Chronic intermittent hypobaric hypoxia ameliorates iron metabolism disorder through ferritinophagy in collagen-induced arthritis mice

Rheumatoid arthritis (RA) is a chronic inflammatory disease that is often complicated by anemia of chronic disease (ACD). Studies have shown that the development of ACD is closely related to iron metabolism disorder. Our previous studies have suggested that chronic intermittent hypobaric hypoxia (CIHH) treatment can improve iron metabolism disorder in obesity and metabolic syndrome rats. However, it is not known whether it affects the iron metabolism disorder caused by arthritis. Therefore, the aim of this study was to observe the effects of CIHH on erythrocyte index and iron metabolism in collagen-induced arthritis (CIA) mice model and to further explore the mechanism of ferritinophagy.

Eight-week-old male DBA/1 mice were randomly divided into four groups: control group (CON), chronic intermittent hypobaric hypoxia treatment group(CIHH, subjected to hypobaric hypoxia simulating 4000-m altitude for 35 days, 6 h daily), collagen-induced arthritis model group(CIA, injected intradermally in the tail with bovine type II collagen and complete Freund's adjuvant suspension), and CIA + CIHH group. During the experimental period, the body weights and joint scores of mice in each group were recorded every four days. A hematology analyzer was used to measure erythrocyte indexes (Red Blood Cell (RBC), Hemoglobin (Hb), Mean Corpuscular Volume (MCV), Mean Corpuscular Hemoglobin (MCH)); serum iron (SI) was measured by micrometry; enzyme-linked immunosorbent assay (ELISA) was used to measure serum ferritin (SF) and soluble transferrin receptor (sTfR); the pathologic and histologic changes of mice knee joints were observed by hematoxylin-eosin staining (HE); ferrous ion concentration was detected by ferrous ion colorimetric test kit; Western blot was applied to detect the iron metabolism (transferrin receptor (TfR), ferroportin1 (FPN1)), divalent metal-ion transporter-1 (DMT1), ferritin heavy chain1 (FTH1))and ferritinophagy indicator (nuclear receptor coactivator 4 (NCOA4)); the application of co-immunoprecipitation (CO-IP) was applied to detect the level of ferritinophagy flux (NCOA4/FTH1).

Compared with CON mice, CIA mice had significantly lower body weight, severer redness, swelling and deformation of joints, impaired erosion of bone tissues, lower erythrocyte indexes, increased hepatic iron deposition, disturbed iron metabolism parameters, in addition, the decreased expression of NCOA4 and ferritinophagy flux, which were all significantly improved after treatment with CIHH.

CIHH significantly ameliorated iron metabolism disorders in CIA mice, possibly by promoting NCOA4-mediated ferritinophagy and increasing iron release and export. This study provides new ideas for the prevention and adjuvant treatment of ACD.