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. 2016 Jun;65(6):1616-29.
doi: 10.2337/db15-1156. Epub 2016 Mar 18.

IKKβ Is Essential for Adipocyte Survival and Adaptive Adipose Remodeling in Obesity

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Free PMC article

IKKβ Is Essential for Adipocyte Survival and Adaptive Adipose Remodeling in Obesity

Se-Hyung Park et al. Diabetes. .
Free PMC article

Abstract

IκB kinase β (IKKβ), a central coordinator of inflammatory responses through activation of nuclear factor-κB (NF-κB), has been implicated as a critical molecular link between inflammation and metabolic disorders; however, the role of adipocyte IKKβ in obesity and related metabolic disorders remains elusive. Here we report an essential role of IKKβ in the regulation of adipose remodeling and adipocyte survival in diet-induced obesity. Targeted deletion of IKKβ in adipocytes does not affect body weight, food intake, and energy expenditure but results in an exaggerated diabetic phenotype when challenged with a high-fat diet (HFD). IKKβ-deficient mice have multiple histopathologies in visceral adipose tissue, including increased adipocyte death, amplified macrophage infiltration, and defective adaptive adipose remodeling. Deficiency of IKKβ also leads to increased adipose lipolysis, elevated plasma free fatty acid (FFA) levels, and impaired insulin signaling. Mechanistic studies demonstrated that IKKβ is a key adipocyte survival factor and that IKKβ protects murine and human adipocytes from HFD- or FFA-elicited cell death through NF-κB-dependent upregulation of antiapoptotic proteins and NF-κB-independent inactivation of proapoptotic BAD protein. Our findings establish IKKβ as critical for adipocyte survival and adaptive adipose remodeling in obesity.

Figures

Figure 1
Figure 1
Deficiency of adipocyte IKKβ does not affect diet-induced weigh gain but results in an exaggerated diabetic phenotype when challenged with an HFD. A: IKKβ mRNA expression levels in major organs of IKKβF/F and IKKβΔAd mice were analyzed by quantitative PCR (n = 3–7). B: Western blot analysis of IKKβ protein levels in subWAT, epiWAT, liver, and macrophages of IKKβF/F and IKKβΔAd mice. C: Growth curves of ND- or HFD-fed male IKKβF/F and IKKβΔAd mice (n = 19–28). Food intake (D), total activity (E), VO2 (F), and VCO2 (G) of 16-week-old male IKKβF/F and IKKβΔAd mice fed the HFD for 12 weeks (n = 5). Food intake was averaged from 4-day measurements. Glucose tolerance test (GTT) and the area under the curve (AUC) of GTT (H), insulin tolerance test (ITT), and AUC of ITT (I), and fasting glucose and insulin levels (J) in HFD-fed IKKβF/F and IKKβΔAd mice (n = 10–17). *P < 0.05; **P < 0.01; ***P < 0.001.
Figure 2
Figure 2
Visceral adipose tissue of adipocyte IKKβ-deficient mice fails to expand properly in response to HF feeding. Representative photographs (A) and weight (B) of fat pads from ND- or HFD-fed male IKKβF/F and IKKβΔAd mice (n = 7–10). Representative coronal section MRIs (C) and visceral and subcutaneous adipose tissue volume (D) of HFD-fed male IKKβF/F and IKKβΔAd mice (n = 5–6). ret, retroperitoneal. *P < 0.05; ***P < 0.001.
Figure 3
Figure 3
Deficiency of adipocyte IKKβ causes impaired visceral adipose tissue expansion when challenged with an HFD. A: Representative hematoxylin and eosin staining of BAT, subWAT, epiWAT, and retroperitoneal (ret)WAT of ND- or HFD-fed male IKKβF/F and IKKβΔAd mice. Scale bar, 100 μm. B: Trichrome staining for collagen deposition in epiWAT from ND- or HFD-fed IKKβF/F and IKKβΔAd mice. Scale bar, 100 μm. C: Quantitation of adipocyte cross-sectional sizes from HFD-fed mice, expressed as the ratio of the numbers of cells from IKKβΔAd and IKKβF/F mice defined as small (15–70 μm), medium (70–110 μm), and large (>110 μm).
Figure 4
Figure 4
Loss of adipocyte IKKβ results in severe defects in adipose tissue remodeling in response to dietary changes. A: Growth curves of HFD-fed IKKβF/F and IKKβΔAd mice switched to the ND for 6 weeks (n = 6–10). Representative photographs (B), weight (C), and hematoxylin and eosin staining (D) of subWAT and epiWAT from HFD/ND-fed male IKKβF/F and IKKβΔAd mice (n = 3–7). ***P < 0.001. E: Representative immunofluorescence staining for perilipin (green) of epiWAT from IKKβF/F and IKKβΔAd mice fed HFD/ND. Bottom panels represent the magnification of areas in the top panels. The nuclei were stained with DAPI (blue), and the perilipin-negative adipocytes are indicated by arrows. Scale bar, 100 μm.
Figure 5
Figure 5
IKKβ protects adipocytes from HFD-induced cell death. A: Representative TUNEL staining of epiWAT sections from ND- or HFD-fed IKKβF/F and IKKβΔAd mice. The nuclei were stained with DAPI (blue), and the TUNEL-positive cells were indicated by arrows. Scale bar, 50 μm. B: Representative immunohistochemistry for perilipin of epiWAT sections from ND- or HFD-fed IKKβF/F and IKKβΔAd mice. The nuclei were stained with hematoxylin (blue), and the perilipin-negative adipocytes were indicated by arrows. Scale bar, 100 μm. C: Western blot analysis with the indicated total and phosphorylated (p) antibodies in epiWAT from ND or HFD-fed IKKβF/F and IKKβΔAd mice.
Figure 6
Figure 6
Deficiency of adipocyte IKKβ increases macrophage infiltration and lipolysis in visceral adipose tissue and impairs insulin signaling in adipose tissue and liver. A: Representative immunohistochemistry for the macrophage marker F4/80 in subWAT and epiWAT from ND- or HFD-fed IKKβF/F and IKKβΔAd mice. Scale bar, 100 μm. B: Adipose SV cells isolated from epiWAT of HFD-fed mice were examined for expression of macrophage cell makers F4/80 and CD11b with flow cytometry. The percentages of F4/80+CD11b+ cells are as indicated in the flow profiles (n = 3–5). P < 0.05. C: Expression levels of macrophage markers and inflammatory genes in epiWAT and subWAT of HFD-fed mice were analyzed by quantitative PCR (n = 6). *P < 0.05; **P < 0.01; ***P < 0.001. D: Glycerol release in epiWAT from HFD-fed IKKβF/F and IKKβΔAd mice under basal conditions or stimulated with 1 μmol/L isoproterenol (n = 9–12). *P < 0.05. Plasma FFA concentration (E) and hepatic cholesterol (F) and triglyceride (G) levels in HFD-fed IKKβF/F and IKKβΔAd mice (n = 9–13). *P < 0.05. H: Western blot analysis of phospho(p)-Akt (ser473) and total Akt levels in liver and epiWAT of HFD-fed IKKβF/F and IKKβΔAd mice injected with saline or 0.35 units/kg body weight insulin.
Figure 7
Figure 7
aP2-Cre–mediated IKKβ deletion results in similar defects in adipose remodeling and accentuated inflammatory responses after HF feeding. A: Western blot analysis of IKKβ protein levels in subWAT, epiWAT, liver, and macrophages of IKKβF/F and IKKβΔaP2 mice. B: Growth curves of HFD-fed male IKKβF/F and IKKβΔaP2 mice (n = 24–38). Representative photographs (C) and weight of fat pads (D) of HFD-fed male IKKβF/F and IKKβΔaP2 mice (n = 5–7). *P < 0.05. E: Representative hematoxylin and eosin staining of subWAT and epiWAT of ND- or HFD-fed male IKKβF/F and IKKβΔaP2 mice. Scale bar, 100 μm. F: Representative immunohistochemistry for the macrophage marker F4/80 in subWAT and epiWAT from ND- or HFD-fed IKKβF/F and IKKβΔaP2 mice. Scale bar, 100 μm.
Figure 8
Figure 8
IKKβ protects murine and human adipocytes from FFA-induced cell death. A: 3T3-L1 cells were differentiated into adipocytes and then introduced with control siRNA or siRNA against IKKβ. Western blot analysis with the indicated total and phosphorylated (p) antibodies in control or siIKKβ 3T3-L1 adipocytes treated with vehicle or FFAs for the indicated times. B: 3T3-L1 adipocytes were introduced with control siRNA or siRNA against IKKβ and/or BAD. Western blot analysis with the indicated antibodies in control, siBAD, siIKKβ, or siIKKβ/siBAD 3T3-L1 adipocytes treated with vehicle control or FFAs. C: 3T3-L1 adipocytes were introduced with control siRNA or siRNA against BAD. Western blot analysis with the indicated antibodies in control or siBAD 3T3-L1 adipocytes treated with vehicle control or FFAs in the absence or presence of 5 μmol/L IKKβ inhibitor, BMS-345541. Adipose SV cells isolated from IKKβF/F mice were differentiated into adipocytes and then infected with control lentivirus or lentivirus expressing Cre. Western blot analysis with the indicated antibodies in cells treated with vehicle control or FFAs for 3 h (D) or 24 h (E). F: ADHASCs were differentiated into adipocytes and then treated with FFAs in the presence or absence of 5 μmol/L IKKβ inhibitor, BMS-345541. Western blot analysis with the indicated antibodies in cells treated with control, FFAs and/or BMS-345541. G: Schematic representation of the mechanisms through which IKKβ protects adipocytes from cell death in diet-induced obesity. IKKβ inhibits FFA-induced adipocyte death through NF-κB–dependent upregulation of antiapoptotic proteins and NF-κB–independent inactivation of proapoptotic BAD protein.

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References

    1. Kahn SE, Hull RL, Utzschneider KM.. Mechanisms linking obesity to insulin resistance and type 2 diabetes. Nature 2006;444:840–846 - PubMed
    1. Van Gaal LF, Mertens IL, De Block CE.. Mechanisms linking obesity with cardiovascular disease. Nature 2006;444:875–880 - PubMed
    1. Hotamisligil GS, Erbay E.. Nutrient sensing and inflammation in metabolic diseases. Nat Rev Immunol 2008;8:923–934 - PMC - PubMed
    1. Hayden MS, Ghosh S.. Shared principles in NF-kappaB signaling. Cell 2008;132:344–362 - PubMed
    1. Karin M. Nuclear factor-kappaB in cancer development and progression. Nature 2006;441:431–436 - PubMed

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