Low Macrophage Accumulation in Skeletal Muscle of Obese Type 2 Diabetics and Elderly Subjects

In addition to adipose tissue, recent studies suggest that skeletal muscle may also be a source of low‐grade inflammation, particularly in inactive and/or overweight individuals. The aim of this study was to examine the presence of macrophages in skeletal muscle from obese subjects with type 2 diabetes (T2D) before and after a 9‐month exercise program (vs. a non‐exercising control group) (Study 1) and in young vs. elderly subjects (Study 2). In both studies, CD68 + macrophages in vastus lateralis biopsies were determined by immunohistochemistry and inflammation gene expression measured. Macrophage content (%) was calculated by the number of macrophages per 100 muscle fibers. In Study 1, we found relatively low numbers (2–3%) of CD68 + macrophages in skeletal muscle in obese T2D subjects (BMI = 37.3 ± 5.2 kg/m 2 ), which were unchanged after a 9‐month exercise program ( P = 0.42). Similarly, in Study 2 (BMI = 27.1 ± 2.5 kg/m 2 ), CD68 + macrophages were relatively low in muscle (4–5%) and were not different between young and elderly individuals ( P = 0.42). However, elderly subjects had twofold higher CD68 and CD206 gene expression (both P < 0.002) than young participants. In both studies, CD68 + muscle macrophages were not associated with BMI. In conclusion, we found little evidence of macrophage accumulation in skeletal muscle in obese T2D subjects or in elderly individuals. A 9‐month exercise program was not associated with a decrease in macrophage content.