Background/Purpose: In osteoarthritis (OA), defects in cellular homeostasis, and in particular in autophagy, are evident and precede joint damage. We have shown that there is a defect in autophagy in OA human chondrocytes and cartilage. Indeed, pharmacological activation of autophagy protects against joint damage. Our working hypothesis is that joint damage in OA could be due to a failure of autophagy that can be detected in the blood and tissue of patients. Therefore,identifying biomarkers associated with autophagy defects could facilitate the development of personalized therapeutic strategies to prevent OA progression.

Methods: A comparative analysis of 35 autophagy genes was performed in blood from a Prospective OA Cohort of A Coruña (PROCOAC) of non-OA and knee OA patients. Non-OA patients (Age: 60,13 ± 6,16 years; BMI: 24,65 ± 3,30; Sex: Females/Males; N=30) and Knee OA patients (Age: 68,4 ± 6,07 years; BMI: 29,45 ± 2,86; Sex: Females/Males; N=30, OA grade III-IV) were profiled using PrimePCR autophagy human panel array and analysed using the PrimePCR analysis software (Bio-Rad). Confirmatory studies of the candidate genes were performed in blood and cartilage by using Taqman Technology and immunohistochemistry, respectively. A quantitative proteomic analysis of defective autophagy genes regulated upon deletion of Atg5 in human OA chondrocytes was performed by iTRAQ. Protein identification and quantification were performed using Protein Pilot Software 4.0. Each MS/MS spectrum was searched in the Uniprot/Swissprot database for Homo sapiens. Finally, to evaluate the functional consequences of autophagy defects on human chondrocyte homeostasis, pharmacological inhibition of candidate genes was done.

Results: 15 autophagy-related genes were downregulated in blood from knee OA patients compared to non-OA patients (p<0.05). No upregulation was found. although a trend towards upregulation was found for several genes involved in the mTOR signaling pathway. Importantly, key autophagy-related genes, including ATG16L2, ATG12, ATG4B and MAP1LC3B, involved in relevant process including initiating autophagy, phagophore extension and autophagosome formation, were significant downregulated in knee OA patients (p<0.05). Interestingly, HSP90AA1 and HSPA8, chaperone-mediated autophagy genes involved in stress response and protein folding, were significant downregulated (p<0.001). In addition, several regulators of autophagy and apoptosis, such as BNIP3, BCL-2 and BCL2L1 were downregulated (p<0.01). Confirmatory studies for MAP1LC3B and HSP90AA1, showed a significant downregulation (p<0.001) in blood and cartilage from knee OA patients. Remarkably, total proteome screening of human OA chondrocytes with defective autophagy, showed a significant reduction of HSP90AA1(p<0.05). Remarkably, pharmacological inhibition of HSP90 chaperone reduces chondrocyte homeostasis, suggesting that HSP90AA1 might be a potential biomarker associated with defective autophagy in OA.

Conclusion: We identified biomarkers of defective autophagy as a mechanism of central homeostasis, which gives us a general vision of the disease mechanisms linked to OA clinical reality.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/autophagy-related-molecules-detected-in-blood-and-cartilage-are-biomarkers-of-joint-damage-in-oa/