Long-Lasting Rescue of Network and Cognitive Dysfunction in a Genetic Schizophrenia Model.

Although sensitizing processes occur earlier, schizophrenia is diagnosed in young adulthood, which suggests that it might involve a pathological transition during late brain development in predisposed individuals. Parvalbumin (PV) interneuron alterations have been noticed, but their role in the disease is unclear. Here we demonstrate that adult LgDel+/- mice, a genetic model of schizophrenia, exhibit PV neuron hypo-recruitment and associated chronic PV neuron plasticity together with network and cognitive deficits. All these deficits can be permanently rescued by chemogenetic activation of PV neurons or D2R antagonist treatments, specifically in the ventral hippocampus (vH) or medial-prefrontal cortex during a late-adolescence-sensitive time window. PV neuron alterations were initially restricted to the hippocampal CA1/subiculum, where they became responsive to treatment in late adolescence. Therefore, progression to disease in schizophrenia-model mice can be prevented by treatments supporting vH-mPFC PV network function during a sensitive time window late in adolescence, suggesting therapeutic strategies to prevent the outbreak of schizophrenia.

cGAS-STING drives ageing-related inflammation and neurodegeneration.

Low-grade inflammation is a hallmark of old age and a central driver of ageing-associated impairment and disease1. Multiple factors can contribute to ageing-associated inflammation2; however, the molecular pathways that transduce aberrant inflammatory signalling and their impact in natural ageing remain unclear. Here we show that the cGAS-STING signalling pathway, which mediates immune sensing of DNA3, is a critical driver of chronic inflammation and functional decline during ageing. Blockade of STING suppresses the inflammatory phenotypes of senescent human cells and tissues, attenuates ageing-related inflammation in multiple peripheral organs and the brain in mice, and leads to an improvement in tissue function. Focusing on the ageing brain, we reveal that activation of STING triggers reactive microglial transcriptional states, neurodegeneration and cognitive decline. Cytosolic DNA released from perturbed mitochondria elicits cGAS activity in old microglia, defining a mechanism by which cGAS-STING signalling is engaged in the ageing brain. Single-nucleus RNA-sequencing analysis of microglia and hippocampi of a cGAS gain-of-function mouse model demonstrates that engagement of cGAS in microglia is sufficient to direct ageing-associated transcriptional microglial states leading to bystander cell inflammation, neurotoxicity and impaired memory capacity. Our findings establish the cGAS-STING pathway as a driver of ageing-related inflammation in peripheral organs and the brain, and reveal blockade of cGAS-STING signalling as a potential strategy to halt neurodegenerative processes during old age.

Molecular landscapes of human hippocampal immature neurons across lifespan.

Immature dentate granule cells (imGCs) arising from adult hippocampal neurogenesis contribute to plasticity and unique brain functions in rodents1,2 and are dysregulated in multiple human neurological disorders3-5. Little is known about the molecular characteristics of adult human hippocampal imGCs, and even their existence is under debate1,6-8. Here we performed single-nucleus RNA sequencing aided by a validated machine learning-based analytic approach to identify imGCs and quantify their abundance in the human hippocampus at different stages across the lifespan. We identified common molecular hallmarks of human imGCs across the lifespan and observed age-dependent transcriptional dynamics in human imGCs that suggest changes in cellular functionality, niche interactions and disease relevance, that differ from those in mice9. We also found a decreased number of imGCs with altered gene expression in Alzheimer's disease. Finally, we demonstrated the capacity for neurogenesis in the adult human hippocampus with the presence of rare dentate granule cell fate-specific proliferating neural progenitors and with cultured surgical specimens. Together, our findings suggest the presence of a substantial number of imGCs in the adult human hippocampus via low-frequency de novo generation and protracted maturation, and our study reveals their molecular properties across the lifespan and in Alzheimer's disease.

Aberrant activation of hippocampal astrocytes causes neuroinflammation and cognitive decline in mice.

Reactive astrocytes are associated with neuroinflammation and cognitive decline in diverse neuropathologies; however, the underlying mechanisms are unclear. We used optogenetic and chemogenetic tools to identify the crucial roles of the hippocampal CA1 astrocytes in cognitive decline. Our results showed that repeated optogenetic stimulation of the hippocampal CA1 astrocytes induced cognitive impairment in mice and decreased synaptic long-term potentiation (LTP), which was accompanied by the appearance of inflammatory astrocytes. Mechanistic studies conducted using knockout animal models and hippocampal neuronal cultures showed that lipocalin-2 (LCN2), derived from reactive astrocytes, mediated neuroinflammation and induced cognitive impairment by decreasing the LTP through the reduction of neuronal NMDA receptors. Sustained chemogenetic stimulation of hippocampal astrocytes provided similar results. Conversely, these phenomena were attenuated by a metabolic inhibitor of astrocytes. Fiber photometry using GCaMP revealed a high level of hippocampal astrocyte activation in the neuroinflammation model. Our findings suggest that reactive astrocytes in the hippocampus are sufficient and required to induce cognitive decline through LCN2 release and synaptic modulation. This abnormal glial-neuron interaction may contribute to the pathogenesis of cognitive disturbances in neuroinflammation-associated brain conditions.

Proline isomer-specific antibodies reveal the early pathogenic tau conformation in Alzheimer's disease.

cis-trans isomerization of proteins phosphorylated by proline-directed kinases is proposed to control numerous signaling molecules and is implicated in the pathogenesis of Alzheimer's and other diseases. However, there is no direct evidence for the existence of cis-trans protein isomers in vivo or for their conformation-specific function or regulation. Here we develop peptide chemistries that allow the generation of cis- and trans-specific antibodies and use them to raise antibodies specific for isomers of phosphorylated tau. cis, but not trans, p-tau appears early in the brains of humans with mild cognitive impairment, accumulates exclusively in degenerated neurons, and localizes to dystrophic neurites during Alzheimer's progression. Unlike trans p-tau, the cis isomer cannot promote microtubule assembly, is more resistant to dephosphorylation and degradation, and is more prone to aggregation. Pin1 converts cis to trans p-tau to prevent Alzheimer's tau pathology. Isomer-specific antibodies and vaccines may therefore have value for the early diagnosis and treatment of Alzheimer's disease.

Sex and mental health are related to subcortical brain microstructure.

Some mental health problems such as depression and anxiety are more common in females, while others such as autism and attention deficit/hyperactivity (AD/H) are more common in males. However, the neurobiological origins of these sex differences are poorly understood. Animal studies have shown substantial sex differences in neuronal and glial cell structure, while human brain imaging studies have shown only small differences, which largely reflect overall body and brain size. Advanced diffusion MRI techniques can be used to examine intracellular, extracellular, and free water signal contributions and provide unique insights into microscopic cellular structure. However, the extent to which sex differences exist in these metrics of subcortical gray matter structures implicated in psychiatric disorders is not known. Here, we show large sex-related differences in microstructure in subcortical regions, including the hippocampus, thalamus, and nucleus accumbens in a large sample of young adults. Unlike conventional T1-weighted structural imaging, large sex differences remained after adjustment for age and brain volume. Further, diffusion metrics in the thalamus and amygdala were associated with depression, anxiety, AD/H, and antisocial personality problems. Diffusion MRI may provide mechanistic insights into the origin of sex differences in behavior and mental health over the life course and help to bridge the gap between findings from experimental, epidemiological, and clinical mental health research.

APOER2 splicing repertoire in Alzheimer's disease: Insights from long-read RNA sequencing.

Disrupted alternative splicing plays a determinative role in neurological diseases, either as a direct cause or as a driver in disease susceptibility. Transcriptomic profiling of aged human postmortem brain samples has uncovered hundreds of aberrant mRNA splicing events in Alzheimer's disease (AD) brains, associating dysregulated RNA splicing with disease. We previously identified a complex array of alternative splicing combinations across apolipoprotein E receptor 2 (APOER2), a transmembrane receptor that interacts with both the neuroprotective ligand Reelin and the AD-associated risk factor, APOE. Many of the human APOER2 isoforms, predominantly featuring cassette splicing events within functionally important domains, are critical for the receptor's function and ligand interaction. However, a comprehensive repertoire and the functional implications of APOER2 isoforms under both physiological and AD conditions are not fully understood. Here, we present an in-depth analysis of the splicing landscape of human APOER2 isoforms in normal and AD states. Using single-molecule, long-read sequencing, we profiled the entire APOER2 transcript from the parietal cortex and hippocampus of Braak stage IV AD brain tissues along with age-matched controls and investigated several functional properties of APOER2 isoforms. Our findings reveal diverse patterns of cassette exon skipping for APOER2 isoforms, with some showing region-specific expression and others unique to AD-affected brains. Notably, exon 15 of APOER2, which encodes the glycosylation domain, showed less inclusion in AD compared to control in the parietal cortex of females with an APOE ɛ3/ɛ3 genotype. Also, some of these APOER2 isoforms demonstrated changes in cell surface expression, APOE-mediated receptor processing, and synaptic number. These variations are likely critical in inducing synaptic alterations and may contribute to the neuronal dysfunction underlying AD pathogenesis.

Alzheimer's disease risk gene CD2AP is a dose-sensitive determinant of synaptic structure and plasticity.

CD2-Associated protein (CD2AP) is a candidate susceptibility gene for Alzheimer's disease, but its role in the mammalian central nervous system remains largely unknown. We show that CD2AP protein is broadly expressed in the adult mouse brain, including within cortical and hippocampal neurons, where it is detected at pre-synaptic terminals. Deletion of Cd2ap altered dendritic branching and spine density, and impaired ubiquitin-proteasome system activity. Moreover, in mice harboring either one or two copies of a germline Cd2ap null allele, we noted increased paired-pulse facilitation at hippocampal Schaffer-collateral synapses, consistent with a haploinsufficient requirement for pre-synaptic release. Whereas conditional Cd2ap knockout in the brain revealed no gross behavioral deficits in either 3.5- or 12-month-old mice, Cd2ap heterozygous mice demonstrated subtle impairments in discrimination learning using a touchscreen task. Based on unbiased proteomics, partial or complete loss of Cd2ap triggered perturbation of proteins with roles in protein folding, lipid metabolism, proteostasis, and synaptic function. Overall, our results reveal conserved, dose-sensitive requirements for CD2AP in the maintenance of neuronal structure and function, including synaptic homeostasis and plasticity, and inform our understanding of possible cell-type specific mechanisms in Alzheimer's Disease.

Mutation in protein disulfide isomerase A3 causes neurodevelopmental defects by disturbing endoplasmic reticulum proteostasis.

Recessive gene mutations underlie many developmental disorders and often lead to disabling neurological problems. Here, we report identification of a homozygous c.170G>A (p.Cys57Tyr or C57Y) mutation in the gene coding for protein disulfide isomerase A3 (PDIA3, also known as ERp57), an enzyme that catalyzes formation of disulfide bonds in the endoplasmic reticulum, to be associated with syndromic intellectual disability. Experiments in zebrafish embryos show that PDIA3C57Y expression is pathogenic and causes developmental defects such as axonal disorganization as well as skeletal abnormalities. Expression of PDIA3C57Y in the mouse hippocampus results in impaired synaptic plasticity and memory consolidation. Proteomic and functional analyses reveal that PDIA3C57Y expression leads to dysregulation of cell adhesion and actin cytoskeleton dynamics, associated with altered integrin biogenesis and reduced neuritogenesis. Biochemical studies show that PDIA3C57Y has decreased catalytic activity and forms disulfide-crosslinked aggregates that abnormally interact with chaperones in the endoplasmic reticulum. Thus, rare disease gene variant can provide insight into how perturbations of neuronal proteostasis can affect the function of the nervous system.

Elevated dementia risk, cognitive decline, and hippocampal atrophy in multisite chronic pain.

Numerous studies have investigated the impacts of common types of chronic pain (CP) on patients' cognitive function and observed that CP was associated with later dementia. More recently, there is a growing recognition that CP conditions frequently coexist at multiple body sites and may bring more burdens on patients' overall health. However, whether and how multisite CP (MCP) contributes to an increased risk of dementia, compared to single-site CP (SCP) and pain-free (PF), is largely unclear. In the current study, utilizing the UK Biobank cohort, we first investigated dementia risk in individuals (n = 354,943) with different numbers of coexisting CP sites using Cox proportional hazards regression models. We then applied generalized additive models to investigate whether MCP leads to excessive deterioration of participants' (n = 19,116) cognition and brain structure. We found that individuals with MCP were associated with significantly higher dementia risk, broader and faster cognitive impairment, and greater hippocampal atrophy than both PF individuals and those with SCP. Moreover, the detrimental effects of MCP on dementia risk and hippocampal volume aggravated along with the number of coexisting CP sites. Mediation analyses further revealed that the decline of fluid intelligence in MCP individuals was partially mediated by hippocampal atrophy. Our results suggested that cognitive decline and hippocampal atrophy interact biologically and may underlie the increased risk of dementia associated with MCP.

Hierarchical Gradients of Encoded Spatial and Sensory Information in the Neocortex Are Attenuated by Dorsal Hippocampal Lesions.

During navigation, the neocortex actively integrates learned spatial context with current sensory experience to guide behaviors. However, the relative encoding of spatial and sensorimotor information among cortical cells, and whether hippocampal feedback continues to modify these properties after learning, remains poorly understood. Thus, two-photon microscopy of male and female Thy1-GCaMP6s mice was used to longitudinally image neurons spanning superficial retrosplenial cortex and layers II-Va of primary and secondary motor cortices before and after bilateral dorsal hippocampal lesions. During behavior on a familiar cued treadmill, the locations of two obstacles were interchanged to decouple place-tuning from cue-tuning among position-correlated cells with fields at those locations. Subpopulations of place and cue cells each formed interareal gradients such that higher-level cortical regions exhibited higher fractions of place cells, whereas lower-level regions exhibited higher fractions of cue cells. Position-correlated cells in the motor cortex also formed translaminar gradients; more superficial cells were more likely to exhibit fields and were more sparsely and precisely tuned than deeper cells. After dorsal hippocampal lesions, a neural representation of the learned environment persisted, but retrosplenial cortex exhibited significantly increased cue-tuning, and, in motor cortices, both position-correlated cell recruitment and population activity at the unstable obstacle locations became more homogeneously elevated across laminae. Altogether, these results support that the hippocampus continues to modulate cortical responses in familiar environments, and the relative impact of descending feedback obeys hierarchical interareal and interlaminar gradients opposite to the flow of ascending sensory inputs.

Chinese Verbal Fluency Deficiency in Temporal Lobe Epilepsy with and without Hippocampal Sclerosis: A Multiscale Study.

To test a Chinese character version of the phonemic verbal fluency task in patients with temporal lobe epilepsy (TLE) and assess the verbal fluency deficiency pattern in TLE with and without hippocampal sclerosis, a cross-sectional study was conducted including 30 patients with TLE and hippocampal sclerosis (TLE-HS), 28 patients with TLE and without hippocampal sclerosis (TLE-NHS), and 29 demographically matched healthy controls (HC). Both sexes were enrolled. Participants finished a Chinese character verbal fluency (VFC) task during functional MRI. The activation/deactivation maps, functional connectivity, degree centrality, and community features of the left frontal and temporal regions were compared. A neural network classification model was applied to differentiate TLE-HS and TLE-NHS using functional statistics. The VFC scores were correlated with semantic fluency in HC while correlated with phonemic fluency in TLE-NHS. Activation and deactivation deficiency was observed in TLE-HS and TLE-NHS (p < 0.001, k ≥ 10). Functional connectivity, degree centrality, and community features of anterior inferior temporal gyri were impaired in TLE-HS and retained or even enhanced in TLE-NHS (p < 0.05, FDR-corrected). The functional connectivity was correlated with phonemic fluency (p < 0.05, FDR-corrected). The neural network classification reached an area under the curve of 0.90 in diagnosing hippocampal sclerosis. The VFC task is a Chinese phonemic verbal fluency task suitable for clinical application in TLE. During the VFC task, functional connectivity of phonemic circuits was impaired in TLE-HS and was enhanced in TLE-NHS, representing a compensative phonemic searching strategy applied by patients with TLE-NHS.

G272V and P301L Mutations Induce Isoform Specific Tau Mislocalization to Dendritic Spines and Synaptic Dysfunctions in Cellular Models of 3R and 4R Tau Frontotemporal Dementia.

Tau pathologies are detected in the brains of some of the most common neurodegenerative diseases including Alzheimer's disease (AD), Lewy body dementia (LBD), chronic traumatic encephalopathy (CTE), and frontotemporal dementia (FTD). Tau proteins are expressed in six isoforms with either three or four microtubule-binding repeats (3R tau or 4R tau) due to alternative RNA splicing. AD, LBD, and CTE brains contain pathological deposits of both 3R and 4R tau. FTD patients can exhibit either 4R tau pathologies in most cases or 3R tau pathologies less commonly in Pick's disease, which is a subfamily of FTD. Here, we report the isoform-specific roles of tau in FTD. The P301L mutation, linked to familial 4R tau FTD, induces mislocalization of 4R tau to dendritic spines in primary hippocampal cultures that were prepared from neonatal rat pups of both sexes. Contrastingly, the G272V mutation, linked to familial Pick's disease, induces phosphorylation-dependent mislocalization of 3R tau but not 4R tau proteins to dendritic spines. The overexpression of G272V 3R tau but not 4R tau proteins leads to the reduction of dendritic spine density and suppression of mEPSCs in 5-week-old primary rat hippocampal cultures. The decrease in mEPSC amplitude caused by G272V 3R tau is dynamin-dependent whereas that caused by P301L 4R tau is dynamin-independent, indicating that the two tau isoforms activate different signaling pathways responsible for excitatory synaptic dysfunction. Our 3R and 4R tau studies here will shed new light on diverse mechanisms underlying FTD, AD, LBD, and CTE.

Amyloid-ß Causes NMDA Receptor Dysfunction and Dendritic Spine Loss through mGluR1 and AKAP150-Anchored Calcineurin Signaling.

Neuronal excitatory synapses are primarily located on small dendritic protrusions called spines. During synaptic plasticity underlying learning and memory, Ca2+ influx through postsynaptic NMDA-type glutamate receptors (NMDARs) initiates signaling pathways that coordinate changes in dendritic spine structure and synaptic function. During long-term potentiation (LTP), high levels of NMDAR Ca2+ influx promote increases in both synaptic strength and dendritic spine size through activation of Ca2+-dependent protein kinases. In contrast, during long-term depression (LTD), low levels of NMDAR Ca2+ influx promote decreased synaptic strength and spine shrinkage and elimination through activation of the Ca2+-dependent protein phosphatase calcineurin (CaN), which is anchored at synapses via the scaffold protein A-kinase anchoring protein (AKAP)150. In Alzheimer's disease (AD), the pathological agent amyloid-ß (Aß) may impair learning and memory through biasing NMDAR Ca2+ signaling pathways toward LTD and spine elimination. By employing AKAP150 knock-in mice of both sexes with a mutation that disrupts CaN anchoring to AKAP150, we revealed that local, postsynaptic AKAP-CaN-LTD signaling was required for Aß-mediated impairment of NMDAR synaptic Ca2+ influx, inhibition of LTP, and dendritic spine loss. Additionally, we found that Aß acutely engages AKAP-CaN signaling through activation of G-protein-coupled metabotropic glutamate receptor 1 (mGluR1) leading to dephosphorylation of NMDAR GluN2B subunits, which decreases Ca2+ influx to favor LTD over LTP, and cofilin, which promotes F-actin severing to destabilize dendritic spines. These findings reveal a novel interplay between NMDAR and mGluR1 signaling that converges on AKAP-anchored CaN to coordinate dephosphorylation of postsynaptic substrates linked to multiple aspects of Aß-mediated synaptic dysfunction.

Iron Deposition and Distribution Across the Hippocampus Is Associated with Pattern Separation and Pattern Completion in Older Adults at Risk for Alzheimer's Disease.

Elevated iron deposition in the brain has been observed in older adult humans and persons with Alzheimer's disease (AD), and has been associated with lower cognitive performance. We investigated the impact of iron deposition, and its topographical distribution across hippocampal subfields and segments (anterior, posterior) measured along its longitudinal axis, on episodic memory in a sample of cognitively unimpaired older adults at elevated familial risk for AD (N = 172, 120 females, 52 males; mean age = 68.8 ± 5.4 years). MRI-based quantitative susceptibility maps were acquired to derive estimates of hippocampal iron deposition. The Mnemonic Similarity Task was used to measure pattern separation and pattern completion, two hippocampally mediated episodic memory processes. Greater hippocampal iron load was associated with lower pattern separation and higher pattern completion scores, both indicators of poorer episodic memory. Examination of iron levels within hippocampal subfields across its long axis revealed topographic specificity. Among the subfields and segments investigated here, iron deposition in the posterior hippocampal CA1 was the most robustly and negatively associated with the fidelity memory representations. This association remained after controlling for hippocampal volume and was observed in the context of normal performance on standard neuropsychological memory measures. These findings reveal that the impact of iron load on episodic memory performance is not uniform across the hippocampus. Both iron deposition levels as well as its spatial distribution, must be taken into account when examining the relationship between hippocampal iron and episodic memory in older adults at elevated risk for AD.

Norepinephrine Drives Sleep Fragmentation Activation of Asparagine Endopeptidase, Locus Ceruleus Degeneration, and Hippocampal Amyloid-ß42 Accumulation.

Chronic sleep disruption (CSD), from insufficient or fragmented sleep and is an important risk factor for Alzheimer's disease (AD). Underlying mechanisms are not understood. CSD in mice results in degeneration of locus ceruleus neurons (LCn) and CA1 hippocampal neurons and increases hippocampal amyloid-ß42 (Aß42), entorhinal cortex (EC) tau phosphorylation (p-tau), and glial reactivity. LCn injury is increasingly implicated in AD pathogenesis. CSD increases NE turnover in LCn, and LCn norepinephrine (NE) metabolism activates asparagine endopeptidase (AEP), an enzyme known to cleave amyloid precursor protein (APP) and tau into neurotoxic fragments. We hypothesized that CSD would activate LCn AEP in an NE-dependent manner to induce LCn and hippocampal injury. Here, we studied LCn, hippocampal, and EC responses to CSD in mice deficient in NE [dopamine ß-hydroxylase (Dbh)-/-] and control male and female mice, using a model of chronic fragmentation of sleep (CFS). Sleep was equally fragmented in Dbh -/- and control male and female mice, yet only Dbh -/- mice conferred resistance to CFS loss of LCn, LCn p-tau, and LCn AEP upregulation and activation as evidenced by an increase in AEP-cleaved APP and tau fragments. Absence of NE also prevented a CFS increase in hippocampal AEP-APP and Aß42 but did not prevent CFS-increased AEP-tau and p-tau in the EC. Collectively, this work demonstrates AEP activation by CFS, establishes key roles for NE in both CFS degeneration of LCn neurons and CFS promotion of forebrain Aß accumulation, and, thereby, identifies a key molecular link between CSD and specific AD neural injuries.

Tau regulates Arc stability in neuronal dendrites via a proteasome-sensitive but ubiquitin-independent pathway.

Tauopathies are neurodegenerative disorders characterized by the deposition of aggregates of the microtubule-associated protein tau, a main component of neurofibrillary tangles. Alzheimer's disease (AD) is the most common type of tauopathy and dementia, with amyloid-beta pathology as an additional hallmark feature of the disease. Besides its role in stabilizing microtubules, tau is localized at postsynaptic sites and can regulate synaptic plasticity. The activity-regulated cytoskeleton-associated protein (Arc) is an immediate early gene that plays a key role in synaptic plasticity, learning, and memory. Arc has been implicated in AD pathogenesis and regulates the release of amyloid-beta. We found that decreased Arc levels correlate with AD status and disease severity. Importantly, Arc protein was upregulated in the hippocampus of Tau KO mice and dendrites of Tau KO primary hippocampal neurons. Overexpression of tau decreased Arc stability in an activity-dependent manner, exclusively in neuronal dendrites, which was coupled to an increase in the expression of dendritic and somatic surface GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors. The tau-dependent decrease in Arc was found to be proteasome-sensitive, yet independent of Arc ubiquitination and required the endophilin-binding domain of Arc. Importantly, these effects on Arc stability and GluA1 localization were not observed in the commonly studied tau mutant, P301L. These observations provide a potential molecular basis for synaptic dysfunction mediated through the accumulation of tau in dendrites. Our findings confirm that Arc is misregulated in AD and further show a physiological role for tau in regulating Arc stability and AMPA receptor targeting.

Reticulons 1 and 3 are essential for axonal growth and synaptic maintenance associated with intellectual development.

Reticulon (RTN) proteins are a family of proteins biochemically identified for shaping tubular endoplasmic reticulum, a subcellular structure important for vesicular transport and cell-to-cell communication. In our recent study of mice with knockout of both reticulon 1 (Rtn1) and Rtn3, we discovered that Rtn1-/-;Rtn3-/- (brief as R1R3dKO) mice exhibited neonatal lethality, despite the fact that mice deficient in either RTN1 or RTN3 alone exhibit no discernible phenotypes. This has been the first case to find early lethality in animals with deletion of partial members of RTN proteins. The complete penetrance for neonatal lethality can be attributed to multiple defects including the impaired neuromuscular junction found in the diaphragm. We also observed significantly impaired axonal growth in a regional-specific manner, detected by immunohistochemical staining with antibodies to neurofilament light chain and neurofilament medium chain. Ultrastructural examination by electron microscopy revealed a significant reduction in synaptic active zone length in the hippocampus. Mechanistic exploration by unbiased proteomic assays revealed reduction of proteins such as FMR1, Staufen2, Cyfip1, Cullin-4B and PDE2a, which are known components in the fragile X mental retardation pathway. Together, our results reveal that RTN1 and RTN3 are required to orchestrate neurofilament organization and intact synaptic structure of the central nervous system.

Fluc-EGFP reporter mice reveal differential alterations of neuronal proteostasis in aging and disease.

The cellular protein quality control machinery is important for preventing protein misfolding and aggregation. Declining protein homeostasis (proteostasis) is believed to play a crucial role in age-related neurodegenerative disorders. However, how neuronal proteostasis capacity changes in different diseases is not yet sufficiently understood, and progress in this area has been hampered by the lack of tools to monitor proteostasis in mammalian models. Here, we have developed reporter mice for in vivo analysis of neuronal proteostasis. The mice express EGFP-fused firefly luciferase (Fluc-EGFP), a conformationally unstable protein that requires chaperones for proper folding, and that reacts to proteotoxic stress by formation of intracellular Fluc-EGFP foci and by reduced luciferase activity. Using these mice, we provide evidence for proteostasis decline in the aging brain. Moreover, we find a marked reaction of the Fluc-EGFP sensor in a mouse model of tauopathy, but not in mouse models of Huntington's disease. Mechanistic investigations in primary neuronal cultures demonstrate that different types of protein aggregates have distinct effects on the cellular protein quality control. Thus, Fluc-EGFP reporter mice enable new insights into proteostasis alterations in different diseases.

Cognitive Trajectories and Alzheimer Disease Biomarkers: From Successful Cognitive Aging to Clinical Impairment.

OBJECTIVE: Cross-sectional definitions of successful cognitive aging have been widely utilized, but longitudinal measurements can identify people who do not decline. We performed this study to contrast maintenance with declining trajectories, including clinical conversion. METHODS: We included baseline cognitively unimpaired Alzheimer's Disease Neuroimaging Initiative participants with 3 or more cognitive testing sessions (n = 539, follow-up 6.1 ± 3.5 years) and calculated slopes of an episodic memory composite (MEM) to classify them into two groups: maintainers (slope ≥ 0) and decliners (slope < 0). Within decliners, we examined a subgroup of individuals who became clinically impaired during follow-up. These groups were compared on baseline characteristics and cognitive performance, as well as both cross-sectional and longitudinal Alzheimer disease (AD) biomarker measures (beta-amyloid [Aß], tau, and hippocampal volume). RESULTS: Forty-one percent (n = 221) of the cohort were MEM maintainers, and 33% (n = 105) of decliners converted to clinical impairment during follow-up. Compared to those with superior baseline scores, maintainers had lower education and were more likely to be male. Maintainers and decliners did not differ on baseline MEM scores, but maintainers did have higher non-MEM cognitive scores. Maintainers had lower baseline global Aß, lower tau pathology, and larger hippocampal volumes than decliners, even after removing converters. There were no differences in rates of change of any AD biomarkers between any cognitive trajectory groups except for a higher rate of hippocampal atrophy in clinical converters compared to maintainers. INTERPRETATION: Using longitudinal data to define cognitive trajectory groups reduces education and sex bias and reveals the prognostic importance of early onset of accumulation of AD pathology. ANN NEUROL 2024;96:378-389.