Interactions Between AMPA Receptors and 5HT2C Receptors: Is TARP γ8 Important?

Peter Donoghue1, Michael Spedding3, Abdel Ennaceur4, Megan Holmes2, Christopher Thompson1, Paul Chazot1

1Durham University, Durham, UK, 2Edinburgh Queen’s Medical Research Institute, Edinburgh, UK, 3Institute de Recherches Servier, Paris, France, 4Sunderland Pharmacy School, Sunderland, UK

AMPA receptors are known to not only mediate fast excitatory neurotransmission within the CNS, but to also possess an increasingly significant role in a variety of neurological mood disorders predominantly associated with other neurotransmitter systems (Bleakman et al 2007). 5HT2C receptors on the other hand, are a subtype of 5HT receptor predominantly expressed within the CNS and that have an identified role in a diverse range of mood disorders including anxiety and depression (Nunes-de-Souza et al 2008). A growing body of evidence suggests many neurological disorders contain a component from both of these neurotransmitter systems, with a wide variety of potential common interacting proteins, and as such potential drug targets for novel clinical agents, especially antidepressants. One such group of proteins are the Transmembrane AMPA receptor regulatory proteins (TARPs), a family of proteins (γ2, γ3, γ4, γ7, γ8) possessing roles in cell surface trafficking, synaptic targeting and AMPA receptor modulatory effects (Payne, 2008).

Using a novel antibody generated and demonstrating specificity for the C-terminal domain of the TARP γ8 isoform (Donoghue et al., 2007), we have utilised immunopurification techiniques (described in Payne et al 2006) to confirm association with AMPA receptor subunits GluR1 and GluR2 together with known AMPA receptor-interacting proteins (PSD-95 and MAP-1B). In addition, a 5HT2C receptor-like species associating with TARP γ8 was purified, confirmed using three commercial anti-5HT2C receptor antibodies.

In addition to a putative physical interaction between TARP γ8 and 5HT2C receptors within a multiprotein complex, potentially together with AMPA receptors, we have used ligand autoradiography, immunohistochemistry and immunoblotting techniques (Payne et al 2006) to provide new evidence for a functional interaction between AMPA receptors, TARP γ8 and 5HT2C receptors. By comparing mice with a knockdown in 5HT2C receptor expression (>75% decrease; mice produced by the laboratory of Prof. Megan Holmes) with their respective controls, we have identified profound differences in the levels of forebrain TARP γ8 receptor expression (66% increase in 5HT2C knockdown *p <0.05, n = 3 individual animals compared with control) and cortical [3H] AMPA binding levels (100% increase in 5HT2C knockdown *p <0.05, n = 3 individual animals, compared with control), in addition to altered expression of specific AMPA receptor subunits, GluR1 and GluR2. Current work is focused on characterising the nature of this apparent functional interaction.

This work was funded by a BBSRC/ Servier CASE award.

Bleakman et al (2007) CNS Neurol Disord Drug Targets 6:117-26

Donoghue et al (2007) Proceedings of the British Pharmacological Society at http://www.pa2online.org/abstracts/Vol5/Issue2abst050P.html

Nunes-de-Souza et al (2008) Behav Brain Res. 187:72-79

Payne (2008) Mol Membr Biol 25:353-62.

Payne et al (2006) J Neurosci. 26:8600-8608