Lipocalin 2 as a Putative Modulator of Local Inflammatory Processes in the Spinal Cord and Component of Organ Cross talk After Spinal Cord Injury

Astrocyte-derived lipocalin 2 promotes inflammation and scarring after spinal cord injury by activating SMAD in mice

BACKGROUND

The inflammatory response and scar formation after spinal cord injury (SCI) limit nerve regeneration and functional recovery. Our research group has previously shown that the expression of astrocyte-derived lipocalin 2 (Lcn2) is upregulated after SCI, which correlates with neuronal apoptosis and functional recovery. Therefore, we speculate that astrocyte-specific knockdown of Lcn2 after SCI may lead to a better prognosis.

METHODS

Tissue RNA sequencing, Western blotting, PCR, and immunofluorescence assays were conducted to assess the expression of Lcn2 following SCI in mice. Adeno-associated virus 9 (AAV9) transfection was employed to specifically reduce the expression of Lcn2 in astrocytes, and subsequent evaluations of scarring and inflammation were conducted. In vitro experiments involved treating primary astrocytes with TGF-β or an A1-induced mixture (C1q, TNF-α and IL-1α) following Lcn2 knockdown. Finally, the intrathecal injection of recombinant Lcn2 (ReLcn2) protein was conducted post-injury to further confirm the role of Lcn2 and its underlying mechanism in SCI.

RESULTS

Lcn2 expression was elevated in astrocytes after SCI at 7 dpi (days post injury). Lcn2 knockdown in astrocytes is beneficial for neuronal survival and functional recovery after SCI, and is accompanied by a reduced inflammatory response and inhibited scar formation. The inhibition of SMAD-associated signaling activation was identified as a possible mechanism, and in vitro experiments further confirmed this finding. ReLcn2 further activated SMAD-associated signaling and aggravated motor function after SCI.

CONCLUSION

The upregulation of Lcn2 expression in astrocytes is involved in neuroinflammation and scar formation after SCI, and the activation of SMAD-associated signaling is one of the underlying mechanisms.

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.

Associations between Microglia and Astrocytic Proteins and Tau Biomarkers across the Continuum of Alzheimer's Disease

Recent investigations implicate neuroinflammatory changes, including astrocyte and microglia activation, as crucial in the progression of Alzheimer's disease (AD) Thus, we compared selected proteins reflecting neuroinflammatory processes to establish their connection to AD pathologies. Our study, encompassing 80 subjects with (n = 42) AD, (n = 18) mild cognitive impairment (MCI) and (n = 20) non-demented controls compares the clinical potential of tested molecules. Using antibody-based methods, we assessed concentrations of NGAL, CXCL-11, sTREM1, and sTREM2 in cerebrospinal fluid (CSF). Proinflammatory proteins, NGAL, and CXCL-11 reached a peak in the early stage of the disease and allowed for the identification of patients with MCI. Furthermore, the concentration of the anti-inflammatory molecule sTREM2 was highest in the more advanced stage of the disease and permitted differentiation between AD and non-demented controls. Additionally, sTREM2 was biochemically linked to tau and pTau in the AD group. Notably, NGAL demonstrated superior diagnostic performance compared to classical AD biomarkers in discriminating MCI patients from controls. These findings suggest that proteins secreted mainly through microglia dysfunction might play not only a detrimental but also a protective role in the development of AD pathology.

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.

Unveiling the role of astrocytes in postoperative cognitive dysfunction

Alzheimer's disease (AD) is the most common neurodegenerative disorder, characterized by progressive cognitive decline and the accumulation of amyloid-beta plaques, tau tangles, and neuroinflammation in the brain. Postoperative cognitive dysfunction (POCD) is a prevalent and debilitating condition characterized by cognitive decline following neuroinflammation and oxidative stress induced by procedures. POCD and AD are two conditions that share similarities in the underlying mechanisms and pathophysiology. Compared to normal aging individuals, individuals with POCD are at a higher risk for developing AD. Emerging evidence suggests that astrocytes, the most abundant glial cells in the central nervous system, play a critical role in the pathogenesis of these conditions. Comprehensive functions of astrocyte in AD has been extensively explored, but very little is known about POCD may experience late-onset AD pathogenesis. Herein, in this context, we mainly explore the multifaceted roles of astrocytes in the context of POCD, highlighting their involvement in neuroinflammation, neurotransmitter regulation, synaptic plasticity and neurotrophic support, and discuss how POCD may augment the onset of AD. Additionally, we discuss potential therapeutic strategies targeting astrocytes to mitigate or prevent POCD, which hold promise for improving the quality of life for patients undergoing surgeries and against AD in the future.

Correlation between neutrophil gelatinase phase lipocalin and cerebral small vessel disease

Background

Cerebral small vessel disease (CSVD) is common in the elderly population. Neutrophil gelatinase-associated lipocalin (NGAL) is closely related to cardiovascular and cerebrovascular diseases. NGAL causes pathological changes, such as damage to the vascular endothelium, by causing inflammation, which results in other related diseases. The purpose of this study was to investigate whether serum NGAL levels could predict disease severity in patients with CSVD.

Methods

The patients with CSVD who visited the Department of Neurology at the First Affiliated Hospital of Zhengzhou University between January 2018 and June 2022 were prospectively included. The total CSVD burden score was calculated using whole-brain magnetic resonance imaging (MRI), and the patients were divided into a mild group (total CSVD burden score < 2 points) and a severe group (total CSVD burden score ≥ 2 points). Age, sex, height, smoking and alcohol consumption history, medical history, and serological results of patients were collected to perform the univariate analysis. Multivariate logistic regression was used to analyze the risk factors that affect CSVD severity. The multiple linear regression method was used to analyze which individual CSVD markers (periventricular white matter hyperintensities, deep white matter hyperintensities, lacune, and cerebral microbleed) play a role in the association between total CSVD burden score and NGAL.

Results

A total of 427 patients with CSVD (140 in the mild group and 287 in the severe group) were included in the study. A multivariate logistic regression analysis showed that the following factors were significantly associated with CSVD severity: male sex [odds ratio(OR), 1.912; 95% confidence interval (CI), 1.150-3.179], age (OR, 1.046; 95% CI, 1.022-1.070), history of cerebrovascular disease (OR, 3.050; 95% CI, 1.764-5.274), serum NGAL level (OR, 1.005; 95% CI, 1.002-1.008), and diabetes (OR, 2.593; 95% CI, 1.424-4.722). A multivariate linear regression shows that periventricular white matter hyperintensities and cerebral microbleed are associated with serum NGAL concentrations (P < 0.05).

Conclusion

Serum NGAL level is closely related to CSVD severity and is a risk factor for the burden of CSVD brain damage. Serum NGAL has high specificity in reflecting the severity of CSVD.

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.

Serum neutrophil gelatinase-associated lipocalin as a potential biomarker for cognitive decline in spinal cord injury

Objective

Neutrophil gelatinase-associated lipoprotein (NGAL), a protein encoded by the lipocalcin-2 (LCN2) gene, has been reported to be involved in multiple processes of innate immunity, but its relationship with spinal cord injury (SCI) remains unclear. This study set out to determine whether NGAL played a role in the development of cognitive impairment following SCI.

Methods

At the Neck-Shoulder and Lumbocrural Pain Hospital, a total of 100 SCI patients and 72 controls were enrolled in the study through recruitment. Through questionnaires, baseline data on the participants' age, gender, education level, lifestyle choices (drinking and smoking) and underlying illnesses (hypertension, diabetes, coronary heart disease, and hyperlipidemia) were gathered. The individuals' cognitive performance was evaluated using the Montreal Cognitive Scale (MoCA), and their serum NGAL levels were discovered using ELISA.

Results

The investigation included 72 controls and 100 SCI patients. The baseline data did not differ substantially between the two groups, however the SCI group's serum NGAL level was higher than the control group's (p < 0.05), and this elevated level was adversely connected with the MoCA score (p < 0.05). According to the results of the ROC analysis, NGAL had a sensitivity of 58.24% and a specificity of 86.72% for predicting cognitive impairment following SCI.

Conclusions

The changes in serum NGAL level could serve as a biomarker for cognitive impairment in SCI patients, and this holds true even after taking in account several confounding variables.

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 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.