Evolution of mammalian chitinase(-like) members of family 18 glycosyl hydrolases

Triad of polar residues implicated in pH specificity of acidic mammalian chitinase

Acidic mammalian chitinase (AMCase) is a mammalian chitinase that has been implicated in allergic asthma. One of only two active mammalian chinases, AMCase, is distinguished from other chitinases by several unique features. Here, we present the novel structure of the AMCase catalytic domain, both in the apo form and in complex with the inhibitor methylallosamidin, determined to high resolution by X-ray crystallography. These results provide a structural basis for understanding some of the unique characteristics of this enzyme, including the low pH optimum and the preference for the beta-anomer of the substrate. A triad of polar residues in the second-shell is found to modulate the highly conserved chitinase active site. As a novel target for asthma therapy, structural details of AMCase activity will help guide the future design of specific and potent AMCase inhibitors.

Differential enzymatic activity of common haplotypic versions of the human acidic Mammalian chitinase protein

Mouse models have shown the importance of acidic mammalian chitinase activity in settings of chitin exposure and allergic inflammation. However, little is known regarding genetic regulation of AMCase enzymatic activity in human allergic diseases. Resequencing the AMCase gene exons we identified 8 non-synonymous single nucleotide polymorphisms including three novel variants (A290G, G296A, G339T) near the gene area coding for the enzyme active site, all in linkage disequilibrium. AMCase protein isoforms, encoded by two gene-wide haplotypes, and differentiated by these three single nucleotide polymorphisms, were recombinantly expressed and purified. Biochemical analysis revealed the isoform encoded by the variant haplotype displayed a distinct pH profile exhibiting greater retention of chitinase activity at acidic and basic pH values. Determination of absolute kinetic activity found the variant isoform encoded by the variant haplotype was 4-, 2.5-, and 10-fold more active than the wild type AMCase isoform at pH 2.2, 4.6, and 7.0, respectively. Modeling of the AMCase isoforms revealed positional changes in amino acids critical for both pH specificity and substrate binding. Genetic association analyses of AMCase haplotypes for asthma revealed significant protective associations between the variant haplotype in several asthma cohorts. The structural, kinetic, and genetic data regarding the AMCase isoforms are consistent with the Th2-priming effects of environmental chitin and a role for AMCase in negatively regulating this stimulus.

Increased chitotriosidase activity in serum of leprosy patients: association with bacillary leprosy

Human phagocyte-specific chitotriosidase is associated with several diseases involving macrophage activation. Since macrophage activation plays an important role in the control of Mycobacterium leprae infection, we studied the association of chitotriosidase with leprosy both in serum and in situ in lesional skin biopsies from patients. Serum samples from 78 Indonesian leprosy patients (39 non-reactional and 39 reactional leprosy patients) and 36 healthy controls (HC) from the same endemic region were investigated. The patients were classified as multibacillary (MB, n=69) or paucibacillary (PB, n=9) based on the bacterial index in slit-skin smears. Thirty-six of the reactional patients had erythema nodosum leprosum (ENL), while only 3 had reversal reaction (RR). Follow-up serum samples after corticosteroid treatment were also obtained from 17 patients with ENL and one with RR. Multibacillary (MB) patients showed increased chitotriosidase activity in serum as compared to paucibacillary (PB) patients and healthy controls. Although no significant difference was observed between reactional and the corresponding non-reactional groups, ENL showed significantly higher chitotriosidase activity as compared to HC. Furthermore, corticosteroid treatment resulted in significant decline of enzyme activity in ENL sera. Chitotriosidase activity correlated with levels of neopterin, another macrophage activation marker, but not with IL-6, IFN-gamma, TNF-alpha and IL-10. Immunohistochemical staining of 6 MB (LL=5, BL=1) lesional skin sections from stored material showed positive staining for chitotriosidase within lipid-laden macrophages suggesting that macrophages are the source of the enzyme detected in serum. Thus, serum chitotriosidase activity is potentially useful in distinguishing MB from PB leprosy and in monitoring response to therapy in ENL.

Chitinases and chitinase-like proteins: potential therapeutic targets for the treatment of T-helper type 2 allergies

Mammalian chitinase and chitinase-like proteins (CLPs) are a family of mediators increasingly associated with infection, T cell-mediated inflammation, wound healing, allergy and asthma. Although our current knowledge of the function of mammalian chitinases and CLPs is very limited, important information can be deduced from research carried out in lower organisms, and in different immunopathological conditions. Enzymatically active mammalian chitinase proteins may have evolved to degrade the copious amounts of chitin mammals are exposed to on a daily basis, and to form an innate barrier to chitin-containing organisms. CLPs are homologous to chitinases but lack the ability to degrade chitin. It is most striking that both chitinases and CLPs are up-regulated in T-helper type 2 (Th2)-driven conditions, and the first evidence is now emerging that these proteins may accentuate Th2 reactivity, and possibly contribute to the repair process that follows inflammation. Following studies demonstrating that chitinase inhibition leads to an attenuated allergic response, several strategies are being used to develop enzyme inhibitors for therapeutic use in human diseases. In this review, we will summarize recent insights into the effects of chitinases and CLPs in the context of Th2-dominated pathology with particular focus on allergy and asthma, discussing whether chitinase enzyme inhibitors may be of therapeutic value.

Identification and characterization of a chitinase-coding gene from Lamprey (Lampetra japonica) with a role in gonadal development and innate immunity

Chitinases (E.3.2.1.14) are ubiquitous hydrolases capable of cleaving the beta-1,4-glycosidic bonds in chitin polymers. The physiological significance of these enzymes in the development and immunity of various animals has recently been reported [Badariotti F, Thuau R, Lelong C, Dubos MP, Favrel P. Characterization of an atypical family 18 chitinase from the oyster Crassostrea gigas: evidence for a role in early development and immunity. Dev Comp Immunol 2007;31(6):559-70]. Lampreys are regarded as the most phylogenetically primitive species that may have an adaptive immune system. However, no chitinase gene has yet been identified in lamprey. We report here the identification and characterization of a chitinase-coding gene from the lamprey Lampetra japonica. The predicted amino acid sequence of the chitinase gene consisted of a typical catalytic domain and a peritrophin-A type chitin-binding domain. Real time RT-PCR analysis showed that the chitinase gene was expressed in various tissues of adult L. japonica, particularly in the liver, where a significant difference between male and female was observed during the pre-spawning period. A significant increase in expression was also observed in vivo following stimulation by bacteria or fungi. These findings seemed to suggest that in L. japonica, chitinase probably plays an important role in gonadal development as well as in innate immunity in response to invasion by microorganisms.

Elevated Plasma YKL-40 Predicts Increased Risk of Gastrointestinal Cancer and Decreased Survival After Any Cancer Diagnosis in the General Population

Purpose

Elevated plasma YKL-40 is a biomarker of poor prognosis in cancer patients. We tested the hypotheses that elevated plasma YKL-40 predicts risk of cancer as well as survival after a cancer diagnosis in the general population.

Patients and Methods

A prospective cohort study of 8,899 subjects (20 to 95 years) from the Danish general population, the Copenhagen City Heart Study, observed for 11 years for cancer incidence and 14 years for death: 1,432 participants had a first incident cancer, 968 of these died. Hazard ratios (HRs) for cancer events and death after events according to plasma YKL-40 in sex and 10 years age percentile categories: 0% to 33%, 34% to 66%, 67% to 90%, 91% to 95%, and 96% to 100%.

Results

The cumulative incidence of gastrointestinal cancer increased with increasing YKL-40 (trend P < .0001). Multifactorially adjusted HRs for gastrointestinal cancer were 1.0 (95% CI, 0.7 to 1.5) for YKL-40 in category 34% to 66%, 1.5 for 67% to 90% (95% CI, 1.0 to 2.3), 2.4 for 91% to 95%, (95% CI, 1.3 to 4.6), and 3.4 for 96% to 100% (95% CI, 1.9 to 6.1) versus YKL-40 category 0% to 33% (P < .0001). Participants with any cancer event and YKL-40 category 91% to 100% had a median survival time after the diagnosis of 1 year versus 4 years in participants with YKL-40 category 0% to 33% (P < .0001). Corresponding values for gastrointestinal cancer were 6 months versus 1 year (P = .007). Multifactorially adjusted HRs for early death were 1.8 (95% CI, 1.3 to 2.5; P < .0001) after any cancer and 2.4 (95% CI, 1.3 to 4.3; P = .005) after gastrointestinal cancer in participants with YKL-40 category 91% to 100% versus 0% to 33%.

Conclusion

In the general population, elevated plasma YKL-40 predicts increased risk of gastrointestinal cancer and decreased survival after any cancer diagnosis.

YKL-40 tissue expression and plasma levels in patients with ovarian cancer

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.

Plasma YKL-40: a BMI-independent marker of type 2 diabetes

OBJECTIVE

YKL-40 is produced by macrophages, and plasma YKL-40 is elevated in patients with diseases characterized by inflammation. In the present study, YKL-40 was examined in relation to obesity, inflammation, and type 2 diabetes.

RESEARCH DESIGN AND METHODS

Plasma YKL-40 and adipose tissue YKL-40 mRNA levels were investigated in 199 subjects who were divided into four groups depending on the presence or absence of type 2 diabetes and obesity. In addition, plasma YKL-40 was examined in healthy subjects during a hyperglycemic clamp, in which the plasma glucose level was kept at 15 mmol/l for 3 h, and during a hyperinsulinemic-euglycemic clamp.

RESULTS

Patients with type 2 diabetes had higher plasma YKL-40 (76.7 vs. 45.1 ng/ml, P = 0.0001) but not higher expression in adipose tissue YKL-40 mRNA (1.20 vs. 0.98, P = 0.2) compared with subjects with a normal glucose tolerance. Within the groups with normal glucose tolerance and type 2 diabetes, obesity subgroups showed no difference with respect to either plasma YKL-40 or adipose tissue YKL-40 mRNA levels. Multivariate regression analysis showed that plasma YKL-40 was associated with fasting plasma glucose (beta = 0.5, P = 0.0014) and plasma interleukin (IL)-6 (beta = 0.2, P = 0.0303). Plasma YKL-40 was not related to parameters of obesity. There were no changes in plasma YKL-40 in healthy subjects during either hyperglycemic or hyperinsulinemic-euglycemic clamps.

CONCLUSIONS

Plasma YKL-40 was identified as an obesity-independent marker of type 2 diabetes related to fasting plasma glucose and plasma IL-6 levels.

Chitotriosidase is the primary active chitinase in the human lung and is modulated by genotype and smoking habit

BACKGROUND

Chitinolytic enzymes play important roles in the pathophysiology of allergic airway responses in mouse models of asthma. Acidic mammalian chitinase (AMCase) and chitotriosidase (CHIT1) have chitinolytic activity, but relatively little is known about their expression in human asthma.

OBJECTIVE

We sought to determine the expression and activity of AMCase and CHIT1 in healthy subjects, subjects with asthma, and habitual smokers, taking account of the null 24-bp duplication in the CHIT1 gene.

METHODS

We measured chitinase activity in bronchoalveolar lavage (BAL) fluid at multiple pHs by using a synthetic chitin substrate. We also determined AMCase and CHIT1 gene expression in epithelial brushings and BAL fluid macrophages by means of real time RT-PCR. Paired DNA samples were genotyped for the CHIT1 duplication.

RESULTS

In all subgroups the pH profile of chitinase activity in BAL fluid matched that of CHIT1, but not AMCase, and chitinase activity was absent in subjects genetically deficient in active CHIT1. Although AMCase protein was detectable in lavage fluid, AMCase transcripts in macrophages were consistent with an isoform lacking enzymatic activity. Median chitinase activity in BAL fluid tended to be lower than normal in asthmatic subjects but was increased 7-fold in habitual smokers, where CHIT1 gene expression in macrophages was increased.

CONCLUSIONS

Chitinase activity in the lung is the result of CHIT1 activity. Although AMCase protein is detectable in the lung, our data indicate that it is inactive. Chitinase activity is not increased in subjects with asthma and in fact tends to be decreased. The high levels of chitinase activity in habitual smokers result from upregulation of CHIT1 gene expression, especially in macrophages.