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Microglia are the resident immune cells of the central nervous system that exert diverse roles in the pathogenesis of ischemic stroke. During the past decades, microglial polarization and chemotactic properties have been well-studied, whereas less attention has been paid to phagocytic phenotypes of microglia in stroke. Generally, whether phagocytosis mediated by microglia plays a beneficial or detrimental role in stroke remains controversial, which calls for further investigations. Most researchers are in favor of the former proposal currently since efficient clearance of tissue debris promotes tissue reconstruction and neuronal network reorganization in part. Other scholars propose that excessively activated microglia engulf live or stressed neuronal cells, which results in neurological deficits and brain atrophy. Upon ischemia challenge, the microglia infiltrate injured brain tissue and engulf live/dead neurons, myelin debris, apoptotic cell debris, endothelial cells, and leukocytes. Cell phagocytosis is provoked by the exposure of “eat-me” signals or the loss of “don ’ t eat-me” signals. We supposed that microglial phagocytosis could be initiated by the specific “eat-me” signal and its corresponding receptor on the specific cell type under pathological circumstances. In this review, we will summarize phagocytic characterizations of microglia after stroke and the potential receptors responsible for this programmed biological progress. Understanding these questions precisely may help to develop appropriate phagocytic regulatory molecules, which are promoting self-limiting inflammation without damaging functional cells.

Background Vascular dementia (VAD) is the second most common type of dementia lacking effective treatments. Pentoxifylline (PTX), a nonselective phosphodiesterase inhibitor, displays protective effects in multiple cerebral diseases. In this study, we aimed to investigate the therapeutic effects and potential mechanisms of PTX in VAD. Methods Bilateral common carotid artery stenosis (BCAS) mouse model was established to mimic VAD. Mouse behavior was tested by open field test, novel object recognition test, Y-maze and Morris water maze (MWM) tests. Histological staining, magnetic resonance imaging (MRI) and electron microscopy were used to define white matter integrity. The impact of PTX on microglia phagocytosis, peroxisome proliferator-activated receptors-γ (PPAR-γ) activation and Mer receptor tyrosine kinase (Mertk) expression was assessed by immunofluorescence, western blotting and flow cytometry with the application of microglia-specific Mertk knockout mice, Mertk inhibitor and PPAR-γ inhibitor. Results Here, we found that PTX treatment alleviated cognitive impairment in novel object recognition test, Y-maze and Morris water maze tests. Furthermore, PTX alleviated white matter injury in corpus callosum (CC) and internal capsule (IC) areas as shown by histological staining and MRI analysis. PTX-treatment group presented thicker myelin sheath than vehicle group by electron microscopy. Mechanistically, PTX facilitated microglial phagocytosis of myelin debris by up-regulating the expression of Mertk in BCAS model and primary cultured microglia. Importantly, microglia-specific Mertk knockout blocked the therapeutic effects of PTX in BCAS model. Moreover, Mertk expression was regulated by the nuclear translocation of PPAR-γ. Through modulating PPAR-γ, PTX enhanced Mertk expression. Conclusions Collectively, our results demonstrated that PTX showed therapeutic potentials in VAD and alleviated ischemic white matter injury via modulating Mertk-mediated myelin clearance in microglia.

Ischemic stroke leads to white matter damage and neurological deficits. However, the characteristics of white matter injury and repair after stroke are unclear. Additionally, the precise molecular communications between microglia and white matter repair during the stroke rehabilitation phase remain elusive. In this current study, MRI DTI scan and immunofluorescence staining were performed to trace white matter and microglia in the mouse transient middle cerebral artery occlusion (tMCAO) stroke model. We found that the most serious white matter damage was on Day 7 after the ischemic stroke, then it recovered gradually from Day 7 to Day 30. Parallel to white matter recovery, we observed that microglia centered around the damaged myelin sheath and swallowed myelin debris in the ischemic areas. Then, microglia of the ischemic hemisphere were sorted by flow cytometry for RNA sequencing and subpopulation analysis. We found that CD11c + microglia increased from Day 7 to Day 30, demonstrating high phagocytotic capabilities, myelin-supportive genes, and lipid metabolism associated genes. CD11c + microglia population was partly depleted by the stereotactic injecting of rAAV2/6M-taCasp3 (rAAV2/6M-CMV-DIO-taCasp3-TEVp) into CD11c-cre mice. Selective depletion of CD11c + microglia disrupted white matter repair, oligodendrocyte maturation, and functional recovery after stroke by Rotarod test, Adhesive Removal test, and Morris Water Maze test. These findings suggest that spontaneous white matter repair occurs after ischemic stroke, while CD11c + microglia play critical roles in this white matter restorative progress.

Background Ischemic stroke triggers excessive microglial activation and sustained neuroinflammation, driving secondary neuronal injury. Recent evidence suggests that dysfunction of the autophagy-lysosome system may be a crucial factor sustaining microglial pro-inflammatory responses, yet the underlying regulatory mechanisms remain unclear. NOD-like receptor family caspase recruitment domain-containing protein 5 (NLRC5) has been widely studied in various immune and inflammatory diseases and exhibits functional heterogeneity under different pathological conditions. However, the role of NLRC5 in modulating post-stroke neuroinflammation remains unclear. Methods NLRC5 expression and localization was examined in a mouse transient middle cerebral artery occlusion (tMCAO) model and postmortem brain tissue from stroke patients. A microglia-specific Nlrc5 knockout (mCKO) mice line was generated to evaluate the effects of Nlrc5 deletion on neurological function, infarct volume, neuronal apoptosis, and inflammatory response after ischemic stroke. Proteomics, mass spectrometry, and molecular biology assays were conducted to elucidate the mechanisms. Results NLRC5 expression was upregulated in the ischemic penumbra of mouse models and appeared higher in postmortem brain tissues from stroke patients, specifically in activated microglia. Strikingly, mCKO mice exhibited significantly improved neurological outcomes, reduced infarct volumes, and attenuated neuronal apoptosis post-stroke. In vitro studies demonstrated that NLRC5 induction by various stimuli, including oxygen-glucose deprivation/reperfusion (OGD/R), lipopolysaccharide (LPS), as well as neuronal debris and supernatant, promoted pro-inflammatory cytokine release and microglia-mediated neurotoxicity, whereas Nlrc5 deletion exerted protective effects. Mechanistically, NLRC5 did not influence autophagosome formation but profoundly disrupted autophagic flux by impairing lysosomal function. Proteomic and biochemical analyses revealed that NLRC5 binds interferon-stimulated gene 15 (ISG15) via its CARD domain, shielding ISG15 from autophagy-lysosomal degradation. Furthermore, NLRC5-induced lysosomal defects and inflammatory responses were abolished in the absence of Isg15 . Conclusion NLRC5 promotes microglial inflammation and exacerbates post-stroke brain injury by stabilizing ISG15 and disrupting lysosomal function and autophagic flux. NLRC5-ISG15 axis is a therapeutic target for immune modulation in ischemic stroke.

Lactate plays diverse roles in brain pathophysiology, including ischemic stroke. Here, the role of lysine lactylation, an epigenetic modification of lactate, in cerebral ischemia is investigated. Using a mouse model of transient middle cerebral artery occlusion, increased brain lactate levels and global protein lactylation are observed. Proteomics analysis reveals significant lactylation of non‐histone proteins in the ischemic penumbra. Lactylation of MeCP2, a transcriptional regulator, is identified as a protective mechanism against stroke‐induced neuronal death. Inhibition of MeCP2 lactylation through chemical or genetic manipulation increases infarct volume and aggravates neurological deficits. Mechanistically, MeCP2 lactylation at K210/K249 represses the transcription of apoptosis‐associated genes, including Pdcd4 and Pla2g6, thereby attenuating neuronal apoptosis. Additionally, HDAC3 and p300 are identified as key enzymes that regulate MeCP2 lactylation post‐stroke. The findings suggest that MeCP2 lactylation offers a potential therapeutic target for alleviating neuronal damage and improving stroke outcomes. MeCP2 lactylation protects against ischemic stroke by reducing brain infarct volume and improving neurological outcomes. Lactylation at K210/K249 exerts neuroprotective effects by repressing the transcription of apoptosis‐associated genes, including Pdcd4 and Pla2g6. HDAC3 and p300 serve as key regulatory enzymes for MeCP2 lactylation following stroke.

Ischemic white matter injury leads to long‐term neurological deficits but currently lacks effective therapies. Although AXL has been implicated in debris clearance and inflammatory regulation, its role in post‐stroke myelin repair remains unclear. Here, we report robust upregulation of microglial AXL in mice after tMCAO. Microglial AXL cKO mice exhibited worse motor and cognitive deficits up to 28 days after tMCAO, accompanied by more severe white matter damage, increased myelin debris, and greater lipid droplets (LDs) accumulation in microglia than WT controls. Longitudinal analysis showed that AXL‐deficient microglia had reduced early phagocytic capacity but increased LDs accumulation and lipid peroxidation at later stages. Transcriptomic profiling revealed altered inflammatory and sphingolipid metabolism pathways in AXL‐deficient microglia. Mechanistically, AXL regulates Smpd1 transcription via EGR1, thereby modulating sphingolipid metabolism and LDs accumulation. Remarkably, supplement with ASM (the Smpd1‐encoded enzyme) in AXL cKO mice reduced LDs accumulation and attenuated ischemic white matter injury. Collectively, these findings identify microglial AXL as an endogenous regulator of myelin repair after ischemic stroke. Microglial AXL drives white matter repair after stroke by orchestrating the cleanup of myelin debris. Mechanistically, AXL signals through EGR1 to boost Smpd1 transcription, regulating sphingolipid metabolism and preventing lipid droplet toxicity. Restoring the pathway with ASM therapy mitigates damage, positioning AXL as a key node for therapeutic intervention.

Background Edaravone-Dexborneol (EDB) presents therapeutic effects due to its anti-inflammatory, antioxidant and anti-apoptotic properties, and has been widely used in ischemic stroke. However, the detailed efficacy and potential target of EDB in Alzheimer’s disease (AD) are still elusive. Methods Male APPswe/PS1dE9 mice were administered with EDB intraperitoneally from 3.5 to 8 months of age. The cognition of mice was assessed by behavioral tests. Synaptic alternations in the hippocampus were detected by electrophysiology and Golgi staining. β-amyloid (Aβ) pathology was mainly observed by immunofluorescence. Oxidative stress-related indicators were evaluated by dedicated kits, while quantitative PCR and ELISA were used to detect pro-inflammatory factors. Proteomics analysis further identified the potential target of EDB. Results EDB was capable of delaying the cognitive decline and ameliorating the synaptic loss in APPswe/PS1dE9 mice. In addition to the anti-inflammation and anti-oxidation effects, EDB treatment mightily ablated the Aβ plaque by promoting microglial phagocytosis. Particularly, we first discovered that EDB could directly bind to S100A9, a pathological molecule that aggravates Aβ pathology and induces oxidative stress and neuroinflammation. EDB inhibited the expression, functional threonine phosphorylation and self-assembly of S100A9. Conclusion Our results indicate that EDB can improve cognitive function and slow down AD progression, and it may serve as a potential agent for AD and other S100A9-related diseases.

Aims Synaptic dysfunction is a hallmark pathology of Alzheimer's disease (AD) and is strongly associated with cognitive impairment. Abnormal phagocytosis by the microglia is one of the main causes of synapse loss in AD. Previous studies have shown that the absence of melanoma 2 (AIM2) inflammasome activity is increased in the hippocampus of APP/PS1 mice, but the role of AIM2 in AD remains unclear. Methods Injection of Aβ1‐42 into the bilateral hippocampal CA1 was used to mimic an AD mouse model (AD mice). C57BL/6 mice injected with AIM2 overexpression lentivirus and conditional knockout of microglial AIM2 mice were used to confirm the function of AIM2 in AD. Cognitive functions were assessed with novel object recognition and Morris water maze tests. The protein and mRNA expression levels were evaluated by western blotting, immunofluorescence staining, and qRT‐PCR. Synaptic structure and function were detected by Golgi staining and electrophysiology. Results The expression level of AIM2 was increased in AD mice, and overexpression of AIM2 induced synaptic and cognitive impairments in C57BL/6 mice, similar to AD mice. Elevated expression levels of AIM2 occurred in microglia in AD mice. Conditional knockout of microglial AIM2 rescued cognitive and synaptic dysfunction in AD mice. Excessive microglial phagocytosis activity of synapses was decreased after knockout of microglial AIM2, which was associated with inhibiting complement activation. Conclusion Our results demonstrated that microglial AIM2 plays a critical role in regulating synaptic plasticity and memory deficits associated with AD, providing a new direction for developing novel preventative and therapeutic interventions for this disease. Synaptic dysfunction is a hallmark pathology of Alzheimer's disease (AD) and is strongly associated with cognitive impairment. Abnormal phagocytosis by the microglia is one of the main causes of synapse loss in AD. Microglial AIM2 plays a critical role in regulating synaptic plasticity and memory deficits associated with AD, providing a new direction for developing novel preventative and therapeutic interventions for this disease.

Spectral domain optical coherence tomography (OCT) is a widely employed, minimally invasive bio-medical imaging technique, which requires a broadband light source, typically implemented by super-luminescent diodes. Recent advances in soliton based photonic integrated frequency combs (soliton microcombs) have enabled the development of low-noise, broadband chipscale frequency comb sources, whose potential for OCT imaging has not yet been unexplored. Here, we explore the use of dissipative Kerr soliton microcombs in spectral domain OCT and show that, by using photonic chipscale Si 3 N 4 resonators in conjunction with 1300 nm pump lasers, spectral bandwidths exceeding those of commercial OCT sources are possible. We characterized the exceptional noise properties of our source (in comparison to conventional OCT sources) and demonstrate that the soliton states in microresonators exhibit a residual intensity noise floor at high offset frequencies that is ca. 3 dB lower than a traditional OCT source at identical power, and can exhibit significantly lower noise performance for powers at the milli-Watt level. Moreover, we demonstrate that classical amplitude noise of all soliton comb teeth are correlated, i.e., common mode, in contrast to superluminescent diodes or incoherent microcomb states, which opens a new avenue to improve imaging speed and performance beyond the thermal noise limit. Superluminescent diodes, that provide a broadband spectrum are typically used in spectral domain coherence tomography. Here, the authors use chipscale silicon nitride resonators to generate soliton microcombs with a lower noise flor that could substitute the diode sources.

Absorption, distribution, metabolism, and excretion (ADME) studies are critical for drug discovery. Conventionally, these tasks, together with other chemical property predictions, rely on domain-specific feature descriptors, or fingerprints. Following the recent success of neural networks, we developed Chemi-Net, a completely data-driven, domain knowledge-free, deep learning method for ADME property prediction. To compare the relative performance of Chemi-Net with Cubist, one of the popular machine learning programs used by Amgen, a large-scale ADME property prediction study was performed on-site at Amgen. For all 13 data sets, Chemi-Net resulted in higher R2 values compared with the Cubist benchmark. The median R2 increase rate over Cubist was 26.7%. We expect that the significantly increased accuracy of ADME prediction seen with Chemi-Net over Cubist will greatly accelerate drug discovery.