PKCα integrates spatiotemporally distinct Ca2+ and autocrine BDNF signaling to facilitate synaptic plasticity

Abstract

The protein kinase C (PKC) enzymes have long been established as critical for synaptic plasticity. However, it is unknown whether Ca-dependent PKC isozymes are activated in dendritic spines during plasticity and, if so, how this synaptic activity is encoded by PKC. Here, using newly developed, isozyme-specific sensors, we demonstrate that classical isozymes are activated to varying degrees and with distinct kinetics. PKCα is activated robustly and rapidly in stimulated spines and is the only isozyme required for structural plasticity. This specificity depends on a PDZ-binding motif present only in PKCα. The activation of PKCα during plasticity requires both NMDA receptor Ca flux and autocrine brain-derived neurotrophic factor (BDNF)-TrkB signaling, two pathways that differ vastly in their spatiotemporal scales of signaling. Our results suggest that, by integrating these signals, PKCα combines a measure of recent, nearby synaptic plasticity with local synaptic input, enabling complex cellular computations such as heterosynaptic facilitation of plasticity necessary for efficient hippocampus-dependent learning.

Rac1 is a downstream effector of PKCα in structural synaptic plasticity

“…The increased activity and spreading of Rac1 promoted by PKCα is consistent with an essential role for PKCα in integrating neurotrophic signals to facilitate plasticity. Moreover, this link between PKCα and Rac1 supports a growing understanding of the molecular mechanisms underlying heterosynaptic facilitation, whereby the induction of plasticity in one spine lowers the threshold of plasticity induction in nearby spines (Colgan et al, 2018;Hedrick et al, 2016).…”

“…Both Rac1 and PKCα activation are downstream of TrkB receptor activation in the stimulated spine (Colgan et al, 2018;Hedrick et al, 2016) (Fig. 3d).…”

“…This demonstrates that Rac1 but not Ras or Cdc42 is downstream of PKCα during sLTP. We next investigated whether the PDZ binding domain of PKCα, which was shown to be critical for its isozyme-specific signaling in spine plasticity (Colgan et al, 2018), was required for downstream regulation of Rac1 (Fig. 3a).…”

“…Plasmids: All the plasmids used were previously developed and described in publication and are available on Addgene (Colgan et al, 2018;Hedrick et al, 2016;Oliveira and Yasuda, 2013).…”

“…A second Ti-sapphire laser tuned at a wavelength of 720 nm was used to uncage 4-methoxy-7-nitroindolinyl-caged-l-glutamate (MNI-caged glutamate) in extracellular solution with a train of 4-8 ms, 2.8-3.0 mW pulses (30 times at 0.5 Hz) in a small region ~0.5 µm from the spine of interest as previously described (Colgan et al, 2018).…”