Lipocalins constitute a superfamily of extracellular proteins that are found in all three kingdoms of life. Although very divergent in their sequences and functions, they show remarkable similarity ...in 3-D structures. Lipocalins bind and transport small hydrophobic molecules. Earlier sequence-based phylogenetic studies of lipocalins highlighted that they have a long evolutionary history. However the molecular and structural basis of their functional diversity is not completely understood. The main objective of the present study is to understand functional diversity of the lipocalins using a structure-based phylogenetic approach. The present study with 39 protein domains from the lipocalin superfamily suggests that the clusters of lipocalins obtained by structure-based phylogeny correspond well with the functional diversity. The detailed analysis on each of the clusters and sub-clusters reveals that the 39 lipocalin domains cluster based on their mode of ligand binding though the clustering was performed on the basis of gross domain structure. The outliers in the phylogenetic tree are often from single member families. Also structure-based phylogenetic approach has provided pointers to assign putative function for the domains of unknown function in lipocalin family. The approach employed in the present study can be used in the future for the functional identification of new lipocalin proteins and may be extended to other protein families where members show poor sequence similarity but high structural similarity.
Inflammation has classically been defined histopathologically, especially by the presence of immune cell infiltrates. However, more recent studies suggest a role for "low-grade" inflammation in a ...variety of disorders ranging from metabolic syndrome to cancer, which is defined by modest elevations in pro-inflammatory gene expression. Consequently, there is a need for cost-effective, non-invasive biomarkers that, ideally, would have the sensitivity to detect low-grade inflammation and have a dynamic range broad enough to reflect classic robust intestinal inflammation. Herein, we report that, for assessment of intestinal inflammation, fecal lipocalin 2 (Lcn-2), measured by ELISA, serves this purpose. Specifically, using a well-characterized mouse model of DSS colitis, we observed that fecal Lcn-2 and intestinal expression of pro-inflammatory cytokines (IL-1β, CXCL1, TNFα) are modestly but significantly induced by very low concentrations of DSS (0.25 and 0.5%), and become markedly elevated at higher concentrations of DSS (1.0 and 4.0%). As expected, careful histopathologic analysis noted only modest immune infiltrates at low DSS concentration and robust colitis at higher DSS concentrations. In accordance, increased levels of the neutrophil product myeloperoxidase (MPO) was only detected in mice given 1.0 and 4.0% DSS. In addition, fecal Lcn-2 marks the severity of spontaneous colitis development in IL-10 deficient mice. Unlike histopathology, MPO, and q-RT-PCR, the assay of fecal Lcn-2 requires only a stool sample, permits measurement over time, and can detect inflammation as early as 1 day following DSS administration. Thus, assay of fecal Lcn-2 by ELISA can function as a non-invasive, sensitive, dynamic, stable and cost-effective means to monitor intestinal inflammation in mice.
For many years, neutrophil gelatinase-associated lipocalin (NGAL) has been considered the most promising biomarker of acute kidney injury (AKI). Commercial assays and point-of-care instruments, now ...available in many hospitals, allow rapid NGAL measurements intended to guide the clinician in the management of patients with or at risk of AKI. However, these assays likely measure a mixture of different NGAL forms originating from different tissues. Systemic inflammation, commonly seen in critically ill patients, and several comorbidities contribute to the release of NGAL from haematopoietic and non-haematopoietic cells. The unpredictable release and complex nature of the molecule and the inability to specifically measure NGAL released by tubular cells have hampered its use a specific marker of AKI in heterogeneous critically ill populations. In this review, we describe the nature and cellular sources of NGAL, its biological role and diagnostic ability in AKI and the increasing concerns surrounding its diagnostic and clinical value.
The lipocalin proteins are a large family of small extracellular proteins that demonstrate significant heterogeneity in sequence similarity and have highly conserved crystal structures. They have a ...variety of functions, including acting as carrier proteins, transporting retinol, participating in olfaction, and synthesizing prostaglandins. Importantly, they also play a critical role in human diseases, including cancer. Additionally, they are involved in regulating cellular homeostasis and immune response and dispensing various compounds. This comprehensive review provides information on the lipocalin family, including their structure, functions, and implications in various diseases. It focuses on selective important human lipocalin proteins, such as lipocalin 2 (LCN2), retinol binding protein 4 (RBP4), prostaglandin D2 synthase (PTGDS), and α
-microglobulin (A1M).
Glycoprotein prostaglandin D2 synthase (PTGDS) is a member of the lipocalin superfamily and plays dual roles in prostaglandins metabolism and lipid transport. PTGDS has been involved in various ...cellular processes including the tumorigenesis of solid tumors, yet its role in carcinogenesis is contradictory and the significance of PTGDS in hematological malignancies is ill-defined. Here, we aimed to explore the expression and function of PTGDS in diffuse large B-cell lymphoma (DLBCL), especially the potential role of PTGDS inhibitor, AT56, in lymphoma therapy. Remarkable high expression of PTGDS was found in DLBCL, which was significantly correlated with poor prognosis. PTGDS overexpression and rhPTGDS were found to promote cell proliferation. Besides, in vitro and in vivo studies indicated that PTGDS knockdown and AT56 treatment exerted an anti-tumor effect by regulating cell viability, proliferation, apoptosis, cell cycle, and invasion, and enhanced the drug sensitivity to adriamycin and bendamustine through promoting DNA damage. Moreover, the co-immunoprecipitation-based mass spectrum identified the interaction between PTGDS and MYH9, which was found to promote DLBCL progression. PTGDS inhibition led to reduced expression of MYH9, and then declined activation of the Wnt-β-catenin-STAT3 pathway through influencing the ubiquitination and degradation of GSK3-β in DLBCL. The rescue experiment demonstrated that PTGDS exerted an oncogenic role through regulating MYH9 and then the Wnt-β-catenin-STAT3 pathway. Based on point mutation of glycosylation sites, we confirmed the N-glycosylation of PTGDS in Asn51 and Asn78 and found that abnormal glycosylation of PTGDS resulted in its nuclear translocation, prolonged half-life, and enhanced cell proliferation. Collectively, our findings identified for the first time that glycoprotein PTGDS promoted tumorigenesis of DLBCL through MYH9-mediated regulation of Wnt-β-catenin-STAT3 signaling, and highlighted the potential role of AT56 as a novel therapeutic strategy for DLBCL treatment.
Aims Neutrophil gelatinase-associated lipocalin (NGAL or lipocalin-2) is a glycoprotein with bacteriostatic properties. Growing evidence suggests that NGAL may also be involved in cell survival, ...inflammation, and matrix degradation. We therefore aimed to investigate the role of NGAL in heart failure (HF). Methods and results Our main findings were (i) patients with acute post-myocardial infarction (MI) HF (n = 236) and chronic HF (n = 150) had elevated serum levels of NGAL (determined by enzyme immunoassay), significantly correlated with clinical and neurohormonal deterioration, (ii) in patients with HF following acute MI, elevated NGAL levels of at baseline were associated with adverse outcomes (median of 27 months follow-up), (iii) in a rat model of post-MI HF, NGAL/lipocalin-2 gene expression was increased in the non-ischaemic part of the left ventricle primarily located to cardiomyocytes, (iv) strong NGAL immunostaining was found in cardiomyocytes within the failing myocardium both in experimental and clinical HF, (v) interleukin-1β and agonists for toll-like receptors 2 and 4, representing components of the innate immune system, were potent inducers of NGAL/lipocalin-2 in isolated neonatal cardiomyocytes. Conclusion Our demonstration of enhanced systemic and myocardial NGAL expression in clinical and experimental HF further support a role for innate immune responses in the pathogenesis of HF.
Background
Neutrophil gelatinase-associated lipocalin (NGAL) is a multi-potent 25-kDa protein mainly secreted by neutrophils. In inflammatory bowel disease (IBD), overexpression of NGAL in colon ...epithelium has been previously shown. This is the first study analyzing serum and urinary NGAL levels in IBD patients, with regard to specific characteristics of patients and disease.
Methods
Serum and urinary NGAL levels were determined in 181 patients with IBD, 93 with ulcerative colitis (UC), and 88 with Crohn’s disease (CD), 82 healthy controls (HC), and 41 patients with irritable bowel syndrome (IBS).
Results
Serum NGAL levels were elevated in IBD patients (88.19 ± 40.75 ng/mL) compared with either HC (60.06 ± 24.18 ng/mL) or IBS patients (60.80 ± 20.30 ng/mL),
P
< 0.0001. No significant difference was shown between UC (86.62 ± 35.40 ng/mL) and CD (89.92 ± 46.05 ng/mL). Significantly higher levels of serum NGAL were observed in patients with active (120.1 ± 38.46) versus inactive IBD (61.58 ± 15.98),
P
< 0.0001. Serum NGAL displayed a strong ability to distinguish active IBD from inactive disease, healthy controls, or IBS patients with a sensitivity of 100, 95, and 95% and a specificity of 68, 83, and 79%, respectively, performing better than erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) in the assessment of disease activity in both UC and CD. Urinary NGAL levels showed neither significant difference among patients and controls nor correlation with disease activity.
Conclusions
Serum NGAL is elevated particularly in active IBD and correlates with established markers of inflammation and disease activity, implicating its role in the pathophysiology of IBD.
Attraction of neutrophils to sites of infection or tissue injury is an essential prerequisite for an efficient innate immune response. Herein, we provide novel evidence that the antimicrobial ...protein, neutrophil gelatinase associated lipocalin (24p3 or lipocalin‐2, Lcn2) is a central regulator of this process. Lcn2 is produced by several cell types but high amounts are released by neutrophils. Using human and murine neutrophils, we found that the addition of recombinant Lcn2 significantly stimulated their migration, which was independent of IL‐8/keratinocyte chemokine formation. Mechanistically, this could be traced back to Lcn2‐mediated changes of Erk1/2 signaling. Accordingly, the i.p. injection of Lcn2 into C57BL/6 mice stimulated the mobilization of neutrophils while we found a significantly reduced neutrophil chemotactic activity of cells obtained from Lcn2 KO mice. This observation transmitted to a reduced accumulation of neutrophils in intra‐dermal lesions infected with Salmonella typhimurium in Lcn2 KO mice as compared to WT mice. This was not only due to a reduced chemotaxis but also to an impaired cellular adhesion of neutrophils in the absence of Lcn2. We herein describe a novel role of Lcn2 as an important paracrine chemoattractant and an indispensable factor for neutrophil function in inflammation.
To report the nonrandomized first-in-human phase I trial of PRS-050, a novel, rationally engineered Anticalin based on human tear lipocalin that targets and antagonizes vascular endothelial growth ...factor A (VEGF-A).
Patients with advanced solid tumors received PRS-050 at 0.1 mg/kg to 10 mg/kg by IV in successive dosing cohorts according to the 3+3 escalation scheme. The primary end point was safety.
Twenty-six patients were enrolled; 25 were evaluable. Two patients experienced dose-limiting toxicity, comprising grade (G) 3 hypertension and G3 pyrexia, respectively. The maximum tolerated dose was not reached. Most commonly reported treatment-emergent adverse events (AEs) included chills (52%; G3, 4%), fatigue (52%; G3, 4%), hypertension (44%; G3, 16%), and nausea (40%, all G1/2). No anti-PRS-050 antibodies following multiple administration of the drug were detected. PRS-050 showed dose-proportional pharmacokinetics (PK), with a terminal half-life of approximately 6 days. Free VEGF-A was detectable at baseline in 9/25 patients, becoming rapidly undetectable after PRS-050 infusion for up to 3 weeks. VEGF-A/PRS-050 complex was detectable for up to 3 weeks at all dose levels, including in patients without detectable baseline-free VEGF-A. We also detected a significant reduction in circulating matrix metalloproteinase 2, suggesting this end point could be a pharmacodynamic (PD) marker of the drug's activity.
PRS-050, a novel Anticalin with high affinity for VEGF-A, was well-tolerated when administered at the highest dose tested, 10 mg/kg. Based on target engagement and PK/PD data, the recommended phase II dose is 5 mg/kg every 2 weeks administered as a 120-minute infusion.
ClinicalTrials.gov NCT01141257 http://clinicaltrials.gov/ct2/show/NCT01141257.
Lipocalin-type prostaglandin D synthase (L-PGDS; EC:5.3.99.2) is an enzyme with dual functional roles as a prostaglandin D
-synthesizing enzyme and as an extracellular transporter for diverse ...lipophilic compounds in the cerebrospinal fluid (CSF). Transport of hydrophobic endocannabinoids is mediated by serum albumin in the blood and intracellularly by the fatty acid binding proteins, but no analogous transport mechanism has yet been described in CSF. L-PGDS has been reported to promiscuously bind a wide variety of lipophilic ligands and is among the most abundant proteins found in the CSF. Here, we examine the binding of several classes of endogenous and synthetic ligands to L-PGDS. Endocannabinoids exhibited low affinity toward L-PGDS, while cannabinoid metabolites and synthetic cannabinoids displayed higher affinities for L-PGDS. These results indicate that L-PGDS is unlikely to function as a carrier for endocannabinoids in the CSF, but it may bind and transport a subset of cannabinoids.
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