Lipocalin-2 as a therapeutic target for brain injury: An astrocentric perspective

Regulating astrocyte phenotype by Lcn2 inhibition toward ischemic stroke therapy

Astrocytes can be reacted to "reactive astrocytes" after ischemia-reperfusion injury, in which A1 phenotype causes neuronal and oligodendrocyte death, whereas the A2 phenotype exerts neuroprotective effects, thus regulating reactive astrocyte to A2 type is a potential target for stroke therapy. Lcn2 level is highly associated with the phenotypic polarization of astrocytes. We found that silencing the Lcn2 gene by adeno-associated virus (AAV)-Lcn2 shRNA adenovirus resulted in a dramatic decrease in A1-type astrocytes and increase in A2 astrocytes in MCAO mice. Hence, a nanoplatform was developed for stroke therapy by inhibiting Lcn2. This system was fabricated by N-acetyl Pro-Gly-Pro peptide-decorated rod-shaped poly (lactic-co-glycolic acid) nanoparticles loading with rolipram (AP@R). The nanodrug can be efficiently taken up by neutrophils simultaneously through morphology-mediated passive targeting and Cxcr2 receptor-mediated active targeting, subsequently crossing the blood-brain barrier (BBB) by hitchhiking neutrophils. When accumulating at the brain parenchyma, the released rolipram can inhibit the Lcn2 level, thereby reversing the astrocyte phenotype to alleviate neuroinflammation and promote BBB repair. This work provides a new strategy for treating ischemic stroke.

Hydroxysafflower yellow A alleviates the inflammatory response in astrocytes following cerebral ischemia by inhibiting the LCN2/STAT3 feedback loop

Lipocalin-2 (LCN2), an acute phase protein mainly expressed in astrocytes (Ast), is closely related to the production of inflammatory cytokines following ischemic stroke. During the pathophysiological process of ischemic stroke, the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway is activated. Despite evidence suggesting some link between the two, the relationship between the JAK2/STAT3 signaling pathway and the LCN2 expression in Ast following brain ischemia is incompletely understood. Hydroxysafflower yellow A (HSYA), an active ingredient found in Carthamus tinctorius L flowers, has been demonstrated to effectively mitigate cerebral ischemia via its anti-inflammatory effect. However, whether HSYA mitigates the neuroinflammatory damage after ischemic stroke by disrupting the interaction between the JAK2/STAT3 signaling pathway and LCN2 in Ast is unknown. Focusing on these two scientific questions, we established an in vivo middle cerebral artery occlusion/reperfusion (MCAO/R) rat model and in vitro primary astrocyte oxygen glucose deprivation/reperfusion (OGD/R) model. In vivo results showed that HSYA treatment alleviated nerve damage and inhibited the expression of LCN2 and inflammatory factors in Ast. In vitro results showed after OGD/R the expression of LCN2 and inflammatory cytokines increased and the JAK2/STAT3 was activated in Ast. Meanwhile, after OGD/R the JAK2/STAT3 activation in Ast increased LCN2 expression, and the inhibition of LCN2 expression by HSYA decreased the JAK2/STAT3 activation in Ast. These findings suggest that there is an interaction between the LCN2 and JAK2/STAT3 in Ast after ischemic stroke, which can enhance the inflammatory factors and exacerbate neuroinflammatory injury. Therefore, we conclude that HSYA may inhibit the LCN2/STAT3 loop in Ast, thereby mitigating neuroinflammation after cerebral ischemia.

Mechanism of LCN2 in cerebral ischemia-reperfusion injury

Cerebral ischemia-reperfusion injury (CIRI) is a complex pathophysiological process faced by brain tissues after ischemic stroke treatment, which involves mechanisms of inflammatory response, oxidative stress and apoptosis, and severely affects treatment outcome. Lipocalin-2 (LCN2), an acute-phase protein, is significantly up-regulated after CIRI and promotes neural repair by enhancing astrocyte phagocytosis, but its over-activation may also trigger secondary inflammation and demyelination injury. LCN2 also plays a key role in neuroinflammation regulation by regulating the polarization state of astrocytes and the release of inflammatory factors, and may affect the integrity of the blood-brain barrier and a variety of pathologic injury processes. In view of the important role of LCN2 in CIRI, this article reviews the mechanism of LCN2, aiming to provide new ideas and methods for the treatment of ischemic stroke.

Crosstalk between lipocalin-2 and IL-6 in traumatic brain injury: Closely related biomarkers

Clinical biomarkers are crucial for diagnosing and predicting outcomes in patients with traumatic brain injury (TBI). In this study, we performed an unbiased analysis of plasma proteins in acute TBI patients using bead-based multiplex assays and identified a strong positive correlation between LCN2 and IL-6 levels. Based on these findings, we hypothesized that LCN2 and IL-6 are closely related circulating biomarkers for TBI. Our previous and current studies demonstrate that the expression of LCN2, IL-6, and its receptors is upregulated in patients with chronic traumatic encephalopathy, in mouse models of traumatic and ischemic injury, and in an in vitro scratch injury model. Lcn2-deficiency reduced the injury-induced expression of IL-6 and its receptors in both animal and scratch injury models. These results suggest an augmented LCN2-dependent IL-6 signaling in the injured brain. As both LCN2 and IL-6 are secreted proinflammatory mediators, we further explored the possibility of cross-regulation between LCN2 and IL-6. In cultured glial cells, treatment with recombinant LCN2 protein enhanced the microglial expression of IL-6, while IL-6 protein treatment increased astrocytic LCN2 expression. Moreover, IL-6 expression and release were elevated in LCN2-overexpressing transgenic mice. Mechanistically, IL-6 enhanced astrocytic LCN2 expression through STAT3 signaling, while LCN2 upregulated microglial IL-6 expression through the NF-κB pathway. Taken together, our results suggest an important role of the LCN2-IL-6 axis in amplifying neuroinflammation through a positive feedback loop in secondary brain injury conditions. Finally, this study implies the utility of LCN2 and IL-6 as closely related biomarkers for TBI diagnosis and prognosis.

LCN2 induces neuronal loss and facilitates sepsis-associated cognitive impairments

Sepsis-associated encephalopathy (SAE) is a severe neurological syndrome marked by widespread brain dysfunctions due to sepsis. Despite increasing data supporting the hypothesis of neuronal damage, the exact mechanism of sepsis-related cognitive disorders and therapeutic strategies remain unclear and need further investigation. In this study, a sepsis model was established in C57 mice using lipopolysaccharide (LPS). The findings demonstrated that LPS exposure induced neuronal loss, synaptic and cognitive deficits accompanied by mitochondrial damage. Bioinformatics and western blot analyses demonstrated a significant increase in Lipocalin-2 (LCN2) during sepsis as a key hub gene involved in immune and neurological inflammation. Interestingly, the recombinant LCN2 protein exhibited similar effects on synaptic dysfunction and cognitive deficits in C57 mice. Conversely, downregulating LCN2 effectively nullified the impact of LPS, leading to the amelioration of synaptic and cognitive deficits, neuronal loss, and reactive oxygen species (ROS)-associated mitochondrial damage. These findings suggest a novel etiopathogenic mechanism of SAE, which is initiated by the increased LCN2, leading to neuronal loss and cognitive deficit. Inhibition of LCN2 could be therapeutically beneficial in treating sepsis-induced synaptic and cognitive impairments.

Ablation of lipocalin-2 reduces neuroinflammation in a mouse model of Krabbe disease

Lipocalin-2 (LCN2) is an acute-phase secretory molecule significantly upregulated in various neuroinflammatory and demyelinating conditions. Krabbe disease (KD) is a neurodegenerative lysosomal disorder caused by a galactosylceramidase (GALC) deficiency, accumulating cytotoxic psychosine in nervous systems, and subsequent neuroinflammation. Here, we show that LCN2 is highly overexpressed in GALC-deficient astrocytes. To further understand if the elevated LCN2 is critical for KD progression, we globally deleted Lcn2 in the Galc-knockout (KO) mouse model. Interestingly, the Galc and Lcn2 double KO mice showed dramatically reduced neuroinflammation including gliosis. Pro-inflammatory cytokines such as TNF-α, MMP3, and MCP-1 were significantly downregulated in the brain of the double KO mice compared to Galc-KO. In addition, the ablation of Lcn2 marginally increased the survival and attenuated disease progression in Galc-KO mice. However, the accumulation of psychosine was not altered in the brain by LCN2 deficiency. Our findings suggest that the upregulation of LCN2 is crucial for the aggravation of neuroinflammation in a mouse model of Krabbe disease.

Lipocalin-2 as a therapeutic target for diabetes neurological complications

INTRODUCTION

Diabetes mellitus, a chronic disorder with persistent hyperglycemia, severely affects the quality of life through significant neurological impairments, including neuropathy and cognitive dysfunction. Inflammation and oxidative stress are key factors in these complications, and Lipocalin-2 (LCN2), which is involved in inflammation and iron homeostasis, is crucial in these processes.

AREA COVERED

This review explores the potential of LCN2 as a therapeutic target for mitigating diabetes neurological complications. By examining the mechanisms by which LCN2 contributes to neuroinflammation, we discuss the therapeutic strategies that target LCN2 to alleviate diabetic neuropathy and cognitive dysfunction.

EXPERT OPINION

To fully grasp the impact of LCN2 on neurological health, it is essential to understand its multifaceted role in metabolic regulation. Because effective LCN2-targeting drugs must penetrate the blood - brain barrier, various strategies are being developed to meet this requirement. Such therapeutics could treat various neurological complications, including diabetic encephalopathy, retinopathy, and peripheral neuropathy. While animal models offer insights into pathophysiology and potential treatments, their limitations must be acknowledged. Therefore, future research should bridge the gaps between animal findings, human studies, and clinical applications. Moreover, comprehensive personalized approaches, including LCN2-targeting drugs, lifestyle changes, and regularly monitoring individual patients, may be required to manage diabetic complications.

Unveiling the role of astrogliosis in Alzheimer's disease Pathology: Insights into mechanisms and therapeutic approaches

Alzheimer's disease (AD) is one of the most debilitating age-related disorders that affect people globally. It impacts social and cognitive behavior of the individual and is characterized by phosphorylated tau and Aβ accumulation. Astrocytesmaintain a quiescent, anti-inflammatory state on anatomical level, expressing few cytokines and exhibit phagocytic activity to remove misfolded proteins. But in AD, in response to specific stimuli, astrocytes overstimulate their phagocytic character with overexpressing cytokine gene modules. Upon interaction with generated Aβ and neurofibrillary tangle, astrocytes that are continuously activated release a large number of inflammatory cytokines. This cytokine storm leads to neuroinflammation which is also one of the recognizable features of AD. Astrogliosis eventually promotes cholinergic dysfunction, calcium imbalance, oxidative stress and excitotoxicity. Furthermore, C5aR1, Lcn2/, BDNF/TrkB and PPARα/TFEB signaling dysregulation has a major impact on the disease progression. This review clarifies numerous ways that lead to astrogliosis, which is stimulated by a variety of processes that exacerbate AD pathology and make it a suitable target for AD treatment. Drugs under clinical and preclinical investigations that target several pathways managing astrogliosis and are efficacious in ameliorating the pathology of the disease are also included in this study. D-ALA2GIP, TRAM-34, Genistein, L-serine, MW150 and XPro1595 are examples of few drugs targeting astrogliosis. Therefore, this study may aid in the development of a potent therapeutic agent for ameliorating astrogliosis mediated AD progression.

Lipocalin-2 aggravates blood-brain barrier dysfunction after intravenous thrombolysis by promoting endothelial cell ferroptosis via regulating the HMGB1/Nrf2/HO-1 pathway

BACKGROUND

Disruption of the blood-brain barrier (BBB) is a major contributor to hemorrhagic transformation (HT) in patients with acute ischemic stroke (AIS) following intravenous thrombolysis (IVT). However, the clinical therapies aimed at BBB protection after IVT remain limited.

METHODS

One hundred patients with AIS who underwent IVT were enrolled (42 with HT and 58 without HT 24 h after IVT). Based on the cytokine chip, the serum levels of several AIS-related proteins, including LCN2, ferritin, matrix metalloproteinase-3, vascular endothelial-derived growth factor, and X-linked inhibitor of apoptosis, were detected upon admission, and their associations with HT were analyzed. After finding that LCN2 was related to HT in patients with IVT, we clarified whether the modulation of LCN2 influenced BBB dysfunction and HT after thrombolysis and investigated the potential mechanism.

RESULTS

In patients with AIS following IVT, logistic regression analysis showed that baseline serum LCN2 (p = 0.023) and ferritin (p = 0.046) levels were independently associated with HT. A positive correlation between serum LCN2 and ferritin levels was identified in patients with HT. In experimental studies, recombinant LCN2 (rLCN2) significantly aggravated BBB dysfunction and HT in the thromboembolic stroke rats after thrombolysis, whereas LCN2 inhibition by ZINC006440089 exerted opposite effects. Further mechanistic studies showed that, LCN2 promoted endothelial cell ferroptosis, accompanied by the induction of high mobility group box 1 (HMGB1) and the inhibition of nuclear translocation of nuclear factor E2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) proteins. Ferroptosis inhibitor ferrostatin-1 (fer-1) significantly restricted the LCN2-mediated BBB disruption. Transfection of LCN2 and HMGB1 siRNA inhibited the endothelial cell ferroptosis, and this effects was reversed by Nrf2 siRNA.

CONCLUSION

LCN2 aggravated BBB disruption after thrombolysis by promoting endothelial cell ferroptosis via regulating the HMGB1/Nrf2/HO-1 pathway, this may provide a promising therapeutic target for the prevention of HT after IVT.

Lipocalin-2 drives neuropsychiatric and cutaneous disease in MRL/lpr mice

Introduction

Approximately 20-40% of patients with systemic lupus erythematosus (SLE) experience neuropsychiatric SLE (NPSLE), which often manifests as cognitive dysfunction and depression. Currently, there are no approved treatments for NPSLE because its underlying mechanisms are unclear. Identifying relevant mediators and understanding their contribution to pathogenesis are crucial for developing targeted treatment options. Lipocalin 2 (LCN2) is a multifunctional acute-phase protein that plays important roles in immune cell differentiation, migration, and function. LCN2 has been implicated in models of neuroinflammatory disease.

Methods

We generated an LCN2-deficient MRL/lpr mouse to evaluate the effects of LCN2 on this classic NPSLE model. To evaluate the effects of LCN2 deficiency on behavior, the mice underwent a battery of behavioral tests evaluating depression, memory, and anxiety. Flow cytometry was used to quantify immune cell populations in the brain, blood, and secondary lymphoid organs. Cutaneous disease was quantified by scoring lesional skin, and skin infiltrates were quantified through immunofluorescent staining. Systemic disease was evaluated through measuring anti-nuclear antibodies by ELISA.

Results

In this study, we found that LCN2 deficiency significantly attenuates neuropsychiatric and cutaneous disease in MRL/lpr lupus prone mice, likely by decreasing local infiltration of immune cells into the brain and skin and reducing astrocyte activation in the hippocampus. Anti-nuclear antibodies and kidney disease were not affected by LCN2.

Discussion

As there was no effect on systemic disease, our results suggest that the inflammatory effects of LCN2 were localized to the skin and brain in this model. This study further establishes LCN2 as a potential target to ameliorate organ injury in SLE, including neuropsychiatric and cutaneous disease.

Spinal lipocalin 2 as a factor in the development of central post-stroke pain

Central poststroke pain (CPSP) is a type of central neuropathic pain whose mechanisms remain unknown. Recently, we showed that activated astrocytes and microglial cells are present in the spinal cord of CPSP model mice. Activated glial cells exacerbate cerebral ischemic pathology by increasing the expression of inflammatory factors. However, the involvement of spinal glial cells in CPSP remains unknown. We hypothesized that spinal glial cell-derived molecules cause hyperexcitability or promoted the development of CPSP. In this study, we identified glial cell-derived factors involved in the development of CPSP using a bilateral common carotid occlusion (BCAO)-induced CPSP mouse model. Male ddY mice were subjected to BCAO for 30 min. The von Frey test assessed mechanical hypersensitivity in the right hind paw of mice. BCAO mice showed hypersensitivity to mechanical stimuli and astrocyte activation in the spinal cord 3 days after treatment. DNA microarray analysis revealed a significant increase in lipocalin 2 (LCN2), is known as neutrophil gelatinase-associated lipocalin, in the superficial dorsal horns of BCAO-induced CPSP model mice. LCN2 colocalized with GFAP, an astrocyte marker. Spinal GFAP-positive cells in BCAO mice co-expressed signal transducer and activator of transcription 3 (STAT3). The increase in the fluorescence intensity of LCN2 and GFAP in BCAO mice was suppressed by intrathecal injection of AG490, an inhibitor of JAK2 and downstream STAT3 activation, or anti-LCN2 antibody. Our findings indicated that LCN2 in spinal astrocytes may be a key molecule and may be partly involved in the development of CPSP.

Astrocyte-secreted lipocalin-2 elicits bioenergetic failure-induced neuronal death that is causally related to high fatality in a mouse model of hepatic encephalopathy

Hepatic encephalopathy (HE) is a neurological complication arising from acute liver failure with poor prognosis and high mortality; the underlying cellular mechanisms are still wanting. We previously found that neuronal death caused by mitochondrial dysfunction in rostral ventrolateral medulla (RVLM), which leads to baroreflex dysregulation, is related to high fatality in an animal model of HE. Lipocalin-2 (Lcn2) is a secreted glycoprotein mainly released by astrocytes in the brain. We noted the presence of Lcn2 receptor (Lcn2R) in RVLM neurons and a parallel increase of Lcn2 gene in astrocytes purified from RVLM during experimental HE. Therefore, our guiding hypothesis is that Lcn2 secreted by reactive astrocytes in RVLM may underpin high fatality during HE by eliciting bioenergetic failure-induced neuronal death in this neural substrate. In this study, we first established the role of astrocyte-secreted Lcn2 in a liver toxin model of HE induced by azoxymethane (100 μg/g, ip) in C57BL/6 mice, followed by mechanistic studies in primary astrocyte and neuron cultures prepared from postnatal day 1 mouse pups. In animal study, immunoneutralization of Lcn2 reduced apoptotic cell death in RVLM, reversed defunct baroreflex-mediated vasomotor tone and prolonged survival during experimental HE. In our primary cell culture experiments, Lcn2 produced by cultured astrocytes and released into the astrocyte-conditioned medium significantly reduced cell viability of cultured neurons. Recombinant Lcn2 protein reduced cell viability, mitochondrial ATP (mitoATP) production, and pyruvate dehydrogenase (PDH) activity but enhanced the expression of pyruvate dehydrogenase kinase (PDK) 1, PDK3 and phospho-PDHA1 (inactive PDH) through MAPK/ERK pathway in cultured neurons, with all cellular actions reversed by Lcn2R knockdown. Our results suggest that astrocyte-secreted Lcn2 upregulates PDKs through MAPK/ERK pathway, which leads to reduced PDH activity and mitoATP production; the reinforced neuronal death in RVLM is causally related to baroreflex dysregulation that underlies high fatality associated with HE.

Lipocalin-2 as a mediator of neuroimmune communication

Lipocalin-2, a neutrophil gelatinase-associated lipocalin, is a 25-kDa secreted protein implicated in a broad range of inflammatory diseases affecting the brain and periphery. It is a pleotropic protein expressed by various immune and nonimmune cells throughout the body. Importantly, the surge in lipocalin-2 levels in disease states has been associated with a myriad of undesirable effects, further exacerbating the ongoing pathological processes. In the brain, glial cells are the principal source of lipocalin-2, which plays a definitive role in determining their functional phenotypes. In different central nervous system pathologies, an increased expression of glial lipocalin-2 has been linked to neurotoxicity. Lipocalin-2 mediates a crosstalk between central and peripheral immune cells under neuroinflammatory conditions. One intriguing aspect is that elevated lipocalin-2 levels in peripheral disorders, such as cancer, metabolic conditions, and liver diseases, potentially incite an inflammatory activation of glial cells while disrupting neuronal functions. This review comprehensively summarizes the influence of lipocalin-2 on the exacerbation of neuroinflammation by regulating various cellular processes. Additionally, this review explores lipocalin-2 as a mediator of neuroimmune crosstalk in various central nervous system pathologies and highlights the role of lipocalin-2 in carrying inflammatory signals along the neuroimmune axis.

Aquaporin-4 deletion leads to reduced infarct volume and increased peri-infarct astrocyte reactivity in a mouse model of cortical stroke

Aquaporin-4 (AQP4) is the main water channel in brain and is enriched in perivascular astrocyte processes abutting brain microvessels. There is a rich literature on the role of AQP4 in experimental stroke. While its role in oedema formation following middle cerebral artery occlusion (MCAO) has been studied extensively, its specific impact on infarct volume remains unclear. This study investigated the effects of total and partial AQP4 deletion on infarct volume in mice subjected to distal medial cerebral artery (dMCAO) occlusion. Compared to MCAO, this model induces smaller infarcts confined to neocortex, and less oedema. We show that AQP4 deletion significantly reduced infarct volume as assessed 1 week after dMCAO, suggesting that the role of AQP4 in stroke goes beyond its effect on oedema formation and dissolution. The reduction in infarct volume was associated with increased astrocyte reactivity in the peri-infarct areas. No significant differences were observed in the number of microglia among the genotypes. These findings provide new insights in the role of AQP4 in ischaemic injury indicating that AQP4 affects both infarct volume and astrocyte reactivity in the peri-infarct zone. KEY POINTS: Aquaporin-4 (AQP4) is the main water channel in brain and is enriched in perivascular astrocyte processes abutting microvessels. A rich literature exists on the role of AQP4 in oedema formation following middle cerebral artery occlusion (MCAO). We investigated the effects of total and partial AQP4 deletion on infarct volume in mice subjected to distal medial cerebral artery occlusion (dMCAO), a model inducing smaller infarcts confined to neocortex and less oedema compared to MCAO. AQP4 deletion significantly reduced infarct volume 1 week after dMCAO, suggesting a broader role for AQP4 in stroke beyond oedema formation. The reduction in infarct volume was associated with increased astrocyte reactivity in the peri-infarct areas, while no significant differences were observed in the number of microglia among the genotypes. These findings provide new insights into the role of AQP4 in stroke, indicating that AQP4 affects both infarct volume and astrocyte reactivity in the peri-infarct zone.

Aberrant activation of hippocampal astrocytes causes neuroinflammation and cognitive decline in mice

Reactive astrocytes are associated with neuroinflammation and cognitive decline in diverse neuropathologies; however, the underlying mechanisms are unclear. We used optogenetic and chemogenetic tools to identify the crucial roles of the hippocampal CA1 astrocytes in cognitive decline. Our results showed that repeated optogenetic stimulation of the hippocampal CA1 astrocytes induced cognitive impairment in mice and decreased synaptic long-term potentiation (LTP), which was accompanied by the appearance of inflammatory astrocytes. Mechanistic studies conducted using knockout animal models and hippocampal neuronal cultures showed that lipocalin-2 (LCN2), derived from reactive astrocytes, mediated neuroinflammation and induced cognitive impairment by decreasing the LTP through the reduction of neuronal NMDA receptors. Sustained chemogenetic stimulation of hippocampal astrocytes provided similar results. Conversely, these phenomena were attenuated by a metabolic inhibitor of astrocytes. Fiber photometry using GCaMP revealed a high level of hippocampal astrocyte activation in the neuroinflammation model. Our findings suggest that reactive astrocytes in the hippocampus are sufficient and required to induce cognitive decline through LCN2 release and synaptic modulation. This abnormal glial-neuron interaction may contribute to the pathogenesis of cognitive disturbances in neuroinflammation-associated brain conditions.

The interaction of lipocalin-2 and astrocytes in neuroinflammation: mechanisms and therapeutic application

Neuroinflammation is a common pathological process in various neurological disorders, including stroke, Alzheimer's disease, Parkinson's disease, and others. It involves the activation of glial cells, particularly astrocytes, and the release of inflammatory mediators. Lipocalin-2 (Lcn-2) is a secretory protein mainly secreted by activated astrocytes, which can affect neuroinflammation through various pathways. It can also act as a pro-inflammatory factor by modulating astrocyte activation and polarization through different signaling pathways, such as NF-κB, and JAK-STAT, amplifying the inflammatory response and aggravating neural injury. Consequently, Lcn-2 and astrocytes may be potential therapeutic targets for neuroinflammation and related diseases. This review summarizes the current knowledge on the role mechanisms, interactions, and therapeutic implications of Lcn-2 and astrocytes in neuroinflammation.

Knockdown of LCN2 Attenuates Brain Injury After Intracerebral Hemorrhage via Suppressing Pyroptosis

Objective

The aims of this study are to screen novel differentially expressed genes (DEGs) for intracerebral hemorrhage (ICH) and reveal the role of Lipocalin-2 (LCN2) in ICH.

Methods

We constructed the ICH model by injection of autologous whole blood into the right basal ganglia in rats. RNA-sequencing and bioinformatics analyses were performed to identify the DEGs between ICH and sham rats, and some important ones were confirmed using quantitative real-time PCR (qRT-PCR). LCN shRNA was used to knockdown of LCN2 in ICH rats. Pathological examination was carried out using 2,3,5-triphenyltetrazolium chloride (TTC) staining and Hematoxylin-eosin (HE) staining. Immunohistochemistry detected Caspase-3, and co-staining of Terminal dUTP nick end labeling (TUNEL) and NEUN staining were performed for neuron apoptosis assessment. Western blot analysis was performed to quantify pyroptosis-related proteins. Enzyme-linked immunosorbent assay (ELISA) was used to measure inflammatory cytokine levels.

Results

ICH rats exhibited significant hematomas, higher brain water content, obvious interstitial edema, and inflammatory infiltration, as well as more apoptotic cells in brain tissues. RNA-seq analysis identified 103 upregulated and 81 downregulated DEGs. The expression of LCN2, HSPB1, CXCL10, and MEF2B were upregulated in ICH rats. ICH triggered the release of interleukin (IL)-1β, tumor necrosis factor-α (TNF-α), and IL-18, and promoted the expression of pyroptosis-related proteins Caspase-1, GSDMD, NLRP3, and ASC. LCN2 knockdown attenuated the pathological characteristics of ICH, and also reduced pyroptosis in brain tissues.

Conclusion

Inhibition of LCN2 attenuates brain injury after ICH via suppressing pyroptosis, which provide guidance for ICH management.

Role of Lipocalin-2 in N1/N2 Neutrophil Polarization After Stroke

BACKGROUND

Neutrophils and Lipocalin-2 (LCN2) play pivotal roles in cerebral ischemiareperfusion (I/R) injury. However, their contribution is not fully clarified.

OBJECTIVE

This study aimed to explore the role of LCN2 and its association with neutrophil polarization in I/R injury.

METHODS

A mouse model of middle cerebral artery occlusion (MCAO) was used to induce cerebral ischemia. LCN2mAb was administered 1 h and Anti-Ly6G was administered for 3d before MCAO. The role of LCN2 in the polarity transition of neutrophils was explored using an in vitro HL-60 cell model.

RESULTS

LCN2mAb pretreatment had neuroprotective effects in mice. The expression of Ly6G was not significantly different, but the expression of N2 neutrophils was increased. In the in vitro study, LCN2mAb-treated N1-HL-60 cells induced N2-HL-60 polarization.

CONCLUSION

LCN2 may affect the prognosis of ischemic stroke by mediating neutrophil polarization.

Genome-wide meta-analysis of 92 cardiometabolic protein serum levels

OBJECTIVES

Global cardiometabolic disease prevalence has grown rapidly over the years, making it the leading cause of death worldwide. Proteins are crucial components in biological pathways dysregulated in disease states. Identifying genetic components that influence circulating protein levels may lead to the discovery of biomarkers for early stages of disease or offer opportunities as therapeutic targets.

METHODS

Here, we carry out a genome-wide association study (GWAS) utilising whole genome sequencing data in 3,005 individuals from the HELIC founder populations cohort, across 92 proteins of cardiometabolic relevance.

RESULTS

We report 322 protein quantitative trait loci (pQTL) signals across 92 proteins, of which 76 are located in or near the coding gene (cis-pQTL). We link those association signals with changes in protein expression and cardiometabolic disease risk using colocalisation and Mendelian randomisation (MR) analyses.

CONCLUSIONS

The majority of previously unknown signals we describe point to proteins or protein interactions involved in inflammation and immune response, providing genetic evidence for the contributing role of inflammation in cardiometabolic disease processes.

Molecular biomarkers for vascular cognitive impairment and dementia

As disease-specific interventions for dementia are being developed, the ability to identify the underlying pathology and dementia subtypes is increasingly important. Vascular cognitive impairment and dementia (VCID) is the second most common cause of dementia after Alzheimer disease, but progress in identifying molecular biomarkers for accurate diagnosis of VCID has been relatively limited. In this Review, we examine the roles of large and small vessel disease in VCID, considering the underlying pathophysiological processes that lead to vascular brain injury, including atherosclerosis, arteriolosclerosis, ischaemic injury, haemorrhage, hypoperfusion, endothelial dysfunction, blood-brain barrier breakdown, inflammation, oxidative stress, hypoxia, and neuronal and glial degeneration. We consider the key molecules in these processes, including proteins and peptides, metabolites, lipids and circulating RNA, and consider their potential as molecular biomarkers alone and in combination. We also discuss the challenges in translating the promise of these biomarkers into clinical application.

P2X7R influences tau aggregate burden in human tauopathies and shows distinct signalling in microglia and astrocytes

The purinoceptor P2X7R is a promising therapeutic target for tauopathies, including Alzheimer's disease (AD). Pharmacological inhibition or genetic knockdown of P2X7R ameliorates cognitive deficits and reduces pathological tau burden in mice that model aspects of tauopathy, including mice expressing mutant human frontotemporal dementia (FTD)-causing forms of tau. However, disagreements remain over which glial cell types express P2X7R and therefore the mechanism of action is unresolved. Here, we show that P2X7R protein levels increase in human AD post-mortem brain, in agreement with an upregulation of P2RX7 mRNA observed in transcriptome profiles from the AMP-AD consortium. P2X7R protein increases mirror advancing Braak stage and coincide with synapse loss. Using RNAScope we detect P2RX7 mRNA in microglia and astrocytes in human AD brain, including in the vicinity of senile plaques. In cultured microglia, P2X7R activation modulates the NLRP3 inflammasome pathway by promoting the formation of active complexes and release of IL-1β. In astrocytes, P2X7R activates NFκB signalling and increases production of the cytokines CCL2, CXCL1 and IL-6 together with the acute phase protein Lcn2. To further explore the role of P2X7R in a disease-relevant context, we expressed wild-type or FTD-causing mutant forms of tau in mouse organotypic brain slice cultures. Inhibition of P2X7R reduces insoluble tau levels without altering soluble tau phosphorylation or synaptic localisation, suggesting a non-cell autonomous role of glial P2X7R on pathological tau aggregation. These findings support further investigations into the cell-type specific effects of P2X7R-targeting therapies in tauopathies.

Astrocyte lipocalin-2 modestly effects disease severity in a mouse model of multiple sclerosis while reducing mature oligodendrocyte protein and mRNA expression

Roles for lipocalin-2 (LCN2, also referred to as neutrophil gelatinase associated lipocalin, NGAL) in the progression of disease in multiple sclerosis and its animal models have been reported; however, the importance of astrocyte-derived LCN2, a major source of LCN2, have not been defined. We found that clinical scores in experimental autoimmune encephalomyelitis (EAE) were modestly delayed in mice with conditional knockout of LCN2 from astrocytes, associated with a small decrease in astrocyte GFAP expression. Immunostaining and qPCR of spinal cord samples showed decreased oligodendrocyte proteolipid protein and transcription factor Olig2 expression, but no changes in PDGFRα expression. These results suggest astrocyte LCN2 contributes to early events in EAE and reduces damage to mature oligodendrocytes at later times.

Astrocytes in human central nervous system diseases: a frontier for new therapies

Astroglia are a broad class of neural parenchymal cells primarily dedicated to homoeostasis and defence of the central nervous system (CNS). Astroglia contribute to the pathophysiology of all neurological and neuropsychiatric disorders in ways that can be either beneficial or detrimental to disorder outcome. Pathophysiological changes in astroglia can be primary or secondary and can result in gain or loss of functions. Astroglia respond to external, non-cell autonomous signals associated with any form of CNS pathology by undergoing complex and variable changes in their structure, molecular expression, and function. In addition, internally driven, cell autonomous changes of astroglial innate properties can lead to CNS pathologies. Astroglial pathophysiology is complex, with different pathophysiological cell states and cell phenotypes that are context-specific and vary with disorder, disorder-stage, comorbidities, age, and sex. Here, we classify astroglial pathophysiology into (i) reactive astrogliosis, (ii) astroglial atrophy with loss of function, (iii) astroglial degeneration and death, and (iv) astrocytopathies characterised by aberrant forms that drive disease. We review astroglial pathophysiology across the spectrum of human CNS diseases and disorders, including neurotrauma, stroke, neuroinfection, autoimmune attack and epilepsy, as well as neurodevelopmental, neurodegenerative, metabolic and neuropsychiatric disorders. Characterising cellular and molecular mechanisms of astroglial pathophysiology represents a new frontier to identify novel therapeutic strategies.

A Proteomics Investigation of Salivary Profiles as Potential Biomarkers for Autism Spectrum Disorder (ASD)

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder that affects approximately 1/68 children, with a more recent study suggesting numbers as high as 1/36. According to Diagnostic and Statistical Manual of Mental Disorders, the etiology of ASD is unknown and diagnosis of this disorder is behavioral. There is currently no biomarker signature for ASD, however, identifying a biomarker signature is crucial as it would aid in diagnosis, identifying treatment targets, monitoring treatments, and identifying the etiology of the disorder. Here we used nanoliquid chromatography-tandem mass spectrometry (nanoLC-MS/MS) to investigate the saliva from individuals with ASD and matched controls in a 14 vs 14 study. We found numerous proteins to have statistically significant dysregulations, including lactotransferrin, transferrin, polymeric immunoglobulin receptor, Ig A L, Ig J chain, mucin 5 AC, and lipocalin 1 isoform X1. These findings are consistent with previous studies by our lab, and others, and point to dysregulations in the immune system, lipid metabolism and/or transport, and gastrointestinal disturbances, which are common and reoccurring topics in ASD research.

Lipocalin-2: a therapeutic target to overcome neurodegenerative diseases by regulating reactive astrogliosis

Glial cell activation precedes neuronal cell death during brain aging and the progression of neurodegenerative diseases. Under neuroinflammatory stress conditions, lipocalin-2 (LCN2), also known as neutrophil gelatinase-associated lipocalin or 24p3, is produced and secreted by activated microglia and reactive astrocytes. Lcn2 expression levels are known to be increased in various cells, including reactive astrocytes, through the activation of the NF-κB signaling pathway. In the central nervous system, as LCN2 exerts neurotoxicity when secreted from reactive astrocytes, many researchers have attempted to identify various strategies to inhibit LCN2 production, secretion, and function to minimize neuroinflammation and neuronal cell death. These strategies include regulation at the transcriptional, posttranscriptional, and posttranslational levels, as well as blocking its functions using neutralizing antibodies or antagonists of its receptor. The suppression of NF-κB signaling is a strategy to inhibit LCN2 production, but it may also affect other cellular activities, raising questions about its effectiveness and feasibility. Recently, LCN2 was found to be a target of the autophagy‒lysosome pathway. Therefore, autophagy activation may be a promising therapeutic strategy to reduce the levels of secreted LCN2 and overcome neurodegenerative diseases. In this review, we focused on research progress on astrocyte-derived LCN2 in the central nervous system.

Astrocytes of the optic nerve exhibit a region-specific and temporally distinct response to elevated intraocular pressure

BACKGROUND

The optic nerve is an important tissue in glaucoma and the unmyelinated nerve head region remains an important site of many early neurodegenerative changes. In both humans and mice, astrocytes constitute the major glial cell type in the region, and in glaucoma they become reactive, influencing the optic nerve head (ONH) microenvironment and disease outcome. Despite recognizing their importance in the progression of the disease, the reactive response of optic nerve head astrocytes remains poorly understood.

METHODS

To determine the global reactive response of ONH astrocytes in glaucoma we studied their transcriptional response to an elevation in IOP induced by the microbead occlusion model. To specifically isolate astrocyte mRNA in vivo from complex tissues, we used the ribotag method to genetically tag ribosomes in astrocytes, restricting analysis to astrocytes and enabling purification of astrocyte-associated mRNA throughout the entire cell, including the fine processes, for bulk RNA-sequencing. We also assessed the response of astrocytes in the more distal myelinated optic nerve proper (ONP) as glaucomatous changes manifest differently between the two regions.

RESULTS

Astrocytes of the optic nerve exhibited a region-specific and temporally distinct response. Surprisingly, ONH astrocytes showed very few early transcriptional changes and ONP astrocytes demonstrated substantially larger changes over the course of the experimental period. Energy metabolism, particularly oxidative phosphorylation and mitochondrial protein translation emerged as highly upregulated processes in both ONH and ONP astrocytes, with the former showing additional upregulation in antioxidative capacity and proteolysis. Interestingly, optic nerve astrocytes demonstrated a limited neuroinflammatory response, even when challenged with a more severe elevation in IOP. Lastly, there were a greater number of downregulated processes in both astrocyte populations compared to upregulated processes.

CONCLUSION

Our findings demonstrate an essential role for energy metabolism in the response of optic nerve astrocytes to elevated IOP, and contrary to expectations, neuroinflammation had a limited overall role. The transcriptional response profile is supportive of the notion that optic nerve astrocytes have a beneficial role in glaucoma. These previously uncharacterized transcriptional response of optic nerve astrocytes to injury reveal their functional diversity and a greater heterogeneity than previously appreciated.

Regulators of phagocytosis as pharmacologic targets for stroke treatment

Stroke, including ischemic and hemorrhagic stroke, causes massive cell death in the brain, which is followed by secondary inflammatory injury initiated by disease-associated molecular patterns released from dead cells. Phagocytosis, a cellular process of engulfment and digestion of dead cells, promotes the resolution of inflammation and repair following stroke. However, professional or non-professional phagocytes also phagocytose stressed but viable cells in the brain or excessively phagocytose myelin sheaths or prune synapses, consequently exacerbating brain injury and impairing repair following stroke. Phagocytosis includes the smell, eating and digestion phases. Notably, efficient phagocytosis critically depends on phagocyte capacity to take up dead cells continually due to the limited number of phagocytes vs. dead cells after injury. Moreover, phenotypic polarization of phagocytes occurring after phagocytosis is also essential to the proresolving and prorepair properties of phagocytosis. Much has been learned about the molecular signals and regulatory mechanisms governing the sense and recognition of dead cells by phagocytes during the smell and eating phase following stroke. However, some key areas remain extremely understudied, including the mechanisms involved in digestion regulation, continual phagocytosis and phagocytosis-induced phenotypic switching following stroke. Here, we summarize new discoveries related to the molecular mechanisms and multifaceted effects of phagocytosis on brain injury and repair following stroke and highlight the knowledge gaps in poststroke phagocytosis. We suggest that advancing the understanding of poststroke phagocytosis will help identify more biological targets for stroke treatment.

Lipocalin-2-mediated astrocyte pyroptosis promotes neuroinflammatory injury via NLRP3 inflammasome activation in cerebral ischemia/reperfusion injury

BACKGROUND

Neuroinflammation is a vital pathophysiological process during ischemic stroke. Activated astrocytes play a major role in inflammation. Lipocalin-2 (LCN2), secreted by activated astrocytes, promotes neuroinflammation. Pyroptosis is a pro-inflammatory form of programmed cell death that has emerged as a new area of research in stroke. Nevertheless, the potential role of LCN2 in astrocyte pyroptosis remains unclear.

METHODS

An ischemic stroke model was established by middle cerebral artery occlusion (MCAO) in vivo. In this study, in vitro, oxygen-glucose deprivation and reoxygenation (O/R) were applied to cultured astrocytes. 24p3R (the LCN2 receptor) was inhibited by astrocyte-specific adeno-associated virus (AAV-GFAP-24p3Ri). MCC950 and Nigericin sodium salt (Nig) were used to inhibit or promote the activation of NLRP3 inflammasome pharmacologically, respectively. Histological and biochemical analyses were performed to assess astrocyte and neuron death. Additionally, the neurological deficits of mice were evaluated.

RESULTS

LCN2 expression was significantly induced in astrocytes 24 h after stroke onset in the mouse MCAO model. Lcn2 knockout (Lcn2^-/-) mice exhibited reduced infarct volume and improved neurological and cognitive functions after MCAO. LCN2 and its receptor 24p3R were colocalized in astrocytes. Mechanistically, suppression of 24p3R by AAV-GFAP-24p3Ri alleviated pyroptosis-related pore formation and the secretion of pro-inflammatory cytokines via LCN2, which was then reversed by Nig-induced NLRP3 inflammasome activation. Astrocyte pyroptosis was exacerbated in Lcn2^-/- mice by intracerebroventricular administration of recombinant LCN2 (rLCN2), while this aggravation was restricted by blocking 24p3R or inhibiting NLRP3 inflammasome activation with MCC950.

CONCLUSION

LCN2/24p3R mediates astrocyte pyroptosis via NLRP3 inflammasome activation following cerebral ischemia/reperfusion injury.

Up-regulation of LCN2 in the anterior cingulate cortex contributes to neural injury-induced chronic pain

Chronic pain caused by disease or injury affects more than 30% of the general population. The molecular and cellular mechanisms underpinning the development of chronic pain remain unclear, resulting in scant effective treatments. Here, we combined electrophysiological recording, in vivo two-photon (2P) calcium imaging, fiber photometry, Western blotting, and chemogenetic methods to define a role for the secreted pro-inflammatory factor, Lipocalin-2 (LCN2), in chronic pain development in mice with spared nerve injury (SNI). We found that LCN2 expression was upregulated in the anterior cingulate cortex (ACC) at 14 days after SNI, resulting in hyperactivity of ACC glutamatergic neurons (ACC^Glu) and pain sensitization. By contrast, suppressing LCN2 protein levels in the ACC with viral constructs or exogenous application of neutralizing antibodies leads to significant attenuation of chronic pain by preventing ACC^Glu neuronal hyperactivity in SNI 2W mice. In addition, administering purified recombinant LCN2 protein in the ACC could induce pain sensitization by inducing ACC^Glu neuronal hyperactivity in naïve mice. This study provides a mechanism by which LCN2-mediated hyperactivity of ACC^Glu neurons contributes to pain sensitization, and reveals a new potential target for treating chronic pain.

Voluntary running exercise modifies astrocytic population and features in the peri-infarct cortex

Rehabilitative exercise following a brain stroke has beneficial effects on the morphological plasticity of neurons. Particularly, voluntary running exercise after focal cerebral ischemia promotes functional recovery and ameliorates ischemia-induced dendritic spine loss in the peri-infarct motor cortex layer 5. Moreover, neuronal morphology is affected by changes in the perineuronal environment. Glial cells, whose phenotypes may be altered by exercise, are known to play a pivotal role in the formation of this perineuronal environment. Herein, we investigated the effects of voluntary running exercise on glial cells after middle cerebral artery occlusion. Voluntary running exercise increased the population of glial fibrillary acidic protein-positive astrocytes born between post-operative days (POD) 0 and 3 on POD15 in the peri-infarct cortex. After exercise, transcriptomic analysis of post-ischemic astrocytes revealed 10 upregulated and 70 downregulated genes. Furthermore, gene ontology analysis showed that the 70 downregulated genes were significantly associated with neuronal morphology. In addition, exercise reduced the number of astrocytes expressing lipocalin 2, a regulator of dendritic spine density, on POD15. Our results suggest that exercise modifies the composition of astrocytic population and their phenotype.

Lipocalin-2 Deficiency Diminishes Canonical NLRP3 Inflammasome Formation and IL-1β Production in the Subacute Phase of Spinal Cord Injury

Spinal cord injury (SCI) results in the production of proinflammatory cytokines due to inflammasome activation. Lipocalin 2 (LCN2) is a small secretory glycoprotein upregulated by toll-like receptor (TLR) signaling in various cells and tissues. LCN2 secretion is induced by infection, injury, and metabolic disorders. In contrast, LCN2 has been implicated as an anti-inflammatory regulator. However, the role of LCN2 in inflammasome activation during SCI remains unknown. This study examined the role of Lcn2 deficiency in the NLRP3 inflammasome-dependent neuroinflammation in SCI. Lcn2^-/- and wild-type (WT) mice were subjected to SCI, and locomotor function, formation of the inflammasome complex, and neuroinflammation were assessed. Our findings demonstrated that significant activation of the HMGB1/PYCARD/caspase-1 inflammatory axis was accompanied by the overexpression of LCN2 7 days after SCI in WT mice. This signal transduction results in the cleaving of the pyroptosis-inducing protein gasdermin D (GSDMD) and the maturation of the proinflammatory cytokine IL-1β. Furthermore, Lcn2^-/- mice showed considerable downregulation in the HMGB1/NLRP3/PYCARD/caspase-1 axis, IL-1β production, pore formation, and improved locomotor function compared with WT. Our data suggest that LCN2 may play a role as a putative molecule for the induction of inflammasome-related neuroinflammation in SCI.

Circulating lipocalin-2 as a novel biomarker for early neurological deterioration and unfavorable prognosis after acute ischemic stroke

INTRODUCTION

Lipocalin-2 (LCN2) is an acute-phase protein that could mediate neuroinflammation after brain injury. We aimed to evaluate if LCN2 level was associated with early neurological deterioration (END) in acute ischemic stroke patients, thus hindering clinical recovery.

METHODS

We conducted a prospective study of acute ischemic stroke patients between June 2021 and February 2022. Serum LCN2 concentration was measured after admission using an enzyme-linked immunosorbent assay. Outcomes included END and 90-day poor functional outcome (modified Rankin Scale 3-6). The National Institutes of Health Stroke Scale increment ≥4 points within 72 h after admission was defined as END.

RESULTS

A total of 253 acute ischemic stroke patients (mean age, 65.2 ± 13.4 years; 64.0% male) were recruited. In the multivariate adjustment, increased serum LCN2 levels (per 1-SD increase of LCN2) were associated with a higher risk of END (odds ratio [OR], 1.64; 95% confidence interval [CI], 1.20-2.25; p = .002) and 90-day poor outcome (OR, 1.73; 95% CI, 1.22-2.45; p = .002). Restricted cubic splines found a linear relationship between LCN2 level and 90-day unfavorable outcome (END, p = .001 for linearity; 90-day poor outcome, p = .013 for linearity). Subgroup analysis further confirmed the significant association of LCN2 with clinical outcomes.

CONCLUSIONS

This study demonstrated that higher circulating LCN2 level was associated with an increased risk of early clinical worsening and 90-day unfavorable outcomes in ischemic stroke patients.

Exploratory Transcriptomic Profiling Reveals the Role of Gut Microbiota in Vascular Dementia

Stroke is the second most common cause of cognitive impairment and dementia. Vascular dementia (VaD), a cognitive impairment following a stroke, is common and significantly impacts the quality of life. We recently demonstrated via gut microbe transplant studies that the gut microbe-dependent trimethylamine-N-oxide (TMAO) pathway impacts stroke severity, both infarct size and long-term cognitive outcomes. However, the molecular mechanisms that underly the role of the microbiome in VaD have not been explored in depth. To address this issue, we performed a comprehensive RNA-sequencing analysis to identify differentially expressed (DE) genes in the ischemic cerebral cortex of mouse brains at pre-stroke and post-stroke day 1 and day 3. A total of 4016, 3752 and 7861 DE genes were identified at pre-stroke and post-stroke day 1 and day 3, respectively. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis indicated pathways of neurodegeneration in multiple diseases, chemokine signaling, calcium signaling, and IL-17 signaling as the key enriched pathways. Inflammatory response genes interleukin-1 beta (Il-1β), chemokines (C-X-C motif chemokine ligand 10 (Cxcl10), chemokine ligand 2 (Ccl2)), and immune system genes (S100 calcium binding protein 8 (S100a8), lipocalin-2 (Lcn2)) were among the most significantly upregulated genes. Hypocretin neuropeptide precursor (Hcrt), a neuropeptide, and transcription factors such as neuronal PAS domain protein 4 (Npas4), GATA binding protein 3 (Gata3), and paired box 7 (Pax7) were among the most significantly downregulated genes. In conclusion, our results indicate that higher plasma TMAO levels induce differential mRNA expression profiles in the ischemic brain tissue in our pre-clinical stroke model, and the predicted pathways provide the molecular basis for regulating the TMAO-enhanced neuroinflammatory response in the brain.

Role of lipocalin 2 in stroke

Stroke is the second leading cause of death worldwide; however, the treatment choices available to neurologists are limited in clinical practice. Lipocalin 2 (LCN2) is a secreted protein, belonging to the lipocalin superfamily, with multiple biological functions in mediating innate immune response, inflammatory response, iron-homeostasis, cell migration and differentiation, energy metabolism, and other processes in the body. LCN2 is expressed at low levels in the brain under normal physiological conditions, but its expression is significantly up-regulated in multiple acute stimulations and chronic pathologies. An up-regulation of LCN2 has been found in the blood/cerebrospinal fluid of patients with ischemic/hemorrhagic stroke, and could serve as a potential biomarker for the prediction of the severity of acute stroke. LCN2 activates reactive astrocytes and microglia, promotes neutrophil infiltration, amplifies post-stroke inflammation, promotes blood-brain barrier disruption, white matter injury, and neuronal death. Moreover, LCN2 is involved in brain injury induced by thrombin and erythrocyte lysates, as well as microvascular thrombosis after hemorrhage. In this paper, we review the role of LCN2 in the pathological processes of ischemic stroke; intracerebral hemorrhage; subarachnoid hemorrhage; and stroke-related brain diseases, such as vascular dementia and post-stroke depression, and their underlying mechanisms. We hope that this review will help elucidate the value of LCN2 as a therapeutic target in stroke.

Lipocalin-2 Is a Key Regulator of Neuroinflammation in Secondary Traumatic and Ischemic Brain Injury

Reactive glial cells are hallmarks of brain injury. However, whether these cells contribute to secondary inflammatory pathology and neurological deficits remains poorly understood. Lipocalin-2 (LCN2) has inflammatory and neurotoxic effects in various disease models; however, its pathogenic role in traumatic brain injury remains unknown. The aim of the present study was to investigate the expression of LCN2 and its role in neuroinflammation following brain injury. LCN2 expression was high in the mouse brain after controlled cortical impact (CCI) and photothrombotic stroke (PTS) injury. Brain levels of LCN2 mRNA and protein were also significantly higher in patients with chronic traumatic encephalopathy (CTE) than in normal subjects. RT-PCR and immunofluorescence analyses revealed that astrocytes were the major cellular source of LCN2 in the injured brain. Lcn2 deficiency or intracisternal injection of an LCN2 neutralizing antibody reduced CCI- and PTS-induced brain lesions, behavioral deficits, and neuroinflammation. Mechanistically, in cultured glial cells, recombinant LCN2 protein enhanced scratch injury-induced proinflammatory cytokine gene expression and inhibited Gdnf gene expression, whereas Lcn2 deficiency exerted opposite effects. Together, our results from CTE patients, rodent brain injury models, and cultured glial cells suggest that LCN2 mediates secondary damage response to traumatic and ischemic brain injury by promoting neuroinflammation and suppressing the expression of neurotropic factors.

Reciprocal interactions between innate immune cells and astrocytes facilitate neuroinflammation and brain metastasis via lipocalin-2

Brain metastasis still encompass very grim prognosis and therefore understanding the underlying mechanisms is an urgent need toward developing better therapeutic strategies. We uncover the intricate interactions between recruited innate immune cells and resident astrocytes in the brain metastatic niche that facilitate metastasis of melanoma and breast cancer. We show that granulocyte-derived lipocalin-2 (LCN2) induces inflammatory activation of astrocytes, leading to myeloid cell recruitment to the brain. LCN2 is central to inducing neuroinflammation as its genetic targeting or bone-marrow transplantation from LCN2^-/- mice was sufficient to attenuate neuroinflammation and inhibit brain metastasis. Moreover, high LCN2 levels in patient blood and brain metastases in multiple cancer types were strongly associated with disease progression and poor survival. Our findings uncover a previously unknown mechanism, establishing a central role for the reciprocal interactions between granulocytes and astrocytes in promoting brain metastasis and implicate LCN2 as a prognostic marker and potential therapeutic target.

Diagnosis of cerebral malaria: Tools to reduce Plasmodium falciparum associated mortality

Cerebral malaria (CM) is a major cause of mortality in Plasmodium falciparum (Pf) infection and is associated with the sequestration of parasitised erythrocytes in the microvasculature of the host's vital organs. Prompt diagnosis and treatment are key to a positive outcome in CM. However, current diagnostic tools remain inadequate to assess the degree of brain dysfunction associated with CM before the window for effective treatment closes. Several host and parasite factor-based biomarkers have been suggested as rapid diagnostic tools with potential for early CM diagnosis, however, no specific biomarker signature has been validated. Here, we provide an updated review on promising CM biomarker candidates and evaluate their applicability as point-of-care tools in malaria-endemic areas.

Specific Blood RNA Profiles in Individuals with Acute Spinal Cord Injury as Compared with Trauma Controls

Background

Spinal cord injury (SCI) is known to cause a more robust systemic inflammatory response than general trauma without CNS injury, inducing severe secondary organ damage, especially the lung and liver. Related studies are principally focused on the mechanisms underlying repair and regeneration in the injured spinal cord tissue. However, the specific mechanism of secondary injury after acute SCI is widely overlooked, compared with general trauma.

Methods

Two datasets of GSE151371 and GSE45376 related to the blood samples and spinal cord after acute SCI were selected to identify the differentially expressed genes (DEGs). In GSE151371, functional enrichment analysis on specific DEGs of blood samples was performed. And the top 15 specific hub genes were identified from intersectional genes between the specific upregulated DEGs of blood samples in GSE151371 and the upregulated DEGs of the spinal cord in GSE45376. The specific functional enrichment analysis and the drug candidates of the hub genes and the miRNAs-targeted hub genes were also analyzed and predicted.

Results

DEGs were identified, and a total of 64 specific genes were the intersection of upregulated genes of the spinal cord in GSE45376 and upregulated genes of human blood samples in GSE151371. The top 15 hub genes including HP, LCN2, DLGAP5, CEP55, HMMR, CDKN3, PRTN3, SKA3, MPO, LTF, CDC25C, MMP9, NEIL3, NUSAP1, and CD163 were calculated from the 64 specific genes. Functional enrichment analysis of the top 15 hub genes revealed inflammation-related pathways. The predicted miRNAs-targeted hub genes and drug candidates of hub genes were also performed to put forward reasonable treatment strategies.

Conclusion

The specific hub genes of acute SCI as compared with trauma without CNS injury were identified. The functional enrichment analysis of hub genes showed a specific immune response. Several predicted drugs of hub genes were also obtained. The hub genes and the predicted miRNAs may be potential biomarkers and therapeutic targets and require further validation.

Activated AMPK mitigates diabetes-related cognitive dysfunction by inhibiting hippocampal ferroptosis

Clinical and preclinical interest in Type 2 diabetes (T2D)-associated cognitive dysfunction (TDACD) has grown in recent years. However, the precise mechanisms underlying TDACD need to be further elucidated. Ferroptosis was reportedly involved in neurodegenerative diseases and diabetes-related organ injuries; however, its role in TDACD remains elusive. In this study, mice fed with a high-fat-diet combined with streptozotocin (HFD-STZ) were used as a T2D model to assess the role of ferroptosis in cognitive dysfunction. We found that ferroptosis was mainly activated in hippocampal neurons but not in microglia or astrocytes. Accordingly, increased levels of transferrin receptor and decreased levels of ferritin, GPX4, and SLC7A11 were observed in hippocampal neurons. In addition, pre-treatment with liproxstatin-1, a ferroptosis inhibitor, attenuated iron accumulation and oxidative stress response, which resulted in improved cognitive function in the HFD-STZ group. Furthermore, we found that p-AMP-activated protein kinase (AMPK) was decreased in the HFD-STZ group. Pre-treatment with AMPK agonist increased the expression of AMPK and GPX4, but decreased lipocalin 2 (LCN2) in the hippocampus that resulted in improved spatial learning ability in the HFD-STZ group. Taken together, we found that activation of neuronal ferroptosis in the hippocampus contributed to cognitive impairment of HFD-STZ mice. Furthermore, AMPK activation may reduce hippocampal ferroptosis, and consequently improve cognitive performance in diabetic mice.

Remodeling of astrocyte secretome in amyotrophic lateral sclerosis: uncovering novel targets to combat astrocyte-mediated toxicity

Amyotrophic lateral sclerosis (ALS) is an adult-onset paralytic disease characterized by progressive degeneration of upper and lower motor neurons in the motor cortex, brainstem and spinal cord. Motor neuron degeneration is typically caused by a combination of intrinsic neuronal (cell autonomous) defects as well as extrinsic (non-cell autonomous) factors such as astrocyte-mediated toxicity. Astrocytes are highly plastic cells that react to their microenvironment to mediate relevant responses. In neurodegeneration, astrocytes often turn reactive and in turn secrete a slew of factors to exert pro-inflammatory and neurotoxic effects. Various efforts have been carried out to characterize the diseased astrocyte secretome over the years, revealing that pro-inflammatory chemokines, cytokines and microRNAs are the main players in mediating neuronal death. As metabolomic technologies mature, these studies begin to shed light on neurotoxic metabolites such as secreted lipids. In this focused review, we will discuss changes in the astrocyte secretome during ALS. In particular, we will discuss the components of the reactive astrocyte secretome that contribute to neuronal death in ALS.

Lipocalin-2 participates in sepsis-induced myocardial injury by mediating lipid accumulation and mitochondrial dysfunction

BACKGROUND

Sepsis-induced cardiomyopathy (SIC) is one major cause of death for sepsis but lacks timely diagnosis and specific treatment due to unclear mechanisms. Lipocalin-2 (LCN-2) is a key regulator of lipid metabolism which has been recently proved closely related to sepsis, however, the relationship between LCN-2 and septic myocardial injury remains unknown. We aim to explore the role of LCN-2 in the pathological progress of SIC based on clinical and laboratory evidence.

METHODS

Consecutive patients admitted to the intensive care unit (ICU) from August 2021 to April 2022 fulfilling the criteria of severe sepsis were included. The level of LCN-2 in plasma was assayed and analyzed with clinical characteristics. Biostatistical analysis was performed for further identification and pathway enrichment. Mouse model for SIC was thereafter established, in which plasma and tissue LCN-2 levels were tested. RNA sequencing was used for verification and to reveal the possible mechanism. Mitochondrial function and intracellular lipid levels were assayed to further assess the biological effects of targeting LCN-2 in cardiomyocytes with small interference RNAs (siRNAs).

RESULTS

The level of LCN-2 in plasma was markedly higher in patients with severe sepsis and was associated with higher cardiac biomarkers and lower LVEF. In the in vivo experiment, circulating LCN-2 from plasma was found to increase in SIC mice. A higher level of LCN-2 transcription in myocardial tissue was also found in SIC and showed a clear time relationship. RNA sequencing analysis showed the level of LCN-2 was associated with several gene-sets relevant to mitochondrial function and lipid metabolism-associated pathways. The suppression of LCN-2 protected mitochondrial morphology and limited the production of ROS, as well as restored the mitochondrial membrane potential damaged by LPS. Neutral lipid staining showed prominent lipid accumulation in LPS group, which was alleviated by the treatment of siLCN2.

CONCLUSION

The level of LCN-2 is significantly increased in SIC at both circulating and tissue levels, which is correlated with the severity of myocardial injury indicators, and may work as an early and great predictor of SIC. LCN-2 probably participates in the process of septic myocardial injury through mediating lipid accumulation and affecting mitochondrial function.

Emerging role of neutrophil extracellular traps in the complications of diabetes mellitus

Immune dysfunction is widely regarded as one of the central tenants underpinning the pathophysiology of diabetes mellitus (DM) and its complications. When discussing immunity, the role of neutrophils must be accounted for: neutrophils are the most abundant of the circulating immune cells and are the first to be recruited to sites of inflammation, where they contribute to host defense via phagocytosis, degranulation, and extrusion of neutrophil extracellular traps (NETs). NETs are composed of DNA associated with nuclear and cytosolic neutrophil proteins. Although originally reported as an antimicrobial strategy to prevent microbial dissemination, a growing body of evidence has implicated NETs in the pathophysiology of various autoimmune and metabolic disorders. In these disorders, NETs propagate a pathologic inflammatory response with consequent tissue injury and thrombosis. Many diabetic complications—such as stroke, retinopathy, impaired wound healing, and coronary artery disease—involve these mechanisms. Therefore, in this review, we discuss laboratory and clinical data informing our understanding of the role of NETs in the development of these complications. NET markers, including myeloperoxidase, citrullinated histone H3, neutrophil elastase, and cell-free double-stranded DNA, can easily be measured in serum or be detected via immunohistochemical/immunocytochemical staining of tissue specimens. Therefore, NET constituents potentially constitute reliable biomarkers for use in the management of diabetic patients. However, no NET-targeting drug is currently approved for the treatment of diabetic complications; a candidate drug will require the outcomes of well-designed, robust clinical trials assessing whether NET inhibition can benefit patients in terms of morbidity, quality of life, health expenditures, and mortality. Therefore, much work remains to be done in translating these encouraging pieces of data into clinical trials for NET-targeting medications to be used in the clinic.

Lipocalin 2 attenuates oligodendrocyte loss and immune cell infiltration in mouse models for multiple sclerosis

Multiple sclerosis (MS) is a central nervous system disease characterized by both degenerative and inflammatory processes. Various mediators are involved in the interplay of degeneration and innate immunity on one hand and peripheral adaptive immunity on the other hand. The secreted protein lipocalin 2 (LCN2) is an inflammatory modulator in a variety of pathologies. Although elevated intrathecal levels of LCN2 have been reported in MS patients, it's functional role is widely unknown. Here, we identified a subpopulation of astrocytes as a source of LCN2 in MS lesions and respective animal models. We investigated the functional role of LCN2 for both autoimmune and degenerative aspects in three MS mouse models including both wild type (WT) and Lcn2^-/- mouse strains. While the experimental autoimmune encephalomyelitis (EAE) model reflects primary autoimmunity, the cuprizone model reflects selective oligodendrocyte loss and demyelination. In addition, we included a combinatory Cup/EAE model in which primary cytodegeneration is followed by inflammatory lesions within the forebrain. While in the EAE model, the disease outcome was comparable in between the two mouse strains, cuprizone intoxicated Lcn2^-/- animals showed an increased loss of oligodendrocytes. In the Cup/EAE model, Lcn2^-/- animals showed increased inflammation when compared to WT mice. Together, our results highlight LCN2 as a potentially protective molecule in MS lesion formation, which might be able to limit loss of oligodendrocytes immune-cell invasion. Despite these findings, it is not yet clear which glial cell phenotype (and to which extent) contributes to the observed neuroprotective effects, that is, microglia and/or astroglia or even endothelial cells in the brain.

Improvement of Depressed Mood with Green Tea Intake

Being in a prolonged depressed state increases the risk of developing depression. To investigate whether green tea intake is effective in improving depression-like moods, we used an experimental animal model of depression with lipopolysaccharide (LPS) and clarified the effects of green tea on the biological stress response and inflammation in the brain. Regarding the stress reduction effect of green tea, we found that the sum of caffeine (C) and epigallocatechin gallate (E) relative to the sum of theanine (T) and arginine (A), the major components of green tea, or the CE/TA ratio, is important. The results showed that depression-like behavior, adrenal hypertrophy as a typical stress response, and brain inflammation were suppressed in mice fed green tea components with CE/TA ratios of 2 to 8. In addition, the expression of Npas4, which is reduced in anxiety and depression, was maintained at the same level as controls in mice that consumed green tea with a CE/TA ratio of 4. In clinical human trials, the consumption of green tea with CE/TA ratios of 3.9 and 4.7 reduced susceptibility to subjective depression. These results suggest that the daily consumption of green tea with a CE/TA ratio of 4–5 is beneficial to improving depressed mood.

Lipocalin-2-Mediated Insufficient Oligodendrocyte Progenitor Cell Remyelination for White Matter Injury After Subarachnoid Hemorrhage via SCL22A17 Receptor/Early Growth Response Protein 1 Signaling

Insufficient remyelination due to impaired oligodendrocyte precursor cell (OPC) differentiation and maturation is strongly associated with irreversible white matter injury (WMI) and neurological deficits. We analyzed whole transcriptome expression to elucidate the potential role and underlying mechanism of action of lipocalin-2 (LCN2) in OPC differentiation and WMI and identified the receptor SCL22A17 and downstream transcription factor early growth response protein 1 (EGR1) as the key signals contributing to LCN2-mediated insufficient OPC remyelination. In LCN-knockdown and OPC EGR1 conditional-knockout mice, we discovered enhanced OPC differentiation in developing and injured white matter (WM); consistent with this, the specific inactivation of LCN2/SCl22A17/EGR1 signaling promoted remyelination and neurological recovery in both atypical, acute WMI due to subarachnoid hemorrhage and typical, chronic WMI due to multiple sclerosis. This potentially represents a novel strategy to enhance differentiation and remyelination in patients with white matter injury.

Coffee Polyphenol, Chlorogenic Acid, Suppresses Brain Aging and Its Effects Are Enhanced by Milk Fat Globule Membrane Components

Mice feed with coffee polyphenols (CPP, chlorogenic acid) and milk fat globule membrane (MFGM) has increased survival rates and helps retain long-term memory. In the cerebral cortex of aged mice, CPP intake decreased the expression of the proinflammatory cytokine TNF-α, and lysosomal enzyme cathepsin B. The suppression of inflammation in the brain during aging was thought to result in the suppression of the repressor element 1-silencing transcription factor (REST) and prevention of brain aging. In contrast, CPP increased the expression of REST, cAMP-responsive element binding (CREB) and transforming growth factor β1 (TGF-β1) in the young hippocampus. The increased expression of these factors may contribute to the induction of neuronal differentiation and the suppression of memory decline with aging. Taken together, these results suggest that CPP increases CREB in the young hippocampus and suppresses inflammation in the old brain, resulting in a preventive effect on brain aging. The endotoxin levels were not elevated in the serum of aged mice. Although the mechanism of action of MFGM has not yet been elucidated, the increase in survival rate with both CPP and MFGM intake suggests that adding milk to coffee may improve not only the taste, but also the function.

Aerobic Physical Exercise as a Non-medical Intervention for Brain Dysfunction: State of the Art and Beyond

Brain disorders, including stroke, Alzheimer's disease, depression, and chronic pain, are difficult to effectively treat. These major brain disorders have high incidence and mortality rates in the general population, and seriously affect not only the patient's quality of life, but also increases the burden of social medical care. Aerobic physical exercise is considered an effective adjuvant therapy for preventing and treating major brain disorders. Although the underlying regulatory mechanisms are still unknown, systemic processes may be involved. Here, this review aimed to reveal that aerobic physical exercise improved depression and several brain functions, including cognitive functions, and provided chronic pain relief. We concluded that aerobic physical exercise helps to maintain the regulatory mechanisms of brain homeostasis through anti-inflammatory mechanisms and enhanced synaptic plasticity and inhibition of hippocampal atrophy and neuronal apoptosis. In addition, we also discussed the cross-system mechanisms of aerobic exercise in regulating imbalances in brain function, such as the “bone-brain axis.” Furthermore, our findings provide a scientific basis for the clinical application of aerobic physical exercise in the fight against brain disorders.