Investigating lubricin and known cartilage-based biomarkers of osteoarthritis

ABSTRACT

Introduction: Osteoarthritis (OA) is a degenerative disease which primarily affects hyaline cartilage, leading to pain, stiffness and loss of mobility of the entire articulation. Diagnosis is commonly based on symptoms and radiographs, but there is a growing interest in detecting novel biomarkers, in serum, urine and synovial fluid, which can be predictors of disease onset and progression.

Areas covered: This review provides an overview of the main biomarkers currently used in OA clinical practice, with a focus on lubricin, a surface glycoprotein secreted in the synovial fluid that lubricates the cartilage and reduces the coefficient of friction within the joint. Key findings of the last years are presented throughout the article.

Expert opinion: Analysis of biomarkers might suggest personalized protocols of treatment, guide the classification of OA phenotypes, contribute to precision medicine, avoid further unnecessary exams, facilitate drug discovery or refine treatment guidelines. For all these reasons, the investigation of novel cartilage-based biomarker of osteoarthritis needs to be promoted and improved.

KEYWORDS:

• Biomarkers
• cartilage
• lubricin
• osteoarthritis
• proteoglycans

Article Highlights

• Osteoarthritis (OA) affects articular cartilage and represents a worldwide burden, as the most common chronic disease of the joints. It progressively leads to pain, stiffness and swelling.

• Diagnosis of onset and progression, apart from traditional approaches (MRI, radiography, clinical symptoms), can be based on biomarkers detection in biological fluids.

• Biomarkers are extremely important to be monitored to evaluate the progression of OA and can be represented by molecules deriving from synthesis and degradation metabolisms of cartilage, bone, synovium, as well as inflammatory processes and genetic elements.

• Lubricin is a secreted glycoprotein (>200 kDa) encoded by the gene PRG4, which is responsible for lubrication of the joints during the movement. OA processes influence the presence of this molecule, usually by downregulating its expression.

• Further investigations are needed to improve the use of already known biomarkers. Application of omics techniques or system biology, in this field, is an opportunity to better understand the pathophysiology of OA and discover new biomarkers.

Declaration of Interest

The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Reviewers Disclosure

A reviewer on this manuscript has disclosed being a co-investigator of a patent application involving using Lubricin as a biological marker for joint degradation. Peer reviewers on this manuscript have no other relevant financial relationships or otherwise to disclose.

Additional information

Funding

This study was supported by the University Research Project Grant [Triennial Research Plan 2016–2018]; Department of Biomedical and Biotechnological Sciences [BIOMETEC], University of Catania, Italy.