Roles of MEPE-derived peptides, inflammation, and oxidative stress in chondrocyte hypertrophy and extracellular matrix mineralisation

Abstract

Osteoarthritis (OA) is an age-related degenerative whole joint disorder affecting > 9 million people in the UK. OA is characterised by progressive cartilage degradation, low-grade inflammation, chondrocyte hypertrophy and pathological extracellular matrix (ECM) mineralisation. The cellular mechanisms underlying chondrocyte dysfunction during disease onset and progression are not yet fully understood which contributes to the current lack of disease-modifying treatments for OA. This study explored how inflammatory cytokines, oxidative stress and peptides from Matrix Extracellular Phosphoglycoprotein (MEPE) affect chondrocyte phenotype and ECM regulation in healthy and mineralising conditions.
Chondrogenic ATDC5 cells were characterised from early chondrocyte differentiation through to hypertrophy and mineral deposition. Treatment withInterleukin-1β (IL-1β) induced a pro-inflammatory gene expression profile, downregulating key chondrogenic and matrix-related genes, indicative of cartilage degradation. Although IL-1β treatment resulted in profound transcriptional changes, these were not associated with increases in levels of reactive oxygen species (ROS)in the cells, indicating that the inflammatory pathways activated by IL-1β were independent of, and did not result in, increases in ROS.
The role of oxidative stress in influencing chondrocyte phenotype was further investigated by inducing oxidative stress in ATDC5 cells. Treatment with menadione significantly increased mineralisation of the ECM but did not alter deposition of glycosaminoglycans in the ECM. These findings suggest that redox imbalance may contribute to the pathological mineralisation of chondrocyte ECM, but not to matrix degradation.
Two bioactive peptides derived from MEPE, ASARM and AC-100, were previously shown to have beneficial effects on cartilage and joint structure respectively. A novel synthetic phosphomimetic version of ASARM was produced and shown to inhibit ECM mineralisation in a manner comparable to native phosphorylated ASARM. Furthermore, this novel peptide was also successfully produced as a recombinant fusion protein using a novel drug delivery platform with potential for delivery to arthritic joints in vivo.
The effects of AC-100 on osteoblasts have been demonstrated previously, but it’s effects on chondrocytes were investigated here for the first time. Treatment of ATDC5 chondrocytes with AC-100 resulted in upregulation of 13 genes and downregulation of 6 genes. Furthermore, phospho-kinase arrays revealed phosphorylation of various intracellular kinases in response to AC-100 suggesting activation of integrin signalling.
Overall, this study provides valuable insights into the roles of increased inflammation, oxidative stress and MEPE-derived peptides in influencing chondrocyte phenotype. The results presented here support a view of OA as a disease of failed phenotypic stability rather than one of aberrant inflammation and degeneration.

Date of Award	Jul 2026
Original language	English
Awarding Institution	University of Brighton
Supervisor	Lisa Mullen (Supervisor), Katherine Staines (Supervisor) & Fabio Simoes (Supervisor)