Lithium reverses increased rates of cerebral protein synthesis in a mouse model of fragile X syndrome
Highlights
► Chronic lithium reverses increased cerebral protein synthesis in Fmr1 KO mice ► Chronic lithium has little effect on cerebral protein synthesis in WT mice ► PI3K/Akt pathway signaling does not fully account for effects on hippocampal rCPS ► MAPK/ERK 1/2 pathway signaling does not fully account for effects on hippocampal rCPS
Introduction
Individuals with fragile X syndrome (FXS), an inherited form of intellectual disability, show a broad spectrum of morphologic, cognitive, behavioral, neurological, and psychological features (Chonchaiya et al., 2009). FXS is caused by the silencing of the FMR1 gene and the consequent absence of its protein product, fragile X mental retardation protein (FMRP) (Brown, 2002). FMRP is a RNA-binding protein that associates with polyribosomes and negatively regulates translation of certain mRNAs (Penagarikano et al., 2007). It is thought that absence of FMRP results in a dysregulation of protein synthesis and that it is this dysregulation that has such profound consequences for development and function of the nervous system. Protein synthesis in the nervous system is required for normal nervous system development and maintenance. It is also essential for implementation of long lasting changes in synaptic strength such as occur in long term potentiation (LTP) and long term depression (LTD). Some forms of both LTD and LTP are impaired in Fmr1 knockout (KO) mice (Huber et al., 2004, Larson et al., 2005, Li et al., 2002, Suvrathan et al., 2010, Wilson and Cox, 2007, Zhao et al., 2005), and it has been proposed that a dysregulation of protein synthesis may underlie these impairments.
In accord with the idea that a dysregulation of protein synthesis may be at the heart of the defect in FXS, we have shown that adult male Fmr1 KO mice have elevated regional rates of cerebral protein synthesis (rCPS) compared with wild type (WT) littermates (Qin et al., 2005). We measured rCPS in vivo with a quantitative autoradiographic method (Smith et al., 1988). Effects were regionally selective occurring mainly in hippocampus, thalamus and hypothalamus. Other investigators have monitored the incorporation of 35S-methionine/cysteine into new protein in vitro. Their findings also indicate that incorporation is higher in hippocampal slices from Fmr1 KO mice (Dölen et al., 2007, Osterweil et al., 2010).
Treatment for FXS is largely symptom-based and multidisciplinary. Current treatments include special education, behavioral interventions, physical therapy and symptom-directed pharmacotherapy. There are several classes of pharmacotherapeutic agents currently under investigation in FXS that are aimed at the biochemical processes thought to underlie the disease. Among them are mGluR antagonists, antibiotics, and GABA agonists (Levenga et al., 2010). Lithium, an effective mood stabilizer for the treatment of bipolar disorder, has been used successfully in individuals with FXS to stabilize mood dysregulation (Al-Semaan et al., 1999). Results of a pilot add-on trial demonstrated that lithium may improve behavior, adaptive skills, and verbal memory in patients with FXS (Berry-Kravis et al., 2008). We and other groups have demonstrated that chronic dietary lithium treatment ameliorates many of the behavioral deficits seen in Fmr1 KO mice (Liu et al., 2011, Mines et al., 2010, Yuskaitis et al., 2010). Moreover, lithium treatment partially normalized the immature dendritic spine morphology in medial prefrontal cortex (Liu et al., 2011). Lithium has also been shown to modify abnormal behavior and morphology in a Drosophila model of FXS (McBride et al., 2005). Taken together results from these studies suggest that lithium could provide significant therapeutic benefits in FXS.
How lithium treatment may effect these therapeutic outcomes is not understood. In the current study, we measure rCPS in WT and Fmr1 KO mice to investigate whether lithium may act through an effect on the control of translation. Our results indicate that, in addition to its effects on behavior and morphology, lithium also normalizes the elevated rCPS in Fmr1 KO mice. We also present in this paper effects of lithium treatment on some of the steps in signaling pathways that control cap-dependent translation.
Section snippets
Animals
Male WT and Fmr1 KO mice (n = 79), generated by FVB/NJ-fmr1tm1Cgr breeding pairs (heterozygous females and homozygous males), were used. The generation of Fmr1 KO mice and their genotyping by PCR amplification of tail DNA were described previously (Qin et al., 2005). All mice were group housed in a central facility and maintained under controlled conditions of normal humidity and temperature with standard alternating 12-h periods of light and darkness. All procedures were carried out in
Cerebral protein synthesis
We studied WT and Fmr1 KO mice under two conditions, control with normal rodent chow and experimental with lithium-supplemented chow. Physiological variables were measured at the time of determination of rCPS. The four groups were well matched with regard to age, body weight, and physiological status (Table 1). Arterial plasma leucine concentration was affected by the lithium treatment; leucine concentrations were lower in the lithium-treated mice regardless of genotype (F(1, 29) = 30.51, p <
Discussion
The central finding of our study is that chronic treatment with lithium reversed the increased rCPS found in Fmr1 KO mice and had little, if any, effect on rCPS in WT mice. Increased rCPS in the untreated Fmr1 KO mice were found primarily in the limbic system and hypothalamus, whereas the effects of lithium occurred throughout the brain. We extended our studies to examine in hippocampus the effects of lithium treatment on some of the signaling pathways that influence translation. Our results
Acknowledgments
We thank Zengyan Xia for overseeing the breeding colony and Tom Burlin for analyzing plasma samples for amino acid concentrations. We also thank Dr. De-Maw Chuang for helpful discussions at the outset of these studies. The research was supported by the Intramural Research Program of the National Institute of Mental Health, National Institutes of Health.
References (48)
Effect of lithium on the rate of protein synthesis in the sea urchin embryo
Exp. Cell Res.
(1968)- et al.
Analysis of gene expression with cDNA microarrays in rat brain after 7 and 42 days of oral lithium administration
Brain Res. Bull.
(2002) - et al.
Chronic lithium chloride administration to rats decreases brain protein level of epsilon (epsilon) subunit of eukaryotic initiation factor-2B
Neurosci. Lett.
(2002) - et al.
Molecular actions and therapeutic potential of lithium in preclinical and clinical studies of CNS disorders
Pharmacol. Ther.
(2010) - et al.
Fragile X: a family of disorders
Adv. Pediatr.
(2009) - et al.
Correction of fragile X syndrome in mice
Neuron
(2007) - et al.
Potential therapeutic interventions for fragile X syndrome
Trends Mol. Med.
(2010) - et al.
Reduced cortical synaptic plasticity and GluR1 expression associated with fragile X mental retardation protein deficiency
Mol. Cell. Neurosci.
(2002) - et al.
Pharmacological rescue of synaptic plasticity, courtship behavior, and mushroom body defects in a Drosophila model of fragile X syndrome
Neuron
(2005) - et al.
Elevated glycogen synthase kinase-3 activity in Fragile X mice: key metabolic regulator with evidence for treatment potential
Neuropharmacology
(2009)
Regulation of Akt mRNA and protein levels by glycogen synthase kinase-3beta in adrenal chromaffin cells: effects of LiCl and SB216763
Eur. J. Pharmacol.
Ribosomal protein S6 phosphorylation: from protein synthesis to cell size
TIBS
Effect of potassium and lithium ions on protein synthesis in the sea urchin embryo
Exp. Cell Res.
Does protein synthesis decline in lithium-treated sea urchin embryos because RNA synthesis is inhibited?
Exp. Cell Res.
Lithium ameliorates altered glycogen synthase kinase-3 and behavior in a mouse model of fragile X syndrome
Biochem. Pharmacol.
Drosophila fragile X-related gene regulates the MAP1B homolog Futsch to control synaptic structure and function
Cell
Schizoaffective disorder in a fragile-X carrier
Aust. N. Z. J. Psychiatry
Open-label treatment trial of lithium to target the underlying defect in fragile X syndrome
J. Dev. Behav. Pediatr.
The molecular biology of the fragile X mutation
Lithium activates the serine/threonine kinase Akt-1 and suppresses glutamate-induced inhibition of Akt-1 activity in neurons
Proc. Natl. Acad. Sci. U. S. A
Microarray gene expression profiling of mouse brain mRNA in a model of lithium treatment
Psychiatr. Genet.
On protein synthesis during the development of lithium-treated embryos
Experientia
Lithium acutely inhibits and chronically up-regulates and stabilizes glutamate uptake by presynaptic nerve endings in mouse cerebral cortex
Proc. Natl. Acad. Sci. U. S. A
Lithium-mediated downregulation of PKB/Akt and cyclin E with growth inhibition in hepatocellular carcinoma cells
Int. J. Cancer
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2021, Neuroscience and Biobehavioral ReviewsCitation Excerpt :Interestingly, lithium treatment mitigated many phenotypes in Fmr1 KO mice, from cellular dysfunction to behavioural alterations reminiscent of FXS and Autism; chronic lithium treatment reduced learning and memory impairments, social anxiety and hyperactivity, and improved the immature dendritic spine phenotype (Liu et al., 2011; Liu and Smith, 2014). Lithium treatment reduces levels of p-Akt and p-mTOR (Liu et al., 2012) and reinforces the inhibition of GSK3β (Min et al., 2009; Yuskaitis et al., 2010). In FXS, lithium could act on the phosphorylation levels of these protein synthesis regulators, rescue excessive protein synthesis, and normalize the activity of GSK3β, to consequently ameliorate phenotypes in Fmr1 KO mice.
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2018, Brain ResearchCitation Excerpt :FMRP can regulate the translation of target mRNAs through multiple mechanisms, and in addition to ribosome stalling, can also repress translation by association with the RNA-induced silencing complex (RISC) (Muddashetty et al., 2011) and other mechanisms (Richter et al., 2015). Observations of increased basal rates of protein synthesis and loss of stimulus-induced protein synthesis in both the mouse model of FXS (Gross et al., 2010; Liu et al., 2012; Sharma et al., 2010) and cells from FXS patients (Gross and Bassell, 2012) further provide evidence for translational dysregulation as underlying core mechanism of FXS. Mouse models of FXS have demonstrated dysregulated metabotropic glutamate receptor 5 (mGlu5) activation of protein synthesis and signal transduction (Bear et al., 2004; Gross et al., 2010; Osterweil et al., 2010; Sharma et al., 2010).