Patient-responsive protein biomarkers for cartilage degeneration and repair identified in the infrapatellar fat pad

Cartilage defects (CDs) are regarded as early manifestation of osteoarthritis (OA). The infrapatellar fat pad (IPFP) is an important mediator in maintaining joint homeostasis, disease progression and tissue repair, with a crucial role of its secreted proteins. Here, we investigate the proteome of the IPFP in relation to clinical status and response to surgical treatment of CDs.
In order to characterize the proteome of the IPFP, samples from a cohort of 53 patients who received surgical treatment for knee CDs were analyzed with label-free proteomics. Patients were divided based on validated outcome scores for pain and knee function, preoperatively and at 1-year postoperatively, and on MRI assessment of the defect severity, fibrosis and synovitis.
Specific proteins were differentially abundant in patients with MRI features and better clinical outcome after CD surgery, including a downregulation of cartilage intermediate layer protein 2 (CILP-2) and microsomal glutathione s-transferase 1 (MGST1), and an upregulation of aggrecan (ACAN), and proteoglycan 4 (PRG4). Pathways related to cell interaction, oxidation and matrix remodeling were altered.
Proteins in the IPFP that have a function in extracellular matrix, inflammation and immunomodulation were identified as potentially relevant markers for cartilage repair monitoring.