Abstract
Osteoarthritis (OA) is a multifactorial disease that affects millions of Canadians. Although, there is not one specific mechanism that causes OA, the biological outcome is cartilage degradation. The articular cartilage in joints is composed primarily of the proteoglycan aggrecan and type II collagen (Col II) which together provide cartilage with functional properties. In OA, the imbalance of the anabolic and catabolic activities of chondrocytes favors cartilage catalysis. The main inflammatory cytokine involved in cartilage degradation is interleukin (IL) 1β. It has previously been demonstrated that Link N, a 16 residue peptide derived from proteolytic cleavage of link protein, can stimulate matrix proteins in normal cartilage and intervertebral discs (IVDs). Recently, we showed that a shorter sequence of Link N (sLink N), consisting of the first 8 residues of the peptide, has the potential to increase synthesis of matrix proteins in IVD cells in vitro and stimulate repair in ex vivo IVD organ culture. There are currently no treatments that actively repair cartilage in OA joints. In the present study, we aimed to evaluate the potential of sLink N as a therapeutic agent in the repair of OA cartilage.
OA cartilage was isolated from four donors undergoing total knee replacement (50–70 y). Cells were recovered from the cartilage of each knee by sequential digestion with Pronase followed by Collagenase, and expanded in PrimeGrowth culture medium (Wisent Bioproducts, Canada; Cat# 319–510-CL, −S1, and −S2). After 7 days in culture, cells were treated for 24h with sLink N (0.5, 5, 50, 500 or 5000 ng/ml) or sLink N in combination with IL-1β (1 ng/ml) to mimic an inflammatory milieu. Conditioned media was collected and measured for proteoglycan (GAG) release using the safranin O and for Col II synthesis by Western blotting. Human articular cartilage explants including cartilage with subchondral bone were prepared from the same donors using the PrimeGrowth Isolation kit (Wisent, Canada) and cultured for 21 days in presence of IL-1β (1ng/ml) and sLink N (0.5, 5, 50, 500 or 5000 ng/ml). Aggrecan and Col II were extracted with guanidine buffer and measured by Western blotting.
Treatment of OA chondrocytes significantly increased the GAG and Col II synthesis. The EC50 dose-response of sLink N on GAG synthesis was 67 ± 41 nM [65 ± 40 ng/ml] and the GAG synthesis reached a maximum of 194 ± 30% with the highest dose above control. When chondrocytes were cultured in the presence of IL-1β, GAG synthesis was also elevated by sLink N above control. Treatment of OA cartilage explants with sLink N increased the content of aggrecan and Col II even in the presence of IL-1β.
Our results suggest that sLink N is a growth factor supplement that can increase cartilage matrix protein synthesis, and a chondroprotective agent, by modulating the catabolic effects of IL-1β. sLink N is the first small-peptide to demonstrate potential in cartilage repair of OA joints.
