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Small-conductance Ca2+-activated potassium type 2 channels regulate the formation of contextual fear memory.

Murthy SR, Sherrin T, Jansen C, Nijholt I, Robles M, Dolga AM, Andreotti N, Sabatier JM, Knaus HG, Penner R, Todorovic C, Blank T - PLoS ONE (2015)

Bottom Line: We provided the evidence that the post-training cleavage of the SK2 channels was responsible for the observed bidirectional effect of SK2 channel blockade on memory consolidation.Application of the synthetic peptide comprising a leucine-zipper domain of the C-terminal fragment to Jurkat cells impaired SK2 channel-mediated currents, indicating that the endogenously cleaved fragment might exert its effects on memory formation by blocking SK2 channel-mediated currents.The modulation of fear memory by down-regulating SK2 C-terminal cleavage might have applicability in the treatment of anxiety disorders in which fear conditioning is enhanced.

View Article: PubMed Central - PubMed

Affiliation: Section on Cellular Neurobiology, Program on Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland, United States of America.

ABSTRACT
Small-conductance, Ca2+ activated K+ channels (SK channels) are expressed at high levels in brain regions responsible for learning and memory. In the current study we characterized the contribution of SK2 channels to synaptic plasticity and to different phases of hippocampal memory formation. Selective SK2 antisense-treatment facilitated basal synaptic transmission and theta-burst induced LTP in hippocampal brain slices. Using the selective SK2 antagonist Lei-Dab7 or SK2 antisense probes, we found that hippocampal SK2 channels are critical during two different time windows: 1) blockade of SK2 channels before the training impaired fear memory, whereas, 2) blockade of SK2 channels immediately after the training enhanced contextual fear memory. We provided the evidence that the post-training cleavage of the SK2 channels was responsible for the observed bidirectional effect of SK2 channel blockade on memory consolidation. Thus, Lei-Dab7-injection before training impaired the C-terminal cleavage of SK2 channels, while Lei-Dab7 given immediately after training facilitated the C-terminal cleavage. Application of the synthetic peptide comprising a leucine-zipper domain of the C-terminal fragment to Jurkat cells impaired SK2 channel-mediated currents, indicating that the endogenously cleaved fragment might exert its effects on memory formation by blocking SK2 channel-mediated currents. Our present findings suggest that SK2 channel proteins contribute to synaptic plasticity and memory not only as ion channels but also by additionally generating a SK2 C-terminal fragment, involved in both processes. The modulation of fear memory by down-regulating SK2 C-terminal cleavage might have applicability in the treatment of anxiety disorders in which fear conditioning is enhanced.

No MeSH data available.


Related in: MedlinePlus

Cleavage of SK2 channel protein after contextual fear conditioning training.Western blot analysis of SK2 protein levels in (A) hippocampal tissue obtained from naïve mice or 1 h and 3 h after training (context+shock). In the context group, mice were exposed to the training context without receiving a foot-shock. In the shock group, mice received a foot-shock immediately after they were exposed to the training context and were removed immediately after the foot-shock. Experiment was performed twice. (B) Representative immunoblot of SK2 protein levels in hippocampal tissue from naïve, trained and trained vehicle- or Lei-Dab7-injected mice. Mice were injected either 0.5 h before or 0 h after training as indicated. Hippocampal tissue was removed 1 h after training. The SK2(538–555) antibody recognized the 64-kDa SK2 protein and a 10-kDa SK2 C-terminal fragment (top). (C) SK2 protein levels in hippocampal tissue from naïve non-injected, Lei-Dab7-injected naïve, or vehicle-injected trained mice. Hippocampal tissue was removed 90 or 210 min after injection (1h and/or 3h after training). The number of individual samples per treatment was five. Data presented are the mean ± SEM. Statistically significant differences: *p < 0.05 versus naive, #p < 0.005 versus 3 hours context and conditioning groups, ap<0.05 versus training + vehicle.
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pone.0127264.g005: Cleavage of SK2 channel protein after contextual fear conditioning training.Western blot analysis of SK2 protein levels in (A) hippocampal tissue obtained from naïve mice or 1 h and 3 h after training (context+shock). In the context group, mice were exposed to the training context without receiving a foot-shock. In the shock group, mice received a foot-shock immediately after they were exposed to the training context and were removed immediately after the foot-shock. Experiment was performed twice. (B) Representative immunoblot of SK2 protein levels in hippocampal tissue from naïve, trained and trained vehicle- or Lei-Dab7-injected mice. Mice were injected either 0.5 h before or 0 h after training as indicated. Hippocampal tissue was removed 1 h after training. The SK2(538–555) antibody recognized the 64-kDa SK2 protein and a 10-kDa SK2 C-terminal fragment (top). (C) SK2 protein levels in hippocampal tissue from naïve non-injected, Lei-Dab7-injected naïve, or vehicle-injected trained mice. Hippocampal tissue was removed 90 or 210 min after injection (1h and/or 3h after training). The number of individual samples per treatment was five. Data presented are the mean ± SEM. Statistically significant differences: *p < 0.05 versus naive, #p < 0.005 versus 3 hours context and conditioning groups, ap<0.05 versus training + vehicle.

Mentions: To gain further insights into the mechanisms by which SK2 channels are involved in contextual fear memory consolidation, we performed Western immunoblots to analyze hippocampal SK2 protein levels in naïve mice and 1 h or 3 h after the training procedure with the help of an SK2 antibody raised against an epitope from the distal C-terminal domain [16]. We detected the expected 64-kDa protein band corresponding to full-length SK2 and a 10-kDa protein band 1 h and 3 h after fear conditioning and exposure to the context alone (ANOVA, F6, 28 = 10.3; p < 0.05) (Bonferroni correction; p < 0.05 vs. naïve mice). The SK2 10-kDa band intensity obtained with the 3 h samples was decreased when compared to the 10-kDa band intensity detected with the 1 h samples (Bonferroni corrections; #p < 0.05; 1 h training/context vs. 3 h training/context groups). This SK2 10-kDa band was absent in hippocampal lysates from naïve mice as well as in the shock control group (Fig 5A).


Small-conductance Ca2+-activated potassium type 2 channels regulate the formation of contextual fear memory.

Murthy SR, Sherrin T, Jansen C, Nijholt I, Robles M, Dolga AM, Andreotti N, Sabatier JM, Knaus HG, Penner R, Todorovic C, Blank T - PLoS ONE (2015)

Cleavage of SK2 channel protein after contextual fear conditioning training.Western blot analysis of SK2 protein levels in (A) hippocampal tissue obtained from naïve mice or 1 h and 3 h after training (context+shock). In the context group, mice were exposed to the training context without receiving a foot-shock. In the shock group, mice received a foot-shock immediately after they were exposed to the training context and were removed immediately after the foot-shock. Experiment was performed twice. (B) Representative immunoblot of SK2 protein levels in hippocampal tissue from naïve, trained and trained vehicle- or Lei-Dab7-injected mice. Mice were injected either 0.5 h before or 0 h after training as indicated. Hippocampal tissue was removed 1 h after training. The SK2(538–555) antibody recognized the 64-kDa SK2 protein and a 10-kDa SK2 C-terminal fragment (top). (C) SK2 protein levels in hippocampal tissue from naïve non-injected, Lei-Dab7-injected naïve, or vehicle-injected trained mice. Hippocampal tissue was removed 90 or 210 min after injection (1h and/or 3h after training). The number of individual samples per treatment was five. Data presented are the mean ± SEM. Statistically significant differences: *p < 0.05 versus naive, #p < 0.005 versus 3 hours context and conditioning groups, ap<0.05 versus training + vehicle.
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pone.0127264.g005: Cleavage of SK2 channel protein after contextual fear conditioning training.Western blot analysis of SK2 protein levels in (A) hippocampal tissue obtained from naïve mice or 1 h and 3 h after training (context+shock). In the context group, mice were exposed to the training context without receiving a foot-shock. In the shock group, mice received a foot-shock immediately after they were exposed to the training context and were removed immediately after the foot-shock. Experiment was performed twice. (B) Representative immunoblot of SK2 protein levels in hippocampal tissue from naïve, trained and trained vehicle- or Lei-Dab7-injected mice. Mice were injected either 0.5 h before or 0 h after training as indicated. Hippocampal tissue was removed 1 h after training. The SK2(538–555) antibody recognized the 64-kDa SK2 protein and a 10-kDa SK2 C-terminal fragment (top). (C) SK2 protein levels in hippocampal tissue from naïve non-injected, Lei-Dab7-injected naïve, or vehicle-injected trained mice. Hippocampal tissue was removed 90 or 210 min after injection (1h and/or 3h after training). The number of individual samples per treatment was five. Data presented are the mean ± SEM. Statistically significant differences: *p < 0.05 versus naive, #p < 0.005 versus 3 hours context and conditioning groups, ap<0.05 versus training + vehicle.
Mentions: To gain further insights into the mechanisms by which SK2 channels are involved in contextual fear memory consolidation, we performed Western immunoblots to analyze hippocampal SK2 protein levels in naïve mice and 1 h or 3 h after the training procedure with the help of an SK2 antibody raised against an epitope from the distal C-terminal domain [16]. We detected the expected 64-kDa protein band corresponding to full-length SK2 and a 10-kDa protein band 1 h and 3 h after fear conditioning and exposure to the context alone (ANOVA, F6, 28 = 10.3; p < 0.05) (Bonferroni correction; p < 0.05 vs. naïve mice). The SK2 10-kDa band intensity obtained with the 3 h samples was decreased when compared to the 10-kDa band intensity detected with the 1 h samples (Bonferroni corrections; #p < 0.05; 1 h training/context vs. 3 h training/context groups). This SK2 10-kDa band was absent in hippocampal lysates from naïve mice as well as in the shock control group (Fig 5A).

Bottom Line: We provided the evidence that the post-training cleavage of the SK2 channels was responsible for the observed bidirectional effect of SK2 channel blockade on memory consolidation.Application of the synthetic peptide comprising a leucine-zipper domain of the C-terminal fragment to Jurkat cells impaired SK2 channel-mediated currents, indicating that the endogenously cleaved fragment might exert its effects on memory formation by blocking SK2 channel-mediated currents.The modulation of fear memory by down-regulating SK2 C-terminal cleavage might have applicability in the treatment of anxiety disorders in which fear conditioning is enhanced.

View Article: PubMed Central - PubMed

Affiliation: Section on Cellular Neurobiology, Program on Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland, United States of America.

ABSTRACT
Small-conductance, Ca2+ activated K+ channels (SK channels) are expressed at high levels in brain regions responsible for learning and memory. In the current study we characterized the contribution of SK2 channels to synaptic plasticity and to different phases of hippocampal memory formation. Selective SK2 antisense-treatment facilitated basal synaptic transmission and theta-burst induced LTP in hippocampal brain slices. Using the selective SK2 antagonist Lei-Dab7 or SK2 antisense probes, we found that hippocampal SK2 channels are critical during two different time windows: 1) blockade of SK2 channels before the training impaired fear memory, whereas, 2) blockade of SK2 channels immediately after the training enhanced contextual fear memory. We provided the evidence that the post-training cleavage of the SK2 channels was responsible for the observed bidirectional effect of SK2 channel blockade on memory consolidation. Thus, Lei-Dab7-injection before training impaired the C-terminal cleavage of SK2 channels, while Lei-Dab7 given immediately after training facilitated the C-terminal cleavage. Application of the synthetic peptide comprising a leucine-zipper domain of the C-terminal fragment to Jurkat cells impaired SK2 channel-mediated currents, indicating that the endogenously cleaved fragment might exert its effects on memory formation by blocking SK2 channel-mediated currents. Our present findings suggest that SK2 channel proteins contribute to synaptic plasticity and memory not only as ion channels but also by additionally generating a SK2 C-terminal fragment, involved in both processes. The modulation of fear memory by down-regulating SK2 C-terminal cleavage might have applicability in the treatment of anxiety disorders in which fear conditioning is enhanced.

No MeSH data available.


Related in: MedlinePlus