Elsevier

Neuroscience

Volume 163, Issue 3, 20 October 2009, Pages 825-837
Neuroscience

Developmental Neuroscience
Research Paper
A putative amino acid transporter of the solute carrier 6 family is upregulated by lithium and is required for resistance to lithium toxicity in Drosophila

https://doi.org/10.1016/j.neuroscience.2009.07.027Get rights and content

Abstract

Lithium is an efficacious drug for the treatment of mood disorders, and its application is also considered a potential therapy for brain damage. However, the mechanisms underlying lithium's therapeutic action and toxic effects in the nervous system remain largely elusive. Here we report on the use of a versatile genetic model, the fruit fly Drosophila melanogaster, to discover novel molecular components involved in the lithium-responsive neurobiological process. We previously identified CG15088, which encodes a putative nutrient amino acid transporter of the solute carrier 6 (SLC6) family, as one of the genes most significantly upregulated in response to lithium treatment. This gene was the only SLC6 gene induced by lithium, and was thus designated as Lithium-inducible SLC6 transporter or List. Either RNA interference (RNAi)–mediated knockdown or complete deletion of List resulted in a remarkable increase in the susceptibility of adult flies to lithium's toxic effects, whereas transgenic expression of wild-type List significantly suppressed the lithium hypersensitive phenotype of List-deficient flies. Other ions such as sodium, potassium and chloride did not induce List upregulation, nor did they affect the viability of flies with suppressed List expression. These results indicate that lithium's biochemical or physical properties, rather than general osmotic responses, are responsible for the lithium-induced upregulation of List, as well as for the lithium-susceptible phenotype observed in List knockdown flies. Interestingly, flies became significantly more susceptible to lithium toxicity when List RNAi was specifically expressed in glia than when it was expressed in neurons or muscles, which is consistent with potential glial expression of List. These results show that the List transporter confers resistance to lithium toxicity, possibly as a consequence of its amino acid transporter activity in CNS glia. Our results have provided a new avenue of investigation toward a better understanding of the molecular and cellular mechanisms that underlie lithium-responsive neurobiological process.

Section snippets

Fly stocks and culture conditions

Flies were reared at 25 °C in a 12-h light/dark cycle, on a conventional cornmeal/glucose/yeast/agar medium supplemented with the mold inhibitor methyl 4-hydroxybenzoate (0.05%). The Canton-S (CS) strain was used as the wild-type control. daughterless (da)-GAL4, Actin5C (Act5C)-GAL4, and tubulin (tub)-GAL4 were obtained from Wayne Johnson (University of Iowa, Iowa City, IA, USA). embryonic lethal abnormal vision (elav)-GAL4 on the X chromosome was obtained from Pam Geyer (University of Iowa,

An RNAi transgene effectively suppresses expression of the lithium-inducible SLC6 family transporter gene List

In our recent microarray-based gene expression analysis, CG15088 was identified as one of the genes in the Drosophila head that are most significantly upregulated by lithium treatment (Kasuya et al., 2009). CG15088 encodes a member of the SLC6 transporter family (Thimgan et al 2006, Romero-Calderon et al 2007). In the previous report (Miller et al., 2008), it was tentatively referred to as dmNAT2 for Drosophila melanogaster NAT2, based solely on its sequence similarity to the NAT1 gene, dmNAT1.

Discussion

Here we have shown that the suppression or complete deletion of List, the Drosophila lithium-inducible SLC6 gene that encodes a putative amino acid transporter, leads to a remarkable increase in the fly's susceptibility to lithium, and that glial expression of List is the primary requirement for resistance to lithium toxicity. Our results have identified the List transporter as a novel molecular player that is critically involved in mediating the physiological effects of lithium. In addition,

Acknowledgments

This study was supported by grants from the NIH (R03 MH078271), American Parkinson's Disease Association Research (APDA) and National Alliance for Research on Schizophrenia and Depression (NARSAD) to T.K.

References (57)

  • F. Presse et al.

    Lithium increases melanin-concentrating hormone mRNA stability and inhibits tyrosine hydroxylase gene expression in PC12 cells

    Brain Res Mol Brain Res

    (1997)
  • R.B. Rothman et al.

    Monoamine transporters and psychostimulant drugs

    Eur J Pharmacol

    (2003)
  • M. Schou

    Lithium treatment at 52

    J Affect Disord

    (2001)
  • M.S. Sonders et al.

    Channels in transporters

    Curr Opin Neurobiol

    (1996)
  • V.K. Tam et al.

    Nephrotic syndrome and renal insufficiency associated with lithium therapy

    Am J Kidney Dis

    (1996)
  • T. Turan et al.

    Effects of short- and long-term lithium treatment on kidney functioning in patients with bipolar mood disorder

    Prog Neuropsychopharmacol Biol Psychiatry

    (2002)
  • L. Willoughby et al.

    A comparison of Drosophila melanogaster detoxification gene induction responses for six insecticides, caffeine and phenobarbital

    Insect Biochem Mol Biol

    (2006)
  • P.X. Yuan et al.

    Lithium stimulates gene expression through the AP-1 transcription factor pathway

    Brain Res Mol Brain Res

    (1998)
  • Adityanjee et al.

    The syndrome of irreversible lithium-effectuated neurotoxicity

    Clin Neuropharmacol

    (2005)
  • S. Barolo et al.

    GFP and beta-galactosidase transformation vectors for promoter/enhancer analysis in Drosophila

    Biotechniques

    (2000)
  • S. Benzer

    Behavioral mutants of Drosophila isolated by countercurrent distribution

    Proc Natl Acad Sci U S A

    (1967)
  • Z. Berger et al.

    Lithium rescues toxicity of aggregate-prone proteins in Drosophila by perturbing Wnt pathway

    Hum Mol Genet

    (2005)
  • E. Berry-Kravis et al.

    Open-label treatment trial of lithium to target the underlying defect in fragile X syndrome

    J Dev Behav Pediatr

    (2008)
  • A. Bocchetta et al.

    Thyroid abnormalities during lithium treatment

    Acta Psychiatr Scand

    (1991)
  • E. Bossi et al.

    Ionic selectivity of the coupled and uncoupled currents carried by the amino acid transporter KAAT1

    Pflugers Arch

    (1999)
  • D.Y. Boudko et al.

    Ancestry and progeny of nutrient amino acid transporters

    Proc Natl Acad Sci U S A

    (2005)
  • G. Campbell et al.

    RK2, a glial-specific homeodomain protein required for embryonic nerve cord condensation and viability in Drosophila

    Development

    (1994)
  • M. Castagna et al.

    Molecular characteristics of mammalian and insect amino acid transporters: implications for amino acid homeostasis

    J Exp Biol

    (1997)
  • Cited by (10)

    • Molecular basis of essential amino acid transport from studies of insect nutrient amino acid transporters of the SLC6 family (NAT-SLC6)

      2012, Journal of Insect Physiology
      Citation Excerpt :

      CG15088 transporter-like protein has been identified by a lithium induced shift of its expression level (Kasuya et al., 2009a). It is expressed in the adult brain and required for lithium resistance (Kasuya et al., 2009b). However, putative transporter roles for both of these proteins have not been directly demonstrated.

    View all citing articles on Scopus
    View full text