Biology subjects

Sacktor, T. C.

Publications and source records attributed to Sacktor, T. C..

9 recordsLinked to original sources

bioRxiv2026

PKMζ-KIBRA interactions, molecular turnover, and memory

How can the molecules that strengthen synaptic connections maintain memory in the face of molecular turnover? Our previous work showed that persistent interaction between the postsynaptic scaffolding protein, KIBRA, and the autonomously active PKC isoform, PKM{zeta}, is crucial for maintaining synaptic long-term potentiation (LTP) and memory for at least a month. This duration is longer than the lifespans of individual KIBRA and PKM{zeta} molecules. Biophysical modeling of the interaction suggests oligomers of KIBRA-PKM{zeta} dimers, but not individual dimers or monomers, can overcome molecular turnover by continually incorporating newly synthesized KIBRA and PKM{zeta}, replacing those that have degraded. Here we used AlphaFold 3 to predict the structures of KIBRA-PKM{zeta} heterodimers and heterohexamers and to examine the sites of action of two structurally distinct inhibitors of KIBRA-PKM{zeta} interaction that disrupt established late-LTP and long-term memory. The structures predict that the peptide K-ZAP blocks formation of heterodimers, whereas the small molecule {zeta}-stat prevents PKM{zeta} of one heterodimer from binding a second KIBRA and PKM{zeta}, essential for forming larger oligomeric structures. We show that {zeta}-stat, like K-ZAP, disrupts 1-month-old spatial memory. Thus, continual formation of KIBRA-PKM{zeta} oligomers can be a core molecular mechanism driving the persistence of long-term memory in the face of molecular turnover.

neuroscience↗

bioRxiv2025

PKMζ-PKC{iota}/{lambda} double-knockout reveals the atypical PKCs are crucial for hippocampal late-LTP and spatial long-term memory

PKM{zeta}, a persistently active atypical PKC (aPKC) isoform, is thought to maintain late-phase long-term potentiation (late-LTP) and long-term memory. However, PKM{zeta}-knockout mice still exhibit hippocampal LTP and spatial memory while lacking neocortical LTP, questioning whether this kinase is fundamental to enduring synaptic potentiation and memory. Tsokas et al. (2016) showed the other aPKC, PKC{iota}/{lambda}, likely compensates for PKM{zeta} during maintenance in the hippocampus of PKM{zeta}-null mice. In wild-type mice, PKC{iota}/{lambda} drives early-LTP and short-term memory, while PKM{zeta} compensates for PKC{iota}/{lambda} knockout by supporting both early- and late-phase processes. Here we show PKC{iota}/{lambda} persistently increases during maintenance in two mouse models: PKM{zeta}-conditional knockout (cKO) mice, and double-knockout mice carrying both conditional deletion of PKC{iota}/{lambda} and constitutive loss of PKM{zeta}. In the double-knockout mice, PKC{iota}/{lambda} was measured while the kinase was still present, prior to its inducible ablation, to characterize its compensatory upregulation in late-LTP before removal. To test whether this compensation was functional, we ablated PKC{iota}/{lambda} in the hippocampus of the double-knockout mice. The double-knockout eliminated late-LTP, whereas individual knockout of either aPKC alone showed normal-appearing LTP. Double-knockout also abolished spatial long-term memory without affecting short-term memory. Thus, when PKM{zeta} is absent, PKC{iota}/{lambda} persists to maintain hippocampal late-LTP and long-term memory.

neuroscience↗

bioRxiv2025

Persistently increased expression of PKMzeta and unbiased gene expression profiles identify hippocampal molecular traces of a long-term active place avoidance memory and 'shadow' proteins

Long-term memory formation transiently activates Ca2+-calmodulin kinase II and atypical protein kinase C isoform iota/lambda, whereas persistent activation of the other atypical PKC, protein kinase M zeta (PKM{zeta}), together with its interacting partner, the scaffolding-protein KIBRA (Wwc1), are necessary for maintaining potentiated synapses and memory. Here, we use immediate-early gene (IEG) Arc activation during active place avoidance memory expression to tag memory-activated neurons with EYFP-ChR2. PKM{zeta} immunohistochemistry identified which hippocampal synaptic pathways are persistently altered. EYFP-PKM{zeta} colocalization persistently increases in the hippocampal trisynaptic pathway (dentate gyrus [DG][->]CA3[->]CA1) tracing a one-month-old PKM{zeta} engram. DG, CA3, and CA1 transcriptional profiling identifies that memory persistence correlates with upregulated immediate-early-genes Arc, Fos, and NPas4 in DG, but not with PKM{zeta} or most genes known to be crucial for LTP and memory. This rules out strong memory-related transcriptional regulation, but not regulation of mRNA translation or altered stability of "shadow proteins" like PKM{zeta} that, despite being crucial for memory maintenance, evade detection by unbiased transcriptome profiling. In contrast, our method Correlation Signal Co-cluster Reduction (C-SCoRe) incorporates weak linear and non-linear gene correlations and highlights network interaction changes predicting memory, and related IEG and Prkcz/Wwc1 expression. Manifold transcriptional relationships can reveal shadow molecular components of long-term memory.

neuroscience↗

bioRxiv2024

Maintenance of synaptic plasticity by negative-feedback of synaptic protein elimination: Dynamic modeling of KIBRA-PKMζ interactions in LTP and memory

Activity-dependent modifications of synaptic efficacies are a cellular substrate of learning and memory. Current theories propose that the long-term maintenance of synaptic efficacies and memory is accomplished via a positive-feedback loop at the level of production of a protein species or a protein state. Here we propose a qualitatively different theoretical framework based on negative feedback at the level of protein elimination. This theory is motivated by recent experimental findings regarding the binding of PKM{zeta} and KI-BRA, two synaptic proteins involved in maintenance of memory, and on how this binding downregulates the proteins degradation. We demonstrate this theoretical framework with two different models. First, a simple abstract model to explore generic features of the negative-feedback process. Second, a biophysical model based on PKM{zeta}-KIBRA dimers that cooperatively form larger complexes at active synapses. These larger complexes have slower degradation and diffusion, allowing for bistability of potentiated and unpotentiated synaptic states. The results of these models are qualitatively consistent with existing experiments showing reversal of long-term potentiation and erasure of long-term memory by inhibition of KIBRA-PKM{zeta} interactions. The theory generates novel predictions that could be experimentally tested to further validate or reject the negative-feedback theory.

neuroscience↗

bioRxiv2024

Increased protein kinase Mζ expression by Minocycline and N-acetylcysteine restoreslate-phase long-term potentiation and spatial learning after closed head injury in mice

Cognitive deficits frequently arise after traumatic brain injury. The murine closed head injury (CHI) models these deficits since injured mice cannot acquire Barnes maze. Dosing of minocycline plus N-acetylcysteine beginning 12 hours post-CHI (MN12) restores Barnes maze acquisition by an unknown mechanism. Increased hippocampal synaptic efficacy is needed to acquire Barnes maze, synaptic long-term potentiation (LTP) models this increased synaptic efficacy in vitro. LTP has an early phase (E-LTP) lasting up to one hour that is mediated by second messengers that is followed by a late phase (L-LTP) that needs new synthesis of protein kinase M zeta (PKM{zeta}). PKM{zeta} has constitutive kinase activity because it lacks the autoinhibitory regulatory domain found in other PKCs. Due to its constitutive activity, the amount of PKM{zeta} kinase activity is determined by PKM{zeta} protein levels. We report that CHI bilaterally decreases PKM{zeta} levels in the CA3 and CA1 hippocampus. MN12 increases CA1 PKM{zeta} expression. CHI inhibits E-LTP in slices from the ipsilesional hippocampus and inhibits L-LTP in slices from both hippocamppi. MN12 treatment reestablishes both E-LTP and L-LTP in slices from the injured MN12-treated hippocampus. The restoration of L-LTP from injured MN12-treated hippocampus is mediated by PKM{zeta} because L-LTP is blocked by the specific PKM{zeta} inhibitor, {zeta}-stat. Hippocampal {zeta}-stat infusions also prevents Barnes maze acquisition in injured, MN12-treated mice. These data suggest that post-injury minocycline plus N-acetylcysteine targets PKM{zeta} to improve synaptic plasticity and cognition in mice with closed-head injury.

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bioRxiv2024

Amygdala stimulation transforms short-term memory into remote memory by persistent activation of atypical PKC in the anterior cingulate cortex

Although many studies have addressed the role of the amygdala in modulating long-term memory, it is not known whether weak training plus amygdala stimulation can transform a short-term memory into a remote memory. Object place recognition (OPR) memory after strong training remains hippocampus-dependent through the persistent action of PKM{zeta} for at least 6 days, but it is unknown whether weak training plus amygdala stimulation can transform short-term memory into an even longer memory, and whether such memory is stored through more persistent action of PKM{zeta} in hippocampus. We trained rats to acquire OPR and 15 min or 5 h later induced a brief pattern of electrical stimulation in basolateral amygdala (BLA). Our results reveal that a short-term memory lasting < 4 h can be converted into remote memory lasting at least 3 weeks if the BLA is activated 15 min, but not 5 h after learning. To examine how this remote memory is maintained, we injected ZIP, an inhibitor of atypical PKCs (aPKCs), PKM{zeta} and PKC{iota}/{lambda}, into either hippocampal CA1, dentate gyrus (DG), or anterior cingulate cortex (ACC). Our data reveal amygdala stimulation produces consolidation into remote memory, not by persistent aPKC activation and capture by synaptic tagging processes in the hippocampal formation, but in ACC. Our data establish a powerful modulating role of the BLA in forming remote memory and open a path in the search for neurological restoration of memory, based on enhancing synaptic plasticity in aging or neurodegenerative disorders such as Alzheimers disease.

neuroscience↗

bioRxiv2020

PKMζ traces hippocampal LTP maintenance and spatial long-term memory

PKM{zeta} is an autonomously active PKC isoform crucial for the maintenance of synaptic long-term potentiation (LTP) and long-term memory. Unlike other protein kinases that are transiently stimulated by second messengers, PKM{zeta} is persistently activated through sustained increases in kinase protein expression. Therefore, visualizing increases in PKM{zeta} expression during long-term memory storage might reveal the sites of its persistent action and thus the location of memory-associated LTP maintenance in the brain. Using quantitative immunohistochemistry validated by the lack of staining in PKM{zeta}-null mice, we examined the amount and distribution of PKM{zeta} in subregions of the hippocampal formation of wild-type mice during LTP maintenance and spatial long-term memory storage. During LTP maintenance in hippocampal slices, PKM{zeta} increases in the pyramidal cell body and stimulated dendritic layers of CA1 for at least 2 h. During spatial memory storage, PKM{zeta} increases in CA1 pyramidal cells for at least 1 month, paralleling the persistence of the memory. The subset of CA1 pyramidal cells that are tagged by immediate early gene Arc-driven transcription of fluorescent proteins, whose expression increases during initial memory formation, also expresses the persistent increase of PKM{zeta} during memory storage. In the memory-tagged cells, the increased PKM{zeta} expression persists in dendritic compartments within stratum radiatum for 1 month, indicating the long-term storage of information in the CA3-to-CA1 pathway during remote spatial memory. We conclude that persistent increases in PKM{zeta} trace the molecular mechanism of LTP maintenance and thus the sites of information storage within brain circuitry during long-term memory.

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bioRxiv2019

Conditions for synaptic specificity during the maintenance phase of synaptic plasticity

Activity-dependent modifications of synaptic efficacies are a cellular substrate of learning and memory. Experimental evidence shows that these modifications are synapse-specific and that the long-lasting effects are associated with the sustained increase in concentration of specific proteins like PKM{zeta}. However, such proteins are likely to diffuse away from their initial synaptic location and spread out to neighboring synapses, potentially compromising synapse-specificity. In this paper we address the issue of synapse-specificity during memory maintenance. Assuming that the long-term maintenance of synaptic plasticity is accomplished by a molecular switch we perform simulations using the reaction-diffusion package in NEURON and analytical calculations to determine the limits of synaptic-specificity during maintenance. Moreover, we explore the effects of the diffusion and degradation rates of proteins and of the geometrical characteristics of dendritic spines on synapse specificty. We conclude that the necessary conditions for synaptic specificity during maintenance require that protein synthesis occurs in dendritic spines and that the activated dendritic spines exhibit small neck diameters.

neuroscience↗

bioRxiv2017

Layer-Specific Molecular Dynamics of PKMζ in Sensorimotor Cortex During Acquisition and Storage of Procedural Memory

Procedural memories, such as for riding a bicycle, can be maintained without practice for long periods of time and are thought to be supported by the persistent reorganization of sensorimotor cortices (S1/M1). Whereas enhanced synaptic strength and structural changes accompany the learning of motor tasks, the persistent molecular modifications that store long-term procedural memories within specific layers of sensorimotor cortex have not been identified. The persistent increase in the autonomously active, atypical PKC isoform, PKM{zeta}, is a putative molecular mechanism for maintaining enhanced synaptic strength during long-term potentiation (LTP) and several forms of long-term memory. Here we examine whether persistent increases in PKM{zeta} store long-term memory for a reaching task in rat sensorimotor cortex that could reveal the sites of procedural memory storage. Perturbing PKM{zeta} synthesis with PKM{zeta} -antisense oligodeoxynucleotides or blocking atypical PKC activity with zeta inhibitory peptide (ZIP) in S1/M1 disrupts and erases the maintenance of long-term motor memories. Only memories that are maintained without daily reinforcement are affected, indicating atypical PKCs (via ZIP) and PKM{zeta} specifically (via antisense) stores consolidated long-term procedural memories. Analysis of changes in the amount of PKM{zeta} in S1/M1 reveals PKM{zeta} increases in layers II/III and V of both S1 and M1 cortices as performance improves to an asymptote during training. After storage for 1 month without reinforcement, the increase in M1 layer V but not other layers persists without decrement. Thus, the sustained increases in PKM{zeta} reveal that the persistent molecular changes storing long-term procedural memory are localized to the descending output layer of primary motor cortex.

neuroscience↗