Background/Purpose: In osteoarthritis (OA) defects in Autophagy are evident and precede joint damage. 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: 61,44 ± 1,16 years; BMI: 25,25 ± 0,52; Females, n=18) and Knee OA patients (Age: 65,50 ± 1,05 years; BMI: 29,55 ± 0,67; Females, n=18, OA grade III-IV) were profiled using an autophagy gene expression array. Confirmatory studies of the candidate genes were performed in blood from Non-OA patients (Age: 60,13 ± 1,12 years; BMI: 24,85 ± 0,59; Sex: Females; n=30) and Knee-OA patients (Age: 68,4 ± 1,11 years; BMI: 29,65 ± 0,55; Females; n=30, OA grade III-IV) by using Taqman Technology. Moreover, the candidate gene was evaluated as a potential biomarker in human cartilage from Normal (n=19) and OA (n=20) patients and in both spontaneous aging (2, 6, 12, 18, and 30 months old, n=3/each time) and surgically-induced OA (10 weeks after surgery, n=4/each) in mice by immunohistochemistry. Remarkably, the consequences of candidate gene silencing on autophagy, FOXO signaling, inflammation, senescence, oxidative stress and cell death by apoptosis was investigated by gene expression and flow cytometry.

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 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). Confirmatory studies for MAP1LC3B and HSP90AA1, showed a significant downregulation (p< 0.001) in blood from knee OA patients. Remarkably, total proteome screening of human OA chondrocytes with defective autophagy, showed a significant reduction of HSP90AA1 (p< 0.05). Moreover, pharmacological inhibition of HSP90 chaperone reduces chondrocyte homeostasis.  Remarkably, HSP90AA1 expression was reduced in OA cartilage (p < 0.01) and in spontaneous aging and surgically-induced OA in mice (p< 0.05). Interestingly, HSP90AA1 silencing increased LC3 and FOXO1 expression (p < 0.01) and increased NFkB and p16 expression (p< 0.05) at 48h post-transfection. In addition, HSP90AA1 silencing increased cell death by apoptosis and mitochondrial ROS production 72h post-transfection (p < 0.05). These data indicate 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/hsp90aa1-a-chaperone-mediated-autophagy-mediator-is-a-biomarker-of-joint-damage-in-osteoarthritis/