Miro proteins prime mitochondria for Parkin translocation and mitophagy (2018)
Figure 2

FIGURE 2. Miro1 recruits Parkin to polarized mitochondria

A. The pattern of Parkin translocation caused by Miro1 overexpression is different from A&O-induced translocation. The figure illustrates puncta-like EYFP-Parkin on mitochondria in antimycin and oligomycin-treated (both 10 µM for 3h) PC6 cells (middle panels), whereas in Miro1-overexpressing cells, EYFP-Parkin appears along rod-shaped mitochondria visualised with CFP-mito (lower panels). The merged panels present EYFP-Parkin (green) and CFP-mito (red).

B. Overexpression of myc-Miro1 and untagged Miro2, but not myc-Miro2, induce EYFP-Parkin translocation to mitochondria. ****P < 0.0001 vs control group, n = 5-6 dishes, 20 fields per dish, one-way ANOVA or t-test.

C. Quantification of EYFP-Parkin signal heterogeneity in PC6 cells demonstrates that Miro1 overexpression induces Parkin translocation from the cytosol to mitochondria, which is significantly weaker than PINK1 overexpression- or A&O (3 h)-induced translocation. **P < 0.01 and ****P < 0.0001 vs control group, n = 18-32 cells from 3 dishes per group, Kruskal-Wallis test.

D, E Miro1 overexpression does not cause mitochondrial depolarization. (D) Representative image of Miro1 and EYFP-Parkin-transfected cells stained with TMRE. The merged panels present EYFP-Parkin (green) and TMRE (red).

(E) Relative TMRE intensity quantified in neurons transfected with Miro1 (detected by CFP-mito co-transfection); the control group is non-transfected cells in the same image. The relative TMRE signal was slightly increased in Miro1 overexpressing neurons but unaffected in Miro shRNAs-expressing neurons. Note that FCCP treatment (3 μM for 15 min) almost completely abolished TMRE fluorescence. ****P < 0.0001 vs control group, n = 94-186 cells from 4 dishes per group, Kruskal-Wallis test.

F. Co-expression of HA-Parkin with Miro1 does not suppress mitochondrial motility in axons of cortical neurons. Overexpression of Miro1 alone increased the motion time in both directions as well as the relative mitochondrial velocity. Co-transfection of Parkin did not affect significantly the motility parameters. Data are presented as Tukey boxplot. *P < 0.05, **P < 0.01, ***P < 0.001 and ****P < 0.0001, n = 689-846 individual mitochondria from 39-44 axons per group pooled from at least from 10 individual dishes from 4 independent experiments, Kruskal-Wallis test.

G. Parkin overexpression does not induce degradation of myc-Miro1 in control conditions. Representative Western blot image and analysis of myc-Miro1 expression in HEK cells. Treatment with A&O (both 15 µM) for 3h in the absence of MG132 led to slight degradation of myc-Miro1. Co-expression of EYFP-Parkin did not induce degradation of Miro1 although an additional band above the Miro1 band was present. However, Parkin co-expression enhanced Miro1 degradation when cells were treated with A&O. *P < 0.05 and ****P < 0.0001, ns: not significant, n = 4 independent experiments, one way ANOVA. Note that only the main band of myc-Miro1 at 80 kDa was analysed and that YFP was used to compensate in groups not expressing EYFP-Parkin.

H. EYFP-Parkin co-immunoprecipitates with overexpressed myc-Miro1, both in DMSO- or A&O (both 15 µM for 3h) treated HEK cells.

I. Endogenous Parkin co-immunoprecipitates with endogenous Miro1. Miro1 was immunoprecipitated from non-transfected and non-treated HEK cells using mouse monoclonal anti-Miro1 antibody and immunoblotted for endogenous Parkin.

Data information: Data are presented as means ± SEM.