To confirm that A20 regulates p-p65 S536 in individual neurons, we measured the fluorescence intensity of p65 and p-p65 S536 staining in transfected cultured hippocampal neurons (Fig. vitro were recapitulated in vivo where increasing or decreasing A20 expression in mouse brains reduced and enhanced spine density, respectively. Functionally, A20 knockdown significantly increased the amplitude, but not frequency of miniature excitatory postsynaptic currents, suggesting a role in postsynaptic efficacy. A20 negatively regulated NF-B activation in neurons and A20 mutants deficient in either the deubiquitinase or the ubiquitin ligase activity failed to suppress NF-B activation or reduce spine morphogenesis. Finally, selective inhibition of NF-B abolished A20 knockdown-elicited spine formation, suggesting that A20 exerts its modulation on synapses through NF-B signaling. Together, our study reveals a URB754 previously unknown role for A20, the only known ubiquitin editing enzyme with both deubiquitinase and ubiquitin ligase activity, in dendritic arborization, spine remodeling, and synaptic plasticity. and were sampled. Scale bars, 5 m. em G /em , Quantifications of densities of total and classified spines from em D /em . n = 8 in each group (left) and n = 13 and 15 for GFP and A20/GFP, respectively (right). em H /em , Quantifications of densities of total and classified spines from em F /em . n = 13 and 19 in shLuc and shA20 groups, respectively (left), and n = 15 and 14 in shLuc and shA20 groups, respectively (right). n = 3 mice used in each group. *p 0.05, ***p 0.001; unpaired t assessments. 2.4. URB754 A20 decreases the expression and clustering of PSD-95 and GluA1 We next examined how A20 regulates the level and clustering of the -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor subunit GluA1, the major subunit forming synaptic and extrasynaptic AMPARs (Lu et al., 2009; Traynelis et al., 2010; Wenthold et al., 1996), and the synaptic scaffold PSD-95 in cultured hippocampal neurons. Overexpressing A20/GFP significantly reduced the protein levels of PSD-95 and GluA1 (Fig. 5A). In contrast, knocking down A20 significantly increased PSD-95 and GluA1 levels (Fig. 5B). Immunofluorescence confocal microscopy showed that A20 knockdown significantly increased the intensity of PSD-95 clusters (Fig. 5C, ?,F).F). In addition, the cluster intensities of both surface and total GluA1 were increased in A20 knockdown neurons (Fig. 5D-?-F).F). These data are consistent with the slot URB754 hypothesis (Elias and Nicoll, 2007) that PSD-95 serves as a postsynaptic slot scaffold that controls GluA1 figures at synapses. Taken together, our results suggest that A20 negatively regulates synapse maturation and/or function. Open in a separate window Physique 5. A20 regulation of PSD-95 and GluA1 clustering. em A /em , Western blot (left) and quantifications (right) showing that A20 overexpression reduces PSD-95 and GluA1 total levels. n = 4C5 impartial experiments. *p 0.05; unpaired t assessments. em B /em , Western blot (left) and quantifications (right) showing that A20 knockdown increases PSD-95 and GluA1 total levels. n = 3C5 impartial experiments. *p 0.05; unpaired t assessments. em C /em , PSD-95 clusters (reddish) in shLuc/GFP or shA20/GFP expressing neurons. Level bars, 20 m (above) and 5 m (below). em D /em , sGluA1 clusters (reddish) in A20 knockdown and control neurons. Level bars, 20 m (above) and 5 m (below). em E /em , Total GluA1 clusters (reddish) in A20 knockdown and control neurons. Level bars, 20 m (above) and 5 m (below). Boxes indicate where the dendritic segments were zoomed in at a higher magnification. em F /em , Quantifications of PSD-95, GluA1, and sGluA1 cluster intensities in em C-E /em . n = 63, 51, 232, 242, 144, and 151 dendritic branches, respectively, for PSD-95, sGluA1, and GluA1 clusters in shLuc and shA20 neurons in the order shown. ***P 0.001, unpaired t test. 2.5. A20 knockdown increases synaptic strength To directly investigate whether A20 regulates synaptic strength, we performed whole-cell patch-clamp recordings on infected rat hippocampus neurons and measured the amplitude and frequency of AMPA receptor-mediated miniature excitatory postsynaptic currents (mEPSCs). A20 F2RL2 knockdown significantly increased mEPSC amplitude (Fig. 6A, ?,B,B, ?,C),C), URB754 indicating a larger quantity of postsynaptic AMPA receptors and/or an increased presynaptic release probability. However, the mEPSC frequency, an index of presynaptic release probability or the number.