Nerve growth factor orchestrates NGAL and matrix metalloproteinases activity to promote colorectal cancer metastasis.

PURPOSE: Colorectal cancer (CRC) is one most cancer type of high incidence and high mortality rate. Metastasis play an important role in survival rate and life quality of colorectal cancer patients. Nerve growth factor (NGF) has been shown to be involved in the metastasis and deterioration in many cancers, but the detail mechanisms in promoting the metastasis of colorectal cancer remain unknown. In this study, we aimed to explore the mechanism of NGF promoting colorectal cancer metastasis to provide new insights for developing NGF anti-colorectal cancer drugs. METHODS: We examined the expression of NGF in human colorectal cancer by immunohistochemical staining, and Western blot to evaluate the relationship between NGF and colorectal cancer metastasis. Using biochemical experiments including wound healing assay, transwell migration and invasion assay, RT-PCR, Western blot and ELISA to explore the relative mechanism of NGF promoting colorectal cancer cells metastasis in vivo. RESULTS: Our results found that the high expression of NGF was related with high incidence of metastasis. The binding of NGF to TrkA phosphorylated TrkA, which activated MAPK/Erk signaling pathway increasing the expression NGAL to enhance the activity of MMP2 and MMP9, promoted colorectal cancer metastasis. CONCLUSION: Our finding demonstrated that NGF increased NGAL expression to enhance MMPs activity to promoted colorectal cancer cell metastasis by TrkA-MAPK/Erk axis.

Cerebralcare Granule® combined with nimodipine improves cognitive impairment in bilateral carotid artery occlusion rats by reducing lipocalin-2.

AIMS: Clinically, Cerebralcare Granule® (CG) has been widely utilized to treat various types of headache, chronic cerebral insufficiency and other diseases, and the effect is significant. Clinical studies have shown that CG can significantly relieve vascular dementia (VaD), however, the molecular mechanisms haven't been established. To clear the therapeutic mechanisms of CG against VaD, a hypothesis was proposed that CG could treat neurovascular injury by inhibiting the production of lipocalin-2 (LCN 2). MAIN METHODS: 90 dementia rats were selected by water maze test and randomly divided into 6 groups, including nimodipine (NM), CG L (low dose) (0.314 g kg-1), CG H (high dose) (0.628 g kg-1), and combined group (CG + NM). And in vitro neuronal cell OGD modeling to evaluate the effect of CG on JAK2/STAT3. KEY FINDINGS: CG could significantly shorten the escape latency of two-vessel occlusion (2-VO) rats, increase their exploratory behavior, alleviate the symptoms of VaD and improve the ultrastructural pathological damage of neurovascular unit and accelerate the recovery of cerebral blood perfusion. CG combined with NM is better than NM alone. It was further showed that CG could inhibit the pathogenicity of LCN 2 through JAK2/STAT3 pathway and suppress the production of inflammatory cytokines. It plays a role in the protection of cerebral microvasculature and BBB in 2-VO rats. SIGNIFICANCE: Taken together, there data has supported notion that CG can protect the integrity of cerebral blood vessels and BBB and improve cognitive impairment through mainly inhibiting LCN 2, which provides scientific evidence for clinical application.

Electroacupuncture improves repeated social defeat stress-elicited social avoidance and anxiety-like behaviors by reducing Lipocalin-2 in the hippocampus.

BACKGROUND: Post-traumatic stress disorder (PTSD) is a trauma-related disorder that is associated with pro-inflammatory activation and neurobiological impairments in the brain and leads to a series of affective-like behaviors. Electroacupuncture (EA) has been proposed as a clinically useful therapy for several brain diseases. However, the potential role of EA treatment in PTSD and its molecular and cellular mechanisms has rarely been investigated. METHODS: We used an established preclinical social defeat stress mouse model to study whether EA treatment modulates PTSD-like symptoms and understand its underlying mechanisms. To this end, male C57BL/6 mice were subjected to repeated social defeat stress (RSDS) for 6 consecutive days to induce symptoms of PTSD and treated with EA at Baihui (GV 20) and Dazhui (GV 14) acupoints. RESULTS: The stimulation of EA, but not needle insertion at Baihui (GV 20) and Dazhui (GV 14) acupoints effectively improved PTSD-like behaviors such as, social avoidance and anxiety-like behaviors. However, EA stimulation at the bilateral Tianzong (SI11) acupoints did not affect the PTSD-like behaviors obtained by RSDS. EA stimulation also markedly inhibited astrocyte activation in both the dorsal and ventral hippocampi of RSDS-treated mice. Using next-generation sequencing analysis, our results showed that EA stimulation attenuated RSDS-enhanced lipocalin 2 expression in the hippocampus. Importantly, using double-staining immunofluorescence, we observed that the increased lipocalin 2 expression in astrocytes by RSDS was also reduced by EA stimulation. In addition, intracerebroventricular injection of mouse recombinant lipocalin 2 protein in the lateral ventricles provoked social avoidance, anxiety-like behaviors, and the activation of astrocytes in the hippocampus. Interestingly, the overexpression of lipocalin 2 in the brain also altered the expression of stress-related genes, including monoamine oxidase A, monoamine oxidase B, mineralocorticoid receptor, and glucocorticoid receptor in the hippocampus. CONCLUSIONS: This study suggests that the treatment of EA at Baihui (GV 20) and Dazhui (GV 14) acupoints improves RSDS-induced social avoidance, anxiety-like behaviors, astrocyte activation, and lipocalin 2 expression. Furthermore, our findings also indicate that lipocalin 2 expression in the brain may be an important biomarker for the development of PTSD-related symptoms.

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

Lipocalin 2 (LCN2), an immunomodulator, regulates various cellular processes such as iron transport and defense against bacterial infection. Under pathological conditions, LCN2 promotes neuroinflammation via the recruitment and activation of immune cells and glia, particularly microglia and astrocytes. Although it seems to have a negative influence on the functional outcome in spinal cord injury (SCI), the extent of its involvement in SCI and the underlying mechanisms are not yet fully known. In this study, using a SCI contusion mouse model, we first investigated the expression pattern of Lcn2 in different parts of the CNS (spinal cord and brain) and in the liver and its concentration in blood serum. Interestingly, we could note a significant increase in LCN2 throughout the whole spinal cord, in the brain, liver, and blood serum. This demonstrates the diversity of its possible sites of action in SCI. Furthermore, genetic deficiency of Lcn2 (Lcn2-/-) significantly reduced certain aspects of gliosis in the SCI-mice. Taken together, our studies provide first valuable hints, suggesting that LCN2 is involved in the local and systemic effects post SCI, and might modulate the impairment of different peripheral organs after injury.

Lipocalin-2 mediates the rejection of neural transplants.

Lipocalin-2 (LCN2) has been implicated in promoting apoptosis and neuroinflammation in neurological disorders; however, its role in neural transplantation remains unknown. In this study, we cultured and differentiated Lund human mesencephalic (LUHMES) cells into human dopaminergic-like neurons and found that LCN2 mRNA was progressively induced in mouse brain after the intrastriatal transplantation of human dopaminergic-like neurons. The induction of LCN2 protein was detected in a subset of astrocytes and neutrophils infiltrating the core of the engrafted sites, but not in neurons and microglia. LCN2-immunoreactive astrocytes within the engrafted sites expressed lower levels of A1 and A2 astrocytic markers. Recruitment of microglia, neutrophils, and monocytes after transplantation was attenuated in LCN2 deficiency mice. The expression of M2 microglial markers was significantly elevated and survival of engrafted neurons was markedly improved after transplantation in LCN2 deficiency mice. Brain type organic cation transporter (BOCT), the cell surface receptor for LCN2, was induced in dopaminergic-like neurons after differentiation, and treatment with recombinant LCN2 protein directly induced apoptosis in dopaminergic-like neurons in a dose-dependent manner. Our results, therefore, suggested that LCN2 is a neurotoxic factor for the engrafted neurons and a modulator of neuroinflammation. LCN2 inhibition may be useful in reducing rejection after neural transplantation.

Lipocalin-2 deficiency may predispose to the progression of spontaneous age-related adiposity in mice.

Lipocalin-2 (Lcn2) is an innate immune protein elevated by several orders of magnitude in various inflammatory conditions including aging and obesity. Recent studies have shown that Lcn2 is secreted by adipocytes in response to inflammation and is categorized as a new adipokine cross-linking innate immunity and metabolic disorders including obesity. However, the involvement of Lcn2 and its function during the progression of obesity is largely unknown. Recently, browning of white adipose tissue (WAT) has gained attention as a therapeutic strategy to combat obesity. Herein, we have shown that treatment of mature 3T3-L1 adipocytes with recombinant Lcn2 (rec-Lcn2) resulted in the up-regulation of thermogenic and beige/brown markers (UCP1, PRDM16, ZIC-1 and TBX1) and increased mitochondrial activity. Additionally, global Lcn2 genetic knockout (Lcn2KO) mice exhibited accelerated weight gain and visceral fat deposition with age, when compared to wild type (WT) mice. Taken together, both in vitro and in vivo studies suggest that Lcn2 is a naturally occurring adipokine, and may serve as an anti-obesity agent by upregulating the thermogenic markers resulting in the browning of WAT. Therefore, Lcn2 and its downstream signaling pathways could be a potential therapeutic target for obesity.

Differential regulation of Lipocalin 2 (LCN2) in doxorubicin-resistant 4T1 triple negative breast cancer cells.

Chemoresistance is a multifactorial and complex phenomenon, leading to re-adjustment of several intracellular signaling pathways and expression patterns which compromises the efficacy of cancer drug chemo-therapy. Via comparative analysis of sensitive and doxorubicin-resistant 4T1 cells, here we show that Lipocalin 2 (LCN2) is downregulated at the mRNA and protein level in resistant cells. The pro-inflammatory cytokine, IL-1ß was found to be a potent inducer of LCN2 expression most likely involving STAT3 activation. Upregulation in both sensitive and resistant 4T1 cells argues against complete silencing of the LCN2 gene. Coinciding with LCN2 downregulation, we observed an increased activation of bone morphogenetic protein (BMP)-signaling in resistant cells, as evidenced by higher Smad1/5/9 phosphorylation and Id1 target gene expression. Blockade of the BMP-pathway by Dorsomorphin increased the expression of LCN2. Conversely, BMP2, which is known to be a pro-tumorigenic ligand in breast cancer, potently inhibited LCN2 expression at both the mRNA and protein level in resistant cells. These findings indicate that in doxorubicin-resistant 4T1 cells, LCN2 expression is negatively regulated by BMP signaling.

Lipocalin-2 counteracts metabolic dysregulation in obesity and diabetes.

Regulation of food intake is a recently identified endocrine function of bone that is mediated by Lipocalin-2 (LCN2). Osteoblast-secreted LCN2 suppresses appetite and decreases fat mass while improving glucose metabolism. We now show that serum LCN2 levels correlate with insulin levels and ß-cell function, indices of healthy glucose metabolism, in obese mice and obese, prediabetic women. However, LCN2 serum levels also correlate with body mass index and insulin resistance in the same individuals and are increased in obese mice. To dissect this apparent discrepancy, we modulated LCN2 levels in mice. Silencing Lcn2 expression worsens metabolic dysfunction in genetic and diet-induced obese mice. Conversely, increasing circulating LCN2 levels improves metabolic parameters and promotes ß-cell function in mouse models of ß-cell failure acting as a growth factor necessary for ß-cell adaptation to higher metabolic load. These results indicate that LCN2 up-regulation is a protective mechanism to counteract obesity-induced glucose intolerance by decreasing food intake and promoting adaptive ß-cell proliferation.

Sex-specific metabolic functions of adipose Lipocalin-2.

OBJECTIVE: Lipocalin-2 (LCN2) is a secreted protein involved in innate immunity and has also been associated with several cardiometabolic traits in both mouse and human studies. However, the causal relationship of LCN2 to these traits is unclear, and most studies have examined only males. METHODS: Using adeno-associated viral vectors we expressed LCN2 in either adipose or liver in a tissue specific manner on the background of a whole-body Lcn2 knockout or wildtype mice. Metabolic phenotypes including body weight, body composition, plasma and liver lipids, glucose homeostasis, insulin resistance, mitochondrial phenotyping, and metabolic cage studies were monitored. RESULTS: We studied the genetics of LCN2 expression and associated clinical traits in both males and females in a panel of 100 inbred strains of mice (HMDP). The natural variation in Lcn2 expression across the HMDP exhibits high heritability, and genetic mapping suggests that it is regulated in part by Lipin1 gene variation. The correlation analyses revealed striking tissue dependent sex differences in obesity, insulin resistance, hepatic steatosis, and dyslipidemia. To understand the causal relationships, we examined the effects of expression of LCN2 selectively in liver or adipose. On a Lcn2-null background, LCN2 expression in white adipose promoted metabolic disturbances in females but not males. It acted in an autocrine/paracrine manner, resulting in mitochondrial dysfunction and an upregulation of inflammatory and fibrotic genes. On the other hand, on a null background, expression of LCN2 in liver had no discernible impact on the traits examined despite increasing the levels of circulating LCN2 more than adipose LCN2 expression. The mechanisms underlying the sex-specific action of LCN2 are unclear, but our results indicate that adipose LCN2 negatively regulates its receptor, LRP2 (or megalin), and its repressor, ERα, in a female-specific manner and that the effects of LCN2 on metabolic traits are mediated in part by LRP2. CONCLUSIONS: Following up on our population-based studies, we demonstrate that LCN2 acts in a highly sex- and tissue-specific manner in mice. Our results have important implications for human studies, emphasizing the importance of sex and the tissue source of LCN2.

Lipocalin-2 (Lcn-2) Attenuates Polymicrobial Sepsis with LPS Preconditioning (LPS Tolerance) in FcGRIIb Deficient Lupus Mice.

In patients with active lupus, spontaneous endotoxemia and possibly tolerance to lipopolysaccharide (LPS) is a potentially adverse complication. Similarly, previous reports have demonstrated that FcGRIIb deficient mice (FcGRIIb-/-; a lupus mouse model) are susceptible to LPS tolerance-induced decreased cytokine responses that inadequate for the organismal control. Thus, understanding the relationship between FcGRIIb and LPS tolerance could improve the therapeutic strategy for lupus. LPS tolerance can be induced through sequential LPS stimulations in either cells or a model organism. In RAW264.7 (a mouse macrophage cell-line), sequential LPS stimulation induced the secretion of Lipocalin-2 (Lcn-2) despite reduced cytokine secretion and severe energy depletion, as measured by the extracellular flux analysis, typical of LPS tolerance. In contrast, treatment with recombinant Lcn-2 (rLcn-2) attenuated LPS tolerance, as shown by an increase in secreted cytokines and altered macrophage polarization toward M1 (increased iNOS and TNF-α) in RAW264.7 cells. These results suggest a role of Lcn-2 in LPS tolerance attenuation. In bone marrow derived macrophages, Lcn-2 level was similar in LPS tolerant FcGRIIb-/- and wild-type (WT) cells despite the increased LPS tolerance of FcGRIIb-/- cells, suggesting relatively low basal levels of Lcn-2 produced in FcGRIIb-/- cells. In addition, attenuation of LPS tolerance effectuated by granulocyte-monocyte colony stimulating factor (GM-CSF) reduced Lcn-2 in both cell types, implying an inverse correlation between Lcn-2 and the severity of LPS tolerance. Consequently, rLcn-2 improved LPS tolerance only in FcGRIIb-/- macrophages and attenuated disease severity of cecal ligation and puncture (CLP) sepsis pre-conditioning with sequential LPS injection (LPS-CLP model) only in FcGRIIb-/- mice, but not in WT mice. To summarize, inadequate Lcn-2 production in FcGRIIb-/- macrophage might, at least in part, be responsible for the inordinate LPS tolerance compared with WT cells. Additionally, supplementation of rLcn-2 attenuates LPS tolerance in FcGRIIb-/- macrophages in vitro, and in FcGRIIb-/- mice with LPS-CLP sepsis in vivo. In conclusion, Lcn-2 secreted by macrophages is possibly an autocrine signal to counter the reduced cytokine secretion in LPS tolerance.

Paradoxical role of lipocalin-2 in metabolic disorders and neurological complications.

Lipocalin-2 (LCN2), also known as 24p3 and neutrophil gelatinase-associated lipocalin (NGAL), is a 25-kDa secreted protein implicated in various metabolic and inflammatory diseases. Early studies suggest the protective function of LCN2 in which it acts as a bacteriostatic agent that competes with bacteria for iron-bound siderophores. However, both detrimental and beneficial roles of LCN2 have recently been documented in metabolic and neuroinflammatory diseases. Metabolic inflammation, as observed in diabetes and obesity, has been closely associated with the upregulation of LCN2 in blood plasma and several tissues in both humans and rodents, suggesting its pro-diabetic and pro-obesogenic role. On the contrary, other studies imply an anti-diabetic and anti-obesogenic role of LCN2 whereby a deficiency in the Lcn2 gene results in the impairment of insulin sensitivity and enhances the high-fat-diet-induced expansion of fat. A similar dual role of LCN2 has also been reported in various animal models for neurological disorders. In the midst of these mixed findings, there is no experimental evidence to explain why LCN2 shows such a contrasting role in the various studies. This debate needs to be resolved (or reconciled) and an integrated view on the topic is desirable. Herein, we attempt to address this issue by reviewing the recent findings on LCN2 in metabolic disorders and assess the potential cellular or molecular mechanisms underlying the dual role of LCN2. We further discuss the possibilities and challenges of targeting LCN2 as a potential therapeutic strategy for metabolic disorders and neurological complications.

Lipocalin 2 Does Not Play A Role in Celastrol-Mediated Reduction in Food Intake and Body Weight.

Celastrol is a leptin-sensitizing agent with profound anti-obesity effects in diet-induced obese (DIO) mice. However, the genes and pathways that mediate celastrol-induced leptin sensitization have not been fully understood. By comparing the hypothalamic transcriptomes of celastrol and vehicle-treated DIO mice, we identified lipocalin-2 (Lcn2) as the gene most strongly upregulated by celastrol. LCN2 was previously suggested as an anorexigenic and anti-obesity agent. Celastrol increased LCN2 protein levels in hypothalamus, liver, fat, muscle, and bone marrow, as well as in the plasma. However, genetic deficiency of LCN2 altered neither the development of diet-induced obesity, nor the ability of celastrol to promote weight loss and improve obesity-associated dyshomeostasis. We conclude that LCN2 is dispensable for both high fat diet-induced obesity and its therapeutic reduction by celastrol.

The Klebsiella pneumoniae citrate synthase gene, gltA, influences site specific fitness during infection.

Klebsiella pneumoniae (Kp), one of the most common causes of healthcare-associated infections, increases patient morbidity, mortality, and hospitalization costs. Kp must acquire nutrients from the host for successful infection; however, the host is able to prevent bacterial nutrient acquisition through multiple systems. This includes the innate immune protein lipocalin 2 (Lcn2), which prevents Kp iron acquisition. To identify novel Lcn2-dependent Kp factors that mediate evasion of nutritional immunity during lung infection, we undertook an InSeq study using a pool of >20,000 transposon mutants administered to Lcn2+/+ and Lcn2-/- mice. Comparing transposon mutant frequencies between mouse genotypes, we identified the Kp citrate synthase, GltA, as potentially interacting with Lcn2, and this novel finding was independently validated. Interestingly, in vitro studies suggest that this interaction is not direct. Given that GltA is involved in oxidative metabolism, we screened the ability of this mutant to use a variety of carbon and nitrogen sources. The results indicated that the gltA mutant has a distinct amino acid auxotrophy rendering it reliant upon glutamate family amino acids for growth. Deletion of Lcn2 from the host leads to increased amino acid levels in bronchioloalveolar lavage fluid, corresponding to increased fitness of the gltA mutant in vivo and ex vivo. Accordingly, addition of glutamate family amino acids to Lcn2+/+ bronchioloalveolar lavage fluid rescued growth of the gltA mutant. Using a variety of mouse models of infection, we show that GltA is an organ-specific fitness factor required for complete fitness in the spleen, liver, and gut, but dispensable in the bloodstream. Similar to bronchioloalveolar lavage fluid, addition of glutamate family amino acids to Lcn2+/+ organ lysates was sufficient to rescue the loss of gltA. Together, this study describes a critical role for GltA in Kp infection and provides unique insight into how metabolic flexibility impacts bacterial fitness during infection.

Lipocalin-2: Its perspectives in brain pathology and possible roles in cognition.

Lipocalin-2 (LCN2) has been known to play an important role in pathological conditions, specifically in response to inflammation, infection and injury to cells. Recently, several research teams have been interested in investigating its association with cognition during the progression of pathology. Previous studies have demonstrated that LCN2 is not correlated with cognitive function under normal physiological conditions, although LCN2 has been negatively associated with cognition and some neuropathologies. Increasing LCN2 production is associated with reduced cognitive performance in a rodent model. However, further studies are needed to explore the potential underlying mechanisms of LCN2 on cognitive dysfunction, as well as its clinical relevance. This review aims to summarise the evidence available from in vitro, in vivo and clinical studies concerning the possible role of LCN2 on cognitive function following the onset of pathological conditions. Any contradictory evidence is also assessed and presented.

Neutrophil Gelatinase-Associated Lipocalin2 Exaggerates Cardiomyocyte Hypoxia Injury by Inhibiting Integrin ß3 Signaling.

BACKGROUND The neutrophil inflammatory protein, lipocalin-2 (NGAL), is elevated in certain forms of cardiac hypertrophy and acute heart failure. However, the specific role of NGAL in cardiac hypoxia injury is unclear. This study aimed to elucidate the functional role of NGAL in cardiomyocyte hypoxia injury. MATERIAL AND METHODS Neonatal rat cardiomyocytes were transfected with adenovirus [(Ad-NGAL] to overexpress human-NGAL and then were exposed to hypoxia for 24 h to establish a hypoxia model. Cell inflammation was detected by RT-PCT and ELISA assay. Cell apoptosis was detected by TUNEL assay. Oxidative stress was also detected by commercial kits. RESULTS An increased inflammatory response, apoptosis, and augmented oxidative stress were observed after exposure to hypoxia, while NGAL overexpression in cells increased the expression and release of inflammatory cytokines. NGAL overexpression also increased the number of apoptotic cells and the imbalance of Bax/Bcl-2 protein expression. Moreover, NGAL overexpression increased the levels of reactive oxygen species and oxidase activity, but reduced anti-oxidase activity. Mechanistically, we found that NGAL decreased the expression of integrin ß3, but not the expression of integrin avß3 and avß5, thus inhibiting the downstream protein AKT. When we used the constitutively activated AKT overexpression adenovirus to activate AKT, the deteriorated phenotype by NGAL was counteracted. CONCLUSIONS NGAL can directly affect cardiomyocytes and cause cardiomyocyte deteriorated hypoxia injury through inhibiting integrin ß3 signaling.

Voluntary running rescues the defective hippocampal neurogenesis and behaviour observed in lipocalin 2-null mice.

The continuous generation of new neurons in the adult mammalian hippocampus is a form of neural plasticity that modulates learning and memory functions, and also emotion (anxiety and depression). Among the factors known to modulate adult hippocampal neurogenesis and brain function, lipocalin-2 (LCN2) was recently described as a key regulator of neural stem cells (NSCs) proliferation and commitment, with impact on several dimensions of behaviour. Herein, we evaluated whether voluntary running, a well-known regulator of cell genesis, rescue the deficient adult hippocampal neurogenesis observed in mice lacking LCN2. We observed that running, by counteracting oxidative stress in NSCs, reverses LCN2-null mice defective hippocampal neurogenesis, as it promotes NSCs cell cycle progression and maturation, resulting in a partial reduction in anxiety and improved contextual behaviour. Together, these findings demonstrate that running is a positive modulator of adult hippocampal neurogenesis and behaviour in mice lacking LCN2, by impacting on the antioxidant kinetics of NSCs.

Liver parenchymal cells lacking Lipocalin 2 (LCN2) are prone to endoplasmic reticulum stress and unfolded protein response.

Unfolded protein response (UPR) is an adaptive mechanism allowing the endoplasmic reticulum (ER) to react to an accumulation of unfolded proteins in its lumen, also known as ER stress. The UPR is interconnected with inflammation through several pathways such as reactive oxygen species (ROS) production resulting from the protein folding or alternatively, activation of nuclear factor-κB (NF-κB) and c-Jun N-terminal kinase (JNK) via IRE1, or induction of acute phase response (APR). Lipocalin 2 (LCN2) is one of the APR proteins induced under inflammatory conditions and up-regulated during ER stress. Upon incubation of Lcn2-/- and wild type (wt) primary hepatocytes with tunicamycin (TM) or thapsigargin (TG) we found the Lcn2-/- hepatocytes to react with strong UPR to the ER stress, as evidenced by significantly increased levels of Grp94, Bip and Chop mRNA and protein compared to the wt. TM and TG-treated hepatocytes activated p65 NF-κB and JNK, the pathways that respond to stress stimuli and playing a central role in inflammation and apoptosis, respectively. ER stress further activated and cleaved full-length CREBH/CREB3L3, the hepatocyte specific transcription factor to induce systemic inflammatory responses. Upregulation of the C/EBP homologous protein (CHOP) was very prominent in Lcn2-/- hepatocytes and sustained until 48 h, resulting in hepatocyte apoptosis as evidenced by increased cleaved caspase 3. We also explored the UPR of the Lcn2 null mouse livers in acute intoxication and inflammation stages with a single application of lipopolysaccharide (LPS) or carbon tetrachloride (CCl4). The Lcn2 null mice clearly developed stronger UPR in LPS- and CCl4-induced ER stress compared to the wt. Our findings indicate that the upregulation of LCN2 during ER stress-induced inflammatory responses protects hepatocytes from being overwhelmed by UPR upon liver injury.

The Iron Tug-of-War between Bacterial Siderophores and Innate Immunity.

Iron is necessary for the survival of almost all aerobic organisms. In the mammalian host, iron is a required cofactor for the assembly of functional iron-sulfur (Fe-S) cluster proteins, heme-binding proteins and ribonucleotide reductases that regulate various functions, including heme synthesis, oxygen transport and DNA synthesis. However, the bioavailability of iron is low due to its insolubility under aerobic conditions. Moreover, the host coordinates a nutritional immune response to restrict the accessibility of iron against potential pathogens. To counter nutritional immunity, most commensal and pathogenic bacteria synthesize and secrete small iron chelators termed siderophores. Siderophores have potent affinity for iron, which allows them to seize the essential metal from the host iron-binding proteins. To safeguard against iron thievery, the host relies upon the innate immune protein, lipocalin 2 (Lcn2), which could sequester catecholate-type siderophores and thus impede bacterial growth. However, certain bacteria are capable of outmaneuvering the host by either producing "stealth" siderophores or by expressing competitive antagonists that bind Lcn2 in lieu of siderophores. In this review, we summarize the mechanisms underlying the complex iron tug-of-war between host and bacteria with an emphasis on how host innate immunity responds to siderophores.

Cyclic Dimeric Guanosine Monophosphate: Activation and Inhibition of Innate Immune Response.

Cyclic dimeric guanosine monophosphate (c-di-GMP) is a universally conserved second messenger that contributes to the pathogenicity of numerous bacterial species. In recent years, growing evidence has shown that bacterial extracellular c-di-GMP can interact with the innate immune system and regulate host immune responses. This review summarizes our current understanding on the dual roles of bacterial c-di-GMP in pathogen-host interaction: activation of the antibacterial innate immune response through the cytosolic surveillance pathway and inhibition of innate immune defense for iron restriction.

Light-Induced Lipocalin 2 Facilitates Cellular Apoptosis by Positively Regulating Reactive Oxygen Species/Bim Signaling in Retinal Degeneration.

Purpose: Lipocalin 2 (LCN2) is reported to be one of the key regulators of cell survival and death; however, its effect on retinal degeneration is unclear. Therefore, we aimed to investigate the role of LCN2 and its underlying mechanisms in light-induced retinal degeneration. Methods: A recombinant lentivirus expressing a short hairpin RNA targeting LCN2 mRNA and a recombinant lentivirus overexpressing LCN2 were used to downregulate and upregulate retinal LCN2, respectively. Seven days after intravitreal injection of the lentiviruses, rats were exposed to blue light (2500 lux) for 24 hours. Retinal function and morphology were evaluated with ERG and hematoxylin-eosin staining, respectively. TUNEL staining was used to detect apoptotic cells. The levels of reactive oxygen species (ROS) were evaluated with dihydroethidium labeling. Western blotting and real-time PCR were used to examine protein and mRNA expression levels, respectively. Results: Retinal LCN2 expression was significantly upregulated after light exposure. Light exposure reduced the amplitudes of a- and b-waves on the ERG and the thickness of the outer nuclear layer and promoted photoreceptor apoptosis. These phenomena were clearly attenuated by LCN2 knockdown, whereas LCN2 overexpression had the opposite effects. The overexpression of LCN2 facilitated photoreceptor apoptosis by increasing ROS generation and Bim expression. On the opposite, LCN2 knockdown mitigated the generation of light-exposure-induced ROS and the activation of the Bim-mediated mitochondrial apoptotic pathway. Conclusions: Light-induced LCN2 is a proapoptotic factor in the retina, and LCN2 knockdown protects photoreceptors from apoptosis by inhibiting ROS production and Bim expression. LCN2 is a potential therapeutic target for light-induced retinal degeneration.