CNTNAP4 knockdown increases α-synuclein expression in MN9D cells. (A) Effects of different concentrations of MPP+ on CNTNAP4, TH, DAT, and α-synuclein expression levels in MN9D cells were determined by Western blotting. (B and C) The interference or overexpression efficiency of transfected CNTNAP4 siRNAs or plasmids in MN9D cells were confirmed by Western blotting. (D and E) Effects of CNTNAP4 siRNA or plasmid transfection on TH, DAT, and α-synuclein expression levels in MN9D cells were determined by Western blotting. (F) Immunocytochemical staining of α-synuclein upon CNTNAP4 knockdown in MN9D cells. Magnified CNTNAP4 and α-synuclein staining are shown in the right-hand column, which are expansions of the boxed areas in the merged column (scale bars, 20 µm; n = 3 per group). Results are expressed as the mean ± SEM. **p < 0.01, *p < 0.05 vs. control group. Statistical significance was determined by one-way ANOVAs for A, B and D, and Student's t-tests for C and E.