Hsp90 Inhibition Protects Against Biomechanically Induced Osteoarthritis in Rats

Abstract

Objective. Although articular cartilage has evolved to facilitate joint mobilization, severe loading can induce chondrocyte apoptosis, which is related to the progression of osteoarthritis (OA). To avoid apoptosis, chondrocytes synthesize heat-shock proteins (HSPs). This study was undertaken to examine the roles of Hsp70 and Hsp90 in biomechanically induced OA, and the possibility of using Hsp90 inhibition as an intervention strategy for OA management.Methods. OA was biomechanically induced in rats by means of strenuous running. Disease progression was compared between running rats treated with Hsp90 inhibitor and untreated running controls. Hsp70 and Hsp90 protein levels in articular cartilage were determined by Western blotting. OA progression was monitored using contrast-enhanced micro-computed tomography to measure cartilage degradation and subchondral bone changes and single-photon-emission computed tomography to examine synovial macrophage activation and histologic features.Results. Chronic cartilage loading led to early OA development, characterized by degeneration of cartilage extracellular matrix. In vivo Hsp90 inhibition resulted in increased Hsp70 synthesis, which suggests that Hsp90 activity limits Hsp70 production. Hsp90 inhibitor treatment increased cartilage sulfated glycosaminoglycan levels to concentrations even beyond baseline and protected against cartilage degradation, stimulated subchondral bone thickness, and suppressed macrophage activation.Conclusion. Our findings indicate that Hsp90 plays a pivotal role in biomechanically induced chondrocyte stress responses. Intervention strategies that inhibit Hsp90 can potentially protect or improve cartilage health and might prevent OA development.

Increased physical activity severely induces osteoarthritic changes in knee joints with papain induced sulfate-glycosaminoglycan depleted cartilage

“…Healthy cartilage, though, also shows a difference between medial and lateral cartilage, and attenuation values of medial cartilage were about 10% lower compared with lateral cartilage for both sedentary and running animals. This means that medial cartilage is likely to have more sGAG in the medial tibia compartment, which we also found in another study described previously [48]. Rats are known to put more weight on their medial compartment [49].…”

TGF-β2 is involved in the preservation of the chondrocyte phenotype under hypoxic conditions

“…Polypeptide concentration was determined using routine bicinchoninic acid (BCA) protein assay reagent (Thermo Fisher Scientific Inc., Rockford, IL) as described earlier (van der Windt et al, 2012) and immunoblotting was performed as described elsewhere by our group (Caron et al, 2013). Concisely, equal amounts of polypeptides were separated by routine SDS-PAGE, subsequently transferred by electro-blotting and detected on an Odyssey infrared imaging system (Li-Cor Biosciences) as described earlier (Siebelt et al, 2013), but using primary polyclonal goat anti-Col2a1, polyclonal rabbit anti-Sox9 (Caron et al, 2013) and mouse monoclonal anti-␤-tubulin (G-8; Santa Cruz Biotechnology Inc., Santa Cruz, CA) antibodies. For dot blot analyses, the pooled polypeptide fractions were spotted onto 0.45 m nitrocellulose membranes using a BioDot ® Apparatus (both: Bio-Rad, München, Germany) and processed as described above for Western blots, except that an anti-human TGF-␤2-specific antibody (Proteintech, Chicago, IL; 1:1000) was used.…”

The role of imaging in early hip OA

“…Chondrocytes are sensitive to mechanical stimuli and when exposed to high-peak forces, they can start to produce cytokines and enzymes that can degrade cartilage ECM 32 . Chronic cartilage loading through strenuous running induces clear cartilage sGAG loss 33 which is thought to result from pathological chondrocyte stress responses 34 . A loss of sGAG is considered one of the earliest hallmarks of OA, which happens well before OA is detected radiographically 35,36 .…”