Caveolin-1 Knockout Mice Exhibit Impaired Induction of Mglur-Dependent Long-Term Depression at CA3- CA1 Synapses

Caveolin-1 knockout mice exhibit impaired induction of mGluR-dependent long-term depression at CA3- CA1 synapses Yukihiro Takayasu1, Koichi Takeuchi2, Ranju Kumari2, Michael V. L. Bennett3, R. Suzanne Zukin, and Anna Francesconi3 The Dominick P. Purpura Department of Neuroscience, The Albert Einstein College of Medicine, Bronx, NY 10461 Contributed by Michael V. L. Bennett, October 15, 2010 (sent for review October 5, 2010) Group I metabotropic glutamate receptors (mGluR1/5) are impor- extracellular signal-regulated kinase (ERK) signaling (16). Cor- −/− tant to synaptic circuitry formation during development and to tical neurons from Cav1 mice show enhanced basal ERK1/2 forms of activity-dependent synaptic plasticity. Dysregulation of phosphorylation and prolonged phosphorylation/activation of mGluR1/5 signaling is implicated in some disorders of neuro- ERK1/2 in response to stimulation by the group I mGluR-se- development, including fragile X syndrome, the most common lective agonist DHPG (16). However, the full impact of caveolin- inherited form of intellectual disabilities and leading cause of 1 on synaptic function and plasticity is unclear. autism. Site(s) in the intracellular loops of mGluR1/5 directly bind Activation of group I mGluRs elicits long-term depression caveolin-1, an adaptor protein that associates with membrane (mGluR-LTD) at Schaffer collateral-CA1 (Sch-CA1) synapses, rafts. Caveolin-1 is the main coat component of caveolae and a form of NMDA receptor (NMDAR)-independent synaptic plasticity (22) that requires de novo protein synthesis in the adult organizes macromolecular signaling complexes with effector – proteins and membrane receptors. We report that long-term (23 27). mGluR-LTD induced by DHPG is absent in the mGluR5 KO mouse (24). In the present study, we examined mGluR-LTD at depression (LTD) elicited by a single application of the group I Cav1−/− Cav1−/− mGluR selective agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) these synapses in mice lacking caveolin-1 ( ). mice are viable and fertile (28, 29), although they develop pathological was markedly attenuated at Schaffer collateral-CA1 synapses of −/− features including vascular and pulmonary dysfunction and im- mice lacking caveolin-1 (Cav1 ), as assessed by field recording. In paired liver regeneration (15). They do not show gross neuroan- contrast, multiple applications of DHPG produced LTD comparable atomical abnormalities, but they do exhibit motor and behavioral to that in WT mice. Passive membrane properties, basal glutama- deficits, including decreased exploratory activity, impaired spatial tergic transmission and NMDA receptor (NMDAR)-dependent LTD memory, and increased anxiety (30, 31). were unaltered. The remaining LTD was reduced by anisomycin, Here, we report that mGluR-LTD at Schaffer collateral-CA1 −/− an inhibitor of protein synthesis, by U0126, an inhibitor of MEK1/2 synapses of Cav1 mice induced by a single brief (5 min) kinases, and by rapamycin, an inhibitor of mammalian target of application of (RS)-3,5-dihydroxyphenylglycine (DHPG) was rapamycin (mTOR), suggesting mediation by the same mechanisms markedly reduced relative to that in wild-type (WT) mice. In- as in WT. mGluR1/5-dependent activation (phosphorylation) of creasing the duration of DHPG application had little or no effect MEK and extracellular signal-regulated kinase (ERK1/2) was al- on the magnitude of LTD. Multiple applications of DHPG in- −/− −/− tered in Cav1 mice; basal phosphorylation was increased, but creased the LTD; the saturating level was the same in Cav1 a single application of DHPG had no further effect, and after mice as in WT, but more applications were required. Basal −/− DHPG, phosphorylation was similar in WT and Cav1 mice. Taken glutamatergic synaptic transmission, presynaptic function, and together, our findings suggest that caveolin-1 is required for nor- NMDAR-dependent LTD were normal. Basal phosphorylation mal coupling of mGluR1/5 to downstream signaling cascades and of MEK and ERK1/2, signaling kinases required for the in- induction of mGluR-LTD. duction of mGluR-LTD, were elevated in the hippocampus of −/− Cav1 mice, but were not further increased by brief application fi roup I metabotropic glutamate receptors (mGluRs), of DHPG. Together, these ndings suggest that caveolin-1 fi GmGluR1 and mGluR5, are G protein-coupled receptors orchestrates signaling events required for ef cacious induction of enriched at excitatory synapses throughout the brain, where they mGluR-LTD at CA1 synapses. regulate neuronal excitation (1, 2). mGluR1/5s play an important Results role in the establishment of synaptic circuitry during brain de- −/− velopment (3, 4) and in activity-dependent forms of synaptic mGluR-LTD at Sch-CA1 Synapses Is Impaired in Cav1 Mice. Acti- plasticity, including long-term potentiation and long-term de- vation of group I mGluRs (mGluR1/5) with the selective agonist pression as occur in associative learning (5–8). Dysregulated DHPG (32) elicits a form of homosynaptic long-term depression mGluR1/5 signaling is implicated in neurological, psychiatric, (chemical mGluR-LTD) of synaptic transmission at Schaffer and cognitive disorders (8), including fragile X syndrome, the collateral to CA1 (Sch-CA1) pyramidal cell synapses that is in- most common inherited cause of intellectual disabilities (9, 10). dependent of NMDA receptor (NMDAR) activation (24, 33). The broad spectrum of physiological and pathological functions To examine whether caveolin-1 has a role in mGluR-LTD, we in which mGluRs participate is related to their capacity to ini- tiate diverse signaling events by G protein-dependent and -independent mechanisms (11, 12). Author contributions: Y.T., R.S.Z., and A.F. designed research; Y.T., K.T., R.K., and A.F. Membrane rafts (13, 14) and caveolae (15) are specialized performed research; Y.T., K.T., R.K., M.V.L.B., R.S.Z., and A.F. analyzed data; and Y.T., membrane domains of the plasma membrane, enriched in cho- M.V.L.B., R.S.Z., and A.F. wrote the paper. lesterol and glycosphingolipids, that serve as platforms to com- The authors declare no conflict of interest. partmentalize specific signaling activities at the cell surface. 1Present address: Department of Otolaryngology, Gunma University Graduate School of Caveolin-1 is an adaptor protein that interacts with an array of Medicine, Maebashi, Gunma 371-8511, Japan. receptors, including mGluR1 and mGluR5 (16–18) and effector 2K.T. and R.K. contributed equally to this work. fi proteins, and modi es signaling strength and duration by regu- 3To whom correspondence may be addressed. E-mail: [email protected] lating the activity of its interacting partners (19–21). Binding to or [email protected]. caveolin-1 attenuates the rate of mGluR1 constitutive in- This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. ternalization and attenuates mGluR1-mediated activation of 1073/pnas.1015553107/-/DCSupplemental. 21778–21783 | PNAS | December 14, 2010 | vol. 107 | no. 50 www.pnas.org/cgi/doi/10.1073/pnas.1015553107 Downloaded by guest on October 3, 2021 applied DHPG (100 μM, 5 min) to hippocampal slices from WT fEPSCs in area CA1 (35–37). LFS induced robust depression of −/− −/− and Cav1 mice aged 20–34 d (Fig. 1A). In WT slices, DHPG fEPSPs in slices from both WT and Cav1 mice, as assessed produced a robust depression of evoked field potential (fEPSP) 35–40 min after stimulation (WT depression to 83 ± 5% of −/− slope values to 76 ± 3% of pre-DHPG baseline, assessed at 50–55 baseline, n =9;Cav1 depression to 79 ± 4% of baseline, n = −/− −/− min after DHPG (n = 10; Fig. 1A), consistent with previous 8; P > 0.05 Cav1 vs. WT, P < 0.001 Cav1 or WT vs. −/− reports (24). In contrast, in slices from Cav1 mice, DHPG baseline; Fig. 1C). To confirm the dependence of this form of produced less mGluR-LTD (depression of fEPSPs to 90 ± 3% of synaptically induced LTD on activation of NMDARs, LFS was −/− baseline, n = 10, P < 0.01 Cav1 vs. WT; Fig. 1A). The short-term delivered in the presence of the selective NMDAR antagonist D- depression of fEPSPs, measured at 4–6 min after onset of DHPG APV (50 μM). Application of D-APV abolished LFS-LTD in −/− −/− application, was also decreased in Cav1 compared with WT slices from Cav1 mice (Fig. 1D). Collectively, these observa- −/− mice (Cav1 to 67 ± 4%, n = 10, vs. WT to 51 ± 4%, n = 10; P < tions indicate that the cellular machinery underlying this form of −/− −/− 0.05 Cav1 vs. WT). Attenuation of short- and long-term syn- LTD remains intact in Cav1 mice. aptic depression in response to DHPG was also observed in slices −/− −/− from P10-11 Cav1 mice (Fig. S1), indicating that caveolin-1 also Saturating Levels of mGluR-LTD Are the Same in WT and Cav1 affects mGluR-LTD at earlier ages. However, the mechanisms are Mice. DHPG-induced LTD at Sch-CA1 synapses is a saturable likely to be different, because at this early age, mGluR-dependent form of plasticity that shares a common expression mechanism, LTD is presynaptic and not dependent on protein synthesis (34). internalization of AMPA receptors, with NMDAR-independent Application of DHPG in the presence of the selective mGluR1 LTD induced by paired-pulse low-frequency stimulation (24). To antagonist LY367385 (100 μM) together with the mGluR5 an- further investigate the properties of the reduced mGluR-LTD in −/− −/− tagonist MPEP (10 μM) to Cav1 slices failed to induce LTD of Cav1 mice, we used repeated applications of DHPG. In WT fEPSPs (responses were 99 ± 2% of baseline, n = 6; Fig. 1B), mice, two consecutive applications of DHPG produced maximal A consistent with a requirement for group I mGluR activation. To- depression of the fEPSPs (Fig. 2 ), in corroboration of others gether, these findings indicate that both short- and long-term (24). In contrast, four applications of DHPG were required to Cav1−/− B mGluR1/5-dependent synaptic depression induced by a single achieve maximal LTD in slices from mice (Fig.

Load more