Tianeptine Enhances Energy-related Processes in the Hippocampal Non-synaptic Mitochondria in a Rat Model of Depression

Highlights

• CSIS and chronic Tian treatment up-regulate components of proteasome and ubiquitin system.

• Cytosol sub-proteome is differently regulated by Tian if concurrent with CSIS.

• CSIS and Tian up-regulate the expression of GAPDH, while concurrently they result with decreased expression of GAPDH.

• In CSIS, Tian stimulated first line of antioxidative defence via Cu-Zn SOD up-regulation.

• Tian up-regulates NSM proteins involved in energy processes.

Abstract

Tianeptine (Tian) has been widely used in treating mood and anxiety disorders, and recently as a nootropic to improve cognitive performance. However, its mechanisms of action are insufficiently clear. We used a comparative proteomic approach to identify sub-proteome changes in hippocampal cytosol and non-synaptic mitochondria (NSM) following chronic Tian treatment (3 weeks, 10 mg/kg/day) of adult male Wistar rats and rats exposed to chronic social isolation stress (CSIS) (6 weeks), an animal model of depression. Behavioural assessment of depressive and anxiety-like behaviours was based on sucrose preference, forced swim test and marble burying. Selected differently expressed proteins were validated by Western blot and/or immunohistochemical analysis. Tian normalized the behavioural alternations induced by CSIS, indicating its antidepressant and anxiolytic efficacy. Proteomic data showed that Tian increased the expression of proteasome system elements and redox system enzymes, enhanced energy metabolism and increased glyceraldehyde-3-phosphate dehydrogenase expression bound to NSM in control rats. Tian-treatment of CSIS-stressed rats resulted in a minor suppression of the increase in proteasome elements and antioxidative enzymes, except for an increase in Cu-Zn superoxide dismutase, and increased the level of Lactate dehydrogenase. Our results indicate on an increased NSM functionality in controls and suppression of the CSIS-induced impairment of NSM functionality by Tian treatment as well as on the CSIS-caused discrepancy in Tian effects relative to controls.

Introduction

Identifying biochemical markers of depression and therapy has been the goal of many studies. The growing incidence of chronic stress exposure is recognized as one of the factors that contribute to the onset of disease. Translation studies use chronic social isolation (CSIS), a psychosocial stressor, as a rodent model for studying depression (Post, 1992, Wallace et al., 2009). Despite all the efforts made thus far, the underlying pathology of depression and its treatment remain unclear.

Tianeptine (Tian) is an atypical antidepressant and anxiolytic from a group of selective serotonin reuptake enhancers that works in contrast to the prevailing monoamine theory of depression, but still alleviates the symptoms of depression and anxiety (Nickel et al., 2003). It counteracts and reverses stress-induced morphological changes of the hippocampus and amygdala (Magariños et al., 1999, Czéh et al., 2001, Belleau et al., 2018). The antidepressant and anxiolytic properties of Tian have been attributed to the normalization of GABA- and glutamate-mediated neurotransmission (Szegedi et al., 2011, Perić et al., 2019) and neuroplasticity (Reagan et al., 2007, Della et al., 2012), with probable indirect contribution to the dopaminergic system (Sacchetti et al., 1993). Also, being a potent agonist of glutamate AMPA receptors categorizes Tian as a nootropic: the acute administration of Tian improves cognitive performance in healthy subjects within hours (Zoladz et al., 2010). The same cognitive effects have been observed in depressed patients (Smith, 2013, Jeon et al., 2014). Unlike this immediate effect, Tian exerts anxiolytic and antidepressant properties only after chronic treatment (Delbende et al., 1994, Waintraub et al., 2002, Burghardt et al., 2004, Preskorn, 2004) and by a mechanism still insufficiently clear, but obviously distal from its direct mechanism of action.

The hippocampus has gained a lot of attention in depression-related research, with many studies reporting volume loss over the course of the illness, as well as subsequent functional alterations (Sapolsky, 2001, Dunlop and Mayberg, 2007, MacQueen and Frodl, 2011, Milne et al., 2012) and impaired activity in depressive patients, revealed by imaging studies (Savitz and Drevets, 2009). So, the interconnection of mitochondrial dysfunction with the pathology of depression implicated the so called “mitochondrial hypothesis” of depression (Zuccoli et al., 2017, Allen et al., 2018). Also, divergence of mitochondrial pathways has been related with the pathophysiology of anxiety-like behaviour while targeting of mitochondria has been shown to exert the anxiolytic efficacy (Filiou et al., 2011, Nussbaumer et al., 2016, Filiou and Sandi, 2019).

We employed comparative proteomics approach for characterization of all activated molecular signalling pathways responsive to the effects of stress and antidepressant (Bayés and Grant, 2009, Hosp and Mann, 2017). Consistent with the chronic nature of stress exposure, as well as the delayed response to the onset of action of antidepressants, we examined non-synaptic mitochondria (NSM) (in addition to cytosol), which unlike those localized in synaptic terminals, reflect protein expression changes (Villa et al., 2016). Our previous proteomic study revealed energy- and proteasomal system – related modifications by chronic administration of a typical SSRI drug, fluoxetine, in cytosol and NSM (Filipović et al., 2017). Hence, this proteomic study was conducted on cytosol and NSM hippocampal fractions of adult male Wistar rats exposed to CSIS (6 weeks) and after chronic Tian treatment in controls and CSIS-exposed rats (last 3 weeks of CSIS) with the aim to profile the sub-proteome changes representative of possible time-consuming events underlying the nootropic and antidepressant/anxiolytic properties of Tian. A bioinformatic analysis defined the most activated biological processes. Our results may aid in highlighting the possible routes of Tian’s nootropic and antidepressant activity.