Qingre Huoxue decoction and its active compound Quercetin modulate bone remodeling by inhibiting ATF4 hyperactivation to attenuate bone erosion in rheumatoid arthritis

Background: Rheumatoid arthritis (RA) is characterized by synovial inflammation and bone erosion driven by osteoblast-osteoclast imbalance. Qingre Huoxue decoction (QRHXD), a traditional Chinese medicine, alleviates RA symptoms, yet its mechanism in mitigating bone erosion remains unclear. Methods: Network pharmacology identified active compounds and targets of QRHXD. Collagen-induced arthritis (CIA) rats were treated with QRHXD or Methotrexate. Arthritis severity (HE staining), bone microstructure (X-ray micro-CT), osteoblast/osteoclast markers (RT-qPCR, TRAP staining), and ATF4 expression (Western blot, immunofluorescence staining) were assessed. Primary osteoblasts from CIA rats were treated with QRHXD or its active compound to validate ATF4 modulation. Results: QRHXD reduced joint swelling, arthritis scores, and bone loss in CIA rats, restoring trabecular parameters (Tb.N, Tb.Th, BV/TV) and suppressing bone resorption markers (TRAP, CTX-1, RANKL). Moreover, the number of osteoclast was significantly reduced. Protein interaction analysis highlighted ATF4 as a core regulator of bone remodeling and potentially regulated by the active compound Quercetin in QRHXD. Both QRHXD and Quercetin inhibited ATF4 hyperactivation in CIA osteoblasts, rebalancing RUNX2 and RANKL expression, with Quercetin showing greater efficacy. Molecular docking further exhibited strong binding affinity between Quercetin and the ATF4-regulating transcription factors RAD21, CBFB and HDAC2. Conclusion: QRHXD attenuates bone erosion in RA by inhibiting ATF4 hyperactivation via Quercetin, restoring osteoblast-osteoclast crosstalk.