Role of macrophages in depot-dependent browning of white adipose tissue

Sympathetic stimulation induces beige adipocytes in white adipose tissue (WAT), known as browning of WAT. In this study, exposure of mice to cold ambient temperature (10 A degrees C) for 24 h induced the mRNA expression of uncoupling protein 1 (UCP1), a marker for beige adipocytes, in inguinal WAT, but not in perigonadal WAT. Thus, we examined the role of macrophages in depot-dependent WAT browning in mice. Flowcytometric analysis showed that total number of macrophages was higher in perigonadal WAT than in inguinal WAT. Cold exposure failed to change the expression of macrophage marker genes in inguinal WAT; however, it increased the mRNA expression of CD11c and tumor necrosis factor-alpha in perigonadal WAT, indicating that proinflammatory M1 macrophage is activated. The removal of macrophages using clodronate significantly enhanced cold-induced UCP1 mRNA expression in perigonadal WAT. These results suggest that M1 macrophages are involved in the phenotype of perigonadal WAT that hardly undergo browning.