Limits...
Activity-Dependent Bidirectional Regulation of GAD Expression in a Homeostatic Fashion Is Mediated by BDNF-Dependent and Independent Pathways.

Hanno-Iijima Y, Tanaka M, Iijima T - PLoS ONE (2015)

Bottom Line: Additional results indicated that these two GAD genes differ in their responsiveness to chronic changes in neuronal activity, which could be partially caused by differential dependence on BDNF.In parallel to activity-dependent bidirectional scaling in GAD expression, the present study further observed that a chronic change in neuronal activity leads to an alteration in neurotransmitter release from GABAergic neurons in a homeostatic, bidirectional fashion.Therefore, the differential expression of GAD65 and 67 during prolonged changes in neuronal activity may be implicated in some aspects of bidirectional homeostatic plasticity within mature GABAergic presynapses.

View Article: PubMed Central - PubMed

Affiliation: Tokai University Institute of Innovative Science and Technology, Medical Division, Kanagawa, Japan; School of Medicine, Tokai University, Kanagawa, Japan.

ABSTRACT
Homeostatic synaptic plasticity, or synaptic scaling, is a mechanism that tunes neuronal transmission to compensate for prolonged, excessive changes in neuronal activity. Both excitatory and inhibitory neurons undergo homeostatic changes based on synaptic transmission strength, which could effectively contribute to a fine-tuning of circuit activity. However, gene regulation that underlies homeostatic synaptic plasticity in GABAergic (GABA, gamma aminobutyric) neurons is still poorly understood. The present study demonstrated activity-dependent dynamic scaling in which NMDA-R (N-methyl-D-aspartic acid receptor) activity regulated the expression of GABA synthetic enzymes: glutamic acid decarboxylase 65 and 67 (GAD65 and GAD67). Results revealed that activity-regulated BDNF (brain-derived neurotrophic factor) release is necessary, but not sufficient, for activity-dependent up-scaling of these GAD isoforms. Bidirectional forms of activity-dependent GAD expression require both BDNF-dependent and BDNF-independent pathways, both triggered by NMDA-R activity. Additional results indicated that these two GAD genes differ in their responsiveness to chronic changes in neuronal activity, which could be partially caused by differential dependence on BDNF. In parallel to activity-dependent bidirectional scaling in GAD expression, the present study further observed that a chronic change in neuronal activity leads to an alteration in neurotransmitter release from GABAergic neurons in a homeostatic, bidirectional fashion. Therefore, the differential expression of GAD65 and 67 during prolonged changes in neuronal activity may be implicated in some aspects of bidirectional homeostatic plasticity within mature GABAergic presynapses.

No MeSH data available.


Related in: MedlinePlus

Chronically increased activity enhances GAD expression via a Ca2+-dependent mechanism triggered by NMDA-R activation.(A) Cultured cortical neurons were treated with 50 μM bicuculline in the presence or absence of AP5 (200 μM) on DIV14 for the final day in the culture and were harvested on DIV15. (B) Shows relative mRNA expression levels of GAD65 in cultured cortical neurons treated as shown in (A). F(2, 46) = 43.72 (p < .0001), one-way ANOVA. (n = 3–6 in each group). (C) Relative protein levels of GAD65, GAD67, NR1, and GluR2/3 measured by immunoblotting. Bicuculline induced a significant increase in GAD65 protein that was completely blocked by AP5. GAD67: F(2, 25) = 14.09; GAD65: F (2, 23) = 21.78 (p < .0001), one-way ANOVA. (n = 3–5 in each group). Bic: bicuculline.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4524701&req=5

pone.0134296.g002: Chronically increased activity enhances GAD expression via a Ca2+-dependent mechanism triggered by NMDA-R activation.(A) Cultured cortical neurons were treated with 50 μM bicuculline in the presence or absence of AP5 (200 μM) on DIV14 for the final day in the culture and were harvested on DIV15. (B) Shows relative mRNA expression levels of GAD65 in cultured cortical neurons treated as shown in (A). F(2, 46) = 43.72 (p < .0001), one-way ANOVA. (n = 3–6 in each group). (C) Relative protein levels of GAD65, GAD67, NR1, and GluR2/3 measured by immunoblotting. Bicuculline induced a significant increase in GAD65 protein that was completely blocked by AP5. GAD67: F(2, 25) = 14.09; GAD65: F (2, 23) = 21.78 (p < .0001), one-way ANOVA. (n = 3–5 in each group). Bic: bicuculline.

Mentions: We next checked the NMDA-R–mediated Ca2+ dependence of GAD expression. Increased expression of GAD65 with bicuculline treatment was dramatically reduced by the application of AP5, a selective blocker of Ca2+-permeable ion channels and NMDA-Rs (Fig 2A and 2B). This confirmed that GAD expression is actually dependent on NMDA-Rs. The same results were confirmed at the protein level. While bicuculline treatment strongly increased GAD65 protein by immunoblot analysis, this effect was completely blocked by AP5 (Fig 2C). However, while GAD67 definitely had a tendency to be up regulated, we did not observe a significant increase at the protein level (Fig 2C). In contrast, neither bicuculline nor AP5 significantly affected the protein level of any NMDA-R subunit tested (i.e., NR1, NR2A, and NR2B) (Fig 2C). Additionally, we showed that bicuculline-induced increases in GAD65 expression were nearly completely blocked with the transcription inhibitor actinomycin D (S1 Fig). These data reveal that dynamic changes in GAD expression are largely regulated through NMDA-R activity on the transcriptional level.


Activity-Dependent Bidirectional Regulation of GAD Expression in a Homeostatic Fashion Is Mediated by BDNF-Dependent and Independent Pathways.

Hanno-Iijima Y, Tanaka M, Iijima T - PLoS ONE (2015)

Chronically increased activity enhances GAD expression via a Ca2+-dependent mechanism triggered by NMDA-R activation.(A) Cultured cortical neurons were treated with 50 μM bicuculline in the presence or absence of AP5 (200 μM) on DIV14 for the final day in the culture and were harvested on DIV15. (B) Shows relative mRNA expression levels of GAD65 in cultured cortical neurons treated as shown in (A). F(2, 46) = 43.72 (p < .0001), one-way ANOVA. (n = 3–6 in each group). (C) Relative protein levels of GAD65, GAD67, NR1, and GluR2/3 measured by immunoblotting. Bicuculline induced a significant increase in GAD65 protein that was completely blocked by AP5. GAD67: F(2, 25) = 14.09; GAD65: F (2, 23) = 21.78 (p < .0001), one-way ANOVA. (n = 3–5 in each group). Bic: bicuculline.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4524701&req=5

pone.0134296.g002: Chronically increased activity enhances GAD expression via a Ca2+-dependent mechanism triggered by NMDA-R activation.(A) Cultured cortical neurons were treated with 50 μM bicuculline in the presence or absence of AP5 (200 μM) on DIV14 for the final day in the culture and were harvested on DIV15. (B) Shows relative mRNA expression levels of GAD65 in cultured cortical neurons treated as shown in (A). F(2, 46) = 43.72 (p < .0001), one-way ANOVA. (n = 3–6 in each group). (C) Relative protein levels of GAD65, GAD67, NR1, and GluR2/3 measured by immunoblotting. Bicuculline induced a significant increase in GAD65 protein that was completely blocked by AP5. GAD67: F(2, 25) = 14.09; GAD65: F (2, 23) = 21.78 (p < .0001), one-way ANOVA. (n = 3–5 in each group). Bic: bicuculline.
Mentions: We next checked the NMDA-R–mediated Ca2+ dependence of GAD expression. Increased expression of GAD65 with bicuculline treatment was dramatically reduced by the application of AP5, a selective blocker of Ca2+-permeable ion channels and NMDA-Rs (Fig 2A and 2B). This confirmed that GAD expression is actually dependent on NMDA-Rs. The same results were confirmed at the protein level. While bicuculline treatment strongly increased GAD65 protein by immunoblot analysis, this effect was completely blocked by AP5 (Fig 2C). However, while GAD67 definitely had a tendency to be up regulated, we did not observe a significant increase at the protein level (Fig 2C). In contrast, neither bicuculline nor AP5 significantly affected the protein level of any NMDA-R subunit tested (i.e., NR1, NR2A, and NR2B) (Fig 2C). Additionally, we showed that bicuculline-induced increases in GAD65 expression were nearly completely blocked with the transcription inhibitor actinomycin D (S1 Fig). These data reveal that dynamic changes in GAD expression are largely regulated through NMDA-R activity on the transcriptional level.

Bottom Line: Additional results indicated that these two GAD genes differ in their responsiveness to chronic changes in neuronal activity, which could be partially caused by differential dependence on BDNF.In parallel to activity-dependent bidirectional scaling in GAD expression, the present study further observed that a chronic change in neuronal activity leads to an alteration in neurotransmitter release from GABAergic neurons in a homeostatic, bidirectional fashion.Therefore, the differential expression of GAD65 and 67 during prolonged changes in neuronal activity may be implicated in some aspects of bidirectional homeostatic plasticity within mature GABAergic presynapses.

View Article: PubMed Central - PubMed

Affiliation: Tokai University Institute of Innovative Science and Technology, Medical Division, Kanagawa, Japan; School of Medicine, Tokai University, Kanagawa, Japan.

ABSTRACT
Homeostatic synaptic plasticity, or synaptic scaling, is a mechanism that tunes neuronal transmission to compensate for prolonged, excessive changes in neuronal activity. Both excitatory and inhibitory neurons undergo homeostatic changes based on synaptic transmission strength, which could effectively contribute to a fine-tuning of circuit activity. However, gene regulation that underlies homeostatic synaptic plasticity in GABAergic (GABA, gamma aminobutyric) neurons is still poorly understood. The present study demonstrated activity-dependent dynamic scaling in which NMDA-R (N-methyl-D-aspartic acid receptor) activity regulated the expression of GABA synthetic enzymes: glutamic acid decarboxylase 65 and 67 (GAD65 and GAD67). Results revealed that activity-regulated BDNF (brain-derived neurotrophic factor) release is necessary, but not sufficient, for activity-dependent up-scaling of these GAD isoforms. Bidirectional forms of activity-dependent GAD expression require both BDNF-dependent and BDNF-independent pathways, both triggered by NMDA-R activity. Additional results indicated that these two GAD genes differ in their responsiveness to chronic changes in neuronal activity, which could be partially caused by differential dependence on BDNF. In parallel to activity-dependent bidirectional scaling in GAD expression, the present study further observed that a chronic change in neuronal activity leads to an alteration in neurotransmitter release from GABAergic neurons in a homeostatic, bidirectional fashion. Therefore, the differential expression of GAD65 and 67 during prolonged changes in neuronal activity may be implicated in some aspects of bidirectional homeostatic plasticity within mature GABAergic presynapses.

No MeSH data available.


Related in: MedlinePlus