Temporal lobe epilepsy is a common, chronic neurological disorder characterized by recurrent spontaneous seizures. MicroRNAs (miRNAs) are small, noncoding RNAs that regulate post-transcriptional expression of protein-coding mRNAs, which may have key roles in the pathogenesis of neurological disorders. In experimental models of prolonged, injurious seizures (status epilepticus) and in human epilepsy, we found upregulation of miR-134, a brain-specific, activity-regulated miRNA that has been implicated in the control of dendritic spine morphology. Silencing of miR-134 expression in vivo using antagomirs reduced hippocampal CA3 pyramidal neuron dendrite spine density by 21% and rendered mice refractory to seizures and hippocampal injury caused by status epilepticus. Depletion of miR-134 after status epilepticus in mice reduced the later occurrence of spontaneous seizures by over 90% and mitigated the attendant pathological features of temporal lobe epilepsy. Thus, silencing miR-134 exerts prolonged seizure-suppressant and neuroprotective actions; determining whether these are anticonvulsant effects or are truly antiepileptogenic effects requires additional experimentation.

Silencing microRNA-134 produces neuroprotective and prolonged seizure-suppressive effects

Fascins are actin-binding proteins that cross-link filamentous actin into tightly packed parallel bundles. These bundles are important for the organization and morphology of an extremely diverse set of sub-cellular structures that include dynamic and stable cell-surface protrusions, stress fibres, and the specialized actin bundles of photoreceptor and stereocilia cells. In this review, we discuss the fascin gene family and its evolution, the actin-bundling activity of fascins and the molecular pathways by which it is regulated, and the role of the diverse actin/fascin structures in normal cellular processes. We discuss the mechanisms by which fascins contribute to disease pathologies, especially cancer, where fascin-1 is emerging as a novel therapeutic target in carcinoma metastasis.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/path.2894

The roles of fascins in health and disease

Endogenous neuroprotection: mitochondria as gateways to cerebral preconditioning?

Human immunodeficiency virus (HIV)-1 infection of the CNS produces changes in dendritic morphology that correlate with cognitive decline in patients with HIV-1 associated dementia (HAD). Here, we investigated the effects of HIV-1 transactivator of transcription (Tat), a protein released by virus-infected cells, on synapses between hippocampal neurons using an imaging-based assay that quantified clusters of the scaffolding protein postsynaptic density 95 fused to green fluorescent protein (PSD95-GFP). Tat (24 h) decreased the number of PSD95-GFP puncta by 50 +/- 7%. The decrease was concentration-dependent (EC(50) = 6 +/- 2 ng/ml) and preceded cell death. Tat acted via the low-density lipoprotein receptor-related protein (LRP) because the specific LRP blocker, receptor associated protein (RAP), prevented the Tat-induced decrease in the number of PSD95-GFP puncta. Ca(2+) influx through the NMDA receptor was necessary for Tat-induced synapse loss. Expression of an ubiquitin ligase inhibitor protected synapses, implicating the ubiquitin-proteasome pathway. In contrast to synapse loss, Tat induced cell death (48 h) required activation of nitric oxide synthase. The ubiquitin ligase-inhibitor nutlin-3 prevented synapse loss but not cell death induced by Tat. Thus, the pathways diverged, consistent with the hypothesis that synapse loss is a mechanism to reduce excess excitatory input rather than a symptom of the neuron's demise. Furthermore, application of RAP to cultures treated with Tat for 16 h reversed synapse loss. These results suggest that the impaired network function and decreased neuronal survival produced by Tat involve distinct mechanisms and that pharmacologic targets, such as LRP, might prove useful in restoring function in HAD patients.

https://www.jneurosci.org/content/jneuro/28/48/12604.full.pdf

Human Immunodeficiency Virus Protein Tat Induces Synapse Loss via a Reversible Process That Is Distinct from Cell Death

https://estudogeral.sib.uc.pt/bitstream/10316/25489/1/1-s2.0-S0301008213001032-main.pdf

Role of the ubiquitin–proteasome system in brain ischemia: Friend or foe?

Rapid Degradation of Bim by the Ubiquitin-Proteasome Pathway Mediates Short-term Ischemic Tolerance in Cultured Neurons

Ischemic tolerance is an endogenous neuroprotective mechanism in brain and other organs, whereby prior exposure to brief ischemia produces resilience to subsequent normally injurious ischemia. Although many molecular mechanisms mediate delayed (gene-mediated) ischemic tolerance, the mechanisms underlying rapid (protein synthesis-independent) ischemic tolerance are relatively unknown. Here we describe a novel mechanism for the induction of rapid ischemic tolerance mediated by the ubiquitin-proteasome system. Rapid ischemic tolerance is blocked by multiple proteasome inhibitors [carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG132), MG115 (carbobenzoxy-L-leucyl-L-leucyl-L-norvalinal), and clasto-lactacystin-beta-lactone]. A proteomics strategy was used to identify ubiquitinated proteins after preconditioning ischemia. We focused our studies on two actin-binding proteins of the postsynaptic density that were ubiquitinated after rapid preconditioning: myristoylated, alanine-rich C-kinase substrate (MARCKS) and fascin. Immunoblots confirm the degradation of MARCKS and fascin after preconditioning ischemia. The loss of actin-binding proteins promoted actin reorganization in the postsynaptic density and transient retraction of dendritic spines. This rapid and reversible synaptic remodeling reduced NMDA-mediated electrophysiological responses and renders the cells refractory to NMDA receptor-mediated toxicity. The dendritic spine retraction and NMDA neuroprotection after preconditioning ischemia are blocked by actin stabilization with jasplakinolide, as well as proteasome inhibition with MG132. Together these data suggest that rapid tolerance results from changes to the postsynaptic density mediated by the ubiquitin-proteasome system, rendering neurons resistant to excitotoxicity.

https://www.jneurosci.org/content/jneuro/28/1/50.full.pdf

Daniel John Torrey

Papers

Rapid Degradation of Bim by the Ubiquitin-Proteasome Pathway Mediates Short-term Ischemic Tolerance in Cultured Neurons

Ubiquitin proteasome-mediated synaptic reorganization: a novel mechanism underlying rapid ischemic tolerance.

Activation of the caspase 8 pathway mediates seizure-induced cell death in cultured hippocampal neurons