Memory and mRNA translation
Many studies by our group and others have shown that mRNA translation into protein is required for memory consolidation, i.e., the conversion of labile, short term memory to relatively stable, long term memory (Gal-Ben-Ari and Rosenblum. 2012; Rosenberg et al. 2014). Since the foundation of the lab in 2001, we have been studying the regulation of mRNA translation into protein as a major molecular mechanism underlying learning and memory.
Over the years, we have focused on specific molecules that serve as key regulators of protein synthesis, and shown them to be potential targets for memory enhancement in health and disease (e.g., mild dementia, Alzheimer’s disease). These molecules include the eukaryotic initiation factor 2α (eIF2α) and its kinases (enzymes regulating its phosphorylation levels, and thereby, its activity). eIF2α has four known kinases, all known to be functional in the brain.
We have shown that eIF2α and at least two of its kinases, protein kinase R (PKR) and PKR-like endoplasmic reticulum kinase (PERK), play an essential role in learning and memory. For example, eIF2α+/S51A mice (genetic reduction of eIF2α phosphorylation) have enhanced synaptic plasticity and enhanced hippocampal- and cortical-dependent learning (Costa-Mattioli et al. 2007). Furthermore, we have shown that treatment with a protein kinase R (PKR) inhibitor (C16) (rats, WT mice) or genetic deletion of eIF2α kinase PKR (PKR KO mice) results in enhanced memory in the conditioned taste aversion paradigm (associative learning) and the novel taste learning paradigm (both paradigms are cortical-dependent) (Stern et al. 2013). Moreover, phosphorylation of eIF2α is increased with age in rats and mice, and in the ApoE4 mouse model of sporadic Alzheimer’s disease, phosphorylation levels of PKR and eIF2α are increased (Segev et al. 2013), and PKR inhibition rescues memory impairment, as shown in the contextual fear conditioning paradigm (hippocampal-dependent) (Segev et al. 2015). Our findings regarding PKR, as a potential target for memory enhancement in health and disease, have been granted a patent (US 8,334,262 B2). Based on our findings regarding PKR and this patent, in 2015 we founded a start-up company (Protekt Therapeutics, part of the FuturX biotechnological incubator, Israel) aiming to develop PKR inhibitors, invested by Takeda Pharmaceuticals and Johnson & Johnson.
In addition to PKR, we have shown that PERK plays an essential role in learning and memory and synaptic plasticity as well, and serves as the major regulator of eIF2α phosphorylation. We have shown that reduction of either the expression levels (knockdown using a viral vector) or the activity of PERK (using a pharmacological inhibitor), in the insular cortex resulted in enhanced performance in the cortical-dependent novel taste learning and conditioned taste aversion paradigms (Ounallah-Saad et al. 2014). Similar inhibition of PERK activity or reduction of its expression levels in the CA1 region of the hippocampus in young adult male mice enhances neuronal excitability and improves cognitive function in the hippocampal depended trace fear conditioning (associative learning) paradigm. In addition, PERK knockdown or inhibition rescues the age-dependent cellular phenotype of reduced excitability and memory decline. Specifically, the reduction of PERK expression in the CA1 region of the hippocampus of middle-aged male mice using a viral vector rejuvenates hippocampal function and improves hippocampal-dependent learning (Sharma et al. 2018). This mechanism underlying aging both on the whole animal, behavioral level and on the neuronal function level points to PERK as a promising therapeutic target for age-dependent brain malfunction (US patent application 15335466).
While eIF2α and its regulating kinases regulate the initiation (first) phase of protein synthesis, considered to be the rate limiting phase of protein synthesis, we have shown that another molecule, eukaryotic elongation factor 2 kinase (eEF2K), a major regulator of the elongation (second) phase of protein synthesis, is also essential for memory formation and synaptic plasticity consolidation (Taha et al. 2013; Heise et al. 2017). eEF2K is the only known kinase of eukaryotic elongation factor 2 (eEF2). We have found that genetic deletion of eEF2K (knock-out, KO) in mice, which leads to complete loss of eEF2 phosphorylation, differentially affects hippocampal-dependent memory formation. From a clinical perspective, our results identify eEF2K as a potential novel target for antiepileptic drugs, since pharmacological and genetic inhibition of eEF2K can revert the epileptic phenotype in a mouse model of human epilepsy (Heise et al. 2017). Currently, we are examining the function of the eEF2 pathway in the dentate gyrus (DG) of the hippocampus. (Taha et al., manuscript in preparation).
In our latest manuscript, we delved into the field of depression, and tested the hypothesis that both eEF2K and another kinase, Ca2+ /calmodulin-dependent protein kinase II (CaMKII), mediate the anti-depressant effect of ketamine. We identified CaMKII as new target for ketamine (and have a provisional patent on it, US application number 62/556,440). Interestingly, our results suggest that drugs selectively targeting calcium-calmodulin dependent kinases, specifically eEF2K, may offer a novel strategy for the treatment of major depressive disorder (Adaikkan et al. 2018).
References
Messenger RNA Translation Defects in Neurodegenerative Diseases. Erik Storkebaum, Ph.D., Kobi Rosenblum, Ph.D., and Nahum Sonenberg, Ph.D. March 16, 2023N Engl J Med 2023; 388:1015-1030
DOI: 10.1056/NEJMra221579
eIF2α controls memory consolidation via excitatory and somatostatin neurons. Vijendra Sharma , Rapita Sood , Abdessattar Khlaifia , Mohammad Javad Eslamizade , Tzu-Yu Hung , Danning Lou , Azam Asgarihafshejani , Maya Lalzar , Stephen J Kiniry , Matthew P Stokes , Noah Cohen , Alissa J Nelson , Kathryn Abell , Anthony P Possemato , Shunit Gal-Ben-Ari , Vinh T Truong , Peng Wang , Adonis Yiannakas , Fatemeh Saffarzadeh , A Claudio Cuello , Karim Nader , Randal J Kaufman , Mauro Costa-Mattioli , Pavel V Baranov , Albert Quintana , Elisenda Sanz , Arkady Khoutorsky , Jean-Claude Lacaille , Kobi Rosenblum , Nahum Sonenberg .Nature 2020 Oct;586(7829):412-416. doi: 10.1038/s41586-020-2805-8. Epub 2020 Oct 7
Measuring mRNA translation in neuronal processes and somata by tRNA-FRET Koltun B, Ironi S, Gershoni-Emek N, Barrera I, Hleihil M, Nanguneri S, Sasmal R, Agasti SS, Nair D, Rosenblum K. Nucleic Acids Res. 2020 Jan 24. pii: gkaa042. doi: 10.1093/nar/gkaa042. [Epub ahead of print]
Genetic or pharmacological reduction of PERK enhances cortical-dependent taste learning. Ounallah-Saad H, Sharma V, Edry E, Rosenblum K. J Neurosci. 2014 Oct 29;34(44):14624-32. doi: 10.1523/JNEUROSCI.2117-14.2014
Local Inhibition of PERK Enhances Memory and Reverses Age-Related Deterioration of Cognitive and Neuronal Properties. Sharma V, Ounallah-Saad H, Chakraborty D, Hleihil M, Sood R, Barrera I, Edry E, Kolatt Chandran S, Ben Tabou de Leon S, Kaphzan H, Rosenblum K. J Neurosci. 2018 Jan 17;38(3):648-658. doi: 10.1523/JNEUROSCI.0628-17.2017. Epub 2017 Dec 1.
Calcium/Calmodulin-Dependent Protein Kinase II and Eukaryotic Elongation Factor 2 Kinase Pathways Mediate the Antidepressant Action of Ketamine. Adaikkan C, Taha E, Barrera I, David O, Rosenblum K. Biol Psychiatry. 2018 Jul 1;84(1):65-75. doi: 10.1016/j.biopsych.2017.11.028. Epub 2017 Dec 5
PKR Inhibition Rescues Memory Deficit and ATF4 Overexpression in ApoE ε4 Human Replacement Mice. Segev Y, Barrera I, Ounallah-Saad H, Wibrand K, Sporild I, Livne A, Rosenberg T, David O, Mints M, Bramham CR, Rosenblum K. J Neurosci. 2015 Sep 23;35(38):12986-93. doi: 10.1523/JNEUROSCI.5241-14.2015.