Neuron derived fractalkine promotes microglia to absorb hematoma via CD163/HO-1 after intracerebral hemorrhage

New targets in spontaneous intracerebral hemorrhage

PURPOSE OF REVIEW

Intracerebral hemorrhage (ICH) is a devastating stroke with limited medical treatments; thus, timely exploration of emerging therapeutic targets is essential. This review focuses on the latest strategies to mitigate secondary brain injury post-ICH other than targeting surgery or hemostasis, addressing a significant gap in clinical practice and highlighting potential improvements in patient outcomes.

RECENT FINDINGS

Promising therapeutic targets to reduce secondary brain injury following ICH have recently been identified, including attenuation of iron toxicity and inhibition of ferroptosis, enhancement of endogenous resorption of hematoma, and modulation of perihematomal inflammatory responses and edema. Additionally, novel insights suggest the lymphatic system of the brain may potentially play a role in hematoma clearance and edema management. Various experimental and early-phase clinical trials have demonstrated these approaches may potentially offer clinical benefits, though most research remains in the preliminary stages.

SUMMARY

Continued research is essential to identify multifaceted treatment strategies for ICH. Clinical translation of these emerging targets could significantly enhance the efficacy of therapeutic interventions and potentially reduce secondary brain damage and improve neurological recovery. Future efforts should focus on large-scale clinical trials to validate these approaches, to pave the way for more effective treatment protocols for spontaneous ICH.

TRIOL attenuates intracerebral hemorrhage injury by bidirectionally modulating microglia- and neuron-mediated hematoma clearance

Intracerebral hemorrhage (ICH) represents the most severe subtype of stroke, and the lack of effective clinical pharmacotherapies poses a substantial threat to human health. Hematoma plays a crucial role in determining the prognosis of ICH patients by causing primary mechanical extrusion, followed by secondary brain injuries, such as cerebral edema, iron-mediated oxidative stress, and inflammation resulting from its degradation products. 5α-androst-3β,5α,6β-triol (TRIOL) is a neuroprotective steroid currently undergoing phase II clinical trial for acute ischemic stroke with anti-oxidative and anti-inflammatory properties. However, whether TRIOL can protect brain against ICH injury remains unclear. In this study, we found that TRIOL significantly improved neurological function while reducing hematoma volume, cerebral edema, and tissue damage after ICH. Moreover, TRIOL enhanced microglial hematoma clearance through promoting CD36-mediated erythrophagocytosis and CD163-associated hemoglobin scavenging, while simultaneously reducing the release of microglial inflammatory factors and activating the antioxidative transcription factor Nrf2. Additionally, TRIOL inhibited neuron mediated hematoma absorption by suppressing heme oxygenase 2 (HO-2) and protected neurons against ICH-induced damage in vitro and in vivo. TRIOL also mitigated neuronal iron-dependent oxidative damage by increasing ferritin levels but decreasing divalent metal transporter 1 (DMT1) expression. Overall, these findings highlight the promising potential of TRIOL as a drug candidate for treating ICH.

Microglial HO-1 aggravates neuronal ferroptosis via regulating iron metabolism and inflammation in the early stage after intracerebral hemorrhage

Heme oxygenase 1 (HO-1), an enzyme involved in heme catabolism, has been shown upregulated in microglia cells and plays a critical roles in neurological damages after intracerebral hemorrhage (ICH). However, the mechanisms by which HO-1 mediates the neuronal damages are still obscure. Here, our findings demonstrate that HO-1 over-expression exacerbates the pro-inflammatory response of microglia and induces neuronal ferroptosis through promoting intracellular iron deposition in the ICH model both in vitro and in vivo. Furthermore, in the co-cultured ICH model in vitro, we verify that HO-1 over-expression disrupts the balance of iron metabolism in microglia, which increases the iron efflux to the extracellular space and promotes iron ion uptake in neurons, leading to lipid peroxidation injury and further contributing to neuronal ferroptosis. Moreover, the specific ferroptosis inhibitor Ferrostatin-1 (Fer-1) treatment could mitigate the damages in the co-cultured HT22 cells that caused by HO-1 over-expression in microglia, and improve the neurological function in the ICH model in mice. By shedding light on the mechanisms of aggravating neuronal ferroptosis due to HO-1 overexpression in the early stages after ICH, our study provides insights into the potential therapy of targeting HO-1 to treat ICH.

HO-1 represses NF-κB signaling pathway to mediate microglia polarization and phagocytosis in intracerebral hemorrhage

BACKGROUND

Microglia polarization plays a crucial role in inflammatory injury of brain following intracerebral hemorrhage (ICH). Heme oxygenase-1 (HO-1) has demonstrated protective properties against inflammation and promote hematoma clearance after ICH. The objective of this study was to explore impacts of HO-1 on microglia polarization and phagocytosis after ICH, along with the underlying mechanism.

METHODS

ICH model was constructed in C57BL/6 mice. Neurological deficit of ICH mice was evaluated. HE detected pathological changes of mouse brain tissue. Immunofluorescence staining tested co-localization between HO-1 or NF-κB p65 and IBA1. The expressions of gene and proteins were detected by RT-qPCR and Western blot, respectively. Flow cytometry determined microglial polarization phenotype and neuron apoptosis. Cell viability of neuron was assessed by CCK-8. Red blood cells labeled by PKH-26 and co-cultured with microglia for examining microglial erythrophagocytosis.

RESULTS

Both HO-1 and NF-κB p65 phosphorylation were elevated in brain tissues of ICH mice. ZnPP, a HO-1 inhibitor, could exacerbate microglial M1 polarization and nerve injury, as well as repress microglial erythrophagocytosis in vitro and hematoma clearance in vivo. On the contrary, Tat-NBD, a NF-κB inhibitor, greatly suppressed microglial M1 polarization, and induced M2 polarization and microglial erythrophagocytosis, thus improving nerve injury and hematoma clearance after ICH. Notably, it was observed that NF-κB p65 could be activated by ZnPP treatment, and the regulatory roles of ZnPP on microglial polarization and erythrophagocytosis after ICH in vivo and in vitro were all diminished by Tat-NBD.

CONCLUSION

Therefore, our data demonstrated that HO-1 alleviated nerve injury and induced M2 polarization and phagocytosis of microglia after ICH via inhibiting NF-κB signaling pathway, which could provide deepen the pathological understanding of ICH and provide potential intervention targets and drug candidate for ICH.

Fractalkine/CX3CR1 axis is critical for neuroprotection induced by hypoxic postconditioning against cerebral ischemic injury

Microglial activation-mediated neuroinflammation is a major contributor to neuronal damage after cerebral ischemia. The Fractalkine (FKN)/CX3C chemokine receptor 1 (CX3CR1) axis plays a critical role in regulating microglial activation and neuroinflammation. The aim of this study is to ascertain the role and mechanism of FKN/CX3CR1 axis in hypoxic postconditioning (HPC)-induced anti-inflammatory and neuroprotective effects on transient global cerebral ischemia (tGCI). We found that HPC suppressed microglial activation and alleviated neuroinflammation in hippocampal CA1 after tGCI. Meanwhile, HPC upregulated the expression of FKN and CX3CR1 in neurons, but it downregulated the expression of CX3CR1 in glial cells after tGCI. In addition, the overexpression of FKN induced by the administration of FKN-carried lentivirus reduced microglial activation and inhibited neuroinflammation in CA1 after tGCI. Furthermore, silencing CX3CR1 with CX3CRi-carried lentivirus in CA1 after tGCI suppressed microglial activation and neuroinflammation and exerted neuroprotective effects. Finally, the overexpression of FKN caused a marked increase of neuronal CX3CR1 receptors, upregulated the phosphorylation of Akt, and reduced neuronal loss of rats in CA1 after tGCI. These findings demonstrated that HPC protected against neuronal damage in CA1 of tGCI rats through inhibiting microglial activation and activating Akt signaling pathway via FKN/CX3CR1 axis.

Revisiting the role of the complement system in intracerebral hemorrhage and therapeutic prospects

Intracerebral hemorrhage (ICH) is a stroke subtype characterized by non-traumatic rupture of blood vessels in the brain, resulting in blood pooling in the brain parenchyma. Despite its lower incidence than ischemic stroke, ICH remains a significant contributor to stroke-related mortality, and most survivors experience poor outcomes that significantly impact their quality of life. ICH has been accompanied by various complex pathological damage, including mechanical damage of brain tissue, hematoma mass effect, and then leads to inflammatory response, thrombin activation, erythrocyte lysis, excitatory amino acid toxicity, complement activation, and other pathological changes. Accumulating evidence has demonstrated that activation of complement cascade occurs in the early stage of brain injury, and the excessive complement activation after ICH will affect the occurrence of secondary brain injury (SBI) through multiple complex pathological processes, aggravating brain edema, and pathological brain injury. Therefore, the review summarized the pathological mechanisms of brain injury after ICH, specifically the complement role in ICH, and its related pathological mechanisms, to comprehensively understand the specific mechanism of different complements at different stages after ICH. Furthermore, we systematically reviewed the current state of complement-targeted therapies for ICH, providing a reference and basis for future clinical transformation of complement-targeted therapy for ICH.

H3K9 trimethylation dictates neuronal ferroptosis through repressing Tfr1

Spontaneous intracerebral hemorrhage (ICH) is a devastating disease with high morbidity and mortality worldwide. We have previously shown that ferroptosis contributes to neuronal loss in ICH mice. The overload of iron and dysfunction of glutathione peroxidase 4 (GPx4) promote neuronal ferroptosis post-ICH. However, how epigenetic regulatory mechanisms affect the ferroptotic neurons in ICH remains unclear. In the current study, hemin was used to induce ferroptosis in N2A and SK-N-SH neuronal cells to mimic ICH. The results showed that hemin-induced ferroptosis was accompanied by an increment of global level of trimethylation in histone 3 lysine 9 (H3K9me3) and its methyltransferase Suv39h1. Transcriptional target analyses indicated that H3K9me3 was enriched at the promoter region and gene body of transferrin receptor gene 1 (Tfr1) and repressed its expression upon hemin stimulation. Inhibition of H3K9me3 with inhibitor or siRNA against Suv39h1 aggravated hemin- and RSL3-induced ferroptosis by upregulating Tfr1 expression. Furthermore, Suv39h1-H3K9me3 mediated repression of Tfr1 contributes to the progression of ICH in mice. These data suggest a protective role of H3K9me3 in ferroptosis post ICH. The knowledge gained from this study will improve the understanding of epigenetic regulation in neuronal ferroptosis and shed light on future clinical research after ICH.

ACSL4-Mediated Ferroptosis and Its Potential Role in Central Nervous System Diseases and Injuries

As an iron-dependent regulated form of cell death, ferroptosis is characterized by iron-dependent lipid peroxidation and has been implicated in the occurrence and development of various diseases, including nervous system diseases and injuries. Ferroptosis has become a potential target for intervention in these diseases or injuries in relevant preclinical models. As a member of the Acyl-CoA synthetase long-chain family (ACSLs) that can convert saturated and unsaturated fatty acids, Acyl-CoA synthetase long-chain familymember4 (ACSL4) is involved in the regulation of arachidonic acid and eicosapentaenoic acid, thus leading to ferroptosis. The underlying molecular mechanisms of ACSL4-mediated ferroptosis will promote additional treatment strategies for these diseases or injury conditions. Our review article provides a current view of ACSL4-mediated ferroptosis, mainly including the structure and function of ACSL4, as well as the role of ACSL4 in ferroptosis. We also summarize the latest research progress of ACSL4-mediated ferroptosis in central nervous system injuries and diseases, further proving that ACSL4-medicated ferroptosis is an important target for intervention in these diseases or injuries.

Magnetic Targeting Nanocarriers Combined with Focusing Ultrasound for Enhanced Intracerebral Hemorrhage Therapy

Intracerebral hemorrhage (ICH) remains a significant cause of morbidity and mortality around the world, and surgery is still the most direct and effective way to remove ICH. However, the potential risks brought by surgery, such as normal brain tissue damage, post-operative infection, and difficulty in removing deep hematoma, are still the main problems in the surgical treatment of ICH. Activation of the peroxisome proliferator-activated receptor gamma (PPARγ) is reported to show a good therapeutic effect in hematoma clearance. Herein, a magnetic targeting nanocarrier loaded with a PPARγ agonist (15d-PGJ2-MNPs) is synthesized, which could be magnetically targeted and enriched in the area of the hematoma after intravenous injection. Subsequent application of focusing ultrasound (FUS) could enhance drug diffusion, which activates the PPARγ receptors on macrophages around the hematoma for better hematoma clearance. The 15d-PGJ2-MNP treatment alleviates brain injury, accelerates hematoma clearance, attenuates neuroinflammation, reduces brain edema and significantly improves the deficits in sensory and motor function and spatial learning ability in the ICH mouse model. This work proposes an effective magnetic targeting plus FUS method to treat ICH, highlighting its great potential in the treatment of hemorrhagic stroke.

Research progress of endogenous hematoma absorption after intracerebral hemorrhage

Non-traumatic intraparenchymal brain hemorrhage is referred to as intracerebral hemorrhage (ICH). Although ICH is associated with a high rate of disability and case fatality, active intervention can significantly lower the rate of severe disability. Studies have shown that the speed of hematoma clearance after ICH determines the patient's prognosis. Following ICH, depending on the hematoma volume and mass effect, either surgical- or medication-only conservative treatment is chosen. The goal of promoting endogenous hematoma absorption is more relevant because surgery is only appropriate for a small percentage of patients, and open surgery can cause additional trauma to patients. The primary method of removing hematoma after ICH in the future will involve understanding how to produce and manage macrophage/microglial endogenous phagocytic hematomas. Therefore, it is necessary to elucidate the regulatory mechanisms and key targets for clinical purposes.

The roles of chemokines following intracerebral hemorrhage in animal models and humans

Intracerebral hemorrhage (ICH) is one common yet devastating stroke subtype, imposing considerable burdens on families and society. Current guidelines are limited to symptomatic treatments after ICH, and the death rate remains significant in the acute stage. Thus, it is crucial to promote research to develop new targets on brain injury after ICH. In response to hematoma formation, amounts of chemokines are released in the brain, triggering the infiltration of resident immune cells in the brain and the chemotaxis of peripheral immune cells via the broken blood-brain barrier. During the past decades, mounting studies have focused on the roles of chemokines and their receptors in ICH injury. This review summarizes the latest advances in the study of chemokine functions in the ICH. First, we provide an overview of ICH epidemiology and underlying injury mechanisms in the pathogenesis of ICH. Second, we introduce the biology of chemokines and their receptors in brief. Third, we outline the roles of chemokines in ICH according to subgroups, including CCL2, CCL3, CCL5, CCL12, CCL17, CXCL8, CXCL12, and CX3CL1. Finally, we summarize current drug usage targeting chemokines in ICH and other cardio-cerebrovascular diseases. This review discusses the expressions of these chemokines and receptors under normal or hemorrhagic conditions and cell-specific sources. Above all, we highlight the related data of these chemokines in the progression and outcomes of the ICH disease in preclinical and clinical studies and point to therapeutic opportunities targeting chemokines productions and interactions in treating ICH, such as accelerating hematoma absorption and alleviating brain edema.

Neuroinflammation in retinitis pigmentosa: Therapies targeting the innate immune system

Retinitis pigmentosa (RP) is an important cause of irreversible blindness worldwide and lacks effective treatment strategies. Although mutations are the primary cause of RP, research over the past decades has shown that neuroinflammation is an important cause of RP progression. Due to the abnormal activation of immunity, continuous sterile inflammation results in neuron loss and structural destruction. Therapies targeting inflammation have shown their potential to attenuate photoreceptor degeneration in preclinical models. Regardless of variations in genetic background, inflammatory modulation is emerging as an important role in the treatment of RP. We summarize the evidence for the role of inflammation in RP and mention therapeutic strategies where available, focusing on the modulation of innate immune signals, including TNFα signaling, TLR signaling, NLRP3 inflammasome activation, chemokine signaling and JAK/STAT signaling. In addition, we describe epigenetic regulation, the gut microbiome and herbal agents as prospective treatment strategies for RP in recent advances.