ATP13A2 inhibits αsyn multimerization via regulating the ubiquitin-proteasome system (UPS). (a) Visualization of ubiquitin levels in cell lysates from ATP13A2 KD, fLuc, ATP13A2 WT, and ATP13A2 DN cells without and with oxidative stress treatment. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) levels were used as standard. (b) Quantification of polyubiquitin levels relative to glyceraldehyde 3-phosphate dehydrogenase (GAPDH) (n = 4). Statistical analysis was performed using a one-way ANOVA test with Bonferroni. The error bars represent the SEM. ** p < 0.01, ns, not significant. (c) Visualization of αsyn multimers after cross-linking in fLuc and ATP13A2 WT cells under oxidative stress without and with 1 µM MG132. (d) Quantification of αsyn multimer-to-monomer ratio (n = 4). Statistical analysis was performed with column statistics (one-sample t-test) comparing test values to the hypothetical value of 1. * p < 0.05, ns, not significant.