CD14 modulates inflammation-driven insulin resistance

Abstract

Objective: The study objective was to evaluate the possible role of the macrophage molecule CD14 in insulin resistance.

Research design and methods: The effects of recombinant human soluble CD14 (rh-sCD14) on insulin sensitivity (clamp procedure) and adipose tissue gene expression were evaluated in wild-type (WT) mice, high fat-fed mice, ob/ob mice, and CD14 knockout (KO) mice. We also studied WT mice grafted with bone marrow stem cells from WT donor mice and CD14 KO mice. Finally, CD14 was evaluated in human adipose tissue and during differentiation of human preadipocytes.

Results: rh-sCD14 led to increased insulin action in WT mice, high-fat-fed mice, and ob/ob mice, but not in CD14 KO mice, in parallel to a marked change in the expression of 3,479 genes in adipose tissue. The changes in gene families related to lipid metabolism were most remarkable. WT mice grafted with bone marrow stem cells from WT donor mice became insulin resistant after a high-fat diet. Conversely, WT mice grafted with cells from CD14 KO mice resisted the occurrence of insulin resistance in parallel to decreased mesenteric adipose tissue inflammatory gene expression. Glucose intolerance did not worsen in CD14 KO mice grafted with bone marrow stem cells from high fat-fed WT mice when compared with recipient KO mice grafted with cells from CD14 KO donor mice. CD14 gene expression was increased in whole adipose tissue and adipocytes from obese humans and further increased after tumor necrosis factor-α.

Conclusions: CD14 modulates adipose tissue inflammatory activity and insulin resistance.

FIG. 1.

Glucose tolerance time course in WT mice. A and B: Glucose tolerance test (top) and the corresponding area under the curve (μmol/L/min, middle) and glucose infusion rates (bottom) in WT mice grafted with cells from CD14 KO mice (CD14^−/−) and fed normal chow or HFD. Data are from 6–8 mice per group. *P < 0.05 and **P < 0.01 for WT mice grafted with cells from CD14 KO mice vs. WT mice grafted with cells from WT donor using Student t test. Glucose infusion rate calculations were made during the last 60 min of the 180-min clamp in steady-state condition. C: Glucose tolerance test in CD14 KO mice (CD14^−/−) grafted with cells from CD14 KO or WT mice and fed normal chow or HFD (n = 6–8 mice per group). AUC, area under the curve; BM, bone marrow; GIR, glucose infusion rate; NC, normal chow; OGTT, oral glucose tolerance test.

FIG. 2.

Gene expression in fat from CD14^−/− mice and HFD effect. mRNA concentration coding for TNF-α (A), IL1-β (B), plasminogen activator inhibitor-1 (C), and inflammatory index (D) in the mesenteric and subcutaneous adipose depots from WT mice grafted with cells from WT or CD14 KO mice (CD14^−/−) fed HFD. The inflammatory index was calculated as follows. The relative mRNA concentration was quantified as fold change over an internal control gene (RPL19) for all individuals and for all cytokines considered. Then all relative quantifications were pooled (including plasminogen activator inhibitor-1, IL1-β, and TNF-α). Data are from 6–8 mice per group. *P < 0.05 and **P < 0.01 for WT mice grafted with cells from CD14 KO mice vs. WT mice grafted with cells from WT donor using Student t test. BM, bone marrow; PAI, plasminogen activator inhibitor.

FIG. 3.

Effects of rh-sCD14 on insulin action and glucose turnover. A: Glucose turnover rates (mg/kg/min) of WT and CD14 KO mice infused with rh-sCD14 or saline during a hyperinsulinemic glucose clamp (n = 6–8 mice per group). *P < 0.05 for sCD14 vs. saline treatment, using Student t test. Effects of rh-sCD14 (n = 9) or vehicle (n = 9) in high fat–fed mice on (B) fasting glucose and insulin concentrations and (C) glucose after IPGTTs. Glucose (2 g/kg) was injected intraperitoneally after an overnight fast. Effects of treatment with rh-sCD14 or vehicle in ob/ob mice on body weight (D), fasting glucose and insulin concentrations (n = 4–5) (E), and IPGTT (F). Dashed line, mice treated with vehicle; continuous line, mice treated with rh-sCD14. G: Glucose/insulin ratio. Two-way ANOVA test indicated a significant difference between the glucose (P = 0.002) and insulin (P < 0.0001) curves of sCD14- and vehicle-treated mice. *P < 0.05 for sCD14 vs. vehicle treatment, using Student t test. (A high-quality color representation of this figure is available in the online issue.)

FIG. 4.

CD14 gene expression in obese subjects and during adipogenesis. A: The 95% CI for the mean of CD14 mRNA expression according to obesity status. B: Study of CD14 mRNA expression during in vitro differentiation of human adipocytes. **P < 0.005 in comparison with day 0. C: Study of CD14 mRNA in isolated preadipocytes and adipocytes from lean and obese subjects. *P < 0.05 in comparison with preadipocyte. **P < 0.005 in comparison with preadipocyte. ⁺P < 0.05 in comparison with lean cells. ⁺⁺P < 0.005 in comparison with lean cells. D: TNF-α (100 ng/mL) administration during 48 h significantly increased CD14 gene expression in human adipocytes (P = 0.003). SC, subcutaneous.