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

Abstract

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 and reduced epileptic seizure severity 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 activity-dependent miRNA/RBP crosstalk during synaptic scaling, with potential implications for neural network homeostasis and epileptogenesis.

Ca 2+ /calmodulin binding to PSD ‐95 mediates homeostatic synaptic scaling down

“…Notably, BIC increased spine head diameter in neurons expressing the E17R and T19K mutants by ~9% and ~3%, respectively, augmenting the actual difference in spine size changes between WT and mutants although none of these effects reached statistical significance. This observation is analogous to findings by Rajman et al (), that is, treatments that prevented down scaling BIC increased rather than decreased spine size (see Discussion). Remarkably, we found that BIC robustly increased spine length by 20–30% for WT as well as the PSD‐95 mutants.…”

“…One possibility is that differences in the culturing conditions are responsible for this difference. However, similar to the increase in spine size we observed in neurons expressing the Ca 2+ /CaM‐binding‐deficient PSD‐95 mutants (Fig EV4A), the work by Rajman et al () also found such an increase when blocking scaling down. In detail, chronic picrotoxin treatment, which, like BIC, increases network activity by inhibiting GABA A receptors, resulted in a modest spine enlargement when miR129, which is required for down scaling, was down regulated with anti‐miR129 plasmid.…”

“…Recent work showed that BIC treatment results in a 15–20% decrease in spine size (Rajman et al , ). In our cultures, the BIC‐induced decrease in spine size was minimal in neurons expressing WT PSD‐95 (~5%) and did not reach statistical significance.…”

MicroRNAs in neural development: from master regulators to fine-tuners

“…Finally, although miRNA-based therapeutics in the brain are still in their infancy, in large part due to the difficulty of delivering miRNAtargeting oligonucleotides into the brain, some advances have been made. A notable example is that of epilepsy, for which injection of several miRNA antagomirs has proven to be beneficial for the reduction of seizures and associated neurodegeneration in the hippocampus (Gross et al, 2016;Jimenez-Mateos et al, 2012;Rajman et al, 2017). In addition, the virus-directed expression of miR-223 has been shown to be neuroprotective following transient global ischemia and excitotoxic injury (Harraz et al, 2012).…”

Silencing MicroRNA-155 Attenuates Kainic Acid-Induced Seizure by Inhibiting Microglia Activation

“…About 60% of all human proteins are estimated to be directly regulated by miRNAs [7]. Recent research suggests that miRNAs play key roles in the pathogenesis of a variety of neurological disorders, including epilepsy [8-11]. Moreover, some miRNAs have been found differentially expressed in the brain under pathological conditions and might therefore represent both therapeutic targets and diagnostic or prognostic biomarkers for epilepsy [12-15].…”