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Antiphospholipid syndrome (APS) is characterized by thrombus formation, poor pregnancy outcomes, and a proinflammatory response. H3K4me3‐related monocytes activation are key regulators of APS pathogenesis. Therefore, H3K4me3 CUT&Tag and ATAC‐seq are performed to examine the epigenetic profiles. The results indicate that the H3K4me3 signal and chromatin accessibility at the FOXJ2 promoter are enhanced in an in vitro monocyte model by stimulation with β2GPI/anti‐β2GPI, which mimics APS, and decreases after OICR‐9429 administration. Furthermore, FOXJ2 is highly expressed in patients with primary APS (PAPS) and is the highest in patients with triple‐positive antiphospholipid antibodies (aPLs). Mechanistically, FOXJ2 directly binds to the SLAMF8 promoter and activates SLAMF8 transcription. SLAMF8 further interacts with TREM1 to stimulate TLR4/NF‐κB signaling and prohibit autophagy. Knockdown of FOXJ2, SLAMF8, or TREM1 blocks TLR4/NF‐κB and provokes autophagy, subsequently inhibiting the release of inflammatory and thrombotic indicators. A mouse model of vascular APS is established via β2GPI intraperitoneal injection, and the results suggest that OICR‐9429 administration attenuates the inflammatory response and thrombus formation by inactivating FOXJ2/SLAMF8/TREM1 signaling. These findings highlight the overexpression of H3K4me3‐mediated FOXJ2 in APS, which consequently accelerates APS pathogenesis by triggering inflammation and thrombosis via boosting the SLAMF8/TREM1 axis. Therefore, OICR‐9429 is a promising candidate drug for APS therapy. [ABSTRACT FROM AUTHOR]

Background: Alterations of the trimethylation of histone 3 lysine 4 (H3K4me3) mark in monocytes are implicated in the development of autoimmune diseases. Therefore, the purpose of our study was to elucidate the role of H3K4me3‐mediated epigenetics in the pathogenesis of antiphospholipid syndrome (APS). Methods: H3K4me3 Cleavage Under Targets and Tagmentation and Assay for Transposase‐Accessible Chromatin were performed to determine the epigenetic profiles. Luciferase reporter assay, RNA immunoprecipitation, RNA pull‐down, co‐immunoprecipitation and chromatin immunoprecipitation were performed for mechanistic studies. Transmission electron microscopy and propidium iodide staining confirmed cell pyroptosis. Primary monocytes from patients with primary APS (PAPS) and healthy donors were utilised to test the levels of key molecules. A mouse model mimicked APS was constructed with beta2‐glycoprotein I (β2GPI) injection. Blood velocity was detected using murine Doppler ultrasound. Results: H3K4me3 signal and open chromatin at the ARID5B promoter were increased in an in vitro model of APS. The epigenetic factor ARID5B directly activated LINC01128 transcription at its promoter. LINC01128 promoted the formation of the BTF3/STAT3 complex to enhance STAT3 phosphorylation. Activated STAT3 interacted with the NLRP3 promoter and subsequently stimulated pyroptosis and apoptosis. ARID5B or BTF3 depletion compensated for LINC01128‐induced pyroptosis and apoptosis by inhibiting STAT3 phosphorylation. In mice with APS, β2GPI exposure elevated the levels of key proteins of pyroptosis and apoptosis pathways in bone marrow‐derived monocytes, reduced the blood velocity of the ascending aorta, increased the thrombus size of the carotid artery, and promoted the release of interleukin (IL)‐18, IL‐1β and tissue factor. Patients with PAPS had the high‐expressed ARID5B and LINC01128, especially those with triple positivity for antiphospholipid antibodies. Moreover, there was a positive correlation between ARID5B and LINC01128 expression. Conclusion: This study indicated that ARID5B/LINC01128 was synergistically upregulated in APS, and they aggravated disease pathogenesis by enhancing the formation of the BTF3/STAT3 complex and boosting p‐STAT3‐mediated pyroptosis and apoptosis, thereby providing candidate therapeutic targets for APS. Highlights: The H3K4me3 mark and chromatin accessibility at the ARID5B promoter are increased in vitro model mimicked APS.ARID5B‐mediated LINC01128 induces pyroptosis and apoptosis via p‐STAT3 by binding to BTF3.ARID5B is high‐ expressed in patients with primary APS and positively correlated with LINC01128 expression.OICR‐9429 treatment mitigates pyroptosis and related inflammation in vivo and in vitro models mimicked APS. [ABSTRACT FROM AUTHOR]