Small conductance Ca-activated K channels (SK channels) affect excitability and contribute to shaping excitatory postsynaptic potentials (EPSPs). SK2 channels are expressed throughout the dendritic arbors of hippocampal CA1 neurons and contribute to synaptic plasticity and learning and memory. We have recently found that the SK2 gene encodes two isoforms of the SK2 protein. SK2-L contains an additional 209 N- terminal amino acids compared to SK2-S that is completely contained within the SK2-L protein. In mice that selectively lack the SK2-L isoform (SK2-Sonly) dendritic and spine expression is drastically reduced and the SK2 channel contribution to synaptically evoked EPSPs is abolished. These results form the basis for the overriding hypothesis of this application: The unique SK2-L N-terminal domain confers dendritic and spine localization and function to SK2 channels that is accomplished by selective association with targeting proteins. We will use an integrated repertoire of electrophysiology, immunoEM, molecular biology, and biochemistry to test the following specific hypotheses. 1. Hypothesis: The loss of either isoform alters CA1 cellular physiology and hippocampal-dependent learning. Use SK2-Sonly and SK2-Lonly mice to determine: A) the subcellular distributions of SK2-L and SK2-S in CA1 neurons;B) the effects of SK2-S and SK2-L on synaptic plasticity and EPSPs, and on SK2 internalization following the induction of LTP;C) memory encoding in hippocampal-dependent spatial and non-spatial learning tasks. WT, SK2-Sonly/SK2-Lonly, and SK2-/- mice will serve as controls. 2. Hypothesis: The SK2-L N-terminus contains determinants that are necessary and sufficient for dendritic targeting. A) Determine the subcellular distributions of SK2-S, or SK2-L without or with SK2-S expressed in hippocampal neurons from SK2-/- mice that lack both SK2 isoforms. B) i. Identify the domains responsible for dendritic localization;ii. Determine whether these motifs are autonomous. 3. Hypothesis: Proteomics using SK2-Lonly or SK2-Sonly mice will identify proteins that specifically co-assemble with SK2-L subunits and mediate dendritic targeting. Protein complexes associated with SK2 channels will be immunopurified from SK2-Lonly or SK2-Sonly mouse brain using an antibody specific for SK2-L, or a pan-SK2 antibody, respectively. Parallel experiments using SK2-/- mice will serve as a negative control. Proteins that specifically co-assemble with SK2-L will be identified by mass spectrometry and investigated for their functional significance.

Public Health Relevance

SK2 channels, one type of Ca2+-activated K+ channel, influence learning and memory. Blocking SK2 channels facilitates learning in animal models of brain damage, and reverses the navigation failure in an animal model associated with the development of cognitive disorders in Alzheimer's disease as well as during normal brain aging. These studies will reveal novel mechanisms for how SK2 channels influence information processing and storage in the brain, and will suggest novel interventional strategies that target different isoforms of SK2 channels to treat learning deficits associated with trauma, pathology and normal aging.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS038880-13
Application #
8399100
Study Section
Neurotransporters, Receptors, and Calcium Signaling Study Section (NTRC)
Program Officer
Talley, Edmund M
Project Start
2000-07-01
Project End
2014-11-30
Budget Start
2012-12-01
Budget End
2014-11-30
Support Year
13
Fiscal Year
2013
Total Cost
$361,928
Indirect Cost
$126,910
Name
Oregon Health and Science University
Department
Neurosciences
Type
Schools of Medicine
DUNS #
096997515
City
Portland
State
OR
Country
United States
Zip Code
97239
Wang, Kang; Lin, Mike T; Adelman, John P et al. (2014) Distinct Ca2+ sources in dendritic spines of hippocampal CA1 neurons couple to SK and Kv4 channels. Neuron 81:379-87
Wu, Wendy W; Bryant, Damani N; Dorsa, Daniel M et al. (2013) Ovarian hormone loss impairs excitatory synaptic transmission at hippocampal CA3-CA1 synapses. J Neurosci 33:16158-69
McKay, Bridget M; Oh, M Matthew; Galvez, Roberto et al. (2012) Increasing SK2 channel activity impairs associative learning. J Neurophysiol 108:863-70
Wu, Wendy W; Adelman, John P; Maylie, James (2011) Ovarian hormone deficiency reduces intrinsic excitability and abolishes acute estrogen sensitivity in hippocampal CA1 pyramidal neurons. J Neurosci 31:2638-48
Allen, Duane; Bond, Chris T; Lujan, Rafael et al. (2011) The SK2-long isoform directs synaptic localization and function of SK2-containing channels. Nat Neurosci 14:744-9
Lin, Mike T; Lujan, Rafael; Watanabe, Masahiko et al. (2010) Coupled activity-dependent trafficking of synaptic SK2 channels and AMPA receptors. J Neurosci 30:11726-34
Lujan, Rafael; Maylie, James; Adelman, John P (2009) New sites of action for GIRK and SK channels. Nat Rev Neurosci 10:475-80
Thorneloe, K S; Knorn, A M; Doetsch, P E et al. (2008) Small-conductance, Ca(2+) -activated K+ channel 2 is the key functional component of SK channels in mouse urinary bladder. Am J Physiol Regul Integr Comp Physiol 294:R1737-43
Zhang, Qian; Timofeyev, Valeriy; Lu, Ling et al. (2008) Functional roles of a Ca2+-activated K+ channel in atrioventricular nodes. Circ Res 102:465-71
Stackman Jr, Robert W; Bond, Chris T; Adelman, John P (2008) Contextual memory deficits observed in mice overexpressing small conductance Ca2+-activated K+ type 2 (KCa2.2, SK2) channels are caused by an encoding deficit. Learn Mem 15:208-13

Showing the most recent 10 out of 15 publications