Integration of nuclear Ca2+ transients and subnuclear protein shuttling provides a novel mechanism for the regulation of CREB-dependent gene expression.

Nuclear Ca2+ waves elicited by NMDAR and L-type voltage-gated Ca2+-channels as well as protein transport from synapse-to-nucleus are both instrumental in control of plasticity-related gene expression. At present it is not known whether fast [Ca2+]n transients converge in the nucleus with signaling of synapto-nuclear protein messenger. Jacob is a protein that translocate a signalosome from N-methyl-D-aspartate receptors (NMDAR) to the nucleus and that docks this signalosome to the transcription factor CREB. Here we show that the residing time of Jacob in the nucleoplasm strictly correlates with nuclear [Ca2+]n transients elicited by neuronal activity. A steep increase in [Ca2+]n induces instantaneous uncoupling of Jacob from LaminB1 at the nuclear lamina and promotes the association with the transcription factor cAMP-responsive element-binding protein (CREB) in hippocampal neurons. The size of the Jacob pool at the nuclear lamina is controlled by previous activity-dependent nuclear import, and thereby captures the previous history of NMDAR-induced nucleocytoplasmic shuttling. Moreover, the localization of Jacob at the nuclear lamina strongly correlates with synaptic activity and [Ca2+]n waves reflecting ongoing neuronal activity. In consequence, the resulting extension of the nuclear residing time of Jacob amplifies the capacity of the Jacob signalosome to regulate CREB-dependent gene expression and will, thereby, compensate for the relatively small number of molecules reaching the nucleus from individual synapses.

Jacob-induced transcriptional inactivation of CREB promotes Aß-induced synapse loss in Alzheimer's disease.

Synaptic dysfunction caused by soluble ß-amyloid peptide (Aß) is a hallmark of early-stage Alzheimer's disease (AD), and is tightly linked to cognitive decline. By yet unknown mechanisms, Aß suppresses the transcriptional activity of cAMP-responsive element-binding protein (CREB), a master regulator of cell survival and plasticity-related gene expression. Here, we report that Aß elicits nucleocytoplasmic trafficking of Jacob, a protein that connects a NMDA-receptor-derived signalosome to CREB, in AD patient brains and mouse hippocampal neurons. Aß-regulated trafficking of Jacob induces transcriptional inactivation of CREB leading to impairment and loss of synapses in mouse models of AD. The small chemical compound Nitarsone selectively hinders the assembly of a Jacob/LIM-only 4 (LMO4)/ Protein phosphatase 1 (PP1) signalosome and thereby restores CREB transcriptional activity. Nitarsone prevents impairment of synaptic plasticity as well as cognitive decline in mouse models of AD. Collectively, the data suggest targeting Jacob protein-induced CREB shutoff as a therapeutic avenue against early synaptic dysfunction in AD.

Molecular Mechanisms of Memory Consolidation That Operate During Sleep.

The role of sleep for brain function has been in the focus of interest for many years. It is now firmly established that sleep and the corresponding brain activity is of central importance for memory consolidation. Less clear are the underlying molecular mechanisms and their specific contribution to the formation of long-term memory. In this review, we summarize the current knowledge of such mechanisms and we discuss the several unknowns that hinder a deeper appreciation of how molecular mechanisms of memory consolidation during sleep impact synaptic function and engram formation.

The nuclear lamina is a hub for the nuclear function of Jacob.

Jacob is a synapto-nuclear messenger protein that couples NMDAR activity to CREB-dependent gene expression. In this study, we investigated the nuclear distribution of Jacob and report a prominent targeting to the nuclear envelope that requires NMDAR activity and nuclear import. Immunogold electron microscopy and proximity ligation assay combined with STED imaging revealed preferential association of Jacob with the inner nuclear membrane where it directly binds to LaminB1, an intermediate filament and core component of the inner nuclear membrane (INM). The association with the INM is transient; it involves a functional nuclear export signal in Jacob and a canonical CRM1-RanGTP-dependent export mechanism that defines the residing time of the protein at the INM. Taken together, the data suggest a stepwise redistribution of Jacob within the nucleus following nuclear import and prior to nuclear export.

Inhibition of formyl peptide receptors improves the outcome in a mouse model of Alzheimer disease.

BACKGROUND: An important hallmark of Alzheimer's disease (AD) is the increase of Aß1-42 burden and its accumulation to senile plaques, leading the reactive gliosis and neurodegeneration. The modulation of glia cell function represents an attractive therapeutic strategy, but is currently limited by an incomplete understanding of its relevance for AD. The chemotactic G-protein coupled formyl peptide receptor (FPR), which is known to modulate Aß1-42 uptake and signal transduction, might be one candidate molecule regulating glia function in AD. Here, we investigate whether the modulation of FPR exerts beneficial effects in an AD preclinical model. METHODS: To address this question, APP/PS1 double-transgenic AD mice were treated for 20 weeks with either the pro-inflammatory FPR agonist fMLF, the FPR1/2 antagonist Boc2 or the anti-inflammatory FPR2 agonist Ac2-26. Spatial learning and memory were evaluated using a Morris water maze test. Immunohistological staining, gene expression studies, and flow cytometry analyses were performed to study neuronal loss, gliosis, and Aß-load in the hippocampus and cortex, respectively. RESULTS: FPR antagonism by Boc2-treatment significantly improved spatial memory performance, reduced neuronal pathology, induced the expression of homeostatic growth factors, and ameliorated microglia, but not astrocyte, reactivity. Furthermore, the elevated levels of amyloid plaques in the hippocampus were reduced by Boc2-treatment, presumably by an induction of amyloid degradation. CONCLUSIONS: We suggest that the modulation of FPR signaling cascades might be considered as a promising therapeutic approach for alleviating the cognitive deficits associated with early AD. Additional studies are now needed to address the downstream effectors as well as the safety profile of Boc2.

Environmental Enrichment Prevents Transcriptional Disturbances Induced by Alpha-Synuclein Overexpression.

Onset and progression of neurodegenerative disorders, including synucleinopathies such as Parkinson's disease, have been associated with various environmental factors. A highly compelling association from a therapeutic point of view has been found between a physically active lifestyle and a significantly reduced risk for Parkinson's disease. Mimicking such conditions in animal models by promoting physical activity, social interactions, and novel surroundings yields in a so-called enriched environment known to enhance adult neurogenesis, increase synaptic plasticity, and decelerate neuronal loss. Yet, the genes that connect beneficial environmental cues to the genome and delay disease-related symptoms have remained largely unclear. To identify such mediator genes, we used a 2 × 2 factorial design opposing genotype and environment. Specifically, we compared wildtype to transgenic mice overexpressing human SNCA, a key gene in synucleinopathies encoding alpha-synuclein, and housed them in a standard and enriched environment from weaning to 12 months of age before profiling their hippocampal transcriptome using RNA-sequencing. Under standard environmental conditions, differentially expressed genes were overrepresented for calcium ion binding, membrane, synapse, and other Gene Ontology terms previously linked to alpha-synuclein biology. Upregulated genes were significantly enriched for genes attributed to astrocytes, microglia, and oligodendrocytes. These disturbances in gene activity were accompanied by reduced levels of several presynaptic proteins and the immediate early genes EGR1 and NURR1. Intriguingly, housing transgenic animals in the enriched environment prevented most of these perturbations in gene activity. In addition, a sustained activation specifically in transgenic animals housed in enriched conditions was observed for several immediate early genes including Egr1, Nr4a2/Nurr1, Arc, and Homer1a. These findings suggest a compensatory mechanism through an enriched environment-activated immediate early gene network that prevented most disturbances induced by alpha-synuclein overexpression. This regulatory framework might harbor attractive targets for novel therapeutic approaches that mimic beneficial environmental stimuli.

A combinatorial approach to identify calpain cleavage sites in the Machado-Joseph disease protein ataxin-3.

Ataxin-3, the disease protein in Machado-Joseph disease, is known to be proteolytically modified by various enzymes including two major families of proteases, caspases and calpains. This processing results in the generation of toxic fragments of the polyglutamine-expanded protein. Although various approaches were undertaken to identify cleavage sites within ataxin-3 and to evaluate the impact of fragments on the molecular pathogenesis of Machado-Joseph disease, calpain-mediated cleavage of the disease protein and the localization of cleavage sites remained unclear. Here, we report on the first precise localization of calpain cleavage sites in ataxin-3 and on the characterization of the resulting breakdown products. After confirming the occurrence of calpain-derived fragmentation of ataxin-3 in patient-derived cell lines and post-mortem brain tissue, we combined in silico prediction tools, western blot analysis, mass spectrometry, and peptide overlay assays to identify calpain cleavage sites. We found that ataxin-3 is primarily cleaved at two sites, namely at amino acid positions D208 and S256 and mutating amino acids at both cleavage sites to tryptophan nearly abolished ataxin-3 fragmentation. Furthermore, analysis of calpain cleavage-derived fragments showed distinct aggregation propensities and toxicities of C-terminal polyglutamine-containing breakdown products. Our data elucidate the important role of ataxin-3 proteolysis in the pathogenesis of Machado-Joseph disease and further emphasize the relevance of targeting this disease pathway as a treatment strategy in neurodegenerative disorders.

Thalamus pathology in multiple sclerosis: from biology to clinical application.

There is a broad consensus that MS represents more than an inflammatory disease: it harbors several characteristic aspects of a classical neurodegenerative disorder, i.e. damage to axons, synapses and nerve cell bodies. While the clinician is equipped with appropriate tools to dampen peripheral cell recruitment and, thus, is able to prevent immune-cell driven relapses, effective therapeutic options to prevent the simultaneously progressing neurodegeneration are still missing. Furthermore, while several sophisticated paraclinical methods exist to monitor the inflammatory-driven aspects of the disease, techniques to monitor progression of early neurodegeneration are still in their infancy and have not been convincingly validated. In this review article, we aim to elaborate why the thalamus with its multiple reciprocal connections is sensitive to pathological processes occurring in different brain regions, thus acting as a "barometer" for diffuse brain parenchymal damage in MS. The thalamus might be, thus, an ideal region of interest to test the effectiveness of new neuroprotective MS drugs. Especially, we will address underlying pathological mechanisms operant during thalamus degeneration in MS, such as trans-neuronal or Wallerian degeneration. Furthermore, we aim at giving an overview about different paraclinical methods used to estimate the extent of thalamic pathology in MS patients, and we discuss their limitations. Finally, thalamus involvement in different MS animal models will be described, and their relevance for the design of preclinical trials elaborated.