Effects of antidepressants on GluR2 Q/R site-RNA editing in modified HeLa cell line

Abstract

Marked reduction of RNA editing at the glutamine (Q)/arginine (R) site of the glutamate receptor subunit type 2 (GluR2) in motor neurons may be a contributory cause of neuronal death specifically in sporadic ALS. It has been shown that deregulation of RNA editing of several mRNAs plays a causative role in diseases of the central nervous system such as depression. We analyzed the effects of eight antidepressants on GluR2 Q/R site-RNA editing in a modified HeLa cell line that stably expresses half-edited GluR2 pre-mRNA. We also measured changes in RNA expression levels of adenosine deaminase acting on RNA type 2 (ADAR2), the specific RNA editing enzyme of the GluR2 Q/R site, and GluR2, in order to assess the molecular mechanism causing alteration of this site-editing. The editing efficiency at the GluR2 Q/R site was significantly increased after treatment with seven out of eight antidepressants at a concentration of no more than 10 μM for 24 h. The relative abundance of ADAR2 mRNA to GluR2 pre-mRNA or to β-actin mRNA was increased after treatment with six of the effective antidepressants, whereas it was unchanged after treatment with milnacipran. Our results suggest that antidepressants have the potency to enhance GluR2 Q/R site-editing by either upregulating the ADAR2 mRNA expression level or other unidentified mechanisms. It may be worth investigating the in vivo efficacy of antidepressants with a specific therapeutic strategy for sporadic ALS in view.Key Words: AMPA receptor; GluR2, RNA editing; adenosine deaminase acting on RNA type 2 (ADAR2); antidepressant; amyotrophic lateral sclerosis (ALS) 2 IntroductionAmyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that affects approximately 1 in 2,000 people over their lifetime (Cleveland el al., 2001). ALS is characterized by a selective loss of upper and lower motor neurons that initiates a progressive paralysis with muscle wasting in mid-life, and is usually fatal within 1-5 years after onset. Approximately 5-10% of all ALS cases are familial, and at least five causal genes have been so far identified in individuals affected with familial ALS (SOD1, ALS2, senataxin, vesicle-trafficking protein/synaptobrevin-associated membrane protein, and TDP-43), although the mechanism underlying motor neuron death of familial ALS pathology has not been elucidated (Rosen et al., 1993; Hadano et al., 2001; Yang et al., 2001;Chen et al., 2004; Nishimura et al., 2004; Yokoseki et al., 2008;Gitcho et al., 2008; Kabashi et al., 2008;Sreedharan et al., 2008; Van Deerlin et al., 2008). However, sporadic ALS accounts for the majority of all ALS cases, and one clue to the pathomechanism of sporadic ALS, low editing efficiency of GluR2 mRNA, has been elucidated (Takuma et al., 1999; Kawahara et al., 2004).One of the most plausible hypotheses for selective neuronal death in sporadic ALS is excitotoxicity mediated by abnormally Ca 2+ -permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors, a subtype of ionotropic glutamate rece...

Individual Stress Vulnerability Is Predicted by Short-Term Memory and AMPA Receptor Subunit Ratio in the Hippocampus

“…Accordingly, mice lacking the GluR1 subunit, thus with a relatively higher GluR2-to-GluR1 ratio, have recently been postulated as a model of depression (Chourbaji et al, 2008). Furthermore, antidepressants have been shown to modulate AMPA receptor mRNA expression, mRNA editing, and receptor phosphorylation, thereby affecting AMPA receptor expression and function (Barbon et al, 2006;Svenningsson et al, 2007;Sawada et al, 2009). Importantly, elevations of stress hormones per se do not seem to have a direct influence on the mRNA expression of AMPA receptor subunits, (Liu et al, 2006), but rather on AMPA receptor trafficking and mobility (Martin et al, 2009).…”

The Glutamate Hypothesis in ALS: Pathophysiology and Drug Development

“…Antidepressants, for example, enhance GluR2 Q/R site-editing in a modified HeLa cell line expressing half-edited GluR2 pre-mRNA, probably by upregulating expression of ADAR2 (adenosine deaminase that acts on RNA) mRNA [78]. This strategy needs to be developed further but could, in theory, be used to examine efficacy of antidepressants for ALS in vivo.…”

When you can’t trust the DNA: RNA editing changes transcript sequences

“…The initial discovery of glutamate channel A-to-I editing was seminal for many more editing events identified subsequently, which similarly affect mRNAs encoding neurologically important membrane channels and receptors. Hence, the investigation of A-to-I editing has in fact become an important component of neurobiological studies on nervous functions and psychological disorders [197][198][199][200][201][202]. Strikingly, some of these editing sites are conserved across very wide phylogenetic distances, e.g., ranging from insect to squid in the case of a potassium channel [203].…”