Objective To observe the inhibiting activities of fibronectin (FN) and citrullinated fibronectin (cFN) on disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4),and to explore the extracellular regulative mechanisms of ADAMTS-4.Methods FN was incubated with peptidylarginine deaminase type 4 (PADI4).Western blotting analysis was used to verify the citrullination of FN.The binding activity of FN and cFN to ADAMTS-4 were investigated by enzyme-linked immunosorbent assay (ELISA).The proteolytic ability of ADAMTS-4 after binding to FN and cFN were measured with the aggrecanase activity assay kit.One-way ANOVA,LSD-t test and t-test were used for statistical analysis.Results The immunosignal of citrulline was detected in FN after incubated with PADI4,but not in the absence of PADI4.A higher absorbance at 405 nm was detected when the full-length ADAMTS-4 protein was incubated with FN (2.182±0.042) than cFN (0.624±0.033; t=50.522,P＜0.01).Additionally,the recombinant ADAMTS-4 protein with a truncation at the C-terminus displayed low absorbance at 405 nm when the enzyme was incubated with both FN(0.971±0.024) and cFN(0.934±0.012; t=2.388,P＞0.05).Large amounts of ARGxx peptide were detected with full-length ADAMTS-4 in aggrecanase activity assay [(0.908±0.088) nmol/L],but significantly less when in the presence of FN and ADAMTS-4 [(0.573±0.000) nmol/L,P＜0.05].The production of this peptide was more when full-length ADAMTS-4 was incubated with cFN [(0.830±0.020) nmol/L,P＜0.05] than with FN.The reaction containing the truncated ADAMTS-4 without FN or cFN yielded the highest concentration of ARGxx peptide [(36.420±3.673) nmol/L],peptide production was not significantly altered when FN [(41.099±0.101) nmol/L] or eFN [(41.064±0.083) nmol/L] were added to the reaction.Conclusion FN could bind to ADAMTS-4 and inhibit its proteolytic activity.After citrullinated by PADI4,the binding activity of cFN is weakened and less inhibition to ADAMTS-4.

BACKGROUND:The shoulder joint,as a non-weight-bearing joint of the human upper limb,is considered a perfect compromise between flexibility and stability.The traditional experimental mechanics research of shoulder joints has some limitations due to the complexity of internal structure,measurement techniques and ethical issues.The finite element analysis method is applied to the research of shoulder joints,which provides valuable reference conclusions for the discussion of shoulder joint diseases and the decision of surgical methods. OBJECTIVE:To review the status of finite element research in the field of the shoulder joint,and to put forward the prospect of future research. METHODS:The finite element analysis method was used to search the literature on shoulder joint complex-related diseases in PubMed,Web of Science,WanFang and CNKI databases by computer.Chinese search terms were"shoulder joint,finite element analysis,rotator cuff injury,glenoid labrum,shoulder joint replacement".English search terms were"FE,should joint,glenohumeral joint,rotator cuff tears,glenoid labrum,shoulder arthroplasty".The search period was mainly from January 2010 to January 2023.Some important documents were also tracked,retrieved and read. RESULTS AND CONCLUSION:(1)With the open network of model data and the establishment of relevant model databases,finite element research has become more and more standardized and reproducible.(2)The widely validated finite element model of the shoulder joint deepens our understanding of the shoulder field to enable more efficient clinical decision-making.(3)With the continuous development of computer technology and software development,future finite element research is bound to become an indispensable practical tool for clinical scientific research.