High Expression Of Chitinase-3-like Protein-1 (YKL-40) Promotes Choroidal Neovascularization Through MAPK Signaling Pathway

Background:Age-related macular degeneration(AMD)is the dominant eye disease that causes irreversible visual impairment and blindness in elder population in the world,the incidence of which increases with age.According to the clinical guideline of 2016 Ophthalmology,AMD can be divided into early stage,progressing stage and advanced stage.Moreover,on the basis of pathological characteristics,advanced stage AMD is divided into two categories:dry and wet.The formation of choroidal neovascularization is a characteristic change of wet AMD,and it is the principal reason for the loss of vision.However,the specific molecular mechanism of the formation of CNV remains poorly understood,and there is a lack of long-term and effective treatment for wet AMD.Therefore,it is of importance to find new therapeutic target for wet AMD.The chitinase-3-like protein-1(YKL-40),also known as human cartilage glycoprotein 39(human cartilage glycoprotein-39,HC-gp39),is a secretory protein that can be secreted by macrophages,neutrophils and vascular smooth muscle cells.Rakic has reported that YKL-40 is expressed in normal human retina and is highly expressed in CNV tissues of patients,and estrogen can reduce the expression level of YKL-40 in mice.It is reported that YKL-40 is highly expressed in various types of tumors and plays a vital role in angiogenesis by stimulating the migration and recombination of vascular endothelial cells,while anti YKL-40 neutralizing antibody exerts an inhibitory effect on the growth of tumor and the formation of neovascularization.In addition,YKL-40 may also participate in the process of acute and chronic inflammatory reactions.Based on the aforementioned background,the following aspects areinvestigated in our present study:(1)What is the expression level of YKL-40 in serum in patients with wet age-related macular degeneration?(2)Whether YKL-40 is involved in the formation of CNV in the laser-induced mouse choroidal neovascularization model?(3)The possible molecular mechanism of YKL-40 in the formation of CNV.We aim to provide new evidence for discovering new therapeutic target to protect against wet AMD.Purpose:The purpose of this study is to explore the expression and significance of YKL-40 in serum of patients with wet AMD and to investigate the role and possible molecular mechanism of YKL-40 in the formation of CNV in mice.Methods:45 hospitalized patients diagnosed as wet AMD in our department of Ophthalmology and 20 healthy volunteers as control group were included.The name,gender,age,current medical history,family history and other medical history data were collected.The venous blood of the subjects was collected.After centrifugation,the supernatants were collected.The levels of YKL-40 and VEGF in serum were detected by enzyme-linked immunosorbent assay(ELISA).The choroidal neovascularization models were induced by 532 nm laser photocoagulation in C57BL/6J mice,and no photocoagulation was performed in group Control.2x10~6 FITC-dextran fluorescein was perfused in group Day 7 and Day 14.The CNV model was identified by RPE/choroidal flatmount and HE staining.The mRNA levels of YKL-40 and VEGF in neuroretina and RPE/choroid complex were analyzed by real-time PCR.The localization and expression of YKL-40 in eyes were determined by immunofluorescence staining.The protein expressions of each group were evaluated by Western blot.Results:The expression levels of YKL-40 and VEGF in wet AMD patients were significantly higher than that in the control group,and the differences were statistically significant.The mRNA levels of YKL-40 and VEGF were significantly higher in group Day 7 both in neuroretina and RPE/choroid complex and in group Day 14 in RPE/choroid complex(P<0.05).Meanwhile,the protein levels of YKL-40,VEGF and p-ERK1/2 increased significantly.Furthermore,the results of immunofluorescence staining showed that YKL-40 was mainly expressed in the retinal ganglion cell layer,inner plexiform layer and inner nuclear layer of mice induced by laser and the expressions of YKL-40 after photocoagulation.Conclusions:The high expression level of YKL-40 correlates with VEGF positively in serum,suggesting that YKL-40 is closely related to the pathogenesis and development of wet AMD.The high expression of YKL-40 after laser induction may increase the phosphorylation level of ERK1/2,activating MAPK pathway to promote choroidal neovascularization.Accordingly,YKL-40 may provide a novel diagnostic and therapeutic strategy for wet AMD.