Karim Nader and the unification of memory erasure: PKMζ inhibition and reconsolidation blockade

Karim Nader is rightly celebrated for his seminal studies on memory reconsolidation. This commentary celebrates another related contribution - his work on memory maintenance by the autonomously active PKC isoform, PKM zeta. There are two methods for erasing previously established long-term memory maintenance: 1) inhibiting PKM zeta, and 2) blocking reconsolidation. Prior to Nader's research on PKM zeta, these two forms of memory erasure were thought to be fundamentally different. Inhibiting PKM zeta in a brain region disrupts memory held in storage. But if the inhibitor is injected into the same region immediately after memory retrieval, the drug has no effect. Conversely, inhibiting protein synthesis immediately after memory retrieval blocks reconsolidation. But protein synthesis inhibitors have no effect on memory held in storage without retrieval. The work of Paolo Virginia Migues, Nader, and colleagues, however, revealed an unexpected link between the mechanisms of memory maintenance by PKM zeta and the kinase's regulation of postsynaptic AMPAR trafficking that potentiates synaptic transmission and expresses memory during retrieval. This insight led Matteo Bernabo, Nader, and colleagues to observe that memory retrieval first rapidly degrades PKM zeta, and then induces the resynthesis of the kinase to restore maintenance of the retrieved memory. This finding explains why a PKM zeta inhibitor such as ZIP, if injected in a brain region storing a memory, does not erase the memory immediately after retrieval - the kinase maintaining the retrieved memory has been degraded but not yet resynthesized. Moreover, Bernabo et al. showed that suppressing the resynthesis of PKM zeta after its degradation prevents memory reconsolidation, reproducing the effect of general protein synthesis inhibition. Thus, Nader and colleagues demonstrated PKM zeta inhibition and reconsolidation blockade disrupt in different ways the same molecular mechanism of memory maintenance - PKM zeta inhibition erases all memories maintained in storage by the kinase; reconsolidation blockade disrupts specific recalled memories maintained by PKM zeta by preventing resynthesis of the kinase after its degradation.

Automated summary

Karim Nader's research explores memory reconsolidation and memory maintenance by PKM zeta. He found that inhibiting PKM zeta or blocking reconsolidation can erase long-term memory. The study also revealed a connection between PKM zeta's regulation of AMPAR trafficking and memory maintenance. PKM zeta inhibition erases all memories stored by the kinase, while reconsolidation blockade disrupts specific recalled memories by preventing the resynthesis of PKM zeta.