Activity-Dependent Pre-miR-134 Dendritic Localization Is Required for Hippocampal Neuron Dendritogenesis

microRNAs (miRNAs) have emerged as critical regulators of neuronal dendrite development. Specific precursor (pre-)miRNAs are actively transported to dendrites, but whether this process is regulated by neuronal activity and involved in activitydependent dendritogenesis is unknown. Here we show that BDNF, a neurotrophin that is released in response to increased neuronal activity, promotes dendritic accumulation of pre-miR-134. Dendritic accumulation, but not transcription of pre-miR-134, is abrogated by treatment of neurons with the NMDA receptor (NMDAR) antagonist APV. Furthermore, APV interferes with BDNF-mediated repression of the known miR-134 target Pumilio 2 (Pum2) in a miR-134 binding site-specific manner. At the functional level, both APV treatment and knockdown of the pre-miR-134 transport protein DHX36 antagonize BDNF-induced dendritogenesis. These effects are likely mediated by reduced dendritic miR-134 activity, since both transfection of a synthetic miR-134 duplex or of a dendritically targeted pre-miR-134-181a chimera rescues BDNF-dependent dendritogenesis in the presence of APV. In conclusion, we have identified a novel NMDAR-dependent mechanism involved in the activity-dependent control of miRNA function during neuronal development

The dynamic recruitment of TRBP to neuronal membranes mediates dendritogenesis during development

MicroRNAs are important regulators of local protein synthesis during neuronal development. We investigated the dynamic regulation of microRNA production and found that the majority of the microRNA‐generating complex, consisting of Dicer, TRBP, and PACT, specifically associates with intracellular membranes in developing neurons. Stimulation with brain‐derived neurotrophic factor (BDNF), which promotes dendritogenesis, caused the redistribution of TRBP from the endoplasmic reticulum into the cytoplasm, and its dissociation from Dicer, in a Ca2+‐dependent manner. As a result, the processing of a subset of neuronal precursor microRNAs, among them the dendritically localized pre‐miR16, was impaired. Decreased production of miR‐16‐5p, which targeted the BDNF mRNA itself, was rescued by expression of a membrane‐targeted TRBP. Moreover, miR‐16‐5p or membrane‐targeted TRBP expression blocked BDNF‐induced dendritogenesis, demonstrating the importance of neuronal TRBP dynamics for activity‐dependent neuronal development. We propose that neurons employ specialized mechanisms to modulate local gene expression in dendrites, via the dynamic regulation of microRNA biogenesis factors at intracellular membranes of the endoplasmic reticulum, which in turn is crucial for neuronal dendrite complexity and therefore neuronal circuit formation and function.ISSN:1469-221XISSN:1469-317

Pervasive compartment-specific regulation of gene expression during homeostatic synaptic scaling

Synaptic scaling is a form of homeostatic plasticity which allows neurons to adjust their action potential firing rate in response to chronic alterations in neural activity. Synaptic scaling requires profound changes in gene expression, but the relative contribution of local and cell-wide mechanisms is controversial. Here we perform a comprehensive multi-omics characterization of the somatic and process compartments of primary rat hippocampal neurons during synaptic scaling. We uncover both highly compartment-specific and correlating changes in the neuronal transcriptome and proteome. Whereas downregulation of crucial regulators of neuronal excitability occurs primarily in the somatic compartment, structural components of excitatory postsynapses are mostly downregulated in processes. Local inhibition of protein synthesis in processes during scaling is confirmed for candidate synaptic proteins. Motif analysis further suggests an important role for trans-acting post-transcriptional regulators, including RNA-binding proteins and microRNAs, in the local regulation of the corresponding mRNAs. Altogether, our study indicates that, during synaptic scaling, compartmentalized gene expression changes might co-exist with neuron-wide mechanisms to allow synaptic computation and homeostasis.ISSN:1469-221XISSN:1469-317

MicroRNA-138 controls hippocampal interneuron function and short-term memory in mice

The proper development and function of neuronal circuits rely on a tightly regulated balance between excitatory and inhibitory (E/I) synaptic transmission, and disrupting this balance can cause neurodevelopmental disorders, for example, schizophrenia. MicroRNA-dependent gene regulation in pyramidal neurons is important for excitatory synaptic function and cognition, but its role in inhibitory interneurons is poorly understood. Here, we identify miR138-5p as a regulator of short-term memory and inhibitory synaptic transmission in the mouse hippocampus. Sponge-mediated miR138-5p inactivation specifically in mouse parvalbumin (PV)-expressing interneurons impairs spatial recognition memory and enhances GABAergic synaptic input onto pyramidal neurons. Cellular and behavioral phenotypes associated with miR138-5p inactivation are paralleled by an upregulation of the schizophrenia (SCZ)-associated Erbb4, which we validated as a direct miR138-5p target gene. Our findings suggest that miR138-5p is a critical regulator of PV interneuron function in mice, with implications for cognition and SCZ. More generally, they provide evidence that microRNAs orchestrate neural circuit development by fine-tuning both excitatory and inhibitory synaptic transmission.ISSN:2050-084

Characterizing Light-Regulated Retinal MicroRNAs Reveals Rapid Turnover as a Common Property of Neuronal MicroRNAs

SummaryAdaptation to different levels of illumination is central to the function of the retina. Here, we demonstrate that levels of the miR-183/96/182 cluster, miR-204, and miR-211 are regulated by different light levels in the mouse retina. Concentrations of these microRNAs were downregulated during dark adaptation and upregulated in light-adapted retinas, with rapid decay and increased transcription being responsible for the respective changes. We identified the voltage-dependent glutamate transporter Slc1a1 as one of the miR-183/96/182 targets in photoreceptor cells. We found that microRNAs in retinal neurons decay much faster than microRNAs in nonneuronal cells. The high turnover is also characteristic of microRNAs in hippocampal and cortical neurons, and neurons differentiated from ES cells in vitro. Blocking activity reduced turnover of microRNAs in neuronal cells while stimulation with glutamate accelerated it. Our results demonstrate that microRNA metabolism in neurons is higher than in most other cells types and linked to neuronal activity.PaperCli

Bipolar-associated miR-499-5p controls neuroplasticity by downregulating the Cav1.2 subunit CACNB2

Bipolar disorder (BD) is a chronic mood disorder characterized by manic and depressive episodes. Dysregulation of neuroplasticity and calcium homeostasis are frequently observed in BD patients, but the underlying molecular mechanisms are largely unknown. Here, we show that miR-499-5p regulates dendritogenesis and cognitive function by downregulating the BD risk gene CACNB2. miR-499-5p expression is increased in peripheral blood of BD patients, as well as in the hippocampus of rats which underwent juvenile social isolation. In rat hippocampal neurons, miR-499-5p impairs dendritogenesis and reduces surface expression and activity of the L-type calcium channel Cav1.2. We further identified CACNB2, which encodes a regulatory beta-subunit of Cav1.2, as a direct functional target of miR-499-5p in neurons. miR-499-5p overexpression in the hippocampus in vivo induces short-term memory impairments selectively in rats haploinsufficient for the Cav1.2 pore forming subunit Cacna1c. In humans, miR-499-5p expression is negatively associated with gray matter volumes of the left superior temporal gyrus, a region implicated in auditory and emotional processing. We propose that stress-induced miR-499-5p overexpression contributes to dendritic impairments, deregulated calcium homeostasis, and neurocognitive dysfunction in BD.ISSN:1469-221XISSN:1469-317

A microRNA-129-5p/Rbfox crosstalk coordinates homeostatic downscaling of excitatory synapses

Synaptic downscaling is a homeostatic mechanism that allows neurons to reduce firing rates during chronically elevated network activity. Although synaptic downscaling is important in neural circuit development and epilepsy, the underlying mechanisms are poorly described. We performed small RNA profiling in picrotoxin (PTX)-treated hippocampal neurons, a model of synaptic downscaling. Thereby, we identified eight microRNAs (miRNAs) that were increased in response to PTX, including miR-129-5p, whose inhibition blocked synaptic downscaling in vitro and reduced epileptic seizure severity in vivo. Using transcriptome, proteome, and bioinformatic analysis, we identified the calcium pump Atp2b4 and doublecortin (Dcx) as miR-129-5p targets. Restoring Atp2b4 and Dcx expression was sufficient to prevent synaptic downscaling in PTX-treated neurons. Furthermore, we characterized a functional crosstalk between miR-129-5p and the RNA-binding protein (RBP) Rbfox1. In the absence of PTX, Rbfox1 promoted the expression of Atp2b4 and Dcx. Upon PTX treatment, Rbfox1 expression was downregulated by miR-129-5p, thereby allowing the repression of Atp2b4 and Dcx. We therefore identified a novel activitydependent miRNA/RBP crosstalk during synaptic scaling, with potential implications for neural network homeostasis and epileptogenesis