# Commentary: Chronic SSRI stimulation of astrocytic 5-HT2B receptors change multiple gene expressions/editings and metabolism of glutamate, glucose and glycogen: a potential paradigm shift

Sophie M. Banas, Silvina L. Diaz, Stéphane Doly, Arnauld Belmer, Luc Maroteaux

► To cite this version:

Sophie M. Banas, Silvina L. Diaz, Stéphane Doly, Arnauld Belmer, Luc Maroteaux. Commentary: Chronic SSRI stimulation of astrocytic 5-HT2B receptors change multiple gene expressions/editings and metabolism of glutamate, glucose and glycogen: a potential paradigm shift. Frontiers in Behavioral Neuroscience, 2015, 9, pp.207. 10.3389/fnbeh.2015.00207. [https://doi.org/10.3389/fnbeh.2015.00207](https://doi.org/10.3389/fnbeh.2015.00207)

HAL Id: hal-01225050

https://hal.sorbonne-universite.fr/hal-01225050v2

Submitted on 14 Oct 2015

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Commentary: Chronic SSRI stimulation of astrocytic 5-HT<sub>2B</sub> receptors change multiple gene expressions/editings and metabolism of glutamate, glucose and glycogen: a potential paradigm shift

Sophie M. Banas, Silvina L. Diaz, Stéphane Doly, Arnauld Belmer and Luc Maroteaux*

INSERM UMR S-839, Institut du Fer à Moulin, Université Pierre et Marie Curie, Paris, France

**Keywords:** serotonin transporter gene, serotonin, neurotransmitter reuptake, depression, mouse models, receptors, cell surface

## A commentary on

Chronic SSRI stimulation of astrocytic 5-HT<sub>2B</sub> receptors change multiple gene expressions/editings and metabolism of glutamate, glucose and glycogen: a potential paradigm shift

by Hertz, L., Rothman, D. L., Li, B., and Peng, L. (2015). *Front. Behav. Neurosci.* 9:25. doi: 10.3389/fnbeh.2015.00025

**OPEN ACCESS**

**Edited by:**
Allan V. Kalueff,
ZENEREI Institute, USA and
Guangdong Ocean University, China

**Reviewed by:**
Matthew O. Parker,
Queen Mary University of London, UK
Tatyana Strekalova,
Maastricht University, Netherlands

*Correspondence:
Luc Maroteaux,
luc.maroteaux@upmc.fr

**Received:** 18 May 2015
**Accepted:** 20 July 2015
**Published:** 05 August 2015

**Citation:**
Banas SM, Diaz SL, Doly S, Belmer A and Maroteaux L (2015) Commentary: Chronic SSRI stimulation of astrocytic 5-HT<sub>2B</sub> receptors change multiple gene expressions/editings and metabolism of glutamate, glucose and glycogen: a potential paradigm shift
Front. Behav. Neurosci. 9:207. doi: 10.3389/fnbeh.2015.00207

Working on the serotonin (5-hydroxytryptamine, 5-HT) 5-HT<sub>2B</sub> receptor since several years, we have read with high interest the review by Hertz et al. (2015). Previous studies from our group demonstrated that a direct injection in mouse raphe nucleus of the 5-HT<sub>2B</sub> agonist BW723C86 has the ability to increase extracellular levels of serotonin, which can be blocked by the selective 5-HT<sub>2B</sub> receptor antagonist RS127445 (Doly et al., 2008, 2009). We also reported that an acute injection of paroxetine 2 mg/kg in mice knocked out for the 5-HT<sub>2B</sub> receptor gene or in wild type mice injected with RS127445 (0.5 mg/kg) triggers a strong reduction in extracellular accumulation of 5-HT in hippocampus (Diaz et al., 2012). Following these observations, we showed that acute and chronic BW723C86 injection (3 mg/kg) can mimic the fluoxetine (3 mg/kg) and paroxetine (1 mg/kg) behavioral and biochemical antidepressant effects in mice (Diaz and Maroteaux, 2011; Diaz et al., 2012).

Hertz and coworkers used some of our published data on mice to support that fluoxetine and other SSRIs are acting as direct 5-HT<sub>2B</sub> receptor agonists independently of the serotonin transporter (SERT), based on their work on astrocytes. These authors forgot other important informations provided in Diaz's paper (Diaz et al., 2012), i.e., the absence of antidepressant effects of either fluoxetine or BW723C86 in mice lacking either the serotonin transporter (knockout for SERT) or differentiated serotonin neurons (knockout for Pet1). These data (i) rule out that the antidepressant effects of the 5-HT<sub>2B</sub> agonist BW723C86 or of fluoxetine could be independent of SERT; (ii) they indicate that serotonin neurons expressing SERT (and 5-HT<sub>2B</sub> receptors) are necessary for the 5-HT<sub>2B</sub> receptor effects independently of other cell types; (iii) they rule out the possibility that SSRIs mediate antidepressant effects only by stimulating directly putative astrocytic 5-HT<sub>2B</sub> receptors, which should be intact in these two mutant mice (SERT KO and Pet1 KO). A previous work (Launay et al., 2006) demonstrated a 5-HT<sub>2B</sub> receptor-mediated control of SERT
<table><caption>TABLE 1 | Affinity constants (pKi) for different binding compounds to Human 5-HT<sub>2C</sub> and 5-HT<sub>2B</sub> receptors.</caption><thead><tr><th rowspan="2">Compounds</th><th colspan="2">5-HT<sub>2B</sub> Human</th><th colspan="2">5-HT<sub>2C</sub> Human</th></tr><tr><th>pkl</th><th>Ki (nM)</th><th>pKi</th><th>Ki (nM)</th></tr></thead><tbody><tr><td>Fluoxetine<sup>b</sup></td><td>&lt;5</td><td>&gt;10,000</td><td>6.95</td><td>112</td></tr><tr><td>Norfluoxetine<sup>b</sup></td><td>&lt;5</td><td>&gt;10,000</td><td>7.04</td><td>91</td></tr><tr><td>Paroxetine<sup>b</sup></td><td>&lt;5</td><td>&gt;10,000</td><td>&lt;5</td><td>&gt;10,000</td></tr><tr><td>Fluoxetine<sup>k</sup></td><td>&lt;5</td><td>&gt;10,000</td><td>6.40 ± 0.03</td><td>400</td></tr><tr><td>BW723C86<sup>k</sup></td><td>7.33 ± 0.03</td><td>47</td><td>7.11 ± 0.21</td><td>78</td></tr></tbody></table>

Pharmacological determinations were performed on transfected cells expressing the relevant receptor by heterologous competition. Values are from Bonhaus et al. (1997) (b) and Knight et al. (2004) (k).

activity in primary neurons from raphe nuclei, in which the BW723C86/5-HT<sub>2B</sub> receptor coupling promotes phosphorylations of SERT that can easily explain our findings in mice by a direct regulation of SERT by 5-HT<sub>2B</sub> receptors in a cell autonomous manner.

Furthermore, Hertz and coworkers state “The ability of all five currently used SSRIs to stimulate the 5-HT<sub>2B</sub> receptor equipotentially in cultured astrocytes has been known for several years.” This information originates from one of their previous observation on astrocyte cultures that “One micromolar of paroxetine, fluvoxamine or sertraline increased cPLA<sub>2a</sub> expression during chronic treatment; citalopram had a similar effect at 0.1–0.5 µM” (Zhang et al., 2010). Hertz and coworkers validated these data in one of their former review (Hertz et al., 2012), which reproduced their own earlier data (Kong et al., 2002), showing an half maximum effect (competition of mesulergine by fluoxetine on astrocytes) of 1 µM. However, in this review, they say that this initial calculation was “incorrect” and indicated that the Ki value of fluoxetine was in fact 70 nM on putative 5-HT<sub>2B</sub> astrocytic receptors (Hertz et al., 2012). These values, which are not supported by other published experimental evidence by these authors, are divergent from all published pharmacological values obtained with identified receptors: Bonhaus et al. (1997) and Knight et al. (2004) found

Ki values for cloned human 5-HT<sub>2B</sub> receptors over 10 µM for fluoxetine, norfluoxetine and paroxetine (Table 1).

To sum up, it is clear from our experiments in mice that acute or chronic fluoxetine (and paroxetine) cannot act by a direct 5-HT<sub>2B</sub> receptor stimulation independently of SERT and serotonergic neurons. Furthermore, our pharmacological determination in mice is in accordance with affinity of SSRIs for human 5-HT<sub>2B</sub> receptors with Ki values over 5 µM (Diaz et al., 2012) and with no agonist activity (unpublished), while SSRI Ki values for SERT are in nanomolar range. Many SSRIs have published Ki values around 1 µM for muscarinic acetylcholine and histamine receptors or other monoamine transporters. The contribution of these other receptors/transporters in astrocytes could explain the findings of Hertz and coworkers independently of putative direct agonist effects at 5-HT<sub>2B</sub> receptors. Finally, the published evidence for 5-HT<sub>2B</sub> receptor expression in microglia (Krabbe et al., 2011; Kolodziejczak et al., 2015) add another level of complexity, as the concept of the tripartite synapse has recently been expanded to the monoaminergic systems to explain antidepressant drug responses (Quesseveur et al., 2013). A full set of research is still needed to understand the putative role for 5-HT in glial cells including astrocytes and/or microglia in respect to the relationship between SSRIs, serotonergic neurons and 5-HT<sub>2B</sub> receptors. The needs for further research is warranted to determine how this receptor subtype contribute to SSRI antidepressant effects.

## Sources of Funding

Funding for this study was provided by the CNRS, the INSERM, the UPMC, and by grants from the Fondation de France, the Fondation pour la Recherche Médicale “Equipe FRM DEQ2014039529,” the French Ministry of Research (Agence Nationale pour la Recherche ANR-12-BSV1-0015-01 and the Investissements d’Avenir programme ANR-11-IDEX-0004-02). ML’s team is part of the École des Neurosciences de Paris Ile-de-France network and of the Bio-Psy Labex. SD has been supported by fellowships from IBRO and then from Region Ile de France DIM STEM.

## References

Bonhaus, D. W., Weinhardt, K. K., Taylor, M., Desouza, A., Mcneele, P. M., Szczepanski, K., et al. (1997). RS-102221: a novel high affinity and selective, 5-HT2C receptor antagonist. *Neuropharmacology* 36, 621–629. doi: 10.1016/S0028-3908(97)00049-X

Diaz, S., Doly, S., Narboux-Nême, N., Fernandez, S., Mazot, P., Banas, S., et al. (2012). 5-HT2B receptors are required for serotonin-selective antidepressant actions. *Mol. Psychiatry* 17, 154–163. doi: 10.1038/mp.2011.159

Diaz, S., and Maroteaux, L. (2011). Implication of 5-HT2B receptors in the serotonin syndrome. *Neuropharmacology* 61, 495–502. doi: 10.1016/j.neuropharm.2011.01.025

Doly, S., Bertran-Gonzalez, J., Callebert, J., Bruneau, A., Banas, S. M., Belmer, A., et al. (2009). Role of serotonin via 5-HT2B receptors in the reinforcing effects of MDMA in mice. *PLoS ONE* 4:e7952. doi: 10.1371/journal.pone.0007952

Doly, S., Valjent, E., Setola, V., Callebert, J., Hervé, D., Launay, J. M., et al. (2008). Serotonin 5-HT2B receptors are required for 3,4-methylenedioxymethamphetamine-induced hyperlocomotion and

5-HT release *in vivo* and *in vitro*. *J. Neurosci.* 28, 2933–2940. doi: 10.1523/JNEUROSCI.5723-07.2008

Hertz, L., Li, B., Song, D., Ren, J., Dong, L., Chen, Y., et al. (2012). Astrocytes as a 5-HT2B-mediated SERT-independent SSRI target, slowly altering depression-associated genes and function. *Curr. Signal Transduct. Ther.* 7, 65–80. doi: 10.2174/1574362799278154

Hertz, L., Rothman, D. L., Li, B., and Peng, L. (2015). Chronic SSRI stimulation of astrocytic 5-HT2B receptors change multiple gene expressions/editings and metabolism of glutamate, glucose and glycogen: a potential paradigm shift. *Front. Behav. Neurosci.* 9:25. doi: 10.3389/fnbeh.2015.00025

Knight, A. R., Misra, A., Quirk, K., Benwell, K., Revell, D., Kennett, G., et al. (2004). Pharmacological characterisation of the agonist radioligand binding site of 5-HT2A, 5-HT2B and 5-HT2C receptors. *Naunyn Schmiedebergs. Arch. Pharmacol.* 370, 114–123. doi: 10.1007/s00210-004-0951-4

Kolodziejczak, M., Bechade, C., Gervasi, N., Irinopoulou, T., Banas, S. M., Cordier, C., et al. (2015). Serotonin modulates developmental microglia via 5-HT receptors: potential implication during synaptic refinement of retinogeniculate projections. *ACS Chem. Neurosci.* 6, 1219–1230. doi: 10.1021/cn5003489
Kong, E. K., Peng, L., Chen, Y., Yu, A. C., and Hertz, L. (2002). Upregulation of 5-HT2B receptor density and receptor-mediated glycogenolysis in mouse astrocytes by long-term fluoxetine administration. *Neurochem. Res.* 27, 113–120. doi: 10.1023/A:1014862808126

Krabbe, G., Matyash, V., Pannasch, U., Mamer, L., Boddeke, H. W. G. M., and Kettenmann, H. (2011). Activation of serotonin receptors promotes microglial injury-induced motility but attenuates phagocytic activity. *Brain Behav. Immun.* 26, 419–428. doi: 10.1016/j.bbi.2011.12.002

Launay, J. M., Schneider, B., Loric, S., Da Prada, M., and Kellermann, O. (2006). Serotonin transport and serotonin transporter-mediated antidepressant recognition are controlled by 5-HT2B receptor signaling in serotonergic neuronal cells. *FASEB J.* 20, 1843–1854. doi: 10.1096/fj.06-5724com

Quesseveur, G., Gardier, A. M., and Guiard, B. P. (2013). The monoaminergic tripartite synapse: a putative target for currently available antidepressant drugs. *Curr. Drug Targets* 14, 1277–1294. doi: 10.2174/13894501113149990209

Zhang, S., Li, B., Lovatt, D., Xu, J., Song, D., Goldman, S. A., et al. (2010). 5-HT2B receptors are expressed on astrocytes from brain and in culture and are a chronic target for all five conventional 'serotonin-specific reuptake inhibitors'. *Neuron Glia Biol.* 6, 113–125. doi: 10.1017/S1740925X10000141

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2015 Banas, Diaz, Doly, Belmer and Maroteaux. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.