PKA/AKAP1 and PP2A/Bβ2 Regulate Neuronal Morphogenesis via Drp1 Phosphorylation and Mitochondrial Bioenergetics

Abstract

Mitochondrial shape is determined by fission and fusion reactions, perturbation of which can contribute to neuronal injury and disease. Mitochondrial fission is catalyzed by dynamin-related protein 1 (Drp1), a large GTPase of the dynamin family that is highly expressed in neurons and regulated by various posttranslational modifications, including phosphorylation. We report here that reversible phosphorylation of Drp1 at a conserved Ser residue by an outer mitochondrial kinase (PKA/AKAP1) and phosphatase (PP2A/Bβ2) impacts dendrite and synapse development in cultured rat hippocampal neurons. PKA/AKAP1-mediated phosphorylation of Drp1 at Ser656 increased mitochondrial length and dendrite occupancy, enhancing dendritic outgrowth but paradoxically decreasing synapse number and density. Opposing PKA/AKAP1, PP2A/Bβ2-mediated dephosphorylation of Drp1 at Ser656 fragmented and depolarized mitochondria and depleted them from dendrites, stunting dendritic outgrowth but augmenting synapse formation. Raising and lowering intracellular calcium reproduced the effects of dephospho-Drp1 and phospho-Drp1on dendrite and synapse development, respectively, while boosting mitochondrial membrane potential with l-carnitine-fostered dendrite at the expense of synapse formation without altering mitochondrial size or distribution. Thus, outer mitochondrial PKA and PP2A regulate neuronal development by inhibiting and promoting mitochondrial division, respectively. We propose that the bioenergetic state of mitochondria, rather than their localization or shape per se, is the key effector of Drp1, altering calcium homeostasis to modulate neuronal morphology and connectivity.

Death-associated Protein 3 Regulates Mitochondrial-encoded Protein Synthesis and Mitochondrial Dynamics

“…1), consistent with the report that DAP3 is a component of the mitochondrial ribosomal small subunit (31). In addition, we show that knockdown of DAP3 leads to mitochondrial protein synthesis defects and mitochondrial dissipation, which may alter the antagonistic activities of PKA and calcineurin on mitochondria (41,43), resulting in the dephosphorylation of Drp1 at Ser-637 and mitochondrial fragmentation. It has been reported that ectopic overexpression of DAP3 caused mitochondrial fragmentation (33).…”

Mitochondrial dynamics in neuronal injury, development and plasticity

“…Also, Drp1-dependent mitochondrial fission is necessary for dendritic localization of mitochondria (Fig. 5), as well as spine formation and synaptogenesis in hippocampal cultures (Li et al, 2004;Dickey and Strack, 2011). Ca 2+ uptake by postsynaptic mitochondria has been shown to be necessary for long-term potentiation (LTP) of nociceptive inputs to the spinal cord (Fig.…”

“…Given the importance of processes, such as ATP production, Ca 2+ transients, neurotransmitter metabolism and ROS signaling, in synaptic transmission it is not surprising that recent work has illustrated that perturbations in mitochondrial physiology exert profound effects on neuronal development and function. Mitochondrial ATP production, Ca 2+ buffering, neurotransmitter metabolism and ROS signaling themselves are spatially and temporally regulated in neurons through mitochondrial localization (Brodin et al, 1999;Jayashankar and Rafelski, 2014;Li et al, 2004;Niescier et al, 2013;Rueda et al, 2014;Sheng, 2014;Vos et al, 2010), mitochondrial bioenergetics (Rueda et al, 2014;Dickey and Strack, 2011), and mitochondrial biogenesis (Cheng et al, 2012), all of which are strongly influenced by mitochondrial dynamics, which entails mitochondrial fission, fusion and transport.…”

“…Furthermore, the importance of mitochondrial dynamics has been documented in neuronal development (Li et al, 2004;Dickey and Strack, 2011;Chan, 2006;Ishihara et al, 2009) and survival Merrill et al, 2013;Dagda et al, 2008;Merrill et al, 2011;Cho et al, 2010;Nakamura et al, 2010). However, also there, the specific mechanisms often await elucidation.…”

A Calcineurin Docking Motif (LXVP) in Dynamin-related Protein 1 Contributes to Mitochondrial Fragmentation and Ischemic Neuronal Injury

“…Mitochondrial shape influences rates of respiration (1)(2)(3)(4), calcium homeostasis (5-7), and transport of the organelle especially in highly polarized cells such as neurons (8). In addition, mitochondrial fission contributes to efficient cellular execution by apoptosis (9).…”