Defective synaptic transmission causes disease signs in a mouse model of juvenile neuronal ceroid lipofuscinosis

Targeted rescue of synaptic plasticity improves cognitive decline in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a frequent complication of severe systemic infection resulting in delirium, premature death, and long-term cognitive impairment. We closely mimicked SAE in a murine peritoneal contamination and infection (PCI) model. We found long-lasting synaptic pathology in the hippocampus including defective long-term synaptic plasticity, reduction of mature neuronal dendritic spines, and severely affected excitatory neurotransmission. Genes related to synaptic signaling, including the gene for activity-regulated cytoskeleton-associated protein (Arc/Arg3.1) and members of the transcription-regulatory EGR gene family, were downregulated. At the protein level, ARC expression and mitogen-activated protein kinase signaling in the brain were affected. For targeted rescue we used adeno-associated virus-mediated overexpression of ARC in the hippocampus in vivo. This recovered defective synaptic plasticity and improved memory dysfunction. Using the enriched environment paradigm as a non-invasive rescue intervention, we found improvement of defective long-term potentiation, memory, and anxiety. The beneficial effects of an enriched environment were accompanied by an increase in brain-derived neurotrophic factor (BDNF) and ARC expression in the hippocampus, suggesting that activation of the BDNF-TrkB pathway leads to restoration of the PCI-induced reduction of ARC. Collectively, our findings identify synaptic pathomechanisms underlying SAE and provide a conceptual approach to target SAE-induced synaptic dysfunction with potential therapeutic applications to patients with SAE.

Treatment of non-epileptic episodes of anxious, fearful behavior in adolescent juvenile neuronal ceroid lipofuscinosis (CLN3 disease)

Background

Recurrent non-epileptic episodes of frightened facial and body expression occur in more than half of post-adolescent patients with juvenile neuronal ceroid lipofuscinosis (JNCL, CLN3 disease). Clinically, the episodes look similar to the attacks of paroxysmal sympathetic hyperactivity (PSH) commonly seen following traumatic brain injury (TBI). The episodes occur when the patients are exposed to separation, hear loud sounds or are otherwise bothered by discomfort and as in PSH following TBI, the attacks are difficult to prevent and/or treat.

Aim and methods

Based on present knowledge of triggering factors, the neural anxiety/fear circuit, its afferent and efferent pathways and documented CLN3 disease-impact on these tracks, the current study discusses a rational approach how to prevent and/or treat the attacks.

Results

Patients with JNCL have a disturbed somatosensory modulation leading to a reduced threshold of pain; a degeneration within the neural anxiety/fear circuit leading to an imbalance of central network inhibition and excitation pathways; and finally, an, with advancing age, increasing autonomic imbalance leading to a significant dominance of the sympathetic neural system.

Discussion

Theoretically, there are three points of attack how to prevent or treat the episodes: (1) increase in threshold of discomfort impact; (2) modulation of imbalance of central network inhibition and excitation, and (3) restoring the balance between the sympathetic and parasympathetic neural systems prompted by a parasympathetic withdrawal. As to (1) and (2), prevention should have the greatest priority. As regards (3), research of transcutaneous vagal stimulation treatment in JNCL is warranted.

Juvenile CLN3 disease is a lysosomal cholesterol storage disorder: similarities with Niemann-Pick type C disease

BACKGROUND

The most common form of neuronal ceroid lipofuscinosis (NCL) is juvenile CLN3 disease (JNCL), a currently incurable neurodegenerative disorder caused by mutations in the CLN3 gene. Based on our previous work and on the premise that CLN3 affects the trafficking of the cation-independent mannose-6 phosphate receptor and its ligand NPC2, we hypothesised that dysfunction of CLN3 leads to the aberrant accumulation of cholesterol in the late endosomes/lysosomes (LE/Lys) of JNCL patients' brains.

METHODS

An immunopurification strategy was used to isolate intact LE/Lys from frozen autopsy brain samples. LE/Lys isolated from samples of JNCL patients were compared with age-matched unaffected controls and Niemann-Pick Type C (NPC) disease patients. Indeed, mutations in NPC1 or NPC2 result in the accumulation of cholesterol in LE/Lys of NPC disease samples, thus providing a positive control. The lipid and protein content of LE/Lys was then analysed using lipidomics and proteomics, respectively.

FINDINGS

Lipid and protein profiles of LE/Lys isolated from JNCL patients were profoundly altered compared to controls. Importantly, cholesterol accumulated in LE/Lys of JNCL samples to a comparable extent than in NPC samples. Lipid profiles of LE/Lys were similar in JNCL and NPC patients, except for levels of bis(monoacylglycero)phosphate (BMP). Protein profiles detected in LE/Lys of JNCL and NPC patients appeared identical, except for levels of NPC1.

INTERPRETATION

Our results support that JNCL is a lysosomal cholesterol storage disorder. Our findings also support that JNCL and NPC disease share pathogenic pathways leading to aberrant lysosomal accumulation of lipids and proteins, and thus suggest that the treatments available for NPC disease may be beneficial to JNCL patients. This work opens new avenues for further mechanistic studies in model systems of JNCL and possible therapeutic interventions for this disorder.

FUNDING

San Francisco Foundation.

Early postnatal administration of an AAV9 gene therapy is safe and efficacious in CLN3 disease

CLN3 disease, caused by biallelic mutations in the CLN3 gene, is a rare pediatric neurodegenerative disease that has no cure or disease modifying treatment. The development of effective treatments has been hindered by a lack of etiological knowledge, but gene replacement has emerged as a promising therapeutic platform for such disorders. Here, we utilize a mouse model of CLN3 disease to test the safety and efficacy of a cerebrospinal fluid-delivered AAV9 gene therapy with a study design optimized for translatability. In this model, postnatal day one administration of the gene therapy virus resulted in robust expression of human CLN3 throughout the CNS over the 24-month duration of the study. A range of histopathological and behavioral parameters were assayed, with the therapy consistently and persistently rescuing a number of hallmarks of disease while being safe and well-tolerated. Together, the results show great promise for translation of the therapy into the clinic, prompting the launch of a first-in-human clinical trial (NCT03770572).

A method to estimate the cellular composition of the mouse brain from heterogeneous datasets

The mouse brain contains a rich diversity of inhibitory neuron types that have been characterized by their patterns of gene expression. However, it is still unclear how these cell types are distributed across the mouse brain. We developed a computational method to estimate the densities of different inhibitory neuron types across the mouse brain. Our method allows the unbiased integration of diverse and disparate datasets into one framework to predict inhibitory neuron densities for uncharted brain regions. We constrained our estimates based on previously computed brain-wide neuron densities, gene expression data from in situ hybridization image stacks together with a wide range of values reported in the literature. Using constrained optimization, we derived coherent estimates of cell densities for the different inhibitory neuron types. We estimate that 20.3% of all neurons in the mouse brain are inhibitory. Among all inhibitory neurons, 18% predominantly express parvalbumin (PV), 16% express somatostatin (SST), 3% express vasoactive intestinal peptide (VIP), and the remainder 63% belong to the residual GABAergic population. We find that our density estimations improve as more literature values are integrated. Our pipeline is extensible, allowing new cell types or data to be integrated as they become available. The data, algorithms, software, and results of our pipeline are publicly available and update the Blue Brain Cell Atlas. This work therefore leverages the research community to collectively converge on the numbers of each cell type in each brain region.

The mitochondrial protein Sideroflexin 3 (SFXN3) influences neurodegeneration pathways in vivo

Synapses are a primary pathological target in neurodegenerative diseases. Identifying therapeutic targets at the synapse could delay progression of numerous conditions. The mitochondrial protein SFXN3 is a neuronally enriched protein expressed in synaptic terminals and regulated by key synaptic proteins, including α-synuclein. We first show that SFXN3 uses the carrier import pathway to insert into the inner mitochondrial membrane. Using high-resolution proteomics on Sfxn3-KO mice synapses, we then demonstrate that SFXN3 influences proteins and pathways associated with neurodegeneration and cell death (including CSPα and Caspase-3), as well as neurological conditions (including Parkinson's disease and Alzheimer's disease). Overexpression of SFXN3 orthologues in Drosophila models of Parkinson's disease significantly reduced dopaminergic neuron loss. In contrast, the loss of SFXN3 was insufficient to trigger neurodegeneration in mice, indicating an anti- rather than pro-neurodegeneration role for SFXN3. Taken together, these results suggest a potential role for SFXN3 in the regulation of neurodegeneration pathways.

Mass spectrometry-based proteomics in neurodegenerative lysosomal storage disorders

The major function of the lysosome is to degrade unwanted materials such as lipids, proteins, and nucleic acids; therefore, deficits of the lysosomal system can result in improper degradation and trafficking of these biomolecules. Diseases associated with lysosomal failure can be lethal and are termed lysosomal storage disorders (LSDs), which affect 1 in 5000 live births collectively. LSDs are inherited metabolic diseases caused by mutations in single lysosomal and non-lysosomal proteins and resulting in the subsequent accumulation of macromolecules within. Most LSD patients present with neurodegenerative clinical symptoms, as well as damage in other organs. The discovery of new biomarkers is necessary to understand and monitor these diseases and to track therapeutic progress. Over the past ten years, mass spectrometry (MS)-based proteomics has flourished in the biomarker studies in many diseases, including neurodegenerative, and more specifically, LSDs. In this review, biomarkers of disease pathophysiology and monitoring of LSDs revealed by MS-based proteomics are discussed, including examples from Niemann-Pick disease type C, Fabry disease, neuronal ceroid-lipofuscinoses, mucopolysaccharidosis, Krabbe disease, mucolipidosis, and Gaucher disease.

Neuronal genetic rescue normalizes brain network dynamics in a lysosomal storage disorder despite persistent storage accumulation

Although neurologic symptoms occur in two-thirds of lysosomal storage disorders (LSDs), for most we do not understand the mechanisms underlying brain dysfunction. A major unanswered question is if the pathogenic hallmark of LSDs, storage accumulation, induces functional defects directly or is a disease bystander. Also, for most LSDs we do not know the impact of loss-of-function in individual cell types. Understanding these critical questions are essential to therapy development. Here, we determined the impact of genetic rescue in distinct cell types on neural circuit dysfunction in CLN3 disease, the most common pediatric dementia and a paradigmatic neurodegenerative LSD. We restored Cln3 expression via AAV-mediated gene delivery and conditional genetic rescue in a CLN3 disease mouse model. Surprisingly, we found that low-level rescue of Cln3 expression in neurons alone normalized clinically-relevant electrophysiologic markers of network dysfunction, despite the presence of substantial residual histopathology, in contrast to restoring expression in astrocytes. Thus, loss of CLN3 function in neurons, not storage accumulation, underlies neurologic dysfunction in CLN3 disease, implying that storage clearance may be an inappropriate target for therapy development and an ineffectual biomarker.

Differential gene expression analysis following olfactory learning in honeybee (Apis mellifera L.)

Insects change their stimulus-response through the perception of associating these stimuli with important survival events such as rewards, threats, and mates. Insects develop strong associations and relate them to their experiences through several behavioral procedures. Among the insects, Apis species, Apis mellifera ligustica are known for their outstanding ability to learn with tremendous economic importance. Apis mellifera ligustica has a strong cognitive ability and promising model species for investigating the neurobiological basis of remarkable olfactory learning abilities. Here we evaluated the olfactory learning ability of A. mellifera by using the proboscis extension reflex (PER) protocol. The brains of the learner and failed-learner bees were examined for comparative transcriptome analysis by RNA-Seq to explain the difference in the learning capacity. In this study, we used an appetitive olfactory learning paradigm in the same age of A. mellifera bees to examine the differential gene expression in the brain of the learner and failed-learner. Bees that respond in 2nd and 3rd trials or only responded to 3rd trials were defined as learned bees, failed-learner individuals were those bees that did not respond in all learning trials The results indicate that the learning ability of learner bees was significantly higher than failed-learner bees for 12 days. We obtained approximately 46.7 and 46.4 million clean reads from the learner bees failed-learner bees, respectively. Gene expression profile between learners' bees and failed-learners bees identified 74 differentially expressed genes, 57 genes up-regulated in the brains of learners and 17 genes were down-regulated in the brains of the bees that fail to learn. The qRT-PCR validated the differently expressed genes. Transcriptome analyses revealed that specific genes in learner and failed-learner bees either down-regulated or up-regulated play a crucial role in brain development and learning behavior. Our finding suggests that down-regulated genes of the brain involved in the integumentary system, storage proteins, brain development, sensory processing, and neurodegenerative disorder may result in reduced olfactory discrimination and olfactory sensitivity in failed-learner bees. This study aims to contribute to a better understanding of the olfactory learning behavior and gene expression information, which opens the door for understanding of the molecular mechanism of olfactory learning behavior in honeybees.

On the cusp of cures: Breakthroughs in Batten disease research

Batten disease is a family of rare, lysosomal disorders caused by mutations in one of at least 13 genes, which encode a diverse set of lysosomal and extralysosomal proteins. Despite decades of research, the development of effective therapies has remained intractable. But now, the field is experiencing rapid, unprecedented progress on multiple fronts. New tools are providing insights into previously unsolvable problems, with molecular functions now known for nine Batten disease proteins. Protein interactome data are uncovering potential functional overlap between several Batten disease proteins, providing long-sought links between seemingly disparate proteins. Understanding of cellular etiology is elucidating contributions from and interactions between various CNS cell types. Collectively, this explosion in insight is hastening an unparalleled period of therapeutic breakthroughs, with multiple therapies showing great promise in preclinical and clinical studies. The coming years will provide a continuation of this rapid progress, with the promise of effective treatments giving patients hope.

CLN3, at the crossroads of endocytic trafficking

The CLN3 gene was identified over two decades ago, but the primary function of the CLN3 protein remains unknown. Recessive inheritance of loss of function mutations in CLN3 are responsible for juvenile neuronal ceroid lipofuscinosis (Batten disease, or CLN3 disease), a fatal childhood onset neurodegenerative disease causing vision loss, seizures, progressive dementia, motor function loss and premature death. CLN3 is a multipass transmembrane protein that primarily localizes to endosomes and lysosomes. Defects in endocytosis, autophagy, and lysosomal function are common findings in CLN3-deficiency model systems. However, the molecular mechanisms underlying these defects have not yet been fully elucidated. In this mini-review, we will summarize the current understanding of the CLN3 protein interaction network and discuss how this knowledge is starting to delineate the molecular pathogenesis of CLN3 disease. Accumulating evidence strongly points towards CLN3 playing a role in regulation of the cytoskeleton and cytoskeletal associated proteins to tether cellular membranes, regulation of membrane complexes such as channels/transporters, and modulating the function of small GTPases to effectively mediate vesicular movement and membrane dynamics.

ATR regulates neuronal activity by modulating presynaptic firing

Ataxia Telangiectasia and Rad3-related (ATR) protein, as a key DNA damage response (DDR) regulator, plays an essential function in response to replication stress and controls cell viability. Hypomorphic mutations of ATR cause the human ATR-Seckel syndrome, characterized by microcephaly and intellectual disability, which however suggests a yet unknown role for ATR in non-dividing cells. Here we show that ATR deletion in postmitotic neurons does not compromise brain development and formation; rather it enhances intrinsic neuronal activity resulting in aberrant firing and an increased epileptiform activity, which increases the susceptibility of ataxia and epilepsy in mice. ATR deleted neurons exhibit hyper-excitability, associated with changes in action potential conformation and presynaptic vesicle accumulation, independent of DDR signaling. Mechanistically, ATR interacts with synaptotagmin 2 (SYT2) and, without ATR, SYT2 is highly upregulated and aberrantly translocated to excitatory neurons in the hippocampus, thereby conferring a hyper-excitability. This study identifies a physiological function of ATR, beyond its DDR role, in regulating neuronal activity.

A lysosomal enigma CLN5 and its significance in understanding neuronal ceroid lipofuscinosis

Neuronal Ceroid Lipofuscinosis (NCL), also known as Batten disease, is an incurable childhood brain disease. The thirteen forms of NCL are caused by mutations in thirteen CLN genes. Mutations in one CLN gene, CLN5, cause variant late-infantile NCL, with an age of onset between 4 and 7 years. The CLN5 protein is ubiquitously expressed in the majority of tissues studied and in the brain, CLN5 shows both neuronal and glial cell expression. Mutations in CLN5 are associated with the accumulation of autofluorescent storage material in lysosomes, the recycling units of the cell, in the brain and peripheral tissues. CLN5 resides in the lysosome and its function is still elusive. Initial studies suggested CLN5 was a transmembrane protein, which was later revealed to be processed into a soluble form. Multiple glycosylation sites have been reported, which may dictate its localisation and function. CLN5 interacts with several CLN proteins, and other lysosomal proteins, making it an important candidate to understand lysosomal biology. The existing knowledge on CLN5 biology stems from studies using several model organisms, including mice, sheep, cattle, dogs, social amoeba and cell cultures. Each model organism has its advantages and limitations, making it crucial to adopt a combinatorial approach, using both human cells and model organisms, to understand CLN5 pathologies and design drug therapies. In this comprehensive review, we have summarised and critiqued existing literature on CLN5 and have discussed the missing pieces of the puzzle that need to be addressed to develop an efficient therapy for CLN5 Batten disease.

Mechanisms and regulation of protein synthesis in mitochondria

Mitochondria are cellular organelles responsible for generation of chemical energy in the process called oxidative phosphorylation. They originate from a bacterial ancestor and maintain their own genome, which is expressed by designated, mitochondrial transcription and translation machineries that differ from those operating for nuclear gene expression. In particular, the mitochondrial protein synthesis machinery is structurally and functionally very different from that governing eukaryotic, cytosolic translation. Despite harbouring their own genetic information, mitochondria are far from being independent of the rest of the cell and, conversely, cellular fitness is closely linked to mitochondrial function. Mitochondria depend heavily on the import of nuclear-encoded proteins for gene expression and function, and hence engage in extensive inter-compartmental crosstalk to regulate their proteome. This connectivity allows mitochondria to adapt to changes in cellular conditions and also mediates responses to stress and mitochondrial dysfunction. With a focus on mammals and yeast, we review fundamental insights that have been made into the biogenesis, architecture and mechanisms of the mitochondrial translation apparatus in the past years owing to the emergence of numerous near-atomic structures and a considerable amount of biochemical work. Moreover, we discuss how cellular mitochondrial protein expression is regulated, including aspects of mRNA and tRNA maturation and stability, roles of auxiliary factors, such as translation regulators, that adapt mitochondrial translation rates, and the importance of inter-compartmental crosstalk with nuclear gene expression and cytosolic translation and how it enables integration of mitochondrial translation into the cellular context.

Densities and numbers of calbindin and parvalbumin positive neurons across the rat and mouse brain

The calcium-binding proteins parvalbumin and calbindin are expressed in neuronal populations regulating brain networks involved in spatial navigation, memory processes, and social interactions. Information about the numbers of these neurons across brain regions is required to understand their functional roles but is scarcely available. Employing semi-automated image analysis, we performed brain-wide analysis of immunohistochemically stained parvalbumin and calbindin sections and show that these neurons distribute in complementary patterns across the mouse brain. Parvalbumin neurons dominate in areas related to sensorimotor processing and navigation, whereas calbindin neurons prevail in regions reflecting behavioral states. We also find that parvalbumin neurons distribute according to similar principles in the hippocampal region of the rat and mouse brain. We validated our results against manual counts and evaluated variability of results among researchers. Comparison of our results to previous reports showed that neuron numbers vary, whereas patterns of relative densities and numbers are consistent.

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Brain-wide, semi-automatic quantification of parvalbumin and calbindin neurons

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Largely complementary distribution of calbindin and parvalbumin neurons in mice

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Comparison with several previous studies shows variable numbers but similar trends

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Similar distribution of parvalbumin neurons in the rat and mouse hippocampal region

Modulation of Kv4.2/KChIP3 interaction by the ceroid lipofuscinosis neuronal 3 protein CLN3

Voltage-gated potassium (Kv) channels of the Kv4 subfamily associate with Kv channel-interacting proteins (KChIPs), which leads to enhanced surface expression and shapes the inactivation gating of these channels. KChIP3 has been reported to also interact with the late endosomal/lysosomal membrane glycoprotein CLN3 (ceroid lipofuscinosis neuronal 3), which is modified because of gene mutation in juvenile neuronal ceroid lipofuscinosis (JNCL). The present study was undertaken to find out whether and how CLN3, by its interaction with KChIP3, may indirectly modulate Kv4.2 channel expression and function. To this end, we expressed KChIP3 and CLN3, either individually or simultaneously, together with Kv4.2 in HEK 293 cells. We performed co-immunoprecipitation experiments and found a lower amount of KChIP3 bound to Kv4.2 in the presence of CLN3. In whole-cell patch-clamp experiments, we examined the effects of CLN3 co-expression on the KChIP3-mediated modulation of Kv4.2 channels. Simultaneous co-expression of CLN3 and KChIP3 with Kv4.2 resulted in a suppression of the typical KChIP3-mediated modulation; i.e. we observed less increase in current density, less slowing of macroscopic current decay, less acceleration of recovery from inactivation, and a less positively shifted voltage dependence of steady-state inactivation. The suppression of the KChIP3-mediated modulation of Kv4.2 channels was weaker for the JNCL-related missense mutant CLN3R334C and for a JNCL-related C-terminal deletion mutant (CLN3ΔC). Our data support the notion that CLN3 is involved in Kv4.2/KChIP3 somatodendritic A-type channel formation, trafficking, and function, a feature that may be lost in JNCL.

Neuropathophysiology of Lysosomal Storage Diseases: Synaptic Dysfunction as a Starting Point for Disease Progression

About two thirds of the patients affected with lysosomal storage diseases (LSD) experience neurological manifestations, such as developmental delay, seizures, or psychiatric problems. In order to develop efficient therapies, it is crucial to understand the neuropathophysiology underlying these symptoms. How exactly lysosomal storage affects biogenesis and function of neurons is still under investigation however recent research highlights a substantial role played by synaptic defects, such as alterations in synaptic spines, synaptic proteins, postsynaptic densities, and synaptic vesicles that might lead to functional impairments in synaptic transmission and neurodegeneration, finally culminating in massive neuronal death and manifestation of cognitive symptoms. Unveiling how the synaptic components are affected in neurological LSD will thus enable a better understanding of the complexity of disease progression as well as identify crucial targets of therapeutic relevance and optimal time windows for targeted intervention.

Synapse alterations precede neuronal damage and storage pathology in a human cerebral organoid model of CLN3-juvenile neuronal ceroid lipofuscinosis

The juvenile form of neuronal ceroid Lipofuscinosis (JNCL) is the most common form within this group of rare lysosomal storage disorders, causing pediatric neurodegeneration. The genetic disorder, which is caused by recessive mutations affecting the CLN3 gene, features progressive vision loss, cognitive and motor decline and other psychiatric conditions, seizure episodes, leading to premature death. Animal models have traditionally aid the understanding of the disease mechanisms and pathology and are very relevant for biomarker research and therapeutic testing. Nevertheless, there is a need for establishing reliable and predictive human cellular models to study the disease. Since patient material, particularly from children, is scarce and difficult to obtain, we generated an engineered a CLN3-mutant isogenic human induced pluripotent stem cell (hiPSC) line carrying the c.1054C → T pathologic variant, using state of the art CRISPR/Cas9 technology. To prove the suitability of the isogenic pair to model JNCL, we screened for disease-specific phenotypes in non-neuronal two-dimensional cell culture models as well as in cerebral brain organoids. Our data demonstrates that the sole introduction of the pathogenic variant gives rise to classical hallmarks of JNCL in vitro. Additionally, we discovered an alteration of the splicing caused by this particular mutation. Next, we derived cerebral organoids and used them as a neurodevelopmental model to study the particular effects of the CLN3^Q352X mutation during brain formation in the disease context. About half of the mutation -carrying cerebral organoids completely failed to develop normally. The other half, which escaped this severe defect were used for the analysis of more subtle alterations. In these escapers, whole-transcriptome analysis demonstrated early disease signatures, affecting pathways related to development, corticogenesis and synapses. Complementary metabolomics analysis confirmed decreased levels of cerebral tissue metabolites, some particularly relevant for synapse formation and neurotransmission, such as gamma-amino butyric acid (GABA). Our data suggests that a mutation in CLN3 severely affects brain development. Furthermore, before disease onset, disease -associated neurodevelopmental changes, particular concerning synapse formation and function, occur.

Combining super-resolution microscopy with neuronal network recording using magnesium fluoride thin films as cover layer for multi-electrode array technology

We present an approach for fabrication of reproducible, chemically and mechanically robust functionalized layers based on MgF₂ thin films on thin glass substrates. These show great advantages for use in super-resolution microscopy as well as for multi-electrode-array fabrication and are especially suited for combination of these techniques. The transparency of the coated substrates with the low refractive index material is adjustable by the layer thickness and can be increased above 92%. Due to the hydrophobic and lipophilic properties of the thin crystalline MgF₂ layers, the temporal stable adhesion needed for fixation of thin tissue, e.g. cryogenic brain slices is given. This has been tested using localization-based super-resolution microscopy with currently highest spatial resolution in light microscopy. We demonstrated that direct stochastic optical reconstruction microscopy revealed in reliable imaging of structures of central synapses by use of double immunostaining of post- (homer1 and GluA2) and presynaptic (bassoon) marker structure in a 10 µm brain slice without additional fixing of the slices. Due to the proven additional electrical insulating effect of MgF₂ layers, surfaces of multi-electrode-arrays were coated with this material and tested by voltage-current-measurements. MgF₂ coated multi-electrode-arrays can be used as a functionalized microscope cover slip for combination with live-cell super-resolution microscopy.

Neuronal network dysfunction precedes storage and neurodegeneration in a lysosomal storage disorder

Accumulation of lysosomal storage material and late-stage neurodegeneration are hallmarks of lysosomal storage disorders (LSDs) affecting the brain. Yet, for most LSDs, including CLN3 disease, the most common form of childhood dementia, it is unclear what mechanisms drive neurologic symptoms. Do deficits arise from loss of function of the mutated protein or toxicity from storage accumulation? Here, using in vitro voltage-sensitive dye imaging and in vivo electrophysiology, we find progressive hippocampal dysfunction occurs before notable lysosomal storage and neuronal loss in 2 CLN3 disease mouse models. Pharmacologic reversal of lysosomal storage deposition in young mice does not rescue this circuit dysfunction. Additionally, we find that CLN3 disease mice lose an electrophysiologic marker of new memory encoding - hippocampal sharp-wave ripples. This discovery, which is also seen in Alzheimer's disease, suggests the possibility of a shared electrophysiologic signature of dementia. Overall, our data describe new insights into previously unknown network-level changes occurring in LSDs affecting the central nervous system and highlight the need for new therapeutic interventions targeting early circuit defects.

The neuronal ceroid lipofuscinosis protein Cln7 functions in the postsynaptic cell to regulate synapse development

The neuronal ceroid lipofuscinoses (NCLs) are a group of fatal, monogenic neurodegenerative disorders with an early onset in infancy or childhood. Despite identification of the genes disrupted in each form of the disease, their normal cellular role and how their deficits lead to disease pathology is not fully understood. Cln7, a major facilitator superfamily domain-containing protein, is affected in a late infantile-onset form of NCL. Cln7 is conserved across species suggesting a common function. Here we demonstrate that Cln7 is required for the normal growth of synapses at the Drosophila larval neuromuscular junction. In a Cln7 mutant, synapses fail to develop fully leading to reduced function and behavioral changes with dysregulation of TOR activity. Cln7 expression is restricted to the post-synaptic cell and the protein localizes to vesicles immediately adjacent to the post-synaptic membrane. Our data suggest an involvement for Cln7 in regulating trans-synaptic communication necessary for normal synapse development.

LGI1 antibodies alter Kv1.1 and AMPA receptors changing synaptic excitability, plasticity and memory

Leucine-rich glioma-inactivated 1 (LGI1) is a secreted neuronal protein that forms a trans-synaptic complex that includes the presynaptic disintegrin and metalloproteinase domain-containing protein 23 (ADAM23), which interacts with voltage-gated potassium channels Kv1.1, and the postsynaptic ADAM22, which interacts with AMPA receptors. Human autoantibodies against LGI1 associate with a form of autoimmune limbic encephalitis characterized by severe but treatable memory impairment and frequent faciobrachial dystonic seizures. Although there is evidence that this disease is immune-mediated, the underlying LGI1 antibody-mediated mechanisms are unknown. Here, we used patient-derived immunoglobulin G (IgG) antibodies to determine the main epitope regions of LGI1 and whether the antibodies disrupt the interaction of LGI1 with ADAM23 and ADAM22. In addition, we assessed the effects of patient-derived antibodies on Kv1.1, AMPA receptors, and memory in a mouse model based on cerebroventricular transfer of patient-derived IgG. We found that IgG from all patients (n = 25), but not from healthy participants (n = 20), prevented the binding of LGI1 to ADAM23 and ADAM22. Using full-length LGI1, LGI3, and LGI1 constructs containing the LRR1 domain (EPTP1-deleted) or EPTP1 domain (LRR3-EPTP1), IgG from all patients reacted with epitope regions contained in the LRR1 and EPTP1 domains. Confocal analysis of hippocampal slices of mice infused with pooled IgG from eight patients, but not pooled IgG from controls, showed a decrease of total and synaptic levels of Kv1.1 and AMPA receptors. The effects on Kv1.1 preceded those involving the AMPA receptors. In acute slice preparations of hippocampus, patch-clamp analysis from dentate gyrus granule cells and CA1 pyramidal neurons showed neuronal hyperexcitability with increased glutamatergic transmission, higher presynaptic release probability, and reduced synaptic failure rate upon minimal stimulation, all likely caused by the decreased expression of Kv1.1. Analysis of synaptic plasticity by recording field potentials in the CA1 region of the hippocampus showed a severe impairment of long-term potentiation. This defect in synaptic plasticity was independent from Kv1 blockade and was possibly mediated by ineffective recruitment of postsynaptic AMPA receptors. In parallel with these findings, mice infused with patient-derived IgG showed severe memory deficits in the novel object recognition test that progressively improved after stopping the infusion of patient-derived IgG. Different from genetic models of LGI1 deficiency, we did not observe aberrant dendritic sprouting or defective synaptic pruning as potential cause of the symptoms. Overall, these findings demonstrate that patient-derived IgG disrupt presynaptic and postsynaptic LGI1 signalling, causing neuronal hyperexcitability, decreased plasticity, and reversible memory deficits.

Astrocytes in juvenile neuronal ceroid lipofuscinosis (CLN3) display metabolic and calcium signaling abnormalities

Juvenile neuronal ceroid lipofuscinosis (JNCL) is a lysosomal storage disease caused by autosomal recessive mutations in ceroid lipofuscinosis 3 (CLN3). Children with JNCL experience progressive visual, cognitive, and motor deterioration with a decreased life expectancy (late teens-early 20s). Neuronal loss is thought to occur, in part, via glutamate excitotoxicity; however, little is known about astrocyte glutamate regulation in JNCL. Spontaneous Ca²⁺ oscillations were reduced in murine Cln3^Δex7/8 astrocytes, which were also observed following glutamate or cytokine exposure. Astrocyte glutamate transport is an energy-demanding process and disruptions in metabolic pathways could influence glutamate homeostasis in Cln3^Δex7/8 astrocytes. Indeed, basal mitochondrial respiration and ATP production were significantly reduced in Cln3^Δex7/8 astrocytes. These changes were not attributable to reduced mitochondria, since mitochondrial DNA levels were similar between wild type and Cln3^Δex7/8 astrocytes. Interestingly, despite these functional deficits in Cln3^Δex7/8 astrocytes, glutamate transporter expression and glutamate uptake were not dramatically affected. Concurrent with impaired astrocyte metabolism and Ca²⁺ signaling, murine Cln3^Δex7/8 neurons were hyper-responsive to glutamate, as reflected by heightened and prolonged Ca²⁺ signals. These findings identify intrinsic metabolic and Ca²⁺ signaling defects in Cln3^Δex7/8 astrocytes that may contribute to neuronal dysfunction in CLN3 disease. This article is part of the Special Issue "Lysosomal Storage Disorders".

De-palmitoylation by N-(tert-Butyl) hydroxylamine inhibits AMPAR-mediated synaptic transmission via affecting receptor distribution in postsynaptic densities

AIMS

Palmitoylation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) subunits or their "scaffold" proteins produce opposite effects on AMPAR surface delivery. Considering AMPARs have long been identified as suitable drug targets for central nervous system (CNS) disorders, targeting palmitoylation signaling to regulate AMPAR function emerges as a novel therapeutic strategy. However, until now, much less is known about the effect of palmitoylation-deficient state on AMPAR function. Herein, we set out to determine the effect of global de-palmitoylation on AMPAR surface expression and its function, using a special chemical tool, N-(tert-Butyl) hydroxylamine (NtBuHA).

METHODS

BS³ protein cross-linking, Western blot, immunoprecipitation, patch clamp, and biotin switch assay.

RESULTS

Bath application of NtBuHA (1.0 mM) reduced global palmitoylated proteins in the hippocampus of mice. Although NtBuHA (1.0 mM) did not affect the expression of ionotropic glutamate receptor subunits, it preferentially decreased the surface expression of AMPARs, not N-methyl-d-aspartate receptors (NMDARs). Notably, NtBuHA (1.0 mM) reduces AMPAR-mediated excitatory postsynaptic currents (mEPSCs) in the hippocampus. This effect may be largely due to the de-palmitoylation of postsynaptic density protein 95 (PSD95) and protein kinase A-anchoring proteins, both of which stabilized AMPAR synaptic delivery. Furthermore, we found that changing PSD95 palmitoylation by NtBuHA altered the association of PSD95 with stargazin, which interacted directly with AMPARs, but not NMDARs.

CONCLUSION

Our data suggest that the palmitoylation-deficient state initiated by NtBuHA preferentially reduces AMPAR function, which may potentially be used for the treatment of CNS disorders, especially infantile neuronal ceroid lipofuscinosis (Batten disease).

Altered Cerebellar Short-Term Plasticity but No Change in Postsynaptic AMPA-Type Glutamate Receptors in a Mouse Model of Juvenile Batten Disease

Juvenile Batten disease is the most common progressive neurodegenerative disorder of childhood. It is associated with mutations in the CLN3 gene, causing loss of function of CLN3 protein and degeneration of cerebellar and retinal neurons. It has been proposed that changes in granule cell AMPA-type glutamate receptors (AMPARs) contribute to the cerebellar dysfunction. In this study, we compared AMPAR properties and synaptic transmission in cerebellar granule cells from wild-type and Cln3 knock-out mice. In Cln3Δex1-6 cells, the amplitude of AMPA-evoked whole-cell currents was unchanged. Similarly, we found no change in the amplitude, kinetics, or rectification of synaptic currents evoked by individual quanta, or in their underlying single-channel conductance. We found no change in cerebellar expression of GluA2 or GluA4 protein. By contrast, we observed a reduced number of quantal events following mossy-fiber stimulation in Sr2+, altered short-term plasticity in conditions of reduced extracellular Ca2+, and reduced mossy fiber vesicle number. Thus, while our results suggest early presynaptic changes in the Cln3Δex1-6 mouse model of juvenile Batten disease, they reveal no evidence for altered postsynaptic AMPARs.