Mechanism of Neuroprotective Mitochondrial Remodeling by PKA/AKAP1
Figure 10
PKA phosphorylation and T55D mutation prolong the lifetime of mitochondrial Drp1 foci.
(A, B) HeLa cells transfected with GFP-Drp1 (green), dsRed2/mito (COX8 matrix targeting sequence, red), ± PKA catalytic subunit were imaged for ≥1 h at 37°C, capturing images every 30 s. (A) Representative frames of time lapse series (see Video S3). Blue lines connect GFP-Drp1 punctae that could be tracked for at least 5 min; x symbols denote mitochondrial fission events. Note that GFP-Drp1 punctae often split with the fragmenting mitochondrion. (B) Cumulative frequency plot of Drp1 punctae lifetimes and average lifetimes (bar graph inset; means ± s.e.m. of 35–62 cells and 11,000 to 40,000 punctae per condition from two independent experiments). (C) Model of mitochondrial fusion by PKA/AKAP1. GTP-bound Drp1 translocates to mitochondria to assemble into oligomeric complexes. Drp1 assembly stimulates GTP hydrolysis, leading to mitochondrial fission and release of Drp1 into the cytosol to complete the cycle. OMM-anchored PKA/AKAP1 phosphorylates Drp1 at SerPKA, stabilizing the GTP-bound state to promote growth of Drp1 complexes to a size that is incompatible with membrane scission. Protein phosphatases (PP), including calcineurin, dephosphorylate Drp1 SerPKA to return Drp1 into its active, rapidly cycling state.