Chitinase-3-like protein 1 (CHI3L1), also known as YKL-40, is a secreted glycoprotein that is approximately 40kDa in size that in humans is encoded by the CHI3L1 gene. [5] [6] [7] The name YKL-40 is derived from the three N-terminal amino acids present on the secreted form and its molecular mass. YKL-40 is expressed and secreted by various cell-types including macrophages, chondrocytes, fibroblast-like synovial cells, vascular smooth muscle cells, and hepatic stellate cells. The biological function of YKL-40 is unclear. It is not known to have a specific receptor. Its pattern of expression is associated with pathogenic processes related to inflammation, extracellular tissue remodeling, fibrosis and solid carcinomas [8] and asthma. [9]
Chitinases catalyze the hydrolysis of chitin, which is an abundant glycopolymer found in insect exoskeletons and fungal cell walls. The glycoside hydrolase 18 family of chitinases includes eight human family members. This gene encodes a glycoprotein member of the glycosyl hydrolase 18 family. The protein lacks chitinase activity and is secreted by activated macrophages, chondrocytes, neutrophils and synovial cells. The protein is thought to play a role in the process of inflammation and tissue remodeling. [7] YKL-40 lacks chitinase activity due to mutations within the active site (conserved sequence: DXXDXDXE; YKL-40 sequence: DGLDLAWL). [8]
YKL-40 has been linked to activation of the AKT pro-survival (anti-apoptotic) signaling pathway. YKL-40 promotes angiogenesis through VEGF-dependent and independent pathways. [10]
YKL-40 is a migration factor for primary astrocytes and its expression is controlled by NFI-X3, STAT3, and AP-1. [11]
CHI3l1 is induced by a variety of cancers and in the presence of semaphorin 7A (protein) can inhibit multiple anti-tumor immune system responses. Activating an antiviral immune pathway known as the RIG-like helicase (RLH) has the ability to counter CHI3l1 induction. Cancer cells can offset RLH by stimulating NLRX1. Poly(I:C), an RNA-like molecule, can stimulate RLH activation. RLH activation can also inhibit the expression of receptor IL-13Rα2 and pulmonary metastasis. It stores NK cell accumulation and activation. It augments the expression of IFN-α/β, chemerin and its receptor ChemR23, p-cofilin, LIMK2 and PTEN and inhibiting BRAF and NLRX1 in a MAVS-dependent manner. [12]
It is assumed that YKL-40 plays a role in cancer cell proliferation, survival, invasiveness and in the regulation of cell-matrix interactions. It is suggested that YKL-40 is a marker associated with a poorer clinical outcome in genetically defined subgroups of different tumors. YKL-40 was recently introduced into (restricted) clinical practice. A few techniques are available for its detection. [8]
YKL-40 is a Th2 promoting cytokine that is present at high levels in the tumor microenvironment and in the serum of cancer patients. [13] [14] Elevated levels of YKL-40 correlate strongly with stage and outcome of various types of cancer, which establish YKL-40 as a biomarker of disease severity. [15] Targeting YKL-40 with neutralizing antibodies is effective as a treatment in animal models of glioblastoma multiforme. [16]
YKL-40 also enhances tumor survival in response to gamma-irradiation. [10]
As Alzheimer's disease progresses, soluble amyloid beta aggregates in the brain can induce the activation of microglia, which triggers synthesis of pro-inflammatory mediators. [17] This leads to increased Chi3l1 expression in astrocytes. [17] There is evidence that YKL-40 levels are elevated in Alzheimer's patients compared to cognitively normal individuals. [17] Elevated levels of YKL-40 mRNA were found in Alzheimer's-inflicted brains in comparison with normal controls. [17] Additionally, YKL-40 is correlated other dementia biomarkers, such as tau proteins and amyloid beta. [17] YKL-40 is being examined as a novel Alzheimer's biomarker quantified in the cerebrospinal fluid or blood. [18]
In Huntington's disease YKL-40 has an increasing trend in cerebrospinal fluid in the later disease stages and correlates highly with symptom severity. [19] [20]
Chitinases are hydrolytic enzymes that break down glycosidic bonds in chitin. They catalyse the following reaction:
In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide structural and biochemical support to surrounding cells. Because multicellularity evolved independently in different multicellular lineages, the composition of ECM varies between multicellular structures; however, cell adhesion, cell-to-cell communication and differentiation are common functions of the ECM.
Synovial fluid, also called synovia,[help 1] is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its egg white–like consistency, the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement. Synovial fluid is a small component of the transcellular fluid component of extracellular fluid.
Bone morphogenetic protein 6 is a protein that in humans is encoded by the BMP6 gene.
Osteonectin (ON) also known as secreted protein acidic and rich in cysteine (SPARC) or basement-membrane protein 40 (BM-40) is a protein that in humans is encoded by the SPARC gene.
Pseudoachondroplasia is an inherited disorder of bone growth. It is a genetic autosomal dominant disorder. It is generally not discovered until 2–3 years of age, since growth is normal at first. Pseudoachondroplasia is usually first detected by a drop of linear growth in contrast to peers, a waddling gait or arising lower limb deformities.
Aggrecan (ACAN), also known as cartilage-specific proteoglycan core protein (CSPCP) or chondroitin sulfate proteoglycan 1, is a protein that in humans is encoded by the ACAN gene. This gene is a member of the lectican (chondroitin sulfate proteoglycan) family. The encoded protein is an integral part of the extracellular matrix in cartilagenous tissue and it withstands compression in cartilage.
Lysosome-associated membrane protein 2 (LAMP2), also known as CD107b and Mac-3, is a human gene. Its protein, LAMP2, is one of the lysosome-associated membrane glycoproteins.
alpha-2-HS-glycoprotein also known as fetuin-A is a protein that in humans is encoded by the AHSG gene. Fetuin-A belongs to the fetuin class of plasma binding proteins and is more abundant in fetal than adult blood.
Lysosomal-associated membrane protein 1 (LAMP-1) also known as lysosome-associated membrane glycoprotein 1 and CD107a, is a protein that in humans is encoded by the LAMP1 gene. The human LAMP1 gene is located on the long arm (q) of chromosome 13 at region 3, band 4 (13q34).
Proteoglycan 4 or lubricin is a proteoglycan that in humans is encoded by the PRG4 gene. It acts as a joint/boundary lubricant.
Cartilage intermediate layer protein 1 is a protein that in humans is encoded by the CILP gene.
Fibromodulin is a protein that in humans is encoded by the FMOD gene.
Interleukin 17 receptor A, also known as IL17RA and CDw217, is a human gene.
Leucine-rich alpha-2-glycoprotein 1 is a protein which in humans is encoded by the gene LRG1.
Chondromodulin-1 is a protein that in humans is encoded by the LECT1 gene.
Secretomics is a type of proteomics which involves the analysis of the secretome—all the secreted proteins of a cell, tissue or organism. Secreted proteins are involved in a variety of physiological processes, including cell signaling and matrix remodeling, but are also integral to invasion and metastasis of malignant cells. Secretomics has thus been especially important in the discovery of biomarkers for cancer and understanding molecular basis of pathogenesis. The analysis of the insoluble fraction of the secretome has been termed matrisomics.
Gene therapy is being studied as a treatment for osteoarthritis (OA). Unlike pharmacological treatments which are administered systemically, gene therapy aims to establish sustained, synthesis of gene products and tissue rehabilitation within the joint.
Thymidine kinase is an enzyme, a phosphotransferase : 2'-deoxythymidine kinase, ATP-thymidine 5'-phosphotransferase, EC 2.7.1.21 that catalyzes the reaction:
MFAP4 is an extracellular matrix protein encoded by the MFAP4 gene. It is part of the MFAP family of proteoglycans, which are involved in cell adhesion, intercellular interactions and the assembly and/or maintenance of elastic fibres.
This article incorporates text from the United States National Library of Medicine, which is in the public domain.