Clearance of β-amyloid and synapses by the optogenetic depolarization of microglia is complement selective

Mettl3-m6A-NPY axis governing neuron-microglia interaction regulates sleep amount of mice

Sleep behavior is regulated by diverse mechanisms including genetics, neuromodulation and environmental signals. However, it remains completely unknown regarding the roles of epitranscriptomics in regulating sleep behavior. In the present study, we showed that the deficiency of RNA m6A methyltransferase Mettl3 in excitatory neurons specifically induces microglia activation, neuroinflammation and neuronal loss in thalamus of mice. Mettl3 deficiency remarkably disrupts sleep rhythm and reduces the amount of non-rapid eye movement sleep. We also showed that Mettl3 regulates neuropeptide Y (NPY) via m6A modification and Mettl3 conditional knockout (cKO) mice displayed significantly decreased expression of NPY in thalamus. In addition, the dynamic distribution pattern of NPY is observed during wake-sleep cycle in cKO mice. Ectopic expression of Mettl3 and NPY significantly inhibits microglia activation and neuronal loss in thalamus, and restores the disrupted sleep behavior of cKO mice. Collectively, our study has revealed the critical function of Mettl3-m6A-NPY axis in regulating sleep behavior.

Microglial modulation of neuronal network function and plasticity

Microglia are the resident immune cells of the central nervous system (CNS), which have been classically viewed as involved in CNS responses to damage and tissue repair. However, microglia are constantly sensing neuronal network activity and changes in the CNS milieu, establishing complex state-dependent microglia-neuron interactions that impact their functions. By doing so, microglia perform a wide range of physiological roles, including brain homeostasis maintenance, control of neural connectivity, network function modulation, as well as functional and morphological plasticity regulation in health and disease. Here, the author reviews recent evidence of the modulations induced by microglia, a highly heterogeneous cell type, on synaptic and intrinsic neuronal properties, and on neuronal network patterns during perinatal development and adulthood. The reviewed evidence clearly indicates that microglia are important, if not essential, for brain function and plasticity in both health and disease.

Astrocyte-neuron communication through the complement C3-C3aR pathway in Parkinson's disease

Neuroinflammation and autoimmunity are pivotal in the pathogenesis of neurodegenerative diseases. Complement activation and involvement of astrocyte-neuron C3/C3aR pathway have been observed, yet the mechanisms influencing α-synuclein (α-syn) pathology and neurodegeneration remain unclear. In this study, elevated levels of complement C3 were detected in the plasma of α-syn PFF-induced mice and the substantia nigra of A53T transgenic mice. Colocalization of complement C3 with astrocytes was also observed. Overexpression of complement C3 exacerbated motor dysfunction, dopaminergic neuron loss, and phosphorylated α-syn expression in mice injected with α-syn preformed fibrils (α-syn PFFs). Conversely, downregulation of complement C3 protected α-syn PFF-induced mice. Molecular investigations revealed that inhibition of Toll-like receptor 2 (TLR2) or NF-κB reduced complement C3 expression in primary astrocytes following α-syn PFF treatment. Astrocyte-neuron communication via the C3/C3aR pathway influenced α-syn PFF-induced neuronal apoptosis and α-syn pathology, potentially through modulation of GSK3β. These findings underscore the critical role of astrocyte-neuron communication via the C3/C3aR pathway in PD pathogenesis, highlighting its potential as a therapeutic target.

Astrocyte-derived MFG-E8 facilitates microglial synapse elimination in Alzheimer's disease mouse models

Region-specific synapse loss is an early pathological hallmark in Alzheimer's disease (AD). Emerging data in mice and humans highlight microglia, the brain-resident macrophages, as cellular mediators of synapse loss; however, the upstream modulators of microglia-synapse engulfment remain elusive. Here, we report a distinct subset of astrocytes, which are glial cells essential for maintaining synapse homeostasis, appearing in a region-specific manner with age and amyloidosis at onset of synapse loss. These astrocytes are distinguished by their peri-synaptic processes which are 'bulbous' in morphology, contain accumulated p62-immunoreactive bodies, and have reduced territorial domains, resulting in a decrease of astrocyte-synapse coverage. Using integrated in vitro and in vivo approaches, we show that astrocytes upregulate and secrete phagocytic modulator, milk fat globule-EGF factor 8 (MFG-E8), which is sufficient and necessary for promoting microglia-synapse engulfment in their local milieu. Finally, we show that knocking down Mfge8 specifically from astrocytes using a viral CRISPR-saCas9 system prevents microglia-synapse engulfment and ameliorates synapse loss in two independent amyloidosis mouse models of AD. Altogether, our findings highlight astrocyte-microglia crosstalk in determining synapse fate in amyloid models and nominate astrocytic MFGE8 as a potential target to ameliorate synapse loss during the earliest stages of AD.

Osmundacetone ameliorates Alzheimer's-like pathologies by inhibiting β-amyloid fibrillation, oxidative damage and neuroinflammation in APP/PS1 transgenic mice

BACKGROUND

β-Amyloid (Aβ) fibrillation is critical for Aβ deposition and cytotoxicity during the progression of Alzheimer's disease (AD). Consequently, anti-Aβ monoclonal antibody drugs targeting Aβ oligomers and aggregation are considered potential therapeutic strategies for AD treatment. Similar to the working mechanisms of anti-Aβ monoclonal antibody drugs, our study identified osmundacetone (OAC), a small-molecule compound isolated from the traditional Chinese medicine Rhizoma Osmundae, as exerting anti-AD effects by targeting Aβ.

PURPOSE

This study sought to determine whether OAC influences the Aβ burden in APP/PS1 mice and to identify potential regulatory mechanisms.

METHODS

Five-month-old APP/PS1 mice were injected intraperitoneally with OAC at a dose of 1 mg/kg for 12 weeks. The cognitive functions of the mice were assessed via the Morris water maze test and the open field test. Osmundacetone was analyzed via molecular docking, an isothermal dose‒response fingerprint-cellular context thermal shift assay, a thioflavine T fluorescence assay, and an atomic force microscopy assay to analyze the effects of OAC on Aβ fibrillation. Immunofluorescence, immunoblotting, and immunohistochemistry were used to assess Aβ clearance, AD pathology, oxidative stress, and inflammatory responses.

RESULTS

The innovative biochemical and physical data illustrated that the ability of OAC to inhibit Aβ fibrillation was accomplished by binding directly to Aβ, which differed from the majority of previously reported natural polyphenols that modulate the Aβ content and structure in an indirect manner. The inhibition of Aβ fibrosis by OAC subsequently promoted Aβ lysosomal degradation, resulting in a decreased Aβ burden in APP/PS1 mice. Furthermore, OAC treatment inhibited oxidative damage by upregulating glutathione peroxidase expression and attenuated the production of inflammatory factors by downregulating nuclear factor-kB phosphorylation in APP/PS1 mice.

CONCLUSION

These findings demonstrate, for the first time, that OAC could reduce the brain Aβ burden in APP/PS1 mice by inhibiting Aβ fibrillation through direct binding to Aβ and improve cognitive dysfunction by attenuating oxidative damage and neuroinflammation. These findings indicate that OAC may be a promising candidate for the treatment of AD.

Updates in Alzheimer's disease: from basic research to diagnosis and therapies

Alzheimer's disease (AD) is the most common neurodegenerative disorder, characterized pathologically by extracellular deposition of β-amyloid (Aβ) into senile plaques and intracellular accumulation of hyperphosphorylated tau (pTau) as neurofibrillary tangles. Clinically, AD patients show memory deterioration with varying cognitive dysfunctions. The exact molecular mechanisms underlying AD are still not fully understood, and there are no efficient drugs to stop or reverse the disease progression. In this review, we first provide an update on how the risk factors, including APOE variants, infections and inflammation, contribute to AD; how Aβ and tau become abnormally accumulated and how this accumulation plays a role in AD neurodegeneration. Then we summarize the commonly used experimental models, diagnostic and prediction strategies, and advances in periphery biomarkers from high-risk populations for AD. Finally, we introduce current status of development of disease-modifying drugs, including the newly officially approved Aβ vaccines, as well as novel and promising strategies to target the abnormal pTau. Together, this paper was aimed to update AD research progress from fundamental mechanisms to the clinical diagnosis and therapies.

Therapeutic Targets in Innate Immunity to Tackle Alzheimer's Disease

There is an urgent need for effective disease-modifying therapeutic interventions for Alzheimer's disease (AD)-the most prevalent cause of dementia with a profound socioeconomic burden. Most clinical trials targeting the classical hallmarks of this disease-β-amyloid plaques and neurofibrillary tangles-failed, showed discrete clinical effects, or were accompanied by concerning side effects. There has been an ongoing search for novel therapeutic targets. Neuroinflammation, now widely recognized as a hallmark of all neurodegenerative diseases, has been proven to be a major contributor to AD pathology. Here, we summarize the role of neuroinflammation in the pathogenesis and progression of AD and discuss potential targets such as microglia, TREM2, the complement system, inflammasomes, and cytosolic DNA sensors. We also present an overview of ongoing studies targeting specific innate immune system components, highlighting the progress in this field of drug research while bringing attention to the delicate nature of innate immune modulations in AD.

Biasing microglia to help, not hurt

Blocking complement signaling biases microglia to destroy amyloid aggregates, not neuronal synapses.