Effects of ketamine administration on mTOR and reticulum stress signaling pathways in the brain after the infusion of rapamycin into prefrontal cortex

https://doi.org/10.1016/j.jpsychires.2016.12.002Get rights and content

Abstract

Recent studies show that activation of the mTOR signaling pathway is required for the rapid antidepressant actions of glutamate N-methyl-D-aspartate (NMDA) receptor antagonists. A relationship between mTOR kinase and the endoplasmic reticulum (ER) stress pathway, also known as the unfolded protein response (UPR) has been shown. We evaluate the effects of ketamine administration on the mTOR signaling pathway and proteins of UPR in the prefrontal cortex (PFC), hippocampus, amygdala and nucleus accumbens, after the inhibiton of mTOR signaling in the PFC. Male adult Wistar rats received pharmacological mTOR inhibitor, rapamycin (0.2 nmol), or vehicle into the PFC and then a single dose of ketamine (15 mg/kg, i.p.). The immunocontent of mTOR, eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), eukaryotic elongation factor 2 kinase (eEF2K) homologous protein (CHOP), PKR-like ER kinase (PERK) and inositol-requiring enzyme 1 (IRE1) – alpha were determined in the brain. The mTOR levels were reduced in the rapamycin group treated with saline and ketamine in the PFC; p4EBP1 levels were reduced in the rapamycin group treated with ketamine in the PFC and nucleus accumbens; the levels of peEF2K were increased in the PFC in the vehicle group treated with ketamine and reduced in the rapamycin group treated with ketamine. The PERK and IRE1-alpha levels were decreased in the PFC in the rapamycin group treated with ketamine. Our results suggest that mTOR signaling inhibition by rapamycin could be involved, at least in part, with the mechanism of action of ketamine; and the ketamine antidepressant on ER stress pathway could be also mediated by mTOR signaling pathway in certain brain structures.

Introduction

Major depressive disorder (MDD), a serious mental disorder, is the leading cause of disability and a major contributor to disease burden in the world's population (Ghasemi et al., 2014). Despite antidepressant treatment patients continue to experience low remission rates, residual subsyndromal symptoms, relapses and persistent functional impairment (Naughton et al., 2014). Unfortunately, the delayed onset time and the low remission rate of conventional antidepressants are still major challenges (Giacobbe et al. 2009; Machado-Vieira et al., 2009). Therefore, there is an urgent need to look for a fast-acting and effective antidepressant in the near future. Converging evidence from in vivo brain imaging studies, postmortem investigations, and gene expression studies implicates abnormalities in glutamatergic signaling in the pathophysiology of MDD (Manji et al., 2003, Sanacora et al., 2008, Skolnick et al., 2009). Ketamine, a glutamate N-methyl-d-aspartate (NMDA) receptor antagonist, was associated with rapid antidepressant effects in patients with major depressive disorder in a number of studies and case reports, including treatment-resistant major depression (Berman et al., 2000, Zarate et al., 2006, Mathew et al., 2010, Aan Het Rot et al., 2012). Antidepressant activity by ketamine was observed within hours of a single subanesthetic intravenous infusion, representing a potential paradigm shift in therapeutic approaches for major depressive disorder (Berman et al., 2000). Preclinical studies also showed that ketamine has antidepressant effects in some animal models of depression (Chaturvedi et al., 1999, Maeng et al., 2008a, Maeng et al., 2008b, Réus et al., 2015a, Réus et al., 2015b).

The mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase, which modulates cell growth, proliferation, motility, survival, and protein synthesis (Hay and Sonenberg, 2006). Several studies suggest that ketamine and other fast-acting antidepressants, mediated by glutamate and/or neurotrophic receptors, stimulate the mTOR pathway in the prefrontal cortex (PFC) (Li et al., 2010, Palucha-Poniewiera et al., 2014), leading to transient activation of the downstream effectors, 4E-binding protein 1 (4E-BP1) and protein S6 kinase (p70S6K), which regulate gene expression and protein synthesis (Tang et al., 2015). mTOR is also activated in depressed patients' peripheral blood after acute ketamine administration (Denk et al., 2011, Yang et al., 2013). These studies may indicate an association between marked deficits in synaptic proteins and dysregulation of mTOR signaling in MDD (Karolewicz et al., 2011). It has been reported that neuronal mTOR function is influenced by the activity of growth factors, insulin, cytokines, as well as glutamate activity via NMDA receptors and metabotropic glutamate receptors (mGluR) (Antion et al., 2008, Gong et al., 2006, Hay and Sonenberg, 2006, Hoeffer and Klann, 2010). Activated mTOR phosphorylates p70 ribosomal p70S6K followed by p70S6K-induced phosphorylation of ribosomal protein S6 and eukaryotic initiation factor 4B (eIF-4B), which promotes the initiation of protein translation (Chandran et al., 2013). mTOR also phosphorylates and inactivates the eukaryotic initiation factor 4E-BP1 reducing its affinity for the eukaryotic initiation factor 4E (eIF4E) leading to release of, eIF4E to facilitate translation initiation (Chandran et al. 2013). Thus, mTOR controls the efficiency of protein translation within cells via its critical downstream targets. Cellular processes, including apoptosis, autophagy, translation, energy metabolism, and inflammation are controlled by the mTOR kinase and the endoplasmic reticulum (ER) stress pathway, also known as the unfolded protein response (UPR) (Appenzeller-Herzog and Hall, 2012). Kato et al. (2012) and Nakajima et al. (2011) pointed out that in some pathological situations cellular toxicity caused by the ER stress are related to chronic activation of mTOR complex 1 (mTORC1). This implies in an apparent paradox in which under specific conditions, mTOR protein, a regulator of cell growth and division, can also signal the cell death (Appenzeller-Herzog and Hall, 2012). Indeed, some studies have already demonstrated that mTORC1 operates both upstream and downstream of ER stress signals, which can either enhance or antagonize the anabolic output of mTORC1 (Polak and Hall, 2009, Hotamisligil, 2010). Upon prolonged ER stress, mTORC1 can contribute to apoptotic signaling by suppressing the survival kinase Akt through feedback inhibition (Polak and Hall, 2009, Hotamisligil, 2010). Likewise, chronic ER stress can also obstruct activation of Akt by mTOR complex 2 (mTORC2). These two signaling networks have traditionally been considered as separate pathways, but the identification of mTOR-UPR interconnections is a promising new area for research.

There is abundant evidence linking mTOR signaling to synaptic plasticity, memory, neurological disorders and cancer (Gong et al., 2006, Hay and Sonenberg, 2006, Hoeffer and Klann, 2010). However, to date there are no studies that implicate the effects caused by the inhibition of mTOR pathway and treatment with ketamine in the PFC in other brain structures related to depression, such as hippocampus, amygdala and nucleus accumbens; and its relation with proteins of mTOR signaling pathway and UPR. The evaluation and understanding of the intersections and synergisms (or antagonisms) between the outputs of mTOR and UPR is of uttermost importance. Possible routes of crosstalk between these signaling networks are fundamental to cell health. Thus, the aim of this study was to evaluate the effects of the administration of ketamine on the proteins of mTOR signaling pathway, such as mTOR, 4EBP1 and eukaryotic elongation factor 2 kinase (eEF2K), and on the proteins of UPR, such as homologous protein (CHOP), PKR-like ER kinase (PERK) and inositol-requiring enzyme 1 (IRE1)-alpha in the PFC, hippocampus, amygdala and nucleus accumbens, after the inhibiton of mTOR signaling in the PFC.

Section snippets

Animals

Male Adult (60 days old) Wistar rats, weighing between 250 and 300 g, were housed five to a cage with food and water available ad libitum, and were maintained on a 12-h light/dark cycle (lights on at 7:00 a.m.). In vivo studies were performed in accordance with the National Institutes of Health guidelines and also with the approval of the ethics committee from University of Southern Santa Catarina (UNESC) under protocol 031-2014-01.

Experimental design and treatment

First, all rats (n = 20 total) underwent a surgical procedure

Effects of ketamine after the inhibition of mTOR pathway in the PFC with rapamycin on mTOR, p4EBP1 and eEF2K levels in brain structures

Fig. 1 illustrates the effect of ketamine after the inhibition of mTOR in the PFC on proteins related to the mTOR signaling pathway in the PFC, hippocampus, amygdala and nucleus accumbens. mTOR levels were decreased in the PFC in the rapamycin group treated with saline when compared to the vehicle group treated with saline and in the rapamycin group treated with ketamine when compared to vehicle group treated to saline and to vehicle group treated with ketamine (F (3-12) = 11.335; p = 0.003;

Discussion

mTOR is a protein kinase involved in cell proliferation, mortality, survival, and protein synthesis (Hay and Sonenberg, 2006). Changes in this signaling cascade have been hypothesized to be a common pathophysiological feature of neuropsychiatric disorders (Hoeffer and Klann, 2010). In fact, a postmortem study showed considerable deficits in mTOR signaling in the PFC of subjects diagnosed with MDD (Jernigan et al., 2011). Rapid activation of the mTOR signaling pathway resulting in rapid

Contributors

GZR, HMA and JQ performed the research; ZMI, HMA, MABS, DM, JPD, ABM and JBIS worked on surgical structures procedures, the pharmacological treatment, and in the removal of brain structures; MM, MA, BS and FDP worked on the western blotting analysis. HMA and GZR analyzed the data and wrote the paper. All authors approved the final version of the manuscript.

Conflict of interest

The authors have no potential conflict of interest.

Role of funding source

None.

Acknowledgements

The Translational Psychiatry Program (USA) is funded by the Department of Psychiatry and Behavioral Sciences, McGovern Medical School, The University of Texas Health Science Center at Houston (UTHealth). Laboratory of Neurosciences (Brazil) is one of the centers of the National Institute for Molecular Medicine (INCT-MM) and one of the members of the Center of Excellence in Applied Neurosciences of Santa Catarina (NENASC). Its research is supported by grants from CNPq (JQ and FDP), FAPESC (JQ

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