neurodegenerative disease characterized by selective loss of dopaminergic neurons in the substantia nigra (SN). Neuroinflammation induced by over-activation of microglia leads to the death of dopaminergic neurons in the pathogenesis of PD. Therefore, downregulation of microglial activation may aid in the treatment of PD. Polydatin (PLD) has been reported to pass through the blood-brain barrier and protect against motor degeneration in the SN. However, the molecular mechanisms underlying the effects of PLD in the treatment of PD remain unclear. The present study aimed to determine whether PLD protects against dopaminergic neurodegeneration by inhibiting the activation of microglia in a rat model of lipopolysaccharide (LPS)-induced PD. Our findings indicated that PLD treatment protected dopaminergic neurons and ameliorated motor dysfunction by inhibiting microglial activation and the release of pro-inflammatory mediators. Furthermore, PLD treatment significantly increased levels of p-AKT, p-GSK-3βSer9, and Nrf2, and suppressed the activation of NF-κB in the SN of rats with LPS-induced PD. To further explore the neuroprotective mechanism of PLD, we investigated the effect of PLD on activated microglial BV-2 cells. Our findings indicated that PLD inhibited the production of pro-inflammatory mediators and the activation of NF-κB pathways in LPS-induced BV-2 cells. Moreover, our results indicated that PLD enhanced levels of p-AKT, p-GSK-3βSer9, and Nrf2 in BV-2 cells. After BV-2 cells were pretreated with MK2206 (an inhibitor of AKT), NP-12 (an inhibitor of GSK-3β), or Brusatol (BT; an inhibitor of Nrf2), treatment with PLD suppressed the activation of NF-κB signaling pathways and the release of pro-inflammatory mediators in activated BV-2 cells via activation of the AKT/GSK3β-Nrf2 signaling axis. Taken together, our results are the first to demonstrate that PLD prevents dopaminergic neurodegeneration due to microglial activation via regulation of the AKT/GSK3β-Nrf2/NF-κB signaling axis.

The intestinal epithelial barrier is important to mucosal immunity, although how it is maintained after damage is unclear. Here, we show that G protein-coupled receptor 109A (GPR109A) supports barrier integrity and decreases mortality in a mouse cecum ligation and puncture (CLP) sepsis model. Data from 16S RNA sequencing showed that the intestinal microbiota of WT and Gpr109a−/− mice clustered differently and their compositions were disrupted after CLP surgery. GPR109A-deficient mice showed increased mortality, intestinal permeability, altered inflammation, and lower tight junction gene expression. After eliminating the intestinal flora with antibiotics, all experimental mice died within 48 h of CLP surgery. This demonstrates the critical role of the gut microbiota in CLP-induced sepsis. Importantly, mortality and other pathologies in the model were decreased after Gpr109a−/− mice received WT gut microbiota. These findings indicate that GPR109A regulates the gut microbiota, contributing to intestinal epithelial barrier integrity and decreased mortality in CLP-induced sepsis.