ASSESSING TRANSFERRIN RECEPTOR 2 FUNCTION IN INTESTINAL INFLAMMATION AND BONE LOSS DURING COLITIS
Osteopenia is a common complication of inflammatory bowel disease. Transferrin receptor 2 (Tfr2) is a major regulator of systemic iron levels, bone mass, and inflammation. Given iron's vital role in immunity and Tfr2's involvement in maintaining iron homeostasis, we hypothesize that Tfr2 deficiency impacts colonic inflammation progression and subsequent damage to bone tissue.
Twelve-week-old male Tfr2-deficient mice (Tfr2-/-) and wild-type (Tfr2+/+) littermates as well as mice lacking Tfr2 in myeloid cells (Tfr2fl/fl;LysMCre+) were analyzed for their susceptibility to experimental colitis. Colitis severity was assessed through changes in body weight, disease activity index (including stool consistency and bleeding), and colon length. Colon, serum, and bones were collected for qPCR, ELISA, flow cytometry, and µCT.
Colonic inflammation progressed more robustly in Tfr2-/- mice, characterized by significant colon shortening [1.5-, 1.2-fold; p<0.05], elevated colonic mRNA levels of Tnfa, Il1b, Il6, Nos2, Rankl/Opg [3-, 5-, 8-, 3.5, 2.5-fold; p<0.05], and increased infiltration of macrophages (F4/80+) and monocytes (Ly6C+) in the colon [2-, 2.2-fold; p<0.01] in comparison to Tfr2+/+ mice. Furthermore, colitic Tfr2-/- mice exhibited enhanced systemic bone loss, higher serum levels of TRAcP5b, along with lower P1NP [-7.9%, 1.4-, 1.5-fold; p<0.05] compared to colitic Tfr2+/+ mice. To assess iron burden contribution to colitis progression, we used Tfr2fl/fl;LysMCre+ mice with normal iron loading. These mice displayed increased disease development, substantial reduction in colon length, and increased bone loss [1.2-, 1.3-fold, -6.8%; p<0.05] compared to Cre- mice. Taken together, these findings underline a protective role of Tfr2 in the progression of colitis and colitis-induced bone loss.
Twelve-week-old male Tfr2-deficient mice (Tfr2-/-) and wild-type (Tfr2+/+) littermates as well as mice lacking Tfr2 in myeloid cells (Tfr2fl/fl;LysMCre+) were analyzed for their susceptibility to experimental colitis. Colitis severity was assessed through changes in body weight, disease activity index (including stool consistency and bleeding), and colon length. Colon, serum, and bones were collected for qPCR, ELISA, flow cytometry, and µCT.
Colonic inflammation progressed more robustly in Tfr2-/- mice, characterized by significant colon shortening [1.5-, 1.2-fold; p<0.05], elevated colonic mRNA levels of Tnfa, Il1b, Il6, Nos2, Rankl/Opg [3-, 5-, 8-, 3.5, 2.5-fold; p<0.05], and increased infiltration of macrophages (F4/80+) and monocytes (Ly6C+) in the colon [2-, 2.2-fold; p<0.01] in comparison to Tfr2+/+ mice. Furthermore, colitic Tfr2-/- mice exhibited enhanced systemic bone loss, higher serum levels of TRAcP5b, along with lower P1NP [-7.9%, 1.4-, 1.5-fold; p<0.05] compared to colitic Tfr2+/+ mice. To assess iron burden contribution to colitis progression, we used Tfr2fl/fl;LysMCre+ mice with normal iron loading. These mice displayed increased disease development, substantial reduction in colon length, and increased bone loss [1.2-, 1.3-fold, -6.8%; p<0.05] compared to Cre- mice. Taken together, these findings underline a protective role of Tfr2 in the progression of colitis and colitis-induced bone loss.