Abstract
Osteoarthritis (OA) is the most common degenerative joint disease causing joint immobility and chronic pain. Treatment is mainly based on alleviating pain and reducing disease progression. During OA progression the chondrocyte undergoes a hypertrophic switch in which extracellular matrix (ECM) -degrading enzymes are released, actively degrading the ECM. However, cell biological based therapies to slow down or reverse this katabolic phenotype are still to be developed. Bone morphogenetic protein 7 (BMP-7) has been shown to have OA disease-modifying properties. BMP-7 suppresses the chondrocyte hypertrophic and katabolic phenotype and may be the first biological treatment to target the chondrocyte phenotype in OA. However, intra-articular use of BMP-7 is at risk in the proteolytic and hydrolytic joint-environment. Weekly intra-articular injections are necessary to maintain biological activity, a frequency unacceptable for clinical use. Additionally, production of GMP-grade BMP-7 is challenging and expensive. To enable its clinical use, we sought for BMP-7 mimicking peptides better compatible with the joint-environment while still biologically active and which potentially can be incorporated in a drug-delivery system. We hypothesized that human BMP-7 derived peptides are able to mimic the disease modifying properties of the full-length human BMP-7 protein on the OA chondrocyte phenotype.
A BMP-7 peptide library was synthesized consisting of overlapping 20-mer peptides with 18 amino-acids overlap between sequential peptides. OA human articular chondrocytes (HACs) were isolated from OA cartilage from total knee arthroplasty (n=18 donors). HACs were exposed to BMP-7 (1 nM) or BMP-7 library peptides at different concentrations (1, 10, 100 or 1000 nM). Gene-expression levels of important chondrogenic-, hypertrophic-, cartilage degrading- and inflammatory mediators were determined by RT-qPCR. GAG and ALP activity were determined using a colorimetric assay and PGE levels were measured by EIA.
During the BMP-7 peptide library screening human BMP-7 derived peptides were screened for their full-length human BMP-7 mimicking properties at different concentrations (1, 10, 100 or 1000nM) on a pool of human chondrocytes. Gene expression as well as GAG, ALP and PGE2 level analysis revealed two distinct peptide regions in the BMP-7 protein based on their pro-chondrogenic and anti-OA phenotype actions on human OA chondrocytes. The two most promising peptides were further analysed for their OA chondrocyte disease modifying properties in the presence of OA synovial fluid, showing similar OA phenotype suppressive activity.
Conclusively, we successfully identified two peptide regions in the BMP-7 protein with in vitro OA suppressive actions. Further biochemical fine-tuning of the peptides, and in vivo evaluation, will potentially result in the first peptide-based experimental OA treatment, addressing the hypertrophic and katabolic chondrocyte phenotype in OA.
