Park et al. Mol Brain (2020) 13:145 https://doi.org/10.1186/s13041-020-00691-5 RESEARCH Open Access Selective role of the translin/trax RNase complex in hippocampal synaptic plasticity Alan Jung Park1,5*†, Mahesh Shivarama Shetty2,3†, Jay M. Baraban4 and Ted Abel1,2,3* Abstract Activity-dependent local protein synthesis is critical for synapse-specifc, persistent plasticity. Abnormalities in local protein synthesis have been implicated in psychiatric disorders. We have recently identifed the translin/trax micro- RNA-degrading enzyme as a novel mediator of protein synthesis at activated synapses. Additionally, translin knockout (KO) mice, which lack translin/trax, exhibit some of the behavioral abnormalities found in a mouse model of fragile X syndrome (fragile X mental retardation protein-FMRP-KO mice). Therefore, identifying signaling pathways interact- ing with translin/trax to support persistent synaptic plasticity is a translationally relevant goal. Here, as a frst step to achieve this goal, we have assessed the requirement of translin/trax for multiple hippocampal synaptic plasticity paradigms that rely on distinct molecular mechanisms. We found that mice lacking translin/trax exhibited selective impairment in a form of persistent hippocampal plasticity, which requires postsynaptic protein kinase A (PKA) activ- ity. In contrast, enduring forms of plasticity that are dependent on presynaptic PKA were unafected. Furthermore, these mice did not display exaggerated metabotropic glutamate receptor-mediated long-term synaptic depression (mGluR-LTD), a hallmark of the FMRP KO mice. On the contrary, translin KO mice exhibited defcits in N-methyl-D-as- partate receptor (NMDAR) dependent LTD, a phenotype not observed in the FMRP knockouts. Taken together, these fndings demonstrate that translin/trax mediates long-term synaptic plasticity that is dependent on postsynaptic PKA signaling and suggest that translin/trax and FMRP play distinct roles in hippocampal synaptic plasticity. Keywords: Translin, Trax, Long-term potentiation, Long-term depression, Local protein synthesis, Hippocampal synaptic plasticity, FMRP, RNA-binding protein, microRNA, PKA Introduction 3, 5]. Several RNA-binding proteins (RBPs) take part in Extensive evidence suggests that localization of key the trafcking and translational regulation of specifc mRNAs in the vicinity of synapses and activity-medi- mRNAs and thus allowing diversity in the mechanisms ated regulation of their translation contributes to per- engaged by diferent forms of plasticity [6–8]. Te RNA- sistent forms of synaptic plasticity related to long-term binding protein translin is an evolutionarily conserved memory [1–4]. Tis synapse-specifc, activity-dependent brain-enriched protein, which regulates RNA trafck- mechanism requires precisely regulated molecular sign- ing and translational control [9–12]. Together with its aling in presynaptic or postsynaptic compartments [2, partner protein, translin-associated factor X (trax), these proteins form a microRNA-degrading enzyme that *Correspondence: [email protected]; [email protected] can trigger protein synthesis by reversing microRNA- †Alan Jung Park and Mahesh Shivarama Shetty have contributed equally mediated silencing [13–15]. We have previously shown 1 Department of Biology, University of Pennsylvania, Philadelphia, PA, USA that the translin/trax RNase complex mediates activity- 5 Present Address: Gogos Lab, Mortimer B. Zuckerman Mind Brain Behavior Institute, Jerome L. Greene Science Center, Columbia University, dependent local synaptic protein synthesis required for L5-053, 3227 Broadway, New York, NY 10027, USA input-specifc heterosynaptic plasticity (synaptic tagging Full list of author information is available at the end of the article and capture) and memory formation [15]. However, the © The Author(s) 2020, corrected publication 2021. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creat iveco mmons .org/licen ses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/publi cdoma in/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Park et al. Mol Brain (2020) 13:145 Page 2 of 9 mechanisms that regulate translin/trax activity within glutamate receptors (mGluRs), was freshly prepared as a synaptic compartments have not been investigated. 10 mM solution in milliQ water and delivered at 100 μM Our previous fndings suggest that translin/trax may fnal concentration in aCSF as previously described [23]. interact with the cAMP-PKA signaling pathway. Specif- cally, the microRNA targets of translin/trax are predicted Electrophysiology to regulate the expression of PKA-anchoring proteins, Experiments were performed as described [15]. Briefy, cAMP-degrading phosphodiesterases (PDEs), cAMP- both male and female 2–5-month-old mice (4–6 weeks producing Gs-coupled β2-adrenergic receptors and old for LTD) were sacrifced by cervical dislocation adenylyl cyclases [15]. In fact, the cAMP-PKA signaling and hippocampi were quickly collected in chilled, oxy- pathway is highly localized within presynaptic or post- genated aCSF (124 mM NaCl, 4.4 mM KCl, 1.3 mM synaptic compartments by PKA-anchoring proteins and MgSO4⋅7H2O, 1 mM NaH2PO4⋅H2O, 26.2 mM NaHCO3, mediates protein synthesis required for persistent synap- 2.5 mM CaCl2⋅2H2O and 10 mM d-glucose) bubbled with tic plasticity and memory formation [16–20]. Terefore, 95% O2/5% CO2. 400 μm-thick transverse hippocampal investigating whether translin/trax interacts with PKA slices were prepared using a manual slicer (Stoelting) signaling within presynaptic or postsynaptic compart- and placed in an interface recording chamber at 28 °C ments can provide clues to understanding molecular (Fine Science Tools, Foster City, CA). Te slices were mechanisms linking translin/trax to synaptic plasticity constantly perfused with aCSF at 1 ml/min (or 2.5 ml/ and memory formation. min for the mGluR-LTD experiment). Slices were equili- In the present study, we determined the role of trans- brated for at least 2 h in aCSF. All the recordings were lin/trax in distinct forms of synaptic plasticity, which performed in the Schafer collateral synapses in the CA1 require presynaptic or postsynaptic PKA signaling. As stratum radiatum. Te stimulus intensity was set to trax protein is unstable in the absence of translin, in the elicit ~ 40% of the maximum feld-EPSP amplitude deter- current study we used translin KO mice, which lack both mined by an input–output curve in each experiment. translin and trax proteins [15, 21]. Te frst 20-min baseline values were averaged, and the average was used to normalize each initial fEPSP slope. Materials and methods Te input–output relationship was measured as previ- All experiments were performed according to the ously described [15]. To electrically induce long-term National Institutes of Health guidelines and were fully potentiation (LTP), spaced 4-train (four 1 s 100 Hz trains approved by the Institutional Animal Care and Use Com- delivered 5 min apart), massed 4-train (four 1 s 100 Hz mittee at the University of Pennsylvania and at the Uni- trains delivered 5 s apart), theta-burst stimulation (TBS, versity of Iowa. 15 bursts of four 100 Hz pulses delivered for a total of 3 s at 5 Hz), and one-train (one 1 s 100 Hz train) stimula- Translin knockout (KO) mice tion were delivered after 20 min baseline recordings. To Te generation and maintenance of translin KO mice chemically induce LTP, 50 μM of FSK in aCSF was bath (MGI: 2677496) were described previously [21, 22]. Mice applied to the slices for 15 min following 20-min base- were backcrossed to C57BL/6J for more than 15 genera- line recordings. To chemically induce LTD, 100 μM of tions. Heterozygous male and heterozygous female mice DHPG in aCSF was bath applied to the slices for 10 min were mated to produce homozygous translin KO mice following 20-min baseline recordings. For the NMDAR- and wildtype littermates. Mice were maintained on a 12 h LTD experiments, the stimulus intensity was set to light/12 h dark cycle with lights on at 8 am (ZT0). Food elicit ~ 50% of the maximal fEPSP amplitude determined and water were available ad libitum. All experiments were by an input–output curve in each experiment and LTD performed during the light cycle using translin KO mice was induced by a prolonged low-frequency stimulation and wildtype littermates as controls. 2- to 5-month-old (LFS) protocol (1 Hz, 15 min) [24, 25], following 20-min mice were used for all experiments except for the LTD baseline recordings. experiments in which 4- to 6-week-old mice were used. Western blotting Drugs Hippocampal tissue homogenization, protein separation Forskolin (FSK, Molecular grade, Sigma), an adenylyl and transfer to polyvinylidene difuoride (PVDF) mem- cyclase activator, was freshly prepared as a 50 mM solu- branes were performed as previously described [26]. tion in 100% ethanol and delivered at 50 μM fnal con- Membranes were blocked in 5% BSA or 5% non-fat milk centration in artifcial cerebrospinal fuid (aCSF) as in TBST and incubated with primary antibodies (trans- described before [19]. (RS)-3,5-Dihydroxyphenylglycine lin, 1:100,000; FMRP, 1:10,000, Millipore) overnight at (DHPG, Tocris), a potent agonist of group I metabotropic 4 °C.