TNF antagonist sensitizes synovial fibroblasts to ferroptotic cell death in collagen-induced arthritis mouse models

Abstract

Ferroptosis is a nonapoptotic cell death process that requires cellular iron and the accumulation of lipid peroxides. In progressive rheumatoid arthritis (RA), synovial fibroblasts proliferate abnormally in the presence of reactive oxygen species (ROS) and elevated lipid oxidation. Here we show, using a collagen-induced arthritis (CIA) mouse model, that imidazole ketone erastin (IKE), a ferroptosis inducer, decreases fibroblast numbers in the synovium. Data from single-cell RNA sequencing further identify two groups of fibroblasts that have distinct susceptibility to IKE-induced ferroptosis, with the ferroptosis-resistant fibroblasts associated with an increased TNF-related transcriptome. Mechanistically, TNF signaling promotes cystine uptake and biosynthesis of glutathione (GSH) to protect fibroblasts from ferroptosis. Lastly, low dose IKE together with etanercept, a TNF antagonist, induce ferroptosis in fibroblasts and attenuate arthritis progression in the CIA model. Our results thus imply that the combination of TNF inhibitors and ferroptosis inducers may serve as a potential candidate for RA therapy.

Ferroptosis and Autoimmune Diseases

“…Similarly, the increased expression levels of 8-OHdG and 4hydroxynonenal were observed in the inflamed joints of mice with collagen-induced arthritis (CIA). Moreover, increased iron levels in the synovial fluid of patients with RA correlated well with disease activity (81). Consistent with the notion that suppression of synovial fibroblast ferroptosis is one of the mechanisms involved in maintaining the inflammation status in joints, administration of the lipid peroxidation and ferroptosis inducer imidazole ketone erastin (IKE) resulted in a decrease in synovitis severity and prevented the development of arthritis and joint damage in CIA mice (81).…”

“…Consistent with the notion that suppression of synovial fibroblast ferroptosis is one of the mechanisms involved in maintaining the inflammation status in joints, administration of the lipid peroxidation and ferroptosis inducer imidazole ketone erastin (IKE) resulted in a decrease in synovitis severity and prevented the development of arthritis and joint damage in CIA mice (81). Experiments showed that IKE treatment selectively reduced the population of fibroblast activation protein-a (FAPa)-positive synovial fibroblasts that were undetectable under noninflammatory conditions but significantly increased in the inflamed synovium of CIA mice (81). Interestingly, treatment with the Gpx4 inhibitor RSL3 specifically increased cell death in fibroblast activation proteina (FAP)a+ fibroblasts but not in macrophages, endothelial cells, T cells or B cells (81).…”

“…Moreover, increased iron levels in the synovial fluid of patients with RA correlated well with disease activity (81). Consistent with the notion that suppression of synovial fibroblast ferroptosis is one of the mechanisms involved in maintaining the inflammation status in joints, administration of the lipid peroxidation and ferroptosis inducer imidazole ketone erastin (IKE) resulted in a decrease in synovitis severity and prevented the development of arthritis and joint damage in CIA mice (81). Experiments showed that IKE treatment selectively reduced the population of fibroblast activation protein-a (FAPa)-positive synovial fibroblasts that were undetectable under noninflammatory conditions but significantly increased in the inflamed synovium of CIA mice (81).…”

“…An assumption has indicated that oxidative stress-mediated ROS generation may be protective for synovial cells to proliferate in inflamed joints. Examination of the hallmarks of lipid peroxidation in synovial tissues revealed increased levels of the oxidative DNA damage biomarker 8-OHdG and the lipid peroxide 4-hydroxynonenal, an a,b-unsaturated hydroxyalkenal, in patients with RA compared to those in patients with osteoarthritis (OA) (81). Similarly, the increased expression levels of 8-OHdG and 4hydroxynonenal were observed in the inflamed joints of mice with collagen-induced arthritis (CIA).…”

“…Experiments showed that IKE treatment selectively reduced the population of fibroblast activation protein-a (FAPa)-positive synovial fibroblasts that were undetectable under noninflammatory conditions but significantly increased in the inflamed synovium of CIA mice (81). Interestingly, treatment with the Gpx4 inhibitor RSL3 specifically increased cell death in fibroblast activation proteina (FAP)a+ fibroblasts but not in macrophages, endothelial cells, T cells or B cells (81). The increased sensitivity to RSL-induced cell death in synovial fibroblasts prepared from inflamed synovial fluid compared to fibrocytes obtained from peripheral blood suggests that certain environmental factors inside inflamed joints are responsible for preventing synovial fibroblasts from undergoing ferroptosis and producing lipid ROS.…”