Modulation of glial and neuronal migration by lipocalin-2 in zebrafish

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.

Crosstalk of Highly Purified Microglia and Astrocytes in the Frame of Toll-like Receptor (TLR)2/1 Activation

The major immune cells of the central nervous systems (CNS) are microglia and astrocytes, subsets of the glial cell population. The crosstalk between glia via soluble signaling molecules plays an indispensable role for neuropathologies, brain development as well as homeostasis. However, the investigation of the microglia-astrocyte crosstalk has been hampered due to the lack of suitable glial isolation methods. In this study, we investigated for the first time the crosstalk between highly purified Toll-like receptor (TLR)2-knock out (TLR2-KO) and wild-type (WT) microglia and astrocytes. We examined the crosstalk of TLR2-KO microglia and astrocytes in the presence of WT supernatants of the respective other glial cell type. Interestingly, we observed a significant TNF release by TLR2-KO astrocytes, which were activated with Pam3CSK4-stimulated WT microglial supernatants, strongly indicating a crosstalk between microglia and astrocytes after TLR2/1 activation. Furthermore, transcriptome analysis using RNA-seq revealed a wide range of significant up- and down-regulated genes such as Cd300, Tnfrsf9 or Lcn2, which might be involved in the molecular conversation between microglia and astrocytes. Finally, co-culturing microglia and astrocytes confirmed the prior results by demonstrating a significant TNF release by WT microglia co-cultured with TLR2-KO astrocytes. Our findings suggest a molecular TLR2/1-dependent conversation between highly pure activated microglia and astrocytes via signaling molecules. Furthermore, we demonstrate the first crosstalk experiments using ∼100% pure microglia and astrocyte mono-/co-cultures derived from mice with different genotypes highlighting the urgent need of efficient glial isolation protocols, which particularly holds true for astrocytes.

Neutrophils: a subgroup of neglected immune cells in ALS

Amyotrophic lateral sclerosis (ALS) is a chronic, progressive neurodegenerative disease characterized by the loss of motor neurons. Dysregulated peripheral immunity has been identified as a hallmark of ALS. Neutrophils, as the front-line responders of innate immunity, contribute to host defense through pathogen clearance. However, they can concurrently play a detrimental role in chronic inflammation. With the unveiling of novel functions of neutrophils in neurodegenerative diseases, it becomes essential to review our current understanding of neutrophils and to recognize the gap in our knowledge about their role in ALS. Thus, a detailed comprehension of the biological processes underlying neutrophil-induced pathogenesis in ALS may assist in identifying potential cell-based therapeutic strategies to delay disease progression.

Surface Plasmon Resonance Identifies High-Affinity Binding of l-DOPA to Siderocalin/Lipocalin-2 through Iron-Siderophore Action: Implications for Parkinson's Disease Treatment

l-3,4-Dihydroxyphenylalanine (l-DOPA), the dopamine precursor, remains the frontline treatment for Parkinson's disease (PD). With the treatment progress, l-DOPA efficacy decreases, necessitating higher and more frequent doses, with higher risks of dyskinesia. l-DOPA chelates iron through its catechol group, forming the l-DOPA:Fe complex; however, the fate of this complex is unknown. Catechol siderophore-like compounds are known to bind siderocalin (Scn)/lipocalin-2 to form stable siderophore:Fe:Scn complexes. Scn is upregulated in PD patients' substantia nigra and may play a role in PD pathophysiology. Therefore, in this study, we used the surface plasmon resonance (SPR) technique to examine the binding properties of l-DOPA to Scn. We found that l-DOPA formed a stable complex with Scn in the presence of Fe³⁺. Our analysis of the binding properties of l-DOPA precursors and metabolites indicates that the catechol group is necessary but not sufficient to form a stable complex with Scn. Finally, the affinity constant (K_d) of DOPA:Fe³⁺ binding with Scn (0.8 μM) was lower than l-DOPA plasma peak concentrations in l-DOPA preparations in the past six decades. Our results speculate a significant role for the l-DOPA-Scn complex in the decreased bioavailability of l-DOPA with the progress of PD.

In depth understanding of retinitis pigmentosa pathogenesis through optical coherence tomography angiography analysis: a narrative review

Retinitis pigmentosa (RP) is the most recognized inherited retinal disorder involving progressive photoreceptors degeneration which eventually causes blindness. However, the pathogenesis of RP is still unclear, making it difficult to establish satisfying treatments. Evidence have been found to support the theory that vascular dysfunction is associated with the progression of RP. Optical coherence tomography angiography (OCTA) is a newly developed technology that enables visualization as well as quantitative assessment of retinal and choroidal vasculature non-invasively. Advances in OCTA have opened a window for in-depth understanding of RP pathogenesis. Here, we propose a hypothesis of RP pathogenesis based on the current OCTA findings in RP, which includes four stages and two important key factors, vascular dysfunction and microglia activation. Further, we discuss the future animal experiments needed and how advanced OCTA technology can help to further verity the hypothesis. The final goal is to explore potential treatment options with enhanced understanding of RP pathogenesis.

A bacterial immunomodulatory protein with lipocalin-like domains facilitates host-bacteria mutualism in larval zebrafish

Stable mutualism between a host and its resident bacteria requires a moderated immune response to control bacterial population size without eliciting excessive inflammation that could harm both partners. Little is known about the specific molecular mechanisms utilized by bacterial mutualists to temper their hosts' responses and protect themselves from aggressive immune attack. Using a gnotobiotic larval zebrafish model, we identified an Aeromonas secreted immunomodulatory protein, AimA. AimA is required during colonization to prevent intestinal inflammation that simultaneously compromises both bacterial and host survival. Administration of exogenous AimA prevents excessive intestinal neutrophil accumulation and protects against septic shock in models of both bacterially and chemically induced intestinal inflammation. We determined the molecular structure of AimA, which revealed two related calycin-like domains with structural similarity to the mammalian immune modulatory protein, lipocalin-2. As a secreted bacterial protein required by both partners for optimal fitness, AimA is an exemplar bacterial mutualism factor.

Lipocalin-2 as an Infection-Related Biomarker to Predict Clinical Outcome in Ischemic Stroke

OBJECTIVES

From previous data in animal models of cerebral ischemia, lipocalin-2 (LCN2), a protein related to neutrophil function and cellular iron homeostasis, is supposed to have a value as a biomarker in ischemic stroke patients. Therefore, we examined LCN2 expression in the ischemic brain in an animal model and measured plasma levels of LCN2 in ischemic stroke patients.

METHODS

In the mouse model of transient middle cerebral artery occlusion (tMCAO), LCN2 expression in the brain was analyzed by immunohistochemistry and correlated to cellular nonheme iron deposition up to 42 days after tMCAO. In human stroke patients, plasma levels of LCN2 were determined one week after ischemic stroke. In addition to established predictive parameters such as age, National Institutes of Health Stroke Scale and thrombolytic therapy, LCN2 was included into linear logistic regression modeling to predict clinical outcome at 90 days after stroke.

RESULTS

Immunohistochemistry revealed expression of LCN2 in the mouse brain already at one day following tMCAO, and the amount of LCN2 subsequently increased with a maximum at 2 weeks after tMCAO. Accumulation of cellular nonheme iron was detectable one week post tMCAO and continued to increase. In ischemic stroke patients, higher plasma levels of LCN2 were associated with a worse clinical outcome at 90 days and with the occurrence of post-stroke infections.

CONCLUSIONS

LCN2 is expressed in the ischemic brain after temporary experimental ischemia and paralleled by the accumulation of cellular nonheme iron. Plasma levels of LCN2 measured in patients one week after ischemic stroke contribute to the prediction of clinical outcome at 90 days and reflect the systemic response to post-stroke infections.

IL-17 induces MIP-1α expression in primary mouse astrocytes via TRPC channel

Our previous study demonstrated IL-17-mediated induction of MIP-1α through its binding to the cognate IL-17RA and MIP-1α was involved in astrocyte activation. Transient receptor potential canonical (TRPC) channel was involved in astrocyte activation, however, whether TRPC channel regulates MIP-1α expression in the context of multiple sclerosis (MS) remains largely unknown. In this study we identify the essential role of TRPC channel in IL-17-mediated MIP-1α expression and astrocyte activation. Moreover, treatment of astrocytes with IL-17 activated MAPKs and PI3K/Akt signaling pathways with downstream NF-κB pathways. Interestingly, the TRPC blocker-SKF96365 (10 μM) and Norgestimate (10 μM) significantly inhibited the increased expression of MIP-1α via suppression of IL-17-mediated ERK, p38 and JNK MAPKs and PI3K/Akt pathway activation, thereby underscoring the role of TRPC channel in this process. Together these data underpin the role of TRPC channel as a novel target that regulates MIP-1α expression and cell activation-mediated by IL-17 with implications for therapeutic intervention for reversal of neuroinflammation inflicted by IL-17. Understanding the regulation of MIP-1α expression may provide insights into the development of potential therapeutic targets for neuroinflammation associated with MS.

Lipocalin-2 is increased in progressive multiple sclerosis and inhibits remyelination

Objective:

We aimed to examine the regulation of lipocalin-2 (LCN2) in multiple sclerosis (MS) and its potential functional relevance with regard to myelination and neurodegeneration.

Methods:

We determined LCN2 levels in 3 different studies: (1) in CSF and plasma from a case-control study comparing patients with MS (n = 147) with controls (n = 50) and patients with relapsing-remitting MS (n = 75) with patients with progressive MS (n = 72); (2) in CSF and brain tissue microdialysates from a case series of 7 patients with progressive MS; and (3) in CSF at baseline and 60 weeks after natalizumab treatment in a cohort study of 17 patients with progressive MS. Correlation to neurofilament light, a marker of neuroaxonal injury, was tested. The effect of LCN2 on myelination and neurodegeneration was studied in a rat in vitro neuroglial cell coculture model.

Results:

Intrathecal production of LCN2 was increased predominantly in patients with progressive MS (p < 0.005 vs relapsing-remitting MS) and displayed a positive correlation to neurofilament light (p = 0.005). Levels of LCN2 in brain microdialysates were severalfold higher than in the CSF, suggesting local production in progressive MS. Treatment with natalizumab in progressive MS reduced LCN2 levels an average of 13% (p < 0.0001). LCN2 was found to inhibit remyelination in a dose-dependent manner in vitro.

Conclusions:

LCN2 production is predominantly increased in progressive MS. Although this moderate increase does not support the use of LCN2 as a biomarker, the correlation to neurofilament light and the inhibitory effect on remyelination suggest that LCN2 might contribute to neurodegeneration through myelination-dependent pathways.

Role of high-mobility group box 1 in methamphetamine-induced activation and migration of astrocytes

Background

Mounting evidence has indicated that high-mobility group box 1 (HMGB1) is involved in cell activation and migration. Our previous study demonstrated that methamphetamine mediates activation of astrocytes via sigma-1 receptor (σ-1R). However, the elements downstream of σ-1R in this process remain poorly understood. Thus, we examined the molecular mechanisms involved in astrocyte activation and migration induced by methamphetamine.

Methods

The expression of HMGB1, σ-1R, and glial fibrillary acidic protein (GFAP) was examined by western blot and immunofluorescent staining. The phosphorylation of cell signaling pathways was detected by western blot, and cell migration was examined using a wound-healing assay in rat C6 astroglia-like cells transfected with lentivirus containing red fluorescent protein (LV-RFP) as well as in primary human astrocytes. The role of HMGB1 in astrocyte activation and migration was validated using a siRNA approach.

Results

Exposure of C6 cells to methamphetamine increased the expression of HMGB1 via the activation of σ-1R, Src, ERK mitogen-activated protein kinase, and downstream NF-κB p65 pathways. Moreover, methamphetamine treatment resulted in increased cell activation and migration in C6 cells and primary human astrocytes. Knockdown of HMGB1 in astrocytes transfected with HMGB1 siRNA attenuated the increased cell activation and migration induced by methamphetamine, thereby implicating the role of HMGB1 in the activation and migration of C6 cells and primary human astrocytes.

Conclusions

This study demonstrated that methamphetamine-mediated activation and migration of astrocytes involved HMGB1 up-regulation through an autocrine mechanism. Targeting HMGB1 could provide insights into the development of a potential therapeutic approach for alleviation of cell activation and migration of astrocytes induced by methamphetamine.

The role of neutrophil gelatinase associated lipocalin (NGAL) as biological constituent linking depression and cardiovascular disease

Depression is more common in patients with cardiovascular disease than in the general population. Conversely, depression is a risk factor for developing cardiovascular disease. Comorbidity of these two pathologies worsens prognosis. Several mechanisms have been indicated in the link between cardiovascular disease and depression, including inflammation. Systemic inflammation can have long-lasting effects on the central nervous system, which could be associated with depression. NGAL is an inflammatory marker and elevated plasma levels are associated with both cardiovascular disease and depression. While patients with depression show elevated NGAL levels, in patients with comorbid heart failure, NGAL levels are significantly higher and associated with depression scores. Systemic inflammation evokes NGAL expression in the brain. This is considered a proinflammatory effect as it is involved in microglia activation and reactive astrocytosis. Animal studies support a direct link between NGAL and depression/anxiety associated behavior. In this review we focus on the role of NGAL in linking depression and cardiovascular disease.

Tcf3 promotes cell migration and wound repair through regulation of lipocalin 2

Cell migration is an integral part of re-epithelialization during skin wound healing, a complex process involving molecular controls that are still largely unknown. Here we identify a novel role for Tcf3, an essential transcription factor regulating embryonic and adult skin stem cell functions, as a key effector of epidermal wound repair. We show that Tcf3 is upregulated in skin wounds and that Tcf3 overexpression accelerates keratinocyte migration and skin wound healing. We also identify Stat3 as an upstream regulator of Tcf3. We show that the pro-migration effects of Tcf3 are non-cell autonomous and occur independently of its ability to interact with β-catenin. Finally, we identify lipocalin-2 as the key secreted factor downstream of Tcf3 that promotes cell migration in vitro and wound healing in vivo. Our findings provide new insights into the molecular controls of wound-associated cell migration and identify potential therapeutic targets for the treatment of defective wound repair.

Proteome of brain glia: the molecular basis of diverse glial phenotypes

Several different types of nonneuronal glial cells with diverse phenotypes are present in the CNS, and all have distinct indispensible functions. Although glial cells primarily provide neurons with metabolic and structural support in the healthy brain, they may switch phenotype from a "resting" to a "reactive" state in response to pathological insults. Furthermore, this reactive gliosis is an invariant feature of the pathogeneses of CNS maladies. The glial proteome serves as a signature of glial phenotype, and not only executes physiological functions, but also acts as a molecular mediator of the reactive glial phenotype. The glial proteome is also involved in intra- and intercellular communications as exemplified by glia-glia and neuron-glia interactions. The utilization of authoritative proteomic tools and the bioinformatic analyses have helped to profile the brain glial proteome and explore the molecular mechanisms of diverse glial phenotypes. Furthermore, technologic innovations have equipped the field of "glioproteomics" with refined tools for studies of the expression, interaction, and function of glial proteins in the healthy and in the diseased CNS. Glioproteomics is expected to contribute to the elucidation of the molecular mechanisms of CNS pathophysiology and to the discovery of biomarkers and theragnostic targets in CNS disorders.