Lcn2-deficient Mice Research Articles

Lipocalin-2 Alleviates LPS-Induced Inflammation Through Alteration of Macrophage Properties.

PurposeLipocalin-2 (Lcn2) is an acute-phase protein and elevated in several inflammatory diseases. This study aimed to determine whether Lcn2 alleviates inflammation and explore the underlying cellular mechanisms.MethodsC57BL/6 Lcn2-deficient (Lcn2−/-) male mice were intraperitoneally injected with lipopolysaccharide (LPS) to build systemic inflammation model. The inflammatory processes were investigated. The morphology of villi was measured by scanning electron microscopy (SEM). The levels of inflammatory factors were detected by ELISA and qPCR analysis. The production of Lcn2 was determined with immunofluorescence staining by confocal microscope. The molecular mechanism of Lcn2 in bone marrow-derived macrophages (BMDMs) was analyzed by mass spectrometry (MS)-based quantitative proteomic analysis.ResultsCompared to wild-type (WT) mice injected with LPS, Lcn2−/- mice injected with LPS showed increased inflammatory damage in jejunum and ileum, and significantly elevated the levels of multiple pro-inflammatory cytokines. After determining that Lcn2 was mainly located in the cytoplasm of macrophages, we isolated BMDMs from Lcn2−/- mice to evaluate their function. During LPS challenge, transcripts of pro-inflammatory cytokines were all significantly increased in BMDMs from Lcn2−/- mice, while those of anti-inflammatory cytokines were significantly decreased when compared with the cytokines in BMDMs from WT mice. A label-free relative quantitation proteomics analysis showed that LPS-treated BMDMs from Lcn2−/- mice had elevated levels of pro-inflammatory pathways, but reduced phagocytosis and autophagy when compared with LPS-treated BMDMs from WT mice.ConclusionThese findings demonstrated that Lcn2 was a potent protective factor in response to systemic inflammation and might be an indispensable factor for macrophage functions.

Ultra-Early Cerebral Thrombosis Formation After Experimental Subarachnoid Hemorrhage Detected on T2* Magnetic Resonance Imaging.

The mechanisms of brain damage during ultra-early subarachnoid hemorrhage (SAH) have not been well studied. The current study examined the SAH-induced hyperacute brain damage at 4 hours using magnetic resonance imaging and brain histology in a mouse model. SAH was induced by endovascular perforation in adult mice. First, adult male wild-type mice underwent magnetic resonance imaging T2 and T2* 4 hours after an endovascular perforation or a sham operation and were euthanized to assess brain histology. Second, male and female adult lipocalin-2 knockout mice had SAH. All animals underwent magnetic resonance imaging at 4 hours, and the brains were harvested for brain histology. T2* hypointensity vessels were observed in the brain 4 hours after SAH in male wild-type mice. The numbers of T2*-positive vessels were significantly higher in SAH brains than in sham-operated mice. Brain histology showed thrombosis and erythrocyte plugs in the T2*-positive cerebral vessels which may be venules. The number of T2*-positive vessels correlated with SAH grade and the presence of T2 lesions. Brain thrombosis was also accompanied by albumin leakage and neuronal injury. LCN2 deficient male mice had lower numbers of T2*-positive vessels after SAH compared with wild-type male mice. SAH causes ultra-early brain vessel thrombosis that can be detected by T2* gradient-echo sequence at 4 hours after SAH. LCN2 deficiency decreased the number of T2*-positive vessels.

Lipocalin 2 deficiency-induced gut microbiota dysbiosis evokes metabolic syndrome in aged mice.

Lipocalin 2 (Lcn2) is a multifunctional innate immune protein that limits microbial overgrowth. Our previous study demonstrated that the gut microbiota directly induces intestinal Lcn2 production, and Lcn2-deficient (Lcn2-/-) mice exhibit gut dysbiosis. Coincidentally, gut dysbiosis is associated with metabolic syndrome pathogenesis, and elevated Lcn2 levels has been considered a potential clinical biomarker of metabolic syndrome. Yet whether Lcn2 mitigates or exacerbates metabolic syndrome remains inconclusive. Our objective was to determine whether Lcn2 deficiency-induced compositional changes in gut microbiota contribute to gain in adiposity in aged mice. Utilizing Lcn2-/- mice and their wild-type (WT) littermates, we measured metabolic markers, including fasting blood glucose, serum lipids, fat pad weight, and insulin resistance at ages 3, 6, and 9 mo old. Relative to WT mice, aged Lcn2-/- mice exhibited a gain in adiposity associated with numerous features of metabolic syndrome, including insulin resistance and dyslipidemia. Surprisingly, supplementation with a high-fat diet did not further aggravate metabolic syndrome that spontaneously occurs in Lcn2-/- mice by 6 mo of age. Interestingly, chow-fed Lcn2-/- mice displayed marked differences in the bacterial abundance and metabolomic profile of the gut microbiota compared with WT mice. Overall, our results demonstrate that Lcn2 is essential to maintain metabolic and gut microbiotal homeostasis, where deficiency induces spontaneous delayed onset of metabolic syndrome.

Lipocalin-2 mediates HIV-1 induced neuronal injury and behavioral deficits by overriding CCR5-dependent protection

People living with HIV (PLWH) continue to develop HIV-associated neurocognitive disorders despite combination anti-retroviral therapy. Lipocalin-2 (LCN2) is an acute phase protein that has been implicated in neurodegeneration and is upregulated in a transgenic mouse model of HIV-associated brain injury. Here we show that LCN2 is significantly upregulated in neocortex of a subset of HIV-infected individuals with brain pathology and correlates with viral load in CSF and pro-viral DNA in neocortex. However, the question if LCN2 contributes to HIV-associated neurotoxicity or is part of a protective host response required further investigation. We found that the knockout of LCN2 in transgenic mice expressing HIVgp120 in the brain (HIVgp120tg) abrogates behavioral impairment, ameliorates neuronal damage, and reduces microglial activation in association with an increase of the neuroprotective CCR5 ligand CCL4. In vitro experiments show that LCN2 neurotoxicity also depends on microglia and p38 MAPK activity. Genetic ablation of CCR5 in LCN2-deficient HIVgp120tg mice restores neuropathology, suggesting that LCN2 overrides neuroprotection mediated by CCR5 and its chemokine ligands. RNA expression of 168 genes involved in neurotransmission reveals that neuronal injury and protection are each associated with genotype- and sex-specific patterns affecting common neural gene networks. In conclusion, our study identifies LCN2 as a novel factor in HIV-associated brain injury involving CCR5, p38 MAPK and microglia. Furthermore, the mechanistic interaction between LCN2 and CCR5 may serve as a diagnostic and therapeutic target in HIV patients at risk of developing brain pathology and neurocognitive impairment.

13 Lipocalin 2 exerts protective activity by alleviating inflammatory responses

Abstract Lipocalin 2 (Lcn2) is an essential component of the innate immune system and exerts significant immunomodulatory effects in vitro. The aim of current study was to investigate the expression profile of Lcn2 during inflammatory process and explore the role of Lcn2 in the anti-inflammatory responses. Western blot, real-time quantitative PCR, immunofluorescence (IF) and enzyme-linked immunosorbent assay (ELISA) were employed. Firstly, we evaluated the temporospatial expression of Lcn2 of mice after inflammatory stimuli by lipopolysaccharides (LPS). In vivo, LPS induced both mRNA and protein levels of Lcn2 significantly (P < 0.01) in liver, jejunum and ileum. Lcn2 exhibited a continuous increase by 8 h and peaked by 24 h post challenges. Secondly, we challenged Lcn2-deficient (Lcn2-/-) mice and wild-type (WT) mice with peripheral LPS and determined effects on inflammation. In contrast to WT mice, Lcn2-/- mice showed distinct inflammatory injury in liver, jejunum, ileum and spleen with significantly elevated pro-inflammatory cytokines interleukin-6 (IL-6) and interleukin-1b (IL-1b) and decreased anti-inflammatory cytokine interleukin-10 (IL-10). Thirdly, we isolated bone marrow-derived macrophages (BMDM) from Lcn2-/- mice and WT mice to evaluate their functions. After LPS challenge, Lcn2-/- BMDM showed aggravated inflammatory reaction as pro-inflammatory factors tumour necrosis factor-α (TNF-α), IL-6, IL-1b and inducible nitric oxide synthase (iNOS) increased (P < 0.05) while anti-inflammatory cytokines IL-10, transforming growth factor β1 (TGF-β1) and arginase-1(Arg-1) decreased significantly (P < 0.05) compared with WT BMDM. This phenomenon could be relieved when adding recombinant Lcn2 (P < 0.05). The exogenous addition of Lcn2 on mice RAW264.7 macrophages stimulated by LPS also conformed this point. These findings demonstrated that Lcn2 served as a potent protective factor in response to systemic inflammation, and elevated Lcn2 expression during inflammatory conditions was presumed to play an effective role in alleviating inflammatory responses.

Lipocalin 2 Protects Against Escherichia coli Infection by Modulating Neutrophil and Macrophage Function.

Lipocalin 2 (Lcn2) is an essential component of the antimicrobial innate immune system. It attenuates bacterial growth by binding and sequestering the iron-scavenging siderophores to prevent bacterial iron acquisition. Whereas, the ability of Lcn2 to sequester iron is well-described, the role of Lcn2 in regulating immune cells during bacterial infection remains unclear. In this study, we showed that upon infection with Escherichia coli (O157:H7), Lcn2-deficient (Lcn2−/−) mice carried more bacteria in blood and liver, and the acute-phase sera lost their antibacterial activity in vitro. Neutrophils from Lcn2−/− mice were defective in homeostasis and morphological development. E. coli O157:H7 infection of Lcn2−/− mice resulted in a reduced neutrophil migration capacity, with 30% reduction of extravasated neutrophils, and impaired chemotaxis, as shown by a reduction in the secretion of chemoattractants, such as tumor necrosis factor (TNF)-α, monocyte chemoattractant protein (MCP)-1, and macrophage inflammatory protein (MIP)-2, which are instrumental in eliciting a neutrophil response. We also found that some secreted cytokines [interleukin (IL)-6, IL-1β, and TNF-α] were decreased. Transcripts of inflammatory cytokines (IL-6, IL-1β, TNF-α, and IL-10), chemokines (MIP-2 and MCP-1), and iNOS production were all strongly repressed in Lcn2−/− macrophages. Furthermore, Lcn2 could induce the production of chemokines and promote the migration and phagocytosis of macrophages. Thus, Lcn2 deficiency could impair the migration and chemotaxis ability of neutrophils and disturb the normal secretion of inflammatory cytokines of macrophages. Therefore, the heightened sensitivity of Lcn2−/− mice to E. coli O157:H7 is not only due to the antibacterial function of Lcn2 but also a consequence of impaired functions of immune cells, including neutrophils and macrophages.

Abstract P2021: Cutaneous Wound Healing in Diabetic Mice is Improved by Topical Mineralocorticoid Receptor Blockade

Introduction: Chronic skin ulcers resulting from impaired wound healing are a serious complication of diabetes. Unresolved inflammation, associated with the dysregulation of both the phenotype and function of macrophages, is involved in the poor healing of diabetic wounds. Objective: To investigate the role of the mineralocorticoid receptor in the healing delay and specifically in the impaired angiogenesis and prolonged inflammation of diabetic wounds. Methods: 6 mm wounds were created on the back skin of female streptozotocin (STZ)-induced or db/db mice. Wounds were treated topically with canrenoate (Canre: 0.5mM) or PBS twice a day, for 5 (STZ mice) or 7 (db/db mice) days. Wound area was measured at indicated time post-wounding. Wounded skin was collected for histology and molecular analysis. Results: topical pharmacological inhibition of the MR by Canre can resolve prolonged inflammation to improve delayed skin wound healing in diabetic mouse models. The improvement is demonstrated by increasing of 39% of neo-epidermisation and 62% of epidermal keratinocyte proliferation in db/db wounds treated by Canre. Moreover, Canre could improve the reduced blood vessel density in the wound beds of STZ mice (STZ + PBS: 5.33% ± 0.32 vs STZ + Canre: 8.26% ± 0.64) and of db/db mice (db/db + PBS: 1.32% ± 0.29 vs db/db + Canre: 3.31% ± 0.33). The beneficial effect of Canre is associated with an increased ratio of anti-inflammatory M2 macrophages to pro-inflammatory M1 macrophages in diabetic wounds (ratio of M2 to M1 in db/db + PBS vs db/db + Canre: 0.72 ± 0.15 vs 1.72 ± 0.29, respectively). Furthermore, we show that MR blockade leads to downregulated expression of a MR target, lipocalin 2 (Lcn2), which may facilitate macrophage polarization towards the M2 phenotype and promote impaired angiogenesis in diabetic wounds. Indeed, diabetic Lcn2-deficient mice showed improved wound healing, associated with macrophage M2 polarization and angiogenesis. In addition, recombinant Lcn2 protein prevented IL4-induced macrophages switch from M1 to M2 phenotype. Conclusion: topical MR blockade accelerates skin wound healing in diabetic mice via Lcn2 reduction, M2 macrophage polarization, prevention of prolonged inflammation, and induction of angiogenesis.

Cutaneous Wound Healing in Diabetic Mice Is Improved by Topical Mineralocorticoid Receptor Blockade

Skin ulcers resulting from impaired wound healing are a serious complication of diabetes. Unresolved inflammation, associated with the dysregulation of both the phenotype and function of macrophages, is involved in the poor healing of diabetic wounds. Here, we report that topical pharmacological inhibition of the mineralocorticoid receptor (MR) by canrenoate or MR small interfering RNA can resolve inflammation to improve delayed skin wound healing in diabetic mouse models; importantly, wounds from normal mice are unaffected. The beneficial effect of canrenoate is associated with an increased ratio of anti-inflammatory M2 macrophages to proinflammatory M1 macrophages in diabetic wounds. Furthermore, we show that MR blockade leads to downregulation of the MR target, LCN2, which may facilitate macrophage polarization toward the M2 phenotype and improve impaired angiogenesis in diabetic wounds. Indeed, diabetic LCN2-deficient mice showed improved wound healing associated with macrophage M2 polarization and angiogenesis. In addition, recombinant LCN2 protein prevented IL-4-induced macrophage switch from M1 to M2 phenotype. In conclusion, topical MR blockade accelerates skin wound healing in diabetic mice via LCN2 reduction, M2 macrophage polarization, prevention of inflammation, and induction of angiogenesis.

Adipose Lipocalin 2 overexpression protects against age-related decline in thermogenic function of adipose tissue and metabolic deterioration

ObjectivesAging increases the risk for development of adipose tissue dysfunction, insulin resistance, dyslipidemia, and liver steatosis. Lipocalin 2 (Lcn2) deficient mice are more prone to diet-induced obesity and metabolic dysfunction, indicating a protective role for Lcn2 in younger mice. In this study, we determined whether overexpressing Lcn2 in adipose tissue can protect against age-related metabolic deterioration. MethodsWe developed ap2-promoter-driven Lcn2 transgenic (Tg) mice and aged Lcn2 Tg mice for the metabolic assessments. ResultsWe found decreased adipocyte size in inguinal white adipose tissue (iWAT) from 10-month-old Lcn2 Tg mice relative to WT. This was accompanied by increased markers of adipogenesis in iWAT and attenuation of the age-related decline in AMP-activated protein kinase (AMPK) phosphorylation in adipose tissue depots. In addition to improvements in adipose tissue function, whole-body metabolic homeostasis was maintained in aged Lcn2 Tg mice. This included improved glucose tolerance and reduced serum triglycerides in older Lcn2 Tg mice relative to WT mice. Further, liver morphology and liver lipid levels were improved in older Lcn2 Tg mice, alongside a decrease in markers of liver inflammation and fibrosis. ConclusionsWe demonstrate that overexpression of Lcn2 in adipose tissue not only preserves adipose tissue function during aging but also promotes maintenance of glucose tolerance, decreases dyslipidemia, and prevents liver lipid accumulation and steatosis.

Neuropsychiatric lupus is lipocalin-2 dependent

Abstract Neuropsychiatric manifestations of systemic lupus erythematosus (NPSLE) affect approximately 40% of patients. Lipocalin-2 (LCN2), an acute-phase reactant protein, is an established urinary biomarker in lupus patients. Previous studies using LCN2-deficient mice have demonstrated its role in glial migration and chemokine regulation in the brain. We therefore hypothesized that LCN2 is involved in NPSLE pathogenesis. We investigated the lupus prone B6.Sle1.Sle3 (Sle1,3) mouse and the effects of LCN2 deficiency on the development of the neuropsychiatric phenotype exhibited by this strain. Sle1,3, B6.LCN2KO, B6, and Sle1,3-LCN2KO mice (6–10 month old; n=5–10/group) underwent comprehensive neurobehavioral assessment, and brains were evaluated by flow cytometry and RNA sequencing. Sle1,3 mice exhibited significant impairment in spatial (p<0.04) and recognition (p<0.02) memory when compared with B6 mice, and these deficits were attenuated in Sle1,3-LCN2KO mice (p<0.001, p<0.02). Furthermore, Sle1,3 mice demonstrated anhedonia, and this depression-like behavior was significantly reduced with LCN2 deficiency (p=0.01). Flow cytometry showed a significant increase in brain infiltrating CD8+ T cells in Sle1,3 mice, with a reduction in infiltration in the Sle1,3-LCN2KO strain (p=0.06). Preliminary analysis of RNA sequencing from sorted microglia revealed genes involved in cognition and memory that were differentially expressed in Sle1,3 mice were restored to background B6 expression levels in Sle1,3-LCN2KO mice. Our findings establish the Sle1,3 mouse as an NPSLE model and demonstrate that LCN2 deficiency attenuates neurobehavioral deficits and regulates microglial expression of genes essential to NPSLE development.

RNA Nanotherapeutics for the Amelioration of Astroglial Reactivity.

In response to injuries to the CNS, astrocytes enter a reactive state known as astrogliosis, which is believed to be deleterious in some contexts. Activated astrocytes overexpress intermediate filaments including glial fibrillary acidic protein (GFAP) and vimentin (Vim), resulting in entangled cells that inhibit neurite growth and functional recovery. Reactive astrocytes also secrete inflammatory molecules such as Lipocalin 2 (Lcn2), which perpetuate reactivity and adversely affect other cells of the CNS. Herein, we report proof-of-concept use of the packaging RNA (pRNA)-derived three-way junction (3WJ) motif as a platform for the delivery of siRNAs to downregulate such reactivity-associated genes. In vitro, siRNA-3WJs induced a significant knockdown of Gfap, Vim, and Lcn2 in a model of astroglial activation, with a concomitant reduction in protein expression. Knockdown of Lcn2 also led to reduced protein secretion from reactive astroglial cells, significantly impeding the perpetuation of inflammation in otherwise quiescent astrocytes. Intralesional injection of anti-Lcn2-3WJs in mice with contusion spinal cord injury led to knockdown of Lcn2 at mRNA and protein levels in vivo. Our results provide evidence for siRNA-3WJs as a promising platform for ameliorating astroglial reactivity, with significant potential for further functionalization and adaptation for therapeutic applications in the CNS.

Astrocyte-derived lipocalin-2 mediates hippocampal damage and cognitive deficits in experimental models of vascular dementia.

Lipocalin-2 (LCN2) has diverse functions in multiple pathophysiological conditions; however, its pathogenic role in vascular dementia (VaD) is unknown. Here, we investigated the role of LCN2 in VaD using rodent models of global cerebral ischemia and hypoperfusion with cognitive impairment and neuroinflammation. Mice subjected to transient bilateral common carotid artery occlusion (tBCCAo) for 50 min showed neuronal death and gliosis in the hippocampus at 7 days post-tBCCAo. LCN2 expression was observed predominantly in the hippocampal astrocytes, whereas its receptor was mainly detected in neurons, microglia, and astrocytes. Furthermore, Lcn2-deficient mice, compared with wild-type animals, showed significantly weaker CA1 neuronal loss, cognitive decline, white matter damage, blood-brain barrier permeability, glial activation, and proinflammatory cytokine production in the hippocampus after tBCCAo. Lcn2 deficiency also attenuated hippocampal neuronal death and cognitive decline at 30 days after unilateral common carotid artery occlusion (UCCAo). Furthermore, intracerebroventricular (i.c.v) injection of recombinant LCN2 protein elicited CA1-neuronal death and a cognitive deficit. Our studies using cultured glia and hippocampal neurons supported the decisive role of LCN2 in hippocampal neurotoxicity and microglial activation, and the role of the HIF-1α-LCN2-VEGFA axis of astrocytes in vascular injury. Additionally, plasma levels of LCN2 were significantly higher in patients with VaD than in the healthy control subjects. These results indicate that hippocampal damage and cognitive impairment are mediated by LCN2 secreted from reactive astrocytes in VaD.

Lipocalin2, an innate immune protein, modulates iNOS and arginase-1 in macrophages to promote the anti-inflammatory function

Abstract Lipocalin 2 (Lcn2), an innate immune protein, is known to be dramatically up regulated in various inflammatory disorders including autoimmune arthritis, yet its biological role remains unclear. Recently our studies have shown an increase in the accumulation of macrophages in Lcn2 deficient mice compared to wild type (WT) mice in a serum transfer arthritic mouse model. Thus, indicating that the upregulation of Lcn2 might be necessary for the initiation and further resolution of inflammatory processes. In this study, we have investigated the anti-inflammatory function of Lcn2 using murine mouse macrophages. RAW 264.7 cells treated with INFγ and LPS both exhibited pro-inflammatory phenotype, M1, while cells treated with IL-4 displayed an anti-inflammatory phenotype, M2. To determine the anti-inflammatory effects of Lcn2 an IL-10 ELISA revealed that M2 macrophages in the presence of recombinant Lcn2 (rLcn2) significantly increased the expression of IL-10. In addition, arginase-1 expression was found to be significantly upregulated in M2 polarized macrophages in the presence of rLcn2 while inducible nitric oxide synthase (iNOS) expression was down-regulated in the M1 phenotype. However, RAW 264.7 cells treated with Lcn2 alone did not exert either pro- or anti-inflammatory effect. In conclusion, Lcn2 displays the ability to significantly increase the release of anti-inflammatory cytokine, IL-10, thus promoting the anti-inflammatory properties of M2 macrophages. Collectively, our data suggests a crucial role of Lcn2 in the resolution of arthritic inflammation via macrophage polarization, making it a promising target in designing better therapeutic strategies to control the ongoing inflammation during autoimmune arthritis.

Altered mitochondrial and peroxisomal integrity in lipocalin-2-deficient mice with hepatic steatosis

Lipocalin-2 (LCN2) is a secreted adipokine that transports small hydrophobic molecules such as fatty acids and steroids. LCN2 limits bacterial growth by sequestering iron-containing siderophores and in mammalian liver protects against inflammation, infection, injury and other stressors. Because LCN2 modulates hepatic fat metabolism and homeostasis, we performed a comparative profiling of proteins and lipids of wild type (WT) and Lcn2-deficient mice fed either standard chow or a methionine- and choline-deficient (MCD) diet. Label-free proteomics and 2D-DIGE protein expression profiling revealed differential expression of BRIT1/MCPH1, FABP5, HMGB1, HBB2, and L-FABP, results confirmed by Western blotting. Gene ontology enrichment analysis identified enrichment for genes associated with mitochondrial membrane permeabilization and metabolic processes involving carboxylic acid. Measurements of mitochondrial membrane potential, mitochondrial chelatable iron pool, intracellular lipid peroxidation, and peroxisome numbers in primary hepatocytes confirmed that LCN2 regulates mitochondrial and peroxisomal integrity. Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight (MALDI-TOF) mass spectrometry imaging identified significant changes to sphingomyelins, triglycerides, and glycerophospholipids in livers of mice fed an MCD diet regardless of LCN2 status. However, two arachidonic acid-containing glycerophospholipids were increased in Lcn2-deficient livers. Thus, LCN2 influences peroxisomal and mitochondrial biology in the liver to maintain triglyceride balance, handle oxidative stress, and control apoptosis.

Lipocalin-2 deficiency or blockade protects against aortic abdominal aneurysm development in mice.

To study the role of lipocalin-2 (Lcn2) and the effect of Lcn2 blockade via anti-Lcn2 antibody in the development of abdominal aortic aneurysm (AAA). Expression mRNA and protein levels of Lcn2 and its human orthologue neutrophil gelatinase-associated lipocalin (NGAL) in aortic wall samples from experimental mouse and human AAA samples, respectively, were analysed by real-time PCR and immunohistochemistry. Experimental AAA was induced by aortic elastase perfusion in wild-type mice (WT) and Lcn2-deficient mice (Lcn2-/-). NGAL/Lcn2 mRNA and protein levels in human and murine AAA samples were increased compared with healthy aortas. Decreased AAA incidence and reduced aortic expansion were observed in Lcn2-/- mice or mice preoperative treated with a polyclonal anti-Lcn2 antibody compared with WT mice or mice treated with control IgG, respectively, at Day 14 after elastase perfusion. Moreover, immunohistochemical analysis of AAA tissues from Lcn2-/- or anti-Lcn2-treated mice showed diminished elastin damage, reduced microvessels and polymorphonuclear neutrophil (PMN) infiltration, and enhanced preservation of vascular smooth muscle cells compared with WT aortas. Fluorescent molecular tomography revealed decreased MMP activity in AAA of Lcn2-/- mice compared with WT controls. Therapeutic administration of anti-Lcn2 antibody to WT mice 3 days after elastase perfusion decreased aortic dilatation and PMN infiltration compared with WT mice treated with control IgG. Either Lcn2 deficiency or anti-Lcn2 antibody blockade limits AAA expansion in mice by decreasing PMN infiltration in the aorta. Lcn2 modulation may therefore be a viable new therapeutic option for the treatment of AAA.

Pathogenic Upregulation of Glial Lipocalin-2 in the Parkinsonian Dopaminergic System

Lipocalin-2 (LCN2) is a member of the highly heterogeneous secretory protein family of lipocalins and increases in its levels can contribute to neurodegeneration in the adult brain. However, there are no reports on the role of LCN2 in Parkinson's disease (PD). Here, we report for the first time that LCN2 expression is increased in the substantia nigra (SN) of patients with PD. In mouse brains, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment for a neurotoxin model of PD significantly upregulated LCN2 expression, mainly in reactive astrocytes in both the SN and striatum. The increased LCN2 levels contributed to neurotoxicity and neuroinflammation, resulting in disruption of the nigrostriatal dopaminergic (DA) projection and abnormal locomotor behaviors, which were ameliorated in LCN2-deficient mice. Similar to the effects of MPTP treatment, LCN2-induced neurotoxicity was also observed in the 6-hydroxydopamine (6-OHDA)-treated animal model of PD. Moreover, treatment with the iron donor ferric citrate (FC) and the iron chelator deferoxamine mesylate (DFO) increased and decreased, respectively, the LCN2-induced neurotoxicity in vivo In addition to the in vivo results, 1-methyl-4-phenylpyridinium (MPP(+))-induced neurotoxicity in cocultures of mesencephalic neurons and astrocytes was reduced by LCN2 gene deficiency in the astrocytes and conditioned media derived from MPP(+)-treated SH-SY5Y neuronal enhanced glial expression of LCN2 in vitro Therefore, our results demonstrate that astrocytic LCN2 upregulation in the lesioned DA system may play a role as a potential pathogenic factor in PD and suggest that inhibition of LCN2 expression or activity may be useful in protecting the nigrostriatal DA system in the adult brain. Lipocalin-2 (LCN2), a member of the highly heterogeneous secretory protein family of lipocalins, may contribute to neuroinflammation and neurotoxicity in the brain. However, LCN2 expression and its role in Parkinson's disease (PD) are largely unknown. Here, we report that LCN2 is upregulated in the substantia nigra of patients with PD and neurotoxin-treated animal models of PD. Our results suggest that LCN2 upregulation might be a potential pathogenic mechanism of PD, which would result in disruption of the nigrostriatal dopaminergic system through neurotoxic iron accumulation and neuroinflammation. Therefore, inhibition of LCN2 expression or activity may be useful in protecting the nigrostriatal dopaminergic projection in PD.

Tumour stroma-derived lipocalin-2 promotes breast cancer metastasis.

Tumour cell-secreted factors skew infiltrating immune cells towards a tumour-supporting phenotype, expressing pro-tumourigenic mediators. However, the influence of lipocalin-2 (Lcn2) on the metastatic cascade in the tumour micro-environment is still not clearly defined. Here, we explored the role of stroma-derived, especially macrophage-released, Lcn2 in breast cancer progression. Knockdown studies and neutralizing antibody approaches showed that Lcn2 contributes to the early events of metastasis in vitro. The release of Lcn2 from macrophages induced an epithelial-mesenchymal transition programme in MCF-7 breast cancer cells and enhanced local migration as well as invasion into the extracellular matrix, using a three-dimensioanl (3D) spheroid model. Moreover, a global Lcn2 deficiency attenuated breast cancer metastasis in both the MMTV-PyMT breast cancer model and a xenograft model inoculating MCF-7 cells pretreated with supernatants from wild-type and Lcn2-knockdown macrophages. To dissect the role of stroma-derived Lcn2, we employed an orthotopic mammary tumour mouse model. Implantation of wild-type PyMT tumour cells into Lcn2-deficient mice left primary mammary tumour formation unaltered, but specifically reduced tumour cell dissemination into the lung. We conclude that stroma-secreted Lcn2 promotes metastasis in vitro and in vivo, thereby contributing to tumour progression. Our study highlights the tumourigenic potential of stroma-released Lcn2 and suggests Lcn2 as a putative therapeutic target. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Role of lipocalin 2 in intraventricular haemoglobin-induced brain injury

ObjectiveOur recent studies have shown that blood components, including haemoglobin and iron, contribute to hydrocephalus development and brain injury after intraventricular haemorrhage (IVH). The current study investigated the role of...

Therapeutic Role of Interleukin 22 in Experimental Intra-abdominal Klebsiella pneumoniae Infection in Mice

Interleukin 22 (IL-22) is an IL-10-related cytokine produced by T helper 17 (Th17) cells and other immune cells that signals via IL-22 receptor alpha 1 (IL-22Ra1), which is expressed on epithelial tissues, as well as hepatocytes. IL-22 has been shown to have hepatoprotective effects that are mediated by signal transducer and activator of transcription 3 (STAT3) signaling. However, it is unclear whether IL-22 can directly regulate antimicrobial programs in the liver. To test this hypothesis, hepatocyte-specific IL-22Ra1 knockout (Il22Ra1(Hep-/-)) and Stat3 knockout (Stat3(Hep-/-)) mice were generated and subjected to intra-abdominal infection with Klebsiella pneumoniae, which results in liver injury and necrosis. We found that overexpression of IL-22 or therapeutic administration of recombinant IL-22 (rIL-22), given 2 h postinfection, significantly reduced the bacterial burden in both the liver and spleen. The antimicrobial activity of rIL-22 required hepatic Il22Ra1 and Stat3. Serum from rIL-22-treated mice showed potent bacteriostatic activity against K. pneumoniae, which was dependent on lipocalin 2 (LCN2). However, in vivo, rIL-22-induced antimicrobial activity was only partially reduced in LCN2-deficient mice. We found that rIL-22 also induced serum amyloid A2 (SAA2) and that SAA2 had anti-K. pneumoniae bactericidal activity in vitro. These results demonstrate that IL-22, through IL-22Ra1 and STAT3 singling, can induce intrinsic antimicrobial activity in the liver, which is due in part to LCN2 and SAA2. Therefore, IL-22 may be a useful adjunct in treating hepatic and intra-abdominal infections.

Abstract W MP92: Role of Lipocalin 2 in Acute Ventricular Dilatation After Intraventricular Hemorrhage

Background: Acute hydrocephalus is a common complication following hemorrhagic stroke. Although recent studies demonstrated that intraventricular hemorrhage (IVH) causes hydrocephalus, the exact mechanism by which hydrocephalus develops after IVH are not well understood. Lipocalin 2 (LCN2), a siderophore-binding protein, is an acute phase protein in the brain. In the present study, we examined the role of LCN2 in ventricular dilatation in a mouse model of IVH. Methods: First, female wild type C57BL/6 mice (WT, n=8) underwent a right intraventricular injection of hemoglobin (25mg/ml, 20 μl). Control mice (n=6) received saline injection. Ventricular volume was measured at 24 hours using magnetic resonance images. Second, female wild type and LCN2-deficient (LCN2-/-) mice had an intraventricular injection of hemoglobin (25mg/ml, n=5 for each; 50mg/ml, 20 μl, n=7 for WT and n=11 for LCN2-/-). They underwent magnetic resonance images at pre surgery and then 24 hours after surgery. All mice were euthanized at 24 hours after surgery. Brains were used for immunohistochemistry, immunofluorescence and Western blotting. Data are expressed as means±SD. P<0.05 was considered statistically significant. Results: In wild type mice, injection of hemoglobin (25 mg/ml) rather than saline resulted in ventricular dilatation at 24 hours (12.5±2.4 vs. 8.6±1.5 mm3 in the control, p<0.01). Western blotting showed that LCN2 was significantly upregulated in the periventricular area after hemoglobin injection (26362±4165 vs. 2780±579 pixels in the control, p<0.01). LCN2 was expressed in astrocytes, whereas its receptor was detected in astrocytes and microglia/macrophages. Hemoglobin-induced ventricle enlargement was less in LCN2-/- mice (p<0.01) as was periventricular microglia activation (p<0.01). At a higher dose (50 mg/ml), hemoglobin resulted in high mortality in WT mice (86%), but much lower mortality in LCN2-/- mice (27%; p<0.05). Conclusions: Our results indicate that LCN2 has a critical role in hemoglobin-induced ventricular dilatation.