Reduced TGF‐<i>β</i> Expression and CD206‐Positive Resident Macrophages in the Intervertebral Discs of Aged Mice
Yuji Yokozeki, Ayumu Kawakubo, Masayuki Miyagi, Akiyoshi Kuroda, Hiroyuki Sekiguchi, Gen Inoue, Masashi Takaso, Kentaro Uchida
Abstract
Age is a key factor in intervertebral disc (IVD) degeneration; however, the changes that occur in IVDs with age are not fully understood. Tissue‐resident macrophages are critical for tissue homeostasis and are regulated by transforming growth factor‐ (TGF‐) β . We examined changes in the proportion of resident macrophages in young versus aged mice and the role of TGF‐ β in regulating resident macrophages in IVDs. IVDs were harvested from 4‐month (young) and 18‐month‐old (aged) C57BL/6J mice. The proportion of macrophages in IVDs was determined using flow cytometry ( n = 5 for each time point) and the expression of Cd11b , Cd206 , and Tgfb genes, which encode CD11b, CD206, and TGF‐ β protein, respectively, using real‐time PCR. To study the role of TGF‐ β in the polarization of resident macrophages, resident macrophages isolated from IVDs from young and aged mice were treated with recombinant TGF‐ β with and without a TGF‐ β inhibitor (SB431542). Additionally, SB431542 was intraperitoneally injected into young and aged mice, and Cd206 expression was examined using real‐time PCR ( n = 10 for each time point). The proportion of CD11b+ and CD11b+ CD206+ cells was significantly reduced in aged versus young mice, as was Cd11b , Cd206 , and Tgfb expression. TGF‐ β /IL10 stimulation significantly increased the expression of Cd206 , an M2 macrophage marker, in disc macrophages from both young and aged mice. Meanwhile, administration of a TGF‐ β inhibitor significantly reduced Cd206 expression compared to vehicle control in both groups. Conclusion . Resident macrophages decrease with age in IVDs, which may be associated with the concomitant decrease in TGF‐ β . Our findings provide new insight into the mechanisms of age‐related IVD pathology.