Limits...
The macrophage A2B adenosine receptor regulates tissue insulin sensitivity.

Johnston-Cox H, Eisenstein AS, Koupenova M, Carroll S, Ravid K - PLoS ONE (2014)

Bottom Line: High fat diet (HFD)-induced type 2 diabetes continues to be an epidemic with significant risk for various pathologies.As the A2bAR is expressed in different tissues, here, we provide the first lead to cellular mechanism by demonstrating that the receptor's influence on tissue insulin sensitivity is mediated via its expression in macrophages.The molecular mechanism for this effect involves A2bAR-mediated changes in cyclic adenosine monophosphate in macrophages, reducing the expression and release of inflammatory cytokines, which downregulate insulin receptor-2.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, United States of America; Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, Massachusetts, United States of America.

ABSTRACT
High fat diet (HFD)-induced type 2 diabetes continues to be an epidemic with significant risk for various pathologies. Previously, we identified the A2b adenosine receptor (A2bAR), an established regulator of inflammation, as a regulator of HFD-induced insulin resistance. In particular, HFD was associated with vast upregulation of liver A2bAR in control mice, and while mice lacking this receptor showed augmented liver inflammation and tissue insulin resistance. As the A2bAR is expressed in different tissues, here, we provide the first lead to cellular mechanism by demonstrating that the receptor's influence on tissue insulin sensitivity is mediated via its expression in macrophages. This was shown using a newly generated transgenic mouse model expressing the A2bAR gene in the macrophage lineage on an otherwise A2bAR background. Reinstatement of macrophage A2bAR expression in A2bAR mice fed HFD restored insulin tolerance and tissue insulin signaling to the level of control mice. The molecular mechanism for this effect involves A2bAR-mediated changes in cyclic adenosine monophosphate in macrophages, reducing the expression and release of inflammatory cytokines, which downregulate insulin receptor-2. Thus, our results illustrate that macrophage A2bAR signaling is needed and sufficient for relaying the protective effect of the A2bAR against HFD-induced tissue inflammation and insulin resistance in mice.

Show MeSH

Related in: MedlinePlus

Baseline characteristics of CD68-Tg mice.Baseline characteristics were measured in WT, A2bAR KO, and CD68-Tg mice at 12 weeks of age. A. Glucose clearance in the blood post glucose overload (n = 12/group). Data in a. were analyzed by ANOVA followed by Bonferroni comparison test with the following p-values for indicated time points: Time 45 min: p-value  = 0.100922; WT vs CD68-Tg n.s., WT vs A2bAR KO p-value <0.05, CD68-Tg vs A2bAR KO n.s.; Time 60 min: p-value  = 0.003404; WT vs CD68-Tg n.s., WT vs A2bAR KO p-value <0.01, CD68-Tg vs A2bAR KO n.s.; Time 90 min: p-value  = 0.002867; WT vs CD68-Tg p-value <0.05, WT vs A2bAR KO p-value <0.01, CD68-Tg vs A2bAR KO n.s.; Time 120 min: p-value  = 0.016218; WT vs CD68-Tg n.s., WT vs A2bAR KO p-value <0.05, CD68-Tg vs A2bAR KO n.s. B. Insulin levels in the plasma post glucose overload (n = 12/group). C. Glucose clearance in the plasma post insulin overload (n = 12/group), post 6 hours starvation. D. Glucose levels post 16 hour starvation. E. Levels of liver phospho-308 Akt (p308 Akt, 60 kDa), phospho-473 Akt (p473 Akt, 60 kDa), and total Akt (60 kDa) were probed by Western blot analysis, using β-actin (43 kDa) as loading control. Shown are representatives out of 3 sets. F. Quantification of Western Blot results (of panel E) was performed with Image J software (http://rsb.info.nih.gov/ij/). Protein levels were normalized to total Akt and β-actin. G. Fat to Lean ratio at 12 weeks of age. H. Percent fat mass relative to body weight at 12 weeks of age. Data are averages ± SD. *Student two-tail t-test assuming equal variance was found significant only when p-value <0.05. The differences between the experimental groups (CD68-Tg or A2bAR KO vs. WT, or CD68-Tg vs A2bAR KO) were not statistically significant.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4043770&req=5

pone-0098775-g008: Baseline characteristics of CD68-Tg mice.Baseline characteristics were measured in WT, A2bAR KO, and CD68-Tg mice at 12 weeks of age. A. Glucose clearance in the blood post glucose overload (n = 12/group). Data in a. were analyzed by ANOVA followed by Bonferroni comparison test with the following p-values for indicated time points: Time 45 min: p-value  = 0.100922; WT vs CD68-Tg n.s., WT vs A2bAR KO p-value <0.05, CD68-Tg vs A2bAR KO n.s.; Time 60 min: p-value  = 0.003404; WT vs CD68-Tg n.s., WT vs A2bAR KO p-value <0.01, CD68-Tg vs A2bAR KO n.s.; Time 90 min: p-value  = 0.002867; WT vs CD68-Tg p-value <0.05, WT vs A2bAR KO p-value <0.01, CD68-Tg vs A2bAR KO n.s.; Time 120 min: p-value  = 0.016218; WT vs CD68-Tg n.s., WT vs A2bAR KO p-value <0.05, CD68-Tg vs A2bAR KO n.s. B. Insulin levels in the plasma post glucose overload (n = 12/group). C. Glucose clearance in the plasma post insulin overload (n = 12/group), post 6 hours starvation. D. Glucose levels post 16 hour starvation. E. Levels of liver phospho-308 Akt (p308 Akt, 60 kDa), phospho-473 Akt (p473 Akt, 60 kDa), and total Akt (60 kDa) were probed by Western blot analysis, using β-actin (43 kDa) as loading control. Shown are representatives out of 3 sets. F. Quantification of Western Blot results (of panel E) was performed with Image J software (http://rsb.info.nih.gov/ij/). Protein levels were normalized to total Akt and β-actin. G. Fat to Lean ratio at 12 weeks of age. H. Percent fat mass relative to body weight at 12 weeks of age. Data are averages ± SD. *Student two-tail t-test assuming equal variance was found significant only when p-value <0.05. The differences between the experimental groups (CD68-Tg or A2bAR KO vs. WT, or CD68-Tg vs A2bAR KO) were not statistically significant.

Mentions: We also determined the response of CD68-Tg mice to glucose and insulin overload in chow-fed 12-week old mice. There was no difference in glucose clearance (Figure 8A), glucose-stimulated insulin release (Figure 8B), insulin sensitivity (Figure 8C), fasting glucose level (Figure 8D) or liver insulin signaling (assessed by Akt phosphorylation; Figure 8E,F) between the CD68-Tg and A2bAR KO mice. In addition, there was no difference in fat to lean ratio or percent lean mass between CD68-Tg and A2bAR KO mice (Figure 8G,H). These results were not unexpected as the expression of the A2bAR is quite low or not detectable in tissues such as liver or fat under chow diet, while it is upregulated following conditions that stress the animal, such as ischemia, inflammation, and HFD [29], [30], [51]-[53]. Notably, and as previously described [54], glucose clearance under chow diet is more efficient in the A2bAR KO mice compared to control WT mice. This could be due to an inhibitory effect of low level A2bAR in chow diet-fed mice on tissue IL-6 expression, as suggested in [54].


The macrophage A2B adenosine receptor regulates tissue insulin sensitivity.

Johnston-Cox H, Eisenstein AS, Koupenova M, Carroll S, Ravid K - PLoS ONE (2014)

Baseline characteristics of CD68-Tg mice.Baseline characteristics were measured in WT, A2bAR KO, and CD68-Tg mice at 12 weeks of age. A. Glucose clearance in the blood post glucose overload (n = 12/group). Data in a. were analyzed by ANOVA followed by Bonferroni comparison test with the following p-values for indicated time points: Time 45 min: p-value  = 0.100922; WT vs CD68-Tg n.s., WT vs A2bAR KO p-value <0.05, CD68-Tg vs A2bAR KO n.s.; Time 60 min: p-value  = 0.003404; WT vs CD68-Tg n.s., WT vs A2bAR KO p-value <0.01, CD68-Tg vs A2bAR KO n.s.; Time 90 min: p-value  = 0.002867; WT vs CD68-Tg p-value <0.05, WT vs A2bAR KO p-value <0.01, CD68-Tg vs A2bAR KO n.s.; Time 120 min: p-value  = 0.016218; WT vs CD68-Tg n.s., WT vs A2bAR KO p-value <0.05, CD68-Tg vs A2bAR KO n.s. B. Insulin levels in the plasma post glucose overload (n = 12/group). C. Glucose clearance in the plasma post insulin overload (n = 12/group), post 6 hours starvation. D. Glucose levels post 16 hour starvation. E. Levels of liver phospho-308 Akt (p308 Akt, 60 kDa), phospho-473 Akt (p473 Akt, 60 kDa), and total Akt (60 kDa) were probed by Western blot analysis, using β-actin (43 kDa) as loading control. Shown are representatives out of 3 sets. F. Quantification of Western Blot results (of panel E) was performed with Image J software (http://rsb.info.nih.gov/ij/). Protein levels were normalized to total Akt and β-actin. G. Fat to Lean ratio at 12 weeks of age. H. Percent fat mass relative to body weight at 12 weeks of age. Data are averages ± SD. *Student two-tail t-test assuming equal variance was found significant only when p-value <0.05. The differences between the experimental groups (CD68-Tg or A2bAR KO vs. WT, or CD68-Tg vs A2bAR KO) were not statistically significant.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4043770&req=5

pone-0098775-g008: Baseline characteristics of CD68-Tg mice.Baseline characteristics were measured in WT, A2bAR KO, and CD68-Tg mice at 12 weeks of age. A. Glucose clearance in the blood post glucose overload (n = 12/group). Data in a. were analyzed by ANOVA followed by Bonferroni comparison test with the following p-values for indicated time points: Time 45 min: p-value  = 0.100922; WT vs CD68-Tg n.s., WT vs A2bAR KO p-value <0.05, CD68-Tg vs A2bAR KO n.s.; Time 60 min: p-value  = 0.003404; WT vs CD68-Tg n.s., WT vs A2bAR KO p-value <0.01, CD68-Tg vs A2bAR KO n.s.; Time 90 min: p-value  = 0.002867; WT vs CD68-Tg p-value <0.05, WT vs A2bAR KO p-value <0.01, CD68-Tg vs A2bAR KO n.s.; Time 120 min: p-value  = 0.016218; WT vs CD68-Tg n.s., WT vs A2bAR KO p-value <0.05, CD68-Tg vs A2bAR KO n.s. B. Insulin levels in the plasma post glucose overload (n = 12/group). C. Glucose clearance in the plasma post insulin overload (n = 12/group), post 6 hours starvation. D. Glucose levels post 16 hour starvation. E. Levels of liver phospho-308 Akt (p308 Akt, 60 kDa), phospho-473 Akt (p473 Akt, 60 kDa), and total Akt (60 kDa) were probed by Western blot analysis, using β-actin (43 kDa) as loading control. Shown are representatives out of 3 sets. F. Quantification of Western Blot results (of panel E) was performed with Image J software (http://rsb.info.nih.gov/ij/). Protein levels were normalized to total Akt and β-actin. G. Fat to Lean ratio at 12 weeks of age. H. Percent fat mass relative to body weight at 12 weeks of age. Data are averages ± SD. *Student two-tail t-test assuming equal variance was found significant only when p-value <0.05. The differences between the experimental groups (CD68-Tg or A2bAR KO vs. WT, or CD68-Tg vs A2bAR KO) were not statistically significant.
Mentions: We also determined the response of CD68-Tg mice to glucose and insulin overload in chow-fed 12-week old mice. There was no difference in glucose clearance (Figure 8A), glucose-stimulated insulin release (Figure 8B), insulin sensitivity (Figure 8C), fasting glucose level (Figure 8D) or liver insulin signaling (assessed by Akt phosphorylation; Figure 8E,F) between the CD68-Tg and A2bAR KO mice. In addition, there was no difference in fat to lean ratio or percent lean mass between CD68-Tg and A2bAR KO mice (Figure 8G,H). These results were not unexpected as the expression of the A2bAR is quite low or not detectable in tissues such as liver or fat under chow diet, while it is upregulated following conditions that stress the animal, such as ischemia, inflammation, and HFD [29], [30], [51]-[53]. Notably, and as previously described [54], glucose clearance under chow diet is more efficient in the A2bAR KO mice compared to control WT mice. This could be due to an inhibitory effect of low level A2bAR in chow diet-fed mice on tissue IL-6 expression, as suggested in [54].

Bottom Line: High fat diet (HFD)-induced type 2 diabetes continues to be an epidemic with significant risk for various pathologies.As the A2bAR is expressed in different tissues, here, we provide the first lead to cellular mechanism by demonstrating that the receptor's influence on tissue insulin sensitivity is mediated via its expression in macrophages.The molecular mechanism for this effect involves A2bAR-mediated changes in cyclic adenosine monophosphate in macrophages, reducing the expression and release of inflammatory cytokines, which downregulate insulin receptor-2.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, United States of America; Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, Massachusetts, United States of America.

ABSTRACT
High fat diet (HFD)-induced type 2 diabetes continues to be an epidemic with significant risk for various pathologies. Previously, we identified the A2b adenosine receptor (A2bAR), an established regulator of inflammation, as a regulator of HFD-induced insulin resistance. In particular, HFD was associated with vast upregulation of liver A2bAR in control mice, and while mice lacking this receptor showed augmented liver inflammation and tissue insulin resistance. As the A2bAR is expressed in different tissues, here, we provide the first lead to cellular mechanism by demonstrating that the receptor's influence on tissue insulin sensitivity is mediated via its expression in macrophages. This was shown using a newly generated transgenic mouse model expressing the A2bAR gene in the macrophage lineage on an otherwise A2bAR background. Reinstatement of macrophage A2bAR expression in A2bAR mice fed HFD restored insulin tolerance and tissue insulin signaling to the level of control mice. The molecular mechanism for this effect involves A2bAR-mediated changes in cyclic adenosine monophosphate in macrophages, reducing the expression and release of inflammatory cytokines, which downregulate insulin receptor-2. Thus, our results illustrate that macrophage A2bAR signaling is needed and sufficient for relaying the protective effect of the A2bAR against HFD-induced tissue inflammation and insulin resistance in mice.

Show MeSH
Related in: MedlinePlus