TFP5 prevents 1-methyl-4-phenyl pyridine ion-induced neurotoxicity in mouse cortical neurons

The present study aimed to investigate the protective effect of a modified p5 peptide, TFP5, on 1-methyl-4-phenyl pyridine ion (MPP⁺)-induced neurotoxicity in cortical neurons and explore the therapeutic effect of TFP5 on Parkinson's disease (PD). MPP⁺ was applied to a primary culture of mouse cortical neurons to establish the cell model of PD. Neurons were divided into four groups: Control, model (MPP⁺), scrambled peptide (Scb) (Scb + MPP⁺) and TFP5 (TFP5 + MPP⁺) groups. Pretreatment with Scb or TFP5 was applied to the latter two groups, respectively, for 3 h, while phosphate-buffered saline was applied to the control and model groups. MPP⁺ was then applied to all groups, with the exception of the control group, and neurons were cultured for an additional 24 h. Neuron viability was evaluated using a Cell Counting kit-8 (CCK8) assay. To explore the mechanism underlying the protective effects of TFP5, the expression levels of p35, p25 and phosphorylated myocyte enhancer factor 2 (p-MEF2D) were determined by western blotting. Fluorescence microscopy showed that TFP5 was able to pass through cell membranes and distribute around the nucleus. CCK8 assay showed that neuronal apoptosis was dependent on MPP⁺ concentration and exposure time. Cell viability decreased significantly in the model group compared with the control group (55±7 vs. 100±0%; P<0.01), and increased significantly in the TFP5 group compared with the model group (98±2 vs. 55±5%; P<0.01) and Scb group (98±2 vs. 54±4%; P<0.01). Scb exhibited no protective effect. Western blotting results showed that MPP⁺ induced p25 and p-MEF2D expression, TFP5 and Scb did not affect MPP⁺-induced p25 expression, but TFP5 reduced MPP⁺-induced p-MEF2D expression. In summary, TFP5 protects against MPP⁺-induced neurotoxicity in mouse cortical neurons, possibly through inhibiting the MPP⁺-induced formation and elevated kinase activity of a cyclin-dependent kinase 5/p25 complex.