Synaptic Integrity Research Articles

Diminazene Ameliorates Neuroinflammation by Suppression of Astrocytic miRNA-224-5p/NLRP3 Axis in Alzheimer’s Disease Model

ACE2/Ang(1-7)/Mas Receptor, the momentous component of the renin-angiotensin system, has been shown to be involved in Alzheimer's disease (AD). We had previously found that enhancing brain ACE2 activity ameliorated cognitive impairment and attenuated brain neuroinflammation in SAMP8 mice, an animal model of AD. However, the exact mechanism of action of Diminazene (DIZE) has not been revealed. APP/PS1 mice were injected intraperitoneally with DIZE. Cognitive functions, neuronal and synaptic integrity, and inflammation-related markers were assessed by Morris water maze, Nissl staining, Western blotting and ELISA, respectively. Since astrocytes played a crucial role in AD-related neuroinflammation whilst miRNAs were reported to participate in modulating inflammatory responses, astrocytes of APP/PS1 mice were then isolated for high-throughput miRNAs sequencing to identify the most differentially expressed miRNA following DIZE treatment. Afterward, the downstream pathway of this miRNA in the anti-inflammatory action of DIZE was investigated using primary astrocytes. The results showed that DIZE alleviated cognitive impairment and neuronal and synaptic damage in APP/PS1 mice. Simultaneously, DIZE suppressed the secretion of pro-inflammatory cytokines and the expression of NLRP3 inflammasome. Importantly, miR-224-5p was significantly up-regulated in the astrocytes of APP/PS1 mice treated by DIZE, and NLRP3 is one of the targets of miR-224-5p. Upregulation of miR-224-5p inhibited the expression of NLRP3 in Aβ1-42-stimulated cells, whereas miR-224-5p downregulation reversed this effect. Furthermore, the inhibition of miR-224-5p could reverse the inhibitory effect of DIZE on astrocytic NLRP3 inflammasome. These findings firstly suggested that DIZE could inhibit astrocyte-regulated neuroinflammation via miRNA-224-5p/NLRP3 pathway. Furthermore, our study reveals the underlying mechanism by which DIZE suppresses neuroinflammatory responses in AD mice and uncovers the potential of DIZE in AD treatment.

DOPAL initiates αSynuclein-dependent impaired proteostasis and degeneration of neuronal projections in Parkinson’s disease

Dopamine dyshomeostasis has been acknowledged among the determinants of nigrostriatal neuron degeneration in Parkinson’s disease (PD). Several studies in experimental models and postmortem PD patients underlined increasing levels of the dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL), which is highly reactive towards proteins. DOPAL has been shown to covalently modify the presynaptic protein αSynuclein (αSyn), whose misfolding and aggregation represent a major trait of PD pathology, triggering αSyn oligomerization in dopaminergic neurons. Here, we demonstrated that DOPAL elicits αSyn accumulation and hampers αSyn clearance in primary neurons. DOPAL-induced αSyn buildup lessens neuronal resilience, compromises synaptic integrity, and overwhelms protein quality control pathways in neurites. The progressive decline of neuronal homeostasis further leads to dopaminergic neuron loss and motor impairment, as showed in in vivo models. Finally, we developed a specific antibody which detected increased DOPAL-modified αSyn in human striatal tissues from idiopathic PD patients, corroborating the translational relevance of αSyn-DOPAL interplay in PD neurodegeneration.

Synaptic logistics: The presynaptic scaffold protein Piccolo a nodal point tuning synaptic vesicle recycling, maintenance and integrity

Synaptic logistics: The presynaptic scaffold protein Piccolo a nodal point tuning synaptic vesicle recycling, maintenance and integrity

The mitochondria-targeted small molecule SS31 delays progression of behavioral deficits by attenuating β-amyloid plaque formation and mitochondrial/synaptic deterioration in APP/PS1 mice

Alzheimer's disease (AD) is a common neurodegenerative disorder characterized by progressive cognitive dysfunction and an impaired ability to carry out daily life functions. Mitochondrial dysfunction and β-amyloid (Aβ) deposition are the most common causes of AD. Antioxidants have been shown to delay brain aging and AD development; however, it remains unknown whether the antioxidant peptide SS31 can protect mitochondrial and synaptic function and delay the progression of behavioral deficits in early-stage AD in vivo. Therefore, in this study we compared mitochondrial and synaptic changes, as well as the protective effects of SS31, in APP/PS1 transgenic mice and C57BL/6J control mice. The APP/PS1 transgenic mice exhibited elevated expression of Aβ40/Aβ42 and mitochondrial fission protein DLP1 and reduced expression of synaptophysin (SYN) and postsynaptic density protein 95 (PSD95) reductions, as well as increased levels of neuronal apoptosis and ROS in the hippocampus, and long-term treatment with SS31 reversed these effects. Furthermore, the cognitive impairments observed in APP/PS1 transgenic mice were reversed by SS31 treatment. Our findings show that SS31 lowers ROS and Aβ levels, protecting mitochondrial homeostasis and synaptic integrity, and ultimately improving behavioral deficits in early-stage AD. This suggests that SS31 is a potential pharmacological agent for treating or slowing the progression of AD.

Genome-wide analysis reveals novel regulators of synaptic maintenance in Drosophila.

Maintaining synaptic communication is required to preserve nervous system function as an organism ages. While much work has been accomplished to understand synapse formation and development, we understand relatively little regarding maintaining synaptic integrity throughout aging. To better understand the mechanisms responsible for maintaining synaptic structure and function, we performed an unbiased forward genetic screen to identify genes required for synapse maintenance of adult Drosophila neuromuscular junctions. Using flight behavior as a screening tool, we evaluated flight ability in 198 lines from the Drosophila Genetic Reference Panel to identify single nucleotide polymorphisms (SNPs) that are associated with a progressive loss of flight ability with age. Among the many candidate genes identified from this screen, we focus here on 10 genes with clear human homologs harboring SNPs that are most highly associated with synaptic maintenance. Functional validation of these genes using mutant alleles revealed a progressive loss of synaptic structural integrity. Tissue-specific knockdown of these genes using RNA interference (RNAi) uncovered important roles for these genes in either presynaptic motor neurons, postsynaptic muscles, or associated glial cells, highlighting the importance of each component of tripartite synapses. These results offer greater insight into the mechanisms responsible for maintaining structural and functional integrity of synapses with age.

Slingshot homolog-1 amplifies mitochondrial abnormalities by distinctly impairing health and clearance of mitochondria.

Accumulating toxic protein assemblies, including Aβ and tau, and dysfunctional mitochondria are associated with synaptic and neuronal loss in Alzheimer's disease (AD). Such accumulations are thought to be owing to clearance defects in the autophagy-lysosome pathway. Mitochondrial dysfunction is evident in AD brains and animal models at multiple levels, such as mitochondrial genomic mutations, disrupted bioenergetics, deregulated mitochondrial dynamics and impaired clearance of damaged mitochondria (mitophagy). Slingshot homolog-1 (SSH1) is a phosphatase activated by oxidative stress, high intracellular levels of Ca2+ and Aβ42 oligomers (Aβ42O), known for its function to dephosphorylate/activate cofilin through the N-terminal region. SSH1-mediated cofilin dephosphorylation results in Ab42O-induced severing of F-actin and translocation of cofilin to mitochondria, which promotes mitochondria-mediated apoptosis, synaptic loss and synaptic deficits. On the other hand, SSH1-mediated dephosphorylation/deactivation of the autophagy-cargo receptor p62 (SQSTM1), through its C-terminal region, inhibits p62 autophagy flux. However, the interplay between these two different activities of SSH1 in Aβ42O-induced mitochondrial toxicity remains unclear. In this study, we assessed the role of endogenous SSH1 and different regions of SSH1 in regulating mitochondrial health, mitochondrial respiration, clearance of damaged mitochondria and synaptic integrity in vitro and in vivo. Our results indicate that SSH1 suppresses mitochondrial health and respiration through the cofilin-binding N-terminal region, whereas SSH1 impairs mitophagy through a newly identified ~ 100 residue p62-binding domain in the C-terminal region. These results indicate that both N-terminal and C-terminal regions negatively impact mitochondria by distinct and independent modalities to amplify mitochondrial abnormalities, making SSH1 an excellent target to mitigate AD pathogenesis.

Brain-enriched miR-128: Reduced in exosomes from Parkinson's patient plasma, improves synaptic integrity, and prevents 6-OHDA mediated neuronal apoptosis.

Parkinson's disease (PD) is a progressive neurodegenerative disorder associated with the death of mid-brain dopaminergic neurons. Unfortunately, no effective cure or diagnostic biomarkers for PD are available yet. To address this, the present study focuses on brain-enriched small non-coding regulatory RNAs called microRNAs (miRNAs) that are released into the circulation packaged inside small extracellular vesicles called exosomes. We collected blood samples from PD patients and isolated exosomes from the plasma. qPCR-based detection revealed a particular neuron-enriched miR-128 to be significantly decreased in the patient-derived exosomes. Interestingly, a concomitant decreased expression of miR-128 was observed in the cellular models of PD. Fluorescent live cell imaging and flow-cytometry revealed that over-expression of miR-128 can prevent 6-OHDA-mediated mitochondrial superoxide production and induction of neuronal death respectively. This neuroprotective effect was found to be induced by miR-128-mediated inhibition of FoxO3a activation, a transcription factor involved in apoptosis. miR-128 over-expression also resulted in down-regulation of pro-apoptotic FoxO3a targets- FasL and PUMA, at both transcript and protein levels. Further downstream, miR-128 over-expression inhibited activation of caspases-8, -9 and -3, preventing both the intrinsic and extrinsic pathways of apoptosis. Additionally, over expression of miR-128 prevented down-regulation of synaptic proteins- Synaptophysin and PSD-95 and attenuated neurite shortening, thereby maintaining overall neuronal integrity. Thus, our study depicts the intracellular role of miR-128 in neuronal apoptosis and neurodegeneration and its implications as a biomarker being detectable in the circulating exosomes of PD patient blood. Thus, characterization of such exosomal brain-enriched miRNAs hold promise for effective detection and diagnosis of PD.

Endocannabinoid control of neuroinflammation in traumatic brain injury by monoacylglycerol lipase in astrocytes.

Endocannabinoid control of neuroinflammation in traumatic brain injury by monoacylglycerol lipase in astrocytes.

QTC-4-MeOBnE Ameliorated Depressive-Like Behavior and Memory Impairment in 3xTg Mice.

Growing evidence has associated major depressive disorder (MDD) as a risk factor or prodromal syndrome for the occurrence of Alzheimer's disease (AD). Although this dilemma remains open, it is widely shown that a lifetime history of MDD is correlated with faster progression of AD pathology. Therefore, antidepressant drugs with neuroprotective effects could be an interesting therapeutic conception to target this issue simultaneously. In this sense, 1-(7-chloroquinolin-4-yl)-N-(4-methoxybenzyl)-5-methyl-1H-1,2,3-triazole-4- carboxamide (QTC-4-MeOBnE) was initially conceived as a multi-target ligand with affinity to β-secretase (BACE), glycogen synthase kinase 3β (GSK3β), and acetylcholinesterase but has also shown secondary effects on pathways involved in neuroinflammation and neurogenesis in preclinical models of AD. Herein, we investigated the effect of QTC-4-MeOBnE (1mg/kg) administration for 45days on depressive-like behavior and memory impairment in 3xTg mice, before the pathology is completely established. The treatment with QTC-4-MeOBnE prevented memory impairment and depressive-like behavior assessed by the Y-Maze task and forced swimming test. This effect was associated with the modulation of plural pathways involved in the onset and progression of AD, in cerebral structures of the cortex and hippocampus. Among them, the reduction of amyloid beta (Aβ) production mediated by changes in amyloid precursor protein metabolism and hippocampal tau phosphorylation through the inhibition of kinases. Additionally, QTC-4-MeOBnE also exerted beneficial effects on neuroinflammation and synaptic integrity. Overall, our studies suggest that QTC-4-MeOBnE has a moderate effect in a transgenic model of AD, indicating that perhaps studies regarding the neuropsychiatric effects as a neuroprotective molecule are more prone to be feasible.

The interrelationships between neuronal viability, synaptic integrity, microglial responses, and amyloid-beta formation in an in vitro neurotrauma model

The interrelationships between neuronal viability, synaptic integrity, and microglial responses remain in infancy. In dealing with the question, we induced a stretch injury to evaluate the mechanical effects of trauma on rat primary cortical neurons and BV2 microglial cells in a transwell culture system. The viability of primary neurons and BV2 cells was determined by MTT. Synaptic integrity was evaluated by determining the expression of beta-secretase 1 (BACE1), amyloid-beta (Aβ), microtubule-associated protein 2 (MAP2), and synaptophysin (vehicle protein). Both CD16/32-positive (CD16/32+) and CD206-positive (CD206+) microglia cells were detected by immunofluorescence staining. The phagocytic ability of the BV2 cells was determined using pHrodo E. coli BioParticles conjugates and flow cytometry. We found that stretch injury BV2 cells caused reduced viability and synaptic abnormalities characterized by Aβ accumulation and reductions of BACE1, MAP2, and synaptophysin in primary neurons. Intact BV2 cells exhibited normal phagocytic ability and were predominantly CD206+ microglia cells, whereas the injured BV2 cells exhibited reduced phagocytic ability and were predominantly CD16/32+ microglial cells. Like a stretch injury, the injured BV2 cells can cause both reduced viability and synaptic abnormalities in primary neurons; intact BV2 cells, when cocultured with primary neurons, can protect against the stretch-injured-induced reduced viability and synaptic abnormalities in primary neurons. We conclude that CD206+ and CD16/32+ BV-2 cells can produce neuroprotective and cytotoxic effects on primary cortical neurons.

Neuronal vulnerability to brain aging and neurodegeneration in cognitively impaired marmoset monkeys (Callithrix jacchus)

The investigation of neurobiological and neuropathological changes that affect synaptic integrity and function with aging is key to understanding why the aging brain is vulnerable to Alzheimer's disease. We investigated the cellular characteristics in the cerebral cortex of behaviorally characterized marmosets, based on their trajectories of cognitive learning as they transitioned to old age. We found increased astrogliosis, increased phagocytic activity of microglial cells and differences in resting and reactive microglial cell phenotypes in cognitively impaired compared to nonimpaired marmosets. Differences in amyloid beta deposition were not related to cognitive trajectory. However, we found age-related changes in density and morphology of dendritic spines in pyramidal neurons of layer 3 in the dorsolateral prefrontal cortex and the CA1 field of the hippocampus between cohorts. Overall, our data suggest that an accelerated aging process, accompanied by neurodegeneration, that takes place in cognitively impaired aged marmosets and affects the plasticity of dendritic spines in cortical areas involved in cognition and points to mechanisms of neuronal vulnerability to aging.

Photobiomodulation treatment inhibits neurotoxic astrocytic polarization and protects neurons in in vitro and in vivo stroke models

The beneficial effects of photobiomodulation (PBM) on function recovery after stroke have been well-established, while its molecular and cellular mechanisms remain to be elucidated. The current study was designed to investigate the effect of PBM on synaptic proteins and astrocyte polarization of photothrombotic (PT)-stroke induced rats in vivo, and explore the possible effect of PBM treatment on oxygen-glucose deprivation (OGD)-induced neurotoxic astrocytic polarization in vitro. We reported that 2-min PBM treatment (808 nm) for 7 days significantly increased synaptic proteins and neuroprotective astrocytic marker S100 Calcium Binding Protein A10 (S100A10) and inhibited neurotoxic astrocytic marker C3d in the peri-infarct region after ischemic stroke. Cell culture studies of primary cortical neurons and N2a cells showed that single-dose PBM treatment could increase cellular viability, regulate the apoptotic proteins (Caspase 9, Bcl-xL and BAX) and preserve synaptic proteins following OGD exposure. Additionly, PBM decreased the levels of C3d, inducible nitric oxide synthase (iNOS) and interleukin 1β (IL-1β) on astrocytes exposed to OGD. In summary, we demonstrated that PBM could inhibit neurotoxic astrocytic polarization, preserve synaptic integrity and protect neurons against stroke injury both in vitro and in vivo.

Synapse integrity and function: Dependence on protein synthesis and identification of potential failure points.

Synaptic integrity and function depend on myriad proteins - labile molecules with finite lifetimes that need to be continually replaced with freshly synthesized copies. Here we describe experiments designed to expose synaptic (and neuronal) properties and functions that are particularly sensitive to disruptions in protein supply, identify proteins lost early upon such disruptions, and uncover potential, yet currently underappreciated failure points. We report here that acute suppressions of protein synthesis are followed within hours by reductions in spontaneous network activity levels, impaired oxidative phosphorylation and mitochondrial function, and, importantly, destabilization and loss of both excitatory and inhibitory postsynaptic specializations. Conversely, gross impairments in presynaptic vesicle recycling occur over longer time scales (days), as does overt cell death. Proteomic analysis identified groups of potentially essential 'early-lost' proteins including regulators of synapse stability, proteins related to bioenergetics, fatty acid and lipid metabolism, and, unexpectedly, numerous proteins involved in Alzheimer's disease pathology and amyloid beta processing. Collectively, these findings point to neuronal excitability, energy supply and synaptic stability as early-occurring failure points under conditions of compromised supply of newly synthesized protein copies.

Xenon attenuated neonatal lipopolysaccharide exposure induced neuronal necroptosis and subsequently improved cognition in juvenile rats.

Background: Neonatal sepsis is known to cause neurodevelopment impairment and has been reported to increase risks for neurological/psychiatric disorders. In this study, we investigated the effect of xenon, a well-known potent neuroprotective gas, on neonatal sepsis-induced neurodevelopment impairment in rats together with underlying mechanism by focusing on receptor-interacting protein kinase (RIP) mediated neuronal necroptosis. Methods: 3-day-old Sprague-Dawley rat pups were exposed to either 70% xenon or N2 balanced with O2 for 6h, during which lipopolysaccharide (LPS) was injected intraperitoneally for 3 times (500μg/kg for the 1st and 250μg/kg for the second and third dose; n = 6-10/group). In another cohort of 3-day-old rat pups, intracerebroventricular injection of necrostatin-1 (4µg in 4µl saline, a RIP-1-targeted inhibitor of necroptosis) was performed 20min after the third dose of LPS. The learning ability and memory were assessed 25days after LPS injection. Then, their hippocampus was collected for neuronal necroptosis with RIP and MIKL assessments using western blot and in situ immunostaining. Systemic and neuro-inflammation was also assessed. Results: LPS insult resulted in elevation of pro-inflammatory cytokine TNF-𝝰 and IL-6, caused neuronal necroptosis and damaged synaptic integrity at the brain developing stage, which finally led to the long-term cognitive impairment. Xenon inhibited necroptosis associated mediator RIP-1, RIP-3, and MLKL activation, protected neurons and attenuated cognitive dysfunction induced by LPS. Like xenon, the similar pattern changes induced by a RIP-1 inhibitor Necrostatin-1 were also found. Conclusion: This study indicates that necroptosis is involved in neonatal sepsis-induced neurofunctional impairments and xenon may be a novel therapeutic strategy to prevent/treat cognitive impairment in neonatal septic patients.

Alzheimer’s Disease Proteinopathy and Synaptic Integrity: The Protective Role of Physical Activity

AbstractBackgroundAlzheimer’s disease (AD) proteinopathy levels are associated with greater synaptic dysfunction markers in brain tissue and cerebrospinal fluid (CSF). However, it is less well known how physical activity (PA) affects this relationship. We aimed to examine the moderating role of PA on AD proteinopathy and synaptic marker outcomes in typically aging adults.Method43 cognitively normal older adults from the UCSF Memory and Aging Center (Meanage = 72.82; SDage = 6.51; 56% women; 83.7% non‐Hispanic White) self‐reported their physical activity levels via the Physical Activity Scale for the Elderly (PASE) questionnaire and completed lumbar punctures during their annual research visit. CSF was analyzed for p‐tau181 and Aβ42, as well as presynaptic (SNAP‐25, synaptotagmin‐1), postsynaptic (neurogranin‐36), and synaptic growth (GAP‐43) proteins in picograms per milliliter (pg/ml). Separate linear regression models assessed the interactive effect of PA and p‐tau181/Aβ42 ratios on levels of each synaptic marker, covarying for participant demographics.ResultGreater p‐tau181/Aβ42 ratios correlated with worse synaptic integrity (r = 0.364‐ 0.412). Adjusting for age, body mass index, and education, there was a significant interaction between p‐tau181/Aβ42 and physical activity on synaptotagmin‐1 (p = 0.0065), neurogranin‐36 (p = 0.0318), and GAP‐43 (p = 0.0321) CSF protein levels, with SNAP‐25 approaching interaction significance (p = 0.0699). Probing the interaction by tertiles, at higher levels of physical activity, the negative relationships between AD proteinopathy and synaptic integrity outcomes were significantly attenuated.ConclusionPhysical activity significantly moderates the relationship between AD proteinopathy and CSF biomarkers of synaptic integrity. Higher PA engagement may attenuate the adverse link between AD proteinopathy and synapse dysfunction. Our findings highlight the importance of exercise and active lifestyles in promoting and maintaining synapse function regardless of neuropathological burden.

Assessing synaptic integrity in Alzheimer’s brain with UCB‐J

AbstractBackgroundSynaptic loss is an eminent feature of Alzheimer’s disease (AD). Synapses critical for neuronal transmission are regulated by synaptic vesicles (SV), which expresses an integral transmembrane protein called SV protein 2A (SV2A) throughout the brain. Notably, reduced SV2A expression has been implicated in AD and other proteinopathies. UCB‐J is a recently developed PET‐tracer, which target SV2A, to study synaptic integrity in different neurological disorders. Though several UCB‐J in vivo PET studies have been published in AD, there have been some discrepancies between the findings. Many of these studies indicated potential correlations between tau deposition, atrophy, cognitive‐impairment, and loss of UCB‐J binding. Based on these in vivo observations, we found it of utmost relevance to perform extensive pre‐clinical validation of UCB‐J in AD brains with postmortem brain imaging techniques.MethodWe performed radioligand binding assays (saturation and competition) alongside large brain section autoradiography in AD and control brains.Result 3H‐UCB‐J competition studies with unlabelled‐UCB‐J showed one‐binding site (IC50: ∼ 10 nM) in the frontal cortex (FC) of AD and control brains. Saturation studies in FC region of AD and control brains showed much higher specific binding in synaptosomal membrane P2‐fraction (Bmax: 5.8 ‐ 8.7 pmol/mg, Kd ∼ 5.0 nM) as compared to brain homogenates (Bmax: 0.09 ‐ 0.18 pmol/mg, Kd ∼ 4.0 nM). P2‐fraction saturation binding study clearly highlighted the loss of UCB‐J binding in FC of AD brain as compared to control brain. In contrast, large brain hemisphere section autoradiography incubated with 3H‐UCB‐J showed unexpectedly higher regional binding in AD brain sections as compared to control, motivating further mechanistic pre‐clinical validation with other synaptic markers in AD and other proteinopathies.ConclusionOur findings explicitly demonstrated high specificity of UCB‐J for SV2A in AD and control brains. UCB‐J specific binding was much higher in P2‐fraction than brain homogenate (P2‐fraction > brain homogenate) and highlighted the expected loss of UCB‐J binding in AD brain. Competition and saturation binding studies complemented each other and showed only one‐binding site with nM‐affinity in AD and control brains. Unanticipated high UCB‐J binding in AD brain in autoradiography studies indicate potential interaction with other brain tissue component, warrant further investigation.

Age‐dependent effects of the p75 neurotrophin receptor modulator LM11A‐31 on Alzheimer’s disease biomarkers in a 26‐week safety and exploratory endpoint trial

AbstractBackgroundThe p75 neurotrophin receptor (p75NTR) modulates pro‐ and anti‐apoptotic pathways as well as neurite and neuritic spine integrity. This receptor is expressed in cells vulnerable to aging and disease, including basal forebrain cholinergic neurons and hippocampal pyramidal neurons. It is also expressed by glial cells under pathological conditions. Pharmacological modulation of the p75NTR with LM11A‐31 alters both age‐ and disease‐related neuronal dysfunction. For example, LM11A‐31 reverses neuritic pathology in aged mice and reduces amyloid‐induced tau phosphorylation in mouse models of Alzheimer’s disease (AD). In this proof‐of‐concept study, we examined the effects of LM11A‐31 treatment on longitudinal neuroimaging and CSF biomarkers in humans with mild to moderate Alzheimer’s disease. Based on our preclinical work, we hypothesized that age and disease may interact to predict response to LM11A‐31 treatment in humans. Therefore, we additionally conducted subgroup analyses of drug effect in older and younger individuals.MethodParticipants with mild to moderate AD (MMSE score = 18‐26; age 55‐85 years) were enrolled in a 26‐week placebo‐controlled phase 2a safety and exploratory endpoint trial of LM11A‐31. Exploratory outcome measures included structural MRI, CSF AD core biomarkers, and CSF biomarkers related to pathological processes affected in mouse studies including synaptic integrity and inflammation. For placebo and drug, age subgroups were defined using a median‐split: younger (<72 years) and older (> = 72 years).ResultWhole brain structural MRI analyses revealed that 26‐week treatment with LM11A‐31 reduced longitudinal grey matter degeneration in AD‐vulnerable brain regions including the inferior temporal gyrus, insula, frontal operculum and retrosplenial cortex. Furthermore, drug treatment, compared to placebo, prevented longitudinal increases of CSF tau, the presynaptic biomarker SNAP25, and the inflammatory biomarker YKL‐40. Median split analyses demonstrated that drug effects for structural MRI and CSF measures were consistently stronger in younger individuals.ConclusionThis investigation highlights that biomarkers may demonstrate age‐dependency in response to therapeutic interventions in the context of mild‐moderate AD. Our results may inform biomarker selection and design of future studies of LM11A‐31 in human AD.

Microglia: Friends or Foes in Glaucoma? A Developmental Perspective.

Glaucoma is the most prevalent form of optic neuropathy where a progressive degeneration of retinal ganglion cells (RGCs) leads to irreversible loss of vision. The mechanism underlying glaucomatous degeneration remains poorly understood. However, evidence suggests that microglia, which regulate RGC numbers and synaptic integrity during development and provide homeostatic support in adults, may contribute to the disease process. Hence, microglia represent a valid cellular target for therapeutic approaches in glaucoma. Here, we provide an overview of the role of microglia in RGC development and degeneration in the backdrop of neurogenesis and neurodegeneration in the central nervous system and discuss how pathological recapitulation of microglia-mediated developmental mechanisms may help initiate or exacerbate glaucomatous degeneration.

Neuronal nuclear calcium signaling suppression of microglial reactivity is mediated by osteoprotegerin after traumatic brain injury

BackgroundTraumatic brain injury (TBI) is characterized by massive changes in neuronal excitation, from acute excitotoxicity to chronic hyper- or hypoexcitability. Nuclear calcium signaling pathways are involved in translating changes in synaptic inputs and neuronal activity into discrete transcriptional programs which not only affect neuronal survival and synaptic integrity, but also the crosstalk between neurons and glial cells. Here, we report the effects of blunting neuronal nuclear calcium signals in the context of TBI.MethodsWe used AAV vectors to express the genetically encoded and nuclear-targeted calcium buffer parvalbumin (PV.NLS.mCherry) or the calcium/calmodulin buffer CaMBP4.mCherry in neurons only. Upon TBI, the extent of neuroinflammation, neuronal death and synaptic loss were assessed by immunohistochemistry and targeted transcriptome analysis. Modulation of the overall level of neuronal activity was achieved by PSAM/PSEM chemogenetics targeted to parvalbumin interneurons. The functional impact of neuronal nuclear calcium buffering in TBI was assessed by quantification of spontaneous whisking.ResultsBuffering neuronal nuclear calcium unexpectedly resulted in a massive and long-lasting increase in the recruitment of reactive microglia to the injury site, which was characterized by a disease-associated and phagocytic phenotype. This effect was accompanied by a substantial surge in synaptic loss and significantly reduced whisking activity. Transcriptome analysis revealed a complex effect of TBI in the context of neuronal nuclear calcium buffering, with upregulation of complement factors, chemokines and interferon-response genes, as well as the downregulation of synaptic genes and epigenetic regulators compared to control conditions. Notably, nuclear calcium buffering led to a substantial loss in neuronal osteoprotegerin (OPG), whereas stimulation of neuronal firing induced OPG expression. Viral re-expression of OPG resulted in decreased microglial recruitment and synaptic loss. OPG upregulation was also observed in the CSF of human TBI patients, underscoring its translational value.ConclusionNeuronal nuclear calcium signals regulate the degree of microglial recruitment and reactivity upon TBI via, among others, osteoprotegerin signals. Our findings support a model whereby neuronal activity altered after TBI exerts a powerful impact on the neuroinflammatory cascade, which in turn contributes to the overall loss of synapses and functional impairment.

Quantifying postsynaptic receptor dynamics: insights into synaptic function.

The molecular composition of presynaptic and postsynaptic neuronal terminals is dynamic, and yet long-term stabilizations in postsynaptic responses are necessary for synaptic development and long-term plasticity. The need to reconcile these concepts is further complicated by learning- and memory-related plastic changes in the molecular make-up of synapses. Advances in single-particle tracking mean that we can now quantify the number and diffusive properties of specific synaptic molecules, while statistical thermodynamics provides a framework to analyse these molecular fluctuations. In this Review, we discuss the use of these approaches to gain quantitative descriptions of the processes underlying the turnover, long-term stability and plasticity of postsynaptic receptors and show how these can help us to understand the balance between local molecular turnover and synaptic structural identity and integrity.