Macrophage Infiltrates with High Levels of Toll-like Receptor 4 Expression in White Adipose Tissues of Male Chinese

Background And Aims: Macrophages and Toll-like receptor 4 (TLR4) are involved in the inflammatory process of adipogenesis. This study aimed to characterize macrophage infiltrates and the associated TLR4 expression in different locations of white adipose tissues (WAT) of male Chinese and determine their correlations to adipocyte hypertrophy and hyperplasia.

Methods And Results: A total of 30 men, who were lean, overweight or with type 2 diabetes (T2D), were recruited. Their abdominal omental WAT (oWAT) and subcutaneous WAT (scWAT) were obtained. The contents of macrophages in oWAT and scWAT were quantified using anti-CD68 staining. The levels of TLR4 expression were analyzed by western blot assays and the adipocyte size was quantified, followed by linear regression analysis. Significantly higher numbers of macrophages (24.4+/-3.2 vs 6.1+/-2.9, p<0.001), associated with higher levels of TLR4 expression (0.59+/-0.19 vs 0.20+/-0.03, p<0.001), were observed in oWAT, as compared with that in scWAT. Furthermore, the levels of macrophage infiltrates and TLR4 expression in oWAT of subjects who were overweight or/and have T2D were significantly higher than that in the lean group. The average adipocyte diameters and cross-sectional areas in oWAT of subjects who were overweight were significantly greater than those in the lean group (p=0.003 and p=0.04, respectively). Importantly, the numbers of macrophage infiltrates were positively correlated to the levels of TLR4 expression, the sizes of adipocytes, the levels of body mass index and C-reactive protein, respectively.

Conclusion: Our data suggest that macrophage-related TLR4 expression and inflammation contribute to the development of adipocyte hypertrophy in male Chinese.