Scutellaria Barbata Flavonoids Mitigate Alzheimer's Disease-related Aβ25-35 Toxicity in N2a Cells through CREB Phosphorylation.

Abstract

Background: Mouse neuroblastoma cells (N2a) are spontaneously derived from mice and possess the characteristics of neural stem cells. The proliferation, differentiation, and protrusion growth of N2a cells in vitro are consistent with those in vivo. Flavonoids isolated from the aerial parts of Scutellaria barbata (SBFs) can improve learning and memory deficits and protect against neuronal injury in many in vivo AD-- like models. N2a cells exposed to Aβ25-35 for Alzheimer's disease-related toxicity were subsequently used to observe the ameliorative effects of SBFs, and the effective mechanism through which SBFs promote the phosphorylation of CREB was further studied by using BI-D1870, an indirect inhibitor, and Rolipram, an activator of CREB phosphorylation.

Methods: Immunofluorescence (IF) was used to detect the protein expression of the neuron-specific proteins NeuN, NeuroD1, and DCX. N2a cells were exposed to 100 μM Aβ25-35 and treated with SBFs at doses of 17.5, 35 and 75 mg·L-1 or 363 μM Rolipram. Cell morphology was observed under an inverted microscope, the cell survival rate was detected by the Cell Counting Kit-8 (CCK-8) method, and the release of lactate dehydrogenase (LDH) into the cell culture medium was determined by the pyruvate reduction method. The mRNA expression levels of ERK, RSK, CREB, and EGR-1 in cells were detected by real-time quantitative polymerase chain reaction (qPCR). IF and/or western blotting (WB) were used to measure the protein expression levels of BDNF, NGF, TrkB, Ras, ERK/p-ERK, Rsk/p90RSK, CREB/p-CREB-Ser133, and EGR-1 in N2a cells.

Results: NeuN, NeuroD1, and DCX expression in N2a cells was positive, as indicated by green fluorescence. Both Aβ25-35 and BI-D1870 resulted in abnormal morphological changes in N2a cells, reduced the cell survival rate (P<0.01), increased the release of LDH (P<0.01) into the culture medium, and decreased the mRNA expression levels of ERK, RSK, and CREB and the protein expression levels of p-ERK, TrkB, p90RSK, pCreb-SER133, BDNF, NGF and EGR-1 (P<0.01) in cells. However, SBFs, to varying degrees, reversed the aforementioned abnormal changes in N2a cells caused by Aβ25-35 or BI-D1870, and the effects of SBFs were consistent with those of Rolipram.

Conclusion: SBFs protected against N2a cell damage induced by toxic Aβ25-35, and the effective mechanism by which SBFs promote the phosphorylation of CREB at the Ser133 site was confirmed through the application of the indirect CREB phosphorylation inhibitor BI-D1870 and the activator Rolipram. These findings suggest that SBFs may be helpful in the treatment of AD by intervening in CREB phosphorylation.