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1.  Role of breast regression protein 39 (BRP-39)/chitinase 3-like-1 in Th2 and IL-13–induced tissue responses and apoptosis 
The Journal of Experimental Medicine  2009;206(5):1149-1166.
Mouse breast regression protein 39 (BRP-39; Chi3l1) and its human homologue YKL-40 are chitinase-like proteins that lack chitinase activity. Although YKL-40 is expressed in exaggerated quantities and correlates with disease activity in asthma and many other disorders, the biological properties of BRP-39/YKL-40 have only been rudimentarily defined. We describe the generation and characterization of BRP-39−/− mice, YKL-40 transgenic mice, and mice that lack BRP-39 and produce YKL-40 only in their pulmonary epithelium. Studies of these mice demonstrated that BRP-39−/− animals have markedly diminished antigen-induced Th2 responses and that epithelial YKL-40 rescues the Th2 responses in these animals. The ability of interleukin13 to induce tissue inflammation and fibrosis was also markedly diminished in the absence of BRP-39. Mechanistic investigations demonstrated that BRP-39 and YKL-40 play an essential role in antigen sensitization and immunoglobulin E induction, stimulate dendritic cell accumulation and activation, and induce alternative macrophage activation. These proteins also inhibit inflammatory cell apoptosis/cell death while inhibiting Fas expression, activating protein kinase B/AKT, and inducing Faim 3. These studies establish novel regulatory roles for BRP-39/YKL-40 in the initiation and effector phases of Th2 inflammation and remodeling and suggest that these proteins are therapeutic targets in Th2- and macrophage-mediated disorders.
doi:10.1084/jem.20081271
PMCID: PMC2715037  PMID: 19414556
2.  The Chitinase-like Proteins Breast Regression Protein-39 and YKL-40 Regulate Hyperoxia-induced Acute Lung Injury 
Rationale: Prolonged exposure to 100% O2 causes hyperoxic acute lung injury (HALI), characterized by alveolar epithelial cell injury and death. We previously demonstrated that the murine chitinase-like protein, breast regression protein (BRP)–39 and its human homolog, YKL-40, inhibit cellular apoptosis. However, the regulation and roles of these molecules in hyperoxia have not been addressed.
Objectives: We hypothesized that BRP-39 and YKL-40 (also called chitinase-3–like 1) play important roles in the pathogenesis of HALI.
Methods: We characterized the regulation of BRP-39 during HALI and the responses induced by hyperoxia in wild-type mice, BRP-39–null (−/−) mice, and BRP-39−/− mice in which YKL-40 was overexpressed in respiratory epithelium. We also compared the levels of tracheal aspirate YKL-40 in premature newborns with respiratory failure.
Measurements and Main Results: These studies demonstrate that hyperoxia inhibits BRP-39 in vivo in the murine lung and in vitro in epithelial cells. They also demonstrate that BRP-39−/− mice have exaggerated permeability, protein leak, oxidation, inflammatory, chemokine, and epithelial apoptosis responses, and experience premature death in 100% O2. Lastly, they demonstrate that YKL-40 ameliorates HALI, prolongs survival in 100% O2, and rescues the exaggerated injury response in BRP-39−/− animals. In accord with these findings, the levels of tracheal aspirate YKL-40 were lower in premature infants treated with hyperoxia for respiratory failure who subsequently experienced bronchopulmonary dysplasia or death compared with those that did not experience these complications.
Conclusions: These studies demonstrate that hyperoxia inhibits BRP-39/YKL-40, and that BRP-39 and YKL-40 are critical regulators of oxidant injury, inflammation, and epithelial apoptosis in the murine and human lung.
doi:10.1164/rccm.200912-1793OC
PMCID: PMC2970863  PMID: 20558631
BRP-39; YKL-40; hyperoxygen; BPD; HALI
3.  The Chitinase-Like Protein YKL-40 Modulates Cystic Fibrosis Lung Disease 
PLoS ONE  2011;6(9):e24399.
The chitinase-like protein YKL-40 was found to be increased in patients with severe asthma and chronic obstructive pulmonary disease (COPD), two disease conditions featuring neutrophilic infiltrates. Based on these studies and a previous report indicating that neutrophils secrete YKL-40, we hypothesized that YKL-40 plays a key role in cystic fibrosis (CF) lung disease, a prototypic neutrophilic disease. The aim of this study was (i) to analyze YKL-40 levels in human and murine CF lung disease and (ii) to investigate whether YKL-40 single-nucleotide polymorphisms (SNPs) modulate CF lung disease severity. YKL-40 protein levels were quantified in serum and sputum supernatants from CF patients and control individuals. Levels of the murine homologue BRP-39 were analyzed in airway fluids from CF-like βENaC-Tg mice. YKL-40SNPs were analyzed in CF patients. YKL-40 levels were increased in sputum supernatants and in serum from CF patients compared to healthy control individuals. Within CF patients, YKL-40 levels were higher in sputum than in serum. BRP-39 levels were increased in airways fluids from βENaC-Tg mice compared to wild-type littermates. In both CF patients and βENaC-Tg mice, YKL-40/BRP-39 airway levels correlated with the severity of pulmonary obstruction. Two YKL-40 SNPs (rs871799 and rs880633) were found to modulate age-adjusted lung function in CF patients. YKL-40/BRP-39 levelsare increased in human and murine CF airway fluids, correlate with pulmonary function and modulate CF lung disease severity genetically. These findings suggest YKL-40 as a potential biomarker in CF lung disease.
doi:10.1371/journal.pone.0024399
PMCID: PMC3176766  PMID: 21949714
4.  Role of Breast Regression Protein–39 in the Pathogenesis of Cigarette Smoke–Induced Inflammation and Emphysema 
The exaggerated expression of chitinase-like protein YKL-40, the human homologue of breast regression protein–39 (BRP-39), was reported in a number of diseases, including chronic obstructive pulmonary disease (COPD). However, the in vivo roles of YKL-40 in normal physiology or in the pathogenesis of specific diseases such as COPD remain poorly understood. We hypothesized that BRP-39/YKL-40 plays an important role in the pathogenesis of cigarette smoke (CS)–induced emphysema. To test this hypothesis, 10-week-old wild-type and BRP-39 null mutant mice (BRP-39−/−) were exposed to room air (RA) and CS for up to 10 months. The expression of BRP-39 was significantly induced in macrophages, airway epithelial cells, and alveolar Type II cells in the lungs of CS-exposed mice compared with RA-exposed mice, at least in part via an IL-18 signaling–dependent pathway. The null mutation of BRP-39 significantly reduced CS-induced bronchoalveolar lavage and tissue inflammation. However, CS-induced epithelial cell apoptosis and alveolar destruction were further enhanced in the absence of BRP-39. Consistent with these findings in mice, the tissue expression of YKL-40 was significantly increased in the lungs of current smokers compared with the lungs of ex-smokers or nonsmokers. In addition, serum concentrations of YKL-40 were significantly higher in smokers with COPD than in nonsmokers or smokers without COPD. These studies demonstrate a novel regulatory role of BRP-39/YKL-40 in CS-induced inflammation and emphysematous destruction. These studies also underscore that maintaining physiologic concentrations of YKL-40 in the lung is therapeutically important in preventing excessive inflammatory responses or emphysematous alveolar destruction.
doi:10.1165/rcmb.2010-0081OC
PMCID: PMC3135840  PMID: 20656949
YKL-40/BRP-39; COPD; emphysema; cigarette smoke
5.  Role of Chitin and Chitinase/Chitinase-Like Proteins in Inflammation, Tissue Remodeling, and Injury 
Annual review of physiology  2011;73:10.1146/annurev-physiol-012110-142250.
The 18 glycosyl hydrolase family of chitinases is an ancient gene family that is widely expressed from prokaryotes to eukaryotes. In mammals, despite the absence of endogenous chitin, a number of chitinases and chitinase-like proteins (C/CLPs) have been identified. However, their roles have only recently begun to be elucidated. Acidic mammalian chitinase (AMCase) inhibits chitin-induced innate inflammation; augments chitin-free, allergen-induced Th2 inflammation; and mediates effector functions of IL-13. The CLPs BRP-39/YKL-40 (also termed chitinase 3-like 1) inhibit oxidant-induced lung injury, augments adaptive Th2 immunity, regulates apoptosis, stimulates alternative macrophage activation, and contributes to fibrosis and wound healing. In accord with these findings, levels of YKL-40 in the lung and serum are increased in asthma and other inflammatory and remodeling disorders and often correlate with disease severity. Our understanding of the roles of C/CLPs in inflammation, tissue remodeling, and tissue injury in health and disease is reviewed below.
doi:10.1146/annurev-physiol-012110-142250
PMCID: PMC3864643  PMID: 21054166
asthma; fibrosis; BRP-39/YKL-40; AMCase; chitotriosidase
6.  Segmental Allergen Challenge Enhances Chitinase Activity and Levels of CCL18 in Mild Atopic Asthma 
Background
Allergic airway inflammation contributes to the airway remodeling that has been linked to increased obstruction and morbidity in asthma. However, the mechanisms by which allergens contribute to airway remodeling in humans are not fully established. CCL18, chitotriosidase (CHIT1) and YKL-40 are readily detectable in the lungs and contribute to remodeling in other fibrotic diseases, but their involvement in allergic asthma is unclear.
Objective
We hypothesized that CCL18, YKL-40, and CHIT1 bioactivity are enhanced in allergic asthma subjects after segmental allergen challenge and are related to increased profibrotic and Th2-associated mediators in the lungs.
Methods
Levels of CCL18 and YKL-40 protein and CHIT1 bioactivity in bronchoalveolar lavage (BAL) fluid, as well as CCL18, YKL-40, and CHIT1 mRNA levels in BAL cells, were evaluated in patients with asthma at baseline and 48 h after segmental allergen challenge. We also examined the correlation between CCL18 and YKL-40 levels and CHIT1 activity with the levels of other profibrotic factors and chemokines previously shown to be up-regulated after allergen challenge.
Results
CHIT1 activity and YKL-40 and CCL18 levels were elevated after segmental allergen challenge and these levels correlated with those of other profibrotic factors, T cell chemokines, and inflammatory cells after allergen challenge. CCL18 and YKL-40 mRNA levels also increased in BAL cells after allergen challenge.
Conclusions & Clinical Relevance
Our results suggest that CCL18 and YKL-40 levels and CHIT1 activity are enhanced in allergic airway inflammation and thus may contribute to airway remodeling in asthma.
doi:10.1111/cea.12032
PMCID: PMC3623278  PMID: 23331560
asthma; segmental bronchoprovocation; CHIT1; YKL-40; CCL18
7.  Effect of Variation in CHI3L1 on Serum YKL-40 Level, Risk of Asthma, and Lung Function 
The New England journal of medicine  2008;358(16):1682-1691.
BACKGROUND
The chitinase-like protein YKL-40 is involved in inflammation and tissue remodeling. We recently showed that serum YKL-40 levels were elevated in patients with asthma and were correlated with severity, thickening of the subepithelial basement membrane, and pulmonary function. We hypothesized that single-nucleotide polymorphisms (SNPs) that affect YKL-40 levels also influence asthma status and lung function.
METHODS
We carried out a genomewide association study of serum YKL-40 levels in a founder population of European descent, the Hutterites, and then tested for an association between an implicated SNP and asthma and lung function. One associated variant was genotyped in a birth cohort at high risk for asthma, in which YKL-40 levels were measured from birth through 5 years of age, and in two populations of unrelated case patients of European descent with asthma and controls.
RESULTS
A promoter SNP (−131C→G) in CHI3L1, the chitinase 3–like 1 gene encoding YKL-40, was associated with elevated serum YKL-40 levels (P = 1.1×10−13), asthma (P = 0.047), bronchial hyperresponsiveness (P = 0.002), and measures of pulmonary function (P = 0.046 to 0.002) in the Hutterites. The same SNP could be used to predict the presence of asthma in the two case–control populations (combined P = 1.2×10−5) and serum YKL-40 levels at birth (in cord-blood specimens) through 5 years of age in the birth cohort (P = 8.9×10−3 to 2.5×10−4).
CONCLUSIONS
CHI3L1 is a susceptibility gene for asthma, bronchial hyperresponsiveness, and reduced lung function, and elevated circulating YKL-40 levels are a biomarker for asthma and decline in lung function.
doi:10.1056/NEJMoa0708801
PMCID: PMC2629486  PMID: 18403759
8.  Exacerbation of Experimental Autoimmune Encephalomyelitis in the Absence of Breast Regression Protein-39/Chitinase 3-like-1 
We previously reported that YKL-40, the human analog of mouse breast regression protein-39 (BRP-39; chitinase 3-like 1), is elevated in the cerebrospinal fluid of patients with a variety of neuroinflammatory conditions, such as multiple sclerosis and traumatic brain injury. YKL-40 expression in the CNS was predominantly associated with reactive astrocytes in the vicinity of inflammatory lesions. Because previous studies have shown that reactive astrocytes play a critical role in limiting immune infiltration in the mouse model of experimental autoimmune encephalomyelitis (EAE), we explored the role of BRP-39 in regulating neuroinflammation in EAE. Using BRP-39-deficient mice (BRP-39−/−), we demonstrate the importance of BRP-39 in modulating the severity of clinical EAE and CNS neuroinflammation. At disease onset, absence of BRP-39 had little effect on clinical disease or lymphocytic infiltrate, but by 14 days post-immunization (dpi), differences in clinical scores were evident. By 28 dpi, BRP-39−/− mice showed more severe and persistent clinical disease than BRP-39+/+ controls. Histopathological evaluation showed that BRP-39−/− mice had more marked lymphocytic and macrophage infiltrates and gliosis vs. BRP-39+/+ mice. These findings support the role of BRP-39 expression in limiting immune cell infiltration into the CNS and offer a new target to modulate neuroinflammation.
doi:10.1097/NEN.0b013e31826eaee7
PMCID: PMC3481009  PMID: 23041842
BRP-39; Chitinase-like proteins; Experimental autoimmune encephalomyelitis; Multiple sclerosis; Neuroimmunology; YKL-40
9.  Human YKL-39 is a pseudo-chitinase with retained chitooligosaccharide-binding properties 
The Biochemical journal  2012;446(1):149-157.
The chitinase-like proteins YKL-39 (chitinase 3-like-2) and YKL-40 (chitinase 3-like-1) are highly expressed in a number of human cells independent of their origin (mesenchymal, epithelial or haemapoietic). Elevated serum levels of YKL-40 have been associated with a negative outcome in a number of diseases ranging from cancer to inflammation and asthma. YKL-39 expression has been associated with osteoarthritis. However, despite the reported association with disease, the physiological or pathological role of these proteins is still very poorly understood. Although YKL-39 is homologous to the two family 18 chitinases in the human genome, it has been reported to lack any chitinase activity. In the present study, we show that human YKL-39 possesses a chitinase-like fold, but lacks key active-site residues required for catalysis. A glycan screen identified oligomers of N-acetylglucosamine as preferred binding partners. YKL-39 binds chitooligosaccharides and a newly synthesized derivative of the bisdionin chitinase-inhibitor class with micromolar affinity, through a number of conserved tryptophan residues. Strikingly, the chitinase activity of YKL-39 was recovered by reverting two non-conservative substitutions in the active site to those found in the active enzymes, suggesting that YKL-39 is a pseudo-chitinase with retention of chitinase-like ligand-binding properties.
doi:10.1042/BJ20120377
PMCID: PMC3513709  PMID: 22742450
chitinase; chitinase-like proteins; glycan; glycan array; glycobiology; protein structure; lectin; X-ray crystallography
10.  Differential expression and function of breast regression protein 39 (BRP-39) in murine models of subacute cigarette smoke exposure and allergic airway inflammation 
Respiratory Research  2011;12(1):39.
Background
While the presence of the chitinase-like molecule YKL40 has been reported in COPD and asthma, its relevance to inflammatory processes elicited by cigarette smoke and common environmental allergens, such as house dust mite (HDM), is not well understood. The objective of the current study was to assess expression and function of BRP-39, the murine equivalent of YKL40 in a murine model of cigarette smoke-induced inflammation and contrast expression and function to a model of HDM-induced allergic airway inflammation.
Methods
CD1, C57BL/6, and BALB/c mice were room air- or cigarette smoke-exposed for 4 days in a whole-body exposure system. In separate experiments, BALB/c mice were challenged with HDM extract once a day for 10 days. BRP-39 was assessed by ELISA and immunohistochemistry. IL-13, IL-1R1, IL-18, and BRP-39 knock out (KO) mice were utilized to assess the mechanism and relevance of BRP-39 in cigarette smoke- and HDM-induced airway inflammation.
Results
Cigarette smoke exposure elicited a robust induction of BRP-39 but not the catalytically active chitinase, AMCase, in lung epithelial cells and alveolar macrophages of all mouse strains tested. Both BRP-39 and AMCase were increased in lung tissue after HDM exposure. Examining smoke-exposed IL-1R1, IL-18, and IL-13 deficient mice, BRP-39 induction was found to be IL-1 and not IL-18 or IL-13 dependent, while induction of BRP-39 by HDM was independent of IL-1 and IL-13. Despite the importance of BRP-39 in cellular inflammation in HDM-induced airway inflammation, BRP-39 was found to be redundant for cigarette smoke-induced airway inflammation and the adjuvant properties of cigarette smoke.
Conclusions
These data highlight the contrast between the importance of BRP-39 in HDM- and cigarette smoke-induced inflammation. While functionally important in HDM-induced inflammation, BRP-39 is a biomarker of cigarette smoke induced inflammation which is the byproduct of an IL-1 inflammatory pathway.
doi:10.1186/1465-9921-12-39
PMCID: PMC3079621  PMID: 21473774
11.  Expression of the Chitinase Family Glycoprotein YKL-40 in Undifferentiated, Differentiated and Trans-Differentiated Mesenchymal Stem Cells 
PLoS ONE  2013;8(5):e62491.
The glycoprotein YKL-40 (CHI3L1) is a secreted chitinase family protein that induces angiogenesis, cell survival, and cell proliferation, and plays roles in tissue remodeling and immune regulation. It is expressed primarily in cells of mesenchymal origin, is overexpressed in numerous aggressive carcinomas and sarcomas, but is rarely expressed in normal ectodermal tissues. Bone marrow-derived mesenchymal stem cells (MSCs) can be induced to differentiate into various mesenchymal tissues and trans-differentiate into some non-mesenchymal cell types. Since YKL-40 has been used as a mesenchymal marker, we followed YKL-40 expression as undifferentiated MSCs were induced to differentiate into bone, cartilage, and neural phenotypes. Undifferentiated MSCs contain significant levels of YKL-40 mRNA but do not synthesize detectable levels of YKL-40 protein. MSCs induced to differentiate into chondrocytes and osteocytes soon began to express and secrete YKL-40 protein, as do ex vivo cultured chondrocytes and primary osteocytes. In contrast, MSCs induced to trans-differentiate into neurons did not synthesize YKL-40 protein, consistent with the general absence of YKL-40 protein in normal CNS parenchyma. However, these trans-differentiated neurons retained significant levels of YKL-40 mRNA, suggesting the mechanisms which prevented YKL-40 translation in undifferentiated MSCs remained in place, and that these trans-differentiated neurons differ in at least this way from neurons derived from neuronal stem cells. Utilization of a differentiation protocol containing β-mercaptoethanol resulted in cells that expressed significant amounts of intracellular YKL-40 protein that was not secreted, which is not seen in normal cells. Thus the synthesis of YKL-40 protein is a marker for MSC differentiation into mature mesenchymal phenotypes, and the presence of untranslated YKL-40 mRNA in non-mesenchymal cells derived from MSCs reflects differences between differentiated and trans-differentiated phenotypes.
doi:10.1371/journal.pone.0062491
PMCID: PMC3650021  PMID: 23671604
12.  Airway, but not serum or urinary, levels of YKL-40 reflect inflammation in early cystic fibrosis lung disease 
Background
Cystic fibrosis (CF) lung disease begins in early life and is progressive with the major risk factor being an exaggerated inflammatory response. Currently, assessment of neutrophilic inflammation in early cystic fibrosis (CF) lung disease relies on bronchoalveolar lavage (BAL). The chitinase-like protein YKL-40 is raised in sputum and serum of adults with CF. We investigated YKL-40 in BAL, serum and urine to determine whether this reflected inflammation and infection in young children with CF.
Methods
YKL-40 was measured in matched samples of BAL, serum and urine obtained from 36 infants and young children with CF participating in an early surveillance program. Levels were compared to clinical data and markers of inflammation detected in the lung.
Results
YKL-40 in BAL correlated with pulmonary infection [β=1.30 (SE 0.34), p < 0.001] and BAL markers of inflammation [macrophage number: r2 = 0.34, p < 0.001; neutrophil number: r2 = 0.74, p < 0.001; neutrophil elastase: r2 = 0.47, p < 0.001; CXCL8: r2 = 0.45, p < 0.001; IL-β: r2 = 0.62, p < 0.001]. YKL-40 was detectable in serum but levels did not correlate with BAL levels in the same individuals (r2 = 0.04, p = 0.14) or with inflammatory markers. YKL-40 was below the limit of detection in urine (30 pg/ml).
Conclusions
This study demonstrates that levels of the chitinase-like protein YKL-40 reflect airway inflammation and infection in early CF lung disease. The lack of increased YKL-40 in serum in the absence of systemic inflammation limits the benefit of this potential biomarker in early disease.
doi:10.1186/1471-2466-14-28
PMCID: PMC3946043  PMID: 24576297
Cystic fibrosis; YKL-40; Biomarker; Lung disease
13.  YKL-40 - an emerging biomarker in cardiovascular disease and diabetes 
Several inflammatory cytokines are involved in vascular inflammation resulting in endothelial dysfunction which is the earliest event in the atherosclerotic process leading to manifest cardiovascular disease. YKL-40 is an inflammatory glycoprotein involved in endothelial dysfunction by promoting chemotaxis, cell attachment and migration, reorganization and tissue remodelling as a response to endothelial damage. YKL-40 protein expression is seen in macrophages and smooth muscle cells in atherosclerotic plaques with the highest expression seen in macrophages in the early lesion of atherosclerosis. Several studies demonstrate, that elevated serum YKL-levels are independently associated with the presence and extent of coronary artery disease and even higher YKL-40 levels are documented in patients with myocardial infarction. Moreover, elevated serum YKL-40 levels have also been found to be associated with all-cause as well as cardiovascular mortality. Finally, YKL-40 levels are elevated both in patients with type 1 and type 2 diabetes, known to be at high risk for the development of cardiovascular diseases, when compared to non-diabetic persons. A positive association between elevated circulating YKL-40 levels and increasing levels of albuminuria have been described in patients with type 1 diabetes indicating a role of YKL-40 in the progressing vascular damage resulting in microvascular disease.
This review describes the present knowledge about YKL-40 and discusses its relation to endothelial dysfunction, atherosclerosis, cardiovascular disease and diabetes and look ahead on future perspectives of YKL-40 research.
doi:10.1186/1475-2840-8-61
PMCID: PMC2789050  PMID: 19930630
14.  Expression of Osteoarthritis Marker YKL-39 is Stimulated by Transforming Growth Factor Beta (TGF-beta) and IL-4 in Differentiating Macrophages 
Biomarker Insights  2008;3:39-44.
YKL-39 is a Glyco_18 domain containing chitinase-like protein which is currently recognized as a biomarker for the activation of chondrocytes and the progress of the osteoarthritis in human. YKL-39 was identified as an abundantly secreted protein in primary culture of human articular chondrocytes. Two biological activities of YKL-39 might contribute to the disease progression. One is the induction of autoimmune response and second is the participation in tissue remodeling. Other mammalian chitinase-like proteins including chitotriosidase, SI-CLP, YKL-40 and YM1 are expressed by macrophages in various pathological conditions. In contrast, YKL-39 was never reported to be produced by macrophages. We used in vitro model of human monocyte-derived macrophage differentiation to analyse regulation of YKL-39 expression. Expression of YKL-39 was examined by real-time RT-PCR. CD14+ MACS sorted human monocytes differentiated for 6 days under different stimulations including IFNγ, IL-4, dexamethasone and TGF-β. We found that both IL-4 and TGF-β have weak stimulatory effect on YKL-39 expression in all donors tested (3.2 ± 1.7 fold, p = 0.006 and 6.3 ± 3.1 fold, p = 0.014 respectively). However the combination of IL-4 and TGF-β had strong stimulatory effect on the expression of YKL-39 in all analysed individual macrophage cultures (34 ± 36 fold, p = 0.05). IFN-γ did not show statistically significant effect of YKL-39 mRNA expression. Presence of dexamethasone almost completely abolished the stimulatory effects of IL-4 and TGF-β. In summary, we show here for the first time, that human cells of monocyte origin are able to produce YKL-39. Maturation of monocyte derived macrophages in the presence of Th2 cytokine IL-4 and TGF-β leads to the strong activation of YKL-39 expression. Thus elevated levels of YKL-39 observed during chronic inflammations can not be attributed solely to the activity of chondrocytes. In perspective, YKL-39 might serve as a useful biomarker to detect macrophage-specific response in pathologies like tumour, atherosclerosis and Alzheimer disease.
PMCID: PMC2688341  PMID: 19578492
osteoarthritis; chitinase; YKL-39; macrophage; TGF-beta; IL-4
15.  Serum YKL-40 Levels and Chitotriosidase Activity in Patients with Beta-Thalassemia Major 
Disease Markers  2014;2014:965971.
Background. YKL-40 association with human disease has been the object of many years of investigation. β-thalassemia patients are affected by hepatic siderosis, which determines a fibrotic process and tissue remodelling. Chitotriosidase has been found to be increased in thalassemic patients returning to normal in patients submitted to bone marrow transplantation. YKL-40 is associated with macrophage activation in liver and in other tissues. The aim of the study was to analyse the level of serum YKL-40 and plasma chitotriosidase activity of patients with beta-thalassemia to assess whether their expression correlates with liver disease and degree of liver siderosis. Methods. Expression of YKL-40 and chitotriosidase as a marker of inflammation in 69 thalassemic patients were evaluated. We sought to investigate whether these two chitinases could be considered as a significant biomarker to evaluate therapy effectiveness. Results. Surprisingly we found normal value of YKL-40. We, also, analysed chitotriosidase activity in the same patients that was slightly increased as a consequence of macrophage activation. Conclusions. These data would suggest a good treatment for these patients.
doi:10.1155/2014/965971
PMCID: PMC3997983  PMID: 24808626
16.  YKL-40 tissue expression and plasma levels in patients with ovarian cancer 
BMC Cancer  2009;9:8.
Background
YKL-40 (chitinase-3-like-1) is a member of "mammalian chitinase-like proteins". The protein is expressed in many types of cancer cells and the highest plasma YKL-40 levels have been found in patients with metastatic disease, short recurrence/progression-free intervals, and short overall survival. The aim of the study was to determine the expression of YKL-40 in tumor tissue and plasma in patients with borderline ovarian tumor or epithelial ovarian cancer (OC), and investigate prognostic value of this marker.
Methods
YKL-40 protein expression was determined by immunohistochemistry in tissue arrays from 181 borderline tumors and 473 OC. Plasma YKL-40 was determined by ELISA in preoperative samples from 19 patients with borderline tumor and 76 OC patients.
Results
YKL-40 protein expression was found in cancer cells, tumor associated macrophages, neutrophils and mast cells. The tumor cell expression was higher in OC than in borderline tumors (p = 0.001), and associated with FIGO stage (p < 0.0001) and histological subtype (p = 0.0009). Positive YKL-40 expression (≥ 5% staining) was not associated with reduced survival. Plasma YKL-40 was also higher in patients with OC than in patients with borderline tumors (p < 0.0001), and it was positively correlated to serum CA-125 (p < 0.0001) and FIGO stage (p = 0.0001). Univariate Cox analysis of plasma YKL-40 showed association with overall survival (p < 0.0001). Multivariate Cox analysis, including plasma YKL-40, serum CA125, FIGO stage, age and radicality after primary surgery as variables, showed that elevated plasma YKL-40 was associated with a shorter survival (HR = 2.13, 95% CI: 1.40–3.25, p = 0.0004).
Conclusion
YKL-40 in OC tissue and plasma are related to stage and histology, but only plasma YKL-40 is a prognostic biomarker in patients with OC.
doi:10.1186/1471-2407-9-8
PMCID: PMC2645422  PMID: 19134206
17.  Association of Polymorphisms of the CHI3L1 Gene with Asthma and Atopy: A Populations-Based Study of 6514 Danish Adults 
PLoS ONE  2009;4(7):e6106.
Background
YKL-40 is a chitinase-like glycoprotein encoded by the chitinase 3-like 1 gene, CHI3L1, localized at chromosome 1q32.1. Increased levels of serum YKL-40 have been reported to be a biomarker for asthma and a reduced lung function. Interestingly, the C-allele of the -131 C→G (rs4950928) polymorphism of CHI3L1 has been shown to associate with bronchial hyperresponsiveness and reduced lung function suggesting that variations in CHI3L1 may influence risk of asthma. The objective of the present study was to investigate the association of common variation in the CHI3L1 locus with asthma, atopy and lung function in a large population-based sample of adults.
Methods/Principal Findings
Eleven single nucleotide polymorphisms (SNPs) of CHI3L1 including rs4950928 were genotyped in 6514 individuals. Asthma was defined as self-reported history of physician-diagnosed asthma. Total IgE and specific IgE to inhalant allergens were measured on serum samples. Lung function was measured by spirometry. Homozygosity of the rs4950928 G allele as compared to homozygosity of the C allele was associated with self-reported physician diagnosed asthma (OR 1.5 (95% CI, 1.00–2.26)) and with prevalence of atopic asthma (OR 1.93 (95% CI, 1.21–3.07)) after adjustment for age, sex, smoking status, socio-economic class and BMI. Carriers of rs883125 G allele had a significantly lower prevalence of atopy (OR 0.82 (CI, 0.72; 0.94)) as compared to homozygosity of the C allele. None of the SNPs examined were significantly associated with FEV1. However, two SNPs (rs10399931and rs4950930) appeared to be significantly associated with FEV1/FVC-ratio. Subgroup analyses of never-smokers did not consistently influence the associations in an either positively og negatively way.
Conclusions
In contrast to previous studies, the rs4950928 G allele, and not the C allele, was found to be associated with asthma. A few other SNPs of the CHI3L1 was found to be significantly associated with atopy and FEV1/FVC ratio, respectively. Thus, more studies seem warranted to establish the role of CHI3L1 gene in asthma and atopy.
doi:10.1371/journal.pone.0006106
PMCID: PMC2699472  PMID: 19568425
18.  The Chitinase and Chitinase-Like Proteins: A Review of Genetic and Functional Studies in Asthma and Immune-Mediated Diseases 
Purpose of Review
This review provides an overview of the chitinase and chitinase-like proteins, chitotriosidase (CHIT1), YKL-40, and acid mammalian chitinase (AMCase), and to summarize the genetic studies of asthma and immune mediated diseases with polymorphisms in the genes encoding these proteins: CHIT1, CHI3L1, and CHIA, respectively.
Recent Findings
Polymorphisms in the CHIT1, CHIA, and CHI3L1 genes influence chitotriosidase enzyme activity, AMCase activity, and YKL-40 levels, respectively. Regulatory SNPs in CHI3L1 were also associated with asthma, atopy, and immune-mediated diseases, and nonsynonymous SNPs in CHIA were associated with asthma. No CHIT1 polymorphisms, including a common nonfunctional 24-bp duplication allele, have been associated with asthma.
Summary
These genes represent novel asthma susceptibility genes. Variation in CHI3L1 and CHIA have been associated with asthma risk. Polymorphisms in CHIT1 have not yet been associated with asthma, but few studies have been reported. Given that chitotriosidase is the major chitinase in the airways and a common nonfunctional allele is present in many populations, additional studies of this gene are also warranted. Lastly, studies of all three genes need to be conducted in populations of diverse ancestries.
doi:10.1097/ACI.0b013e3283306533
PMCID: PMC3018778  PMID: 19644363
Chitotriosidase; CHIT1; YKL-40; CHI3L1; AMCase; CHIA
19.  Variation in CHI3LI in Relation to Type 2 Diabetes and Related Quantitative Traits 
PLoS ONE  2009;4(5):e5469.
Background
CHI3LI encoding the inflammatory glycoprotein YKL-40 is located on chromosome 1q32.1. YKL-40 is involved in inflammatory processes and patients with Type 2 Diabetes (T2D) have elevated circulating YKL-40 levels which correlate with their level of insulin resistance. Interestingly, it has been reported that rs10399931 (−329 G/A) of CHI3LI contributes to the inter-individual plasma YKL-40 levels in patients with sarcoidosis, and that rs4950928 (−131 C/G) is a susceptibility polymorphism for asthma and a decline in lung function. We hypothesized that single nucleotide polymorphisms (SNPs) or haplotypes thereof the CHI3LI locus might influence risk of T2D. The aim of the present study was to investigate the putative association between SNPs and haplotype blocks of CHI3LI and T2D and T2D related quantitative traits.
Methods/Principal Findings
Eleven SNPs of CHI3LI were genotyped in 6514 individuals from the Inter99 cohort and 2924 individuals from the outpatient clinic at Steno Diabetes Center. In cas-control studies a total of 2345 T2D patients and 5302 individuals with a normal glucose tolerance test were examined.
We found no association between rs10399931 (OR, 0.98 (CI, 0.88–1.10), p = 0.76), rs4950928 (0.98 (0.87–1.10), p = 0.68) or any of the other SNPs with T2D. Similarly, we found no significant association between any of the 11 tgSNPs and T2D related quantitative traits, all p>0.14. None of the identified haplotype blocks of CHI3LI showed any association with T2D, all p>0.16.
Conclusions/Significance
None of the examined SNPs or haplotype blocks of CHI3LI showed any association with T2D or T2D related quantitative traits. Estimates of insulin resistance and dysregulated glucose homeostasis in T2D do not seem to be accounted for by the examined variations of CHI3LI.
doi:10.1371/journal.pone.0005469
PMCID: PMC2674946  PMID: 19421404
20.  YKL-40—A Protein in the Field of Translational Medicine: A Role as a Biomarker in Cancer Patients? 
Cancers  2010;2(3):1453-1491.
YKL-40 is a 40 kDa glycoprotein produced by cancer cells, inflammatory cells and stem cells. It probably has a role in cell proliferation and differentiation, inflammation, protection against apoptosis, stimulation of angiogenesis, and regulation of extracellular tissue remodelling. Plasma levels of YKL-40 are often elevated in patients with localized or advanced cancer compared to age-matched healthy subjects. Several studies have demonstrated that high plasma YKL-40 is an independent prognostic biomarker of short survival in patients with different types of cancer. However, there is not yet sufficient data to support determination of plasma YKL-40 outside research projects as a biomarker for screening of gastrointestinal cancer and determination of treatment response and poor prognosis before or during treatment and follow-up. Plasma YKL-40 is also elevated in patients with other diseases than cancer, e.g., severe infections, cardiovascular disease, diabetes, chronic obstructive lung disease, asthma, liver fibrosis and rheumatoid arthritis. Co-morbidity should therefore always be considered in patients with cancer, since other sources than cancer cells can increase plasma YKL-40 levels. Future focused translational research projects combining basic and clinical research are needed in a joint effort to answer questions of the complex function and regulation of YKL-40 and the question if plasma YKL-40 is a clinical useful biomarker in patients with cancer.
doi:10.3390/cancers2031453
PMCID: PMC3837317  PMID: 24281168
biomarker; cancer; CHI3L1; inflammation; YKL-40; tissue remodelling
21.  Overexpression of YKL-40 Predicts Plaque Instability in Carotid Atherosclerosis with CagA-Positive Helicobacter Pylori Infection 
PLoS ONE  2013;8(4):e59996.
Objectives
YKL-40 has been demonstrated to be related to atherosclerosis, but its role in predicting plaque status and the outcome of carotid atherosclerosis (CAS) caused by CagA-positive helicobacter pylori remains unclear. This study was aimed to investigate the role of YKL-40 in predicting the outcome of carotid atherosclerosis with CagA-positive Helicobacter pylori infection.
Methods
The serum concentrations of YKL-40, C-reaction protein in 310 patients undergoing color Duplex assessment of carotid atherosclerosis were recorded and divided into 3 groups according to the infectious statuses of helicobacter pylori. We also examined serum YKL-40, C-reaction protein and the plaque morphology in animal model of carotid atherosclerosis with different types of helicobacter pylori infection.
Results
Overexpression of YKL-40 was only found in carotid atherosclerosis group with CagA-positive helicobacter pylori infection; C-reaction protein failed to distinguish different infectious statuses of helicobacter pylori infection. In patients with CagA-positive helicobacter pylori infection, elevated YKL-40 expression was accompanied by more severe clinical symptoms. We also confirmed similar findings in rabbit model of carotid atherosclerosis with CagA-positive helicobacter pylori infection. We found that in 7 rabbits treated with anti-helicobacter pylori therapy, the serum YKL-40 level decreased and the plaque became more stable.
Conclusion
Our findings suggested that increased serum YKL-40 level indicates plaque instability and more severe clinical symptoms of carotid atherosclerosis with CagA-positive helicobacter pylori infection. Compared with C-reaction protein, YKL-40 seems to be a more specific predictor of plaque status and outcome of carotid atherosclerosis with CagA-positive helicobacter pylori infection.
doi:10.1371/journal.pone.0059996
PMCID: PMC3616092  PMID: 23573226
22.  YKL-40 Expression in Traumatic Brain Injury: An Initial Analysis 
Journal of Neurotrauma  2010;27(7):1215-1223.
Abstract
YKL-40 (chitinase 3-like protein 1) is expressed in a broad spectrum of inflammatory conditions and cancers. We have previously reported that YKL-40 levels are elevated in the cerebrospinal fluid (CSF) of macaques and humans with lentiviral encephalitis, as well as multiple sclerosis (MS). The current study assessed temporal CSF YKL-40 levels in subjects with severe traumatic brain injury (TBI; Glasgow Coma Scale [GCS] score ≤8). We also evaluated temporal expression of YKL-40 after parasagittal controlled cortical impact (CCI) injury over the parietal cortex (2.8 mm deep, 4 m/sec). We demonstrate that CSF YKL-40 levels are elevated after acute TBI, and that YKL-40 levels are higher in patients who died following injury than in patients who survived. YKL-40 levels significantly correlate with CSF levels of inflammatory cytokines such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), as well as the inflammatory marker C-reactive protein (CRP). After CCI, in situ hybridization (ISH) showed that YKL-40 transcription is primarily associated with reactive astrocytes in pericontusional cortex. Tissue YKL-40 transcription time course analysis after CCI showed that YKL40 transcription in astrocytes began 1 day after injury, remained elevated for several days, and then declined by day 12. Similarly to our temporal CSF measurements in humans, YKL-40 induction after CCI is coincident with IL-1β expression. Taken together these findings demonstrate that YKL-40 is induced in astrocytes during acute neuroinflammation, is temporally related to inflammatory mediator expression, and may be a useful biomarker for understanding secondary injury and for patient prognosis.
doi:10.1089/neu.2010.1310
PMCID: PMC2942903  PMID: 20486806
chitinase; controlled cortical impact; cytokine; gliosis; neuroinflammation; traumatic brain injury; YKL-40
23.  The Association between Genetic Variations of CHI3L1, Levels of the Encoded Glycoprotein YKL-40 and the Lipid Profile in a Danish Population 
PLoS ONE  2012;7(10):e47094.
Background
The inflammatory biomarker YKL-40 seems to play a role in atherosclerosis and is elevated in patients with obesity, cardiovascular disease and type 2 diabetes. Single nucleotide polymorphisms (SNPs) of the YKL-40 encoding gene, CHI3L1, are associated with inter-individual YKL-40 levels. One study has described an association between a promoter polymorphism of CHI3L1 and levels of low density lipoprotein. The objective of this study was to evaluate the influence of YKL-40 on lipid parameters by determining the association between polymorphisms of CHI3L1, serum YKL-40 and levels of the differentiated lipid profile in a Danish general population.
Methodology/Principle Findings
12 SNPs of CHI3L1 were genotyped, and serum YKL-40 and parameters of the lipid profile were measured in 2,656 Danes. Lipid profile and genotypes were available in another Danish population (n = 6,784) for replication. Cholesterol and triglyceride levels increased with increasing YKL-40 quartile (both p<0.0001), and YKL-40 correlated with triglyceride levels (β = 0.15, p<0.0001). Low density lipoprotein levels increased slightly from the 1st to the 3rd quartile (p = 0.006). The highest YKL-40 quartile was associated with a greater risk of hypercholesterolemia compared to the lowest YKL-40 quartile (odds ratio 1.36, p = 0.009). Minor homozygosity of rs12123883 was associated with higher triglyceride levels (p = 0.022) and a higher prevalence of low high density lipoprotein (p = 0.012), but these associations could not be confirmed in the replication population.
Conclusions/Significance
Serum YKL-40 correlates with triglyceride levels in a representative group of the general Danish population. No consistent associations between SNPs of CHI3L1 and lipid levels could be documented.
doi:10.1371/journal.pone.0047094
PMCID: PMC3465269  PMID: 23071724
24.  Usefulness of Plasma YKL-40 in Management of Community-Acquired Pneumonia Severity in Patients 
Plasma YKL-40 level has been reported as playing a significant role in community-acquired pneumonia (CAP). However, the correlation between plasma level of YKL-40 and the severity of CAP has not been reported. This study identifies the relationship between plasma level changes of the YKL-40 gene in adult patients hospitalized with CAP. The ELISA was used to measure the plasma YKL-40 level from 61 adult CAP patients before and after antibiotic treatment and from 60 healthy controls. The plasma YKL-40 levels were significantly increased in patients with CAP compared to normal controls. Moreover, the plasma concentration of YKL-40 correlated with the severity of CAP based on the pneumonia severity index (PSI) score (r = 0.630, p < 0.001), the CURB-65 (confusion, uremia, respiratory rate, BP, age 65 years) score (r = 0.640, p < 0.001), the Acute Physiology And Chronic Health Evaluation II (APACHE II) score (r = 0.539, p < 0.001) and length of hospital stay (r = 0.321, p = 0.011), respectively. In conclusion, plasma YKL-40 may play a role in the diagnosis and clinical assessment of CAP severity, which could potentially guide the development of treatment strategies.
doi:10.3390/ijms141122817
PMCID: PMC3856092  PMID: 24256818
community-acquired pneumonia; YKL-40; severity
25.  Utility of Serum YKL-40 as a Tumor-Specific Marker of Hepatobiliary Malignancies 
Gut and Liver  2010;4(4):537-542.
Background/Aims
Serum YKL-40 has been linked to several human cancers. We investigated the potential role of serum YKL-40 as a marker of hepatobiliary malignancies.
Methods
Archived serum samples of patients undergoing liver transplantation evaluation at the Mayo Clinic Rochester were used to measure YKL-40 levels. Patients were divided into three groups: hepatocellular carcinoma (HCC), cholangiocarcinoma (CCA), and end-stage liver disease (ESLD) without malignancies. The Model for ESLD (MELD) score was used to quantify the severity of liver disease.
Results
The median serum YKL-40 level was highest in the ESLD group at 296 ng/mL, compared to 259 ng/mL in the HCC group and 80 ng/mL in the CCA group (p<0.01). There was a significant correlation between the MELD score and serum YKL-40 level (r=0.50, p<0.01). In a multivariate analysis, there was no significant difference in serum YKL-40 level between ESLD and HCC. CCA was associated with lower YKL-40 levels, a finding that was attributable to a lower prevalence of cirrhosis.
Conclusions
The serum YKL-40 level has little utility as a cross-sectional screening tool for hepatobiliary malignancies, namely HCC and CCA. The role of YKL-40 as a surveillance marker in the follow-up of individual patients remains to be determined.
doi:10.5009/gnl.2010.4.4.537
PMCID: PMC3021612  PMID: 21253305
Hepatocellular carcinoma; Cholangiocarcinoma; End stage liver disease; Model for end-stage liver disease; YKL-40

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