Ubiquitin-proteasome-dependent degradation of HIF-1α by cannabidiol disrupts pro-angiogenic synoviocyte-endothelial crosstalk in rheumatoid arthritis.

BACKGROUND: Cannabidiol (CBD), a major non-psychoactive phytocannabinoid derived from Cannabis sativa L., has shown therapeutic potential in rheumatoid arthritis (RA). However, the mechanisms by which CBD modulates synovial angiogenesis remain unclear.

PURPOSE: This study aimed to investigate whether CBD attenuates RA progression by suppressing synovial angiogenesis and to elucidate the underlying molecular mechanisms.

METHODS: An adjuvant-induced arthritis (AIA) rat model was established to evaluate the therapeutic effects of CBD in vivo using arthritis scoring, micro-CT, and histopathological, immunohistochemical, and immunofluorescence analyses. In vitro, cytotoxicity was determined using the CCK-8 assay, followed by evaluations of CBD's direct effects on the proliferation, migration, invasion, and inflammatory responses of RA fibroblast-like synoviocytes (RA-FLS) were evaluated, alongside Cell Counting Kit-8 (CCK-8) for cytotoxicity screening. Furthermore, the paracrine regulation of angiogenesis was assessed using a conditioned medium (CM) transfer system from hypoxia-stimulated RA-FLS applied to human umbilical vein endothelial cells (HUVECs). Molecular mechanisms were analyzed via Western blotting, RT-qPCR, ELISA, co-immunoprecipitation (Co-IP), molecular docking, and targeted proteasome inhibition (MG132).

RESULTS: In vivo, CBD (5 and 10 mg/kg) treatment markedly alleviated joint inflammation, synovial angiogenesis, and structural bone destruction in AIA rats. In vitro, non-cytotoxic concentrations of CBD (2.4-4.8 μM) significantly suppressed aberrant RA-FLS proliferation, migration, invasion, and pro-inflammatory cytokine secretion. Mechanistically, CBD abrogated the hypoxia-induced accumulation of hypoxia-inducible factor-1α (HIF-1α) protein in RA-FLS without significantly altering HIF1A mRNA expression. This reduction was effectively reversed by MG132. Co-IP and molecular docking analyses revealed that CBD directly enhances the polyubiquitination of HIF-1α through stable structural interactions, driving a ubiquitin-proteasome-dependent degradation mechanism. Consequently, CBD dose-dependently decreased the extracellular secretion of vascular endothelial growth factor A (VEGFA) and angiopoietin-2 (ANG-2) from RA-FLS. Functionally, CM from CBD-treated RA-FLS disrupted the pro-angiogenic paracrine crosstalk-independent of direct CBD carryover-significantly impairing HUVEC migration, capillary-like tube formation, and downstream VEGFR2 (Tyr1175) phosphorylation.

CONCLUSION: CBD attenuates RA pathogenesis not only by directly suppressing RA-FLS hyperactivity but also by severing the pro-angiogenic paracrine crosstalk between RA-FLS and endothelial cells. These effects are driven by the ubiquitin-proteasome-dependent degradation of HIF-1α in RA-FLS via direct structural engagement, which depletes VEGFA/ANG-2 production and subsequent endothelial VEGFR2 activation. These findings highlight CBD as a promising disease-modifying anti-angiogenic therapeutic agent for RA.