Amyloid-β(25-35) Modulates the Expression of GirK and KCNQ Channel Genes in the Hippocampus

PLoS One. 2015 Jul 28;10(7):e0134385. doi: 10.1371/journal.pone.0134385. eCollection 2015.

Abstract

During early stages of Alzheimer's disease (AD), synaptic dysfunction induced by toxic amyloid-β (Aβ) is present before the accumulation of histopathological hallmarks of the disease. This scenario produces impaired functioning of neuronal networks, altered patterns of synchronous activity and severe functional deficits mainly due to hyperexcitability of hippocampal networks. The molecular mechanisms underlying these alterations remain unclear but functional evidence, shown by our laboratory and others, points to the involvement of receptors/channels which modulate neuronal excitability, playing a pivotal role in early Aβ-induced AD pathogenesis. In particular, two potassium channels that control neuronal excitability, G protein-coupled activated inwardly-rectifying potassium channel (GirK), and voltage-gated K channel (KCNQ), have been recently linked to Aβ pathophysiology in the hippocampus. Specifically, by using Aβ25-35, we previously found that GirK conductance is greatly decreased in the hippocampus, and similar effects have also been reported on KCNQ conductance. Thus, in the present study, our goal was to determine the effect of Aβ on the transcriptional expression pattern of 17 genes encoding neurotransmitter receptors and associated channels which maintain excitatory-inhibitory neurotransmission balance in hippocampal circuits, with special focus in potassium channels. For this purpose, we designed a systematic and reliable procedure to analyze mRNA expression by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) in hippocampal rat slices incubated with Aβ25-35. We found that: 1) Aβ down-regulated mRNA expression of ionotropic GluN1 and metabotropic mGlu1 glutamate receptor subunits as previously reported in other AD models; 2) Aβ also reduced gene expression levels of GirK2, 3, and 4 subunits, and KCNQ2 and 3 subunits, but did not change expression levels of its associated GABAB and M1 receptors, respectively. Our results provide evidence that Aβ can modulate the expression of these channels which could affect the hippocampal activity balance underlying learning and memory processes impaired in AD.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amyloid beta-Peptides / pharmacology*
  • Animals
  • G Protein-Coupled Inwardly-Rectifying Potassium Channels / genetics*
  • Gene Expression Regulation / drug effects*
  • Hippocampus / drug effects
  • Hippocampus / metabolism*
  • Hippocampus / pathology
  • KCNQ Potassium Channels / genetics*
  • Peptide Fragments / pharmacology*
  • RNA, Messenger / genetics
  • Rats
  • Rats, Wistar
  • Real-Time Polymerase Chain Reaction
  • Reverse Transcriptase Polymerase Chain Reaction

Substances

  • Amyloid beta-Peptides
  • G Protein-Coupled Inwardly-Rectifying Potassium Channels
  • KCNQ Potassium Channels
  • Peptide Fragments
  • RNA, Messenger
  • amyloid beta-protein (25-35)

Grant support

This work was supported by Spanish Ministry of Economy and Competitivity Grants (BFU2009-07341 to JY; SAF2010-14878 and BFU2011-22740 to JDNL; BFU2014-56164-P to LJD and JDNL); Fundación Eugenio Rodríguez Pascual to JDNL; Fundación Tatiana Pérez de Guzmán el Bueno to LJD. JDNL held a Ramón y Cajal Research Fellow (RYC-2009-03827). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.