Targeting adipocyte ESRRA alleviates osteoarthritis via interrupting inter-organelle crosstalk of complement C3-CFD-MAC cascade.

Osteoarthritis is an aging-related systemic disease involving the crosstalk of multiple organs/tissues in metabolism and inflammation, yet little is known about the contribution of liver and marrow adipose tissue (MAT). Here we show that MAT-derived complement factor D (CFD) and component 3 (C3) derived from steatotic liver coordinately drive excessive alternative complement activation, resulting in cartilage damage in mice during aging and metabolic disorders. Mechanistically, estrogen-related receptor α (ESRRA) transcriptionally upregulates CFD responding to bone marrow adipocytes (BMAds) expansion. Inhibition of ESRRA/CFD signaling in BMAds blocks the chondrocyte senescence and catabolism triggered by C3 that is released from steatotic hepatocyte, interrupting C3-CFD-MAC cascade, thereby suppressing ERK1/2 phosphorylation and mitochondrial dysfunction. Adipocyte-specific ablation or pharmacological inhibition of ESRRA reduces CFD levels particularly in adipocyte-rich bone marrow, attenuating osteoarthritis progression in aged mice. Our findings highlight a key liver-MAT-cartilage axis bridged by C3-CFD-MAC pathway, raising the potential for adipocyte ESRRA-targeting therapies for aging-related metabolic osteoarthritis.