(A) Lentiviruses carrying eGFP-AP2M1 WT or T156A (TA) were transduced into LRRK2 WT, KO or GSKI hippocampal neurons, and Tfn internalization was monitored. (B) Lentiviruses carrying eGFP-AP2M1 WT or T156A (TA) were transduced into LRRK2 GSKI hippocampal neurons pretreated with 0.1 μM MLi-2 for 2 hours, and Tfn internalization was monitored. Scale bars, 30 μm. (C and D) Quantification of Tfn internalization at the cell bodies (indicated in white boxes) represented and described in panels (A) and (B), respectively. Data are means ± SEM from three independent experiments, with the means from the n ≥ 15 cells (C) and n ≥ 40 cells (D) quantified in each experiment (data file S1) indicated by the triangles. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001 by Student’s t tests for two comparisons or one-way ANOVA followed by a Tukey’s post hoc test.