Heparan Sulfate Deficiency in Cartilage: Enhanced BMP-Sensitivity, Proteoglycan Production and an Anti-Apoptotic...

Area of Science:

• Biomedical Engineering
• Musculoskeletal Biology
• Cellular Mechanobiology

Background:

• Osteoarthritis (OA) is a leading cause of global disability, characterized by cartilage degeneration and pain.
• Reduced heparan sulfate (HS) content has shown protective effects in OA animal models, but mechanisms are unclear.
• Understanding chondrocyte mechano-response in HS-deficient cartilage is crucial for developing novel OA therapies.

Purpose of the Study:

• To investigate if low HS content alters chondrocyte mechano-response to loading.
• To identify pathways involved in HS-related chondro-protection under mechanical stress.
• To explore the role of HS in regulating chondrocyte sensitivity to growth factors.

Main Methods:

• Generated HS-deficient engineered cartilage using rib chondrocytes from Exostosin 1 (Ext1) hypomorphic mice.
• Applied cyclic unconfined compression to engineered cartilage in a bioreactor.
• Analyzed molecular responses using transcriptome profiling, bioinformatics, and qPCR.

Main Results:

• HS-deficient chondrocytes exhibited enhanced response to BMP stimulation and increased GAG/DNA synthesis.
• Loading induced similar activation of ERK and P38 signaling in both HS-deficient and wildtype chondrocytes.
• HS-deficient cartilage showed a load-induced anti-apoptotic gene expression signature, including downregulation of Bnip3.

Conclusions:

• HS-deficiency enhances chondrocyte GAG production and BMP sensitivity.
• Reduced HS content confers an anti-apoptotic phenotype in chondrocytes following mechanical loading.
• These findings suggest HS-deficiency may protect cartilage from load-induced erosion, offering potential therapeutic targets for OA.