Accelerated recovery from acute hypoxia in obese mice is due to obesity-associated up-regulation of interleukin-1 receptor antagonist

Abstract

The proinflammatory consequences of obesity are thought to be due, in part, to macrophage infiltration into adipose tissue. There are, however, potential antiinflammatory consequences of obesity that include obesity-associated up-regulation of IL-1 receptor antagonist (IL-1RA). Here we show that obesity-associated up-regulation of IL-1RA speeds recovery from hypoxia. We found that high-fat diet-fed (HFD) mice recovered from acute hypoxia 5 times faster than normal-diet-fed (ND) mice. HFD mice had a 10-fold increase in serum IL-1RA when compared with ND mice. White adipose tissue (WAT) was a significant source of IL-RA, generating 330 +/- 77 pg/mg protein in HFD mice as compared with 15 +/- 5 pg/mg protein in ND mice. Peritoneal macrophages isolated from HFD mice showed little difference in IL-1RA production when compared with ND mice, but WAT macrophages from HFD mice generated 11-fold more IL-1RA than those from ND mice. When ND mice were given an ip transfer of the stromal vascular fraction portion of WAT from HFD mice, serum IL-1RA increased 836% and recovery from acute hypoxia was faster than in mice that did not receive a stromal vascular fraction transfer. To determine whether IL-1RA was important to this accelerated recovery, ND mice were administered exogenous IL-1RA prior to hypoxia, and their recovery matched that of HFD mice. Inversely, when IL-1RA was immunoabsorbed in HFD mice with IL-1RA antiserum, recovery from acute hypoxia was attenuated. Taken together these data demonstrate that HFD-induced obesity speeds recovery from hypoxia due to obesity-associated up-regulation of IL-1RA.

Figure 1

HFD-induced obesity speeds recovery from acute hypoxia. Baseline behavior was measured in ND and HFD mice immediately before hypoxia exposure (−2 h). Mice were then placed in either a normoxic or hypoxic environment for 2 h. Behavioral recovery from hypoxia was measured 0, 2, 6, and 10 h after return of animals to normoxia. Results are expressed as percentages of the baseline measurement, means ± sem: n = 6. *, P < 0.05, hypoxia vs. normoxia; #, P < 0.05, ND vs. HFD.

Figure 2

IL-1 and its counterregulatory proteins are altered by HFD-induced obesity. IL-1α (A), IL-1β (B), IL-1RA (C), and IL-1R2 (D) mRNA were measured in brain and perigonadal WAT by real-time RT-PCR. Results are expressed as relative change in target mRNA to glyceraldehyde-3-phosphate dehydrogenase (ΔmRNA) and as means ± sem: n = 6–8. *, P < 0.05, **, P < 0.001 ND vs. HFD; #, P < 0.05 −2 h vs. 0 h, 2 h ND; +, P < 0.05 −2 h vs. 0 h, 2 h HFD.

Figure 3

WAT in HFD mice is a key source of IL-1RA. A, IL-1RA protein was measured in WAT, liver, and brain tissue homogenates by ELISA. Results are expressed as means ± sem: n = 4. *, P < 0.05; **, P < 0.005, ND vs. HFD. B, IL-1RA protein produced by PerMφs and AtMφs cultured in vitro for 2 h in normoxic conditions was measured by ELISA. Results are expressed as means ± sem: n = 3. *, P < 0.05, ND vs. HFD. C, IL-1RA protein produced by PerMφs and AtMφs cultured in vitro for 2 h in hypoxic conditions was measured by ELISA. Results are expressed as means ± sem: n = 3. *, P < 0.05, ND vs. HFD.

Figure 4

Accelerated hypoxia recovery can be transferred from HFD mice to ND mice. A, ND mice were ip injected with (transfer) or without (sham) HFD mouse SVF. Serum and peritoneal fluid IL-1RA protein was measured by ELISA 3 h after transfer. Results are expressed as means ± sem: n = 3. *, P < 0.05 sham vs. transfer. B, ND mice were ip injected with (transfer) or without (sham) SVF mouse stromal vascular fraction 3 h before hypoxia exposure. Baseline behavior was measured in sham and transferred mice immediately before hypoxia exposure (−2 h). Mice were then placed in either a normoxic or hypoxic environment for 2 h. Behavioral recovery from hypoxia was measured 0, 2, 6, and 10 h after return of animals to normoxia. Results are expressed as means ± sem: n = 3–5. *, P < 0.05 normoxia vs. hypoxia.

Figure 5

Exogenous administration of IL-1RA improves recovery from hypoxia. A, ND mice were injected sc with (IL-1RA) or without (sham) anakinra (1.4 mg/kg) 1 h before hypoxia exposure. Baseline behavior was measured in sham and anakinra (IL-1RA) administered to mice immediately before hypoxia exposure (−2 h). Mice were then placed in either a normoxic or hypoxic environment for 2 h. Behavioral recovery from hypoxia was measured 0, 2, 6, and 10 h after return of animals to normoxia. Results are expressed as means ± sem: n = 6. *, P < 0.05, hypoxia vs. normoxia; #, P < 0.05 IL-1RA vs. sham. B, ND mice were injected with IL-1RA, as in A, and serum IL-1RA protein was measured by ELISA, at the times indicated. Results are expressed as means ± sem: n = 3–4. *, P < 0.005 vs. 0 h.

Figure 6

Accelerated hypoxia recovery in HFD mice is reliant on IL-1RA. A, HFD mice were injected ip with IL-1RA antiserum or without nonimmune serum 1 h before hypoxia exposure. Baseline behavior was measured in nonimmune serum and IL-1RA antiserum administered to mice immediately before hypoxia exposure (−2 h). Mice were then placed in either a normoxic or hypoxic environment for 2 h. Behavioral recovery from hypoxia was measured 0, 2, 6, and 10 h after return of animals to normoxia. Results are expressed as means ± sem: n = 3. *, P < 0.05 nonimmune serum vs. IL-1RA antiserum: #, P < 0.05 vs. −2 h. B, IL-1RA protein was measured in serum and WAT from the mice in A immediately after the 10-h time point. Results are expressed as means ± sem: n = 3. *, P < 0.05.