Publicação
Regulation of hnRNP A2/B1 and hnRNP K by synaptic activity and BDNF in the hippocampus
| Resumo: | Synaptic plasticity describes the process by which connections between neurons, or synapses, change in strength. By definition, it is a functional term referring to an increase or decrease in synaptic efficacy, which is accompanied by structural changes at synapses.Long-term potentiation (LTP) is the most studied form of synaptic plasticity and it has been widely recognized that synaptic changes that underpin certain forms of learning and memory may be similar to those involved in the expression of LTP. Some of the structural, biochemical and functional modifications at the synapse associated with synaptic plasticity require activity-dependent transport and translation of dendritic-localized mRNAs, with concomitant alterations in the synaptic proteome. It is becoming evident that dendritic protein synthesis has a crucial role in several forms of synaptic plasticity, including brain-derived neurotrophic factor (BDNF)-mediated LTP. Dendritic transcripts required for local protein synthesis are transported in a repressed state along the microtubule cytoskeleton as components of large messenger ribonucleoprotein complexes (mRNPs). In order to be transported, dendritic mRNAs must contain a cis-acting element in their sequence that is recognized by specific RNA binding proteins that, together with other factors, form a functional mRNP granule that engage with motor proteins for the transport. When they reach their destination, usually in, or in the vicinity of activated synapses, the translational-block is relieved and the mRNAs are translated upon neuronal activation. Among the molecular components of neuronal mRNPs, there are several members of the heterogeneous nuclear ribonucleoprotein (hnRNP) family of proteins. hnRNP A2/B1 is one of the best described trans-acting factor involved in the transport of dendritic-localized mRNAs in neurons, but whether this is a constitutive or a regulated process is unknown. hnRNP K is another member of the hnRNP family of proteins present in neuronal mRNPs, but the function of hnRNP K in neurons, and whether this protein plays a role in dendritic mRNA metabolism, remains to be determined. Here we show that both hnRNP A2/B1 and hnRNP K accumulate in dendrites and at the synapse following neuronal activation in hippocampal neurons. Importantly, the activity-dependent delivery of hnRNP A2/B1 into synaptic sites requires BDNF. In addition, we observed that this neurotrophin also upregulates the dendritic and synaptic levels of hnRNP K and hnRNP A2/B1 in primary cultures of hippocampal neurons. Previous studies from our laboratory identified several transcripts associated with hnRNP K in cultured hippocampal neurons, including mRNAs coding for proteins with roles in synaptic plasticity such as GluA1, GluN1, BDNF and CaMKIIẞ. In addition, we demonstrated that the neurotrophin BDNF induces the release of these transcripts from the hnRNPK-containing mRNPs in hippocampal neurons. Herein we show that BDNF also promotes the dissociation of hnRNPK-bound mRNAs locally at the synapse. These results suggest a key role for hnRNP K in the local translation of several proteins that contribute to the late phase of LTP. Accordingly, we demonstrate that hnRNP K-associated mRNAs are differentially regulated during high-frequency stimulation (HFS)-induced LTP in the perforant path-dentate gyrus synapse in live anesthetized rats. Importantly, we show that this form of synaptic potentiation requires TrkB (tropomyosin-related kinase B) signaling. Although our results indicate that BDNF induces the release of the transcripts bound to mRNPs containing hnRNP K, at this time point it is not possible to rule out the contribution of other RNA-binding proteins that were found to co-immunoprecipitate with hnRNP K in a proteomic screen. Altogether, our data support the evidence available pointing to a prominent role of hnRNP A2/B1 in the delivery of transcripts into dendritic domains and suggest that this process is regulated by synaptic activity and by the neurotrophin BDNF. Furthermore, we show that BDNF is required for the activity-induced synaptic delivery of hnRNP A2/B1. We also show that hnRNP K is another hnRNP that is likely to have a major role in the regulation of local mRNA metabolism in dendrites. Ourresults show that hnRNP K and hnRNP K-associated mRNAs are regulated by synaptic activity and BDNF, both in vitro and in vivo,and suggest hnRNP K as an important regulator of neuronal function, in particularin BDNF-induced plasticity events. |
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| Autores principais: | Leal, Graciano |
| Assunto: | Long-term potentiation Hippocampus BDNF hnRNP A2/B1 hnRNP K |
| Ano: | 2014 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso embargado |
| Instituição associada: | Universidade de Coimbra |
| Idioma: | inglês |
| Origem: | Estudo Geral - Universidade de Coimbra |
| Resumo: | Synaptic plasticity describes the process by which connections between neurons, or synapses, change in strength. By definition, it is a functional term referring to an increase or decrease in synaptic efficacy, which is accompanied by structural changes at synapses.Long-term potentiation (LTP) is the most studied form of synaptic plasticity and it has been widely recognized that synaptic changes that underpin certain forms of learning and memory may be similar to those involved in the expression of LTP. Some of the structural, biochemical and functional modifications at the synapse associated with synaptic plasticity require activity-dependent transport and translation of dendritic-localized mRNAs, with concomitant alterations in the synaptic proteome. It is becoming evident that dendritic protein synthesis has a crucial role in several forms of synaptic plasticity, including brain-derived neurotrophic factor (BDNF)-mediated LTP. Dendritic transcripts required for local protein synthesis are transported in a repressed state along the microtubule cytoskeleton as components of large messenger ribonucleoprotein complexes (mRNPs). In order to be transported, dendritic mRNAs must contain a cis-acting element in their sequence that is recognized by specific RNA binding proteins that, together with other factors, form a functional mRNP granule that engage with motor proteins for the transport. When they reach their destination, usually in, or in the vicinity of activated synapses, the translational-block is relieved and the mRNAs are translated upon neuronal activation. Among the molecular components of neuronal mRNPs, there are several members of the heterogeneous nuclear ribonucleoprotein (hnRNP) family of proteins. hnRNP A2/B1 is one of the best described trans-acting factor involved in the transport of dendritic-localized mRNAs in neurons, but whether this is a constitutive or a regulated process is unknown. hnRNP K is another member of the hnRNP family of proteins present in neuronal mRNPs, but the function of hnRNP K in neurons, and whether this protein plays a role in dendritic mRNA metabolism, remains to be determined. Here we show that both hnRNP A2/B1 and hnRNP K accumulate in dendrites and at the synapse following neuronal activation in hippocampal neurons. Importantly, the activity-dependent delivery of hnRNP A2/B1 into synaptic sites requires BDNF. In addition, we observed that this neurotrophin also upregulates the dendritic and synaptic levels of hnRNP K and hnRNP A2/B1 in primary cultures of hippocampal neurons. Previous studies from our laboratory identified several transcripts associated with hnRNP K in cultured hippocampal neurons, including mRNAs coding for proteins with roles in synaptic plasticity such as GluA1, GluN1, BDNF and CaMKIIẞ. In addition, we demonstrated that the neurotrophin BDNF induces the release of these transcripts from the hnRNPK-containing mRNPs in hippocampal neurons. Herein we show that BDNF also promotes the dissociation of hnRNPK-bound mRNAs locally at the synapse. These results suggest a key role for hnRNP K in the local translation of several proteins that contribute to the late phase of LTP. Accordingly, we demonstrate that hnRNP K-associated mRNAs are differentially regulated during high-frequency stimulation (HFS)-induced LTP in the perforant path-dentate gyrus synapse in live anesthetized rats. Importantly, we show that this form of synaptic potentiation requires TrkB (tropomyosin-related kinase B) signaling. Although our results indicate that BDNF induces the release of the transcripts bound to mRNPs containing hnRNP K, at this time point it is not possible to rule out the contribution of other RNA-binding proteins that were found to co-immunoprecipitate with hnRNP K in a proteomic screen. Altogether, our data support the evidence available pointing to a prominent role of hnRNP A2/B1 in the delivery of transcripts into dendritic domains and suggest that this process is regulated by synaptic activity and by the neurotrophin BDNF. Furthermore, we show that BDNF is required for the activity-induced synaptic delivery of hnRNP A2/B1. We also show that hnRNP K is another hnRNP that is likely to have a major role in the regulation of local mRNA metabolism in dendrites. Ourresults show that hnRNP K and hnRNP K-associated mRNAs are regulated by synaptic activity and BDNF, both in vitro and in vivo,and suggest hnRNP K as an important regulator of neuronal function, in particularin BDNF-induced plasticity events. |
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