Section on Nervous System Development and Plasticity, The Eunice Kennedy Shriver National Institute of Child and Human Development, National Institutes of Health, Bethesda, MD 20892-3714, USA.
Proc Natl Acad Sci U S A. 2011 Jul 12;108(28):11650-5. doi: 10.1073/pnas.1017576108. Epub 2011 Jun 22.
Homeostatic mechanisms are required to control formation and maintenance of synaptic connections to maintain the general level of neural impulse activity within normal limits. How genes controlling these processes are co-coordinately regulated during homeostatic synaptic plasticity is unknown. MicroRNAs (miRNAs) exert regulatory control over mRNA stability and translation and may contribute to local and activity-dependent posttranscriptional control of synapse-associated mRNAs. However, identifying miRNAs that function through posttranscriptional gene silencing at synapses has remained elusive. Using a bioinformatics screen to identify sequence motifs enriched in the 3'UTR of rapidly destabilized mRNAs, we identified a developmentally and activity-regulated miRNA (miR-485) that controls dendritic spine number and synapse formation in an activity-dependent homeostatic manner. We find that many plasticity-associated genes contain predicted miR-485 binding sites and further identify the presynaptic protein SV2A as a target of miR-485. miR-485 negatively regulated dendritic spine density, postsynaptic density 95 (PSD-95) clustering, and surface expression of GluR2. Furthermore, miR-485 overexpression reduced spontaneous synaptic responses and transmitter release, as measured by miniature excitatory postsynaptic current (EPSC) analysis and FM 1-43 staining. SV2A knockdown mimicked the effects of miR-485, and these effects were reversed by SV2A overexpression. Moreover, 5 d of increased synaptic activity induced homeostatic changes in synaptic specializations that were blocked by a miR-485 inhibitor. Our findings reveal a role for this previously uncharacterized miRNA and the presynaptic protein SV2A in homeostatic plasticity and nervous system development, with possible implications in neurological disorders (e.g., Huntington and Alzheimer's disease), where miR-485 has been found to be dysregulated.
内稳机制是控制突触连接形成和维持的必要条件，以维持神经冲动活动的总体水平在正常范围内。在同型突触可塑性过程中，控制这些过程的基因如何协同调节尚不清楚。microRNAs（miRNAs）对 mRNA 的稳定性和翻译发挥调节控制作用，可能有助于突触相关 mRNA 的局部和活性依赖性转录后控制。然而，确定在突触中通过转录后基因沉默发挥作用的 miRNAs 一直是难以捉摸的。我们使用生物信息学筛选来识别在快速不稳定的 mRNA 的 3'UTR 中富集的序列基序，鉴定了一种发育和活性调节的 miRNA（miR-485），它以活性依赖的同型方式控制树突棘数量和突触形成。我们发现许多可塑性相关基因包含预测的 miR-485 结合位点，并进一步鉴定出突触前蛋白 SV2A 是 miR-485 的靶标。miR-485 负调控树突棘密度、突触后密度 95（PSD-95）聚集和 GluR2 的表面表达。此外，miR-485 的过表达降低了自发性突触反应和递质释放，如通过微小兴奋性突触后电流（EPSC）分析和 FM 1-43 染色测量。SV2A 的敲低模拟了 miR-485 的作用，而 SV2A 的过表达逆转了这些作用。此外，5 天的增加突触活动诱导了突触特化的同型变化，而 miR-485 抑制剂阻断了这些变化。我们的发现揭示了这种以前未被表征的 miRNA 和突触前蛋白 SV2A 在同型可塑性和神经系统发育中的作用，这可能对神经退行性疾病（如亨廷顿病和阿尔茨海默病）具有重要意义，其中已经发现 miR-485 失调。
