The neuronal pentraxin Nptx2 regulates complement activity and restrains microglia-mediated synapse loss in neurodegeneration

Progress of Chinese Medicine in Regulating Microglial Polarization against Alzheimer's Disease

Alzheimer's disease (AD), the predominant form of dementia, is a neurodegenerative disorder of the central nervous system (CNS) characterized by a subtle onset and a spectrum of cognitive and functional declines. The clinical manifestation of AD encompasses memory deficits, cognitive deterioration, and behavioral disturbances, culminating in a severe impairment of daily living skills. Despite its high prevalence, accounting for 60-70% of all dementia cases, there remains an absence of curative therapeutics. Microglia (MG), the resident immune cells of the CNS, exhibit a bifurcated role in AD pathogenesis. Functioning in a neuroprotective capacity, MGs express scavenger receptors, facilitating the clearance of [Formula: see text]-amyloid protein (A[Formula: see text]) and cellular debris. Conversely, aberrant activation of MGs can lead to the secretion of pro-inflammatory cytokines, thereby propagating neuroinflammatory responses that are detrimental to neuronal integrity. The dynamics of MG activation and the ensuing neuroinflammation are pivotal in the evolution of AD. Chinese medicine (CM), a treasure trove of traditional Chinese cultural practices, has demonstrated significant potential in the therapeutic management of AD. Over the past triennium, CM has garnered considerable research attention for its multifaceted approaches to AD, including the regulation of MG polarization. This review synthesizes current knowledge on the origins, polarization dynamics, and mechanistic interplay of MG with AD pathology. It further explores the nexus between MG polarization and cardinal pathological hallmarks of AD, such as A[Formula: see text] plaque deposition, hyperphosphorylation of tau, synaptic plasticity impairments, neuroinflammation, and brain-gut-axis dysregulation. The review also encapsulates the therapeutic strategies of CM, which encompass monomers, formulae, and acupuncture. These strategies modulate MG polarization in the context of AD treatment, thereby providing a robust theoretical framework in which to conduct future investigative endeavors in both the clinical and preclinical realms.

Biomarkers of Synaptic Degeneration in Alzheimer's Disease

Synapse has been considered a critical neuronal structure in the procession of Alzheimer's disease (AD), attacked by two pathological molecule aggregates (amyloid-β and phosphorylated tau) in the brain, disturbing synaptic homeostasis before disease manifestation and subsequently causing synaptic degeneration. Recently, evidence has emerged indicating that soluble oligomeric amyloid-β (AβO) and tau exert direct toxicity on synapses, causing synaptic damage. Synaptic degeneration is closely linked to cognitive decline in AD, even in the asymptomatic stages of AD. Therefore, the identification of novel, specific, and sensitive biomarkers involved in synaptic degeneration holds significant promise for early diagnosis of AD, reducing synaptic degeneration and loss, and controlling the progression of AD. Currently, a range of biomarkers in cerebrospinal fluid (CSF), such as synaptosome-associated protein 25 (SNAP-25), synaptotagmin-1, growth-associated protein-43 (GAP-43), and neurogranin (Ng), along with functional brain imaging techniques, can detect variations in synaptic density, offering high sensitivity and specificity for Alzheimer's disease (AD) diagnosis. However, these methods face challenges, including invasiveness, high cost, and limited accessibility. In contrast, biomarkers found in blood or urine provide a minimally invasive, cost-effective, and more accessible alternative to traditional diagnostic methods. Notably, neuron-derived exosomes in blood, which contain synaptic proteins, show variations in concentration that can serve as indicators of synaptic injury, providing an additional, less invasive approach to AD diagnosis and monitoring.

Complement and microglia activation mediate stress-induced synapse loss in layer 2/3 of the medial prefrontal cortex in male mice

Spatially heterogeneous synapse loss is a characteristic of many psychiatric and neurological disorders, but the underlying mechanisms are unclear. Here, we show that spatially-restricted complement activation mediates stress-induced heterogeneous microglia activation and synapse loss localized to the upper layers of the medial prefrontal cortex (mPFC) in male mice. Single cell RNA sequencing also reveals a stress-associated microglia state marked by high expression of the apolipoprotein E gene (Apoehigh) localized to the upper layers of the mPFC. Mice lacking complement component C3 are protected from stress-induced layer-specific synapse loss, and the Apoehigh microglia population is markedly reduced in the mPFC of these mice. Furthermore, C3 knockout mice are also resilient to stress-induced anhedonia and working memory behavioral deficits. Our findings suggest that region-specific complement and microglia activation can contribute to the disease-specific spatially restricted patterns of synapse loss and clinical symptoms found in many brain diseases.

Ferroptosis involvement in the neurotoxicity of flunitrazepam in zebrafish

In recent years, psychoactive drugs such as benzodiazepines (BZDs) have been frequently detected in water environments, however, there is still limited understanding regarding their potential impact on neurological health and underlying mechanisms. This study evaluated the neurotoxicity of the typical BZD drug flunitrazepam (FLZ, 0.2 and 5 μg/L) in zebrafish embryos and adults, and investigated the relationship between ferroptosis and FLZ-induced neurotoxicity. The results indicated that acute exposure to FLZ significantly inhibited zebrafish embryo hatching and promotes death, induced larval deformities, and led to abnormal neurobehavioral responses in larvae, likely due to ferroptosis induction. Results from a 30-day subacute exposure to FLZ showed that it decreased motor function and induced cognitive impairment in adult zebrafish. Immunofluorescence of brain tissues revealed a reduction in neurons in the telencephalon and an increase in microglia in the mesencephalon of the zebrafish exposed to FLZ. The ultrastructure of brain mitochondria showed serious damage. Besides, FLZ exposure increased iron levels, reduced GSH/GSSG and increased LPO in brain tissue, which is related to the abnormal expression of genes associated with ferroptosis. In the rescue experiments with co-exposure to deferoxamine (DFO), the motor-related parameters and biochemical indexes related to ferroptosis were restored, suggesting that FLZ can induce ferroptosis. The molecular docking results indicated that FLZ had a higher affinity with transferrin. This study elucidates the close relationship between ferroptosis and FLZ-induced neurotoxicity, which is significant for understanding the physiological damage caused by psychoactive substances and assessing environmental risks.

CSF proteomics identifies early changes in autosomal dominant Alzheimer's disease

In this high-throughput proteomic study of autosomal dominant Alzheimer's disease (ADAD), we sought to identify early biomarkers in cerebrospinal fluid (CSF) for disease monitoring and treatment strategies. We examined CSF proteins in 286 mutation carriers (MCs) and 177 non-carriers (NCs). The developed multi-layer regression model distinguished proteins with different pseudo-trajectories between these groups. We validated our findings with independent ADAD as well as sporadic AD datasets and employed machine learning to develop and validate predictive models. Our study identified 137 proteins with distinct trajectories between MCs and NCs, including eight that changed before traditional AD biomarkers. These proteins are grouped into three stages: early stage (stress response, glutamate metabolism, neuron mitochondrial damage), middle stage (neuronal death, apoptosis), and late presymptomatic stage (microglial changes, cell communication). The predictive model revealed a six-protein subset that more effectively differentiated MCs from NCs, compared with conventional biomarkers.

Overexpression of the schizophrenia risk gene C4 in PV cells drives sex-dependent behavioral deficits and circuit dysfunction

Fast-spiking parvalbumin (PV)-positive cells are key players in orchestrating pyramidal neuron activity, and their dysfunction is consistently observed in myriad brain diseases. To understand how immune complement pathway dysregulation in PV cells drives disease pathogenesis, we have developed a transgenic line that permits cell-type specific overexpression of the schizophrenia-associated C4 gene. We found that overexpression of mouse C4 (mC4) in PV cells causes sex-specific alterations in anxiety-like behavior and deficits in synaptic connectivity and excitability of PFC PV cells. Using a computational model, we demonstrated that these microcircuit deficits led to hyperactivity and disrupted neural communication. Finally, pan-neuronal overexpression of mC4 failed to evoke the same deficits in behavior as PV-specific mC4 overexpression, suggesting that perturbations of this neuroimmune gene in fast-spiking neurons are especially detrimental to circuits associated with anxiety-like behavior. Together, these results provide a causative link between C4 and the vulnerability of PV cells in brain disease.

A human Tau expressing zebrafish model of progressive supranuclear palsy identifies Brd4 as a regulator of microglial synaptic elimination

Progressive supranuclear palsy (PSP) is an incurable neurodegenerative disease characterized by 4-repeat (0N/4R)-Tau protein accumulation in CNS neurons. We generated transgenic zebrafish expressing human 0N/4R-Tau to investigate PSP pathophysiology. Tau zebrafish replicated multiple features of PSP, including: decreased survival; hypokinesia; impaired optokinetic responses; neurodegeneration; neuroinflammation; synapse loss; and Tau hyperphosphorylation, misfolding, mislocalization, insolubility, truncation, and oligomerization. Using automated assays, we screened 147 small molecules for activity in rescuing neurological deficits in Tau zebrafish. (+)JQ1, a bromodomain inhibitor, improved hypokinesia, survival, microgliosis, and brain synapse elimination. A heterozygous brd4+/- mutant reducing expression of the bromodomain protein Brd4 similarly rescued these phenotypes. Microglial phagocytosis of synaptic material was decreased by (+)JQ1 in both Tau zebrafish and rat primary cortical cultures. Microglia in human PSP brains expressed Brd4. Our findings implicate Brd4 as a regulator of microglial synaptic elimination in tauopathy and provide an unbiased approach for identifying mechanisms and therapeutic targets in PSP.

Emerging evidence of context-dependent synapse elimination by phagocytes in the CNS

Precise synapse elimination is essential for the establishment of a fully developed neural circuit during brain development and higher function in adult brain. Beyond immune and nutrition support, recent groundbreaking studies have revealed that phagocytic microglia and astrocytes can actively and selectively eliminate synapses in normal and diseased brains, thereby mediating synapse loss and maintaining circuit homeostasis. Multiple lines of evidence indicate that the mechanisms of synapse elimination by phagocytic glia are not universal but rather depend on specific contexts and detailed neuron-glia interactions. The mechanism of synapse elimination by phagocytic glia is dependent on neuron-intrinsic factors and many innate immune and local apoptosis-related molecules. During development, microglial synapse engulfment in the visual thalamus is primarily influenced by the classic complement pathway, whereas in the barrel cortex, the fractalkine pathway is dominant. In Alzheimer's disease, microglia employ complement-dependent mechanisms for synapse engulfment in tauopathy and early β-amyloid pathology, but microglia are not involved in synapse loss at late β-amyloid stages. Phagocytic microglia also engulf synapses in a complement-dependent way in schizophrenia, anxiety, and stress. In addition, phagocytic astrocytes engulf synapses in a MEGF10-dependent way during visual development, memory, and stroke. Furthermore, the mechanism of a phenomenon that phagocytes selectively eliminate excitatory and inhibitory synapses is also emphasized in this review. We hypothesize that elucidating context-dependent synapse elimination by phagocytic microglia and astrocytes may reveal the molecular basis of synapse loss in neural disorders and provide a rationale for developing novel candidate therapies that target synapse loss and circuit homeostasis.

Glial modulation of synapse development and plasticity: oligodendrocyte precursor cells as a new player in the synaptic quintet

Synaptic communication is an important process in the central nervous system that allows for the rapid and spatially specified transfer of signals. Neurons receive various synaptic inputs and generate action potentials required for information transfer, and these inputs can be excitatory or inhibitory, which collectively determines the output. Non-neuronal cells (glial cells) have been identified as crucial participants in influencing neuronal activity and synaptic transmission, with astrocytes forming tripartite synapses and microglia pruning synapses. While it has been known that oligodendrocyte precursor cells (OPCs) receive neuronal inputs, whether they also influence neuronal activity and synaptic transmission has remained unknown for two decades. Recent findings indicate that OPCs, too, modulate neuronal synapses. In this review, we discuss the roles of different glial cell types at synapses, including the recently discovered involvement of OPCs in synaptic transmission and synapse refinement, and discuss overlapping roles played by multiple glial cell types.

Microglial-derived C1q integrates into neuronal ribonucleoprotein complexes and impacts protein homeostasis in the aging brain

Neuroimmune interactions mediate intercellular communication and underlie critical brain functions. Microglia, CNS-resident macrophages, modulate the brain through direct physical interactions and the secretion of molecules. One such secreted factor, the complement protein C1q, contributes to complement-mediated synapse elimination in both developmental and disease models, yet brain C1q protein levels increase significantly throughout aging. Here, we report that C1q interacts with neuronal ribonucleoprotein (RNP) complexes in an age-dependent manner. Purified C1q protein undergoes RNA-dependent liquid-liquid phase separation (LLPS) in vitro, and the interaction of C1q with neuronal RNP complexes in vivo is dependent on RNA and endocytosis. Mice lacking C1q have age-specific alterations in neuronal protein synthesis in vivo and impaired fear memory extinction. Together, our findings reveal a biophysical property of C1q that underlies RNA- and age-dependent neuronal interactions and demonstrate a role of C1q in critical intracellular neuronal processes.

Loss-of-function of the Zinc Finger Homeobox 4 (ZFHX4) gene underlies a neurodevelopmental disorder

8q21.11 microdeletions encompassing the gene encoding transcription factor ZFHX4, have previously been associated by us with a syndromic form of intellectual disability, hypotonia, decreased balance and hearing loss. Here, we report on 57 individuals, 52 probands and 5 affected family members, with protein truncating variants (n=36), (micro)deletions (n=20) or an inversion (n=1) affecting ZFHX4 with variable developmental delay and intellectual disability, distinctive facial characteristics, morphological abnormalities of the central nervous system, behavioral alterations, short stature, hypotonia, and occasionally cleft palate and anterior segment dysgenesis. The phenotypes associated with 8q21.11 microdeletions and ZFHX4 intragenic loss-of-function variants largely overlap, identifying ZFHX4 as the main driver for the microdeletion syndrome, although leukocyte-derived DNA shows a mild common methylation profile for (micro)deletions only. We identify ZFHX4 as a transcription factor that is increasingly expressed during human brain development and neuronal differentiation. Furthermore, ZFHX4 interacting factors identified via IP-MS in neural progenitor cells, suggest an important role for ZFHX4 in cellular and developmental pathways, especially during histone modifications, cytosolic transport and development. Additionally, using CUT&RUN, we observed that ZFHX4 binds with the promoter regions of genes with crucial roles in embryonic, neuron and axon development. Since loss-of-function variants in ZFHX4 are found with consistent dysmorphic facial features, we investigated whether the disruption of zfhx4 causes craniofacial abnormalities in zebrafish. First-generation (F0) zfhx4 crispant zebrafish, (mosaic) mutant for zfhx4 loss-of-function variants, have significantly shorter Meckel's cartilages and smaller ethmoid plates compared to control zebrafish. Furthermore, behavioral assays show a decreased movement frequency in the zfhx4 crispant zebrafish in comparison with control zebrafish larvae. Although further research is needed, our in vivo work suggests a role for zfhx4 in facial skeleton patterning, palatal development and behavior.

Microglia and Astrocytes in Alzheimer's Disease: Significance and Summary of Recent Advances

Alzheimer's disease, one of the most common forms of dementia, is characterized by a slow progression of cognitive impairment and neuronal loss. Currently, approved treatments for AD are hindered by various side effects and limited efficacy. Despite considerable research, practical treatments for AD have not been developed. Increasing evidence shows that glial cells, especially microglia and astrocytes, are essential in the initiation and progression of AD. During AD progression, activated resident microglia increases the ability of resting astrocytes to transform into reactive astrocytes, promoting neurodegeneration. Extensive clinical and molecular studies show the involvement of microglia and astrocyte-mediated neuroinflammation in AD pathology, indicating that microglia and astrocytes may be potential therapeutic targets for AD. This review will summarize the significant and recent advances of microglia and astrocytes in the pathogenesis of AD in three parts. First, we will review the typical pathological changes of AD and discuss microglia and astrocytes in terms of function and phenotypic changes. Second, we will describe microglia and astrocytes' physiological and pathological role in AD. These roles include the inflammatory response, "eat me" and "don't eat me" signals, Aβ seeding, propagation, clearance, synapse loss, synaptic pruning, remyelination, and demyelination. Last, we will review the pharmacological and non-pharmacological therapies targeting microglia and astrocytes in AD. We conclude that microglia and astrocytes are essential in the initiation and development of AD. Therefore, understanding the new role of microglia and astrocytes in AD progression is critical for future AD studies and clinical trials. Moreover, pharmacological, and non-pharmacological therapies targeting microglia and astrocytes, with specific studies investigating microglia and astrocyte-mediated neuronal damage and repair, may be a promising research direction for future studies regarding AD treatment and prevention.

Identification and experimental validation of m7G-related molecular subtypes, immune signature, and feature genes in Alzheimer's disease

Background

Studies has shown that N7-methylguanosine (m7G) modification plays a critical role in neurological diseases. However, the exact role and association of m7G with the immune microenvironment in Alzheimer's disease (AD) remain largely unknown and unexplored.

Methods

The study datasets comprised 667 AD samples and 503 control samples selected from eight datasets in the Gene Expression Omnibus database; m7G regulator genes were obtained from previous literature. The AD subtypes were identified by consensus clustering analysis according to m7G regulator genes. The clinical characteristics, immune infiltration, and biological functions of the AD subgroups were evaluated. A combination of different types of machine-learning algorithms were used for the identification of AD genes. We also assessed and validated the diagnostic performance of the identified genes via qRT-PCR, immunofluorescence, and immunohistochemical analyses.

Results

Two AD distinct subgroups, namely cluster A and cluster B, were identified. Cluster A had poor pathological progression and immune infiltration, representing a high-risk subgroup for AD. The differentially expressed genes of cluster A were enriched in immune and synapse-related pathways, suggesting that these genes probably contribute to AD progression by regulating immune-related pathways. Additionally, five feature genes (AEBP1, CARTPT, AK5, NPTX2, and COPG2IT1) were identified, which were used to construct a nomogram model with good ability to predict AD. The animal experiment analyses further confirmed that these feature genes were associated with AD development.

Conclusion

To the best of our knowledge, this is the first study to reveal close correlations among m7G RNA modification, the immune microenvironment, and the pathogenesis of AD. We also identified five feature genes associated with AD, further contributing to our understanding of the underlying mechanisms and potential therapeutic targets for AD.

CSMD1 regulates brain complement activity and circuit development

Complement proteins facilitate synaptic elimination during neurodevelopmental pruning, but neural complement regulation is not well understood. CUB and Sushi Multiple Domains 1 (CSMD1) can regulate complement activity in vitro, is expressed in the brain, and is associated with increased schizophrenia risk. Beyond this, little is known about CSMD1 including whether it regulates complement activity in the brain or otherwise plays a role in neurodevelopment. We used biochemical, immunohistochemical, and proteomic techniques to examine the regional, cellular, and subcellular distribution as well as protein interactions of CSMD1 in the brain. To evaluate whether CSMD1 is involved in complement-mediated synapse elimination, we examined Csmd1-knockout mice and CSMD1-knockout human stem cell-derived neurons. We interrogated synapse and circuit development of the mouse visual thalamus, a process that involves complement pathway activity. We also quantified complement deposition on synapses in mouse visual thalamus and on cultured human neurons. Finally, we assessed uptake of synaptosomes by cultured microglia. We found that CSMD1 is present at synapses and interacts with complement proteins in the brain. Mice lacking Csmd1 displayed increased levels of complement component C3, an increased colocalization of C3 with presynaptic terminals, fewer retinogeniculate synapses, and aberrant segregation of eye-specific retinal inputs to the visual thalamus during the critical period of complement-dependent refinement of this circuit. Loss of CSMD1 in vivo enhanced synaptosome engulfment by microglia in vitro, and this effect was dependent on activity of the microglial complement receptor, CR3. Finally, human stem cell-derived neurons lacking CSMD1 were more vulnerable to complement deposition. These data suggest that CSMD1 can function as a regulator of complement-mediated synapse elimination in the brain during development.

Parvalbumin interneuron cell-to-network plasticity: mechanisms and therapeutic avenues

Alzheimer's disease (AD) and schizophrenia (SCZ) represent two major neuropathological conditions with a high disease burden. Despite their distinct etiologies, patients suffering from AD or SCZ share a common burden of disrupted memory functions unattended by current therapies. Recent preclinical analyses highlight cell-type-specific contributions of parvalbumin interneurons (PVIs), particularly the plasticity of their cellular excitability, towards intact neuronal network function (cell-to-network plasticity) and memory performance. Here we argue that deficits of PVI cell-to-network plasticity may underlie memory deficits in AD and SCZ, and we explore two therapeutic avenues: the targeting of PVI-specific neuromodulation, including by neuropeptides, and the recruitment of network synchrony in the gamma frequency range (40 Hz) by external stimulation. We finally propose that these approaches be merged under consideration of recent insights into human brain physiology.

Walnut-Derived Peptides Alleviate Learning and Memory Impairments in a Mice Model via Inhibition of Microglia Phagocytose Synapses

Microglia phagocytose synapses have an important effect on the pathogenesis of neurological disorders. Here, we investigated the neuroprotective effects of the walnut-derived peptide, TWLPLPR(TW-7), against LPS-induced cognitive deficits in mice and explored the underlying C1q-mediated microglia phagocytose synapses mechanisms in LPS-treated HT22 cells. The MWM showed that TW-7 improved the learning and memory capacity of the LPS-injured mice. Both transmission electron microscopy and immunofluorescence analysis illustrated that synaptic density and morphology were increased while associated with the decreased colocalized synapses with C1q. Immunohistochemistry and immunofluorescence demonstrated that TW-7 effectively reduced the microglia phagocytosis of synapses. Subsequently, overexpression of C1q gene plasmid was used to verify the contribution of the TW-7 via the classical complement pathway-regulated mitochondrial function-mediated microglia phagocytose synapses in LPS-treated HT22 cells. These data suggested that TW-7 improved the learning and memory capability of LPS-induced cognitively impaired mice through a mechanism associated with the classical complement pathway-mediated microglia phagocytose synapse.

Potential prognostic value of CSF-targeted proteomics across the Alzheimer's disease continuum

BACKGROUND

Core biomarkers for Alzheimer's disease (AD), such as Aβ42 and tau, have demonstrated high prognostic accuracy but do not fully capture the complex pathophysiology of AD. In this study, our objective was to identify novel cerebrospinal fluid (CSF) biomarkers using proteomics across the entire AD continuum to predict conversion to AD and explore their involvement in AD pathogenesis.

METHODS

A cohort of 186 cognitively normal (CN), 127 subjective memory complaint (SMC), 79 early mild cognitive impairment (EMCI), 249 late MCI (LMCI), and 132 AD individuals was analyzed, with a follow-up period of over 3 years for non-AD participants. CSF 65 peptides, as well as hippocampal and entorhinal volumes were analyzed, and cognitive function was evaluated using the 13-item cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-Cog 13). Cox proportional hazards models and mediation analysis were performed to investigate associations and causal relationships.

RESULTS

During the follow-up, approximately one-fourth (146/580) of the non-AD participants progressed to AD. After adjusting for baseline diagnosis (CN to LMCI) and other variables, multivariable Cox regression analysis identified three peptides (VAELEDEK, VSFELFADK, and VVSSIEQK) as significant predictors of conversion to AD. Incorporating these three peptides into the initial model significantly improved the C-statistic from 0.82 to 0.85 for predicting AD conversion, surpassing the predictive ability of Aβ42 and P-tau. Moreover, hippocampal and entorhinal volumes mediated 30.3-53.8% of the association between the three peptides and ADAS-Cog 13 scores.

CONCLUSIONS

These findings underscore the potential of these three peptides as robust prognostic biomarker candidates for AD conversion across the entire AD continuum, with a mechanism involving the mediation of hippocampal and entorhinal volumes.

Inflammation in the Peripheral Nervous System after Injury

Nerve injury is a common condition that occurs as a result of trauma, iatrogenic injury, or long-lasting stimulation. Unlike the central nervous system (CNS), the peripheral nervous system (PNS) has a strong capacity for self-repair and regeneration. Peripheral nerve injury results in the degeneration of distal axons and myelin sheaths. Macrophages and Schwann cells (SCs) can phagocytose damaged cells. Wallerian degeneration (WD) makes the whole axon structure degenerate, creating a favorable regenerative environment for new axons. After nerve injury, macrophages, neutrophils and other cells are mobilized and recruited to the injury site to phagocytose necrotic cells and myelin debris. Pro-inflammatory and anti-inflammatory factors involved in the inflammatory response provide a favorable microenvironment for peripheral nerve regeneration and regulate the effects of inflammation on the body through relevant signaling pathways. Previously, inflammation was thought to be detrimental to the body, but further research has shown that appropriate inflammation promotes nerve regeneration, axon regeneration, and myelin formation. On the contrary, excessive inflammation can cause nerve tissue damage and pathological changes, and even lead to neurological diseases. Therefore, after nerve injury, various cells in the body interact with cytokines and chemokines to promote peripheral nerve repair and regeneration by inhibiting the negative effects of inflammation and harnessing the positive effects of inflammation in specific ways and at specific times. Understanding the interaction between neuroinflammation and nerve regeneration provides several therapeutic ideas to improve the inflammatory microenvironment and promote nerve regeneration.

Molecular mechanisms underlying microglial sensing and phagocytosis in synaptic pruning

ABSTRACT

Microglia are the main non-neuronal cells in the central nervous system that have important roles in brain development and functional connectivity of neural circuits. In brain physiology, highly dynamic microglial processes are facilitated to sense the surrounding environment and stimuli. Once the brain switches its functional states, microglia are recruited to specific sites to exert their immune functions, including the release of cytokines and phagocytosis of cellular debris. The crosstalk of microglia between neurons, neural stem cells, endothelial cells, oligodendrocytes, and astrocytes contributes to their functions in synapse pruning, neurogenesis, vascularization, myelination, and blood-brain barrier permeability. In this review, we highlight the neuron-derived "find-me," "eat-me," and "don't eat-me" molecular signals that drive microglia in response to changes in neuronal activity for synapse refinement during brain development. This review reveals the molecular mechanism of neuron-microglia interaction in synaptic pruning and presents novel ideas for the synaptic pruning of microglia in disease, thereby providing important clues for discovery of target drugs and development of nervous system disease treatment methods targeting synaptic dysfunction.

Microglia phagocytic mechanisms: Development informing disease

Microglia are tissue-resident macrophages and professional phagocytes of the central nervous system (CNS). In development, microglia-mediated phagocytosis is important for sculpting the cellular architecture. This includes the engulfment of dead/dying cells, pruning extranumerary synapses and axons, and phagocytosing fragments of myelin sheaths. Intriguingly, these developmental phagocytic mechanisms by which microglia sculpt the CNS are now appreciated as important for eliminating synapses, myelin, and proteins during neurodegeneration. Here, we discuss parallels between neurodevelopment and neurodegeneration, which highlights how development is informing disease. We further discuss recent advances and challenges towards therapeutically targeting these phagocytic pathways and how we can leverage development to overcome these challenges.

Overexpression of the schizophrenia risk gene C4 in PV cells drives sex-dependent behavioral deficits and circuit dysfunction

Fast-spiking parvalbumin (PV)-positive cells are key players in orchestrating pyramidal neuron activity, and their dysfunction is consistently observed in myriad brain diseases. To understand how immune complement dysregulation - a prevalent locus of brain disease etiology - in PV cells may drive disease pathogenesis, we have developed a transgenic mouse line that permits cell-type specific overexpression of the schizophrenia-associated complement component 4 (C4) gene. We found that overexpression of mouse C4 (mC4) in PV cells causes sex-specific behavioral alterations and concomitant deficits in synaptic connectivity and excitability of PV cells of the prefrontal cortex. Using a computational network, we demonstrated that these microcircuit deficits led to hyperactivity and disrupted neural communication. Finally, pan-neuronal overexpression of mC4 failed to evoke the same deficits in behavior as PV-specific mC4 overexpression, suggesting that C4 perturbations in fast-spiking neurons are more harmful to brain function than pan-neuronal alterations. Together, these results provide a causative link between C4 and the vulnerability of PV cells in brain disease.

Biofluid biomarkers for Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease, with a complex pathogenesis and an irreversible course. Therefore, the early diagnosis of AD is particularly important for the intervention, prevention, and treatment of the disease. Based on the different pathophysiological mechanisms of AD, the research progress of biofluid biomarkers are classified and reviewed. In the end, the challenges and perspectives of future research are proposed.

Cerebrospinal fluid NPTX2 changes and relationship with regional brain metabolism metrics across mild cognitive impairment due to Alzheimer's disease

BACKGROUND

Neuronal pentraxin-2 (NPTX2), crucial for synaptic functioning, declines in cerebrospinal fluid (CSF) as cognition deteriorates. The variations of CSF NPTX2 across mild cognitive impairment (MCI) due to Alzheimer's disease (AD) and its association with brain metabolism remain elusive, albeit relevant for patient stratification and pathophysiological insights.

METHODS

We retrospectively analyzed 49 MCI-AD patients grouped by time until dementia (EMCI, n = 34 progressing within 2 years; LMCI, n = 15 progressing later/stable at follow-up). We analyzed demographic variables, cognitive status (MMSE score), and CSF NPTX2 levels using a commercial ELISA assay in EMCI, LMCI, and a control group of age-/sex-matched individuals with other non-dementing disorders (OND). Using [18F]FDG PET scans for voxel-based analysis, we explored correlations between regional brain metabolism metrics and CSF NPTX2 levels in MCI-AD patients, accounting for age.

RESULTS

Baseline and follow-up MMSE scores were lower in LMCI than EMCI (p value = 0.006 and p < 0.001). EMCI exhibited significantly higher CSF NPTX2 values than both LMCI (p = 0.028) and OND (p = 0.006). We found a significant positive correlation between NPTX2 values and metabolism of bilateral precuneus in MCI-AD patients (p < 0.005 at voxel level, p < 0.05 with family-wise error correction at the cluster level).

CONCLUSIONS

Higher CSF NPTX2 in EMCI compared to controls and LMCI suggests compensatory synaptic responses to initial AD pathology. Disease progression sees these mechanisms overwhelmed, lowering CSF NPTX2 approaching dementia. Positive CSF NPTX2 correlation with precuneus glucose metabolism links to AD-related metabolic changes across MCI course. These findings posit CSF NPTX2 as a promising biomarker for both AD staging and progression risk stratification.

C5aR1 signaling promotes region- and age-dependent synaptic pruning in models of Alzheimer's disease

INTRODUCTION

Synaptic loss is a hallmark of Alzheimer's disease (AD) that correlates with cognitive decline in AD patients. Complement-mediated synaptic pruning has been associated with this excessive loss of synapses in AD. Here, we investigated the effect of C5aR1 inhibition on microglial and astroglial synaptic pruning in two mouse models of AD.

METHODS

A combination of super-resolution and confocal and tridimensional image reconstruction was used to assess the effect of genetic ablation or pharmacological inhibition of C5aR1 on the Arctic48 and Tg2576 models of AD.

RESULTS

Genetic ablation or pharmacological inhibition of C5aR1 partially rescues excessive pre-synaptic pruning and synaptic loss in an age and region-dependent fashion in two mouse models of AD, which correlates with improved long-term potentiation (LTP).

DISCUSSION

Reduction of excessive synaptic pruning is an additional beneficial outcome of the suppression of C5a-C5aR1 signaling, further supporting its potential as an effective targeted therapy to treat AD.

HIGHLIGHTS

C5aR1 ablation restores long-term potentiation in the Arctic model of AD. C5aR1 ablation rescues region specific excessive pre-synaptic loss. C5aR1 antagonist, PMX205, rescues VGlut1 loss in the Tg2576 model of AD. C1q tagging is not sufficient to induce VGlut1 microglial ingestion. Astrocytes contribute to excessive pre-synaptic loss at late stages of the disease.

Normobaric hyperoxia alleviates complement C3-mediated synaptic pruning and brain injury after intracerebral hemorrhage

BACKGROUND

Intracerebral hemorrhage (ICH) is a common cerebrovascular disease, and the complement cascade exacerbates brain injury after ICH. As the most abundant component of the complement system, complement component 3 (C3) plays essential roles in all three complement pathways. However, the effects of C3 on neurological impairment and brain injury in ICH patients and the related mechanism have not been fully elucidated. Normobaric hyperoxia (NBO) is regarded as a treatment for ICH patients, and recent clinical studies also have confirmed the neuroprotective role of NBO against acute ICH-mediated brain damage, but the underlying mechanism still remains elusive.

AIMS

In the present study, we investigated the effects of complement C3 on NBO-treated ICH patients and model mice, and the underlying mechanism of NBO therapy in ICH-mediated brain injury.

RESULTS

Hemorrhagic injury resulted in the high plasma C3 levels in ICH patients, and the plasma C3 levels were closely related to hemorrhagic severity and clinical outcomes after ICH. BO treatment alleviated neurologic impairments and rescued the hemorrhagic-induced increase in plasma C3 levels in ICH patients and model mice. Moreover, the results indicated that NBO exerted its protective effects of on brain injury after ICH by downregulating the expression of C3 in microglia and alleviating microglia-mediated synaptic pruning.

CONCLUSIONS

Our results revealed that NBO exerts its neuroprotective effects by reducing C3-mediated synaptic pruning, which suggested that NBO therapy could be used for the clinical treatment of ICH.

The role of microglia heterogeneity in synaptic plasticity and brain disorders: Will sequencing shed light on the discovery of new therapeutic targets?

Microglia play a crucial role in interacting with neuronal synapses and modulating synaptic plasticity. This function is particularly significant during postnatal development, as microglia are responsible for removing excessive synapses to prevent neurodevelopmental deficits. Dysregulation of microglial synaptic function has been well-documented in various pathological conditions, notably Alzheimer's disease and multiple sclerosis. The recent application of RNA sequencing has provided a powerful and unbiased means to decipher spatial and temporal microglial heterogeneity. By identifying microglia with varying gene expression profiles, researchers have defined multiple subgroups of microglia associated with specific pathological states, including disease-associated microglia, interferon-responsive microglia, proliferating microglia, and inflamed microglia in multiple sclerosis, among others. However, the functional roles of these distinct subgroups remain inadequately characterized. This review aims to refine our current understanding of the potential roles of heterogeneous microglia in regulating synaptic plasticity and their implications for various brain disorders, drawing from recent sequencing research and functional studies. This knowledge may aid in the identification of pathogenetic biomarkers and potential factors contributing to pathogenesis, shedding new light on the discovery of novel drug targets. The field of sequencing-based data mining is evolving toward a multi-omics approach. With advances in viral tools for precise microglial regulation and the development of brain organoid models, we are poised to elucidate the functional roles of microglial subgroups detected through sequencing analysis, ultimately identifying valuable therapeutic targets.

Association of reduced cerebrospinal fluid NPTX2 levels with postoperative delirium in patients undergoing knee/hip replacement: a prospective cohort study

BACKGROUND

Postoperative delirium (POD) is a common complication with poor prognosis in the elderly, but its mechanism has not been fully elucidated. There is evidence that the changes in synaptic activity in the brain are closely related to the occurrence of POD. And neuronal pentraxin 2 (NPTX2) can regulate synaptic activity in vivo.

AIMS

This study aims to explore whether decreased NPTX2 levels affects POD and whether the cerebrospinal fluid (CSF) biomarkers of POD mediate this association.

METHODS

In this prospective cohort study, we interviewed patients with knee/hip replacement 1 day before surgery to collect patient information and assess their cognitive function. CSF was extracted for measuring the CSF levels of NPTX2 and other POD biomarkers on the day of surgery. And postoperative follow-up visits were performed 1-7 days after surgery.

RESULTS

Finally, 560 patients were included in the study. The patients were divided into POD group and NPOD (non-POD) group. The POD group had a median age of 80 years, a female proportion of 45%, a median BMI of 24.1 kg/m2, and a median years of education of 9 years. The Mann-Whitney U test showed that CSF NPTX2 levels were significantly lower in POD group, compared with the NPOD group (P < 0.05). Univariate binary logistic regression analysis showed that reduced CSF levels of NPTX2 protected against POD (crude OR = 0.994, 95% CI 0.993-0.995, P < 0.001). The receiver-operating characteristic (ROC) curve indicated that CSF NPTX2 level had high predictive value for POD. Mediation analyses showed that CSF T-tau (mediating proportion = 21%) and P-tau (mediating proportion = 29%) had significant mediating effects on the association between CSF NPTX2 and POD.

CONCLUSION

CSF NPTX2 levels were associated with the occurrence of POD. Low CSF NPTX2 levels may be an independent protective factor for POD. CSF T-tau and P-tau could mediate the association between CSF NPTX2 and POD occurrence.

CLINICAL TRIAL REGISTRATION

The trial registration number (TRN): ChiCTR2200064740, Date of Registration: 2022-10-15.

The use of synaptic biomarkers in cerebrospinal fluid to differentiate behavioral variant of frontotemporal dementia from primary psychiatric disorders and Alzheimer's disease

BACKGROUND

Lack of early molecular biomarkers in sporadic behavioral variants of frontotemporal dementia (bvFTD) and its clinical overlap with primary psychiatric disorders (PPD) hampers its diagnostic distinction. Synaptic dysfunction is an early feature in bvFTD and identification of specific biomarkers might improve its diagnostic accuracy. Our goal was to understand the differential diagnostic potential of cerebrospinal fluid (CSF) synaptic biomarkers in bvFTD versus PPD and their specificity towards bvFTD compared with Alzheimer's disease (AD) and controls. Additionally, we explored the association of CSF synaptic biomarkers with social cognition, cognitive performance, and disease severity in these clinical groups.

METHODS

Participants with probable bvFTD (n = 57), PPD (n = 71), AD (n = 60), and cognitively normal controls (n = 39) with available CSF, cognitive tests, and disease severity as frontotemporal lobar degeneration-modified clinical dementia rating scale (FTLD-CDR) were included. In a subset of bvFTD and PPD cases, Ekman 60 faces test scores for social cognition were available. CSF synaptosomal-associated protein 25 (SNAP25), neurogranin (Ng), neuronal pentraxin 2 (NPTX2), and glutamate receptor 4 (GluR4) were measured, along with neurofilament light (NfL), and compared between groups using analysis of covariance (ANCOVA) and logistic regression. Diagnostic accuracy was assessed using ROC analyses, and biomarker panels were selected using Wald's backward selection. Correlations with cognitive measures were performed using Pearson's partial correlation analysis.

RESULTS

NPTX2 concentrations were lower in the bvFTD group compared with PPD (p < 0.001) and controls (p = 0.003) but not compared with AD. Concentrations of SNAP25 (p < 0.001) and Ng (p < 0.001) were elevated in patients with AD versus those with bvFTD and controls. The modeled panel for differential diagnosis of bvFTD versus PPD consisted of NfL and NPTX2 (AUC = 0.96, CI: 0.93-0.99, p < 0.001). In bvFTD versus AD, the modeled panel consisted of NfL, SNAP25, Ng, and GluR4 (AUC = 0.86, CI: 0.79-0.92, p < 0.001). In bvFTD, lower NPTX2 (Pearson's r = 0.29, p = 0.036) and GluR4 (Pearson's r = 0.34, p = 0.014) concentrations were weakly associated with worse performance of total cognitive score. Lower GluR4 concentrations were also associated with worse MMSE scores (Pearson's r = 0.41, p = 0.002) as well as with worse executive functioning (Pearson's r = 0.36, p = 0.011) in bvFTD. There were no associations between synaptic markers and social cognition or disease severity in bvFTD.

CONCLUSION

Our findings of involvement of NTPX2 in bvFTD but not PPD contribute towards better understanding of bvFTD disease pathology.

Genomic analysis in the colon tissues of omega-3 fatty acid-treated rats identifies novel gene signatures implicated in ulcerative colitis

Several long-term intervention trials only studied the ex vivo immunological function to elucidate the beneficial mechanisms of n-3 polyunsaturated fatty acids (PUFA) in the ulcerative colitis (UC). An unbiased whole-transcriptome analysis would be more valuable to obtain a comprehensive understanding of the processes and genes regulated by n-3 PUFA in vivo. In this study, we have performed microarray analysis in the colon tissues of dextran sulfate sodium (DSS)-induced UC in rats supplemented with n-6 PUFA, n-3PUFA and long-chain n-3PUFA (LC-n3PUFA). We have identified the novel gene signatures previously not linked to colitis such as Etv3, Clec4d, CD180, CD72, Megf11, and Angptl4 which are most downregulated in both n-3PUFA and LC-n3PUFA groups compared to the n-6PUFA group. The most upregulated genes were Nr1i3, Nptx2, and Zfp810 in both n-3PUFA and LC-n3PUFA groups. The RT-PCR analysis confirmed similar results. Interestingly, LPS treatment in macrophages upregulated the Megf11, Etv3, CD180, and Angptl4, and correlated with increased secretion of cytokines. Gene silencing of Etv3, Megf11, and CD180 in rats using intravascular delivery of siRNA-lipoparticles attenuated the DSS-induced ulceration and mucosal damage. Thus, our genome-wide microarray analysis identified novel genes regulated by omega-3 PUFA and offers new drug targets that could prevent or reduce UC.

Complement-mediated synapse loss in Alzheimer's disease: mechanisms and involvement of risk factors

The complement system is increasingly recognized as a key player in the synapse loss and cognitive impairments observed in Alzheimer's disease (AD). In particular, the process of complement-dependent synaptic pruning through phagocytosis is over-activated in AD brains, driving detrimental excessive synapse elimination and contributing to synapse loss, which is the strongest neurobiological correlate of cognitive impairments in AD. Herein we review recent advances in characterizing complement-mediated synapse loss in AD, summarize the underlying mechanisms, and discuss the possible involvement of AD risk factors such as aging and various risk genes. We conclude with an overview of key questions that remain to be addressed.

Systematic proteomics in Autosomal dominant Alzheimer's disease reveals decades-early changes of CSF proteins in neuronal death, and immune pathways

Background

To date, there is no high throughput proteomic study in the context of Autosomal Dominant Alzheimer's disease (ADAD). Here, we aimed to characterize early CSF proteome changes in ADAD and leverage them as potential biomarkers for disease monitoring and therapeutic strategies.

Methods

We utilized Somascan® 7K assay to quantify protein levels in the CSF from 291 mutation carriers (MCs) and 185 non-carriers (NCs). We employed a multi-layer regression model to identify proteins with different pseudo-trajectories between MCs and NCs. We replicated the results using publicly available ADAD datasets as well as proteomic data from sporadic Alzheimer's disease (sAD). To biologically contextualize the results, we performed network and pathway enrichment analyses. Machine learning was applied to create and validate predictive models.

Findings

We identified 125 proteins with significantly different pseudo-trajectories between MCs and NCs. Twelve proteins showed changes even before the traditional AD biomarkers (Aβ42, tau, ptau). These 125 proteins belong to three different modules that are associated with age at onset: 1) early stage module associated with stress response, glutamate metabolism, and mitochondria damage; 2) the middle stage module, enriched in neuronal death and apoptosis; and 3) the presymptomatic stage module was characterized by changes in microglia, and cell-to-cell communication processes, indicating an attempt of rebuilding and establishing new connections to maintain functionality. Machine learning identified a subset of nine proteins that can differentiate MCs from NCs better than traditional AD biomarkers (AUC>0.89).

Interpretation

Our findings comprehensively described early proteomic changes associated with ADAD and captured specific biological processes that happen in the early phases of the disease, fifteen to five years before clinical onset. We identified a small subset of proteins with the potentials to become therapy-monitoring biomarkers of ADAD MCs.

Funding

Proteomic data generation was supported by NIH: RF1AG044546.

Emerging perspectives of synaptic biomarkers in ALS and FTD

Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) are debilitating neurodegenerative diseases with shared pathological features like transactive response DNA-binding protein of 43 kDa (TDP-43) inclusions and genetic mutations. Both diseases involve synaptic dysfunction, contributing to their clinical features. Synaptic biomarkers, representing proteins associated with synaptic function or structure, offer insights into disease mechanisms, progression, and treatment responses. These biomarkers can detect disease early, track its progression, and evaluate therapeutic efficacy. ALS is characterized by elevated neurofilament light chain (NfL) levels in cerebrospinal fluid (CSF) and blood, correlating with disease progression. TDP-43 is another key ALS biomarker, its mislocalization linked to synaptic dysfunction. In FTD, TDP-43 and tau proteins are studied as biomarkers. Synaptic biomarkers like neuronal pentraxins (NPs), including neuronal pentraxin 2 (NPTX2), and neuronal pentraxin receptor (NPTXR), offer insights into FTD pathology and cognitive decline. Advanced technologies, like machine learning (ML) and artificial intelligence (AI), aid biomarker discovery and drug development. Challenges in this research include technological limitations in detection, variability across patients, and translating findings from animal models. ML/AI can accelerate discovery by analyzing complex data and predicting disease outcomes. Synaptic biomarkers offer early disease detection, personalized treatment strategies, and insights into disease mechanisms. While challenges persist, technological advancements and interdisciplinary efforts promise to revolutionize the understanding and management of ALS and FTD. This review will explore the present comprehension of synaptic biomarkers in ALS and FTD and discuss their significance and emphasize the prospects and obstacles.

Synapse Regulation

Microglia are the resident immune cells of the brain. As such, they rapidly detect changes in normal brain homeostasis and accurately respond by fine-tuning in a tightly regulated manner their morphology, gene expression, and functional behavior. Depending on the nature of these changes, microglia can thicken and retract their processes, proliferate and migrate, release numerous signaling factors and compounds influencing neuronal physiology (e.g., cytokines and trophic factors), in addition to secreting proteases able to transform the extracellular matrix, and phagocytosing various types of cellular debris, etc. Because microglia also transform rapidly (on a time scale of minutes) during experimental procedures, studying these very special cells requires methods that are specifically non-invasive. The development of such methods has provided unprecedented insights into the roles of microglia during normal physiological conditions. In particular, transcranial two-photon in vivo imaging revealed that presumably "resting" microglia continuously survey the brain parenchyma with their highly motile processes, in addition to modulating their structural and functional interactions with neuronal circuits along the changes in neuronal activity and behavioral experience occurring throughout the lifespan. In this chapter, we will describe how surveillant microglia interact with synaptic elements and modulate the number, maturation, function, and plasticity of synapses in the healthy developing, mature, and aging brain, with consequences on neuronal activity, learning and memory, and the behavioral outcome.

Targeting synapse function and loss for treatment of neurodegenerative diseases

Synapse dysfunction and loss are hallmarks of neurodegenerative diseases that correlate with cognitive decline. However, the mechanisms and therapeutic strategies to prevent or reverse synaptic damage remain elusive. In this Review, we discuss recent advances in understanding the molecular and cellular pathways that impair synapses in neurodegenerative diseases, including the effects of protein aggregation and neuroinflammation. We also highlight emerging therapeutic approaches that aim to restore synaptic function and integrity, such as enhancing synaptic plasticity, preventing synaptotoxicity, modulating neuronal network activity and targeting immune signalling. We discuss the preclinical and clinical evidence for each strategy, as well as the challenges and opportunities for developing effective synapse-targeting therapeutics for neurodegenerative diseases.

Gene Expression at the Tripartite Synapse: Bridging the Gap Between Neurons and Astrocytes

Astrocytes, a major class of glial cells, are an important element at the synapse where they engage in bidirectional crosstalk with neurons to regulate numerous aspects of neurotransmission, circuit function, and behavior. Mutations in synapse-related genes expressed in both neurons and astrocytes are central factors in a vast number of neurological disorders, making the proteins that they encode prominent targets for therapeutic intervention. Yet, while the roles of many of these synaptic proteins in neurons are well established, the functions of the same proteins in astrocytes are largely unknown. This gap in knowledge must be addressed to refine therapeutic approaches. In this chapter, we integrate multiomic meta-analysis and a comprehensive overview of current literature to show that astrocytes express an astounding number of genes that overlap with the neuronal and synaptic transcriptomes. Further, we highlight recent reports that characterize the expression patterns and potential novel roles of these genes in astrocytes in both physiological and pathological conditions, underscoring the importance of considering both cell types when investigating the function and regulation of synaptic proteins.

Breakthroughs in Alzheimer's Research: A Path to a More Promising Future?

Background

Alzheimer's disease (AD) is a widespread neurodegenerative disorder with a significant global impact, affecting approximately 50 million individuals, and projections estimate that up to 152 million people will be affected by 2050. AD is characterized by beta-amyloid plaques and tau tangles in the brain, leading to cognitive decline.

Summary

Recent research on AD has made significant strides, including the development of an "amyloid clock" biomarker that tracks AD progression through positron emission tomography (PET) scans. Surf4 and other genes have been discovered to play a role in regulating beta-amyloid toxicity, while inhibiting the enzyme hexokinase-2 has shown positive results in preclinical studies. New brain mapping techniques have identified early brain-based causes of cognitive changes in AD, and biomarkers such as neuronal pentraxin protein Nptx2 and astrocytic 7-subunit of the nicotinic acetylcholine receptors (7nAChRs) show potential for early detection. Other approaches, such as replenishing the enzyme Tip60, selectively degrading the modified protein p-p38 with PRZ-18002, and targeting the protein voltage-dependent anion channel-1 (VDAC1), have shown promise in enhancing cognitive function and preventing pathophysiological alterations linked to AD. Baseline blood samples and other biomarkers such as urine formic acid, p-tau 198, microRNAs, and glial fibrillary acidic protein (GFAP) have also been discovered for early detection and intervention of AD. Additionally, recent FDA approvals for medications such as aducanumab and lecanemab provide options for reducing AD symptoms and improving function, while clinical trials for dementia vaccines show promise for the nasal and beta-amyloid 40 vaccines as well as vaccinations targeting tau.

Key Messages

These advancements in AD research, including biomarker discovery and the development of disease-modifying treatments, are crucial steps towards improving the lives of those affected by AD and finding a cure for this debilitating disease.

Cerebrospinal Fluid Proteomics Identifies Potential Biomarkers for Early-Onset Alzheimer's Disease

Background

Early-onset Alzheimer's disease (EOAD) exhibits a notable degree of heterogeneity as compared to late-onset Alzheimer's disease (LOAD). The proteins and pathways contributing to the pathophysiology of EOAD still need to be completed and elucidated.

Objective

Using correlation network analysis and machine learning to analyze cerebrospinal fluid (CSF) proteomics data to identify potential biomarkers and pathways associated with EOAD.

Methods

We employed mass spectrometry to conduct CSF proteomic analysis using the data-independent acquisition method in a Chinese cohort of 139 CSF samples, including 40 individuals with normal cognition (CN), 61 patients with EOAD, and 38 patients with LOAD. Correlation network analysis of differentially expressed proteins was performed to identify EOAD-associated pathways. Machine learning assisted in identifying crucial proteins differentiating EOAD. We validated the results in an Western cohort and examined the proteins expression by enzyme-linked immunosorbent assay (ELISA) in additional 9 EOAD, 9 LOAD, and 9 CN samples from our cohort.

Results

We quantified 2,168 CSF proteins. Following adjustment for age and sex, EOAD exhibited a significantly greater number of differentially expressed proteins than LOAD compared to CN. Additionally, our data indicates that EOAD may exhibit more pronounced synaptic dysfunction than LOAD. Three potential biomarkers for EOAD were identified: SH3BGRL3, LRP8, and LY6 H, of which SH3BGRL3 also accurately classified EOAD in the Western cohort. LY6 H reduction was confirmed via ELISA, which was consistent with our proteomic results.

Conclusions

This study provides a comprehensive profile of the CSF proteome in EOAD and identifies three potential EOAD biomarker proteins.

WR-PTXF, a novel short pentraxin, protects gut mucosal barrier and enhances the antibacterial activity in Carassius cuvieri × Carassius auratus red var

The pentraxin family is an evolutionarily conserved group that plays an important role in innate immunity. C-reactive protein (CRP) and serum amyloid P component (SAP) are classical members of the short pentraxins and are known to be the major acute phase proteins. In this work, we have cloned a novel pentraxin fusion protein, WR-PTXF, from Carassius cuvieri × Carassius auratus red var. In fish, the biological function of PTXF is essentially unknown. For this purpose, we report the identification and analysis of WR-PTXF and elucidate its role in the antibacterial innate immunity. WR-PTXF contains 224 amino acids and shares 79.8% and 23.0% sequence identities with crucian carp CRP and SAP, respectively. Blast analysis shows that WR-PTXF and goldfish PTXF had the highest similarity (97.3%). WR-PTXF is expressed in multiple tissues and is upregulated by Aeromonas hydrophila infection. WR-PTXF contains a short pentraxin domain and recombinant WR-PTXF protein (rWR-PTXF) can bind the A. hydrophila in a concentration-dependent manner. Further, rWR-PTXF displays apparent bacteriostatic activity against A. hydrophila in vitro by enhancing the uptake of the bound bacteria by host phagocytes. When introduced in vivo, rWR-PTXF not only protects the gut mucosa but also limits the colonization of A. hydrophila in systemic immune organs. Consistently, knockdown of WR-PTXF significantly promotes bacterial dissemination in the tissues of host. These results indicate that WR-PTXF is a classic pattern recognition molecule that exerts a protective effect against bacterial infection.

Immune activation of the p75 neurotrophin receptor: implications in neuroinflammation

Despite structural similarity with other tumor necrosis factor receptor superfamily (TNFRSF) members, the p75 neurotrophin receptor (p75NTR, TNFR16) mediates pleiotropic biological functions not shared with other TNFRs. The high level of p75NTR expression in the nervous system instead of immune cells, its utilization of co-receptors, and its interaction with soluble dimeric, rather than soluble or cell-tethered trimeric ligands are all characteristics which distinguish it from most other TNFRs. Here, we compare these attributes to other members of the TNFR superfamily. In addition, we describe the recent evolutionary adaptation in B7-1 (CD80), an immunoglobulin (Ig) superfamily member, which allows engagement to neuronally-expressed p75NTR. B7-1-mediated binding to p75NTR occurs in humans and other primates, but not lower mammals due to specific sequence changes that evolved recently in primate B7-1. This discovery highlights an additional mechanism by which p75NTR can respond to inflammatory cues and trigger synaptic elimination in the brain through engagement of B7-1, which was considered to be immune-restricted. These observations suggest p75NTR does share commonality with other immune co-modulatory TNFR family members, by responding to immunoregulatory cues. The evolution of primate B7-1 to bind and elicit p75NTR-mediated effects on neuronal morphology and function are discussed in relationship to immune-driven modulation of synaptic actions during injury or inflammation.

Pituitary-immune bidirectional crosstalk under systemic inflammation

The pituitary gland responds to and modulates immune stress through the hypothalamus-pituitary-adrenal axis. A new study in PLOS Biology reveals unconventional bidirectional communication between hormone-producing cells and the immune system upon systemic inflammation.

Single-cell transcriptomic analysis reveals rich pituitary-Immune interactions under systemic inflammation

The pituitary represents an essential hub in the hypothalamus-pituitary-adrenal (HPA) axis. Pituitary hormone-producing cells (HPCs) release several hormones to regulate fundamental bodily functions under normal and stressful conditions. It is well established that the pituitary endocrine gland modulates the immune system by releasing adrenocorticotropic hormone (ACTH) in response to neuronal activation in the hypothalamus. However, it remains unclear how systemic inflammation regulates the transcriptomic profiles of pituitary HPCs. Here, we performed single-cell RNA-sequencing (scRNA-seq) of the mouse pituitary and revealed that upon inflammation, all major pituitary HPCs respond robustly in a cell type-specific manner, with corticotropes displaying the strongest reaction. Systemic inflammation also led to the production and release of noncanonical bioactive molecules, including Nptx2 by corticotropes, to modulate immune homeostasis. Meanwhile, HPCs up-regulated the gene expression of chemokines that facilitated the communication between the HPCs and immune cells. Together, our study reveals extensive interactions between the pituitary and immune system, suggesting multifaceted roles of the pituitary in mediating the effects of inflammation on many aspects of body physiology.

The pentraxin family in autoimmune disease

The pentraxins represent a family of multifunctional proteins composed of long and short pentamers. The latter includes serum amyloid P component (SAP) and C-reactive protein (CRP) whereas the former includes neuronal PTX1 and PTX2 (NPTX1 and NPTX2, respectively), PTX3 and PTX4. These serve as a bridge between adaptive immunity and innate immunity and a link between inflammation and immunity. Similarities and differences between long and short pentamers are examined and their roles in autoimmune disease are discussed. Increased CRP and PTX3 could indicate the activity of rheumatoid arthritis, systemic lupus erythematosus or other autoimmune diseases. Mechanistically, CRP and PTX3 may predict target organ injury, regulate bone metabolic immunity and maintain homeostasis as well as participate in vascular endothelial remodeling. Interestingly, PTX3 is pleiotropic, being involved in inflammation and tissue repair. Given the therapeutic potential of PTX3 and CRP, targeting these factors to exert a beneficial effect is the focus of research efforts. Unfortunately, studies on NPTX1, NPTX2, PTX4 and SAP are scarce and more research is clearly needed to elaborate their potential roles in autoimmune disease.

C5aR1 signaling promotes region and age dependent synaptic pruning in models of Alzheimer's Disease

INTRODUCTION

Synaptic loss is a hallmark of Alzheimer's disease (AD) that correlates with cognitive decline in AD patients. Complement-mediated synaptic pruning has been associated with this excessive loss of synapses in AD. Here, we investigated the effect of C5aR1 inhibition on microglial and astroglial synaptic pruning in two mouse models of AD.

METHODS

A combination of super-resolution and confocal and tridimensional image reconstruction was used to assess the effect of genetic ablation or pharmacological inhibition of C5aR1 on the Arctic48 and Tg2576 models of AD.

RESULTS

Genetic ablation or pharmacological inhibition of C5aR1 rescues the excessive pre-synaptic pruning and synaptic loss in an age and region dependent fashion in two mouse models of AD, which correlates with improved long-term potentiation (LTP).

DISCUSSION

Reduction of excessive synaptic pruning is an additional beneficial outcome of the suppression of C5a-C5aR1 signaling, further supporting its potential as an effective targeted therapy to treat AD.

Synergism of Carbamoylated Erythropoietin and Insulin-like Growth Factor-1 in Immediate Early Gene Expression

Trophic factors are secreted proteins that can modulate neuronal integrity, structure, and function. Previous preclinical studies have shown synergistic effects on decreasing apoptosis and improving behavioral performance after stroke when combining two such trophic factors, erythropoietin (EPO) and insulin-like growth factor-1 (IGF-1). However, EPO can elevate the hematocrit level, which can be life-threatening for non-anemic individuals. A chemically engineered derivative of EPO, carbamoylated EPO (CEPO), does not impact hematological parameters but retains neurotrophic effects similar to EPO. To obtain insight into CEPO and IGF-1 combination signaling, we examined immediate early gene (IEG) expression after treatment with CEPO, IGF-1, or CEPO + IGF-1 in rat pheochromocytoma (PC-12) cells and found that combining CEPO and IGF-1 produced a synergistic increase in IEG expression. An in vivo increase in the protein expression of Npas4 and Nptx2 was also observed in the rat hippocampus. We also examined which kinase signaling pathways might be mediating these effects and found that while AKT inhibition did not alter the pattern of IEG expression, both ERK and JAK2 inhibition significantly decreased IEG expression. These results begin to define the molecular effects of combining CEPO and IGF-1 and indicate the potential for these trophic factors to produce positive, synergistic effects.

Molecular mechanisms of schizophrenia: Insights from human genetics

Schizophrenia is a debilitating psychiatric disorder that affects millions of people worldwide; however, its etiology is poorly understood at the molecular and neurobiological levels. A particularly important advance in recent years is the discovery of rare genetic variants associated with a greatly increased risk of developing schizophrenia. These primarily loss-of-function variants are found in genes that overlap with those implicated by common variants and are involved in the regulation of glutamate signaling, synaptic function, DNA transcription, and chromatin remodeling. Animal models harboring mutations in these large-effect schizophrenia risk genes show promise in providing additional insights into the molecular mechanisms of the disease.

Deep proteomics identifies shared molecular pathway alterations in synapses of patients with schizophrenia and bipolar disorder and mouse model

Synaptic dysfunction is implicated in the pathophysiology of schizophrenia (SCZ) and bipolar disorder (BP). We use quantitative mass spectrometry to carry out deep, unbiased proteomic profiling of synapses purified from the dorsolateral prefrontal cortex of 35 cases of SCZ, 35 cases of BP, and 35 controls. Compared with controls, SCZ and BP synapses show substantial and similar proteomic alterations. Network analyses reveal upregulation of proteins associated with autophagy and certain vesicle transport pathways and downregulation of proteins related to synaptic, mitochondrial, and ribosomal function in the synapses of individuals with SCZ or BP. Some of the same pathways are similarly dysregulated in the synaptic proteome of mutant mice deficient in Akap11, a recently discovered shared risk gene for SCZ and BP. Our work provides biological insights into molecular dysfunction at the synapse in SCZ and BP and serves as a resource for understanding the pathophysiology of these disorders.