Differential Regulation of Microglial Activation in Response to Different Degree of Ischemia

Poria cocos Extract Alleviates tPA-Induced Hemorrhagic Transformation after Ischemic Stroke through Regulation of Microglia M1/M2 Phenotypes Polarization

Delayed thrombolytic therapy with tissue plasminogen activator (tPA), the only FDA-approved drug for ischemic stroke, can cause catastrophic hemorrhagic transformation (HT) after ischemic stroke. However, it remains largely unknown how microglial polarization dynamically changes in HT. Poria cocos is a widely used functional edible fungus in Asia and has been used for more than 2000 years as a food and medicine in China. Our preliminary study found that P. cocos extract (PCE) significantly reduced the volume of cerebral infarction. We performed the effects of PCE on tPA-induced HT in rat models of autologous thromboembolism middle cerebral artery occlusion in vivo and BV-2 cells injured by oxygen-glucose deprivation/reperfusion in vitro. Hemorrhage test and triphenyltetrazolium chloride staining were performed to examine the efficiency of PCE. The expression level of proteins associated with microglia polarization was detected using Western blotting and immunofluorescence staining. Small interfering RNA transfection reveals the regulatory mechanism of PCE on microglia polarization. PCE plus tPA reduced hemorrhage and infarct volumes after ischemic stroke. During tPA-induced HT, M1 microglia increased over time from 3 days onward and remained high for at least 7 days, reaching the peak at 7 days, M2 microglia gradually increased after 3 days and continued to increase for at least 14 days. Furthermore, PCE inhibited the secretion of pro-inflammatory cytokines in M1 microglia and improved the secretion of anti-inflammatory cytokines in M2 microglia, which related to the regulation of the IRF5-IRF4 axis. This current study indicates that PCE alleviates tPA-induced HT after ischemic stroke by modulating microglia M1/M2 phenotype polarization.

Rapamycin Alleviates Neuronal Injury and Modulates Microglial Activation After Cerebral Ischemia

Neurons and microglia are sensitive to cerebral microcirculation and their responses play a crucial part in the pathological processes, while they are also the main target cells of many drugs used to treat brain diseases. Rapamycin exhibits beneficial effects in many diseases; however, whether it can affect neuronal injury or alter the microglial activation after global cerebral ischemia remains unclear. In this study, we performed global cerebral ischemia combined with rapamycin treatment in CX3CR1GFP/+ mice and explored the effects of rapamycin on neuronal deficit and microglial activation. Our results showed that rapamycin reduced neuronal loss, neurodegeneration, and ultrastructural damage after ischemia by histological staining and transmission electron microscopy (TEM). Interestingly, rapamycin suppressed de-ramification and proliferation of microglia and reduced the density of microglia. Immunofluorescence staining indicated that rapamycin skewed microglial polarization toward an anti-inflammatory state. Furthermore, rapamycin as well suppressed the activation of astrocytes. Meanwhile, quantitative real-time polymerase chain reaction (qRT-PCR) analyses revealed a significant reduction of pro-inflammatory factors as well as an elevation of anti-inflammatory factors upon rapamycin treatment. As a result of these effects, behavioral tests showed that rapamycin significantly alleviated the brain injury after stroke. Together, our study suggested that rapamycin attenuated neuronal injury, altered microglial activation state, and provided a more beneficial immune microenvironment for the brain, which could be used as a promising therapeutic approach to treat ischemic cerebrovascular diseases.

Neuroprotective Effects of [Formula: see text]-Terpinene in Rats with Acute Cerebral Ischemia: Modulation of Inflammation, Apoptosis, and Oxidation

The study aimed to assess 𝛾-Terpinene's (𝛾-TER) neuroprotective potential in acute cerebral ischemia, characterized by reduced cerebral blood flow in rats. Middle cerebral artery occlusion (MCAO), a standard method for inducing cerebral ischemia, was employed in male Wistar rats. 𝛾-TER at varying doses (5, 10, and 15 mg/kg) were intraperitoneally administered during reperfusion onset. Neurological outcomes, cerebral infarct size, edema, and enzymatic activities (SOD, GPx, and catalase) in the brain were evaluated using diverse techniques. The study examined gene expression and pathways associated with neuroinflammation and apoptosis using Cytoscape software, identifying the top 10 genes involved. Pro-inflammatory and pro-apoptotic factors were assessed through real-time PCR and ELISA, while apoptotic cell rates were measured using the TUNEL and Flow cytometry assay. Immunohistochemistry assessed apoptosis-related proteins like Bax and bcl-2 in the ischemic area. 𝛾-TER, particularly at doses of 10 and 15 mg/kg, significantly reduced neurological deficits and cerebral infarction size. The 15 mg/kg dose mitigated TNF-α, IL-1β, Bax, and caspase-3 gene and protein levels in the cortex, hippocampus, and striatum compared to controls. Furthermore, Bcl-2 levels increased in these regions. 𝛾-TER show cased neuroprotective effects by suppressing inflammation, apoptosis, and oxidation. In conclusion, 𝛾-TER, possessing natural anti-inflammatory and anti-apoptotic properties, shields the brain against ischemic damage by reducing infarction, edema, oxidative stress, and inflammation. It modulates the expression of crucial genes and proteins associated with apoptosis in diverse brain regions. These findings position 𝛾-TER as a potential therapeutic agent for ischemic stroke.

Regulation of Microglial Activation by Wnt/β-Catenin Signaling After Global Cerebral Ischemia in Mice

Microglia are immunocompetent cells in the central nervous system. Following cerebral ischemia, microglia will be rapidly activated and undergo proliferation, morphological transformation, and changes in gene expression and function. At present, the regulatory mechanisms of microglial activation following ischemia remain largely unclear. In this study, we took advantage of CX3CR1GFP/+ fluorescent mice and a global cerebral ischemia-reperfusion model to investigate the mechanisms of microglial activation following different degrees of global ischemia. Our results showed that the proliferation of microglia was gated by the degree of ischemia. Marked microglial de-ramification and proliferation were observed after 60 min of ischemia but not in transient ischemia (20 min). Immunohistology, qRT-PCR, and Western blotting analysis showed that microglial activation was accompanied with a reduction in Wnt/β-catenin signaling after cerebral ischemia. Downregulation of Wnt/β-catenin signaling using Wnt antagonist XAV939 during 20 min ischemia promoted microglial de-ramification and proliferation. In contrast, enhancing Wnt/β-catenin signaling using Wnt agonist LiCl during 60 min ischemia-reduced microglial de-ramification and proliferation. Importantly, we found that Wnt agonist inhibited inflammation in the ischemic brain and was conducive to animal behavioral recovery. Collectively, these data demonstrated that Wnt/β-catenin signaling played a key role in microglial activation following cerebral ischemia, and regulating microglial activation may be a potential therapeutic strategy for the treatment of ischemic stroke.

Behavioral performance and microglial status in mice after moderate dose of proton irradiation

Cognitive impairment is a remote effect of gamma radiation treatment of malignancies. The major part of the studies on the effect of proton irradiation (a promising alternative in the treatment of radio-resistant tumors and tumors located close to critical organs) on the cognitive abilities of laboratory animals and their relation to morphological changes in the brain is rather contradictory. The aim of this study was to investigate cognitive functions and the dynamics of changes in morphological parameters of hippocampal microglial cells after 7.5 Gy of proton irradiation. Two months after the cranial irradiation, 8- to 9-week-old male SHK mice were tested for total activity, spatial learning, as well as long- and short-term hippocampus-dependent memory. To estimate the morphological parameters of microglia, brain slices of control and irradiated animals each with different time after proton irradiation (24 h, 7 days, 1 month) were stained for microglial marker Iba-1. No changes in behavior or deficits in short-term and long-term hippocampus-dependent memory were found, but an impairment of episodic memory was observed. A change in the morphology of hippocampal microglial cells, which is characteristic of the transition of cells to an activated state, was detected. One day after proton exposure in the brain tissue, a slight decrease in cell density was observed, which was restored to the control level by the 30th day after treatment. The results obtained may be promising with regard to the future use of using high doses of protons per fraction in the irradiation of tumors.