Macrophage content in subcutaneous adipose tissue: associations with adiposity, age, inflammatory markers, and whole-body insulin action in healthy Pima Indians

Abstract

Objective: In severely obese individuals and patients with diabetes, accumulation and activation of macrophages in adipose tissue has been implicated in the development of obesity-associated complications, including insulin resistance. We sought to determine whether in a healthy population, adiposity, sex, age, or insulin action is associated with adipose tissue macrophage content (ATMc) and/or markers of macrophage activation.

Research design and methods: Subcutaneous ATMc from young adult Pima Indians with a wide range of adiposity (13-46% body fat, by whole-body dual-energy X-ray absorptiometry) and insulin action (glucose disposal rate 1.6-9 mg/kg estimated metabolic body size/min, by glucose clamp) were measured. We also measured expression in adipose tissue of factors implicated in macrophage recruitment and activation to determine any association with ATMc and insulin action.

Results: ATMc, as assessed by immunohistochemistry (Mphi) and by macrophage-specific gene expression (CD68, CD11b, and CSF1R), were correlated with percent body fat, age, and female sex. Gene expression of CD68, CD11b, and CSF1R but not Mphi was correlated negatively with glucose disposal rate but not after adjustment for percent body fat, age, and sex. However, adipose tissue expression of plasminogen activator inhibitor type-1 (PAI-1) and CD11 antigen-like family member C (CD11c), markers produced by macrophages, were negatively correlated with adjusted glucose disposal rate (r = -0.28, P = 0.05 and r = -0.31, P = 0.03).

Conclusions: ATMc is correlated with age and adiposity but not with insulin action independent of adiposity in healthy human subjects. However, PAI-1 and CD11c expression are independent predictors of insulin action, indicating a possible role for adipose tissue macrophage activation.

FIG. 1.

Associations of adiposity with fraction of CD68⁺ cells (A) and mRNA expression of macrophage markers (B, CD68 expression [AU, ln]; C, CSF1R expression; D, CD11b expression). Simple correlation coefficients and P values for associations are given. , men; •, women. Fraction of CD68⁺ cells was available in 46 individuals (31 men and 15 women) in whom adipose tissue section, cell morphology, and staining met the required criteria. AU, mRNA values were normalized using mRNA expression of csnk1d.

FIG. 2.

Associations of age with fraction of CD68⁺ cells (A) and mRNA expression of macrophage markers (B, CD68 expression [AU, ln]; C, CSF1R expression; D, CD11b expression). Total r² and P values for the entire GLM are given. Models were built using linear and quadratic terms (macrophage content variable = age age²). , men; •, women. Fraction of CD68⁺ cells was available in 46 individuals (31 men and 15 women) in whom adipose tissue section, cell morphology, and staining met the required criteria. AU, mRNA values were normalized using mRNA expression of csnk1d.

FIG. 3.

Associations between insulin-stimulated glucose uptake and ATM content. Simple correlation coefficients and P values for associations are given. , men; •, women. Fraction of CD68⁺ cells was available in 46 individuals (31 men and 15 women) in whom adipose tissue section, cell morphology, and staining met the required criteria. EMBS, estimated metabolic body size. AU, mRNA values were normalized using mRNA expression of csnk1d.

FIG. 4.

Associations of adipose tissue expression of PAI-1, MMP9, and CD11c with insulin-mediated glucose uptake. Data are simple Spearman's correlation coefficients and P values for associations in 55 individuals (M was missed for one of the subjects). , men; •, women.