C3/C3aR inhibition alleviates GMH-IVH-induced hydrocephalus by preventing microglia-astrocyte interactions in neonatal rats

Complement Inhibition Reduces Early Erythrolysis, Attenuates Brain Injury, Hydrocephalus, and Iron Accumulation after Intraventricular Hemorrhage in Aged Rats

Blood components released by erythrolysis play an important role in secondary brain injury and posthemorrhagic hydrocephalus (PHH) after intraventricular hemorrhage (IVH). The current study examined the impact of N-acetylheparin (NAH), a complement inhibitor, on early erythrolysis, PHH and iron accumulation in aged rats following IVH. This study, on 18-months-old male Fischer 344 rats, was in 3 parts. First, rats had an intracerebroventricular injection of autologous blood (IVH) mixed with NAH or saline, or saline alone. After MRI at four hours, Western blot and immunohistochemistry examined complement activation and electron microscopy choroid plexus and periventricular damage. Second, rats had an IVH with NAH or vehicle, or saline. Rats underwent serial MRI at 4 h and 1 day to assess ventricular volume and erythrolysis. Immunohistochemistry and H&E staining examined secondary brain injury. Third, rats had an IVH with NAH or vehicle. Serial MRIs on day 1 and 28 assessed ventricular volume and iron accumulation. H&E staining and immunofluorescence evaluated choroid plexus phagocytes. Complement activation was found 4 h after IVH, and co-injection of NAH inhibited that activation. NAH administration attenuated erythrolysis, reduced ventricular volume, alleviated periventricular and choroid plexus injury at 4 h and 1 day after IVH. NAH decreased iron accumulation, the number of choroid plexus phagocytes, and attenuated hydrocephalus at 28 days after IVH. Inhibiting complement can reduce early erythrolysis, attenuates hydrocephalus and iron accumulation after IVH in aged animals.

A Novel H2S Donor Alleviates Neuroinflammation and Seizures by Inhibiting the C3-C3aR Pathway

Both astrocytes and microglia are activated in the epileptic brain. There is an interaction between them through the complement 3 (C3)-C3a receptor (C3aR) pathway, which plays a detrimental role in seizures. Our self-developed novel H2S donor has been found to have anti-seizure effects. However, its mechanism remains to be explored. In the present study, we showed that the novel H2S donor can inhibit the activation of astrocytes and microglia and their interaction through C3-C3aR signaling, which contributed to alleviating microglial neuroinflammation and seizures. In LPS-treated astrocytes and pilocarpine-induced epileptic mice, the H2S donor reduced C3 production in astrocytes and regulated the expression of inflammatory cytokines IL-1β and IL-10 in microglia. The H2S donor also reduced the EEG amplitude of hippocampal epileptic waves and relieved seizures in epileptic mice. These effects of the H2S donor can be reversed by intranasal C3 treatment and mimicked by a C3aR antagonist. These findings provide a novel mechanism underlying the anti-seizure effects of the H2S donor. Therefore, the H2S donor has the potential to be used as a candidate for antiepileptic drugs.

Inhibition of C3/C3aR Pathway Alleviates Visual and Optic Nerve Impairments in a Rat Model of Neuromyelitis Optica Spectrum Disorder

Accumulating evidence suggests that the complement C3/C3a receptor (C3aR) pathway plays a pivotal role in the pathogenesis of neurodegenerative and autoimmune disorders, particularly neuromyelitis optica spectrum disorders (NMOSDs). Despite this, the specific pathogenic effect and mechanism of C3/C3aR pathway in NMOSD remains elusive. In this study, we demonstrated for the first time that the expression of C3aR and its upstream ligand C3 is significantly upregulated in the optic nerve of a rat model of NMOSD-related optic neuritis (NMOSD-ON). Our findings reveal that this upregulation leads to blood-brain barrier (BBB) disruption, demyelination and neuronal damage. Through the use of a novel C3aR inhibitor, JR14a, we demonstrate its effectiveness in reducing C3aR expression and mitigating pathological damage in the optic nerve. Furthermore, our transcriptome sequencing analysis of NMOSD optic nerve tissues reveals extensive enrichment of inflammation- and immune response-related pathways, with particular emphasis on the complement and coagulation cascades pathway. This study not only elucidated the crucial role of the C3-C3aR pathway in NMOSD-ON pathogenesis but also provided a new promising therapeutic target for NMOSD through C3aR pathway inhibition.

Long Noncoding RNA GAS5-Involved Progression of Neonatal Hydrocephalus and Inflammatory Responses

Intraventricular hemorrhage results in posthemorrhagic hydrocephalus (PHH). Neonatal hydrocephalus remains a challenging disease due to the high failure rate of all management strategies. We evaluated long noncoding RNA growth arrest-specific 5 (GAS5)-mediated network in neonatal hydrocephalus, providing a new direction for the treatment of hydrocephalus. The PHH model was constructed in neonatal rats after intracerebroventricular injection with GAS5, miR-325-3p, and chaperonin containing T-complex protein 1, subunit 8 (CCT8) plasmids, or oligonucleotides. Next, behavioral tests, measurement of serum inflammation, observation of brain tissue pathology, and calculation of hemoglobin and brain water contents were implemented. GAS5, miR-325-3p, and CCT8 expression, in combination with their interactions, was checked. As the results reported, collagenase infusion induced hydrocephalus, impairing neurological function, enhancing inflammation and neuronal apoptosis, and increasing hemoglobin and brain water contents. GAS5 and CCT8 were up-regulated, while miR-325-3p was down-regulated in hydrocephalic rats. Downregulating GAS5/CCT8 or upregulating miR-325-3p could inhibit inflammatory response and improve neurological function in young hydrocephalic rats. GAS5 promotes CCT8 expression through sponge adsorption of miR-325-3p. GAS5 silencing-mediated protections against hydrocephalus were counteracted by CCT8 overexpression. In summary, GAS5 aggravates neonatal hydrocephalus and inflammatory responses in a way of leasing miR-325-3p-involved regulation of CCT8.

The activation of microglia by the complement system in neurodegenerative diseases

Neurodegenerative diseases (NDDs) are a group of neurological disorders characterized by the progressive loss of neuronal structure and function, leading to cognitive and behavioral impairments. Despite significant research advancements, there is currently no definitive cure for NDDs. With global aging on the rise, the burden of these diseases is becoming increasingly severe, highlighting the urgency of understanding their pathogenesis and developing effective therapeutic strategies. Microglia, specialized macrophages in the central nervous system, play a dual role in maintaining neural homeostasis. They are involved in clearing cellular debris and apoptotic cells, but in their activated state, they release inflammatory factors that contribute significantly to neuroinflammation. The complement system (CS), a critical component of the innate immune system, assists in clearing damaged cells and proteins. However, excessive or uncontrolled activation of the CS can lead to chronic neuroinflammation, exacerbating neuronal damage. This review aims to explore the roles of microglia and the CS in the progression of NDDs, with a specific focus on the mechanisms through which the CS activates microglia by modulating mitochondrial function. Understanding these interactions may provide insights into potential therapeutic targets for mitigating neuroinflammation and slowing neurodegeneration.

C3/C3aR Bridges Spinal Astrocyte-Microglia Crosstalk and Accelerates Neuroinflammation in Morphine-Tolerant Rats

AIMS

Communication within glial cells acts as a pivotal intermediary factor in modulating neuroimmune pathology. Meanwhile, an increasing awareness has emerged regarding the detrimental role of glial cells and neuroinflammation in morphine tolerance (MT). This study investigated the influence of crosstalk between astrocyte and microglia on the evolution of morphine tolerance.

METHODS

Sprague-Dawley rats were intrathecally treated with morphine twice daily for 9 days to establish morphine-tolerant rat model. Tail-flick latency test was performed to identify the analgesic effect of morphine. The role of microglia, astrocyte and C3-C3aR axis in morphine tolerance were elucidated by real-time quantitative polymerase chain reaction, Western blot, and immunofluorescence.

RESULTS

Chronic morphine treatment notably promoted the activation of microglia, upregulated the production of proinflammatory mediators (interleukin-1 alpha (IL-1α), tumor necrosis factor alpha (TNFα), and complement component 1q (C1q)). Simultaneously, it programed astrocytes to a pro-inflammatory phenotype (A1), which mainly expresses complement 3 (C3) and serping1. PLX3397 (a colony-stimulating factor 1 receptor (CSF1R) inhibitor), Compstain (a C3 inhibitor) and SB290157(a C3aR antagonist) could reverse the above pathological process and alleviate morphine tolerance to different extents.

CONCLUSION

Our findings identify C3-C3aR axis as an amplifier of microglia-astrocyte crosstalk, neuroinflammation and a node for therapeutic intervention in morphine tolerance.

Pharmacological Strategies and Surgical Management of Posthemorrhagic Hydrocephalus Following Germinal Matrix-Intraventricular Hemorrhage in Preterm Infants

Germinal matrix-intraventricular hemorrhage (GM-IVH) is a detrimental neurological complication that occurs in preterm infants, especially in babies born before 32 weeks of gestation and in those with a very low birth weight. GM-IVH is defined as a rupture of the immature and fragile capillaries located in the subependymal germinal matrix zone of the preterm infant brain, and it can lead to detrimental neurological sequelae such as posthemorrhagic hydrocephalus (PHH), cerebral palsy, and other cognitive impairments. PHH following GM-IVH is difficult to treat in the clinic, and no levelone strategies have been recommended to pediatric neurosurgeons. Several cellular and molecular mechanisms of PHH following GM-IVH have been studied in animal models, but no effective pharmacological strategies have been used in the clinic. Thus, a comprehensive understanding of molecular mechanisms, potential pharmacological strategies, and surgical management of PHH is urgently needed. The present review presents a synopsis of the pathogenesis, diagnosis, and cellular and molecular mechanisms of PHH following GM-IVH and explores pharmacological strategies and surgical management.

Deconvolution of cell-type-associated markers predictive of response to neoadjuvant radiotherapy

Tumor microenvironent contains prognostic molecular markers and therapeutic targets from different cellular sources, which are still not fully revealed in the resistance and recurrence after radiotherapy for rectal cancer. By integrating the scRNA-seq data, we deconvoluted the bulk transcriptomics of rectal cancer collected before preoperative neoadjuvant radiotherapy (nRT) into fractions and gene expression of the six cell types. The inferred cell-type-associated DEGs, abbreviated as caDEGs, of myeloid and stromal cells were enriched for overlapping yet unique biological processes including immunity, angiogenesis, and metabolism, respectively. Ecotyper analysis indicates that the caDEGs reflects cell states and ecotypes in association with nRT response. By mapping the caDEGs onto the context-free and newly built ligand-receptor and collagen-integrin lists from scRNA-Seq data, respectively, we inferred 297 cell-type-specific trans- and/or cis-collagen-integrin and 219 heterotypic ligand-receptor interactions potentially associated with nRT response, including interactions between stromal-associated COL1A2/COL6A1/COL6A2 and stromal or CMS1-associated ITGA1/B1, between epithelial-associated JAG1 and stromal-associated NOTCHs, between CMS2 epithelial-associated CCL15 and proliferating myeloid-associated CCR1, between myeloid-associated CCL4/CD86 and lymphatic endothelial-associated ACKR2, and between myeloid-associated TNFS13B and B cell-associated TNFRSF13B/C, etc. Intriguingly, results suggest a greater number of down-regulated cell-type-related markers in resistant cancers to nRT. Favorable myeloid-associated CD14, epithelial-associated DYM, stromal-associated COL1A2 and COL3A1, and unfavorable epithelial-associated CELSR3 and KCNH8 markers were inferred at least from two independent nCRT datasets of GSE119409, GSE35452, and GSE45404. The results provide insights into roles of the stromal and immune cells beside epithelial cells in resistance to radiotherapy for rectal cancers. The proposed approach can be applicable to other diseases as well. Codes and additional data are available at https://github.com/Xueling21/rectalNRT_deconv.

JR14a: A novel antagonist of C3aR attenuates neuroinflammation in cerebral ischemia-reperfusion injury

Cerebral ischemia-reperfusion injury (CIRI), a prevalent stroke-related complication, can lead to severe brain damage. Inflammation is a crucial factor in CIRI pathogenesis, and the complement component 3a receptor (C3aR) could be a key mediator in the post-CIRI inflammatory cascade. In this study, the role of C3aR in CIRI was investigated utilizing a middle cerebral artery occlusion (MCAO) model in C3aR knockout (KO) mice. Magnetic resonance imaging (MRI) and neurofunctional assessments revealed that C3aR KO mice exhibited significantly diminished cerebral infarction and improved neurological impairments. Consequently, the focus shifted to searching for a small molecule antagonist of C3aR. JR14a, a new potent thiophene antagonist of C3aR, was injected intraperitoneally into mice 1-h post-MCAO model implementation. The mass spectrometry (MS) results indicated the ability of JR14a to penetrate the blood-brain barrier. Subsequent TTC staining and neurofunctional assessments revealed the efficacy of JR14a in reducing cerebral infarct volume and neurological impairment following MCAO. In addition, immunofluorescence (IF) and immunohistochemistry (IHC) demonstrated attenuated microglial activation, neutrophil infiltration, and blood-brain barrier disruption by JR14a in the MCAO model. Furthermore, enzyme-linked immunosorbent assay (ELISA) and Western blotting supported the role of JR14a in downregulating the expression levels of C3aR, tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6), as well as the phosphorylation of p65. In conclusion, the findings suggested that C3aR could be a potential therapeutic target for CIRI, and JR14a emerged as a promising treatment candidate.

The Crosstalk Between Immune Cells After Intracerebral Hemorrhage

The inflammatory mechanism of intracerebral hemorrhage (ICH) has been widely studied, and it is believed that the regulation of this mechanism is of great significance to the prognosis. In the early stage of the acute phase of ICH, the release of a large number of inflammatory factors around the hematoma can recruit more inflammatory cells to infiltrate the area, further release inflammatory factors, cause an inflammatory cascade reaction, aggravate the volume of cerebral hematoma and edema and further destroy the blood-brain barrier (BBB), according to this, the crosstalk between cells may be of great significance in secondary brain injury (SBI). Because most of the cells recruited are inflammatory immune cells, this paper mainly discusses the cells based on the inflammatory mechanism to discuss their functions after ICH, we found that among the main cells inherent in the brain, glial cells account for the majority, of which microglia are the most widely studied and it can interact with a variety of cells, which is reflected in the literature researches on its pathogenesis and treatment. We believe that exploring multi-mechanism and multi-cell regulated drugs may be the future development trend, and the existing research, the comparison and unification of modeling methods, and the observation of long-term efficacy may be the first problem that researchers need to solve.

A role for P-selectin and complement in the pathological sequelae of germinal matrix hemorrhage

BACKGROUND

Germinal matrix hemorrhage is a devastating disease of pre-term infancy commonly resulting in post-hemorrhagic hydrocephalus, periventricular leukomalacia, and subsequent neurocognitive deficits. We demonstrate vascular expression of the adhesion molecule P-selectin after GMH and investigate a strategy to specifically target complement inhibition to sites of P-selectin expression to mitigate the pathological sequelae of GMH.

METHODS

We prepared two fusion proteins consisting of different anti-P-selectin single chain antibodies (scFv's) linked to the complement inhibitor Crry. One scFv targeting vehicle (2.12scFv) blocked the binding of P-selectin to its PSGL-1 ligand expressed on leukocytes, whereas the other targeting vehicle (2.3scFv) bound P-selectin without blocking ligand binding. Post-natal C57BL/6 J mice on day 4 (P4) were subjected to collagenase induced-intraventricular hemorrhage and treated with 2.3Psel-Crry, 2.12Psel-Crry, or vehicle.

RESULTS

Compared to vehicle treatment, 2.3Psel-Crry treatment after induction of GMH resulted in reduced lesion size and mortality, reduced hydrocephalus development, and improved neurological deficit measurements in adolescence. In contrast, 2.12Psel-Crry treatment resulted in worse outcomes compared to vehicle. Improved outcomes with 2.3Psel-Crry were accompanied by decreased P-selectin expression, and decreased complement activation and microgliosis. Microglia from 2.3Psel-Crry treated mice displayed a ramified morphology, similar to naïve mice, whereas microglia in vehicle treated animals displayed a more ameboid morphology that is associated with a more activated status. Consistent with these morphological characteristics, there was increased microglial internalization of complement deposits in vehicle compared to 2.3Psel-Crry treated animals, reminiscent of aberrant C3-dependent microglial phagocytosis that occurs in other (adult) types of brain injury. In addition, following systemic injection, 2.3Psel-Crry specifically targeted to the post-GMH brain. Likely accounting for the unexpected finding that 2.12Psel-Crry worsens outcome following GMH was the finding that this construct interfered with coagulation in this hemorrhagic condition, and specifically with heterotypic platelet-leukocyte aggregation, which express P-selectin and PSGL-1, respectively.

CONCLUSIONS

GMH induces expression of P-selectin, the targeting of which with a complement inhibitor protects against pathogenic sequelae of GMH. A dual functioning construct with both P-selectin and complement blocking activity interferes with coagulation and worsens outcomes following GMH, but has potential for treatment of conditions that incorporate pathological thrombotic events, such as ischemic stroke.

A Role for P-selectin and Complement in the Pathological Sequelae of Germinal Matrix Hemorrhage

Background Germinal Matrix Hemorrhage is a devastating disease of pre-term infancy commonly resulting in post-hemorrhagic hydrocephalus, periventricular leukomalacia, and subsequent neurocognitive deficits. We demonstrate vascular expression of the adhesion molecule P-selectin after GMH and investigate a strategy to specifically target complement inhibition to sites of P-selectin expression to mitigate the pathological sequelae of GMH. Methods We prepared two fusion proteins consisting of different anti-P-selectin single chain antibodies (scFv's) linked to the complement inhibitor Crry. One scFv targeting vehicle (2.12scFv) blocked the binding of P-selectin to its PSGL-1 ligand expressed on leukocytes, whereas the other targeting vehicle (2.3scFv) bound P-selectin without blocking ligand binding. Post-natal mice on day 4 (P4) were subjected to collagenase induced-intraventricular hemorrhage and treated with 2.3Psel-Crry, 2.12Psel-Crry, or vehicle. Results Compared to vehicle treatment, 2.3Psel-Crry treatment after induction of GMH resulted in reduced lesion size and mortality, reduced hydrocephalus development, and improved neurological deficit measurements in adolescence. In contrast, 2.12Psel-Crry treatment resulted in worse outcomes compared to vehicle. Improved outcomes with 2.3Psel-Crry were accompanied by decreased P-selectin expression, and decreased complement activation and microgliosis. Microglia from 2.3Psel-Crry treated mice displayed a ramified morphology, similar to naïve mice, whereas microglia in vehicle treated animals displayed a more ameboid morphology that is associated with a more activated status. Consistent with these morphological characteristics, there was increased microglial internalization of complement deposits in vehicle compared to 2.3Psel-Crry treated animals, reminiscent of aberrant C3-dependent microglial phagocytosis that occurs in other (adult) types of brain injury. Also, following systemic injection, 2.3Psel-Crry specifically targeted to the post-GMH brain. Likely accounting for the unexpected finding that 2.12Psel-Crry worsens outcome following GMH was the finding that this construct interfered with coagulation in this hemorrhagic condition, and specifically with heterotypic platelet-leukocyte aggregation, which express P-selectin and PSGL-1, respectively. Conclusion GMH induces expression of P-selectin, the targeting of which with a complement inhibitor protects against pathogenic sequelae of GMH. A dual functioning construct with both P-selectin and complement blocking activity interferes with coagulation and worsens outcomes following GMH, but has potential for treatment of conditions that incorporate pathological thrombotic events, such as ischemic stroke.

Bidirectional Communication Between Microglia and Astrocytes in Neuroinflammation

Neuroinflammation is a common feature of diverse nervous system pathologies. In many instances, it begins at an early stage of the disease, paving the way for further exacerbations. The main drivers of neuroinflammation are brain-resident glial cells, such as microglia and astrocytes. Microglia are the primary responders to any insult to the brain parenchyma, translating the signals into diverse molecules. These molecules derived from microglia can regulate the stimuli-dependent reactivity of astrocytes. Once activated, astrocytes in turn, can control microglia phenotypes. Recent evidence indicates that the crosstalk between these glial cells plays an important role in delaying or accelerating neuroinflammation and overall disease progression. To date, various molecules have been recognized as key mediators of the bidirectional communication between microglia and astrocytes. The current review aims to discuss the novel molecules identified recently, which play a critical role in interglial crosstalk, highlighting their therapeutic potential.

Role of complement C1q/C3-CR3 signaling in brain injury after experimental intracerebral hemorrhage and the effect of minocycline treatment

Aim

The complement cascade is activated and may play an important pathophysiologic role in brain injury after experimental intracerebral hemorrhage (ICH). However, the exact mechanism of specific complement components has not been well studied. This study determined the role of complement C1q/C3-CR3 signaling in brain injury after ICH in mice. The effect of minocycline on C1q/C3-CR3 signaling-induced brain damage was also examined.

Methods

There were three parts to the study. First, the natural time course of C1q and CR3 expression was determined within 7 days after ICH. Second, mice had an ICH with CR3 agonists, LA-1 or vehicle. Behavioral score, neuronal cell death, hematoma volume, and oxidative stress response were assessed at 7 days after ICH. Third, the effect of minocycline on C1q/C3-CR3 signaling and brain damage was examined.

Results

There were increased numbers of C1q-positive and CR3-positive cells after ICH. Almost all perihematomal C1q-positive and CR3-positive cells were microglia/macrophages. CR3 agonist LA-1 aggravated neurological dysfunction, neuronal cell death, and oxidative stress response on day 7 after ICH, as well as enhancing the expression of the CD163/HO-1 pathway and accelerating hematoma resolution. Minocycline treatment exerted neuroprotective effects on brain injury following ICH, partly due to the inhibition of C1q/C3-CR3 signaling, and that could be reversed by LA-1.

Conclusions

The complement C1q/C3-CR3 signaling is upregulated after ICH. The activation of C1q/C3-CR3 signaling by LA-1 aggravates brain injury following ICH. The neuroprotection of minocycline, at least partly, is involved with the repression of the C1q/C3-CR3 signaling pathway.

Gypenoside XVII, an Active Ingredient from Gynostemma Pentaphyllum, Inhibits C3aR-Associated Synaptic Pruning in Stressed Mice

Gynostemma pentaphyllum is a herbal medicine widely used in Asian countries, and its saponin extracts have been shown to possess potent anti-inflammatory effects. Gypenoside XVII, an active ingredient isolated from Gynostemma pentaphyllum, has been found to alleviate the inflammation induced by LPS in the BV2 microglia, according to our preliminary study. This study aims to evaluate whether Gypenoside XVII could attenuate depression-like symptoms in vivo and tries to demonstrate the involvement of the complement regulation in its antidepressant-like effect. The results showed that Gypenoside XVII significantly attenuated depression-like behaviors in the forced swimming test, tail suspension test and sucrose preference test. It also alleviated the acute stress-induced hyperactivity of serum corticosterone levels. Additionally, Gypenoside XVII significantly inhibited the activation of microglia and the expression of C3 in mice exposed to chronic unpredictable mild stress (CUMS). Meanwhile, the activation of C3aR/STAT3 signaling and the expression of proinflammatory cytokines was reversed by Gypenoside XVII. Moreover, CUMS induced excessive synaptic pruning by activating microglia, while Gypenoside XVII restored it in the prefrontal cortex. Our data demonstrated that Gypenoside XVII, the active ingredient of Gynostemma pentaphyllum, produced the antidepressant-like effects in mice, which was mediated by the inhibition of complement C3/C3aR/STAT3/cytokine signaling in the prefrontal cortex.

Adiponectin Ameliorates GMH-Induced Brain Injury by Regulating Microglia M1/M2 Polarization Via AdipoR1/APPL1/AMPK/PPARγ Signaling Pathway in Neonatal Rats

Adiponectin (APN), a fat-derived plasma hormone, is a classic anti-inflammatory agent. Multiple studies have demonstrated the beneficial role of APN in acute brain injury, but the effect of APN in germinal matrix hemorrhage (GMH) is unclear, and the underlying molecular mechanisms remain largely undefined. In the current study, we used a GMH rat model with rh-APN treatment, and we observed that APN demonstrated a protective effect on neurological function and an inhibitory effect on neuroinflammation after GMH. To further explore the underlying mechanisms of these effects, we found that the expression of Adiponectin receptor 1 (AdipoR1) primarily colocalized with microglia and neurons in the brain. Moreover, AdiopR1, but not AdipoR2, was largely increased in GMH rats. Meanwhile, further investigation showed that APN treatment promoted AdipoR1/APPL1-mediated AMPK phosphorylation, further increased peroxisome proliferator-activated receptor gamma (PPARγ) expression, and induced microglial M2 polarization to reduce the neuroinflammation and enhance hematoma resolution in GMH rats. Importantly, either knockdown of AdipoR1, APPL1, or LKB1, or specific inhibition of AMPK/PPARγ signaling in microglia abrogated the protective effect of APN after GMH in rats. In all, we propose that APN works as a potential therapeutic agent to ameliorate the inflammatory response following GMH by enhancing the M2 polarization of microglia via AdipoR1/APPL1/AMPK/PPARγ signaling pathway, ultimately attenuating inflammatory brain injury induced by hemorrhage.