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. 2008 Mar 27;57(6):858-71.
doi: 10.1016/j.neuron.2008.01.010.

mGluR1/5-dependent long-term depression requires the regulated ectodomain cleavage of neuronal pentraxin NPR by TACE

Richard W Cho  1 , Joo Min Park, Steffen B E Wolff, Desheng Xu, Carsten Hopf, Jin-Ah Kim, Radhika C Reddy, Ronald S Petralia, Mark S Perin, David J Linden, Paul F Worley
Affiliations

mGluR1/5-dependent long-term depression requires the regulated ectodomain cleavage of neuronal pentraxin NPR by TACE

Richard W Cho et al. Neuron. .

Abstract

Matrix metalloproteases (MMPs) play a role in remodeling the extracellular matrix during brain development and have been implicated in synaptic plasticity. Here, we report that a member of the neuronal pentraxin (NP) family, neuronal pentraxin receptor (NPR), undergoes regulated cleavage by the MMP tumor necrosis factor-alpha converting enzyme (TACE). NPR is enriched at excitatory synapses where it associates with AMPA-type glutamate receptors (AMPAR) and enhances synaptogenesis. However, in response to activation of group 1 mGluRs (mGluR1/5), TACE cleaves NPR and releases the pentraxin domain from its N-terminal transmembrane domain. Cleaved NPR rapidly accumulates in endosomes where it colocalizes with AMPAR. This process is necessary for mGluR1/5-dependent LTD in hippocampal and cerebellar synapses. These observations suggest that cleaved NPR functions to "capture" AMPAR for endocytosis and reveal a bifunctional role of NPs in both synapse strengthening and weakening.

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Figures

Figure 1
Figure 1. NPR associates with Narp, NP1, and AMPAR at excitatory synapses, and is proteolytically processed
(A) Schematic of NPR structure. NPR contains 2 coiled-coil domains and a C-terminal pentraxin domain. Cysteines predicted to form disulfide linkages with other NPR subunits as well as other NPs are labeled. Regions of NPR used to generate Ab LFC-NPR, Ab 4999, and Ab 4450 are identified. Cleavage Sites A and B are identified and occur just before L36 and D176, respectively. Cleavage produces three NPR fragments, Long Form Cleaved (LFC-NPR), N-terminal Fragment (NTF-NPR), and C-terminal Fragment (CTF-NPR). (B) Co-IP analysis of interactions between native NPR, Narp, and NP1 using lysates from WT, NP TKO, NP1 KO, and Narp KO mouse forebrain. The ∼62 kDa band detected by NPR antibody (Ab 4999) corresponds to the molecular weight predicted for full-length NPR. The ∼20 kDa band corresponds to NTF-NPR. (C) GluR1-HA, but not GluR6-HA, co-IPs with NPR from transfected HEK293T cells. (D) GluR1 co-IPs with NPR from forebrain extracts derived from WT mice. NPT KO and NPR KO are provided as control. (E) NPR is localized to excitatory synapses in cultured hippocampal neurons (DIV 14; Ab 4450 at 1:200 labeled live). Scale bar = 10 μm. (F) Multiple fragments of NPR are present in culture medium of NPR transfected HEK293T cells. Western blot analysis was performed on lysates and medium from transfected cells using Ab 4450 and Ab 4999. (G) Identification of NPR cleavage sites. (H) Western blot analysis of NPR protein expression in extracts of adult hippocampus, cerebellum, and cortex using Ab 4450 and Ab 4999.
Figure 2
Figure 2. Transmembrane domain of NPR is necessary and sufficient to inhibit cluster formation
(A) Live cell surface staining of Narp, NPR, and Narp/NPR chimera mutants (CM) in transfected COS-7 cells. (B) Schematic of the Narp, NPR, and Narp/NPR chimera constructs used. Narp signal peptide (closed circle) and NPR transmembrane domain (open box) are illustrated. All constructs have a C-terminal myc tag.
Figure 3
Figure 3. TACE cleaves NPR and promotes clustering with AMPAR
(A) – (B) HEK293T cells were transfected with NPR-myc transgene. Two days after transfection, medium was replaced with drug and vehicle. At the indicated time points, samples of medium were removed. At the end of the time course, cells were lysed. Lysates and medium were then analyzed by Western blot analysis using Ab 4450. (A) PMA (150 nM) stimulates generation of LFC- and CTF-NPR in the medium of transfected HEK293T cells. Generation of LFC- and CTF-NPR is inhibited by TAPI-2 (50 μM). (B) Co-transfection of HEK293T cells with siRNA targeting human TACE (TACE (h) siRNA) reduces PMA (150 nM) stimulated generation of LFC-NPR and CTF-NPR. NPR cleaved products are restored by co-transfection of mouse TACE (TACE (m)) cDNA. Lysates were probed with anti-TACE to confirm knockdown and expression of TACE as well as anti-β-actin as loading control. (C) Representative images of live anti-myc stained NPR-myc transfected COS-7 cells 90 min after treatment with PMA (150 nM) or vehicle. Scale bar = 5 μm. (D) Representative images of live Ab 4450 and anti-HA stained COS-7 cells co-transfected with wtNPR-myc and GluR2-HA 90 min after treatment with PMA (150 nM) or vehicle. Magnified regions of PMA treated cells (boxed) are provided in the right inset. Scale bars = 5 μm.
Figure 4
Figure 4. LFC-NPR co-localizes with internalized AMPAR at synapses
(A) GluR1-BBS transgene co-localizes with endogenous LFC-NPR clusters in cultured hippocampal neurons (DIV14). (B) Internalized GluR1-BBS and endogenous LFC-NPR co-localize in cultured hippocampal neurons (DIV 14) 45 min after DHPG (50 μM) treatment. Scale bar = 10 μm. (C-E) Sections of hippocampus (C, CA1 stratum radiatum; D, CA3 stratum lucidum) or cerebellar molecular layer (E) labeled with Ab LFC-NPR (10 nm gold), single-labeled (C-E). Gold labeling (arrowheads) is in various tubulovesicular structures in the presynaptic terminal (D) and postsynaptic spine (C and D). Labeling for LFC-NPR is also associated with the endosomal complex found in the dendrite shaft near the base of a spine (* in C and E). Inset in E shows labeling in a vesicle (appears to be partly clathrin-coated) that probably is newly endocytosed from the adjacent cell membrane (an unidentified process in contact with the side of an axon terminal in the cerebellum). (F-I) Sections of the hippocampus CA1 stratum radiatum (F, G, and H) and CA3 stratum lucidum (I) synapses double-labeled for LFC-NPR (Ab LFC-NPR; 10 nm gold) and either GluR2/3 (F, G, and H) or GluR2 (I; 5 nm gold), illustrating co-localization (arrowheads) of labeling in postsynaptic tubulovesicular organelles including some distinctive endosomes (* in G and I). Labeling for LFC-NPR co-localizes with AMPAR labeling associated with postsynaptic membrane and adjacent cytoplasm as well as synaptic cleft. The synapse in G is an interneuron dendrite shaft synapse with an oblique synaptic cleft, and those in F, H, and I are synaptic spines. Scale bar (D) is 100 nm in C and D, 125 nm in E and inset, and 50 nm in F. Scale bar (I) is 100 nm in G-I.
Figure 5
Figure 5. mGluR1/5-dependent LTD in neuronal culture requires NPs and TACE-like activity
(A) Representative Western blot using Ab LFC-NPR of lysates from primary cortical cultures at indicated time points after treatment with DHPG (50 μM). Quantification of band intensity at indicated time points compared to control (Mean ± SD, n=3 paired animals, *p < 0.05). (B) Representative Western blot of biotinylated surface GluR1 from primary cortical cultures probed with C-terminal GluR1C antibody 45 min after 5 min treatment with DHPG (50 μM) +/- TAPI-2 (50 μM treated 20 min before DHPG stimulation). Quantification of band intensity ratio of surface GluR1 after DHPG treatment to vehicle control (Mean ± SD, n= 3, *p < 0.05). (C) Representative western blot of biotinylated surface LFC-NPR from primary cortical cultures 45 min after 5 min treatment with DHPG (50 μM) +/- TAPI-2 (50 μM). Quantification of band intensity ratio of treated surface to control surface LFC-NPR (Mean ± SD, n=3, *p < 0.05). (D) Representative Western blot of biotinylated surface GluR1 from WT and NP TKO primary cortical neurons 45 min after treatment with DHPG (50 μM). Quantification of ratio of surface GluR1 after DHPG treatment to vehicle control (Mean ± SD, n=4, *p < 0.05). (E) DHPG (50 μM) stimulated surface GluR1 loss in cultured hippocampal neurons (DIV1 14) is blocked by treatment with TAPI-2 (50 μM). See Figure 5H for quantification. Scale bar = 10 μm. (F) DHPG (50 μM) stimulated surface GluR1 loss is impaired in neuronal cultures derived from NP TKO. See Figure 5I for quantification. Scale bar = 10 μm. (G) DHPG induced GluR1 endocytosis is impaired in TKO hippocampal neurons compared to WT. Internalized GluR1 was measured +/- DHPG (50 μM) at 5 min (not shown), 15 min (not shown), and 45 min using acid strip protocol to visualize internalized labeled GluR1. See Figure 5J for quantification. (H) Quantification of surface GluR1 puncta density after vehicle control or DHPG stimulation +/- TAPI-2. The mean surface GluR1 puncta density per unit length of dendrite was calculated for each treatment and expressed as a ratio (DHPG/vehicle control). These ratios are compared +/- TAPI-2 (mean ± SEM; n> 14; *p < 0.0001). (I) Quantification of density of surface GluR1 per unit length after vehicle control or DHPG stimulation cultured neurons from WT and NP TKO mice. Ratio of DHPG/vehicle control was calculated as described above (mean ± SEM; n > 66; *p < 0.001). (J) Quantification of internalized GluR1 density per unit length after vehicle control or DHPG stimulation in cultured neurons from WT and NP TKO mice at indicated time points (mean ± SEM; 5 min: n>110; 15 min n>160; 45 min n>36; ***p = 0.002; **p = 0.004; *p = 0.04).
Figure 6
Figure 6. mGluR1/5-dependent LTD at the Schaffer-CA1 synapse requires NPR and TACE-like activity
(A) DHPG induced mGluR1/5-dependent LTD is blocked by general MMP inhibitor GM6001 (4 μM) and TACE inhibitor TAPI-2 (50 μM). Single representative traces from before (-10 min) and after (+76 min) DHPG are shown in the corresponding insets. All scale bars = 0.5 mV, 10 ms. All points represent the mean ± SEM of the corresponding group. (B) DHPG induced mGluR1/5-dependent LTD is absent in NPR KO and NP TKO. Representative single traces from before (-15 min) and after (+75 min) DHPG are shown in the inset. (C) PP-1Hz induced mGluR1/5-dependent LTD is blocked by TAPI-2 (50 μM) and is absent in NP TKO and NPR KO mice. Representative single traces from before (-10 min) and after (+50 min) are shown in the inset.
Figure 7
Figure 7. mGluR1-dependent LTD in cultured cerebellar Purkjine neurons requires NPR and TACE
(A) LTD experiments in Purkinje cells derived from mice harboring mutations in NP genes. Test stimuli are iontophoretic pulses of glutamate. Following a baseline recording period, LTD was induced by six, 3 sec long depolarizing steps to 0 mV, each paired with a glutamate test pulse. This is indicated by the horizontal bar at t = 0 min. Exemplar current traces are single, unaveraged records corresponding to the points indicated on the time-course graph. Scale bars = 50 pA, 1 sec. WT (n = 7 cells); NP TKO (n = 8 cells); NPR KO (n = 6 cells); NPR KO, wtNPR transgene (n = 6 cells). (B) LTD experiments in WT Purkinje cells treated with TACE inhibitors. Scale bars = 30 pA, 1 sec. TAPI-2 (n = 7 cells); GM6001 (n = 7 cells); GM6001 control compound (n = 7 cells). (C) LTD experiments in WT Purkinje cells treated with siRNA directed against mouse TACE. Scale bars = 100 pA, 1 sec. TACE (m) siRNA (n = 8 cells); scrambled siRNA (n = 6 cells). (D) LTD experiments in Purkinje cells transfected with either full-length NPR or LFC-NPR. Scale bars = 100 pA. 1 sec. WT, NPR transgene (n = 5 cells); WT, LFC-NPR transgene (n = 7 cells); NPR KO, LFC-NPR transgene (n = 8 cells).
Figure 8
Figure 8. NPs exert bifunctional control of synaptic AMPAR via the regulated action of TACE
Consistent with previous models, NPs can act as synaptogenic agents by recruiting AMPAR to synapses (Xu et al., 2003; Sia et al., 2007). However, upon activation of TACE, consequent to mGluR1/5 or other signaling events, TACE cleaves NPR, and enables NPR with associated NPs to cluster and co-cluster AMPAR at the site of TACE activity, and thereby increase the rate of AMPAR endocytosis. This process is essential for durable LTD.
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