Background/Purpose: We described an association between polymorphisms in the ANP32a gene and osteoarthritis. Osteoarthritis is one of the most common chronic musculoskeletal disorders and a cause of serious morbidity and disablement, particularly in the elderly population. Progressive damage to the articular cartilage and bone leads to pain and loss of joint function. The development of osteoarthritis is very complex and is influenced by both genetic and acquired or environmental risk factors. Anp32a(acidic leucine‐rich nuclear phosphoprotein 32 family member a) functions as a tumor suppressor gene and as a regulator of gene transcription, stabilization of RNA, intracellular transport and apoptosis. Moreover, Anp32a associates with Axin-1 and Phosphatase 2A, molecules that exert a regulating role in the Wingless-type signaling (Wnt) pathway, a signaling cascade with important roles in skeletal development, homeostasis and disease, including in osteoarthritis. But it remains unknown how Anp32a affects cartilage health and osteoarthritis.

Methods: ANP32A expression levels were determined in preserved and damaged areas of articular cartilage of patients with osteoarthritis (OA) by RNA sequencing. Different established mouse models for OA were induced in Anp32a^-/- mice. Genome-wide transcriptome analysis of the articular cartilage, comparing Anp32a^-/- mice to C57Bl/6 wild-type (WT) mice, was performed to understand how loss of Anp32a affects cartilage homeostasis at the molecular level. Chromatin immunoprecipitation-quantitative PCR (CHIP-qPCR) and siRNA-mediated silencing were performed in primary human articular chondrocytes. Detection of Atm and ROS was performed using immunohistochemical staining on mice knee sections of Anp32a^-/- and C57Bl/6 WT mice.

Results: We observed a significant decrease in ANP32A expression, in damaged areas of the cartilage of patients with OA, compared to non-damaged areas in the same patients. In the different OA mouse models, absence of Anp32a resulted in increased cartilage damage as compared to control animals. Transcriptome analysis identified Ataxia-telangiectasia-mutated (Atm) as a potential Anp32a effector gene. Indeed, Atm was highly downregulated in Anp32^-/- mice. Atm is a suppressor of reactive oxygen species (ROS), which are known to induce chondrocyte hypertrophy during endochondral ossification and in the onset of osteoarthritis. It is reported that the detrimental effects of Atm depletion on cartilage homeostasis can be reversed by inhibiting ROS with N-acetyl-cysteine (NAC). We treated our Anp32a^-/- mice in the DMM-induced OA model with NAC, via the drinking water. Effectively, this treatment ameliorated the cartilage damage observed in our Anp32a^-/- mice. CHIP-qPCR demonstrated that Anp32a binds to the Atm gene promoter and influences the recruitment of the RNA polymerase II transcription machinery.

Conclusion: We have demonstrated that Anp32a plays a relevant role in osteoarthritis, and identified Anp32a as an essential regulator of Atm and oxidative stress in cartilage. Our insights have therapeutic implications, as pharmacological blockade of ROS ameliorates osteoarthritis induced in Anp32a^-/- mice.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/anp32a-is-a-critical-regulator-of-oxidative-stress-in-cartilage-and-protects-against-osteoarthritis/