Deletion of interleukin 1 receptor-associated kinase 1 (Irak1) improves glucose tolerance primarily by increasing insulin sensitivity in skeletal muscle

Abstract

Chronic inflammation may contribute to insulin resistance via molecular cross-talk between pathways for pro-inflammatory and insulin signaling. Interleukin 1 receptor-associated kinase 1 (IRAK-1) mediates pro-inflammatory signaling via IL-1 receptor/Toll-like receptors, which may contribute to insulin resistance, but this hypothesis is untested. Here, we used male Irak1 null (k/o) mice to investigate the metabolic role of IRAK-1. C57BL/6 wild-type (WT) and k/o mice had comparable body weights on low-fat and high-fat diets (LFD and HFD, respectively). After 12 weeks on LFD (but not HFD), k/o mice (versus WT) had substantially improved glucose tolerance (assessed by the intraperitoneal glucose tolerance test (IPGTT)). As assessed with the hyperinsulinemic euglycemic glucose clamp technique, insulin sensitivity was 30% higher in the Irak1 k/o mice on chow diet, but the Irak1 deletion did not affect IPGTT outcomes in mice on HFD, suggesting that the deletion did not overcome the impact of obesity on glucose tolerance. Moreover, insulin-stimulated glucose-disposal rates were higher in the k/o mice, but we detected no significant difference in hepatic glucose production rates (± insulin infusion). Positron emission/computed tomography scans indicated higher insulin-stimulated glucose uptake in muscle, but not liver, in Irak1 k/o mice in vivo Moreover, insulin-stimulated phosphorylation of Akt was higher in muscle, but not in liver, from Irak1 k/o mice ex vivo In conclusion, Irak1 deletion improved muscle insulin sensitivity, with the effect being most apparent in LFD mice.

Keywords: Akt PKB; IRAK-1; glucose tolerance; inflammation; insulin resistance; metabolism; muscle.

Figure 1.

Intraperitoneal glucose tolerance tests (IPGTT) are shown. A–D, 6-week-old wild-type and Irak1 k/o mice were fed with either low-fat (A and B, n = 8) or high-fat diets (C and D, n = 8). After 12 weeks on the designated diets, mice were fasted for 5 h. Glucose (1 g/kg) was injected intraperitoneally and blood glucose was measured at 0, 10, 20, 30, 60, and 120 min after injection. B and D, areas under the curve (AUC) were calculated based on the trapezoidal rule. A, ANOVA for repeated measures, p = 0.004. B, AUC_glucose = 10890 ± 840 versus 6850 ± 1100 (mg/dl) × min), p = 0.035. C, ANOVA for repeated measures, p = 0.56. D, AUC_glucose = 14370 ± 1800 versus 15180 ± 1040 (mg/dl) × min), p = 0.59. Data are expressed as mean ± S.E.

Figure 2.

Hyperinsulinemic euglycemic glucose clamp studies in mice fed normal chow diet are shown. A–D, at 28 weeks of age, glucose clamp studies were performed as described under “Experimental Procedures” and previously (94). Mean glucose infusion rates over the 30-min steady-state period at the end of the study were used to estimate the steady-state glucose infusion rate (GIR). Data shown are mean ± S.E. A, for the WT mice (n = 8), blood glucose is indicated with solid circles and GIR with closed triangles. B, for Irak1 k/o mice (n = 10), blood glucose is indicated with open circles and GIR with open triangles. C, GIR normalized for body weight. D, ISI was defined as the GIR (glucose mg/kg/min) divided by the mean glucose level (mg/dl) calculated from the last 30 min of the clamp study when steady-state had been achieved.

Figure 3.

Cardiometabolic biomarkers in mice fed with low-fat diet and high-fat diet are shown. A–L, fasting plasma was obtained after 14 weeks on low-fat diet (A–F) or high-fat diet (G–L). B and H, glucose was measured by YSI 2700 Select Biochemistry Analyzer. Insulin (A and G), adiponectin (D and J), ET-1 (E and K), and CRP (F and L) were measured by ELISA. C and I, QUICKI was calculated as QUICKI = 1/(log (insulin) + log (glucose)) (55, 56, 100). Data are expressed as mean ± S.E.

Figure 4.

In vivo insulin-stimulated [¹⁸F]FDG distribution in mice fed with normal chow diet is shown. A and B, after mice were fasted overnight, [¹⁸F]FDG 11.1 MBq (300 Ci) and insulin (1.125 units/kg) in 200 μl of saline were injected via tail vein under anesthesia. Dynamic imaging was acquired for 30 min by Siemens Inveon Small Animal PET/CT Imaging System. The data were obtained by drawing regions of interest (ROI) over target organs of muscle, abdominal subcutaneous white adipose tissue, liver, and brain (98, 99). The [¹⁸F]FDG bio-distribution in the target organs/tissues were analyzed at three time points: 10, 20, and 30 min. A, time-dependent distribution percentage of injected dose per gram (%ID/g) of [¹⁸F]FDG in the hind limb, liver, and abdominal white fat in Irak1 k/o mice and in wild-type mice. B, relative time-dependent distribution of [¹⁸F]FDG in the hind limb, liver, and abdominal white fat (ratio of [¹⁸F]FDG:specific tissue/brain) in Irak1 k/o mice and in wild-type mice. WT, n = 3; k/o, n = 3; *, p < 0.04; **, p < 0.03. Data shown are mean ± S.E.

Figure 5.

Hyperinsulinemic euglycemic glucose clamp studies with [3-³H]glucose tracer in mice fed with a normal chow diet are shown. A–D, 6 WT and 6 k/o mice underwent glucose clamps with [³H]glucose tracer as described under “Experimental Procedures” and previously (94). At the beginning and the end of each clamp study, blood was collected for calculating insulin-stimulated glucose disposal rates and hepatic glucose production rate. A, GIR normalized for body weight. B, ISI was defined as GIR (mg/kg/min) divided by steady-state glucose level (mg/dl) during the last 30 min of the clamp. C, glucose appearance rate. D, hepatic glucose production rate. Data are expressed as mean ± S.E.

Figure 6.

Immunoblotting analysis of insulin signaling pathways in muscle, liver, and abdominal white adipose tissue is shown. A and B, muscle. C and D, liver. E and F, abdominal white adipose tissue. 20-week-old mice fed with chow diet were fasted for 5 h and then given saline (none) or insulin (10 units/kg body weight) via portal vein injection under anesthesia. 5 min after injection, skeletal muscle from hind limb, abdominal fat, and liver were immediately flash frozen and homogenized. These samples were centrifuged and supernatants of tissue lysates were analyzed by immunoblotting with indicated antibodies. A, C, and E, immunoblots with samples from 6 WT and 7 Irak1 k/o mice. B, D, and F, immunoblots for phospho-Akt were quantified by scanning densitometry and normalized for Akt total protein. Data are expressed as mean ± S.E.